Commissioning an air distribution system is the process of systematically testing and adjusting to ensure it operates as intended and meets design specifications. Without proper commissioning, ventilation and air conditioning systems can deliver poor air quality, uneven temperatures, issues with comfort, wasted energy, and potential safety issues.

In 2024, revisions took place on two key documents, one each from CIBSE and BSRIA, that provide essential – and now significantly updated – information to ensure that systems are commissionable by employing suitably rigorous methods. This CPD will focus on aspects of CIBSE Commissioning Code A: Air Distribution Systems, and outline how the CIBSE and BSRIA documents relate to each other.

The 2024 revision to CIBSE Commissioning Code A (CCA) details the process for setting to work, functionally testing, and regulating ventilation and ductwork systems. It may be employed to verify that systems meet specified air distribution requirements and operate within specified tolerances, ensuring proper levels of air quality, thermal comfort and energy efficiency.

This revision is a significant development on previous editions that originated more than 50 years ago and were last reviewed in 2016. The 2024 revision was created in collaboration with the Building Services Research and Information Association (BSRIA) and the Commissioning Specialists Association (CSA), and focuses primarily on functional testing and regulating aspects. The revisions incorporate new guidance on various specialist systems, emphasise the importance of ongoing commissioning throughout a building’s life-cycle, and address specific considerations for projects involving shell and core construction and fit-outs.

CCA majors on ventilation and ductwork specifics, while reference can be made to CIBSE Commissioning Code M: Commissioning management (2022) for the overarching commissioning management process. The suggested actions are referenced to the RIBA Plan of Work, as shown in Figure 1, and CCA clarifies which activities fall under the responsibility of the commissioning specialist and which are handled by the commissioning management team.

The newly revised BSRIA BG49 2024 (see boxout, ‘BSRIA BG49 and CIBSE Commissioning Code A relationship’) offers detailed methodologies for carrying out the functional testing and regulating procedures outlined in CCA. The collaborative development of CCA aims to provide a comprehensive and standardised approach to commissioning air distribution systems.

CCA 2024 has specific references to a more extensive range of air distribution systems than that of its predecessor, moving beyond the traditional focus on constant air volume (CAV) and variable air volume (VAV) systems. This version of the code also addresses the distinction between shell-and-core construction and category A and B fit-outs.

While primarily considering UK practices, CCA has global relevance and includes guidance for applications, noting that some practices or designs covered may not be common in the UK but are pertinent to international contexts.

CCA 2024 emphasises the significance of well-commissioned and maintained ventilation systems in ensuring a healthy indoor environment and mitigating infection risks. Appendix D underscores the importance of maintaining high air quality within buildings to enhance occupant wellbeing and minimise infection spread, referring to research and guidance from organisations including the Royal Academy of Engineering and CIBSE.

Ongoing testing and balancing throughout a building’s lifespan, together with continuous monitoring and adjustments, are highlighted as being key to maintaining system performance.

Well-informed decisions made at the design stage of ventilation and ductwork systems are fundamental for ensuring successful commissioning. Both BG49 and CCA emphasise the need for competent commissioning specialists to be involved early in the project. Such specialists should be trained, and possess appropriate experience and accreditation, such as that provided by the CSA.

CCA emphasises that a planned and effective working collaboration between the commissioning specialists and other parties during the planning and programming stage is essential to ensure efficient project execution. As detailed in the first of the five supporting appendices, appendix A, a comprehensive specification is essential to define system requirements, tolerances, and demonstration criteria – the requirements and procedures that must be met to prove that a ventilation and ductwork system is performing as specified.

This should be developed in collaboration with designers, contractors and commissioning specialists to ensure that the system is designed for ease of commissioning and operation. This would include taking account of factors such as accessibility of components, test points, and straight ductwork lengths to facilitate commissioning activities. The design team will need to produce system schematics and layout drawings, which indicate component arrangements and access provisions.

The commissioning specialist should review the design documentation to identify any potential challenges and ensure that the system is designed for ease of testing, measurement and adjustment. They should also work with the design team to develop a commissioning plan that outlines the specific tasks to be performed, the timing of those tasks, and the resources required.

CCA Appendix B outlines the duties and responsibilities of installers in relation to the commissioning of ventilation and ductwork systems. It emphasises the installer’s role in achieving an installation that enables successful implementation of commissioning procedures. Installers must have a thorough understanding of the system design and testing requirements, and should prioritise system cleanliness, protecting against contamination during installation, and ensure the removal of debris.

Regular inspections during and upon completion of installation determine readiness for testing. Appendix B also highlights the importance of ductwork leakage testing, which should be conducted prior to ceiling installation or the application of insulation.

CCA explains that the onsite stage of functional testing requires thorough planning and preparation. Method statements and methodologies should be prepared and approved in advance to ensure a safe and efficient testing process. In addition to the specific technical details, the Functional Testing Method Statement/Risk Assessment (often referred to as a RAMS) should outline health and safety arrangements, risk assessments and specific site procedures, and provide detailed information, including system descriptions, preparation requirements, commissioning procedures, roles and responsibilities, instrumentation, and relevant reference documents.

Pre-functional checks are essential to verify system readiness, including ductwork leakage tests and manual fire-damper operation. CCA Appendix B notes that proper documentation of test results and certification of pre-functional testing and static completion are essentially responsibilities of the installer. For significant plant items, such as air handling units (AHUs) and fans, offsite testing can be beneficial. Suitable protection should be provided for equipment that is susceptible to frost damage in cold weather conditions, and maintaining system cleanliness is paramount. CCA outlines precautions to minimise airborne detritus during initial fan startup.

Before commissioning commences, there should be a check on the readiness of the building and systems.

In CCA Appendix C, it is recommended that BG49 and materials from the CSA are referenced for details on equipment, instrumentation and flow-measuring techniques, to satisfy the needs of the various terminal types. Regular calibration of instruments is required to ensure accuracy and reliability of measurements. Guidance is provided on comparing different measurement methods when a system incorporates several terminal types, ensuring consistent evaluation of airflow rates.

Three basic ventilation and ductwork system balancing concepts are introduced in CCA: conventional CAV, VAV, and pressure differential systems, outlining their unique characteristics, functional testing, and regulating procedures. For example, for conventional CAV systems (relating to the principles of the ‘proportional balance’ method¹), it emphasises the use of the ‘initial scan’ to assess system performance and to identify the ‘least favoured terminal’, and cautions against over-restricting the system.

The details of the regulation process for VAV systems are covered, acknowledging their dynamic nature and the need for a detailed methodology tailored to specific system components. It highlights the significance of adhering to manufacturer guidelines and becoming thoroughly familiar with the system. Pressure differential systems enable controlled space pressures for isolating or containing specific areas, such as operating theatres, laboratories, or escape routes where preventing undesired airflow is critical.

The pressure differential may be controlled using self-acting or automatic pressure-stabilising devices. However, it is noted that, although the initial regulation of the system will involve proportional balancing, it may be necessary to partially disrupt this balance to achieve the required pressure differentials.

Beyond the conventional systems, the code introduces more particular applications, including jet-nozzle diffusers, active chilled beams, mechanical ventilation and heat recovery (MVHR) systems, and smoke-control installations.

A comprehensive and detailed report will be needed for each tested or regulated system that would typically include, at least:

• A front sheet detailing the system, asset references, and the testing organisation
• A report sheet noting who carried out the tests, completion date, issues encountered, and any residual tasks
• Specific test sheets covering fan performance, terminal velocity readings and volume flow measurements, along with schematics of the system
• Calibration certificates for instruments used, or a reference to their central register.

Additional documentation, such as pre-functional checks, installation records and cleaning certificates, would also be incorporated as appropriate.

A key element of the functional testing and regulating process is the demonstration to a designated authority, such as the client or design team, to verify it meets specified requirements. Demonstrations should occur shortly after regulation (typically within two weeks) and align with the commissioning specification.

The completed draft report should be issued before the demonstration for review and, once agreed after the demonstrations are completed, it becomes a formal record. Acceptance of a system may require additional steps beyond the demonstration, including proving integration with other systems, confirming functionality with building management system (BMS) controls, or verifying emergency response capabilities. These activities fall outside the scope of CCA, but are within the scope of CIBSE Commissioning Code M.

Figure 2: An example of a calibrated volume flow sensor (connecting to a matched ductwork measuring point) that communicates through MODbus to the BMS. This particular unit can provide calibrated output relating to measured pressure or air velocity, and auto-zeros with a linearity (sensor deviation from a perfectly linear response) of 0.25Pa at pressures less than 100Pa (Source: CMR Controls)

CCA develops guidance for the in-use stage of ventilation and ductwork systems, including review commissioning, fine-tuning, seasonal testing, post-project review, and ongoing commissioning. This is likely to benefit from the application of BMS-connected measuring stations – such as that shown in Figure 2 – which can reliably feed back calibrated flowrate measurements throughout the operational life of the systems.

CCA stresses that the commissioning specialist’s role extends beyond functional testing and includes participation in these activities to ensure sustained optimal performance. The commissioning review process involves identifying both the successful and challenging aspects, addressing any outstanding issues, and documenting the lessons learned.

Fine-tuning and seasonal testing are important to ensure the system’s performance aligns with the design intent under varying occupancy and external climatic conditions, often in collaboration with the building’s facilities management (FM) team.

Post-project review involves evaluating the building’s overall performance against the design goals, which may include periodic revalidation of ventilation and ductwork system performance, and contributions to accreditation schemes such as Breeam and Leed. Occupant feedback, post-occupancy evaluation, and monitoring of occupancy patterns are promoted as some of the tools to inform ongoing commissioning activity.

A concise section, included as Appendix E, provides specific guidance for commissioning air distribution systems in buildings that are completed in stages. It explains the implications of staged building completion, specifically the ‘shell and core/fit-out’ approach, on the commissioning of ventilation and ductwork systems. It acknowledges the challenges posed by incomplete systems during initial stages and the need for meticulous record-keeping to ensure smooth progression of subsequent commissioning activities.

During the ‘shell and core’ phase, the commissioning specialist focuses on proving the functionality of installed equipment and demonstrating the system’s capability to deliver the designed duty. In the ‘fit-out’ phase, the emphasis shifts towards ensuring that the fit-out design adheres to the limitations imposed by the base-build system, and utilises allocated services within permissible limits.

Together, the CCA and BG49 provide a comprehensive guide for professionals involved in the commissioning process, ensuring that air distribution systems operate safely, efficiently and in compliance with industry standards and regulations. The updated 2024 editions reflect transitions in the industry, making them particularly relevant in contemporary building projects.

Both CCA and BG49 are indispensable references for commissioning air distribution systems. This article offers a very brief overview of these excellent resources and aims to encourage further exploration of their detailed guidance. 

© Tim Dwyer 2025.

References:

1. Harrison, E and Gibbard, N C, Balancing airflow in ventilating duct systems, Journal IHVE, 1965 –bit.ly/CJFeb25CPD1

The post Module 244: Commissioning air distribution systems for the 21st century appeared first on CIBSE Journal.

CIBSE TM65, Embodied carbon in building services: A calculation methodology, provides guidance on calculating the embodied carbon emissions of mechanical, electrical and plumbing engineering products used in buildings. Since its 2021 inception, the Technical Memorandum has spawned several significant addenda. This CPD will provide a reminder of the scope of TM65, and explore the regional- and sector-specific addenda that have been published to support and encourage the adoption and application of TM65 as a route to predicting the life-cycle global warming impact of a product.

TM65 and Environmental Product Declarations (EPDs) are standardised ways to assess and report embodied carbon. They each play a distinct role in fostering transparency and driving the reduction of embodied carbon in the building services industry.

EPDs are independently verified and registered documents that communicate transparent information about the life-cycle environmental impact of a product. They are considered the most reliable source of information about the environmental impacts of a product and are a standardised way of declaring carbon emissions associated with a product throughout its life-cycle, using a global warming potential (GWP) indicator. They provide a comprehensive and independently verified assessment of a product’s life-cycle environmental impacts, going beyond just GWP emissions. EPDs are developed from Product Category Rules (PCRs), which provide sets of rules, requirements and guidelines that have been developed following existing standards, such as BS EN ISO 14025¹ and BS EN 15804.²

TM65, and the various additions, serve as a valuable interim methodology for approximating embodied carbon emissions when EPDs are not available. TM65 is specifically relevant when assessing the environmental impact of MEP systems, particularly as it notes that they can constitute a significant portion of a building’s embodied carbon. This is considered to be in the order of at least 30% in new buildings (excluding refrigerant leakage), and potentially up to 75% in retrofit projects. The methodology provided in the TM emphasises the importance of considering the entire life-cycle of these products, including manufacturing, installation, maintenance and end-of-life disposal. While carbon is a primary focus, the document also highlights the importance of considering other environmental and social impacts when specifying products.

TM65 stresses that requesting EPDs created by manufacturers should be the first step in determining the embodied carbon of MEP products. However, owing to the limited availability of EPDs for MEP products, TM65 provides two interim calculation methods that deliver an ersatz alternative to an EPD:

• The ‘basic’ calculation method that requires less information from manufacturers, primarily relying on product weight and material composition breakdown. It uses a scale-up factor to account for life-cycle stages beyond material extraction.
• The ‘mid-level’ calculation method demands more detailed information, including energy consumption during final factory assembly, transport distances and refrigerant leakage rates. It offers a more comprehensive assessment of embodied carbon compared with the basic method.

See boxout panel for more detail on the two methods.

Both calculation methods use a standardised life-cycle stage framework based on BS EN 15978:2011,³ categorising emissions into modules (cross-referenced to the life-cycle modules of BS EN 15978). For example, TM65 currently includes A1-A4 (product and transport), B3 (repair), C2-C4 (end-of life processes) and, in terms of refrigerant leakage, B1 (use) and C1 (deconstruction). B4 (replacement) is aimed at being calculated at a system level. This consistent approach allows for comparisons between products, and contributes to building a broader understanding of embodied carbon in MEP systems.

Regional adaptations of TM65 are crucial for improving the consistency and relevance of these assessments in different geographical contexts. Since the original publication of TM65 in 2021, there have been further publications that focus on specific sectors and regions. The significance of the addenda is emphasised by the very significant financial and technical input provided by organisations, as acknowledged at the start of each publication.

TM65LA, Embodied carbon in building services: Using the TM65 methodology outside the UK, provides a toolkit that defines the process for adapting the TM65 methodology for use outside the UK by offering a step-by-step approach for creating local addenda. It emphasises the importance of considering regional variations in factors such as transport distances and carbon intensities. It also provides guidance on how to use the TM65 methodology for individual projects in regions lacking local addenda, and aims to promote the consistent assessment of embodied carbon emissions in building services globally. Localised addenda have been produced, and co-funded, with local experts, companies and organisations (as acknowledged in each publication).

