Thursday, May 29, 2008

Renewable Energy: Ground-source heat pumps (GSHP)

Lately, I've been talking to a new vegetarian acquaintance -- a physicist with a keen interest in renewable energy -- about geothermal heat pumps, or ground-source heat pumps, to be even more specific (i.e. to distinguish them from air-source heat pumps). I'd mentioned to him my recent visit to an off-grid solar-powered house in the Knowlesville area of NB and he brought up some figures on the cost effectiveness of different types of renewable (and non-renewable) energy in Eastern Canada. Apparently, solar doesn't hold a lotta water for him, mostly because of installation costs and also because of the relatively low amount of sun we get in this colder climate. I did some investigating and am now really intrigued by this type of heating system. Various articles about these ground-source heat pump systems (e.g. this one), claim that by using them, you can lower your heating / cooling costs anywhere from 30-70%. Also, although the initial installation costs are several times higher than installing conventional heating systems, those costs can be recouped within 5-10 years.

Essentially, what happens is that when you dig far enough down into the ground, say, 3 or more metres, you reach a point where the temperature of the earth is constant year-round, varying according to latitude. So the ground source heat pump, using a small amount of electricity and a compressor, extracts heat from the ground to heat your home in the winter, and then in the summer it extracts heat from your home and pumps it back into the ground.

Mother Earth News has a much more detailed (and average-joe-reader-friendly) article on these pumps
here. I hope to share more about this type of system as I learn more, myself.


J said...

I myself have been fascinated with geothermal energy. I've had a few reservations about it though, and I still haven't determined whether or not they are founded or not.

Basically, my fears only apply with economies of scale. If we were to say, tap all the geothermal in viable areas, would that cause the temperature or pressure underground to change? If so, what implications would this have on our climate, etc? I asked someone at the US Geological Survey and they essentially responded by, well, not answering the question.

My other concern is to whether or not it really is renewable. I know they have been pumping geothermal here on the west coast of the US for quite sometime and some of the areas pumped have been 'spent' meaning that they no longer provide energy.

But I do think there is much to be said for it, not trying to be a wet blanket about a technology that is far better than coal, nukes, or oil powered electricity, just concerns that I have.

M said...

I haven't read enough about large-scale geothermal operations, myself, to know. Your questions sound really valid to me. I found a link (
geothermal_energy.htm) that addresses some issues, but generally ends up writing them off, saying that the benefits outweight any potential problems when you compare it to fossil fuels.

Ground-source heat pumps and geothermal heating are two different things, though. The concerns you raise about geothermal heating probably wouldn't apply to ground-source heat pumps.

I'll ask my physicist acquaintance after work if he has some decent links or can address your questions.