This groundbreaking scheme sets a new benchmark for zero carbon educational buildings – an achievement acknowledged at the 2024 CIBSE Building Performance Awards, where it won Project of the Year – Public Use. The judges said the design team met the brief with an exceptional design that successfully combined ‘high-performing building fabric and high-performing engineering services’.

The school’s exemplary eco-credentials responded to the client’s ambitious ‘One Planet Living’ brief and were supported by planning requirements. Its location, between a conservation wetlands area on Metropolitan Open Land and the pioneering BedZED eco-village, meant that the school had to be zero carbon in operation, effectively, to gain planning approval.

Architype, the scheme’s architect and Passivhaus designer, suggested the Passivhaus Plus standard. ‘In 2014, we said, if you want to get this over the line with the planners you need to say you’re net zero, and the only way we believe you can demonstrate that is through Passivhaus Plus,’ says Christian Dimbleby, an associate at Architype, which worked with engineer Introba to develop the scheme.

The school stands on a shallow, insulated, concrete-raft foundation, incorporating ground granulated blast-furnace slag – a by-product of iron production – as a binder to lower the slab’s embodied carbon.

Its foundation is the only major non-timber element in the two-storey school’s construction. The entire superstructure, walls, roof, composite window frames, first-floor slab and cladding are all formed from timber, after Architype used ECCOlab software (an energy, carbon and cost calculator) early in the design process to select materials with low embodied carbon.

To further reduce emissions, all soil excavated during construction has remained on site and has been used to create grass mounds that surround the playgrounds.

To minimise future embodied carbon emissions, partitions between rooms are designed to be moveable, to allow spaces to be easily reconfigured as the school evolves. Similarly, the school is designed to be extended easily to accommodate an increased pupil intake, without the need for reconfiguring the existing structure or major interventions on the building services.

‘We’ve designed the building so the circulation spaces, assembly hall and plant work for a two-form entry,’ says Dimbleby.

The west, east and south elevations of Hackbridge Primary School

As a Passivhaus building, the L-shaped school has a highly insulated and airtight envelope, to minimise fabric heat losses, control heat gains and provide excellent levels of comfort. The large school hall is positioned facing east-west and serves to help block traffic noise from the nearby main road. The hall shelters the adjoining classroom wing, which faces north-south to optimise solar gains.

Brise soleil and an oversailing roof provide shade to the southern elevation to prevent the classrooms from getting too warm in summer, in compliance with Passivhaus overheating criteria and CIBSE TM52.

‘We did a lot of work with Introba on optimising window positioning and sizing,’ Dimbleby explains.

Classrooms have mixed-mode ventilation, allowing teachers to open windows when conditions are suitable.

In winter, heating is provided by an ICAX 70kW ground source heat pump (GSHP) system. This extracts heat from the ground via eight, 130m-deep boreholes and stores it at 42^oC in a 300-litre thermal store.

A low-temperature hot water circuit, operating at 42^oC flow/37^oC return, supplies low-temperature radiators in the classrooms and an oversized heating coil in the air handling unit (AHU).

‘One of the benefits of Passivhaus levels of fabric insulation is that we didn’t have to locate the radiators under the window,’ says Graham Day, associate principal engineer at Introba.

The school meets LETI embodied carbon targets

Using the ground as an interseasonal heat store enables the boreholes to provide cool water to temper the fresh air supply in summer. In this mode, the heat pump is bypassed so that ground-temperature water (at about 10^oC) is circulated to the AHU cooling coil. Coolth is also recovered from exhaust air by the AHU’s thermal wheel.

‘While we’re extracting coolth from the ground we’re warming it up, which helps the heat pump operate more efficiently in winter,’ Day explains. Because supplying cooling only requires a very small amount of power to run the circulating pumps, it is beneficial to do so, adds Day, because it enables the heat pumps to work more efficiently in winter. ‘It is better than free cooling – it is beneficial cooling,’ he says.

For optimum system performance, annual heating and cooling loads should be balanced, so the heat removed from the ground in winter is put back in summer. ‘On this scheme, we’ve not managed to achieve a precise balance, but there is still a beneficial heat exchange,’ Day says.

