On May 24th, 2018, CSV principal Anthony Leaning and architect Stephen Pope presented a continuing education lecture entitled ‘Turning Cold Climate Design Assumptions Upside Down’ at the Ontario Association of Architects annual conference in Toronto. The talk was a continuation of CSV’s outreach on high performance building, sharing our experience with the Passive House standard as applied to affordable multi-family residences. Following the successful certification of the first North American low-rise multi-unit residential building in the Passive House Cold Climate zone (our Salus Clementine project), we’ve got quite a bit to talk about.
Passive House - Transformative Change
Developing Passive House projects has been transformative for our office. We have revised our detailing approaches for greater air tightness and insulation thickness. We use new tools to provide a more finely grained analysis of heat flow through the building enclosure. We design windows differently to ensure that the right comfort factor is achieved, and condensation prevented. We are also making conceptual adjustments to our “building as a system of systems” thinking. The title of our talk refers to a dramatic change in how we think of conditioning the spaces in our buildings. We no longer worry about heating. What concerns us now is removing excess heat from spaces, or better still, preventing it from getting there at all.
Why is August More Important that January?
We live in a heating dominated climate, meaning that it’s colder outside than what we want inside for most of the year. How have we come to the decision that cooling is a bigger problem than heating? Increased use of early hourly energy modelling has identified overheating as a potential problem in highly insulated buildings. This is not new. Issues with overheating showed up with the Natural Resources Canada (NRCan) Advanced Houses program in the 1990s, but the habit of focusing on heating is deeply ingrained in the Canadian building industries. The Passive House Planning Package (PHPP) also follows summer comfort very closely and identifies summer overheating as a challenge. Our experience has shown that conserving heat can be achieved with fixed materials and no moving parts, but cooling a space conventionally requires electricity, cooling equipment, maintenance, and an equipment replacement cycle. Finding a passive way to deliver cooling services would be more resilient, as well as less costly for operations.
Insulate for the winter
By following the Passive House principles of highly insulating and air tight enclosures, with dedicated outdoor air delivery in quantities tightly sized to the occupant population, and heat recovery on exhaust air we can create buildings that need very little heat on the winter peak design day. That’s terrific for winter when heat from daily activities reduces the need for purchased heat.
Ventilate for the summer
In the summer however, the heat from cooking, showers, equipment, and personal activity doesn’t have anywhere to go. It can be hotter outside than in, so the heat can’t get out. One response to the challenge of unwanted summer heat is night time bulk cooling by cross ventilation. Simply moving air through a space to remove humidity can also give summer comfort. These are preferred Passive House strategies. A single detached house conceptually has five sides in which openings could be placed to allow night time cross ventilation to passively cool the house. Many apartments however, have only one exterior face. The ability to cross ventilate is only available to apartments that have two exposures. Not everybody living in an apartment is in a point block with four suites per floor.
Mechanical cooling is not Passive House
The search is now on for Canadian approaches to low-energy cooling. Just throwing air conditioning at the problem works, but commonly causes difficulties keeping within the Passive House electricity budget. Inevitably, it also leads to the major feature of all building elevations being the condensers for split system air conditioners. A passive solution would be cheaper to run, quieter for the neighbours, and much better looking. The answer will always be site dependent, but it likely will include contributions from all design disciplines.
Technical Innovation for Passive Cooling
A curious designer can quickly come up with a wide range of potential approaches: window design, and the design of shading structures; passive ventilation design, including internal shafts to allow single sided apartments access to a second exterior building face (often the roof); radiant cooling using cool, not chilled water and radiant panels, or capillary mats embedded in ceilings; microclimate design to establish cool areas around the buildings from where ventilation air can be drawn; even the use of water features for dehumidification and humidification.
A New Canadian Vernacular
The Canadian urban building boom of the late 1800’s and early 1900’s happened at a time when mechanical ventilation and electric lighting were non-existent. High ceilings and tall double hung windows ensured good daylight access and the ability to passively move air through the major rooms of a dwelling. Fabric awnings kept the sun off merchandise in shop windows, and protected passers-by on the sidewalk from summer rain showers. The next building boom came in the 1960’s by which time new, convenient mechanical and electrical services were available and the old patterns were studiously avoided. As we approach 2020, we recognize that electricity will never be “too cheap to meter”, and that people feel better if they can open a window. Taking a new look at some of the pre-industrial building patterns makes sense.
The old buildings were often drafty, and the space conditioning was often uneven. But the point isn’t to repeat the past in fact, just in concept. New techniques for air sealing and a better understanding of an effective balance between building fabric and building services creates a new opportunity to work out lasting patterns for Canadian cities that can see annual temperature swings of over 70oC.
Over the next series of blogs, we will present discussions of many of these items. A significant part of the 2018 OAA talk looked at the evolution of enclosure heat flow analysis. Passive House uses 2D heat flow analysis to investigate the linear thermal bridging potential of building corners and window installations. We’ll start with this one when we meet next.