How does it work?
Okay, the above is a tad simplistic. We could, if we
wanted to, flow the heating/cooling fluid around the house, but we
tend not to. How a cooling system works is by turning a liquid
into a gas. This liquid to gas process requires energy, and so it
cools its surrounds (we actually lower the pressure surrounding
the liquid). We use a compressor to compress the gas and turn it
into a hot gas. (We also need energy to pump the fluid.) This is
how we would cool the house by expanding the liquid to a gas
(absorbing heat) which cools the house. The gas is then compressed
to produce a higher temperature gas (heat exchange here to get the
hot water for the house) and then allow the hot gas to heat
exchange with the earth, cooling the gas so it turns back into a
liquid, so we can do the expansion again and cool the house.
To heat the house, we pump liquid into the pipes (which are in
the ground). There, the liquid warms up and forms a gas.
Unfortunately, the gas is not hot enough to directly warm the
house, but if we increase the pressure, we can turn the gas into
hotter gas (we can concentrate the heat). This process does
require electrical energy. But, for a little energy, we are
getting a great deal of free energy from the geothermal source
—the earth. Now that the gas is much hotter than the air
temperature, we have a heating cycle.
This nice looking house in Aurora,
Colorado has a geothermal heat pump system that
provides all the heating, cooling, and hot water
needs. For a home of 1,500 square feet with a good
building envelope and a geothermal heat pump, energy
costs are about $1 a day. Much cheaper than the
average energy cost.
These are not cheap systems at about $7,500 for installation in
a new house, but they only use a small amount of energy
(electricity), and they both cool and heat the house (and
provide hot water). Payback time for this investment is about 6
years, so it is worth doing. We will see that, in comparison to
the other methods of heating and cooling the house, this will
have a much lower environmental impact.
The cost is more expensive if the house does not already have the
duct work in place for air handling. If you look back at the
insulation page, you will see that the department of Energy thinks
that geothermal heat pumps can be used in PA. I only know of a few
houses, however, that have an in-ground heat pump.
In lesson 02, we will also discover that the energy from the
ground can also be used to generate electricity. Don't confuse
the two types as it is a very common error:
Geothermal for home heating and cooling
uses solar energy in relatively shallow sites.
Geothermal for electricity generation typically
uses deep geothermal energy for electricity generation. (See
this Department of Energy simple geothermal power plant animation.)