December 17, 2018
by Andrew Peel
The world’s first Passive House car dealership is now nearing completion in Red Deer, Alta. Designed by Cover Architectural Collaborative and Sublime Design, this 1540-m2 (16,600-sf) facility will house a new Scott Subaru dealership.
Most, if not all, large car manufacturers have strict corporate standards regarding esthetics, layout, and service requirements, and Subaru is no exception. Adding to these baseline requirements was a desire to pursue Passive House certification. However, such efforts must not compromise customer or vehicle service. Another major factor impacting facility design was the local winter temperature of –29 C (–20 F). Navigating these requirements proved challenging and demanded the best of the design team.
The building is divided into three main zones:
The showroom includes a car display area, customer reception and lounge, and sales offices on the first floor, as well as back offices, meeting rooms, and a staff kitchen on the second floor. The repair shop comprises a ground floor with six service bays and parts storage and a second floor with mezzanine, storage, and catwalk. The drop-off zone is a single-storey area used to collect customers’ cars for repair and show off new cars housed in the parking lot to customers at night and during periods of
Numerous considerations had to be made to meet passive House standards when designing the enclosure.
The base design of a typical car dealership is ideal for Passive House as it is inherently very compact with a favourable form factor. The better the form factor (i.e. volume to heat loss area), the less heat loss for the same useable space. While there were some design challenges, the main opaque envelope was straightforward. It is a timber-framed construction with:
The R-values are R-68 for walls, R-53 for floors, and R-100 for the roof.
A key challenge was mitigating the impact of the 65 per cent glazing (dictated by corporate design guidelines) on the west-facing storefront. Red Deer is nestled between two of the country’s sunniest cities (Calgary and Edmonton), receiving up to 50 per cent more west radiation than Germany. Overhangs also were not permitted, though these would have limited the impact of solar gain by blocking it when the western summer sun is low. The neighbourhood is flat and contains only low-rise buildings, so no natural shading exists. Deciduous tree planting was explored as part of the landscaping, but found to block too much of the solar gains in winter. External blinds were considered, but were not feasible due to the high wind gusts experienced in Red Deer. The owner also objected on esthetic grounds. Electrochromatic glazing where solar heat gain control can be regulated via an electric charge was explored, but a product of suitable characteristics (e.g. U-value and solar heat gain co-efficient [SHGC] range) could not be found for the project.
Ultimately, insulated spandrel panels in the top row of glazing and automated operable internal blinds with manual override were adopted. Unfortunately, these measures were insufficient to mitigate the high cooling load.
Window comfort has been found to be a key challenge on other cold climate projects. Only one Passive House Institute (PHI)-certified window for cold climates is commercially available in North America, but no certified curtain wall system is on the market. To meet the comfort criterion in Red Deer, the installed window U-value must be ≤ 0.61 W/m2/K (R-9.4). The building relies on centrally distributed heat blown down from above the glazing surfaces to ensure comfort requirements
Overhead doors were another envelope challenge. The initial design called for seven overhead doors. The Passive House consultants devised an alternative design requiring only two. The client felt this disrupted service too much and eventually agreed to a compromise of four.
The initial concern with the doors was heat loss due to operation. Investigations revealed minimal air exchange
(15 m3 [530 cf]/hr/door opening), with negligible impact on heat loss. The greater concern turned out to be standby air leakage. Despite the reduced quantity, the overhead doors comprised 17 per cent of the total opening area in the wall. Conventional North American doors are not rated for airtightness, so could not be relied on. Therefore, the team had to look to Europe both for the doors and for an independent assessment of their airtightness. For this, the project team reviewed EN 13241-1, Industrial, commercial, and garage doors and gates–Product Standard, which defines airtightness classes. A Class 2 would increase the whole building airtightness to 0.08 air changes per hour [ach] @50Pa, representing a 20 per cent rise in whole-building air leakage (the building target for the project was 0.4 to meet the space heating demand). The author’s team located a product with an equivalent leakage of 0.04 ach@50Pa that increased the whole building leakage by an acceptable 10 per cent. Additionally, careful detailing ensured a durable seal between the door frame and the wall.
The unique uses in the building required a detailed investigation of internal heat gains (IHGs). The project team compiled a list of equipment early in the project to support more accurate Passive House Planning Package (PHPP) modelling from the start. As no data on car repair equipment could be found, the project team worked with the client to develop reasonable assumptions around usage and power ratings. Consideration had to be given to heat transfer between the showroom and other zones due to differing interior temperatures—the repair shop and drop-off zones are kept at 18 C (64 F) for the comfort of the repair personnel. Another key element to look into was the heat generated by the engines operated during repairs. The exhaust can reach 340 C (650 F) and its contribution to IHGs varies substantially based on the engine’s run time. Client input on typical repair procedures was crucial to estimate these gains.
Car exhaust also contains harmful pollutants that must be directly exhausted outdoors. To meet code requirements, each of the six service bays required 11 m3 (400 cf)/m of exhaust pipe. Normally, all bays are connected to the same exhaust fan, leading to all of them being exhausted even when only one is in use. For this project, each bay was instead separately vented, cutting the exhaust rate by 83 per cent.
