It won Project of the Year – Leisure at the 2024 CIBSE Building Performance Awards with judges impressed by its careful, low carbon design and application of technology.

What’s more, the performance data has been used as an exemplar case study by the UK Net Zero Carbon Buildings Standard, to help establish a best-practice benchmark for operational and embodied carbon for future leisure centre buildings.

To achieve this remarkable feat, building services engineers Max Fordham – working with architects FaulknerBrowns, the client and main contractor – have taken every design decision as an opportunity to minimise energy consumption further.

As such, the building incorporates a range of passive and active environmental technologies, including the extensive use of daylight and mixed-mode ventilation. In addition, heat is provided by air source heat pumps (ASHPs) incorporating load-shedding controls, while the complex is crowned by a giant biosolar roof that provides up to 20% of the building’s electricity needs.

The £57m sport centre’s low-energy design is a response to the university’s campus energy and sustainability masterplan. Developed by Max Fordham under a previous project, the masterplan includes a requirement for all new buildings to achieve Breeam Outstanding and a Display Energy Certificate (DEC) ‘A’ rating in operation.

Large rectangular rooflights supplement daylight in the pool area

To achieve DEC ‘A’, the design had to target a maximum EUI of 218kWh·m^-2 per year. Ambitiously, Max Fordham set out to meet this already challenging target without the use of fossil fuels. ‘When we started to develop the design in 2016, gas boilers were the standard solution, but we said “this building is not going to complete until 2022, when Grid carbon will be lower, so we should not be basing our design on fossil fuels”,’ says Mark Palmer, director and sports leader at Max Fordham. Opting for an all-electric solution would also ensure the building’s carbon emissions fall further as the Grid continues to decarbonise.

The university’s brief to the design team was for a sports centre with a 25m swimming pool, an eight-court sports hall, 175-station fitness suite, climbing wall, ski simulator, and fitness studios, along with offices and teaching spaces.

Palmer says the starting point in developing the building’s form was to separate the swimming pool from the ‘dry’ areas (the sports hall, fitness suite, and so on), so that the circulation space between can form an environmental buffer zone.

Unusually, the design places the sports hall on top of the ground-floor fitness suite and changing rooms. ‘One of the key decisions was to put the sports hall on the first floor, to ensure that it and the swimming pool could benefit from rooflights, to provide passive heating and daylight, which saves energy and is good for wellbeing,’ says Palmer.

One of the striking giant fans set into the ceiling in the gym. The fans have been designed to generate air movement to reduce the need to drive down the fitness suite air temperature

Flexibility is key to keeping the building’s footprint and embodied energy to a minimum. The swimming pool, for example, has a floating floor, to do away with the need for a learner pool; the squash courts are separated by a moveable partition to enable them to be converted into additional studio space; and the studio spaces incorporate a moveable partition that allow them to flex to accommodate a variety of class sizes and activities. The compact building’s high-performance envelope has been kept deliberately simple to avoid complex junctions and cold bridges.

In addition, the swimming pool envelope has been fortified with additional insulation, to deal with the higher air temperature and humidity in the space. Employing a simple, system-build envelope solution made it easier to build and, Palmer says, gave contractor Wates Construction ‘a fighting chance of delivering on the design airtightness and thermal performance in practice’.

The rooflights in the sports hall and swimming pool are designed to open. They are arranged in strips in the sports hall, strategically positioned between the badminton courts to allow daylight in while minimising the impact of glare on the players.

Max Fordham has eschewed natural ventilation for an innovative cooling and mechanical ventilation solution for the intensively used, 175-station fitness suite. Alongside a conventional fan coil cooling system, a series of large-diameter, high-volume, low-speed horizontal fans have been recessed into the ceiling, like the slowly spinning rotor blades on a series of upturned helicopters. These giant fans have been designed to generate air movement to reduce the need to drive down the fitness suite air temperature. The large fans are supplemented by 13 smaller fans concealed above the ceiling.

The conventional way to deliver comfort to a fitness suite is to lower the air temperature to help people lose heat. Sport England’s guidance, for example, suggests maintaining temperatures as low as 16°C-18°C. But Palmer says this can result in ‘very high energy use’ that often ‘fails to deliver occupant comfort’ because, when we are sedentary, radiation is the primary mechanism of heat exchange. As exercise intensity increases, however, convection and, eventually, the evaporation of sweat become the dominant modes of user heat loss. ‘If the air in a gym is cool, still and humid, your sweat is unable to evaporate to cool you down,’ Palmer explains.

For those undertaking high-intensity exercise, convective and evaporative transfer of body heat are increased significantly by air movement. ‘By creating air movement and controlling humidity, we are able to achieve much better levels of comfort at temperatures that are not as cold,’ Palmer adds. See ‘Fit for purpose’, CIBSE Journal October 2018 for more on this bit.ly/CJRav.

In addition to the giant fans, four-pipe fan coil units (FCUs) have been tucked out of sight above the suite’s slatted wood ceiling. The FCUs provide the space with heating and mechanical cooling. ‘The client was a bit nervous about the effectiveness of our giant fan solution, so the fan coil units have been sized to cool the space conventionally without the need to run the fans,’ says Palmer, who adds that the client need not have worried. ‘Everyone loves this solution: it’s striking to look at and it’s proven to be very effective.’

In addition to ensuring the university’s management and operations teams have a good understanding of the building and its systems, soft landings enabled the engineers to tweak the fan system once the fitness suite was fully operational. They estimate that increasing air movement in the fitness suite, as opposed to relying on a lower temperature setpoint, will result in a 10% reduction in energy use in peak summer conditions.

Heat for the building is supplied by five ASHPs via a low-temperature buffer vessel. To maximise ASHP efficiency, heating is at 45°C flow/40°C return, which, Palmer says, is ‘quite challenging when we need to heat the pool hall to 30°C. To operate the system at these low temperatures relies on high levels of heat recovery and a high-performance building envelope’. The solution also required non-standard fan coils, air handling unit coils and heat exchangers to exploit the low flow temperatures.

Reducing glare

Plots show the direct sun penetration at two points during the year. These simulations are conducted using a bespoke tool, Beam Tracer, created by Max Fordham to calculate specular reflections. Orange represents the direct sun transmitted through the glazing; pink is the reflection from the pool surface. As a result of the steep-angle reflections from direct sun through the top, lights remain at high level and do not enter the occupied zone, where they can cause glare. At low sun angles, some direct sun penetrates into the pool area and can cause glare to occupants. By carefully mapping the path of the sun, lifeguards can be positioned to avoid areas that experience glare from direct sun.

The ASHPs incorporate load-shedding controls to minimise peak heat loads and reduce their size, capital cost and embodied energy. Palmer says minimising heat loads, maximising heat recovery and using load shedding ‘has allowed us to squeeze the combined capacity of the heat pumps down to 525kW, around a quarter the capacity of boilers in a typical leisure centre’. This ensured the heat pump solution was space-efficient and economically viable.

The pool water heat exchanger, for example, has a heat demand of 500kW, which, under the usual control regime, would take up the full heat capacity of the ASHPs, leaving nothing for space and water heating. However, Palmer says the only time it needs to deliver this output is when it is heating the pool water up from cold.

For the majority of the time, the heat exchanger is only required to output about 50kW to maintain the water at a steady temperature – and because the pool water acts like a huge thermal battery, the system can wait until the demand for heat is lower. ‘We put a lot of work into ensuring the heat pumps are not oversized, because it would have been easy to think we needed four times as many heat pumps. But if you are in control of where the heat is going, it allows you to shed some of the loads,’ Palmer explains.

Two additional water source heat pumps are used to raise the water temperature from 45°C to 60°C to supply the hot water calorifiers.

In addition to the five heat pumps dedicated to heating, the sports centre has five, four-pipe heat pump chillers optimised to provide cooling, but which can also provide free heat to the building. These supply the FCUs with chilled water at 6°C/12°C. The units can simultaneously top up the thermal store using heat reclaimed from the cooling side. The heat generated by activity in the fitness suite and dance studios is captured and used to keep the pool warm and preheat hot water for the showers, explains Palmer. 

There is a heat recovery unit on the pool water filter backwash system, too. The backwash is used to clean the water filters. In addition, to maintain pool water quality, 30 litres of water is added to the pool per bather, with a corresponding amount removed. This water is used to flush the centre’s toilets.