Opening windows are key to the Passivhaus strategy

A separate 40kW heat pump connected to the same borehole array is used to preheat the domestic hot-water thermal store to 52^oC. A gas-fired water heater is used to provide top-up heat to the vessel and is available to provide backup to the heating system. ‘Improvements in technology mean that, if we were designing the system today, we’d be able to heat the domestic hot water entirely by heat pump,’ explains Simon Ebbatson, senior principal at Introba.

The temperature in the domestic hot-water network is maintained using a conventional circulation system, but with microbore pipework connections to individual taps.

‘Passivhaus penalises you heavily on dead-leg lengths, so we’ve designed the system to ensure there is no more than a litre of water in any one of these,’ says Day.

To achieve Passivhaus Plus, the school must offset all energy use over the course of a year, including unregulated loads. To do this, it incorporates 424m² of photovoltaic (PV) panels, designed to deliver 81kWp. The panels are supported on frames above the green roof, where a symbiotic relationship means that panels provide shade to the vegetation, while transpiration from the vegetation and evaporation from the growing layer,help cool the panels, improving their output.

Figure 1: EUI of Hackbridge Primary School compared with CIBSE typical and good practice, and LETI school benchmark

The downside of using PVs to achieve an energy balance on a school is that the panels provide the highest electrical output on summer days, when the school is closed. While the school can sell this surplus electricity to the Grid at a relatively low price, it does still have to buy electricity from the Grid at a much higher price to make up for the electricity shortfall on shorter, darker winter days. The school achieves an annual energy balance, but there is still a net cost for electricity. ‘Unfortunately, achieving an energy balance does not necessarily result in a financial balance in today’s market; we hope this may change in future,’ Day says. See Figure 1 for energy performance data.

The school received its first intake of pupils just before the Covid pandemic, which hindered its operational optimisation and, subsequently, its ability to achieve net zero energy in operation. There were also issues with a faulty buffer vessel and three of the photovoltaic inverters failed. School staff, too, struggled to come to terms with the nuances of running a Passivhaus Plus school – for example, knowing when to open the windows and when to take advantage of free cooling.

To their credit, the engineers and architect have remained committed to the project and have continued to be involved through a voluntary soft landings arrangement. In addition, contractor Willmott Dixon has implemented its Energy Synergy process, to measure and verify the school’s operational energy use by comparing metered data against monthly Passive House Planning Package (PHPP) targets, which has helped highlight some anomalies. For example, a building management system (BMS) demand signal to the GSHP stopped working after a software update to the BMS. This was picked up by a sudden increase in gas consumption.

The team’s perseverance has paid off; four years after the school opened, the latest sub-metered data shows energy consumption and generation is very close to the PHPP design targets and on track to achieve net zero energy (see Figure 1).

This pioneering school is finally living up to its A+ Energy Performance Certificate billing. With an energy use intensity of 42kWh.m^-2 per yr, Architype says the school exceeds RIBA’s 2030 operational targets and, with upfront embodied carbon with sequestration of 405kg CO₂e.m^-2, meets LETI’s 2020 embodied carbon targets. 

The building’s impressive green credentials are used to enrich the school curriculum and bolster environmental awareness among the pupils. This makes it a great example of how we can embed environmental design in our school buildings and inspire the next generation.

The post Case study: Passivhaus Plus Hackbridge Primary School appeared first on CIBSE Journal.

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.

‘The payback, although not short, was enough to be well within the design life of the buildings,’ says Gwilym Still, director, Passivhaus leader and partner at Max Fordham, which was the project’s building services engineer, acoustic consultant and Passivhaus designer.

Working with architect Allies and Morrison, Max Fordham set out to develop a scheme that would meet the stringent Passivhaus energy criteria, but that eschewed innovative construction methods and materials in favour of a more conventional palette. The design also accommodates the demands of graduate students, who were consulted throughout development of the brief. ‘We set out to build these buildings with standard components as far as possible, but applied in a different way to help with project delivery and demonstrate the scalability of Passivhaus,’ Still says.

The three-storey Villa Building occupies a gap between two Arts and Crafts-style villas on Cranmer Road. Its design is characterised by a brick façade topped by a tiled, pitched roof incorporating dormers and gables.

To provide lower-cost rentable accommodation, after consultation with the students, the Villa was conceived as a 19-bedroom house with shared bathrooms, kitchens, and a large kitchen-common room on the ground floor. The Stephen Taylor Building is located at the rear of the site.

