Does Net Zero Energy go far enough?

While Canada hurtles towards a Net Zero Energy future for residential construction over the next dozen years, another concept is starting to gain traction with designers, architects and environmentalists: Net Zero Carbon (NZC), or Carbon Neutrality. NZC stretches the Net Zero Energy idea a little bit further, arguing that while a tight building envelope and right-sized mechanical air and heat systems are fine, they alone may not be sufficient to address overall energy efficiency and greenhouse gas concerns. Specifically, they ask, “What if the heat and hot water systems themselves still burn fossil fuels? Are we adequately addressing the greenhouse gas commitments Canada made as part of the Paris Accord?”

Analysis of Canada’s green house gas emissions by industry since 1990 indicates that Canada has made little overall progress. The volume attributed to housing and transportation is steady despite improvements in energy-efficiency, due to increased number of houses, cars and trucks (graphic: Government of Canada)

How much of the problem relates to housing?
Canada has committed to reducing its greenhouse gas emissions by 30 per cent from 1990 levels by 2030. We’re not doing very well so far. In fact, our GHG reduction commitments appear to be in direct conflict with the objective of increasing the country’s economic.

According to Statistics Canada, “Direct and indirect household emissions [motor fuel, residential fuel and indirect emissions from the production of the goods and services that households consume] accounted for 46% of Canada’s total GHG emissions in 2004. Overall, these emissions increased 13% between 1990 and 2004.” Statistics Canada goes on to explain, “Between 1990 and 2004, household GHG emissions intensity decreased by 22%. This was partly due to efficiency gains in the production of goods and services by industry and partly to energy efficiency improvements within Canadian homes. However, spending per capita increased by 25% over the same period. The increase in spending resulted in a 10% increase in indirect GHG emissions from households. This, coupled with the 16% increase in household direct emissions offset most of the gains in efficiency. The end result of these combined effects was an insignificant change in emissions per capita between 1990 and 2004.”
In other words, more people, more houses, more cars won over against energy-efficiency gains.

A focus on older existing homes, not current new home construction
Sheena Sharp of Toronto-based Coolearth Architecture Inc. outlined her thoughts during a seminar at the recent Buildings Show in Toronto. Sharp noted that although well-publicized closings of coal-fired electricity plants reduce GHG’s significantly, they are one-time events. An on-going process is needed.

Like most in the design and construction industry, Sharp recognizes that Net Zero Energy (NZE) is integral to Canada’s residential housing industry in the future. However, what she and her cohorts advocate is a more complete view of the energy use in residential construction and a more aggressive solution to greenhouse gasses. In her view, going beyond NZE towards NZC means electricity generated within the building itself, such as PV arrays, to power the heating, hot water and interior air quality requirements of the house. The end result should, according to her estimates, be at least carbon neutral, possibly even a net positive outcome. She puts emphasis on existing older homes because they are by far the largest GHG emitters versus new homes.

Making Net Zero Carbon a reality
Sharp and Coolearth have put their money where their mouths are, and are currently in the process of transforming a modest semi-detached home in Toronto into what will be a NZC home. To date, the project has focused on the envelope. The high levels of foam and foam panel insulation, along with triple pane windows mounted precisely in outside wall openings, will not surprise those who have been following the latest energy efficiency processes. What is challenging to the Net Zero Carbon concept is that the house, while highly insulated, is in an urban setting. This restricts some of the potential passive envelope benefits, such as optimal orientation for passive heating for example. Sharp and her team also intend to cover the pitched and flat roof sections with large arrays of PV roof top panels, despite the shading issues that are incumbent with a city setting and less-than-ideal array orientation.

The Toronto semi before (left) and artist’s rendering after its completion (right), with new glazing, adjusted roof line, and new siding
(photo: coolearth Architecture Inc.)

Ambitious net energy gains projected
Nevertheless, it is hoped that the home will generate sufficient electricity, backed by power from the provincial power grid through net metering, to not only drive the mechanical systems but to put more power back into the grid system than the home uses. To be specific, Sharp calculates the original house used 36,000 equivalent kilo-watt hours (ekWh) annually. Once the PV arrays are installed, she projects the home will generate a surplus of nearly 10 ekWH. The largest energy savings result from smaller mechanical systems being required in such a tight envelope, estimated to be one air change per hour. This means, for example, that an electrically powered 1 ton heating unit will be sufficient rather than a typical three ton natural gas unit. It is this decreased dependency on fossil fuels that differentiates this NZC home from a NZE home.

Net Zero Carbon concepts aside, Sharp’s point of identifying existing houses as the leading GHG emitters meshes with comments from housing experts like Casey Edge, CEO of the Victoria Residential Builder’s Association (VRBA). Edge has been vocal about the irony of new codes and guidelines targeting hourly air changes in new construction — attempting to reduce them from three to one — while older homes have up to 40 air changes per hour.

Huge industry potential going forward
According to Sharp, her Toronto semi-detached home is like over 75,000 other residences in that city alone. She suggests that developing strategies and incentives to address the existing housing stock could be a huge boost for the industry while significantly helping Canada meet its international GHG reduction obligations.

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