Engineering the sports centre’s low-energy design was ‘the easy bit’, says Palmer, who adds that it is often the execution, rather than the design, that prevents schemes from achieving predicted energy performance. For Ravelin, Max Fordham was novated to Wates Construction under the two-stage design and build contract, and appointed by Wates Building Services to develop its installation and record drawings in Revit. The engineer also worked with Wates’ offsite manufacturer, Prism, to integrate prefabricated service modules and plant skids. ‘It meant we were able to take responsibility for the design from concept to installation,’ says Palmer.

Max Fordham also produced drawings for the client, with all CoBie asset information, as a full BIM project. Palmer is complimentary about how Wates Building Services (now SES) tackled the project. A two-stage procurement route ensured the contractor was able to price ‘every bit of kit specified, to avoid compromises with lower-efficiency alternatives’. Execution was also helped by the soft landings specification insisting that Wates appoint an independent commissioning manager (Banyards). Its task was no doubt helped by the building having more than 200 electricity and heat meters. ‘At completion, the building was properly and fully commissioned so that it performed well from the get-go,’ says Palmer.

Post-occupancy, the soft landings initiative requires Max Fordham to monitor the building and report each month on how the various spaces are performing – a task aided by the engineer having remote access to the BMS and meters.

There were also monthly meetings to gather client feedback. Palmer says: ‘If something was not working, it was raised at the meeting so that, by the next meeting, it had been resolved, which helped ensure the client never lost faith in the design and remained engaged in the low-energy strategy.’

A major challenge with sports buildings is the huge variation in occupancy throughout the day. In the evening, they are usually full and everything is running flat out, whereas, in the middle of the day, they are relatively empty. ‘M&E designs often only focus on meeting peak conditions and do not consider the other times when occupancy drops off,’ explains Palmer. ‘But you have some pretty powerful kit in this building, so you will waste a lot of energy if you don’t turn things down or off when occupancy drops.’

One issue raised post-occupancy was the level of local control that users should be given, particularly over the temperature of the fitness studios after complaints that these were either too hot or too cold.

Post-occupancy evaluation monitoring showed the rooms were performing as designed, with temperatures being maintained at 18°C, and CO₂ levels rising and falling, and the fresh air fans responding accordingly, depending on occupancy. After questioning users throughout the day, however, it became clear that when the spaces were used for high-intensity exercise classes, users found them to be too hot, whereas when they were used for a zen yoga class, for example, users were too cold. ‘We’ve now added a button to each studio to allow the temperature to be changed up or down a couple of degrees for an hour,’ says Palmer.

This approach has clearly worked, and highlights the benefits of a soft landings approach. Perhaps more impressive is that the scheme improved significantly on the original, challenging EUI target of 218kWh·m^-2 per year. 

The post Keeping fit with less energy: Ravelin Sports Centre appeared first on CIBSE Journal.

Renowned for his work in retrofitting commercial heat pumps, Draper has made substantial reductions in carbon and costs in large commercial properties, using an innovative and lean engineering approach.

The award judges praised him for encouraging others to make the changes necessary for large buildings to decarbonise in a cost-effective way. ‘While we saw many great examples of leadership and development of teams, the winner stood out for his creativity and practical delivery of innovation,’ they said. ‘He clearly has a passion for the development and growth of engineering.’

British Land’s 350 Euston Road was the first large-scale heat pump retrofit in a commercial office building. The project was led by Draper who, in 2012, was working for British Land. ‘It was a really steep learning curve,’ he recalls.

British Land was on a mission to reduce its energy use by 40% by 2015. The seven-storey office building’s three gas-fired condensing boilers and two air cooled chillers were approaching the end of their life. Retrofitting heat pumps was the obvious solution, Draper says, because, like most commercial offices, this one required concurrent heating and cooling for a large part of the year.

Model geometry for dynamic heat pump analysis with surrounding built environment

‘If you have a building that needs heating and cooling simultaneously, why would you run a separate heating and cooling plant when you could run a 4-pipe heat pump unit to help improve the building’s energy performance and reduce its carbon footprint,’ he says.

A major challenge in replacing the gas-fired boilers with an air source heat pump (ASHP) is the lower temperature of the heating supply. At Euston Road, the boilers supplied fan coil units (FCUs) on the office floors with water at 70^oC. While heat pumps can now produce water at this temperature, at the time they did not. Instead, the heat pumps were designed to operate at a much more efficient system temperature of 45^oC; with the FCUs supplied with heat at this lower temperature.

The project uses a Climaveneta ASHP, which has three basic operating modes: chilled water only; hot water only; and simultaneous hot and chilled water production. ‘When simultaneous heating and cooling demand occurs, heat energy can be obtained almost for free,’ Draper says.

In 2014, ASHP technology was unable to deliver a sufficient quantity of high-grade heat to meet the heating demand when ambient temperatures were low. For the Euston Road project, when ambient drops below 5^oC the building’s gas boilers kick in to meet the heat demand.

The solution worked. ‘The additional expenditure to retrofit the air source heat pump achieved payback within a year and now saves occupiers £60,000 every year,’ Draper says. In addition, the switch to using an electric heat pump as the primary heat source, as opposed to gas boilers, is helping to reduce carbon emissions by 470 tonnes a year and improve local air quality.

Draper frequently works with Darren Coppins, of Built Physics

Ten years on and the installation is still delivering. ‘What this first project demonstrated quite successfully is the use of a heat pump as a means of recovering heat,’ Draper explains.

Having proven the methodology, Draper has continued to build on this experience and the lessons learned from that initial project, both as an employee of British Land and, subsequently, as managing director of his own consultancy, Twenty One Engineering. He says retrofitting heat pumps is more demanding than installing them in new-build projects. ‘With new-build applications, there is generally more space and it is much easier to design systems from the outset to operate at a lower system temperature of 45^oC/50^oC to maximise heat pump efficiency,’ Draper explains.

He says the challenges for heat pump retrofits include ‘restrictions on plant space using existing plantrooms, limitations on the electrical power available, and the need to provide sufficient heat to existing equipment sized to operate at a higher supply temperature’. In addition, heating demands in offices tend to be higher now than they would have been in a 1990s office, because heat outputs from computer monitors and lighting are less, and office densities are generally lower. On the plus side, with a retrofit you will have the benefit of detailed metering information from the building, ‘so there will be far fewer unknowns’, he says.

My journey from apprentice to CIBSE Engineer of the Year

Draper has gone from ‘worst apprentice’ to ‘true leader’

I started out on an engineering apprenticeship, as a tool maker for e2v. Unfortunately, I cannot stand still, so, at the age of 18, I was told I was the worst apprentice they’d ever had and I was moved to facilities, where I undertook an electrical apprenticeship.

The e2v factory manufactures semiconductors and specialised components for medical, space and industrial applications. It has Class 10 and Class 10,000 clean rooms, and 11 substations – all high-end stuff. Learning about building services on a complex scale changed my mindset and I progressed to factory service engineer.

I left e2v to work for metering company EP&T, as technical lead. Our first big win was for British Land, where I designed and installed the metering system for nine of its buildings. I subsequently drove the energy management process for each, based on the operating data.

In 2011, British Land asked me to join them as senior engineering manager of its Regent’s Place complex. With experience of operating a Class 10 cleanroom, it is easy to transfer these skills to operating commercial office buildings. For the next three years, I drove operations at Regent’s Place to make the multi-let campus one of the most efficient.

In 2012, I started work on retrofitting a heat pump to 350 Euston Road – the first large-scale heat pump retrofit in a commercial building. By 2014, I was in a more central role, advising on how more of British Land’s buildings could target net zero. I started to engage with CIBSE and the Better Building Performance Group.

I left British Land to work, briefly, for a company called Cavendish, before setting up my own company, Twenty One Engineering, to use my skills and experience to deliver turnkey solutions for clients. These included British Land, where I continue to be involved in heat pump retrofits.

I’m a big advocate for apprenticeships, because that’s the route I’ve taken. Until now, no winner of CIBSE Engineer of the Year had done a hands-on apprenticeship – I should not be the only one.

The CIBSE BPA Judges said: ‘While we saw many great examples of leadership and development of teams, the winner stood out for his creativity and practical delivery of innovation. He clearly has a passion for the development and growth of engineering. A true leader by example and a genuine practitioner of engineering leadership.’

