Heat pumps - an idea whose time might well have come

I like to think of myself as a responsible citizen, particularly as regards environmental matters. Hence, I am pretty careful with our energy use; I have solar panels for hot water and electricity production; I drive an electric car; I choose to live in province with a largely green electricity production profile; I subscribe to Bullfrog Power (which uses an additional levy on power bills to reinvest in renewable energy projects). I try to walk the talk, as they say.

One thing that really rankles, then, is our need to rely so heavily on natural gas for winter heating and for the very few occasions we need recourse to air conditioning in Toronto's increasingly hot summers. Gas is one of our largest single bills each month but, more than anything, it is the unavoidable hit to our carbon footprint that rankles.

But is it unavoidable? Just recently, I have been looking into electric heat pumps. There's a whole lot of technical stuff to get my head around, an the more practical aspects of installation, cost, payback periods, etc. It does look promising, though, at least in principle (I have not even started to look into costs, etc, yet).

So, what is a heat pump? The simplest explanation I have come across is one on The Conversation, although a more detailed, and more Canada-centric, explanation can be found on the Province of Ontario's guide to heat pump technology. In fact, I seem to be seeing more and more articles about heat pumps just recently, but that may just be because I am primed to do so.

A heat pump works on the same general principle as a refrigerator: it extracts heat (or cold) from the outside air, concentrates it, and then transfers it, using a small amount of electricity, to the inside of the house to provide space heating (or cooling). While traditional furnaces and boilers convert fuel into heat with much less than 100% efficiency, heat pumps actually operate at efficiencies of well OVER 100%, and are an estimated three to four times as efficient as furnaces.

More specifically, a very cold fluid circulates through coils of tubing in an outdoor unit similar to an air conditioning unit, absorbing energy in the form of heat even in winter conditions (at least up until outdoor temperatures fall VERY low). The fluid vaporizes and circulates in a compressor, which generates heat (compressing any gas heats it up). This heat is then transferred through the walls of the house, and circulated through indoor coils of tubing or  the existing vent system to heat the house. The same system can be used in reverse, taking heat from inside and transferring it outside, very much like a refrigerator does.

This, at least, is the model for an air-source heat pump, the cheapest and most commonly-used technology. In areas of more extreme cold, a ground-source or geothermal heat pump system may be more appropriate. This uses the more stable temperatures underground as a source of heat in winter and as a reservoir for rejected heat in the summer. The need for drilling makes this a substantially more expensive option, though.

I'm just in the early stages of my research, but heat pumps are looking like an interesting possibility at this point.