Its modernist appearance is in response to this area’s more contemporary architecture. Behind its precast concrete and terracotta façade, bookended by grey brickwork stair enclosures, it incorporates 40 en suite study bedrooms spread over two storeys. The building also accommodates a large ground-floor common room that serves the entire campus. This building has been designed, structurally and from a building services perspective, to be able to accommodate an additional top floor at some point in the future.

Despite their different architectural treatments, both buildings are supported by a cross-laminated timber structure set on a concrete raft foundation, and both feature cavity wall construction using mineral wool as a partial fill.

Allies and Morrison says this construction method helped achieve a ‘remarkably good’ airtightness performance: the Villa Building achieved a permeability of 0.17m3/m 2 ·h (0.16 ACH), while the Stephen Taylor Building achieved 0.31m3/m 2 ·h (0.19 ACH), both at a pressure differential of 50 pascals.

The building services, too, are similar. Both buildings are all-electric, with space heating provided by direct electric panel heaters and domestic hot water supplied by point-of-use heaters, to minimise pipework heat losses, along with waste-water heat recovery.

‘We opted for an all-electric solution – even though, at the time, it was harder to achieve from a regulatory compliance point of view – because when you looked at the ongoing decarbonisation of the electricity Grid in the context of the design life of the building, the period when gas would be better than electric was vanishingly short,’ explains Still. Both buildings are orientated in the same direction, with their principal elevations facing north-south.

Max Fordham did some early-stage modelling of daylight levels and heat gains to establish parameters for the window sizes from which the architect could work. Still says Max Fordham revisited these assumptions as the design progressed to check that these parameters were still applicable. The scheme was designed before the publication of CIBSE TM59 Design methodology for the assessment of overheating risk in homes. Nevertheless, Max Fordham tested the scheme’s comfort performance against current and future weather files using IES dynamic thermal modelling. It also used the Passivhaus Planning Package (PHPP) to prove the scheme’s compliance with Passivhaus comfort criteria.

Both buildings feature continuous mechanical ventilation from packaged mechanical ventilation with heat recovery (MVHR) units incorporating summer bypass. The Villa Building uses a cascade system of air transfer, similar to that in a domestic house: two MVHR units on the top floor supply fresh air to the bedrooms; this spills into the corridors and, from there, to the kitchens, shower rooms and toilets, from where it is extracted. The Stephen Taylor Building is based on a series of single MVHR units serving clusters of four en suite bedrooms. In addition, two separate MVHR units serve the two pairs of kitchens.

The exposed cross-laminated timber design of a kitchen in the Stephen Taylor Building

‘The ethos behindthe scheme was to keep things as simple as possible from a ventilation point of view, so there is no interlock with the windows – if someone wants to open a window to increase ventilation, they can,’ Still explains. ‘On both buildings, extract is from the toilets, kitchen and bathrooms – so, if we turned off the vent when someone opened a window, the shower rooms would, for example, start to get humid.’

A single MVHR unit with summer bypass serves the campus common room in the Stephen Taylor Building. Still describes this room as ‘a special case’ because of its predicted intensive occupancy. Here, the MVHR unit incorporates a mini air source heat pump to automatically heat or cool the ventilation air. ‘While you could keep the common room comfortable for most conditions, there were enough hours where it was going to get uncomfortably warm that we put in active cooling,’ explains Still. Ventilation rates are increased further in summer, with windows opened by automatic actuators.

The common room also incorporates underfloor electric heating to keep walls clear of panel radiators. The building’s 100-year service life mean s items such as the MVHR units are designed to be accessible for service and to enable their replacement over the design life of the building. Still says the ductwork is less easy to replace, ‘but it is still possible’.

The scheme was completed in December 2019. On handover, the facilities staff were trained in its operation. In addition, the design team and contractor remained engaged with the college post-occupancy, to answer queries and to help fine-tune systems. Post-occupancy monitoring of energy consumption took place and revealed student behaviour that differed from the design assumptions.

Post-occupancy monitoring of electricity consumption was undertaken from January to April 2020, before occupancy was interrupted by the Covid pandemic. The monitoring showed an expected building energy use intensity (EUI) of 53kWh·m-2 per year, with a peak hea ting load below 10W/m-2. Post-occupancy feedback was also gathered, informally and through a structured survey using BUS methodology, in April 2021.