To assess the viability of a heat pump retrofit, Draper often works with Darren Coppins, of Built Physics, to model the building and its systems. The model references the metered operational data to confirm its accuracy. When the metered energy data does not match that predicted by the model, the team must assess whether the problem is with the building or the model, says Coppins. He adds that it might be down to problems with the existing controls or excessive infiltration, or parts of the building may not be working as they were intended.

‘We can drill into that data to see if it is something that needs to be addressed with building maintenance or whether the model needs to be tweaked to factor in something I’ve not allowed for,’ Coppins says.

When all parties are happy with the accuracy of the model, it is used to assess the operation of the proposed heat pump retrofit.

For an effective heat pump installation, Draper believes designers have to start to think differently about a project. ‘The historical approach to heating and cooling design was focused on meeting peak loads, but the average temperature in the UK probably sits between 8^oC and 15^oC,’ he says.

A heat pump being craned into position

It’s a point on which Coppins picks up. ‘We’ve got very used to using gas, which can be turned on and off very easily, but a heat pump does not work like that,’ he says. ‘With heat pumps, if we size them for peak capacity their lowest turndown won’t be low enough for them to operate efficiently or, potentially, reliably.’

For this reason, Coppins says it is important to optimise the heat pump for how it will run for the majority of the time: ‘We can predict that through building physics; rather than saying this building has a peak load of 3MW, for most of the time its load might actually only be half of that peak.’ He says a smaller-sized 4-pipe heat pump – ‘with a bit of top-up’ from an additional reversible heat pump – can be used to boost the heating and cooling outputs as required, and can provide a more reliable installation.

The downside of this type of solution is that the plant has to be hydraulically separated. For his latest project, however, Draper worked with Coppins to develop a conceptual retrofit design without the need for additional kit. ‘The system has been designed to work efficiently at 50^oC, but – to meet peak demand – we’re planning to boost the heat pump system temperature from 50^oC to 70^oC,’ he says.

Innovative solutions such as this are feasible because Draper is keen to involve manufacturers. ‘Before we finalise our design, we will get the manufacturers in to have a conversation, because not every heat pump is the same and not every application is the same,’ he explains.

Inside a 4-pipe simultaneous heat pump

Another reason the team at Twenty One Engineering is able to develop innovative solutions, Draper believes, is ‘the open relationship we have with British Land as the customer and with Built Physics’.

In the 10 years since Draper became involved in retrofit heat pump installations, he says the biggest technological advance has been with refrigerant gases, because these allow higher circuit temperatures.

‘At Euston Road, we could achieve a circuit temperature of 50^oC at an outside air temperature of 5^oC. When the outside temperature dropped to 0^oC, the system only achieved a temperature in the low-40s – while, at -5^oC, you would struggle to get up to 40^oC,’ he says.

‘Now, with different refrigerant gases, heat pumps can give us a system temperature of 55^oC at -5^oC ambient.’

The post Plantroom pioneer: CIBSE Engineer of the Year Phil Draper appeared first on CIBSE Journal.

Retrofit has also become a companion to life sciences development, mainly because of a lack of new spaces that can handle the structural and services demands of life sciences buildings. There has also been a shift in demand for city-centre locations, driven by proximity to universities, hospitals and a skilled workforce.

Cambridge, Oxford and London, deemed as the life sciences’ ‘golden triangle’, are great examples of this. Both offices and retail have seen a decrease in demand, creating an opportunity to repurpose these spaces for science laboratories, where the demand remains strong. 

The retrofit challenge

All types of laboratories need supplementary ventilation and some form of fume extraction, and this can be a particular challenge for a retrofit in a built-up area.

The higher ventilation rates required to extract fumes from laboratories means risers need to be larger than those for offices to accommodate more intensive services, and ceiling void space needs to increase by 50cm to make room for larger duct work. Existing buildings that already have high floor-to-floor space, such as shopping centres, are more easily retrofitted as laboratories.

In the past, a lot of buildings were thought to be structurally unsuitable, as external vibrations hindered the ability for optical microscopes in labs to achieve stable images. However, recent technological advancements such as active vibration damping, which operates in a similar way to noise-cancelling headphones, have helped overcome such structural issues.

Specification of ventilation starts with a suitable selection of fume cupboards and biosafety cabinets, for the specific application and chemicals that are anticipated to be used. Ducted fume hoods are typically the most effective for removing fumes.

The placement of hoods must be carefully considered to capture contaminants effectively, by ensuring that there are no obstructions blocking airflow to the hood. Computational fluid dynamics (CFD) modelling is often needed to validate the design before implementation. 

A minimum air change rate must be achieved for safety purposes in laboratories and this is typically three times more than conventional office buildings, requiring larger HVAC facilities. 

It is important to consider where the fumes are discharged and their proximity to other air intakes and receptors.

Conventionally, air intakes must be separated from discharges by at least 10 metres, and fumes are discharged vertically at least three metres above other parts of the building. However, for city centres with an abundance of developments, more detailed assessments are often required.

When direct, ducted systems cannot be incorporated, recirculating systems with activated charcoal air filters and scrubbers can be considered, although these are expensive alternatives.

Higher ventilation rates and fume-extraction systems will have a significant impact on a building’s energy use, so it is essential that buildings services pay particular attention to energy efficiency.

As a first step, it is important to work with the scientists who will be occupying the buildings in the design stages, to optimise the parameters and the airflow design, and prevent overdesign. 

Where possible, spaces should be lab-enabled, rather than fully fitted-out. This will provide end users with an adaptable blank template they can fit-out however they want. This is more attractive than receiving a fully fitted-out space that may not meet specific requirements and could put occupiers off at due diligence stage, or lead to expensive refit financial and carbon costs.

Modulating the airflow to match actual demand reduces energy consumption during low-activity periods, while still providing adequate ventilation when needed.

Variable air volume flowrate systems and demand-control ventilation can adjust the ventilation rates based on real-time occupancy and contaminant levels. Implementing scheduling controls can also optimise ventilation operation based on occupancy patterns and laboratory usage schedules.

Rob van Zyl

Natural ventilation can be used in certain situations. There are other considerations such as prioritising recirculation over full ventilation by using activated charcoal filters or liquid scrubbing to wash the air as it passes through. Heat recovery systems must also be implemented wherever practical, to capture and reuse heat or coolness from exhaust air to precondition incoming fresh air.

Typically, the requirement for safe removal of fumes is to discharge fumes at least three metres above the highest point of buildings, and this means having tall and unsightly stacks.

In the UK, planning regulations impose restrictions on the height of stacks and exhaust vents as part of the overall planning permission process. This is primarily to address concerns of air pollution, visual impact, and potential adverse effects on the environment and neighbouring properties.

Planning authorities need evidence to show that vertical stacks are tall enough to adequately control the dispersion of pollutants and they will want to see how the visual impact of stacks on the surrounding landscape have been considered.

Stack heights need to be specified to minimise impact on air quality. They will be based on factors such as the type of emissions, local air quality standards, and the proximity of sensitive receptors, such as residential areas, schools, or hospitals.

The speed at which air is discharged from a ventilation system – the efflux velocity – can determine stack height. By increasing the velocity of vertical discharge, fumes can be pushed higher and the stack height reduced. CFD modelling can be used to predict whether or not the concentration of released fumes will exceed the required parameters of the nearby receptors. It should be borne in mind that higher efflux velocities require more energy. 

The importance of heat recovery

As there is a requirement for labs to have a lot of air circulating in the building, it is important to recover as much of its heat as possible. However, effectively capturing and using waste heat can be difficult in practice. In some cases, the temperature difference may be insufficient to extract heat efficiently, limiting the feasibility and effectiveness of heat recovery.

Integrating heat recovery systems can be difficult, as it will introduce pressure drops. It can also create foul air that can be corrosive, which means the ductwork must be made with corrosion-resistant materials that will not be damaged by this. 

Science buildings are one of the sectors being considered by the Net Zero Carbon Buildings Standard (NZCBS). Simon Wyatt, sustainability partner at Cundall, is leading the NZCBS¹ sector group and is collaborating with market leaders to create assessment frameworks for buildings in the sector. It is still early days for the sector, and there is a lot more data that is needed before benchmarking of life sciences buildings is taken seriously.

