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While there is a push to incorporate energy efficiency measures into new buildings and homes to meet net-zero targets, a case study finds the benefits do not always justify the additional construction price tag for consumers.

The Country Homes Super Semi Energy Efficiency Demonstration Project, which was prepared for the (RESCON), examines the construction costs versus occupant realized energy savings of high performance housing.

The homes used for the study were two halves of a semi-detached in Milton, Ont. – one was an all-electric home designed and built to the (CHBA) net-zero energy program. The other was designed to be a low-carbon hybrid home utilizing fuel-switching, combination hybrid gas and electric heat.

“It’s a builder trying to explore the best ways of advancing energy efficiency but also taking into account the consumer and a cost standpoint,” said Paul De Berardis, vice-president of building standards and engineering with RESCON. “It’s kind of practical optimization of energy efficiency.

“At the end of the day, if we’re offering products that consumers aren’t willing to pay for and can’t afford then there’s a problem.”

The study explores the relationship between annual energy use simulation software modelling versus real-world data.

“We want a little more common sense approach to decision-making from policy-makers and governments when they’re forecasting out where we need to go in terms of a home’s performance and really take into account affordability, constructability and the fact that were trying to build more homes,” De Berardis pointed out. “Everything we do that makes it more complicated and costly to build more homes will ultimately make it that much more challenging to reach some of these increased housing targets that we’re trying to strive for.”

The case study

The homes were ready for occupancy in early summer 2022 and were kept by as rental units over the following year in order retain access to utility costs and other performance data.

Both were occupied by two adults and one child and had similar heating/cooling profiles.

The idea, said De Berardis, was that because the homes are nearly identical, the builder could explore different construction practices that target energy efficiency beyond the building code while evaluating real-life operating costs.

For the net-zero side of the house, approximately a $51,000 upgrade in features was added to achieve National Building Code Tier Five performance. On the hybrid house there was about $4,000 in upgrades to achieve Tier Four performance.

The study found the limited energy savings homeowners realize from added conservation measures do not always justify the incremental construction costs imposed on new housing.

“A lot of our codes and standards focus on policy but they never really backtrack and verify that you’re achieving the intended outcomes in some of these policy and technical code changes that happen,” De Berardis explained. “We think this is a very important feedback loop that’s missing from our codes and standards development process.”

Key findings

The findings showed discrepancies between annual energy use simulation software and the homes’ actual performance, consuming more energy than predicted.

“The (net-zero) home is theoretically supposed to consume as much energy as it’s able to produce…but in a practical sense that was not the case at the outcome of the one-year case study,” said De Berardis. “That was obviously a very big finding in the sense that these homes are designed using modelling software. The modelling software has a lot of assumptions and occupant assumptions as to how much energy they’re using, how much water they’re using.”

The overarching conclusion is that more research is needed to verify and quantify actual energy usage of occupied homes compared to hypothetical annual energy use computer simulations, especially if major policy decisions are based on assumptions derived from software models.

Another key finding for RESCON is a concept referred to as seasonal disparity of power generation.

“Ultimately what that means is when the home was able to produce as much energy (as it needed), it happened during the summer months,” De Berardis explained. “In the summer there is a lot more sunlight, you’re not dealing with snow and precipitation and cloud like you would be in the winter. The solar panels produced a peak output in the summer months but that’s actually when the electrical demand was at its lowest. In the winter, when the electrical load was at its highest to drive the home heating system, that’s when the solar panels were actually able to produce the least amount of energy.”