On Heat Pumps. Geothermal and otherwise

Look people, heat pumps are not that great! Ok, they are kinda great, but here’s the thing… they still run on electricity, ya know? Here’s the math:

1. Making electricity at a power plant: Three units of fossil fuels in, one unit of electricity out.
2. Then it flows to your house. One unit of electricity in (to the heat pump), and THREE units of heat come out. (assuming a COP — coefficient of performance — of 3 … if you are lucky)

Notice something?

3=>1=>3

Yes, you could have just burned some natural gas or propane in a 96% efficient propane furnace right at your house and still been at ~3! And especially (in the case of geothermal) have saved yourself a whole boat load of money in up-front costs!

Now, it’s true… you do get AC “for free”.

And it’s also true… heat pumps now work perfectly fine, even in New England and Canada (Air source heat pumps even work fine down to -5F nowadays). But you’ve still got to remember that the problem that remains is the power-plant (in)efficiency of ~33%.

Now, sure, if you…
1. Live in a part of the country where there is lots of hydro-electricity (Montana?)
or
2. Pay a little extra on your electricity bill for renewable sources (in MA, anyone who gets their electricity from a non-municipal company can do this) (e.g. GREENUP)
or
3. Have solar-electricity (PV) panels on your roof
… then you can feel a little better about using electricity instead of propane or whatever.

And…
1. I do think there is some merit to “site-generated” electricity (PVs)
2. And using electricity does in theory mean you have perhaps more stable prices
(than propane,etc).

So OK, get excited about heat pumps I guess. But stick with the air-source rather than the ground-source (geothermal). The added expense of the ground-loop installation is not worth it from what I have heard from those who have been involved in projects where they have been installed. Ask Marc Rosenbaum who in recent years seems to shy away from specifying the ground-source.

What would be better? Well… if you don’t live in a particularly urban area, then I think a efficient wood stove or pellet stove might be better. People will argue about that… “too much particulate pollution” and “if everyone used wood we’d have no more trees”, but I think both are probably not quite right. Especially if we got our act together in the US (like Europe) and had more options for gasifying wood stoves / pellet stoves / wood-chip stoves.

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  1. Pingback: Yes, our electricity bill was only 68 cents, but… « Erik’s Blog