About the author:
Rob Van Zyl is a management board partner at Cundall

References:

1. UK Net Zero Carbon Buildings Standard www.nzcbuildings.co.uk

The post Science in the city: the challenge of retrofitting labs appeared first on CIBSE Journal.

The day-long event, to be held at The Building Centre in London on 6 June, will include a line-up of CPD accredited seminars, a table-top exhibition area and a lively panel discussion hosted by a well-known industry figure.

Mitsubishi Electric as the headline sponsor will offer insight into current industry trends and introduce some of its cutting-edge product developments.

Joining us for the briefing will bring you right into the middle of a multi-pronged debate on how to reduce carbon emissions in building services which will ultimately help the government reach its stated Net Zero target.

The central theme on the day will be on Building Retrofit and its important role in modernising older, less efficient structures while simultaneously lowering carbon emissions.

This subject will be tackled in a panel discussion from varied angles including upgrades to HVAC systems, insulation, lighting and the integration of renewable energy sources such as solar panels – all with the aim of reducing a building’s carbon footprint.

Why attend?

• Network and share knowledge with professionals all working towards a common goal.
• Gain insight into the latest regulatory requirements and how to comply with them.
• Discover new products and services and learn about new approaches to achieving sustainability goals.
• Boost your professional development.

Want to know more?

Visit our website https://bseeforum.co.uk where you can get all the details about how to buy tickets, exhibit or get involved as a sponsor. Alternatively you can contact Jacqui Henderson on jhendershon@datateam.co.uk or call her 01622 699116.

https://bseeforum.co.uk

The post Momentum builds towards Building Services Forum appeared first on CIBSE Journal.

It served as the city’s seat of governance for more than 600 years, but when York City Council relocated, it wanted to refurbish the historic complex and turn it into a digital hub for the 21st century.

Together, architect Burrell Foley Fischer and SGA Consulting set out to deliver the council’s vision.

The interior of the 15th- century York Guildhall

Alongside the creation of the digital hub, the project involved the refurbishment of the listed elements of the scheme to improve accessibility, occupant comfort and energy efficiency. It also included a new office extension and riverfront restaurant at the side of the complex.

The scheme’s numerous listed elements made for an extremely challenging refurbishment. Except for the listed cast iron radiators in the Victorian council chamber, all of the existing building services had to be replaced, as they were long past their prime. ‘We started by asking what interventions we could make to the listed buildings and then set about working out how to deliver these in the best possible way,’ says Bart Stevens, a director of SGA Consulting.

some materials were transported by river

The building’s location, adjacent to the River Ouse, made a river source heat pump (RSHP) the obvious solution to heat and cool the building. ‘The first time I went to the site, I took one look at the river and said “of course we’ve got to use this”,’ recalls Stevens.

Permission to use the river was obtained from the Environment Agency and the Canal & River Trust, and an unobtrusive route for the abstraction and discharge pipework was devised from the basement plantroom to the river.

Under the new scheme, 110kW of simultaneous heating and cooling is provided by a two-circuit, reverse-cycle RSHP. To optimise its efficiency, the heating circuit runs at 50^oC flow/45^oC return, while cooling is at 6^oC flow/12^oC return. The RSHP is also designed to recover heat if areas of the building require simultaneous heating and cooling.

Pipes taking water from the Ouse to the river source heat pump

A pragmatic fabric-first approach was adopted by SGA Consulting in developing the servicing strategy. Using the heat pump to service the new office extension and restaurant was relatively straightforward, because its fabric thermal performance exceeded Building Regulations minimum. However, the listed status of many existing elements and spaces meant opportunities to improve fabric thermal performance were limited. This had a major impact on how and where the heat pump-derived heat could be used.

The office extension and riverfront restaurant

The lower temperature of the heat pump heating circuit made it ideal as a heat source for underfloor heating, because the large floor area helps compensate for the lower temperature of the emitter. The heat pump is also used to supply heat to fan coil units (FCUs) in some of the office spaces. These incorporate oversized heating coils to compensate for the circuit’s lower flow temperatures.

Operating in reverse mode, the heat pump uses river water, extracted at up to 22^oC and returned at 25^oC, to also provide chilled water to the FCUs in south-facing river frontage rooms. ‘These rooms required cooling as well as heating, so we were justified in replacing the existing radiators with modern FCUs in these rooms,’ explains Stevens. 

Reinstating Victorian natural ventilation

SGA Consulting has resurrected the original Victorian ventilation system to help alleviate stuffiness and overheating in the Grade II*-listed council chamber.

The original building services proposal incorporated a series of FCUs to keep the council chamber comfortable. The units were to be placed outside the chamber and holes knocked through the wall to enable the units to circulate air. Historic England was not keen on the modifications, so an alternative solution had to be devised.

‘I said “I bet the Victorians had a way of ventilating the room”,’ recalls SGA Consulting’s Stevens. Low-level ventilation inlets had been identified in the external walls, hidden behind the cast iron radiators which also provide preheating to air entering the chamber. ‘After hunting around, we managed to find some holes in the ceiling, concealed behind rose-shaped bosses, which allowed the warmed air to exit the chamber and enter the roof space,’ says Stevens. In the roof, the ventilation system was originally linked into the flues from the coal-fired boilers using wooden ductwork . The system exploited the pressure differential caused by the upward flow of air from the boiler flues to induce airflow through the council chamber.

The original council chamber ventilation system

SGA Consulting set out to reinstate the original ventilation system, to enhance the airflow without any discernible visual impact in the council chamber. The coal-fired boilers are long gone, but the system still uses the original boiler flue. Because of fire regulations, the Venturi effect from the boiler flue had to be abandoned, so the airflow is now enhanced through the addition of a small axial flow fan.

To further control airflow in the council chamber, motorised dampers (controlled on CO₂ and temperature) have been added to the low-level intakes behind the radiators. Should they so wish, councillors also have the option of opening windows.

SGA Consulting has also managed to hide four cooling-only FCUs beneath raised daises in the council chamber. This helps keep the space comfortable when the council is in session and the room is full of people. The consultant has also resurrected the original Victorian ventilation system in the chamber to further improve comfort.

A major benefit of using a RSHP to provide cooling was that it removed the need for an external air cooled condenser, which would have been noisy and visually obtrusive in this overlooked, congested and historic part of York.

The RSHP is housed on a plinth in the potentially flood-susceptible basement plantroom.

Alongside the electric RSHP, the scheme also includes three new gas-fired boilers. These supply a conventional low-pressure hot water heating circuit at 80^oC flow/70^oC return to furnish the cast iron radiator circuit in the Victorian parts of the building, along with two domestic hot water calorifiers that serve the new kitchen and toilet blocks. The boilers also provide back-up heat to the heat pump circuit, should the heat pump fail.

‘We used the heat pump in all of the spaces where we could make it work, but the heat losses are so great in the Victorian areas, and the floor areas fixed, so we had to reuse existing cast iron radiators and gas boilers to provide sufficient heat,’ explains Stevens.

The new extension to York Guildhall

Heat losses in the 15th-century Guildhall were also particularly high. The building’s Grade I listing meant that it was too difficult to enhance the thermal performance of the solid stone walls and there were insufficient funds to add secondary glazing to the windows. The team was, however, able to hide additional insulation in the roof as part of the lead-replacement works.

Bomb damage during World War II meant that the roof, floor, and some upper walls of the Guildhall had either been rebuilt or replaced, so English Heritage permitted underfloor heating to be installed in the 7m-high space. Even so, heat losses were so great that the heat pump-supplied underfloor heat system alone was insufficient to keep the space comfortable. ‘The heat losses were too high and we were very limited as to the interventions we could make,’ says Stevens.

Boilers are used on very cold days because of high heat losses in the historic buildings

SGA Consulting’s solution was to supplement the underfloor heating with trench heaters concealed within the floor and connected to the higher-temperature gas-fired boiler circuit, for use on cold winter days.

‘When the outside temperature drops below 5^oC, the trench heaters turn on,’ Stevens explains. As a consequence, trench heating will only deliver 12% of the Guildhall’s annual heating demand, with the rest provided by the heat pump circuit. ‘This type of mixed use shows how heat pumps can be used to provide heating to old buildings where the rate of heat loss would be too high otherwise,’ says Stevens.