Overall, the results were extremely positive, with the building scoring highly in areas such as comfort, lighting, noise, ventilation, effects on health, and appearance. However, the survey did pick up on the initial frustration of some students with the energy efficient lighting controls, which turned off lights earlier than desired in toilet and shower areas. This issue has since been rectified by simply extending the lighting control run-on period.

Max Fordham’s well-engineered approach and its response to student issues certainly made an impression on the judges at this year’s CIBSE Building Performance Awards, where the scheme won Project of the Year (Non-Domestic) . The judges were impressed by the consultant’s focus on optimising building energy performance, and they highlighted the use of feedback from the occupant surveys and the scheme’s comprehensive approach to commissioning. They also admired how detailed analysis of the impact of a range of future climate scenarios had influenced the design and construction of the two buildings.

The post Graduating with honours: Cambridge University’s Passivhaus student housing appeared first on CIBSE Journal.

Roundtable sponsor

Industry experts at a CIBSE Journal roundtable on cooling have unanimously agreed that the industry can take big steps towards decarbonisation if new buildings and systems are well designed to take building loads into account. 

The event, Decarbonisation: a whole life approach to cooling buildings sponsored by Daikin, looked at the complex challenges and potential solutions to staying comfortable on a warming planet. Refrigerant leakage, the challenges of cooling existing buildings, and embodied carbon were some of the topics debated.

Hugh Dugdale, associate principal at Elementa Consulting, kicked off the roundtable by describing his involvement, as one of the authors, in the TM65.1 addendum, which investigated the embodied carbon impact of heating and hot-water equipment for use in residential buildings. He is also exploring the implications of refrigerant leakage, which can have a huge impact on global warming.

‘It’s so strange that there’s so little information about refrigerant leakage, yet it’s a controlled substance,’ he said. ‘It should be easy to record how much refrigerant is topped up and poured into systems each year, but there’s no central database. We have contacted installers to get this information, but it’s very poorly documented.’

Bianca Laura Latini MCIBSE, senior sustainability engineer at Buro Happold, has also looked at refrigerant leakage and explored what will be available at the F-Gas Regulation phases. She has talked to manufacturers about refrigerant development and making low global warming potential (GWP) refrigerants more feasible for clients. Latini has also done work for Bristol City Council on its heating and cooling policy, and a whole life carbon and cost assessment of seven different systems in commercial and residential buildings was carried out.

‘They were all electric, because we started from the premise that they have a net zero carbon city target, and we looked at different kinds of heat pumps versus domestic heating and district heating networks,’ said Latini. ‘The Council was interested to know the feasibility of low-GWP refrigerants. It’s a call to manufacturers to develop low-GWP refrigerants.’

Matteo Dall’Ombra, VRV specialist at Daikin, said refrigerants are key to reducing the carbon footprint of leading air conditioning manufacturers. Daikin has adopted a two-tier strategy for how refrigerants are used and the type of refrigerant specified. Every new product employs the lowest possible GWP refrigerant, which now means the new R-32. This conveys heat efficiently and reduces electricity consumption by approximately 10% compared with air conditioners using refrigerant R-22. 

For products that can’t use R-32, Daikin adopts 100% reclaimed refrigerant. Lower GWP systems will require more careful design and consideration, Daikin bundles these measures with the all new R32 VRV system as default. Latini said that engineers would get used to designing with lower GWP refrigerants as their specification becomes common practice. 

‘Each refrigerant has different applications,’ said Latini. ‘Making it clear to clients which refrigerants are most appropriate is very important. I don’t think there’s much literacy in the built environment as to which refrigerants should be applied to which scenario. The other big issue is that we don’t know much about refrigerant leakage.’

The F-Gas Regulation requires refrigerant top-ups to be recorded, but it’s often challenging to get this information from firms, said Dall’Ombra. Dugdale agreed: ‘It’s so painful getting that data out. It’s hard to get a consensus on estimating charge, which manufacturers could help with. 

‘With a sealed system, such as a heat pump, you know the charge because it’s in the unit. But with a variable refrigerant flow (VRF) system that has pipework installed on site – that you don’t know the length of and the amount of charge within it –a rough estimate on how much is in there must be made. Then a percentage of what is leaking must be calculated, which is difficult because it’s not just liquid filling the pipe. Guidance is required.’ 