TM65ANZ, a local addendum that focuses on Australia and New Zealand, provides alternative assumptions tailored to these regions. Key adjustments include local transport scenarios; refrigerant leakage rates; and a specific carbon factor for landfill. This revises the refrigerant leakage rates to align with Australian and New Zealand standards and practices – this is significant, as refrigerant leakage can have a substantial impact on a product’s overall embodied carbon footprint.

So, for example, it replaces Table 4.4 in TM65 with Table 2.1, providing updated annual leakage rates for the ‘use’ phase (B1) and end-of-life leakage rates for the ‘deconstruction’ phase (C1). These revised rates are based on the Australian Institute of Refrigeration, Air Conditioning and Heating (AIRAH) guidelines that were originally outlined in Methods of Calculating Total Equivalent Warming Impact.⁴

The GWP values for refrigerants are aligned with those used in the Green Star rating system, a prominent sustainability benchmark in Australia and New Zealand. As such, Table 2.2 in TM65ANZ supersedes Table 2.2 in TM65, offering updated GWP values sourced from various bodies, including the California Air Resources Board, the Institute of Refrigeration, and the Intergovernmental Panel on Climate Change’s (IPCC’s) AR5 report.⁵

TM65ANZ acknowledges the unique geographical characteristics of Australia and New Zealand by modifying the transport assumptions. Table 2.8 in TM65ANZ introduces region-specific transport distances, distinguishing between products manufactured within Australia, within New Zealand, or globally (Asia). These revised distances better reflect typical supply chains in the region, which can make a significant impact on the final carbon footprint. For example, products manufactured nationally in Australia are assumed to travel 2,000km by heavy goods vehicle (HGV), whereas products manufactured globally (Asia) are estimated to travel 10,000km by ship and 300km by HGV.

TM65ANZ provides more granular carbon factors for electricity, accounting for variations across Australian states and New Zealand regions. Consequently, Table 2.6 in TM65ANZ supersedes Table 4.10 in TM65, offering region-specific values based on data from the Australian government’s then Department of Industry, Science, Energy and Resources (DISER – now Department of Industry, Science and Resources), and the New Zealand Ministry for the Environment.

Adjustments are made for the carbon factor for landfill emissions (C4) to reflect local waste management practices, by using a value of 0.2kgCO_2e per kg waste that has been sourced from the Australian government’s DISER (and compares with 0.0089kgCO_2e per kg waste in TM65). While TM65ANZ retains the same embodied carbon coefficients for materials (A1) as the original TM65, it emphasises that using locally-sourced EPDs is preferable whenever they are available, and TM65ANZ serves as a valuable interim methodology until EPDs become more widely available in the region.

The most recent addendum to TM65, TM65NA, published in conjunction with ASHRAE, relates to North America (United States, Canada and Mexico). As with TM65ANZ, it incorporates regional factors such as electricity and gas carbon factors based on location, specific transport scenarios, and updated refrigerant leakage rates derived from US regulations. Just as with TM65ANZ, this is not designed as a standalone document; it is intended to be used in conjunction with the core TM65 methodology.

TM65NA introduces North American-specific embodied carbon coefficients for materials such as fibreglass, rockwool and general insulation, sourced from the Embodied Carbon in Construction Calculator (EC3) database.⁶ TM65NA updates the refrigerant leakage rates to align with North American standards and practices. It replaces Table 4.4 in TM65 with Table 2.2, providing updated annual leakage rates for the ‘use’ phase (B1) and end-of-life leakage rates for the ‘deconstruction’ phase (C1). These rates are sourced from ASHRAE Standard 34.⁷ The GWPs for common refrigerants are based on the IPCC’s AR5 and AR6⁸ reports. TM65NA recommends the use of AR6 values (published after the original TM65), as they represent the latest scientific estimates, and Table 2.3 in TM65NA replaces Table 2.2 in TM65.

The geographical scale of North America and the diversity of its supply chains have necessitated revised transport assumptions. Table 2.5 in TM65NA replaces Table 4.9 in TM65, introducing new transport distances based on product complexity, and distinguishing between transport by HGV, rail and sea. This includes assuming that nationally manufactured products (high complexity) travel 6,000km by truck. Additionally, more detailed information is provided in Table 2.11 ‘Default transportation scenarios for North America (A4)’, including common North American scenarios such as ‘partial cross country’ (with 50km HGV and 4,800km by train). This also includes estimates that products sourced from Asia to the West Coast travel 10,000km by sea, and European manufacturing (to the east coast) 5,600km by sea.

Recognising the variability in electricity generation mixes across North America, TM65NA provides more relevant carbon factors for electricity. Table 2.6 includes specific values for various US grid regions, while Table 2.7 offers values for different Canadian provinces. TM65NA emphasises the importance of understanding how the location of manufacturing can affect embodied carbon results, especially in the mid-level calculation method.

The carbon factors for landfill emissions (C4) are aligned with waste management practices in North America. Table 2.12 in TM65NA replaces Table 4.15 in TM65, using a value of 0.052kgCO_2e per kg waste sourced from the US Environmental Protection Agency (EPA). TM65NA acknowledges the need for consistent documentation and calculation methodologies, and highlights ongoing efforts by organisations such as ASHRAE, CIBSE, the International Living Future Institute (ILFI)⁹ and US Green Building Council (USGBC)¹⁰ to improve alignment in North America. It also references initiatives such as the MEP 2040 Challenge,¹¹ which aims to reduce the carbon footprint of building systems.

There are localised worked examples (in both TM65NA and TM65ANZ) for both the basic and mid-level calculation methods. These examples demonstrate how to apply the methodology step by step, and offer insights into data requirements and interpretation of results. A sensitivity analysis is crucial in embodied carbon calculations, particularly when using methodologies such as TM65, to understand the influence of various factors and assumptions on the results.

As TM65 was initially developed for the UK context, it relies on assumptions that may not accurately represent other regions – TM65LA stresses the need for local addenda to address these regional differences. Sensitivity analysis helps in quantifying the impact of variations, such as: transport distances; electricity grid carbon factors; end-of-life processes (recycling rates and disposal methods); and refrigerant choices and leakage rates. This aids more informed decision-making about material choices that might include considering alternative sources of steel (which often determines a large part of a manufactured item’s embodied carbon), such as the lower-carbon steel explored in the panel ‘Reducing steel’s environmental impact’.

Other areas that may be highlighted are manufacturing locations, system suppositions and areas where more data collection – or refinement of assumptions – are needed. Such analysis may be employed to compare the results obtained from basic and mid-level calculation methods, assessing the potential for overestimation or underestimation in the basic method. This comparison helps identify potential discrepancies – such as where the basic method might not adequately capture the embodied carbon impacts – that can prompt further investigation or refinement of the methodology.

The practical examples on sensitivity analysis in both TM65NA and TM65ANZ reveal potentially significant differences in embodied carbon depending not only on the manufacturing location, but also between the two geographic zones, highlighting the importance of regional variations.

Reducing steel’s environmental impact

The quest for reduced embodied carbon has encouraged steel producers to develop processes that reduce emissions in manufacturing. By drawing on renewable sources of electricity to heat electric arc furnaces, and incorporating significant proportions of recycled scrap metal, substantial CO₂ reductions can be delivered, compared with traditional methods.

For example, an international steel manufacturer¹² claims that CO₂ emissions can be as low as 0.3kgCO_2e per kg of finished steel when the source material is 100% recycled scrap steel. (This compares with traditional steel production methods, especially those using blast furnaces, that typically emit around 2-3kgCO_2e per kg of steel.) The air handling unit (AHU) in Figure 1 is an example of how this might make a practical impact on the embodied carbon of MEP products while maintaining function and performance.

So far, there have been three addenda produced to address the needs of particular industry sectors, to understand system-level impact. All three have extensive discussion, applications and worked examples of employing the TM65 methods, and have been developed and co-funded by experts in the respective sectors, as acknowledged in each addenda. In brief, TM65.1 specifically examines the embodied carbon impact of space heating and hot-water systems for residential new-build developments in a UK context, following the same calculation methodology as TM65 at the product level.

A lighting-specific perspective on embodied carbon assessment is provided by TM65.2; it offers guidance on material selection, system boundaries, and reporting specific to lighting equipment. The third sector-related addendum, TM65.3, addresses the embodied carbon in logistics centres, encompassing both MEP and material handling equipment (MHE). It analyses the impact of different building types and systems commonly found in logistics facilities.

TM65 is not intended to replace EPDs, but rather to bridge the gap until EPDs become widely available for all building services equipment, supporting decision-making related to embodied carbon. However, those who apply TM65 are encouraged to request EPDs from manufacturers to signal that there is industry demand, and so encourage manufacturers to invest in EPD development. At the same time, TM65 encourages users to share their embodied carbon calculations with CIBSE to help develop a comprehensive database and refine the methodology further.

A primary aim of TM65 remains to provide an understanding of whole-life carbon and embodied carbon in building services, moving towards a future where EPDs become widely available.

All TM65 resources, including calculation tools, can be accessed at cibse.org/tm65. Upcoming addenda will include guidance tailored to heating, ventilation and air conditioning (HVAC) systems for office environments, and adaptations specific to the United Arab Emirates region.

• Withs thank to Louise Hamot of Introba for her valuable expertise and contributions to this article.

© Tim Dwyer 2024.

References:

1. BS EN ISO 14025:2010 Environmental labels and declarations. Type III environmental declarations. Principles and procedures, BSI 2010.
2. BS EN 15804:2012+A2:2019 Sustainability of construction works – Environmental product declarations — Core rules for the product category of construction products, BSI 2019.
3. BS EN 15978:2011 Sustainability of construction works – Assessment of environmental performance of buildings – Calculation method, BSI 2011.
4. Methods of calculating Total Equivalent Warming Impact (TEWI), AIRAH 2012 – bit.ly/CJDec24CPD1 – accessed 26 October 2024.
5. IPCC AR5 report – bit.ly/CJDec24CPD2.
6. Building Transparency Embodied Carbon in Construction calculator (EC3) Database –bit.ly/CJDec24CPD3 – accessed 26 October 2024.
7. ASHRAE Standard 34-2019 Designation and Safety Classification of Refrigerants, ASHRAE 2019.
8. IPCC AR6 report – bit.ly/CJDec24CPD4.
9. Embodied Carbon Guidance, International Living Future Institute (ILFI) – bit.ly/CJDec24CPD5 – accessed 26 October 2024.
10. Driving Action on Embodied Carbon in Buildings, USGBC, 2023 – bit.ly/CJDec24CPD6 – accessed 26 October 2024.
11. MEP 2040 Challenge – bit.ly/CJDec24CPD7 – accessed 26 October 2024.
12. bit.ly/CJDec24CPD8 – accessed 26 October 2024.

The post Module 243: A global methodology for estimating embodied carbon in building services appeared first on CIBSE Journal.

Design for manufacture and assembly (DfMA) has been applied across various sectors, including automotive, aerospace, and consumer products. More recently, disciplines associated with the built environment have embraced this approach to add value to their offerings.

DfMA can have – and, for some, is already having – a transformative impact on building services engineering by focusing on efficiency, quality and collaboration in the design, fabrication and installation of mechanical, electrical and plumbing (MEP) systems. This CPD article will explore aspects that underpin the concept of DfMA, and consider the benefits and challenges of increased application of modern methods of construction.

DfMA can be considered¹ as involving a four-stage process to optimise product design for efficient manufacture and assembly:

• Functional analysis: ensures the design fulfills its purpose by examining components and identifying areas for simplification.
• Manufacturing analysis: evaluates design feasibility for manufacturing, considering factors such as materials, processes and complexity.
• Handling analysis: assesses ergonomic considerations for handling components during manufacturing and assembly.
• Assembly analysis: examines the assembly process, identifying redundant steps, intricate manipulations and potential bottlenecks.

This systematic approach optimises products for both function and manufacturability. This includes an array of applications, such as modular units delivering pre-assembled risers, waste systems, service pods, pumping and heating stations, and plantrooms. Such modules would typically incorporate ductwork, piping, wiring (power and control), and other systems, which are integrated into standardised frameworks.

These are designed to be manufactured, often offsite, in a controlled factory environment, and later installed as complete units. Components and systems would normally be designed with simplicity and optimisation in mind, to streamline both the process of offsite manufacturing (OSM) and the assembly on site. This can also encourage the use of standardised, readily available components to reduce complexity and manufacturing costs, such as with the prefabrication of the drainage stack illustrated in Figure 1.

Figure 1: Offsite prefabrication of drainage systems in factory conditions allows for faster and more confident installation on site. Specialist fabricators and factory-controlled quality assurance systems (including pressure testing) ensure quality and reliability (Source: Polypipe Building Services)

Successful implementation of DfMA requires early involvement of contractors, subcontractors and suppliers in the design process, to ensure that the manufacturing and assembly of the components are feasible and deliverable. It can benefit from digital technologies, including building information modelling/models (BIM), and digital twins to facilitate design coordination and information sharing among project stakeholders.

Successful building services design requires close coordination between multiple teams, including mechanical, electrical, plumbing, structural and architectural specialists, who have knowledge and understanding of fabrication, installation and operation. DfMA fosters collaboration early in the design phase by encouraging interdisciplinary consideration of assembly constraints and factory fabrication methods.

This encourages smoother communication, more effective coordination and proactive problem-solving from the project’s inception.² It also supports building systems designers to work more closely with manufacturers, to ensure components fit the overall design and construction plan. As DfMA focuses on simplifying assembly, systems are likely to be easier and quicker to install by reducing the number of individual components needed to be assembled on site.

DfMA is a key component of modern methods of construction (MMC), providing the design philosophy and methodology to facilitate the successful implementation of many MMC approaches. While MMC encompasses a range of innovative construction techniques, DfMA provides the framework for the efficient and effective realisation of MMC.

These principles and approach are particularly supportive of the MMC activity related to pre-manufacturing. The use of software systems (such as BIM) for design coordination, clash detection and logistics planning aligns with the principles of process-led site improvements.

BIM can be employed to enable more insightful planning of prefabrication and installation, ensuring that systems are optimised for offsite manufacturing and allowing potential issues to be addressed before construction begins. Essentially, DfMA provides the design foundation for a more efficient, streamlined and integrated construction process, which makes it a key aspect of the broader shift towards MMC.

This approach is particularly useful in projects with tight schedules, such as hospitals and data centres, where timely completion and compliance with design specifications are critical. The implementation of DfMA often leads to the creation of modular systems that have been proven to simplify fabrication, transportation, installation and maintenance,² and reduces the opportunity for errors and defects, producing faster and more predictable project timelines.