After the scheme’s completion in 2022, SGA Consulting followed a soft landings regime for two years, to optimise performance of the building services. Lessons learned include:

• Keeping the Guildhall underfloor heating off on cool summer days because of the long time lag in delivering heat
• Turning off the heat to the domestic hot-water systems over weekends when appropriate
• Reminding the client of the two-speed control for kitchen ventilation.

The strategy to re-use a centuries-old building, revitalising it for use for future generations, achieved significant savings on embodied carbon emissions. Equally importantly, the project succeeded in securing the future of the Guildhall complex; the University of York is taking a long-term lease on the historic buildings to create a business hub for spin-off firms from the university. This will contribute to the city’s future and is proof that historic buildings can be refurbished and remodelled to meet contemporary needs.

SGA Consulting’s approach to the project certainly impressed the judges at this year’s CIBSE Building Performance Awards, where the project won a host of awards, including Building Performance Champion.

The judges said of the scheme: ‘With the challenges we face in renovating millions of existing buildings, the York Guildhall project shows what can be achieved to deliver sustainable building refurbishment, minimise embodied carbon and deliver such a project with the most difficult site-access conditions’. 

The post Bridging the gap: the 2024 CIBSE Building Performance Champion appeared first on CIBSE Journal.

When we say ‘fabric first’ in the context of renewables, however, we are really asking what can be done to the building envelope to reduce heat loss. A reduction in heat loss means that a lower kilowatt (kW) capacity of heating plant is required, meaning lower capital and installation costs. It also means heat pumps can run more efficiently (see panel, ‘Why heat pumps suit fabric first’).

However, if heat losses are high because the fabric first approach cannot be taken, heat pumps will struggle to compete with the boilers they are replacing in terms of running costs. (Improving the fabric efficiency may not be possible if costs are prohibitively high or buildings cannot be altered for conservation reasons.)

So, what can be done if a building owner wants to decarbonise their heat and the existing building thermal envelope cannot be improved? One option, which is nearly always fast, affordable and efficient, is to design a hybrid system combining boilers and heat pumps – but this won’t do if the client brief is for full electrification of heat.

Many argue that high-temperature air source heat pumps (HT ASHPs) have been developed to solve this problem. However, the solution is not as simple as it is often made out to be. For anyone considering this route, it is essential to investigate the building and system to ensure an appropriate design and specification. 

This article considers possible solutions for high-temperature heat pump retrofits and looks at the key areas to investigate before undertaking such a project.

Switching boilers for heat pumps 

Discussions of high-temperature heat pumps allude to bringing the operation range into the familiar 82/71°C or, potentially, 80/60°C range. This, however, can be slightly optimistic, as an 80°C flow temperature for even the most modern of R290 (propane) ASHPs is at the very top end of the performance envelope. 

BS EN 14825:2022, which recommends conditions for testing heat pumps, states that a high-temperature heat pump must deliver 65°C at -7°C/-8°C (dry-bulb/wet-bulb) ambient conditions, with medium and low classifications required to deliver 52°C and 35°C respectively at the same ambient conditions. Even when HT ASHPs are able to deliver 80°C, this falls slightly short of the 82°C flow required by 82/71°C circuits. Added to which, most heat pumps prefer to operate in the 5-10K ΔT range, making a straight swap on 80/60°C circuits not impossible, but challenging. From my experience, in 82/71°C circuits the boiler(s) will nearly always be set to ~85°C to mitigate hydronic inefficiencies, the most common of these being temperature dilution.

Pragmatically, the challenges involved in the detailed design of swapping out boilers for heat pumps are not to be trivialised. Before embarking on a project of this sort, we strongly recommend that a significant amount of investigative engineering is undertaken. Try to ascertain (but not be limited to) the following:

• What were the original design temperature and loads?
• Are there hydronic inefficiencies – such as exposed, poorly insulated pipework or temperature dilution – that can be addressed?
• Has the building been extended/reduced/zoned or had alternative heating systems installed in localised areas
• Can the true building load requirements in summer, winter and transient months be measured or calculated with a degree of accuracy?
• Are any bounding spatial constraints yielding enough to allow for new plant to be installed?
• Does budget allow for 100% of the required heating power to be via ASHPs?
• Are electrical capacities sufficient?
• Are there factors to offset the potential higher running costs, such as PV? 

Design information for dated buildings is often limited to a hand-drawn schematic on the plantroom wall. To add to the confusion, many will have seen a dated building run, at some point, on one boiler out of three during winter, with no complaints. 

Improving our understanding of the building profile can be done through installing items such as ultrasonic heat meters, undertaking a full heat-loss calculation (if budget and time allow) and using known data, such as gas-meter readings. Extrapolation of live data or interpolation of fragmented historic data help piece together the jigsaw, for a greater insight into the true thermal profile.

The goal here is to understand what might be changeable, what can’t change, and the risks. For example:

• Flow temperatures may be reduced by fixing hydronic inefficiencies. 
• Bracketing of the heating system may reduce the requirement to run all circuits at 80°C or 82°C all year, improving running costs (see below, ‘Bracketing’).
• Spatial challenges can be solved by sizing real requirements through measuring and calculation.

This may take months to complete, and can be further complicated by seasonal conditions. Ideally, this would involve at least a year’s worth of data, with any subsequent installation planned for warmer months. 

Bracketing 

Bracketing involves consolidating the heating system into frames of known and weighted data. For example, if the survey data shows a sizable constant temperature (CT) circuit serving an air handling plant exclusively, the decision may be taken to ‘bracket’ this out of the overall heating system.

By bracketing this circuit and serving it directly from its own heat pump plant, we are now able to change the tempering or reheat coils to suit a 55°C flow temperature (or lower). This decision alone could increase the heat pump efficiency by up to 150% from a design temperature of around 80°C.

The same principle can be applied to variable temperature (VT) circuits when the CT circuit is unable to deviate from the current design flow temperature. 

VT circuit bracketing can yield massive efficiency rewards, as the weather compensation can be undertaken at the plant without the use of mixing valves.

With direct weather compensation on HT ASHPs, the flow temperature could range from 35°C-80°C. If heat losses mitigations have been carried out then, potentially, emitters may be changed when and if possible, to allow a more aggressive reduction in flow temperature. 

The proportion of the year when the HT ASHPs must remain at 80°C flow may be offset, in terms of net efficiency, by the period of time that flow temperatures are not required at 80°C via direct weather compensation. 

The weighted aspect of bracketing involves understanding the split in capacity required for each circuit. If VT equates to 80% of the overall load requirement, then addressing that in isolation, with CT remaining on 80°C flow, may impact the overall efficiency of the building sufficiently, without the need to replace air handling unit (AHU) coils. 

Figure 1 shows a two-boiler reverse return header setup, with CT and VT circuits, that is typical of many 82/71°C legacy designs. Using data from the current VT setup (if available), the VT minimum temperature can be reduced below current settings to assess whether the target space temperatures may still be maintained. Even a modest reduction in flow temperature will ensure higher efficiencies.   

Most HT ASHPs would deliver a coefficient of performance (COP) of approximately 2.2 at 65°C flow and -2°C ambient conditions. 

If we were able to drop the weather compensation to below 60°C, output from medium-temperature (MT) and HT ASHPs may be blended, potentially reducing any siting or budget complexities of a full HT. 

In the blended MT/HT example solution shown in Figure 2, the heat pumps are cascaded, with a three-port diverting valve being used to deliver heat to the calorifier. Typically, the MT ASHP(s) would act as lead for the directly weather-compensated circuit, supported by the HT ASHP(s) during peak demands. When higher temperatures are required for more challenging design conditions, the HT ASHP can increase the thermal store temperature up to 80°C.

If Figure 1 (the reverse return arrangement) had been designed on a ΔT of 20K, one solution is the alternate cascading method shown in Figure 3. This uses the thermal store lower and upper stratified sections to provide a cascaded temperature rather than the load. This is an identical philosophy to that used with most hybrid solutions. Temperatures are still key, and with good weather compensation a blend of MT and HT ASHPs can still work. However, this solution is more suited to HT ASHPs as, at a higher design temperature of 80/60°C, MT ASHPs are unable to delivery any useful heat.  