Richard Cobb, net zero carbon associate at Atkins Global, suggested making it mandatory for firms to record information about refrigerant topping up. He suggested using Display Energy Certificates. Dall’Ombra said the ongoing problem is visibility, because this vital information often gets buried in logbooks and is not easily accessible.

Amy Punter, associate director at Hoare Lea and member of the CIBSE Retrofit in Heritage Committee, also suggested a sophisticated leak-detection system linked to a building management system (BMS) that calculates the amount of leakage and automatically records what has been topped up.

The newly published standard IEC 60335-2-40 – which allows the use of refrigerants with a lower GWP, while also ensuring a high level of safety regarding flammability – already allows more sophisticated leak-detection systems, said Dall’Ombra, but he agreed that a central database would be very beneficial.

Asked whether recycling refrigerant was an option, Dall’Ombra added: ‘Reclaimed R-32 is currently not as big yet, because it is relatively new and there’s less stock that can be re-used continually. But there’s no doubt there will be a solution in about two years, with even lower GWP for the smaller residential systems.’

Punter argued that the issue isn’t just about refrigerant leakage; the industry should ensure that buildings are performing as intended and are designed well from the start, she said. 

There has been a tripling of energy consumption used for space cooling since 1990, which is putting electricity grids under strain, especially during periods of extreme heat, such as the one experienced in Europe this summer. As a result, space cooling accounted for nearly 16% of the global building sector’s electricity consumption in 2020 (about 1,885TWh)¹. The panel agreed that, before calculating how much cooling buildings require, passive measures must be applied to minimise the energy used in cooling equipment.

Cobb highlighted some typical passive measures he employs to help cool existing commercial buildings. Taking a fabric-first approach is the first step, he said. A building’s thermal mass within the fabric is then considered, as well as finding ways to upgrade its U-value. 

‘Additional solar shading is key to helping cool a building and we then look at the efficiency of the cooling kit,’ said Cobb. ‘If it’s near the end of life, we look at refurbishing it or installing a new system. If the building’s façade is degraded so much that it needs to be replaced, we would remove the skin, keep the structure if we can, and reclad the building with modern thermal. Historic buildings require a different approach given their façades’ architectural significance.’

Cobb added that refurbishing cooling plant is preferable to replacing it. By keeping some of the components he wants to limit the amount of total carbon spent. ‘I always look at carbon in terms of currency,’ said Cobb. ‘The industry needs to say, this is what we’re going to do to this building and it will cost you this much carbon for its whole life. If we did this, we could reduce carbon by simply changing the materials.’

Stephen MacLoughlin, regional director, and net zero carbon lead at Faith + Gould, agreed that a fabric-first approach and external shading are powerful passive measures. He suggested that the UK could learn from architecture in hotter countries, which employ straightforward solutions to address solar gain. 

MacLoughlin has concerns, though, about the commercial sector and the landlord/tenant situation. Providing comfortable internal conditions for employees when temperatures rise, while also addressing energy efficiencies, will present challenges.

Punter highlighted new guidance by the British Council for Offices that could have an impact on this issue, as it includes relaxing occupant densities in a post-pandemic world. She also mentioned her work with listed buildings dating from the 1400s to the 1960s. There is a real urgency to find ways to decarbonise these buildings, otherwise they will fall into disrepair. Part of the problem, added Punter, is a lack of guidance on how to decarbonise these buildings, which have complex and challenging requirements, and must be assessed case by case.

‘U-value measurement in listed buildings is straightforward; measuring air permeability is the real challenge,’ she said. ‘There is a drive to decarbonise, but I question whether we will we see a shift in what conservation officers will accept. I hope they will be more lenient to allow decarbonisation of heritage buildings and accept cooling measures such as external shading.’

Punter added that the way to sensitively retrofit listed buildings is to share knowledge and push the boundaries.

Beyond cooling equipment, Ben Gholam, structural engineer at Price & Myers, introduced his research and software development on embodied carbon optimisation in building structures. His team has created an ambitious database and identified issues with using concrete to achieve thermal mass in buildings to regulate internal temperatures. (See panel, ‘The trouble with concrete’).  

