Energy modelling for inner city projects - the performance path

Last year the City introduced an energy code to new construction.  The killarney project I am working on now will be my first project permitted under the new rules.  At the time it was a very confusing change, because the new requirements came with little guidance on how to comply, yet significant technical skill may be needed to adapt to the new code.  Now that some time has passed, the process seems to be working itself out into a routine practice, where the builder has two options:

1. Apply for the BP by adopting a checklist of energy related items.  This route is quick and easy but overly rigid.  It doesn't take into account the way the builder wants to assemble the building, and there are some real costs associated with compliance.  This is called the prescriptive approach.  Frequent readers of my website will note that I don't like government checklists, so, that leaves us with option 2.

2. Conduct an energy model, and adjust the performance of the building to comply with the energy code.  This introduces the complexity, cost and time of doing the model, however the benefits are significant to the builder and likely the client as well.  Much more flexibility is found in the performance based model.  Essentially what you must do is create a conceptual building, and determine its annual energy use.  The same building is tested with different performance elements, and these are selected by the builder, and as long as the annual energy use is lower than the conceptual building, the project can be permitted.

After some brief deliberation, I selected the performance based approach, met with an energy model consultant, and the work was done. I have included a screen shot of the outcome of the model.  However, what most people would be interested in is the changes that I was able to select in the building envelope and mechanical systems vs adopting the prescriptive checklist.

Essentially the changes amount to the following;

  • reduction in under slab insulation from a costly (and in my view not needed R16 to R5) - this also has up to a three inch headroom reduction avoidance in the basement, and that is a small bonus.
  • addition of triple pane windows vs. double pane (this is more comfortably interior environment in winter for the occupants)
  • use of a typical R40 attic insulation
  • use of regular efficient gas fired water tank, rather than use of a demand boiler, this is a change I prefer for practical and service reasons
  • use of R20 wall batt insulation vs R22 wall insulation, as I view the window upgrade to be more 'visible' and useful to the buyer than something inside the walls.
 The result here is the building will use less energy than the code prescriptive building would require, yet offers some savings to the builder for material cost and assembly challenges.

The result here is the building will use less energy than the code prescriptive building would require, yet offers some savings to the builder for material cost and assembly challenges.