'Charting new territory' was originally published in Design Quarterly's summer issue. Read the magazine online here.
Passive House (PH) is the world’s fastest growing building performance standard, focused on significant reductions in heating and cooling loads and offering improved occupant comfort. The German standard focuses on reducing building energy demand rather than seeking to satisfy demand by using renewable energy. While this standard is experiencing spectacular growth in the residential construction industry across North America, its applicability in the public and commercial sector is still largely new territory. However, its advantages and applicability could offer significant value in these sectors, where operational costs are often carried by the building owner.
As a rule of thumb, designing residential buildings to the PH standard requires careful consideration of the envelope continuous insulation and airtightness, the performance of windows and doors assemblies, and the efficiency of the mechanical heat recovery ventilation. But how much of this is applicable to non-residential buildings, where uses and occupant loads vary greatly and where energy gains and losses tend to be less predictable?
Our firm is currently working on two non-residential passive house buildings: the 76,000 square foot Clayton Community Centre in Surrey, and the 31,000 square foot Fire Hall 17 in Vancouver — both slated to be the first of their kinds in North America. Both projects have faced challenges that are providing key learnings and insights, some of which may lead to evolution of PH standards to suit more complex building types.
In contrast to residential PH projects, significant challenges are created by internal heat gains, which proved to be enormous contributors of heat in the buildings. The community centre, which will house a community library, and include a variety of recreational uses including a gymnasium and fitness centre, visual and performing arts spaces and a preschool, is expected to operate from 6am until 11pm daily. The long operating hours combined with intense usage result in high internal heat gains, largely from occupants and equipment. The centre anticipates an average of more than 650 people using the facility on an hourly basis, and has a lighting load almost 40 times higher than a typical residential load. Considering these high internal heat gains, a very efficient PH certified HRV system helps reach an overall heating load that is half of the PH limit. However, this also leads to an overheating situation for many months of the year, and has a drastic impact on the cooling loads of the building, pushing them to more than five times than permitted by Passive House.
The solution required a significant re-evaluation of the thick insulation layer around the building that is typically prescribed by Passive House. Lowering the overall R-value of the envelope increased transmission heat losses, but not enough to address the high cooling requirements. The addition of a passive ventilation system combined with strategic solar shading brought the heating and cooling loads into balance and in conformance with PH requirements. Another challenge was the primary energy renewable (PER) that describes how much more renewable energy is required to cover the final energy consumed by the building, including all losses incurred along the way. PH certification limits the PERs to 60 kWh/m2 per year, which is significantly lower than a typical Canadian residential building. The PER added a new consideration for project teams as each appliance or light fixture chosen needed to be accounted for in the overall energy use of the building. For Fire Hall 17, the used-gear driers run up to 20 hours per day. This, combined with significant IT equipment, use of on-site fitness devices and a communal kitchen, led to high energy loads. The final PER calculated for the building is twice the PH requirement. Given that the building use cannot be fundamentally changed to address this overage, the team worked with Passive House Institute to receive an exemption for the necessary usage demands of this highly technical and very specific building type.
This exercise has great value in paving the way to potential modifications to PH standards to increase its application in a wider range of building typologies, including firehalls and community centres, in both North America and globally. Determining PER accurately is an in-depth process, and should be factored into the design process. It requires significant work for both the architectural team and the client team at very early stages of schematic design to document all anticipated appliances and plug loads. It may lead to potential shifts in clients’ expectations and users’ behaviours. In both projects, for example, the process of determining the PER led to questions including whether air-conditioning was necessary, and whether alternative models of fitness equipment might be considered. In this way, we have the potential to reduce consumption through behavioural changes, as well as reduce losses through rigorous design.
Other lessons from both projects included the premium cost of construction to capture the risk for trades to construct to PH standards at this scale of building for the first time, and the challenge of sourcing certified products in North America. Not being able to find airtight overhead doors for the firehall forced the team to divide the building into two different certifiable zones, with the apparatus bay being exempt from the air-tightness requirement. Charting this new territory is a challenge but also an incredible opportunity. Ultimately, achieving PH requires a significant shift in how we practice. It requires significant work up front, and a great deal of testing and modelling of the design along the way using not only the PHPP (Passive House Planning Package) early (and often), but potentially supplemental analysis software. It also requires a significantly more collaborative and iterative design process. We encourage every project team targeting PH to be truly integrated in their design process, and to have open communications among all stakeholders to find effective solutions.
Melissa Higgs is a Principal at hcma. She is currently the principal-in-charge of Surrey’s Clayton Community Centre, anticipated to be the largest Passive House building in Canada and the first certified community centre of its scale in North America.