With a predicted tripling in energy used to cool buildings by 2050, it is essential building services engineers take a holistic approach and collaborate with other engineers and manufacturers to find solutions. The roundtable demonstrated how a meeting of minds from across the sector can stimulate original thinking that might just speed our journey to low carbon cooling

References:
1 IEA, Cooling tracking report, Nov 2021 www.iea.org/reports/cooling

The post Sponsored roundtable: cooling for life appeared first on CIBSE Journal.

The £7m development was completed in October 2015. Two years on, this innovative scheme is living up to expectations, with residents saving up to 42% on the cost of energy, compared with a similar-sized dwelling, and with CO₂ emissions 60% less than the Building Regulations minimum.

The scheme’s pragmatic approach to low energy housing impressed at this year’s CIBSE Building Performance Awards, where it won Project of the Year – Residential. The judges said: ‘Killynure Green was a really commendable approach to a social housing scheme’, and praised the fact that it incorporated ‘lots of references to lessons learned from previous projects that they had reviewed and improved on’.

To design the CSH Level 5 scheme, CHI worked with PDP Architects and engineers Caldwell Consulting. ‘We developed the first Code Levels 3 and 4 schemes – and the first certified Passivhaus social housing – in Ireland. This scheme demonstrates our appetite to try to deliver the best service and homes for tenants that we can,’ says Brian Rankin, energy manager at CHI.

As well as meeting CSH Level 5 criteria, the designers had to ensure the scheme met the requirements of Lifetime Homes and Secured by Design, and the space parameters set by the Department for Communities (DfC).

The design

Killynure Green is built on a sloping site. The architect’s design exploits this gradient by arranging the two-, three- and four-bedroom homes in terraces along its contours. Homes are orientated to face north-south.

Their northern elevation incorporates a big feature window, allowing large amounts of daylight to enter the homes without the need to control solar gains. By contrast, the southern elevation incorporates a double-height, single-glazed wintergarden. This is designed to collect solar gains in winter, with air warmed by the sun drawn into the homes through opening doors and windows. The wintergarden is intended to reduce the home’s heating load. In summer, shading elements and opening vents allow occupants to purge unwanted heat from the space.

The CSH Level 5 homes are built using a proprietary Ultima Timber Frame System – a prefabricated structural system, selected by contractor GEDA Construction to achieve high levels of thermal insulation and airtightness. This off-site solution ensured fabric U-values could be kept between 0.11-0.16 W.m^-2.K^-1.

In addition, enhanced accredited construction details were used to achieve Y values (the proxy for the heat loss through the non-repeating thermal bridging areas of a building) of 0.04 W.m^-2.K^-1 by minimising thermal bridges. Where details differed from standard enhanced details, thermal modelling was carried out to test junctions. All windows are triple-glazed.

Airtightness tests were carried out once the building envelope had been completed, but before the internal linings were finished. This approach proved effective, with the homes having a permeability of between 2-3m³/m².h at 50Pa on completion.

Although the homes are highly insulated, they are not designed to Passivhaus standard. One reason for this was the experience CHI had when developing the first certified Passivhaus social housing scheme in Ireland. Rankin says it found that monitored energy consumption for the scheme was ‘higher than expected because of unrealistic expectations around air permeability due to occupants having the freedom to open windows’. In addition, he says, ‘the design team felt that attempting to achieve Passivhaus standard on this project would involve additional cost’.

The homes do, however, include a mechanical ventilation with heat recovery (MVHR) system to remove stale air and provide fresh, filtered and warmed air. The system is fitted with a summer bypass to supply cooling in warmer weather.

The original design proposed solar thermal panels to heat a thermal store that, in turn, would supply domestic hot water and heat for an underfloor heating system. The system would also have included an air-to-water heat pump for top-up heat. This proposal was abandoned, however, to be replaced by a condensing combination, natural gas boiler-based solution, which was expected to have lower capital and maintenance costs.

‘This switch is one of the main reasons the scheme has performed so well,’ says Rankin. ‘There were no objections from the design teams; they were happy to consider an alternative approach and review its benefits in light of various changes to market conditions and financial incentives for renewables.’ Using gas-fired combi boilers also supported the idea that the scheme could be easily replicated by others.

The impact of the change was a capital cost saving of more than £50k, reduced CO₂ emissions and energy costs, and a simpler system to design, install and maintain. Without the solar thermal panel, the size of the roof-mounted solar PV array could be increased to 4kWp, significantly raising the amount of renewable electricity generated. This, in turn, increased the value of the Renewable Obligation Certificate (ROC) payments that could be claimed by CHI over the scheme’s 20-year life, along with payment for exported electricity. Payback for the PVs is expected to be about six years.

