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June 11, 2007

Geothermal Heat Pumps and Saving the World

Whether your goal is to reduce oil imports, lower carbon dioxide emissions, or just save money, geothermal heat pumps MAY be an answer for you. In many places and under many circumstances, this heat source makes economic sense without any need for subsidy (although, in some places, you can get a subsidy as well). Moreover, we can convert our heating to electricity much faster than we can convert our cars since the houses are permanently attached to the electric grid.

In a sense geothermal heat is something for nothing. You don’t really create heat with your heat pump the way you do with a furnace, you pump existing heat out of the air or ground and use a compressor to step it up to the temperature you want to achieve. The trouble with air-source heat pumps is that the air outside is liable to be pretty cold just when you need heat in your house the most – especially here in Vermont. But ground-source (geothermal) heat pumps get their heat from somewhere in the ground or under water. The deeper you get, the more the temperature stays the same year round.

BTW, heat pumps also work for cooling – same principal. But we don’t do much air conditioning in Vermont residences so I haven’t looked at that in any detail. Obviously, if you do also use energy for air conditioning, it can only improve the case I’m about to make.

OK, the numbers: suppose you use 1000 gallons of oil to heat your home (that’s how most of us heat here in the Northeast despite the fact that we don’t like refineries). At $3.00/gallon (my guess for next winter), that costs $3000 (duh). According to my favorite government spreadsheet, there are 138,690 BTUs in each gallon of No. 2 fuel oil so you’re buying about 140 million BTUs to keep you warm. However, because even a good furnace is only 78% efficient, only 108 million of those BTUs do you any good.

If you were to create all the useful BTUs with conventional electric heat, you’d need to buy about 32,000 kilowatt-hours (3412 BTUs per kWh). At the $.16/kWh we’ll be paying here next winter, that’s $5000 dollars. Stick with oil! Forget that advice this winter (2008): even conventional electric heat at typical Vermont electric rates is competitive with $5.00 gallon heating oil (updated numbers here).

But, according to the same spreadsheet, geothermal is 3.3 times as efficient as conventional heat (because you’re just pumping up what you need). With geothermal you’ll need less than 10,000 kWhs and pay about $1500; you save 50% compared to oil!

According to Excel, the present value of $1500 per year over 20 years at 6.5% interest (actually your heat pump system should last longer) is a little more than $16,000. If you can get a heat pump system with the capacity you need installed for that amount or less, you’ve got yourself a bargain – no subsidies involved. Actually, if it’s a new installation then you have to take into account what a furnace and fuel tanks would have cost as well. Distributing the heat inside the house is best done with circulating water but can be done with hot air as well. Either you already have a system to do that or you’d need to pay for one anyway. You can also get your domestic hot water from the heat pump and save a little more. If the price of oil goes up faster than electricity, you save more – and vice versa.

Can you get geothermal heat with this capacity installed for this amount? Depends. It depends on whether you have land that’s easily dug down into, a well, or a pond. If your house is on cold rock and you have no well or a small one, the collection system in the ground will drive your costs up. Doesn’t work at all for people in apartments or condominiums. On the other hand could be much cheaper if the heat source is readily accessible.

You won’t be emitting any carbon dioxide from your heat pump, of course. But what you’re doing for total emissions depends on where your electricity is coming from. Much of the electricity in the US comes from coal, a lot from natural gas, relatively little from oil, and some is carbon-free hydro and nuclear. Here in Vermont the vast majority of our power comes from Hydro Quebec and Vermont Yankee (nuclear) so there’s clearly less emission when electricity is used for heat than oil or even natural gas. I suspect there’s a net reduction in emissions for oil and gas produced electricity as well as when geothermal replaces combustion but I haven’t done the math – maybe later.

If you’re trying to stop the flow of oil dollars from here to the worst of places, geothermal is a good place to start. In 2005 we in the US burned over 63 4.9 billion gallons of oil to create heat for residences.

As you may have guessed, we’re looking into geothermal. Will let you know how it goes in practice.Now have our heat pump installed. Preliminary observations and pictures here.

A tool for estimating your annual fuel savings if you switch to radiant or geothermal electric heat is here.

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