Managing expectations

As clients start to review boiler-replacement projects and the achievable options to decarbonise asset heat, we must still ensure fabric options are considered first. 

Emitter replacement to suit low-temperature heating will tend to yield a higher efficiency overall than a high-temperature heat pump system. Heat pumps should not be over-specified in terms of capacity, for economic and spatial reasons. 

Ultimately, perfect is the enemy of the good when it comes to decarbonising buildings unable to offer a significant improvement from fabric upgrades. 

However, a well-considered assessment of the building thermal profile delivers essential intelligence for a clearer understanding of the impact of the potential system solutions, to ensure true life-cycle benefit.  

About the author
Ryan Kirkwood is engineering solutions manager at Baxi

The post High hopes: overcoming challenges with high-temperature heat pump integration appeared first on CIBSE Journal.

When considering an existing gas-fired heating system that is operating with relatively high water flow temperatures of
70-80^oC –compared with today’s typical designs of ≤55^oC – application of an electrically driven alternative to match those flow temperatures is fairly straightforward. 

Managing the impact on operational costs and capital expenditure (capex) is much more complex, however, especially given the disproportionate cost per kWh of gas vs electricity currently, and the relatively high capex cost of technologies, such as heat pumps, compared with fossil-fuel alternatives. 

This is where a bivalent approach can become attractive and possibly help bridge some of these gaps. Focusing on using heat pumps as part of this bivalent solution, we can consider two broad types of configuration: bivalent in parallel and bivalent changeover (see Figure 1). 

It is typical in the UK for peak space heating capacity (100% load) to only be required for a small number of hours in the year and, therefore, this makes up a relatively small amount of the total kWh of heat energy delivered. This opens up the possibility of deliberately undersizing your heat pump, in comparison with peak load, and only operating it for certain parts of the year, allowing the gas boiler to provide the extra peak capacity or peak flow temperatures when needed. This approach can help reduce upfront costs and plant space requirements. 

We know that operating a heat pump at the lowest possible flow temperature and the warmest source temperature will usually deliver the highest efficiency and lowest operating cost. But we must also consider how any heat generated is emitted into the building – this is where the infrastructure of the existing system begins to influence the design approach.

The existing heat emitters (fan coils, air handling unit coils, radiators, and so on) must be assessed to understand their deliverable output capacity at different mean temperatures. This will demonstrate what mean temperature is needed at certain ambient conditions to deliver the required capacity. This is a key piece of information needed to model bivalent parallel and bivalent changeover configurations.

Bivalent changeover configuration:

In a bivalent changeover arrangement, the heat pump is deliberately designed not to deliver the peak flow temperature or capacity of the heating system. It will only operate up to a temperature and capacity chosen to match the heat-emitter capabilities and building load at that changeover point.As a result, the heat pump will operate in isolation from the boiler, providing heat to the existing heat emitters until its maximum flow temperature and capacity are reached. At this point, it will turn off and the boiler will take over, delivering the higher-temperature water and increased capacity required to meet the increasing building load. 

This arrangement will deliver a lower proportion of annual space heating load from the heat pump compared with bivalent parallel. However, as the heat pump will not operate at peak design conditions, or be asked to deliver high flow temperatures, it will benefit from increased efficiency, resulting in a lower operating costs.

To maximise the ratio of kWh contribution from the capacity of heat pump provided, our research shows the optimum will be approximately 50-75% of the building peak load, with the maximum flow temperature being approximately 55^oC. Depending on overall system design and existing heat-emitter capabilities, other combinations can also deliver good results. See Table 1 for an example of a bivalent changeover arrangement. Examples are modelled on the Mitsubishi CAHV-R450 YA-HPB.

Bivalent parallel configuration:

This requires the heat pump to be capable of delivering the peak flow temperature of the system, allowing it to work side by side with the boiler at any time of the year. This means the heat pump can be sized to any capacity and, as Figure 4 shows, deliver heat energy on its own when it has the capacity, or in conjunction with the boiler when the load is greater than the heat pump capacity (the example shows a heat pump sized at 50% of peak load). Flow temperature can be fixed or weather-compensated, but the key design principle is that the heat pump is able to deliver the required flow temperature to meet peak heating demands via the existing heat emitters.

This arrangement will deliver a large proportion of annual space heating load from the heat pump, and probably result in the lowest overall carbon emissions. However, operating the heat pump at potentially high flow temperatures and low ambient conditions will reduce its efficiency, so this configuration will probably result in an increased operational cost compared with the gas boiler-only system. 

Special consideration must also be given to the choice of heat pump, to ensure it delivers the necessary flow temperature and capacity in all operational conditions. A cascade arrangement or high-temperature natural refrigerant product may be needed to achieve the required flow temperature. The capacity of the heat pump can be freely selected to meet any site constraints of power supply or plant space, and consideration can be given to capital costs to achieve the optimum balance. 

To maximise the ratio of kWh contribution from the capacity of heat pump provided, our research shows the optimum capacity in relation to the building peak load is likely to be approximately 25-50%. See Table 2 for an example of a bivalent parallel arrangement. Calculations shown are for comparison purposes only

Conclusion

As the two examples show, introducing even a relatively small heat pump into an existing heating system will lead to carbon reductions, but applying that same heat pump capacity in different ways can achieve different outcomes.

Choosing which configuration and capacity of bivalent system is best suited for a specific project depends on budget, existing infrastructure, desired outcome and, most importantly, how it is controlled.

The post The balance of power: the bivalent approach to heat pumps appeared first on CIBSE Journal.

Built in 1906, the listed building’s metamorphosis from government office to leisure destination has resulted in the already colossal, 1,000-room structure being extended by 31% with the addition of a three-storey rooftop extension. There are also four additional basement levels carved out below the Baroque-style edifice to house a spa, swimming pool, ballroom and kitchens.

It is the scale of the project, its location within the Whitehall conservation area, and the need to sensitively restore and preserve many of the building’s historic interiors that have made servicing the new hotel a herculean task. ‘It is all about coordination and trying to get services around the building without disturbing all of its beautiful features,’ says Anthony Hume, technical director and The OWO project manager for building services engineer Aecom.

Hume has been involved with the project since 2017, when Aecom was asked to look at the services in the former office building with a view to it being turned into a luxury hotel. ‘That was the easy bit; the scale of the project is so big it meant nothing could be reused, so the whole lot needed to be stripped out to enable us to start from scratch while respecting the listing,’ he says.

Aecom’s approach has been to service the building as a whole, with dedicated systems for each building – the hotel and high-end residences – where possible

Services had to be installed without disturbing the building’s beautiful features, such as this marble staircase

The hotel has the larger footprint. Its 120 guest rooms occupy Levels 1 to 6, while amenity spaces, restaurants and bars make up the ground floor, and the subterranean ballroom and its associated kitchen are at Basement Level 2.

In developing its servicing solution, Aecom was able to use a survey model created from digital scans of the building. The model was supplemented by digital general arrangement (GA) drawings with embedded photographs.

‘The entire building was catalogued in pictures, so you could click on a GA to reveal a photo of a particular element, which was really useful,’ Hume says.

Surprisingly, given the size of the building, finding enough space for all the plant needed to service a luxury hotel was a major challenge. ‘We knew what the hotel operator needed, so we had to work with EPR Architects to make sure there was enough space for us to deliver that,’ explains Hume.

Ultimately, the quest for sufficient space meant the planned new basement extension had to be dug deeper still to accommodate the building services.

‘There are six levels of basement; some were added purely to accommodate plant,’ Hume adds. Even with an enlarged basement, there was limited space for the air handling units (AHUs). ‘We have over 35 air handling units on this job, simply because we did not have the space to accommodate fewer, larger units,’ he says.

To aid cooperative working and coordination on this complex conversion, the entire project team worked in Autodesk Revit 3D building information modelling (BIM) software. Hume describes the BIM model as ‘an absolute monster’, with more than one million elements, 400,000 of which are related to the mechanical and electrical services.

‘What was fantastic was having this digital design tool combined with a building that already largely existed – so, if we were struggling to route a service digitally, we could get up and walk to the actual space, which was particularly useful when explaining to those new to the project.’

The OWO hotel includes nine restaurants and three bars

Even with digital scans, the engineer was still presented with some surprises. For example, when part of the ceiling was removed the team exposed a series of beams that had been added in World War II to provide enhanced protection to a particular area. The services had to be routed around the reinforcement.

