Power Minute:

The Reference House

Power Minutes explain an energy concept in less than one minute (300 words). Note: This is a living document, check back for updates.

"By 2032, new buildings will be 80% more efficient than a home built today" says Clean BC. This "X% better than Y" seems to be a popular method for reporting progress among environmental initiatives. It is concise, clear, and actionable.

For buildings, to report an improvement in this way, we first must make an assumption for how the building "would have been designed" when the environmental considerations were not in place. To standardize these assumptions in Part 9 residential construction in Canada, EnerGuide Rating System (ERS) has a guideline .

This guideline, in action, goes through each design aspect of the building and replaces any modern choices made with a past common choice option (e.g. condensing boiler becomes conventional tank boiler). This bundle of choices are referred to as "Reference House". The building simulation is then performed once on the reference house and once on the current design. The difference in performance is a metric currently in use for compliance in the BC Step Code (see Power Minute: BC Step Code).

Problems with the Reference House

The Reference House is an inherently opinionated metric. For example, ERS Reference House Crawl Space in HOT2000 is type “SCB_21” with the following description: It is impossible to say how well the above can reflect a “typical” design. Moreover, the Reference House method makes a significant and fundamental assumption that this kind of comparison is effective in all cases (see Power Minute: Performance Gap). A famous statistician once said "all models are wrong, some are useful." Comparing a mathematical model with itself can go wrong in many ways.