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 firstname.lastname@example.org.