This is an update on the previous heat pump blog from last year. If you remember, I had a heat pump installed in December 2019 and I was worried that the heat pump was using a lot of electricity. It turns out that, yes, I did use more electricity but not as much as I thought. So, 3 key take aways:
- I saved (a tiny bit of) money year over year with the heat pump!
- Less carbon was emitted. YEAH!
- I should have put the heat pump in a sunny sheltered location instead of in the shade.
I saved money in 2020 compared with 2019 with the heat pump but not very much ($46.44). Compared with 2018, I spent $92.22 more in 2020 with the heat pump. But more importantly, I consumed over 500 m3 less natural gas in 2020 with the heat pump than in either 2018 or 2019.
- 2018 electricity 4782 kwh used, 1802 m3 NG consumed
- 2019 electricity 5380 kwh used, 1837 m3 NG consumed
- 2020 electricity 6442 kwh used, 1284 m3 NG consumed
Most HVAC installers will advise you to put your heat pump in a shaded location because they are accustomed to installing air conditioners which take warm air and make it colder. To create cool air in summer from hot air is less efficient than starting with not quite so hot air. Seems to me, the same should hold true when taking cold air and making it warmer in winter.
As I am using the heat pump primarily for heating, I want it to function as efficiently as possible in winter to reduce the electricity load. Most heat pumps have an efficiency curve that you can (and should) ask the manufacturer for. It will show you the Temperature vs COP (Coefficient of performance) and kWh used. In other words, it shows how efficiently your heat pump will work over a temperature range. Unsurprisingly, it works more efficiently at the warmer temperatures because it doesn’t take as much energy to heat air when it is, say, 5 ºC compared with -5 ºC. My heat pump, for instance, at temperatures above 10 ºC, is rarely on.
I realized (too late!) that the temperature on the breezy shaded side of my house in winter is often 5 to 10 degrees colder than the south facing sheltered side of my house. That’s on a cloudy day. On a sunny day, the difference can be as much as 20 degrees or more. My heat pump is set to be off at an outdoor temperature below 0 ºC and the auxiliary heat comes on as needed. If the outdoor temperature were 5-10 degrees warmer, then the heat pump would be heating the house more of the time than currently which would save more money and use even less natural gas.
It would be nice if someone (maybe NRCan?) would test this “sunny location” hypothesis and publish their results. My heat pump seems to blow out an enormous amount of cold air when it is on. Perhaps the amount of warm air in the sunny location would be displaced by the cold air blown out and the resulting effect on efficiency would be negligible.
Nevertheless, my plan is to eventually get a cold temperature mini-split inverter type heat pump and put it in the cozy sheltered location.
If anyone has actual (as opposed to theoretical) experience with placing heat pumps in sunny locations, please let us know about it in the comments.