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The Interesting Basics…
Geothermal heat pumps utilize some of the same technology found
in your home's refrigerator. They are both devices that move heat
energy. Your refrigerator removes heat from the food and transfers
it to the air in your home. Your geothermal heat pump removes
heat energy from the earth to heat your home and removes heat
energy from inside your home to cool it.
A Ground Source Heat Pump System consists of a water-to-air or
water-to-water heat pump, connected to a series of long plastic
pipe buried below the earth’s surface, or placed in a pond. These
systems can also utilize well water instead of the earth loop. As
fl uid from the earth loop or well water is moved through the unit, the
heat pump transfers thermal energy that heats or cools the home
or building.
The ground serves as a giant solar collector, storing heat energy. At depths greater than 30 feet deep, the tem-
perature is about the same as the average annual outdoor air temperature for that climate. Air temperatures may
fl uctuate as much as 50
°
F above and below the average annual temperature. However, only a few feet below the
surface, the changes in earth temperatures are much less severe. Earth temperature variations decrease with in-
creasing depth. During heating, the earth serves as a heat source. During cooling, the earth serves as a heat sink.
The earth loop is placed in the ground either horizontally or vertically, or it can be placed in a pond. Water (or water
and anti-freeze) is circulated through the pipe, transporting heat to the heat pump during the heating mode and
away from the heat pump during the cooling mode. The heat transfer takes place inside the heat pump in a water-
to-refrigerant heat exchanger.
HOW GEOTHERMAL SYSTEMS WORK
The Boring Details…
H
EAT
P
UMP
O
PERATION
Geothermal heat pump systems consist of four circuits:
1. Air circuit—The duct system that distributes the air throughout the home or building and returns it to the unit.
2. Refrigerant circuit—A sealed and pressurized circuit of refrigerant including compressor, expansion valve,
water-to-refrigerant heat exchanger, air coil, reversing valve. The refrigerant is either R-22 or R-410A.
3. Ground loop circuit—The piping system buried in the ground or in the pond (or well water), with fl uid that is
circulated by pumps to and from the geothermal unit.
4. Hot water circuit—Domestic water can be heated in a geothermal unit with a device called a desuperheater. A
piping connection is made from the geothermal unit to the water heater.
Each of these circuits is closed and sealed from the others—there is no direct mixing. However, heat energy
does
mix from the refrigeration circuit to the other three circuits.
The air circuit, the earth loop circuit, and the domestic hot water circuit always travel in the same direction. How-
ever, the refrigeration circuit will change direction depending on what mode (heating or cooling) the unit is in. (The
exception to the change in direction of refrigerant fl ow is the fl ow through the compressor. This change of direction
is controlled by the reversing valve.)
ABOUT YOUR WATERFURNACE SYSTEM