Happy handover

Its experience from earlier projects meant that CHI understood the importance of commissioning systems appropriately, and the critical nature of the handover process – from contractor to housing association and housing association to tenants – so everybody understood how to benefit from the homes.

A pre-handover visit took place with the design team, contractor and housing association, to highlight the technologies within each home and to explain how these should be used. Potential tenants were also invited to information sessions, to give them more detail about the scheme and help them decide whether to accept the offer of a home.

Groups of those who decided to move in were then invited to visit the development for a 30-minute presentation in one of the properties, before the keys were handed over.

After the presentation, each tenant was taken to their home so the heating controls, for example, could be set up appropriately for each household. A home user guide was also produced, containing information on the development, plus explanations of the different features, including the wintergarden, MVHR and PV systems. The main contractor and subcontractors were available to help support the handover process.

CHI’s involvement in the detailed monitoring of its passive house development highlighted the cost implications and technical challenges of this approach. For Killynure Green, it opted simply to collect twice-yearly meter readings for the solar PV systems, and annual electricity and natural gas consumption readings. During these visits, tenants are able to raise questions or ask for further support. 

Consumption and cost

All the Killynure Green homes achieved an Energy Performance Certificate (EPC) A rating. This indicates that average energy consumption is expected to be 35kWh/m², with average CO₂ emissions of 6kg/m². The average annual energy running cost for each home is predicted to be £409. The EPCs exclude unregulated energy, such as that used for cooking and by appliances and electronic equipment.

After one year of occupation, in October 2016, meter readings were taken for every home. They showed the overall energy used within the properties was less than the national average for Northern Ireland. For the two- and three-bedroom properties, the average annual total energy costs were £564, compared with the Northern Ireland average for similar-sized properties of around £877 (based on National Energy Efficiency Data in June 2015). This represents a reduction of around 36% for occupants.

All of Killynure Green’s 39 homes have an EPC A rating

For the four-bedroom properties, the average annual energy costs were £682, compared with an average of £1,169 for a similar-sized property – a difference of 42%. Of these total energy costs, each home is paying about £250 per year for heat and hot water.

The solar PV system was expected to generate around 3,108kWh of electricity each year for each home. However, the first year’s analysis showed the PV systems generated an average of 3,318kWh at each property – 7% more than expected – with 28% being used within each home.

The electricity generated by the PV is available free for residents to use, with unused electricity exported to the grid. ‘Tenants can use as much of the generated electricity as they want,’ says Rankin. At the moment, however, they are only using, on average, 28%. If they were to use 60%, tenants would benefit from an additional saving of £160 on their electricity bills. ‘If a number of residents are out working during the day, they may not want to leave equipment running and may not be available to use the solar-generated electricity,’ Rankin explains.

There is a difference between the EPCs’ predicted energy costs and actual energy costs of around £200-250 in each home. Two factors account for this: the proportion of renewable electricity from the solar PV used in each home, and unregulated energy use.

CHI is able to claim Renewable Obligation Certificates (ROC) payments for the PVs, along with payments for exported electricity. In the first 12 months of occupation, Choice received approximately £580 per property in relation to the solar PV systems. According to Rankin, this highlights the benefit of this approach to building new homes. ‘In a private development, if the ROCs and payments for exporting solar PV were made to the homeowners, the average overall annual cost of energy for these homes would be – £90 for each property, so tenants would actually make £90 a year in relation to energy,’ he says.

Even without ROC payments, responses to surveys indicate that tenants’ satisfaction levels are high, with 95% of respondents stating that their electricity costs are lower than in their previous home, and 100% saying their heating costs are lower. In addition, 75% of respondents reported that their monthly electricity costs are less than £30 per month, while 83% said their monthly natural gas costs were also less than £30 per month.

Design for the second phase of homes is now under way, and these properties will also be on social housing tenures. As the Code for Sustainable Homes no longer exists, CHI’s intention is to pilot this second phase to a new, optional, energy efficiency standard outlined by the DfC. These new homes are expected to be some of the first developed in this way in Northern Ireland.

The post Case study: Killynure Green low energy housing appeared first on CIBSE Journal.