MMC promotes standardisation and repeatability, allowing the development of standard systems and sub-systems for use across multiple projects. This is particularly useful in sectors such as housing or healthcare, where repeated designs are common.

One of the most compelling advantages of MMC is the ability to shift a large portion of the work off site, to controlled factory environments. This transition to offsite prefabrication allows for greater control over the quality of components and assemblies, as they are manufactured in a standardised manner, often using automated processes.^3,4

Standardised designs can be prefabricated more efficiently, potentially reducing design time for individual projects. MMC reduces the need for multiple teams of specialists working on site, as much of the work is completed in a factory setting, which helps mitigate common issues such as weather delays, inefficient waste management, and unsafe working conditions.

The precision of factory-based manufacturing delivers a significant reduction in defects⁴ and reduces material waste, ultimately leading to a higher-quality final product. Through the more extensive planning process there is potential to integrate renewable energy sources, smart controls and other sustainable technologies into the systems.

Factory testing and quality control before systems are installed on site can further improve system performance and reduce the risk of defects. Processes can link the construction programme to BIM, enabling detailed cost measurement and analysis, and the creation of a library of construction materials relevant to MMC.⁵

By moving more of the work to a factory environment, engineers can design systems that can be assembled by fewer, highly trained workers. This reduces the demand for onsite labour teams and minimises the need for potentially dangerous activities associated with working in difficult site conditions, such as high-level installations or work in confined spaces.

It also reduces congestion and the number of trades working simultaneously on site, so improving overall site efficiency and safety. The opportunity to closely control material waste and reduce onsite emissions aligns with environmentally-conscious construction practices. By enabling parallel construction activities, MMC reduces the overall construction time.

While modules are being fabricated off site, other onsite tasks can proceed simultaneously, resulting in a faster project completion.² Supply chain management becomes crucial in MMC, as prefabricated components need to be delivered on time and integrated smoothly into the overall construction schedule.

Digital technologies, particularly BIM, play a crucial role in amplifying the benefits of MMC in MEP. BIM facilitates the creation of comprehensive 3D models that aid in clash detection, optimise MEP routing, and generate highly accurate fabrication drawings. The seamless transfer of this digital information to the manufacturing facility further enhances the overall accuracy and efficiency of the construction process.

An MMC framework⁶ developed by the UK government’s former Department for Levelling Up, Housing and Communities (DLUHC; now the Ministry of Housing, Communities and Local Government) outlines seven distinct categories of MMC:

1. 3D primary structural system: This category focuses on volumetric construction, where three-dimensional units, often entire rooms or modules, are manufactured off site and then assembled on site. This approach is particularly well suited to projects with repetitive layouts, such as hotels, student housing, and some residential buildings.
2. 2D primary structural systems: This category involves the offsite manufacture of two-dimensional elements, such as walls, floors and roof panels, which are then assembled on site to form the building’s structure. This category encompasses various materials and systems, including timber frame, light-gauge steel and precast concrete panels.
3. Non-systemised structural components: This category focuses on individual load-bearing elements that are pre-manufactured off site and then incorporated into the building’s structure on site.
4. Additive manufacturing: Although not yet widely used in construction, this category includes innovative techniques such as 3D printing, where building components or even entire structures are created layer by layer on site.
5. Non-structural assemblies and sub-assemblies: This category encompasses pre-manufactured elements that are not part of the building’s primary structure, but contribute to its overall functionality. Examples include prefabricated bathroom pods, kitchen units, utility cupboards and pre-assembled MEP modules.
6. Product-led site improvements: This category focuses on using traditional building materials in innovative ways to improve onsite productivity. This can include using pre-sized or pre-cut materials or employing components designed for faster and easier installation.
7. Process-led site improvements: This category encompasses innovations in onsite processes and technologies that enhance construction efficiency, productivity and safety. Examples include the use of BIM for site logistics and coordination, digital site verification tools, robotics, drones, and worker augmentation technologies.

While the seven categories provide a valuable framework for understanding MMC, a recent collaborative research report⁷ introduces an additional category, referred to as category ‘0’: Precondition: design, standardisation, and digitisation. This category emphasises the crucial role of design thinking, standardisation of components, and digital tools in enabling the successful implementation of MMC.

It highlights that MMC is not merely about offsite manufacturing, but also about a holistic approach that integrates design, manufacturing and onsite assembly processes. However, this proposed category could blur the division between the scopes of DfMA and MMC.

The DLUHC framework is primarily geared towards residential construction. However, the principles and benefits of MMC are applicable across various sectors, including healthcare, education, commercial, and even infrastructure.⁷ There has been a ‘significant increase’ in completed modular housing projects around London that may reflect the framework’s success.⁴

Developers and contractors are recognising the benefits of these techniques and are increasingly incorporating them into their projects. There has been greater collaboration between industry stakeholders, which is essential for the successful implementation of MMC, which has led to the formation of new partnerships and alliances.⁷ Increased investment in MMC-related technologies and businesses indicates a growing confidence in the potential of MMC to transform the construction sector.⁴

It is important to note, however, that the adoption of OSM is still in its early stages and there are challenges to overcome. The perceived barriers largely stem from concerns around cost, logistics and industry readiness. High initial investments in technology, manufacturing facilities and specialised equipment can deter companies, despite the long-term cost savings.

Design flexibility is often seen as limited with OSM, especially for complex projects, which can make it less appealing. Additionally, logistical challenges – such as transporting large, prefabricated components to urban or remote sites – can add to the complexity.

A skills gap within the workforce is another hurdle, as OSM requires proficiency in digital tools, manufacturing processes and system integration – areas in which many construction professionals lack experience. Regulatory and planning processes are often not well suited to offsite methods, causing delays and uncertainty in compliance. The construction industry’s fragmented supply chain can further impact the efficiency of OSM projects, with issues around coordination and reliability.

Culturally, the industry has been slow to embrace OSM because of its conservative nature, and there are concerns over the quality and long-term performance of prefabricated solutions. This resistance is compounded by a perception of risk, as OSM depends heavily on precise coordination, and any disruption can lead to costly delays. Finally, securing finance can be challenging, as lenders are often cautious about its viability compared with traditional methods.

Nonetheless, DfMA, MMC and OSM can deliver significant benefits to building services engineering. A recent report by the UK parliament’s Science and Technology Committee calls for greater adoption of OSM in the construction sector.

It highlights the benefits that are encompassed by DfMA, including improved quality, faster construction times and reduced waste – as, for example, delivered by the drainage stacks in Figure 2. However, the report also confirms the barriers to wider adoption, such as skills gaps, lack of collaboration, and financing challenges.

Figure 2: Scheduled deliveries of standardised prefabricated components reduces the need for onsite storage, while also reducing the time and cost of installation for these drainage stacks. Waste on site is virtually eliminated. Such systems are designed for easy adaptation to most domestic drainage applications in high-rise developments (Source: Polypipe Building Services)

To address these challenges, the report recommends that the government support skills development, promote best practices, and create a favourable funding environment for OSM. It also highlights that collaboration among industry stakeholders is crucial, as is the use of digital tools such as BIM.

By implementing these recommendations, the government can create an increasingly supportive environment for MMC, leading to a more efficient, sustainable and resilient construction industry. This could result in improved quality, faster construction times, reduced waste, and greater value for developers and consumers. Government support can readily reach beyond financial initiatives such as grants, tax incentives or subsidies, to mitigate the upfront costs associated with MMC.

By mandating the appropriate use of MMC for public projects – including schools, hospitals and social housing – the government could help ensure consistent demand for MMC, lessening concerns about the long-term stability of the sector, which is often hindered by irregular workloads and funding streams. 

© Tim Dwyer 2024.

References:

1. Design for manufacture and assembly (DfMA) Guideline: Version 1, Construction Innovation Hub, UKRI, 2022.
2. Reference Materials – Adopting DfMA for MEP works, Aecom Asia Company Limited for HK CIC, 2021.
3.  Bao, Z et al, ‘Design for manufacture and assembly (DfMA) enablers for offsite interior design and construction’, Building Research and Information, 2021, bit.ly/CJNov24CPD31.
4. Bayliss, S and Bergin, R, Modular housing handbook, RIBA Publishing, 2020.
5. Jansen van Vuuren, T and Middleton, C, Methodology for quantifying the benefits of offsite construction, CIRIA 2020.
6. Introducing the MMC definition framework, MHCLG Joint Industry Working Group on MMC, 2019, bit.ly/CJNov24CPD32 – accessed 30 September 2024.
7. Ahmad Alrifai, A et al, Offsite construction – concept design and delivery, Buildoffsite/CIRIA 2023.

The post Module 241: Accelerating modern methods of design and manufacture in buildings appeared first on CIBSE Journal.

The transition from traditional boilers to heat pumps provides an opportunity to improve building thermal performance, increase energy efficiency and reduce carbon emissions. However, successfully replacing boilers with air source heat pumps (ASHPs) involves a detailed and methodical process to ensure optimal performance and deliver energy savings. Based on the experiences of a ‘solutions engineer’, this CPD suggests the early stages that can lead towards a successful transition, focusing on understanding heat usage, measuring and recalculating demands, and experimenting with system options.

The phrase ‘fabric first’ is frequently mooted when discussing ways to improve the environmental performance of buildings. It emphasises designing buildings with appropriate thermal characteristics to increase the opportunity of delivering a building that maintains acceptable, year-round internal conditions with minimal requirements for heating and cooling systems. When discussing renewables – and particularly heat pumps – for existing buildings, ‘fabric first’ typically means enhancing the building envelope to reduce heat losses.

This is crucial, because any heat loss contributes to the total load and, despite the impressive efficiencies of heat pumps, achieving cost-neutral operation compared with gas boilers remains challenging. Reducing heat loss can also lower the required size of heating systems significantly, thereby cutting capital and installation costs associated with the building systems refurbishment.

A key reason heat pumps are closely linked with a ‘fabric first’ approach is because of flow temperatures. ASHPs are more efficient when the source temperature is higher and/or the sink temperature is lower. While the source temperature (ambient temperature) is highly variable in the UK (and not controllable), the sink temperature (flow temperature) can be reduced wherever possible. Lower flow temperatures will reduce the output from emitters that have been designed for higher mean water temperature – so, if less heat is needed because of fabric upgrades, the net result may well be a heating system output that matches the building load.

If the prospect of potentially high costs and unacceptable payback periods, or heritage considerations, prevent changes to the building envelope, a ‘fabric first’ approach may not be feasible, leaving the existing thermal envelope of the building practically unimproved.

For owners of such buildings who wish to decarbonise their heating, a hybrid solution – for example, to maintain the existing gas boilers for peak loads and domestic water generation, and install heat pumps to cover the base load – is often a fast, efficient and affordable approach. However, there is a desire by many owners and operators to skip hybrid solutions and move directly to the full electrification of heat.

High temperature ASHPs (HT ASHPs) have been developed to address this challenge, but the solution is not as straightforward as it seems. Swapping boilers for heat pumps in existing buildings often involves aiming for familiar operation ranges, such as 82/71°C or 80/60°C.

However, achieving an 80°C flow temperature all year round with acceptable efficiencies is optimistic, as even the most advanced R290 (propane) heat pumps are operating at the top end of their performance envelope at 80°C flow. (A high temperature heat pump is classified by BS EN 14825:2022¹ as delivering 65°C at -7°C dry bulb, -8°C wet-bulb ambient conditions, with the medium and low classifications required to deliver 52°C and 35°C respectively, at the same conditions.)

Even when HT ASHPs can deliver 80°C, this falls slightly short of the 82°C flow required by 82/71°C circuits. Additionally, most heat pumps operate most effectively within a 5K to 10K supply/return temperature differential, making a direct swap into 80/60°C circuits challenging. In any case, boilers in 82/71°C circuits are typically set to operate at a flow temperature of around 85°C to mitigate hydronic inefficiencies, such as temperature dilution.

The challenges involved in the detailed design of replacing boilers with heat pumps should not be underestimated and, before starting a project, significant investigative engineering is recommended. The first stage should be to develop a comprehensive understanding of installed, calculated and actual heat usage.

A familiarisation site visit to meet current operational staff and gather information on the original installation can provide intelligence for later desktop studies, including: determining the original design temperature and loads; hydronic inefficiencies, such as exposed, poorly insulated pipework or temperature dilution; and whether the building has been extended, reduced, zoned or had alternative heating systems installed.

It is important, at this early stage, to ascertain the expectations of the building user/owner around the outcome of the current project, as well as to discover any plans for the coming years that may impact the building’s thermal loads and usage.

The process to ascertain current loads should ideally start early in the heating season, to allow for a full season’s measurement and develop a comprehensive understanding of the building’s heating demands. Detailed sketches and drawings should be created to represent the existing heating generation and distribution systems. Aside from helping to understand the layout, these will be essential for any subsequent nodal analysis.

The sketches may be compared against available onsite schematics or operation and maintenance (O&M) manuals, to identify any interim additions or changes to the system. It is important to understand the operational temperature ranges and frequencies, and the load requirements, for each heating circuit. Existing heat meters or temporary ultrasonic heat meters may be used to gather usage data. This requires at least a transitional and winter season to build enough data for extrapolation, and this can be validated with other calculated data.

Heat demands should be recalculated, particularly if the property has undergone remedial works to the thermal envelope. (Original calculations, if available, may be used for comparison.) For space heating, room-by-room heat loss calculations will provide the load requirement to establish the parameters for the distribution circuits, and will be vital for experimenting with novel flow temperatures.

Historic data, such as gas utilisation and building management system (BMS) data, can assist in building a comprehensive picture of current building demands. (Historic meter readings must be treated with caution as, for example, they may include gas used in catering and other processes.) BMS logs can provide invaluable intelligence on variable temperature (VT) circuits and the application of weather compensation curves that can assist in the interpretation of the heating demands.

Experimenting with flow temperatures can reveal new options to decarbonise, reduce capital costs and lower running costs. For most buildings with a setpoint of 21°C, internal emitters do not require flow temperatures of 80°C to 82°C year round.

Reducing flow temperatures during heating months, while carefully monitoring internal comfort temperatures, may yield insightful results. Careful modelling of the building can also provide information for updated emitter requirements and intelligence for optimising weather-compensated flow temperature curves.

After initial investigations and experimentation, it is important to understand the weighting of each circuit in terms of overall demand. The initial step is to assess the peak power demand for each circuit and then establish the usage profile over time to ascertain an overall power profile. This can then be used to inform the determination of the minimum flow temperature that will deliver the required performance using current, or modified, heat emitters.