Perhaps the biggest challenge was in getting the building services from the basement plant spaces to the hotel’s upper levels avoiding many of its listed rooms located on the ground floor. ‘This floor is full of double-height spaces with minimal ceiling voids and some major structural elements, so we made the decision at the outset to avoid using this space,’ says Hume.

Fortunately, Aecom was able to make use of what Hume calls ‘the moat’ – an existing subterranean corridor located at lower ground level that encircles the entire building, following the line of the façade. ‘Using the moat gave us the opportunity to circumvent the entire building to distribute the services,’ he explains.

From the plantrooms on basement levels, services rise up to lower ground level, from where they are routed to the moat. From here, the various services follow the building’s perimeter until they reach the point on the plan closest to where they are required. From the moat, the services are routed up, through the ground floor, to Level 1, where a deep ceiling void provides the space for them to transfer from the building’s perimeter to the foot of a series of internal risers, concealed within the walls, that deliver the services to the upper floors.

For the guest rooms, services from the risers connect to fan coil units (FCUs) to provide heating and cooling. The building’s windows are designed to remain closed. This is partly because of noise, and partly for security reasons in rooms overlooking the royal procession route along Whitehall. Tempered fresh air is supplied to the FCUs from dedicated AHUs located on Level 1. This arrangement was more challenging in the largest guest suites that now occupy the former war rooms, which had listed wood-panelled walls. The panelling had to be carefully removed to enable the services to be installed. FCUs have been hidden behind the panelling, set into recesses carved into the walls. The only clue to their existence are period-style grilles subtly added to the panelling. ‘All you can see now is the grille, but the work to install these units was extensive,’ says Hume.

Windows in the guest rooms are designed to remain closed, partly because of security reasons

The chilled water circuit serving the FCUs circuit is pumped from multiple modules amounting to 3MW of cooling located on Level 6. ‘The condensers are the only plant allowed on the roof and they are in a sunken plant area to keep them hidden below parapet level,’ Hume explains.

Heating is provided by 4MWs of modular gas-fired boilers located at Basement Level 5. The boilers also supply heat to the hotel’s domestic hot water calorifiers, which are located on the same basement level. The boiler flues, however, terminate 11 floors up, when they reach roof level. ‘The flues are the only service in the entire building to have a completely straight riser,
from top to bottom,’ adds Hume.

The residential apartments have a similar servicing strategy to the hotel guest rooms. These are located in a separate wing of the building, surrounding a small courtyard, with a dedicated entrance and basement car parking. Engineers also had to design apartments for intermittent occupancy, as many residents were expected to be absent for large parts of the year.

The project is finally nearing practical completion. Over its six-year duration, legislation changes and enhancements to the hotel operator’s brand standards have necessitated design changes and amendments. For example, Aecom added electric vehicle charging to the residents’ parking areas. ‘The rapid change in car charging requirements over the course of the project meant we needed to add chargers in midway through,’ says Hume.

When The OWO is open to guests and residents later this year, Aecom will still be involved: ‘We’re doing seasonal commissioning post-handover, so that we can adapt the systems as they are being used,’ says Hume. ‘We’ve done the theoretical design, but this allows us to work with the operator to tweak elements to reflect the way that the operator is actually using the building.’ Only then will Aecom be able to say the monumental building’s transformation is complete.

The post Luxury awaits: turning the Old War Office into an upmarket hotel appeared first on CIBSE Journal.

The retention and reuse of a building can limit additional carbon production and policy makers across the UK and Europe are increasingly requiring developers to justify their decision to demolish existing buildings.  

Dublin City Council’s 2022-2028 development plan, for example, requires ‘robust justification’ for demolition and reconstruction works and that re-use should always be considered as a first option.

The policy appears to be having an impact, with property agent Savills saying that ‘emerging evidence points to [the retention and reuse of buildings] as best practice,’ for many developments in its 2023 review of the Dublin office market.

The following contrasting schemes show how consultant engineers in Ireland are helping to trailblaze the reuse of two very different types of office building.

 Tropical Fruit Warehouse

A warehouse building, formerly used for tropical fruit imports (and more recently as a studio by U2), on the quays of the River Liffey in Dublin, has been redeveloped as an office building.

Owned and developed by IPUT Real Estate, designed by architect Henry J Lyons, built by Dutch design and build contractor Octatube, with a façade designed by Arup and building services by O’Connor Sutton Cronin, the scheme comprises three interconnecting elements: a restored 1890s warehouse with a new lightweight cantilevered glass box extension above and a new seven-storey office building behind.

Reuse of the fabric of the double-bay existing warehouse reduced the carbon embodied in the project. A two-storey glass-box extension appearing to float above these is the most eye-catching part of the project.

The early involvement of Arup’s façades team ensured that the lightweight, transparent box could be delivered in keeping with the architectural aspirations.

The double-skinned façade features an outer skin of 8.5m high, 2.5m wide giant laminated glass panes, that reach full height of the two-storey box. The inner double-glazed skin, forming the building’s thermal envelope, is a bespoke steel and glass module. It is recessed top and bottom to give it the appearance of being frameless; all the occupants see is a thin black silicone 24mm-wide vertical joint between units. The double-skin façade has a U-value of 1.1 W·m^-2·K^-1.

A series of glass fins, positioned in line with the joints on the outer leaf, separate the outer leaf from the inner unit. The fins are hung from the building’s roof. The weight of the outer glazed skin is supported on a bespoke stainless steel frame fixed back to the bottom floor slab. 

‘We worked diligently with the contractor to develop bespoke toggled connections that allowed accommodation of the differential vertical movements with the fins providing horizontal restraint to both skins,’ explains Lee Corcoran, senior façade engineer at Arup.

An additional movement challenge was that the cantilevered structure onto which the façade was attached was predicted to deflect under imposed loads. 

Corcoran says: ‘We worked closely with Octatube and structural engineers Torque Consulting Engineers to fully understand the movements associated with the structure at façade connection points so that we could design the system to accommodate the anticipated racking movements and minimise the joint sizes with minimal visual impact.’

The glazed corners of the outer skin were carefully considered through extensive structural calculations and detailing. The final solution to ‘lock’ the corner units incorporates a closed loop structural solution; the large glass panels transfer the lateral load into bespoke stainless steel connections and concealed stainless steel tension rods hidden within the silicone joints at the head and base of the units. 

‘It is a fantastic, discrete solution that no-one will ever see, which is aligned with the essence of the project,’ says Corcoran.

Arup used a low-iron glass for enhanced clarity in both the inner and outer units. 

In the drive to maintain transparency, the architect was keen that the office floors were kept free of window blinds and that the double-skinned façade remained uncluttered by interstitial maintenance walkways. 

A high-performance solar control coating on the outer skin of the double-glazed unit combined with a solar control PVB interlayer on the laminated single-layer outer skin and ventilation to the interstitial cavity removes excess heat.

To finalise the glazing and PVB selection, Octatube built a series of small-scale mock-ups at its Delft HQ. Once the selection was confirmed, a full-scale mock-up was built and subjected to the CWCT sequence B weather performance test. 

Access for cleaning within the cavity is provided by a single walkway concealed at the base of the façade. To enable personnel to move between the two skins, Arup worked with Octatube to shorten the glazed fins so that they stop 1.6m above this walkway. A bespoke abseiling solution was developed to allow for cleaning of individual bays in between the glass fins. 

The location of the glass box above the existing warehouses meant that when it came to constructing it, sequencing was key. As part of the restoration of the warehouses, all of their roof trusses were removed and taken off-site for restoration. This allowed construction of the core and structure to support the glazed box. The box was pre-assembled as far as possible to minimise work at height, ensure build quality and to complete the installation before the warehouse roof trusses were reinstalled.

‘What made the project so successful was our involvement at such an early stage, which meant the design was well considered quite early in the process and that allowed us to engage with a specialist contractor very quickly,’ Corcoran says.

The 85,000ft² office is now entirely leased to TikTok.

Tom Johnson House

Tom Johnson House is a five-storey 1970s office that will become home to Ireland’s Department of the Environment, Climate and Communications

The retrofit of Tom Johnson House, Dublin, is set to turn a five-storey over-basement, 1970s office building into one of the most sustainable buildings in Ireland, ready to become the new headquarters for the Department of the Environment, Climate and Communications (DECC).

