Since 2012, for the well-to-do who want to build a new house anywhere that’s not serviced by a natural gas line in Ontario, the decision making process for custom homes with lots of glass eventually whittles down to installing a Ground Source Heat Pump (GSHP). But is the GSHP a Silver Bullet or a Hail Mary pass when it comes to SB-12′s distorted view of energy efficiency?
Heat pumps are brilliant machines and unlike the electric baseboard heater which converts electrical energy directly into heat, a heat pump uses electrical energy to “move” heat. A GSHP moves heat from the ground into the house in winter time but in summer time, it pumps the heat out of the house back into the ground. The same with an Air Source Heat Pump (ASHP), except that an ASHP moves heat from the air in the house to the air out outside. Because heat pumps move heat instead of generating heat, they are up to 3 times as efficient in their use of utility-based electricity.
It’s that last point that has many new home owners with GSHP in Ontario feeling the sting. As electricity prices keep going up, any GSHP that happens to run on auxiliary heat the during utility’s peak prices, will see a massive spike in heating cost. Remember, time of day use varies from 8.3¢ per kWh to 17.5¢ per kWh and at twice the price, it doesn’t take long. Imagine filling your car’s gas tank during rush hour for $2 a litre as opposed to filing up off-peak for only $1 a litre; when would you shop?
Putting aside Henry Gifford’s contention that “heat pumps actually use more fossil fuel than a furnace or boiler” one cannot deny that their exact energy performance isn’t always cut and dry. There are many factors that go into designing and installing a GSHP system and it should be known that identical systems installed in 2 different locations by different installers and used by a different occupants with different lifestyles will have an impact on the performance of the GSHP.
For example, did you know that some loop fields need to be “recharged” with summer-time heat and actually depend on the occupant using the AC to pump heat back into the ground or risk running out of stored heat the following winter? Did you know that a GSHP system’s loop length is something not to be be trifled with and that it needs to be purged with a very high powered pump when commissioned? Commissioned? Yes, your installer should provide you with a Commissioning Report. You’ll also need a very large electrical panel; 60A for the pump, 60A for the auxiliary heat (read: electric resistance heating).
Where the vagaries of GSHP systems seem to be given short shrift is in the Ontario Building Code. SB-12 relies on old energy modeling software used to calculate “compliance” to building codes and gives the GSHP with electrical resistance backup accolades that might not always be deserved given the potential for variance in their mechanical components, geological fields, occupant lifestyle and control parameters.
Remember, if you’re going to install a GSHP, get it commissioned per link above but first have an expert energy modeler help you reduce your loads. Not all software is equal and you may want to follow many of the Passive House principles to help you design with thermal comfort in mind. If installing lots of thermally weak components like windows, don’t cheap out; invest in high performance windows that are sized to benefit the occupant’s comfort and compliment your HVAC system. We’re also looking forward to the 2017 version of SB-12 that will see the adoption of new more powerful and specialised software – WUFI Passive - that can help the design community avoid thermally weak envelope designs by calculating interior surface temperatures of window frames and exterior walls to avoid drafty feeling rooms and windows condensation.
Remember, don’t paint yourself in a glass corner; if you have large wall(s) of glass in a given room, the room should be thermostatically controlled and zoned independently to optimize comfort. Finally, if you’re betting on the Hail-Mary pass, heed Peter Yost of GBA words “Ground-source heat pump systems work great if you have an expert installer, for both the above- and the below-grade work, and you stick with the leading manufactured systems. Play with either or both of these and you are playing with fire.”