Circuits should be organised with others that have very similar attributes. For example, a priority VT load operating almost continuously at 55°C should not be grouped with a sporadic constant temperature (CT) load requiring 82°C. In such cases, separating the CT load (sometimes referred to as ‘bracketing’ – see boxout) to be supplied by a heat generator independent of heat pump-supplied circuits may provide greater overall efficiency.

Bracketing

Bracketing is used to organise the system into manageable sections based on known and weighted data. For example, considering a significant CT circuit dedicated solely to an air handling plant. In such a case, the decision might be made to ‘bracket’ this circuit out of the main heating system.

By isolating this circuit and connecting it directly to its own heat pump plant, the heating coils may be adjusted to accommodate a flow temperature of 55°C or lower. This adjustment alone has the potential to boost the heat pump’s efficiency by up to 150%, compared with a design temperature of around 80°C.

The same concept applies to VT circuits when the CT circuit cannot deviate from its current design flow temperature. Bracketing VT circuits can lead to significant efficiency gains, as weather compensation can be managed directly at the plant without the need for mixing valves. With direct weather compensation on HT ASHPs, the flow temperature can vary between 35°C and 80°C. If it is feasible, heat emitters may be modified to allow for a more aggressive weather-compensated temperature curve, as illustrated in Figure 2. The periods when the HT ASHPs must maintain an 80°C flow can be balanced out in terms of overall efficiency by the times when lower flow temperatures are sufficient.

The weighting aspect of bracketing involves understanding the capacity requirements for each circuit. For instance, if VT circuits account for 80% of the total load, addressing them independently while keeping the CT circuit at an 80°C flow might enhance the building’s overall efficiency without necessitating the replacement of air handling unit (AHU) coils.

Care should be taken, however, when evaluating potential medium/low-temperature circuits. Even if these circuits represent only a small percentage of the overall peak heating demand, they may still contribute significantly to the overall energy usage.

Although CT circuits nominally maintain a constant temperature, it may be possible to reduce flow temperatures while maintaining the required levels of performance and comfort. This can lead to significant energy savings and improved efficiency. Specific needs of high-temperature CT circuits may be addressed by advanced heat pump technologies or hybrid systems that can manage varying temperature requirements efficiently. For example, when the CT is serving loads such as calorifiers, the higher temperatures required may be delivered by employing a ‘divergent’ cascade heat pump system, as shown in Figure 1.

A common application is where an existing building heating system includes gas boilers operating at 82/71°C. For example, a particular existing application has a 300kW CT distribution system and a 100kW VT distribution system, both running at the same boiler flow temperature (the VT system being indirectly weather-compensated).

Cost and operational constraints mean that replacing CT components to reduce the required flow temperature is not feasible. Through experimentation and recalculations, it transpires that the VT distribution circuit can still operate successfully at 55/45°C.

Three solutions might be considered. The first solution involves replacing the gas boilers with high-temperature heat pumps on a kW-for-kW basis, maintaining the 82/71°C requirement year round. This has the advantage of not requiring significant modifications to the existing circuits, making project execution relatively straightforward. However, the capital costs are extremely high, and the high-temperature heat pumps would be operating at the limit of their operating envelope throughout the year.

The second solution divides off the VT circuit and allocates it to medium- or high-temperature heat pumps, while retaining the gas boilers for the CT distribution. This hybrid solution requires less capital outlay and reduces electrical demand. Additionally, lowering the flow temperature broadens the range of heat pump technology options. The downside is that this approach only partially decarbonises the peak load.

The third solution builds on the second by adding a pre-heat tank for domestic hot water (DHW) served by an ASHP. This configuration retains the gas boilers for the CT distribution while allocating the VT circuit to medium or HT ASHPs. The advantages include a reduction in electrical demand, a broader range of heat pump technology options, and a larger portion of the heat being decarbonised. However, this solution also has its drawbacks, such as the need for additional space for a DHW pre-heat tank and more complex controls and valving.

In refurbishment projects, it is crucial to assess whether there is sufficient electrical capacity to support new systems and, if necessary, to evaluate the financial implications of upgrading electrical systems. Exploring potential options, such as integrating photovoltaic (PV) systems, can help offset higher electrical loads.

As building owners and operators explore boiler replacement projects and the various options for decarbonising their heating systems, priority should be given to fabric improvements. Replacing emitters to deliver low-temperature heating generally results in higher overall efficiency compared with employing high-temperature heat pump systems.

Space and noise constraints are often unavoidable, and the ultimate selection of heat pumps will typically require a compromise, but, in any case, a key engineering consideration is to ensure that the heat pumps are not oversized in terms of load.

Achieving perfection in decarbonisation can be difficult when fabric upgrades are limited, but a thorough understanding of the building’s thermal profile helps guide informed decision-making and ensures realistic expectations are set.

© Tim Dwyer 2024.

We thank Ryan Kirkwood of Baxi Solutions for sharing his notes and expertise, which formed the basis of this article.

References:

1. BS EN 14825:2022 ‘Air conditioners, liquid chilling packages and heat pumps, with electrically driven compressors, for space heating and cooling, commercial and process cooling. Testing and rating at part load conditions and calculation of seasonal performance, BSI 2022 – under review.

The post Module 242: Foundations for transitioning from boilers to air source heat pumps appeared first on CIBSE Journal.

Heat production represents a significant portion of global CO₂ emissions. While cost-effective clean heat solutions exist, barriers such as high upfront costs and lack of market certainty hinder their widespread adoption. Successful clean heat standards place an obligation on heating sector participants to deliver cleaner solutions while providing flexibility around how they achieve these targets.

This CPD largely provides a summary of a recently published international handbook that is aimed at accelerating the rollout of suitable clean heat standards across the globe.

Clean heat standards function by placing a performance requirement on key market participants, compelling them to increase the uptake of clean heat solutions. Unlike equipment standards that regulate individual appliances or buildings, clean heat standards target broader fleets of equipment or the operations of energy suppliers. There are several clean heat standards already in place or under development.

In the UK, for example, it is hoped that the Clean Heat Market Mechanism¹ (CHMM), which will introduce a rising market standard for heat pumps as a proportion of fossil fuel boiler sales, will be in place in 2025, while, in the US, a few states have embarked on setting sector-specific obligations for energy utilities. A recent report² by European ‘clean heat’ industry groups drew on an extensive survey³ of 12 EU member states, and determined that the few policy frameworks in place to support wide-scale clean heating and cooling were not yet strong or consistent enough.

To accelerate the design of standards, the Regulatory Assistance Project (RAP)⁴ – an independent global non-governmental organisation (NGO) – has created a freely accessible handbook⁵ as a resource for the development of properly considered, holistic clean heat standards. The handbook proposes four steps as a route towards a successful design of a standard.

The first step, ‘Assess the potential role’, emphasises the importance of a thorough evaluation before implementing a clean heat standard. This evaluation should encompass a comprehensive understanding of the existing heat decarbonisation landscape, including the challenges, policy gaps and potential equity implications. This highlights the dominance of fossil fuels in the heating sector as a primary challenge.

While the specific situation varies across jurisdictions, it notes that transitioning to renewable heat requires significant effort, as well as substantial policy and market reforms. Understanding the existing heat consumption patterns across different sectors – such as residential, commercial and industrial – is crucial for determining the scope of a clean heat standard. A nuanced approach is advocated to clean heat solutions, recognising that a single solution might not fit all contexts.

While electrification through heat pumps is often touted as a key pathway, the handbook acknowledges the importance of considering the existing electricity grid’s carbon intensity. In regions with carbon-intensive electricity generation, a rapid and large-scale shift to heat pumps could inadvertently increase emissions. Therefore, policymakers should carefully assess the electricity mix and consider complementary measures, such as accelerating renewable energy deployment in the power sector.

Beyond the technical aspects, the handbook delves into the barriers hindering the adoption of clean heat solutions. These barriers encompass a complex interplay of factors, including high upfront costs for clean heat technologies, challenges in accessing financing – particularly for low-income households – and a lack of awareness or information about available options. It emphasises that addressing equity concerns should commence right from the outset.

Recognising that access to affordable heating is already a challenge for many, policymakers are urged to design clean heat standards that do not exacerbate existing inequalities. This involves understanding the specific needs and barriers faced by vulnerable communities, such as low-income households, renters, and residents of remote areas, and incorporating measures to ensure they benefit from the transition to clean heat.

It acknowledges that there will be a need to critically assess the effectiveness of existing clean heat policies in addressing the identified barriers. This involves evaluating the performance of subsidy schemes, carbon taxes, emissions trading systems, and energy efficiency obligation schemes.

For instance, while subsidies can help offset the upfront costs of clean heat technologies, the handbook cautions that their effectiveness depends on factors such as programme design, accessibility, and the adequacy of funding. Similarly, while carbon-pricing mechanisms can incentivise cleaner choices, their impact on low-income households needs careful consideration, potentially requiring complementary measures to mitigate any regressive effects.

The handbook advocates identifying the specific policy gaps that a clean heat standard would address and how it would complement existing initiatives. For example, while carbon taxes and emissions trading systems provide a price signal, they might not guarantee a specific trajectory for clean heat deployment.

Similarly, phaseout policies can be an effective way to reduce fossil fuel heating system sales, but they might not achieve a rapid, complete replacement, as illustrated in Figure 1. This is because of the long lifespan of heating systems and continued installations before the phaseout takes effect.

A well-designed clean heat standard can provide this missing trajectory, ensuring a predictable and consistent pathway for decarbonising the heating sector. Distributional impacts should be considered, ensuring that the costs of compliance do not disproportionately burden low-income households, and that the benefits of clean heat reach vulnerable communities. Addressing equity concerns may involve incorporating sub-targets for low-income households or designing complementary policies to mitigate potential cost increases.

The second step the handbook proposes, ‘Design the obligation’, outlines the critical considerations for structuring the core requirements of a clean heat standard. This includes determining which market bears the obligation to drive the adoption of clean heat solutions. The focus is provided on two primary categories: energy companies and heating appliance manufacturers.

Energy company targets include gas distribution utilities, providers of delivered fossil fuels (such as heating oil and propane), bioenergy firms and electricity companies. This choice presents complex trade-offs. Targeting upstream companies, such as wholesalers, could offer greater leverage and administrative capacity, but might require navigating interstate commerce regulations, particularly in the US. Conversely, downstream retailers, while benefiting from direct customer interactions, might lack the resources of their larger upstream counterparts.

Targeting heating appliance manufacturers (such as with the UK CHMM) would directly influence the production side of the equation, incentivising manufacturers to ramp up the production of cleaner heating technologies, such as heat pumps.

However, implementing this approach necessitates addressing the potential for importing fossil fuel appliances from regions without similar standards, which could undermine the policy’s intended effects. Additionally, size exemptions may be considered for smaller manufacturers based on sales thresholds, to avoid placing disproportionate burdens on them. Crafting these exemptions carefully is crucial to prevent loopholes that could compromise the standard’s effectiveness.

Establishing a clear and achievable target for clean heat deployment is fundamental to the success of any clean heat standard. The target metric should align with the overarching goals of the standard. For instance, if the primary objective is to reduce greenhouse gas emissions, expressing the target in terms of emissions reductions would be logical.

However, if the focus is on promoting specific technologies, the metric could be tailored to track technology adoption rates. A particular UK initiative (not mentioned in the handbook) is the Boiler Upgrade Scheme (BUS)⁶ that promises £2bn of grant funding allocated for air source, ground source and water source heat pumps, plus biomass boilers. However, such a technology-prescriptive scheme misses the opportunity of promoting equally valid variants of heat pumps such as exhaust-air heat pumps (EAHPs), an example of which is shown in Figure 2.

Figure 2: An example of an exhaust-air heat pump (EAHP) charged with R290 (propane) delivering heating, hot water and ventilation in one package, with a SCOP of 4.29 and a measured noise level of 49dB(A) (to EN12102). This is aimed at apartments and new-build houses up to 160m² (Source: NIBE)

While aligning the long-term target with broader climate objectives is vital, there will probably be a need for a phased approach. The initial phases might involve relatively modest targets to allow the market to adapt and avoid sudden cost increases for consumers. Providing certainty about the long-term trajectory and incorporating mechanisms such as banking can encourage continued investment in clean heat solutions.

Beyond setting the overall target, there are additional constraints and sub-targets required to address equity concerns and promote a diverse portfolio of clean heat technologies. Recognising that low-income households often face the greatest barriers to adopting clean heat technologies, sub-targets should be included to ensure that these households benefit from the standard.

These sub-targets could mandate obligated parties to achieve a certain percentage of their clean heat deployments within low-income communities, or offer additional incentives for doing so. This approach helps counteract the risk of clean heat benefits accruing primarily to higher-income households that can more easily afford the upfront costs.

Policymakers can use sub-targets to foster the development of specific technologies deemed crucial for long-term heat decarbonisation, even if those technologies are currently less commercially viable. Conversely, caps can be placed on technologies deemed to have a limited role in the long-term transition, or which pose potential environmental or social risks. For instance, the use of certain biofuels might be capped to mitigate concerns about sustainability and land-use competition.

There must be a transparent and inclusive process for defining eligible actions, potentially allowing for revisions based on technological advancements and market feedback. This iterative approach ensures that the standard remains responsive to emerging technologies and avoids locking in specific pathways prematurely.

Step three in the handbook, ‘Create Flexibilities’, focuses on incorporating flexibility mechanisms into clean heat standard design. Three key flexibility mechanisms are identified:

• Banking and borrowing: This allows obligated parties to adapt to variations in market conditions and project timelines by carrying forward those excess credits to meet future obligations. This incentivises early action and provides a buffer against future uncertainties. Conversely, borrowing allows entities falling short of their targets in a period to defer some of those obligations to the next period – although this needs careful management to prevent delaying overall progress. Setting caps on borrowing and potentially imposing penalties for its use can mitigate this risk.
• Trading compliance credits: Recognising that the cost of implementing clean heat measures can vary significantly across different contexts, these would properly incorporate trading mechanisms. Horizontal trading permits obligate entities to exchange compliance credits among themselves, allowing those achieving reductions at a lower cost to sell credits to those facing higher costs. Expanding the scope to include vertical trading – where accredited non-obligated entities can generate and sell credits – can further enhance cost-effectiveness and stimulate broader market participation in clean heat activities. Establishing clear rules and potentially creating dedicated trading platforms can facilitate efficient market operations.
• Buyouts and alternative compliance mechanisms: Buyout provisions can provide a safety valve for obligated parties facing exceptionally high compliance costs. These provisions allow entities to pay a fee in lieu of directly implementing clean heat measures. However, to prevent buyouts from undermining the standard’s effectiveness, it is crucial to set the buyout price appropriately and, potentially, cap the proportion of obligations that can be met through buyouts. Additionally, dedicating buyout revenues to fund clean heat projects implemented by a designated delivery agent can help ensure that the policy’s overall impact remains aligned with its objectives.

