GEOTHERMAL HEAT-PUMP BASICS
The most efficient way to convert electricity to heat — or cold.
By Seth Masia
Ground-source heat-pump heating (GSHP)
and cooling, often called a geo-exchange
or geothermal system, is a high-efficiency way
to keep a house comfortable. The Environmental
Protection Agency says that a GSHP system can
save 50 to 60 percent on a typical home heating
bill. About 1 million GSHP systems are in use in
the United States, and about 50,000 new systems
are installed annually.
How it works: A traditional air-exchange heat
pump works on the same general principle as a
refrigerator: It uses a fluid (a refrigerant) and a
compressor to move heat from a cooler space to
a warmer space. A refrigerator chills the air inside
itself by warming the air in the room; similarly
an air-exchange heat pump does the opposite,
warming the air inside the house by cooling the
air outside. Think of it as an air conditioner oper-
ating in reverse.
About 1 million ground-source heat pump systems
are in use in the U.S., and
about 50,000 new systems
are installed annually.
A ground-source heat pump does the same thing,
Loopfield is buried deep in soil, where the temperature
is constant year-round. This is a far more efficient heat-
exchange mechanism than blowing air over a
Indoor unit works like an air conditioner in summer,
and in reverse as a heat pump when space heat is
needed. constant-temperature refrigerant runs in
pipes through the basement wall.
but it works off the stable temperature of the soil
or groundwater under your property. Depending
on your geology and climate, the soil beneath
your house and yard remains at a remarkably
stable temperature year-round — in most parts
of the country, within a few degrees of 55° F
( 12° C). A network of pipes buried in the soil can
function as a heat exchanger, keeping its working
fluid — sometimes water, sometimes a refriger-
ant — at that temperature. The heat pump com-
pressor can use that heat to warm the inside of
the house, without burning fuel directly.
Components: A small house typically requires
about 3 tons of heating/cooling capacity, using
about 1,500 feet of tubing buried in loops near the
house (the length of the tube varies with climate).
An electric pump sends the working fluid through
this loop field. A heat pump replaces the original
furnace or boiler, and transfers (or pumps) heat
from the loop field to the inside of the house.
Most systems use polyethylene tubing as the bur-
ied loop field, and pump water through it. Mod-
ern “direct exchange” or DX systems, use a loop
field of copper tubing filled with a refrigerant.
This arrangement is more expensive to purchase,
because of the high cost of the copper and refriger-
ant, but may be less expensive to install because
the buried loop is shorter. It’s also less expensive
to operate because the direct refrigerant-to-earth
heat exchange is more efficient than interposing a
water-to-refrigerant heat exchanger.