To further reduce losses, the team also explored supplying the make-up air directly to the car engines to avoid heating it. This setup was vetoed by the client, due to concerns over impact on servicing. Heat-recovery options on the exhaust, including heat-recovery ventilation (HRV), coaxial tubes, wrap-around coils, and heat pipes, were also explored. None of the manufacturers would warranty their equipment for use in car exhaust systems, rendering these measures infeasible. A further consideration was installing a ground earth tube to preheat the make-up air. The high air volume would require a large capacity at substantial cost. The average winter ground temperature in Red Deer is approximately 4 C (39 F), limiting the energy that can be extracted, and still necessitating the installation of a make-up air system. In the end, the additional heat loss of the exhaust had to be compensated through an improved building airtightness of 0.4 ach@50Pa. This was deemed achievable, given the experience of the architect and Passive House consultant (who had both previously worked on certified projects) and the larger size of the building.
Heating and cooling
Heating and cooling is provided by a ducted variable refrigerant flow (VRF) system, with indoor units concealed within the corridor’s suspended ceilings. The residential models were considered for cost savings, but concerns over equipment longevity steered the team away from this option. Electric resistance coils were installed in the supply air of each indoor unit to provide heat during peak heating conditions, when the heat pumps are expected to stop operating due to low temperatures. The capacity of the coils and heat pumps could have been substantially reduced if the heating loads according to PHPP had been considered in the design.
Despite the low nighttime summer temperatures and humidity levels in Red Deer, active cooling could not be avoided due to the solar and internal heat gains. The team tried diligently to reduce the size of indoor units, but the high solar gains in the showroom worked against this effort. Several scenarios were investigated in PHPP to estimate the peak cooling loads. A comparison of the results from the standard PHPP calculation (average load over the warmest 24 hours) of 11 kW and a worst-case scenario (e.g. peak three hours of solar gain, moveable shading not deployed, and maximum IHGs) revealed a five-factor difference in cooling load. The latter scenario’s result (52 kW) was relatively close to the engineer’s calculated load (57 kW). The results are consistent with findings from a PHI paper that revealed the PHPP cooling load algorithms are inaccurate when high solar gains are present (Figure 1). For more information, refer to Schnieders Jürgen: Planungstools für den Sommerfall im Nichtwohngebäude. In: Arbeitskreis kostengünstige Passivhäuser, Protokollband Nr. 41 Sommerverhalten von Nichtwohngebäuden im Passivhaus-Standard; Projekterfahrung und neue Erkenntnisse, Passivhaus Institut, 2012.
Domestic hot water
Two separate domestic hot water (DHW) loads are present in the building. The first load is for the washrooms and kitchen. The demand is relatively low and is served by a single carbon dioxide (CO2) heat pump. The tank is located in the repair shop to mitigate concerns over freezing of the water pipe transferring heat from the outdoor unit to the storage tank. This provides additional free cooling during summer. The oversized VRF indoor units and electric resistance coils ensure winter cooling can be compensated efficiently.
The second load is to wash each and every car entering the repair shop, per the client’s service requirements. The load is approximately 2020 L/day @ 60 C (530 gal/day @140 F), which could not be met by the CO2 heat pump. Instead, the water is heated by a portable, on-demand, gas-fired water heater, the only service in the building fuelled by natural gas. An electric version was not feasible due to the required electric capacity and operating cost. Additionally, Alberta’s grid is relatively carbon-intense, leading to high carbon emissions. As technology develops and the grid gradually decarbonizes, this unit can easily be replaced by an electric version in the future. The resultant primary energy renewable (PER) demand was 34 kWh/m2/yr (11 kBTU/sf/yr), or 56 per cent of the total building budget, for this service alone (Primary energy renewable (PER) is a different method of evaluating the source energy impact of different fuels, developed by the Passive House Insitute [PHI].). To reduce this, the project team searched for a suitable drainwater heat-recovery device to recapture some of the wastewater heat. No device designed for horizontal installation was found on the market, so one created for vertical installation was specified. The mismatched orientation substantially reduced heat recovery efficiency, but the device still provides a noticeable reduction in the overall DHW demand.
Given the current state of technology, limited equipment options, lack of data on equipment energy demand, and inherently high energy demand to provide the required services, a relaxation of the total building PER target was granted for certification (Figure 2).
The challenges cold climates present to Passive House design are nothing new. However, the combination of climate, project requirements, and operational realities forced the design team members to continually re-evaluate proposed solutions to optimize the design and ensure certifiability. Therefore, a team committed to the project goals and willing to seriously explore alternative solutions is essential for success.
Andrew Peel is founder of PeelPHC. An accredited Passive House certifier and trainer, Peel provides Passive House and sustainability consultancy, certification, and training services to the building sector. His professional and academic experience includes consultancy, program management, authoring technical and non-technical articles, course and lecture delivery, and technical research. Peel holds a bachelor’s degree in electrical engineering and a master’s degree in renewable energy. Peel can be reached at email@example.com.
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