The final stage – step four, ‘Ensure compliance’ – considers the mechanisms that underpin the successful implementation and enforcement of a clean heat standard. There are several key considerations for establishing a robust compliance framework with clear administrative structures.

A specific entity, such as a government agency or regulator, should be designated as the scheme administrator that plays a central role in overseeing the standard’s implementation – including setting detailed rules, managing data collection and reporting, and ensuring compliance with the established framework.

It is important to provide the administrator with the flexibility to adapt to evolving circumstances and refine implementation details through secondary legislation or administrative decisions. This flexibility allows for adjustments based on market dynamics, technological advancements, and lessons learned during the implementation process.

There are actions with directly measurable impacts, such as sales figures for clean heating appliances, and those requiring indirect measurement methods, such as greenhouse gas emission reductions. Indirect methods may include ‘deemed scores’ that assign predefined emission reduction values to standardised clean heat actions.

For instance, a specific type of heat pump installation could be assigned a predetermined emission reduction score based on its technical specifications and average performance estimates. Deemed scores require robust verification mechanisms to prevent gaming the system by prioritising installation speed over quality.

An alternative indirect tool is to employ ‘metered methods’ that rely on actual energy consumption data to determine the impact of clean heat actions. This approach, while more complex and data-intensive, offers greater accuracy, especially for large or complex installations where standardised assumptions might not hold true.

Accounting rules will be required to address the long-term impacts of clean heat actions. This includes assigning appropriate lifetimes to different measures and potentially discounting impacts over time to reflect the time value of emission reductions. Additionally, the rules should provide guidance on addressing the rebound effect, where energy efficiency improvements lead to increased energy consumption owing to changes in consumer behaviour.

Recognising that clean heat standards often operate within a broader policy landscape, any methods should account for additionality – ensuring that the credited emission reductions are genuinely attributable to the clean heat standard rather than other policies or autonomous market trends.

This might involve adjusting targets based on the projected impact of complementary policies or requiring obligated parties to demonstrate the unique contribution of their actions. Effective enforcement mechanisms are crucial for ensuring that obligated parties take their clean heat obligations seriously, and it is important to establish clear and sufficiently stringent penalties for non-compliance.

Setting the penalty price appropriately – high enough to discourage non-compliance but not so high as to be unachievable – is essential. Penalty enforcement should be transparent and prompt, potentially requiring obligated parties to compensate for missed emission reductions in addition to paying financial penalties.

While penalties serve as a deterrent, there is potential for incorporating positive incentives to reward overcompliance and further drive clean heat investments. This could involve financial rewards for exceeding targets or allowing obligated parties to bank excess credits at a premium rate for future use.

By carefully designing and implementing these compliance mechanisms, policymakers can create a robust framework for accountability, transparency and, ultimately, the achievement of clean heat objectives.

In conclusion, the handbook highlights that clean heat standards are promising tools for accelerating the transition to cleaner heating systems, but their success requires a comprehensive policy approach. Policymakers will need to tailor the design of standards to their specific contexts, considering local heating sector characteristics, equity implications, and potential interactions with existing policies.

This will involve addressing barriers to clean heat deployment, ensuring equitable access to affordable solutions, and leveraging market forces through flexibility mechanisms and robust compliance frameworks. l

© Tim Dwyer 2024.

This CPD article is principally drawn from the freely downloadable Clean Heat Standards Handbook⁵ by Marion Santini and team at the Regulatory Assistance Project.

References:

1. bit.ly/CJNov24CPD1 – accessed 6 September 2024.
2. How can Europe fill the clean heat gap, bit.ly/CJNov24CPD2 – accessed 6 September 2024.
3. bit.ly/CJNov24CPD3 – accessed 6 September 2024.
4. bit.ly/CJNov24CPD4 – accessed 6 September 2024.
5. bit.ly/CJNov24CPD5 – accessed 6 September 2024.
6. bit.ly/CJNov24CPD6 – accessed 6 September 2024.

The post Module 239: Decarbonising heat: developing effective clean heat standards appeared first on CIBSE Journal.

Urban lighting significantly influences our perception of safety, security and overall quality of life. This CPD article draws on current Society of Light and Lighting (SLL) guidelines, plus themes and findings from recent research papers on the effects of urban lighting, to explore the human perception of safety in artificially lit urban settings.

The history of artificial lighting at night (ALAN) in public spaces dates back centuries. Early forms of public lighting can be traced back to ancient civilisations, which used oil lamps and torches to illuminate streets and public spaces.

In the 15th century, London and other English cities implemented regulations requiring residents to light their homes at night, but this was primarily for safety and security reasons rather than a formal public lighting system.

The development of gas lighting in the 18th and 19th centuries marked a significant advancement in public lighting. Cities such as London and Paris began to install gas streetlamps that provided more consistent illumination, and these systems were maintained professionally, marking the beginning of modern public lighting infrastructure.

The temperature and intensity of light influence perceptions of brightness and safety. Studies, including that by Li et al,¹ consistently show that warmer colour temperatures (lower Kelvin values) generally enhance feelings of safety, even at the same illuminance levels as cooler light. This could be because warmer light is less disruptive to natural circadian rhythms and is associated with more relaxing environments.

Some studies suggest the spectral sensitivity of human vision under low-light conditions (mesopic vision – see boxout) might mean that ‘whiter’ light sources could offer better visibility for certain tasks. But existing metrics, such as lux (lx), that focus on light intensity might not accurately reflect human perception of brightness, as they don’t fully account for the interplay of rod and cone cells at night.

A certain lux level might appear brighter to a person with a higher density of rod cells compared with someone with a lower density. To address this, researchers are exploring more sophisticated metrics that consider the interplay between rod and cone cells.²

An important aspect of ALAN is that it is a significant environmental stressor impacting biodiversity and human health. As discussed in SLL LG21,³ to protect the night-time environment, it is best to avoid installing exterior lighting unless absolutely necessary.

Unshielded urban lights create a diffuse glow in the sky, negatively affecting nocturnal habitats and species adapted to natural light cycles. According to a 2022 study: ‘A recent skyglow model suggests that about 80% of the world’s population now lives under light-polluted skies… which poses a serious threat to biodiversity and human health.’⁴

Even dim ALAN can disrupt melatonin production in various species, affecting crucial day-night cycles, the study suggests: ‘ALAN can also suppress melatonin, known as the night hormone, in various vertebrate species even at skyglow-like low light levels (0.01-0.03lx)… This may inhibit crucial day-and
night-time cycles.’⁴

However, there are many applications that would normally deserve at least some investigation around the appropriate application of external lighting, such as on roads, cycle routes and pathways, to ensure safe movement. It might also be considered to enhance security by enabling surveillance in areas such as car parks, and allow work to be carried out in places such as transport hubs.

Additionally, exterior lighting can extend the use of outdoor facilities, such as sports pitches, and prolong economic activities in areas such as town centres, as well as highlight landmarks or structures, including historic buildings and bridges.

As discussed in the SLL Code for Lighting,⁵ while lighting can play a role in crime prevention, its effectiveness is not guaranteed. Increased lighting can deter crime by making it harder for criminals to operate undetected and by boosting community confidence. However, lighting alone may not directly reduce crime rates. To be effective, lighting must be well designed, providing adequate illumination, uniform distribution, minimal glare, and a suitable light spectrum. This allows people to identify potential threats and take action, while also enabling witnesses to provide accurate information to authorities. Ultimately, the effectiveness of lighting in crime prevention depends on various factors, including the type of crime, the community’s overall environment, and the presence of other crime-prevention measures.

The most straightforward way that lighting impacts actual safety is by improving visibility. Being able to clearly see pathways, obstacles and other people is essential for avoiding accidents and recognising potential threats. While some light is undoubtedly better than none, research suggests that, beyond a certain level, increasing illuminance doesn’t necessarily lead to a proportional increase in perceived safety.

This is important because simply adding more light fixtures has ecological and financial costs. Uneven illumination creates stark contrasts between light and shadow, potentially obscuring potential threats and contributing to feelings of unease. Conversely, well-distributed light reduces hiding spots and enhances visibility, fostering a sense of safety. Harsh, glaring light can be uncomfortable, impair visibility, and create feelings of vulnerability. This is particularly true for older adults, who are more susceptible to glare-related vision issues.

Employing data published in the seminal paper⁶ by Boyce, the perception of safety by visitors experiencing night-time illuminance compared with daylight visits in car parks in two US cities – shown in Figure 1 – indicates a notable relationship between illuminance and the perceptions of safety in the car parks.

At a sufficiently high illuminance, the difference in ratings of perceived safety for day compared with night approaches zero. For illuminances in the range 0lx to 10lx, small increases in illuminance produce a large increase in perceived safety. Illuminances in the range 10lx to 50lx show diminishing returns.

Many challenge the assumption that increasing illuminance directly translates to increased feelings of safety. Specifically, studies suggest that beyond a certain threshold (around 5lx to 17lx⁷), the positive impact on safety perceptions plateaus, even as illuminance continues to rise. The level of illuminance considered ‘safe’ can vary significantly based on the environment and individual expectations.

For instance, people accustomed to brightly lit urban areas might perceive lower light levels as less safe compared with those living in rural settings.⁷ A recent investigation by Jedon et al⁸ considered how spectral composition and intensity influences alertness and arousal levels, impacting pedestrian behaviour and safety.

They note that psychological constructs such as alertness, vigilance and/or anxiety are not generally considered in pedestrian lighting research, as it mainly focuses on visual performance. They assert that exploring concepts such as alertness, arousal and anxiety could provide a deeper understanding of pedestrian safety.

They consider that, in particular, arousal – the body’s way of preparing for action or heightened awareness – seems promising, as it can be influenced by various environmental factors beyond lighting.

Research, including that by Lis et al,⁹ indicates a strong link between lighting design in urban parks and perceived safety. The study found that park lighting, which enhances ‘spatial legibility’ (how easily people can understand and navigate through a space), significantly impacts people’s sense of safety depending on how different elements of the landscape are illuminated.

Path lighting alone did not improve safety perceptions and reduced legibility, while lighting the surrounding horizontal and vertical elements improved spatial legibility and the sense of safety. Background lighting also boosted safety and preference by making the space more legible and mysterious, while excessive foreground lighting decreased safety and privacy. Respondents preferred lighting that balanced legibility and mystery while preserving privacy, which increased their overall preference for the park.

Glare can impact visual comfort and even safety, particularly for pedestrians. Abboushi et al recently examined¹⁰ several models proposed over the years that have attempted to predict discomfort from glare.

Within the constraints of the datasets that they employed, and considering seven different models, they determined that the direct illuminance from the source, with the intensity of light falling directly from the lamp onto specific areas, such as paths and roads, was practically the most suitable model, as it tended to offer similar or better predictions than the other models.

They also noted that factors such as age can influence glare perception, with older individuals potentially more susceptible to discomfort glare.

Numerous studies have indicated that the presence of other people significantly influences perceptions of safety, often more so than lighting itself. Well-lit spaces that encourage social interaction and create a sense of community can contribute to actual safety by reducing the likelihood of crimes of opportunity.

In a recent study, Hamoodh et al¹¹ examined how lighting conditions can impact how pedestrians perceive others based on subtle cues such as facial expressions and hand gestures. The work supported the assumption of previous lighting research that the face is an important visual cue for the interpersonal evaluations necessary for a pedestrian to feel safe.

Appropriate lighting can enable accurate interpersonal evaluation by making these visual cues more discernible, particularly at night when natural visibility is reduced. An example of providing this in an open area is illustrated in Figure 2.

Individual perceptions of safety are shaped by personal experiences, background, and familiarity with different environments.^11,12 Factors such as age, gender and cultural background can influence how people perceive and respond to different lighting conditions and urban environments. This undoubtedly increases the challenge of providing a universally acceptable night-time environment.

There are increasing opportunities offered by manufacturers for what is sometimes termed ‘smart’ control, but there appears to be limited independent reports on the consequences of advanced control techniques. ‘Smart’ and more traditional control techniques recently reviewed¹³ by Welsh et al, illustrate the variability and complexity that, in some cases, may lead to unintended consequences, such as crime displacement, while, in others, deliver a variety of benefits.

To create safer, more sustainable urban environments, lighting designs need to reach beyond merely maximising illuminance. Prioritising lighting quality, tailoring strategies to specific contexts – which will probably include the application of carefully considered controls – and fostering collaboration can achieve a holistic approach that balances safety, comfort, energy efficiency and ecological responsibility.

Further research is needed to fully understand the complex interplay of factors that influence perception of safety, behaviour and environmental sustainability. This will enable the development of increasingly effective lighting guidelines for urban areas. 

© Tim Dwyer 2024.

References:

1. Li, Y et al, Effects of illuminance and correlated colour temperature of indoor light on emotion perception, Nature Scientific Reports, 2021, bit.ly/CJNov24CPD21.
2. Bullough, J D et al, Impacts of average illuminance, spectral distribution, and uniformity on brightness and safety perceptions under parking lot lighting, Lighting Res. Technol. 2020; 52: 626–640, bit.ly/CJNov24CPD22.
3. SLL Lighting Guide 21: Protecting the night-time environment, CIBSE SLL.
4. Vega, P et al, A systematic review for establishing relevant environmental parameters for urban lighting: translating research into practice, Sustainability 2022, 14, 1107, bit.ly/CJNov24CPD23.
5. SLL Code for Lighting, CIBSE SLL, 2022.
6. Boyce, P R et al, Perceptions of safety at night in different lighting conditions, Lighting Research and Technology 2000.
7. Fisher, B S and Nasar, J L, Fear of crime in relation to three exterior site features: prospect, refuge, and escape, Environment and Behavior, 1992, 24(1), 35-65, bit.ly/CJNov24CPD24.
8. Jedon, R et al, Proposing a research framework for urban lighting: the alertness, arousal and anxiety triad, Lighting Res. Technol. 2023; 55: 658–668,
   bit.ly/CJNov24CPD25.
9. Lis, A, How to light up the night? The impact of city park lighting on visitors’ sense of safety and preferences, Urban Forestry & Urban Greening 89 (2023).
10. Abboushi, B et al, Predicting discomfort from glare with pedestrian-scale lighting: A comparison of candidate models using four independent datasets, Lighting Res. Technol. 2024; 56: 225–246.
11. Hamoodh, K et al, Visual cues to interpersonal evaluations for pedestrians, Lighting Res. Technol. 2023; 55, bit.ly/CJNov24CPD26.
12. Himschoot, E A et al, Feelings of safety for visitors recreating outdoors at night in different artificial lighting conditions, Journal of Environmental Psychology 97, 2024.
13. Welsh, B et al, The impact and policy relevance of street lighting for crime prevention: a systematic review based on a half-century of evaluation research, 2024, bit.ly/CJNov24CPD27.