The Irish Government has made it a top priority to decarbonise public sector projects and drive the green transition to help mitigate climate change. This project, funded by the EU under Ireland’s National Recovery and Resilience Plan 2021 as part of the European Union’s response to the global pandemic, is intended to be an exemplar. 

It will demonstrate that the project’s client, the Office of Public Works (OPW), is helping lead that transition. As such, Tom Johnson House has been designated a Public Sector Retrofit Pathfinder Project by the OPW.

Designed in-house by the commissioners of public works in Ireland and engineered by Lawler Consulting, the refurbishment is designed to take the building from a C3 Building Energy Rating to an A2, which the OPW predicts will reduce primary energy use by 75%, greatly extending the building’s useful life. ‘The OPW brief was for the building to be A2 energy rated; that set strict criteria for what we had to achieve in terms of both fabric and MEP systems’ energy performance,’ says James Long, associate director at Lawler Consulting.

Application of the OPW’s Green Procurement Policy will further mitigate the project’s carbon impact as will the requirement for compliance with EU rules for material input and waste management, re-use and recycling.

The retrofit retains the existing 1970s concrete structure and external brick façade to minimise the carbon embodied in the refurbishment. ‘We’ve reused the existing window openings and fitted new glazing to enable the office to be naturally ventilated,’ explains Long.

A BIM model of Tom Johnson House

Internally, the existing cellular office layout has gone, to be replaced by a predominantly open plan office arrangement. 

The biggest modification by far, however, is the introduction of a new atrium punched through the centre of the building, from roof to ground floor, to allow daylight to enter deep into the building’s core and to further facilitate natural ventilation.

The new atrium divided the existing rooftop plantroom into two halves. As a result, Lawler Consulting’s scheme now serves each half of the building from its own dedicated rooftop plant. ‘We’ve lost a third of the plant space and yet we’re going to deliver enhanced levels of comfort,’ says Long.

Lawler Consulting’s all-electric design includes removal of the existing boilers. These are being replaced by two, 600kW multifunction chiller heat pumps to provide both heating and cooling to the offices. 

A smaller high-temperature heat pump boosts the heating water temperature to heat the domestic hot water. There is no fossil fuel on site.

Office floors are heated by radiators on a low-temperature hot-water system. High occupancy areas, such as meeting rooms, all incorporate active cooling, primarily provided by fan coil units. 

Additional carbon reductions are provided by a 50kW roof-mounted solar PV array.

The scheme also incorporates a large number of EV charging stations. These are controlled to ensure the building’s electrical demand remains within the capacity of the site’s existing 600kVA transformer.

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In June, planning permission was granted by Camden Council for an office redevelopment on the corner of Gray’s Inn Road and Clerkenwell Road, London, for what is believed to be the UK’s largest full-timber, net zero carbon office building.

Building services engineer Max Fordham has used whole life carbon modelling to calculate the embodied and operational carbon of the project. It aims to exceed RIBA 2030 Climate Challenge and Greater London Authority (GLA) planning energy performance targets. 

The designs for the eight-storey project, by architect Piercy & Company, will result in the construction of an 8,826m² (95,000ft²) office building on the site of the former Holborn Town Hall, in central London, for Global Holdings. The eight floors will include contemporary workspaces and a communal rooftop garden and restaurant.

A second 1,115m² (12,000ft²) building – currently known as 88 Gray’s Inn Road ¬ will also be developed on the site, and is expected to include six affordable buildings and a ground-level affordable workspace.

The team aims to outperform the UK Green Building Council’s (UKGBC’s) Net Zero Office target, with the design seeking to lower operational carbon emissions by up to 82% compared with a typical office building. It is also targeting a Nabers UK 5.5* energy rating for the main building. 

One of the headline-grabbing aspects of the development is the main building’s full-timber structure. This will result in a much lower embodied carbon compared with a typical office building using concrete or similar materials, explains Max Fordham’s Edmund Chan, principal engineer and lead project engineer for the 100 Gray’s Inn Road project.

‘Everything in terms of superstructure will be timber, made from highly sustainable glue-laminated (glulam) timber beams and cross-laminated timber slabs as part of the overall design,’ Chan adds.

Embodied carbon in future refits has influenced design

According to Andy Heyne, director at project structural engineers Heyne Tillett Steel, the timber structure, combined with its high-performance façade, should outperform the UKGBC’s Building the case for net zero office baseline target by more than 50%. ‘With more than 2,400 tonnes CO_2e stored within the timber, the structure is effectively carbon negative during its lifetime,’ he says. 

The reinforced-concrete basement walls of the existing buildings will be repurposed for the development. ‘While the basement will be dug deeper [for the new building], we are reusing the foundation on the perimeter. We will be using as much as possible down at that substructure level,’ says Chan. 

The Max Fordham team has gone through a process of identifying, assessing and pre-auditing the existing buildings in terms of soft-strip and deconstruction of building elements. ‘There is a lot of material that can be reused from soft-strip, such as raised access floors, lighting and MEP strip-out material,’ says Chan. 

Delivering performance

Ensuring the materials selected for the building are as suitable as possible for future deconstruction and reuse is also key. ‘Our retained role is to be part of that strategic approach moving forward, using expertise in these areas and working with the contractor and their supply and delivery chains to make that happen,’ says Chan.

In terms of operational carbon, the building will use 100% renewable grid electricity, rooftop photovoltaic panels, an all-electric heating, hot water and cooling system, and demand-driven displacement ventilation for the office floors. 

‘This is one of our first large office projects that went through the updated GLA set of requirements for sustainability and energy efficiency, which includes whole life carbon and circular economy statements,’ says Max Fordham’s principal sustainability consultant and partner, Henry Pelly. Knowledge from the firm’s first Nabers UK 5.5-star project at 11 Belgrave Road (see ‘Ratings winner’, CIBSE Journal, February 2023) was fed into 100 Gray’s Inn Road. 

A key challenge in such a project is to ensure that lifetime embodied carbon calculations are realised. Avoiding compromises that might change aspects of the design – which could impact energy performance and, therefore, embodied carbon – is crucial, says Pelly. 

‘One of the things about embodied carbon is that everything comes as a package and it all fits together,’ he adds. ‘It’s not like you can just pull out one element because everything’s been designed to work together. The timber structure, for example, is prefabricated off site and assembled on site, reducing carbon inputs.’

There are 2,400 tonnes CO2e stored within the scheme’s structural timber

Max Fordham’s approach to embodied carbon and energy performance modelling is to be conservative about potential savings rather than assuming best-case estimates. ‘It is quite helpful to adopt a kind of “worst case” embodied carbon modelling approach so that, at every stage of the process, there are opportunities for improvements,’ Pelly explains. ‘Instead of taking potential opportunities for savings early on in the process – for instance, the raised access floors we are reusing – we don’t assume them for the modelling until they are written into the documents and we know they are definitely going to happen.’ 

This is important to avoid overestimating savings, Pelly adds, and focus on where improvements can be made to the building.  

Similarly, while estimating the carbon impact of future deconstruction at end of life is a challenge, the team’s model includes only what is technically possible now, rather than assuming the potential impact of future technologies. 

The design decisions reflect potential reconfigurations in the future and the consequent embodied whole life carbon impact. For example, the team looked to minimise ductwork by having more air handling units (AHUs) at each floor level, rather than having multiple vertical ducts running from one centralised AHU.

Enabling works on the project are expected to start imminently, with work starting on site in early 2024. Completion is anticipated for the first quarter of 2026.

Responsibility for keeping to embodied carbon budgets will be held by each of the parties under contractual arrangements for individual packages of work, says Chan. ‘For example, in the concrete work package, they may be able to choose to use lower carbon solutions in different parts of the construction sequence, but they can’t pass down any carbon budget “overspend” to the next contractor to make up somewhere down the line.’

Ultimately, achieving net zero carbon requires a ‘whole building’ approach to design, adds Chan. ‘We’ve driven down the building’s operational energy demands by prioritising passive principles and optimising the façade, engineering efficient active systems, and supplementing through low and zero carbon energy sources.’ 

Max Fordham is committed to having the in-use performance realised and verified by others. ‘We want to show that low energy design is not a concept, but a reality in our lifetime,’ he says.

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