The value of measuring energy efficiency in multi-unit residential buildings

February 23, 2024
January 2, 2024
A birds-eye view of the Silver Sage Housing Corporation Horse Dance Lodge.

Energy efficient buildings are extremely important to the future of Canada’s housing industry. Not only is the federal government aiming to have all new homes Net Zero Energy Ready by 2035, energy efficient homes help homeowners and building operators save money on energy costs and insurance claims.

The Silver Sage Housing Corporation Horse Dance Lodge / misatimosimôwin mîhkowâp was built to surpass the energy code requirements Part 3 multi-unit residential buildings, and is designed to have solar panels installed at a later date. 

From the energy modeling done, the building is 28% more energy efficient than code and will consume 48% less heating energy than a code-built equivalent building. This efficiency means the building will save roughly $5,300 per year in energy costs compared to a code-minimum building.

Pictured: Visual comparison of Horse Dance Lodge’s estimated energy consumption of 1470 GJ/year vs. estimated energy usage of a code-built reference building: 2030 GJ/year.

But how did we get those numbers? And why is it important to have these measurements?

Airtight Engineering did the energy modeling for Horse Dance Lodge — both for compliance with the National Energy Code and to support Big Block and Silver Sage's goals of reducing the energy use of the building.

"How do you take something that's really complicated with a lot of moving parts and distill it down to a single number?" asks Matthew Dipple, a Principal at Airtight Engineering.

One way to measure the energy efficiency of a building is to compare it against a current "code minimum" building, said Dipple. But you can also compare the efficiency to aspirational programs like Net Zero, Energy Star or Passive House.

In Canada, we use a metric called "air changes per hour," abbreviated as ACH. Dipple describes this as thinking of a building like a bag full of air — if that bag has leaks and holes in it and we create a pressure difference to force more air into the bag, how many times does the air in the bag change over per hour?

ACH works well when comparing buildings of a certain size, but the larger the building gets, the leakier it gets, even if it has a low ACH number.

"A large building is much leakier than a small house with the same number of air changes per hour because the ratio of the volume to surface is larger," Dipple said. "That's why our energy code for Canada is moving toward ... air leakage per square meter of — so we can compare between different building sizes more easily."

In terms of a visual representation of that high airtightness, the air leakage can further be expressed as “equivalent leakage area,” or roughly equivalent to a "hole" in the wall of the building.

Horse Dance Lodge achieved an impressive airtightness rating of 0.86ACH@50 Pa, which is roughly equivalent to a 357.7 sq in or a 2.5 sq ft "hole" in the building (smaller than a standard 20x20 in throw pillow). A code-built reference building would have a 4.2 sq ft "hole" (or about the size of a queen size pillow). 

(Note: Equivalent leakage area is not an exact measure of the cumulative “holes” in the building, but a good visualization tool.)

These pillow-sized “holes” may seem minor in the grand scheme of 20,000 square foot apartment complexes, but that’s like leaving a window open 24 hours a day, every day of the year. In the Canadian Prairies, the energy costs to reheat or recondition any lost air are significant. For Horse Dance Lodge, reducing that hole by 40% allows far less air to leak out, which helps save on energy bills to the tune of nearly $450 each month.

Special attention was given to the building enclosure in various areas, including:

  • Windows: All Weather Windows, triple glazed
  • Walls: R-24 batt insulation, with 6 inches of exterior insulation
  • Ceiling: R-80 blown-in
  • Foundation: Crawl space with concrete grade beam on piles

Another challenge is that standards are rapidly changing. In Canada, a new building code was introduced in 2020 (which Saskatchewan adopted as of Jan. 1, 2024), another will be released in 2025, and yet another in 2030. These changes are designed to incrementally move the building industry into better energy efficiency requirements for buildings, with the goal of building to net zero standards.

Despite these complications, Dipple says there is huge value in trying to describe energy efficiency in terms of a number.

"As we start to value energy efficiency more in our buildings as a society, that is going to drive us to ask more of our buildings and be more critical of our buildings that aren't very efficient," he said. "Yes, it's challenging to distill the energy efficiency of a building using a few key parameters ... but I do think that exercise is useful to helping us see and appreciate the energy efficiency aspects of a building"

Efficient — and thoughtful

Dipple says the modular aspects of Horse Dance Lodge added a layer of complexity to the project — each individual module might be airtight, but they also had to consider the airtightness of the whole building.

"It's great to see how well it did in terms of airtightness at the end of the day," he said.

He was especially impressed to see the thought put into the building, such as using regular thermostats instead of programmable ones. The heating system itself is efficient and the building owners and operators know from other projects that residents struggle with the programmable ones.

"The fancy thermostat is the gadget we gravitate towards when we think of efficient buildings, but let's take a step back and think about what will be best for these residents."

The mechanicals of the building were carefully selected to deliver exceptional comfort and indoor air quality year-round, including:

  • Fuel Source: Suites, common space, and office heating provided by natural gas; building-wide cooling and vestibule heating provided by electricity; and potential to add solar array to roof at a later date
  • Heating and Cooling: Hydronic in suites and common areas via either boilers or chiller
  • Water Heating: via natural gas boilers
  • Ventilation: Fantech ERVs

Dipple says modular construction lends itself well to energy efficiency because the shape of the building is fairly simple. 

"It has a good amount of windows but not an exorbitant amount of windows," Dipple said. "It doesn't have super complicated architectural jut outs and dormers and wings and protrusions and all the rest. It's amazing how efficient those simple building forms can be. You can have a building that is insulated to the nth degree but if you've made poor architectural decisions, it won't be energy efficient. ... Horse Dance Lodge got that basic geometry and form right."

Plus, the tipi-inspired canopy and sun shades break up the boxy look and double as energy efficient features.

The energy-efficiency of Horse Dance Lodge demonstrates the potential of sustainable multi-unit building practices in Canada. In the face of evolving building codes, the Horse Dance Lodge stands as an example of what can be achieved, and sets a precedent for future construction in the country.

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