The post Module 240: Perception of safety in artificially lit urban settings appeared first on CIBSE Journal.

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As discussed in a UK Parliament briefing paper,¹ air pollution is causally linked to an increased risk of several serious health conditions, including heart disease, stroke, certain cancers, dementia, cognitive decline, impaired lung growth, and various respiratory illnesses. The impact of typical ambient (external) pollutants are represented in Figure 1, as summarised by the European Environment Agency (EEA).²

Additionally, volatile organic compounds (VOCs) – such as formaldehyde – can have a range of health effects, depending on the specific VOC concentration and duration of exposure. These include eye, nose, and throat irritation, headaches, dizziness, and fatigue. Prolonged exposure to VOCs can damage the liver, kidneys and central nervous system, and certain VOCs are known – or suspected – carcinogens.

This covers exposure to the headline VOC groups phthalates³ (commonly used to add flexibility and durability to plastics, such as flooring), and per/poly-fluorinated substances (PFAS)⁴ that are widely used in various building materials, flooring and fabrics owing to their desirable properties like water-, stain- and heat-resistance.

There have been many attempts to quantify the influence of the various sources of pollutants into the internal space; however, individuals are exposed to a wide range of pollutants as they move through different indoor environments, each with its unique set of pollutant sources.

Climate change is likely to adversely impact IAQ by increasing the infiltration of outdoor pollutants including ozone and particulate matter. Higher temperatures and humidity levels promote the growth of mould, dust mites and allergens indoors, contributing to respiratory issues. Inappropriately filtered or controlled HVAC systems can inadvertently circulate these pollutants, further deteriorating air quality.

The recent study⁵ by Saraga et al. examined 127 international peer-reviewed studies, revealing a significant variation in contaminants affecting IAQ in occupied environments, with no clear or consistent pattern emerging. However, the review identified that off-gassing from building materials, surface coatings and wood-based products dominated as sources of VOCs.

There is no practical method of continuously sensing viruses and bacteria in buildings and HVAC systems so the level of risk will typically need to be assessed and proactive control mechanisms employed as deemed necessary, such as high-efficiency filters and ultraviolet germicidal irradiation (UVGI), and by controlling the volumes of ventilation air.

A 2022 report by the UK Department for Environment Food and Rural Affairs (Defra) Air Quality Expert Group⁶ highlighted specific IAQ concerns across different environments. In care homes, limited ventilation resulting from restricted window openings can lead to the accumulation of pollutants.

Several research projects have identified inadequate – or improperly controlled – ventilation as a cause of poor IAQ in social housing. As shown by McGill et al.,⁷ this is not confined to ‘legacy’ homes. They investigated homes built to high sustainable standards, and their findings suggest inadequate IAQ and thermal comfort in the dwellings.

Nurseries and schools, where children spend significant time, often have limited ventilation to reduce heating costs, resulting in high levels of pollutants including carbon monoxide (CO), carbon dioxide (CO₂), particulate matter (PM), and VOCs, especially in urban or high-traffic areas.⁶ Hospitals typically demand specialised consideration of ventilation.⁸

Some workplaces can present specific air quality risks, particularly in sectors like manufacturing and construction, where exposure to substances such as asbestos, particulates and VOCs is common. As noted by the US Environmental Protection Agency (EPA),⁹ office occupants may be exposed to a mix of contaminants from indoor pollution sources that are potentially exacerbated as a result of poorly designed, maintained or operated ventilation systems, and unanticipated or inadequately planned building use.

Office surveys undertaken by the EPA identified asbestos and organics from building materials; formaldehyde from pressed wood products; off-gassing from carpets and other office furnishings; chemicals released from cleaning materials, air fresheners, paints and adhesives; ozone from copying machines; biological contaminants from dirty ventilation systems and water-damaged walls, ceilings and carpets; and pesticides from pest management practices.

Laurent et al considered¹⁰ both the impact of CO₂ and PM_2.5 (particles with a diameter of 2.5µm or less) on the performance of office workers and identified the acute impacts on cognitive function associated with poor IAQ, concluding that benefits from reducing
exposures to PM_2.5 and CO₂ indoors may positively impact productivity, educational attainment, safety and activities where cognitive performance is important.

Chemical reactions, such as those involving nitrogen oxides (NOx) and VOCs in the presence of sunlight and other atmospheric conditions, can form fine particulate matter, known as secondary PM that can contribute significantly to the total PM_2.5 and PM₁₀ levels. The UK Health and Safety Executive (HSE) guideline suggests that total VOC levels should not exceed 300µg.m^-3 averaged over eight hours, and the formaldehyde recommended limit is 100µg.m^-3 over 30 minutes.

The recently published review¹¹ of air-pollution sensors refers to the growing trend of low-cost sensors (LCS) that, as technology develops, allows the wider deployment of sensing devices, which are sufficiently reliable and robust while also being less costly than research- or reference-grade sensors.

The most prevalent PM sensor is optical, which employs LED light scattering to detect particles and is considered as being reasonably accurate for indoor use, but can be affected by humidity and temperature changes. They are likely sufficient for most consumer (and general HVAC) applications and have an accuracy range of ±10-20% compared with reference-grade instruments.

More expensive, laser-scattering sensors provide better accuracy, especially in controlled environments, and are likely to be accurate to within ±5-10% compared with the reference. Regular maintenance, including cleaning and replacing filters, and regular calibration help ensure sensors remain accurate over time.¹²

Non-dispersive infrared (NDIR) is the most common type of CO₂ sensor used in HVAC systems¹³ (and is the technology specified in the England Building Regulation AD Part F1 for typical commercial spaces). They are favoured for their high accuracy, reliability and long-term stability. NDIR technology relies on the principle of infrared absorption by CO₂.

Infrared light is passed through the sensor’s gas chamber and through a CO₂ selective optical filter before reaching the detector. The detector measures the intensity of infrared light and converts it into a calibrated electrical signal – higher concentrations of CO₂ result in a weaker electrical signal. In ideal conditions, a well-calibrated NDIR sensor can provide readings within ±1-5% of the reference value. CO₂ sensors will tend to drift over time, leading to a gradual decrease in the sensor’s ability to accurately measure CO₂ levels.

The choice of VOC sensors for HVAC systems often depends on the specific requirements for sensitivity, response time and budget. Metal-oxide semiconductor (MOS) sensors that measure changes in the resistance of a metal-oxide layer when exposed to gases are relatively low cost but are very susceptible to humidity and temperature variations.

The more expensive NDIR sensors can be employed to provide selective measurements of specific VOCs. Similarly-priced electrochemical sensors measure VOCs through a chemical reaction that generates an electrical current, providing high accuracy for a limited range of VOCs over a relatively short lifespan (said to be in the order of three years).

Photoionisation detectors (PID) – at about 10 times the cost of MOS sensors – use ultraviolet light to ionise VOCs, and can detect low levels of a wide range of VOCs (in the ppb range). However, in common with most high-end sensors, these require regular and relatively frequent calibration and maintenance.

Commercial buildings are normally ventilated with outdoor air to replace the vitiated air and to dilute air contaminants created by occupants and their activities (‘anthropogenic’ activity). Standards and guidelines (such as CIBSE Guide A) specify the minimum amount of outdoor air that is to be supplied by ventilation systems based on occupancy conditions (or area-based values for sparsely occupied spaces).

This assumes that the quality of outdoor air is good. If outdoor concentrations of contaminants are continuously or intermittently high, then it is critical to devise control measures to not inadvertently worsen IAQ through ventilation. Office buildings often have transient occupancy, and conditions that are generally below the maximum capacity and, hence, energy may be wasted through over-ventilation.

An approach to solving this problem is demand control ventilation (DCV), which could be provided by the system in Figure 2.

DCV is a building ventilation strategy that adjusts the amount of outdoor air provided to a space based on the occupancy and activity level and, potentially, in response to the levels of specific pollutants in the indoor (and outdoor) air. In a recirculation air system, this could be by modulating the mixing dampers to vary the proportion of outdoor air, or perhaps by simply using variable speed fans and possibly employing volume control dampers to alter the supply of ventilation air to all – or specific areas of – the building.

Since human respiration produces CO₂, it has often provided a useful proxy to indicate occupancy levels and, where IAQ is dominated by occupancy-related emissions, CO₂-sensing is well established as a means of controlling effective DCV. Sensors, typically placed in the return air ducts or within the occupied spaces, continuously feedback the concentration of CO₂ in the air.

As CO₂ levels rise above a pre-determined threshold (indicating increased occupancy), the DCV system responds by supplying more outdoor air to dilute the contaminants in the indoor air. Conversely, when CO₂ levels are low (indicating reduced occupancy), the system reduces the ventilation rate.

Such systems can also provide reduced, or no, airflow during unoccupied periods – this can be controlled by a combination of sensors and timed switching. Developments of LCS has opened opportunities for more applications of particulate and specific gas sensors that, working alongside CO₂ sensing, can offer a more detailed interpretation of the IAQ in situations that may not be dominated by occupant activity. The DCV control systems use this data to adjust the ventilation rates. DCV systems can significantly reduce energy consumption for heating, cooling and ventilating a building by providing ventilation based on real-time needs. This is particularly important in large buildings or spaces with variable use, such as offices, schools and auditoriums.

As noted in CIBSE Commissioning Code A,¹⁴ the system designer has a prime responsibility for the provision of sufficient outside air. The systems should include a suitable degree of filtration not only to make incoming outside air as ‘clean’ as possible, but also to remove detritus from the return air from the building prior to its travel through an air handling unit (AHU). There may also be a need to employ more extensive methods of air cleaning to allow the recirculation of otherwise contaminated air.

Understanding the diverse range of contaminants – including particulate matter, VOCs and biological aerosols – is crucial for developing effective strategies to mitigate their impact on health and wellbeing. DCV can provide a useful approach to managing IAQ by adjusting ventilation rates based on real-time data, thereby enhancing air quality while optimising energy efficiency. However, as the understanding of indoor pollutants and their effects continues to advance, ventilation systems and their sensing and control mechanisms will need to evolve to ensure the wellbeing of occupants while meeting standards of environmental sustainability.

© Tim Dwyer 2024.

The post Module 238: Measuring and controlling IAQ in indoor environments appeared first on CIBSE Journal.

The growing focus on environmental sustainability has driven the refrigeration, air conditioning and heat pump (RACHP) industry towards adopting refrigerants with lower global warming potential (GWP). The new applications of refrigerants, while beneficial for the environment, often come with new risk considerations compared with traditional choices.

While traditional refrigerants are considered non-flammable (although most of them can burn under certain circumstances), some modern options are classed as flammable. This necessitates stricter safety protocols throughout the entire life-cycle of the RACHP system, from selection and installation to maintenance and disposal.

The presentation by Takizawa¹ provides a useful overview of the properties that impact refrigerant flammability, which include the limits for upper and lower concentrations in air (upper flammability limit (UFL) and lower flammability limit (LFL)); the burning velocity (higher burning velocity signifies a faster burning rate, translating to a faster spread of fire); the minimum ignition energy (MIE) (higher means more difficult to ignite); the quenching distance (the closest a flame can get to a cool surface, such as a metal cabinet, before it goes out); and the flame extinction diameter (which helps explain how heat loss and flame size influence flame stability).

According to the 2020 paper² that followed on from an ASHRAE and AHRI-funded research project involving extensive laboratory testing of A2L refrigerants, it was discovered that when the refrigerant concentration was increased slowly, open flames from candles, matches and cigarette lighters extinguished rather than initiated significant explosions (deflagrations). (The study excluded lubricating oil and high humidity effects on ignition, and did not account for open flames from gas hobs or room heaters.)

However, a still mixture of refrigerant and air (known as a ‘quiescent premixture’) above the LFL can ignite when exposed to very hot (740°C) elements (compared with a cooker element at 480°C) and open flames (matches and butane). This highlights the need for appropriate ventilation for spaces with A2L refrigerants to ensure that the LFL is never reached.

The researchers discovered that other sources likely to be found in occupied premises did not ignite the A2L refrigerant even when in a quiescent premixture. These included a smouldering cigarette, a butane lighter, friction sparks, a mains plug and socket, a light switch, a bread toaster, a hair dryer, a hot plate, and a space heater. The difficulty in igniting an A2L in air is partly attributable to its relatively long quenching distance of approximately 8-25mm that compares with propane at approximately 1.5mm.

Additionally, the minimum ignition energy for a typical A2L is 10J, compared with approximately 0.0003J for methane³ and propane. Under some conditions, the tested A2L refrigerants were observed to act as flame suppressants. (There are interesting videos linked from the paper² that illustrate the test results.)

Several standards influence the application of refrigerants that have their origins in standards organisations, such as the International Standards Organisation (ISO), the International Electrotechnical Commission (IEC), the European Committee for Standardisation (CEN), and the American National Standards Institute (ANSI).

Although some standards are considered global, they are frequently adopted by national, regional, and local standards authorities, sometimes with local deviations. Also, since the development timeline for standards is not common, they do not necessarily agree on specific guidance at any one time.

Standards are informally referred to as ‘vertical’ when applying to a specific industry or group of products and ‘horizontal’ when they are referenced by a wide range of industries. Horizontal standards will, for example, likely account for the requirements of a wide range of system types during the design, installation, commissioning, servicing and end-of-life processes.

BS ISO 817:2014⁴ establishes a system for assigning the safety classification commonly used for refrigerants based on toxicity and flammability data, and provides a means of determining refrigerant concentration limits. The classifications – shown in Table 1 – are synchronised with those of ANSI/ASHRAE Standard 34 Designation and Safety Classification of Refrigerants.

Ensuring a safe system may be by ‘intrinsic safety’ and ‘extrinsic safety’ methods. Intrinsic safety limits the quantity of refrigerant so that any leaks into the space cannot create an unsafe condition.

Extrinsic safety employs alternative measures – such as the physical arrangement of the system, additional safety equipment, and operational procedures – to ensure that a dangerous situation cannot arise. Some equipment, such as refrigerant gas detectors and alarms, may be included as part of the product and some sourced separately and installed on site.

The horizontal standard BS EN 378 Refrigerating systems and heat pumps – Safety and environmental requirements (which is currently under review) is intended to minimise possible hazards to persons, property and the environment across the whole array of refrigerating systems and refrigerants.

