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
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.
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.