It effectively acts as a foundation for risk management, establishes safety benchmarks, and promotes best practices for working with refrigerants in systems that cover many product groups. This standard engages with the work of the various building engineering professionals when working on UK and European projects. (ISO 5149⁵ may be more appropriate for work outside that geographic area.)

The vertical standard BS IEC EN 60335-2 Household and similar electrical appliances – Safety focuses on the specific safety requirements for the appliances (or products) themselves. (Despite its title, this standard relates to commercial applications.)

The recent 2023 revision to BS EN IEC 60335-2-40,⁶ which specifically covers electrical heat pumps, air conditioning and dehumidifiers, included many revisions relating to the safe application of A2L refrigerants. It provides manufacturers with a clear and concise set of guidelines to follow, ensuring that their products are safe, reliable,
and efficient.

In the UK, all refrigerants are subject to Dangerous Substances and Explosive Atmosphere Regulations⁷ (DSEAR). Identified risks must be eliminated or minimised as far as reasonably practicable. Conducting and documenting relevant risk assessments is essential, along with ensuring the proper provision of safety equipment such as leak detection, ventilation, shut-off valves and alarms.

As highlighted by the Federation of Environmental Trade Associations⁸ (FETA) in the Pressure Equipment (Safety) Regulation (PE(S)R), A2L refrigerants are classified as ‘dangerous’ owing to their flammability. Split air-conditioning systems using A1 refrigerants are more likely to be in PE(S)R Category 1 (or possibly exempt and therefore only required to be constructed in accordance with ‘sound engineering practice’ (SEP)).

For these systems, the contractor can self-certify its compliance with the regulations. In contrast, systems with A2L and A3 refrigerants are more likely to be in Category 2 or above, and so will require some form of assessment by an Approved Body before a UK Conformity Assessed (UKCA) mark can be applied to the installed system.

This body must verify the design and technical information and witness a portion of the strength pressure tests. The Cool Concerns briefing note⁹ advises that the contractor acts as the ‘manufacturer’ of the complete system and is usually responsible for the final conformity assessment (see IoR Guidance Note 36¹⁰ for more detail).

One of many ways that manufacturers can achieve a UKCA (or CE) mark is by demonstrating conformity to the requirements of a harmonised safety standards, such as relevant parts of BS EN IEC 60335. BS EN 378-1 notes that product family standards dealing with the safety of refrigerating systems take precedence over horizontal standards covering the same subject, including limits on refrigerant quantities for a particular application. BS EN 378 applies to a far wider, generic set of applications that are outside the scope of individual product standards.

One of the key issues of employing A2L refrigerants in room units, such as would be used in split air conditioning and variable refrigerant flow (VRF) systems, is the allowable charge of refrigerant in a particular space. Fortunately, recent editions of BS EN 378-1 and BS EN IEC 60335-2 are generally consistent on refrigerant quantity limits if the same assumptions are applied to both standards. However, in specific applications, there may be different areas of nuance in the horizontal and vertical standards, and the standards should be consulted for full details.

Both current versions of BS EN 378‑1 (equation C.2) and BS EN 60335-2-40 (equation GG.9) use the same (empirical) intrinsic safety equation to establish the minimum room floor area A_min (m²) that can be used to install an appliance with refrigerant charge m_c (kg) where the room is unventilated, A_min = (m_c/ 2.5 × LFL^1.25 × h₀)² where:

h₀ is assumed release height of leaking refrigerant, greater of (h_inst+h_rel) or 0.6m

h_rel is distance (m) from bottom of appliance to point of release

h_inst is the reference installed height of the unit (0m for floor-mounted, 1.8m for wall-mounted, and 2.2m for ceiling-mounted)

For example, applying a floor-mounted room unit, such as that shown in Figure 1, charged with 2.4kg R32 (an A2L refrigerant) that has an LFL of 0.307kg.m^-3,the minimum allowable room area for the room unit where there is no ventilation would be (2.4/(2.5 x 0.307^1.25 x 0.6))² = 49.02m² in unventilated areas.

Figure 1: An example of a floor-mounted room unit, charged with 2.4kg R32, capable of delivering up to 5kW sensible cooling and 6kW heating (Source: Mitsubishi Electric)

However, when a fan that is incorporated into the unit is either continuously operated, or through an appropriate refrigerant detection system, is able to deliver a sufficient recirculation airflow rate (of at least 30 x m_c/LFLm³.h^–¹, according BS EN 60335-2-40), the allowable minimum room area can be smaller, as it is assumed that the recirculation will prevent potentially leaking refrigerant reaching the LFL, while alarms will also alert users to the leak.

BS EN 378 and BS EN 60335-2-40 suggest that leak detectors should be located where leaking refrigerant may stagnate or concentrate, but they (currently) differ in specific detail. However, the intent is the same in the two standards and, although using different calculation methods, they appear consistent (and the upcoming revisions to BS EN 378 may provide increased similarity in method).

From BS EN 60335-2-40 equation GG.11, the simplified empirical relationship is A_min = m_c/(0.75 × LFL × h_ra) where h_ra is the estimated reaching height of the airflow (m). So, repeating the previous example for a floor-mounted unit with 2.4kg R32, and an estimated reaching height of 0.6m, the minimum room area = 2.4/(0.75 x 0.307 x 0.6) = 17.4m² for the unit with a circulation fan and an inbuilt leak detector.

This provides opportunity for applying the unit in a smaller room by applying extrinsic safety measures where, in the event of a leak, the indoor unit must be capable of increasing the fan speed to maximum and triggering an alarm. (The installation could also comply with BS EN 378-3¹¹ if the system leakage alarm has an independent power source, such as a battery-backed supply.)

In the calculations undertaken above, a key variable is the mounting height of the unit – this should be considered carefully to ensure that the minimum areas are properly representative of an installation. A site variation to the mounting height can significantly impact the installed system, as it determines the extent to which refrigerant, if it leaks out of the system, will disperse through the whole space rather than pooling in a concentrated layer at floor level.

Meeting the requirements of the comprehensive product safety standard may well be considered as appropriate for compliance regardless of the horizontal standard. Indeed, the introductory text to BS EN IEC 60335‑2‑40:2023 explains there is no need to refer to horizontal standards for products within its scope, since they have been taken into consideration when developing the general and particular requirements of this vertical standard.

As with any engineering solution, manufacturers, installers and operators have a responsibility to ensure that installations meet the safety levels established by industry standards. It is crucial to understand how to evaluate and mitigate risks associated with the use of refrigerants, and the systems that incorporate them.

To help address concerns such as refrigerant leakage and detection, while providing flexible heating and cooling solutions, manufacturers have introduced hybrid VRF systems. These systems place all refrigerant-containing components outside of commonly-occupied spaces and use water for heat distribution, thereby minimising both leakage risks and the amount of refrigerant required.

In all cases, the designer should have a clear understanding of why decisions are made and apply the standards that are most appropriate to the application.

© Tim Dwyer 2024.

References:

1. Indoor Air Quality, POSTbrief 54, UK Parliament, 2023.
2. EEA Report No 21/2019 Healthy environment, healthy lives: how the environment influences health and well-being in Europe, EEA 2020, bit.ly/CJOct24CPD21.
3. bit.ly/CJOct24CPD22 – accessed 12 August 2024.
4. bit.ly/CJOct24CPD23 – accessed 12 August 2024.
5. Saraga, DE et al, Source apportionment for indoor air pollution: Current challenges and future directions, Science of the Total Environment, 2023 – bit.ly/CJOct24CPD24.
6. bit.ly/CJOct24CPD25 – accessed 12 August 2024.
7. McGill, G et al, Case study investigation of indoor air quality in mechanically ventilated and naturally ventilated UK social housing, International Journal of Sustainable Built Environment, 4(1), pp.58-77, 2015.
8. Health Technical Memorandum 03-01: Specialised Ventilation for Healthcare Premises, 2021 –bit.ly/CJOct24CPD26.
9. bit.ly/CJOct24CPD27 – accessed 12 August 2024.
10. Laurent, JDC et al, Associations between acute exposures to PM 2.5 and carbon dioxide indoors and cognitive function in office workers: a multicountry longitudinal prospective observational study, Environ. Res. Lett. 16, 2021.
11. Seesaard,T et al, A comprehensive review on advancements in sensors for air pollution applications, Science of the Total Environment, 2024, bit.ly/CJOct24CPD28.
12. Bousiotisa, D et al, Monitoring and apportioning sources of indoor air quality using low-cost particulate matter sensors, Environment International, 2023 – bit.ly/CJOct24CPD29.
13. bit.ly/CJOct24CPD210 – accessed 12 August 2024.
14. Commissioning Code A: Air distribution systems, CIBSE, 2024.

The post Module 237: Safe application of modern refrigerants in RACHP systems appeared first on CIBSE Journal.

This CPD article examines the important role of lighting in educational environments, emphasising how modern systems can enhance student wellbeing, improve the overall learning experience for both traditional and therapeutic learning spaces, and reduce the operational costs of buildings.

UK primary and secondary school students annually spend around 180 days in classrooms, and their internal environment can significantly impact their academic performance. A 2021 transverse study, employing the massive SINPHONIE¹ dataset, highlighted that daylight has the highest impact on overall student progress among all design parameters in schools,² indicating that larger window areas are advantageous, and that appropriate shading is important.

Fig 1 high-output luminaires

The complete lighting solution will influence various factors, including student concentration, behaviour, and overall performance, and the complementary contribution of controlled natural and artificial lighting has been shown to be beneficial.³ A study⁴ involving 84 pupils in the mid-south region of the USA indicated that a ‘focus’ illumination level of 1,000lx, with a cool temperature of 6,500K, could improve activities that required oral reading fluency (ORF) compared with a ‘normal’ lighting level of 500lx and 3,500K, which would be used for other activities.

This aligns with findings⁵ from a series of field and experimental studies showing that appropriate lighting significantly enhances students’ concentration and academic performance.

There are several standards and guides to aid the design and implementation of lighting in educational environments. These include: the 2011 CIBSE LG5⁶ Lighting for Education (currently under review), which provides comprehensive guidelines specifically for educational facilities; the UK DfE School Output Specification Technical Annex 2E – Daylight and Electric Lighting⁷, which provides the minimum requirements for daylighting and electric lighting in schools (and similar premises); and BS EN12464-1:2021⁸ Lighting of Work Places – Part 1: Indoor Work Places, which specifies lighting requirements for indoor workspaces, including educational facilities.

From the USA, the Illuminating Engineering Society’s Recommended Practice for Lighting for Educational Facilities⁹ provides specific guidelines for lighting educational spaces, emphasising the impact of lighting on learning and student wellbeing.

Poor lighting can lead to eye strain, fatigue, and diminished concentration,¹⁰ while well-lit classrooms with the right balance of natural and artificial light can help students remain attentive and behave positively.¹¹ Managing glare can have a significant impact in educational settings, preventing discomfort and improving visual performance.

Figure 2: A refurbishment project at the science block of Radley College replaced outdated lighting systems with task lighting installed directly over desks and workspaces, employing luminaires with opalescent diffusers. This LED module delivers CRI>80, CCT of 4,000K and up to 121lm.W-¹

Fig 2: luminaires with opalescent diffuser

The benefits of reducing visual discomfort and improving performance have been studied extensively, showing significant positive impacts on students’ ability to concentrate and perform academically. For example, Winterbottom and Wilkins¹⁰ found that poor lighting conditions –including glare from windows and fluorescent luminaires – can cause discomfort and impair visual performance, affecting students’ ability to concentrate and learn effectively.

Human-centric lighting solutions can be designed to mimic the profile of natural light – which is thought to regulate circadian rhythms – reducing early-morning tiredness and boosting alertness throughout the day. The use of lighting with adjustable colour temperatures can simulate natural light patterns, helping students maintain better sleep cycles and overall health.¹¹

Current, commercially available LED technology can achieve luminous efficacies of 140-190lm^.W^–¹ compared with circa 100lm^.W^–¹ of common lamps employed from the beginning of this century. This contributes to a significant reduction in the number of required fittings and operational costs. Depending on the choice of luminaire, a colour rendering index (CRI) of greater than 80 is readily available from LED fittings, meeting the typical requirements for educational applications.⁷

Typically, these modules maintain 70%-90% of their initial lumen output after 50,000 hours of operation – an operational life that goes far beyond that of previous technologies, such as fluorescent lamps, which have a maximum life of 15-20,000 hours. This longevity reduces the frequency of repair and replacement, minimising maintenance costs and disruption in the educational environment.

Diffuser optics for such applications should be designed to minimise glare and control ceiling illumination. This is particularly beneficial in classrooms and lecture rooms, where prolonged exposure to improperly controlled light sources can cause eye strain and reduced concentration. These effects have been measured in the field by employing a combination of subjective reports of discomfort, objective assessments of visual performance, and physiological indicators, such as blink rate and pupil size.

Figure 3: High-output LED modules with a wide-beam optic significantly reduced the number of luminaires required in the refurbishment at Darlington College. This die-cast aluminium body LED module with prismatic polycarbonate diffuser delivers CCT of 4000K and up to 130lm.W-¹

Fig 3: High-output LED modules with a wide-beam optic

As well as providing effective solutions for new-build installations, LED lighting systems can be designed as a replacement for legacy systems to deliver significant energy savings and improve visual comfort, so boosting alertness and wellbeing among students. The controllability of suitably equipped LED luminaires, linked together with systems such as digital addressable lighting interface (DALI), can enable more granular control and monitoring.

This can be used to provide flexible lighting schemes that are readily adjusted – manually or automatically – employing features such as daylight dimming, scene setting and scheduling. Employing such control can optimise the lighting provision based on real-time demand, the availability of natural light and the required occupant experience. Such systems also allow for adaptable lighting environments suited to a range of educational activities. For example, in lecture theatres, scene control – such as dimming controls – can allow lighting to be adjusted for presentations, note-taking or video viewing, providing an optimal setting for each activity.⁷

Lighting automation can be integrated with other building management systems to optimise energy use and enable enhanced monitoring and maintenance of lighting systems. LED lights with adjustable brightness and colour temperatures have been shown to reduce anxiety, improve task-switching focus¹² and create a more inclusive learning environment.

Research indicates that lighting conditions can significantly impact cognitive and emotional states. For instance, appropriate lighting has been found to enhance students’ focus, positively affect students’ concentration¹³ and reduce anxiety¹⁴ by creating a more comfortable and adaptable learning environment. Creating calm areas with low or dim lighting can reduce stress and anxiety.

Lighting can play an important role in creating therapeutic and inclusive classrooms that support the wellbeing of all students, including those with neurodiverse needs. Glare from excessively bright sources of light – natural and artificial – and flickering lights can cause discomfort and disrupt concentration, particularly for individuals with photosensitivity and specific neurodiverse conditions.

Figure 4: Installation of low-glare luminaires in IT rooms and science labs for Thornleigh Salesian College limited screen glare, delivered uniformity and optimal spacing to prevent shadowing, and provided adequate lighting for detailed tasks. The light delivered from the opal polycarbonate diffuser, CRI>80, CCT of 4,000K up to 120lm.W-¹

Fig 4: Low-glare luminaires

Additionally, glare can adversely impact students’ ability to read display boards and screens, or to focus on the teacher. Studies¹⁵ have identified the benefit afforded by therapeutic classrooms with stable, adjustable lighting environments that can improve the learning experience for students with neurodiverse needs by minimising sensory overload. LED solutions – which do not flicker or hum – can provide such adjustable lighting environments, offering flexibility in brightness and colour temperature.

Whether new-build or refurbishment, suitable LED luminaires are available that can cater to a wide range of educational applications. For example, Figure 1 illustrates an application that required a high-level installation to meet the varying lighting demands required for a multi-use gymnasium.

The LED luminaires shown in Figure 2 replaced a legacy system to provide task lighting above benches in a school laboratory, improving the quality of lighting and achieving a high uniformity of illuminance across the working plane, with diffuse light levels that minimised shadows.

Figure 3 indicates how an LED lighting system can be styled to accentuate the contemporary design of an existing entrance area, while maintaining the benefits of LED systems. Figure 4 is an application of a low-profile LED fitting, integrated into a modular false ceiling, where the optic is designed to deliver diffuse light to minimise shadows.

All these illustrated LED applications provide high luminous efficacy, and reduce operational costs through lower energy consumption and longer lifespan. The solutions also support institutional goals for sustainability by reducing carbon footprints.

It is beneficial to engage the operator and end user in the development and operation of lighting systems. Staff and students can significantly impact the operational success of an installation, so it is important that they have a decent understanding of the role and control of both natural and artificial lighting, and how to use adjustable lighting systems effectively.

By focusing on energy efficiency, human-centric design and therapeutic benefits, institutions can enhance student wellbeing, improve academic performance and achieve sustainability goals. A holistic approach to design can help ensure that lighting systems contribute towards the best possible environments for learning and development.

About the author
Tim Dwyer

• Thanks to Nicola Lloyd, of Tamlite, for her enthusiastic research assistance]

References:

1. Kephalopoulos, S, SINPHONIE – Schools Indoor Pollution and Health Observatory Network in Europe database on chemical and biological pollutants, European Commission, Joint Research Centre (JRC) 2020 – bit.ly/CJSep24CPD1
2. Baloch, R M, et al, Daylight and school performance in European schoolchildren, International Journal of Environmental Research and Public Health, 2021 – bit.ly/CJSep24CPD2
3. Heschong, L, et al, Daylighting impacts on human performance in school, J Illum Eng Soc 2002.
4. Mott, MS, et al, Illuminating the effects of dynamic lighting on student learning, SAGE Open, 2012.
5. Sleegers, P J C, et al, Lighting affects students’ concentration positively: Findings from three Dutch studies, Lighting Research & Technology, 2013 – doi.org/10.1177/1477153512446099
6. SLL LG5 Lighting Guide 5: Lighting for Education, CIBSE, 2011 (currently under revision).
7. School Output Specification Technical Annex 2E- Daylight and Electric Lighting, UK DfE 2022 – bit.ly/CJSep24CPD3
8. BS EN 12464-1:2021 Light and Lighting – Lighting of Workplaces – Part 1: Indoor Workplaces, BSI 2021.
9. Illuminating Engineering Society. ANSI/IES RP-3-20, Recommended Practice: Lighting Educational Facilities, IES, 2020.
10. Winterbottom, M and Wilkins, A, Lighting and discomfort in the classroom, Journal of Environmental Psychology, 2009 – bit.ly/CJSep24CPD4
11. Wessolowski, N, et al, The effect of variable light on the fidgetiness and social behavior of pupils in school, Journal of Environmental Psychology, 2014 – bit.ly/CJSep24CPD5
12. Hartstein, L E, et al, Light correlated color temperature and task switching performance in preschool-age children: preliminary insights, PLoS ONE, 2018 13(8), e0202973 – doi.org/10.1371/journal.pone.0202973
13. Sleegers, P J, et al, Lighting affects students’ concentration positively: findings from three Dutch studies, Lighting Research & Technology, 2013 – doi.org/10.1177/1477153512446099
14. Hawes, B K, et al, Effects of four workplace lighting technologies on perception, cognition and affective state, International Journal of Industrial Ergonomics 2012 – doi.org/10.1016/j.ergon.2011.09.004
15. Black, M H, et al, Considerations of the built environment for autistic individuals: A review of the literature, Autism 2022 – doi.org/10.1177/13623613221102753

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The supply of appropriate, known air flowrates through mechanical ventilation and air conditioning systems in commercial and industrial applications is fundamental to effective system operation. This CPD module considers the characteristics of moving air and explores the application of pressure-based airflow measurement as a means of assuring air flowrates.

A typical assumption at the design stage is that air flowrates in the installed systems will match the design intent; however, unless the systems are suitably controlled, this is unlikely to be the case. Poor control will, at best, lead to less-effective operation, poorer indoor air quality (IAQ), increased energy use and – for more critical applications, such as fume and smoke extraction – a potential health and safety risk to building occupants.

Whether a system is operating at full or reduced air flowrate, it is important to ensure there is an appropriate supply of outdoor ventilation air to maintain IAQ by diluting indoor pollutants, such as carbon dioxide (CO₂), dust, allergens, microbes, and volatile organic compounds (VOCs). In most ventilation systems, there are minimum flowrates that are required to ensure adequate air distribution that not only maintain IAQ parameters, but – as discussed in the September 2022 CIBSE Journal article¹ exploring Khankari’s work – also may limit the spread of contaminants from a source.

Additionally, properly controlled airflow can be critical in smoke management during a fire, aiding safe evacuation and minimising smoke-inhalation risks. A well-controlled system can readily adapt to changes in building usage or occupancy, ensuring long-term flexibility in working practices while continuing to meet ventilation standards and comply with health and safety standards.

Precise control of airflow ensures that only the necessary amount of air is moved, reducing the energy required for fans and other components. For example, the key benefit provided by variable air volume (VAV) systems is that, by adjusting airflow based on demand, VAV can provide significant fan energy savings compared with constant air volume (CAV) systems.

When using a CAV system, zoning may be used to close off, or reduce, the supply of ventilation air to cater for the specific needs and preferences of different occupants or activities. Zoning allows different areas of the building to be controlled independently and, potentially, provides the opportunity to fully isolate areas of the building that are not in use. This would enable the supply and extract fans to operate at a slower speed. As well as reducing the volume flowrate of the air that needs to be moved by the fan, this also reduces the load on heating and cooling equipment.

System and sub-system pressure drops will be dependent on the characteristics of the ducted system, including roughness and geometry of the ducting materials, the number and type of fittings, such as constrictions or bends that disrupt the air path, as well as the properties of the air itself.

The relationship between air pressure drop, Δp (Pa), and volume flowrate, Q (m³.s^-1), of air flowing through a typical commercial heating ventilation and air conditioning (HVAC) ducted system can be normally characterised as proportional, so Δp∝Q². So, for air flowing through a specific resistance, R, such as a filter or a purpose-made measuring station, Δp = RQ², where R is a constant of resistance that is related to the particular item (for example, the filter, or the measuring station). If the measuring system is calibrated with respect to the specific resistance, R, then the flowrate may be obtained from Q= (Δp/R)^0.5.

Pressure differential sensing (measuring the Δp) is widely applied in HVAC systems as the means of referencing air flowrates. This may be to directly measure pressure differences across components such as air inlet louvres, filters, ducts, or heat exchangers, or be used in association with fully calibrated devices such as venturi measuring stations to provide measurements of air flowrates.

The total pressure, p_t, (Pa) in a moving airstream is the sum of the velocity pressure, p_v, and static pressure, p_s, so p_t = p_v + p_s. The velocity pressure may be readily established as p_v = p_t – p_s. This can be obtained using a liquid manometer, as illustrated in Figure 1, which is connected to a pitot-static tube that is held in the duct. Since velocity pressure may be calculated from p_v = 0.5ρ c², where ρ (kg.m^-3) is the air density (typically assumed as 1.2kg.m^-3), the velocity, c (m.s^-1), of the air can be obtained from (2p_v/ρ)^0.5. And from this, the volume flowrate, Q, may be obtained by multiplying the duct area (m²) by the average air velocity across the duct.

In most HVAC applications – other than when the air passes through a heating or cooling process – the temperature of the air in a particular duct run, along with its density and viscosity, are assumed as nominally constant, so the volume flowrate (and, of course, the associated mass flowrate) remain constant.

Devices such as the pitot-static tube only provide a point measurement. To gather more representative pressure data on a continuous basis, purpose-manufactured measuring devices may be employed. Historically, these have been applied in specialist systems when specific needs demand continuous airflow measurement, such as maintaining required air volume or room air pressure in laboratory or process environments to ensure positive movement of air and contaminants.

However, ensuring adequate outdoor air supply is not limited to specialised applications. For example, any systems that vary the air flowrate require careful design and operation to maintain optimal outdoor air fractions as the total flow modulates. By actively and accurately monitoring volume flowrates of outdoor air, and total and individual zone flows, the control system is able to modulate outdoor and recirculated air proportions effectively.

An example of a commercially available flow pressure sensor, illustrated in Figure 2, is a pair of identical stainless steel pressure probes that may be mounted in a duct. One probe measures the total pressure, while the other measures the static pressure. Unlike the simple pitot-static tube, the probes continuously collect pressure signals across the whole width of the duct and, through an associated electronic pressure transducer, may be precisely calibrated for a particular application.

It is important that the sensor remains stable across the operating range, since a drift of just 1Pa or 2Pa – particularly at the lower end of the range – can cause a significant error in the measurement of the air volume. For example, if designing a system with an air velocity of 4 to 5m.s^-1, with a resulting velocity pressure of under 15Pa, the error in pressure measurement could exceed 10%. This error may be magnified in systems that employ two separate sensing devices to maintain small positive or negative pressures compared with an adjacent, sometimes outdoor, space.

Applications that rely on a small pressure difference to operate effectively include those positively pressurised to prevent ingress of contaminants, such as an airport terminal building designed to prevent the ingress of fumes from aircraft engines, or an office building in a polluted city centre that might otherwise be subject to vehicle pollution. Commonly encountered minimally negatively pressurised zones include hospital critical care spaces, clean rooms and laboratories that all rely on a robust pressure control to prevent cross-contamination. If the pressure sensors drift by just a few per cent in either the supply and extract systems, there is opportunity for significant pressure deviations leading to potential contamination.

Permanent installations, which require more exacting measurements, can incorporate frameworks known as velocity or flow grids, which are designed to capture measurements across a representative section of the flow area, as shown in Figure 3. These tubular grids are strategically populated with holes to obtain a representative average pressure. Total and static pressure are measured independently through holes drilled into sampling tubes at specific orientations.

Such grids come with calibration factors that translate measured pressures into velocities or volumetric flowrates, or are supplied as part of a package with a matched microelectronic transducer and signal conditioner. Their design allows for a stronger pressure signal compared with single-probe measurements, enhancing resolution and reducing potential errors, achieving measurement accuracies within ±0.2% of the full scale. They also offer a significant benefit, as with appropriately matched transducer and signal conditioning they maintain responsiveness at very low pressures, allowing very low air velocities, approaching 0m.s^-1.

The pressure signals from the measuring points then need conversion into a form that can be used by the control systems. This requires a transducer that, in commercial HVAC, commonly employs sensors based on piezoresistive or capacitive principles. However, the reliable, but less well-known, variable reluctance (VR) sensor, has a well-established pedigree in close-control ventilation systems such as those used in laboratories and microchip fabrication plants. Such sensors have proved robust – a manufacturer² reports such sensors with a copper beryllium diaphragm are still providing reliable output after more than 30 years’ continuous use.

Variable reluctance sensor

Typically known as a VR sensor or magnetic pickup, these sensors detect the position of moving metal objects. They operate on the principle of variable reluctance, which is the change in magnetic resistance caused by the movement of a ferromagnetic material in proximity to the sensor. The key components of a basic VR sensor are a permanent or electromagnet to provide a magnetic field; a moving metal object (known as a ferromagnetic ‘target’) that, when it moves, induces a voltage, and potentially a current, in an adjacent coil because of the changing magnetic flux.

Figure 5 shows the basic components for a VR pressure differential sensor, as used in HVAC applications. It consists of a ductile ferromagnetic diaphragm that provides a thin, movable membrane separating two air chambers. The coils are positioned on either side of the diaphragm.

When a pressure difference exists across the diaphragm, it deflects. This movement alters the magnetic flux path between the core and the coils. The reluctance, which is the resistance to magnetic flux, changes based on the diaphragm’s position. The VR sensor coils are typically driven by an alternating current (AC) signal. The varying reluctance caused by diaphragm deflection affects the induced current in the coils. This change in current can be processed by local microelectronic circuitry to provide a calibrated digital or analogue output that corresponds to the pressure difference.

VR sensors can handle the wide range of pressure differential commonly encountered in HVAC systems and are able to detect small changes in pressure. The simple design, with minimal moving parts, adds to their reliability and long lifespan, while their small size allows for easy integration into various HVAC components. The key component is the diaphragm – the material for this must maintain ductility and integrity over extended periods of use.

The two pressure connections shown in Figure 5 are connected by tubes to the pressure outlets of the measuring device, and the diaphragm deflects in response to any pressure difference across it. When close-coupled with packaged local microelectronic conditioning, as in the example unit shown in Figure 4, the digital output may be transmitted to the local building management system (BMS) – using a protocol such as RS485 for Modbus connectivity – to ensure that the BMS receives the measurement that is representative of the sensor output (rather than employing uncertain BMS-based analogue-to-digital conversions). VR sensors can provide a cost-effective option for pressure differential sensing in HVAC compared with some alternative technologies, particularly when total life-cycle energy use, operating costs and environmental impact are considered.

Closely controlling the airflow in a building ventilation system offers significant benefits, from energy efficiency and cost savings to enhanced indoor air quality, thermal comfort and safety. These advantages make it a crucial aspect of modern building design and operation – and worthy of careful consideration when developing ducted air-distribution systems for HVAC applications.

About the author
Tim Dwyer

The post Module 235: Robust sensing and control of airflow in commercial ventilation systems appeared first on CIBSE Journal.