Ground Source Heat Pumps (GSHP)

How Ground Source Heat Pumps Work

Ground-Source Heat Pumps are heating and cooling systems that transfer heat between the earth and your home. Ground-source heat pumps operate similarly to a refrigerator, but on a much larger scale. A refrigerator moves heat out of the refrigerator or freezer to an outside coil, which is warm to the touch due to the heat it has extracted. The ground-source heat pump uses a more sophisticated version of the same technology to pump heat from the ground into the house during heating, and from the house into the ground when cooling.

Ground-source heat pumps do not burn fossil fuels; they use electricity to run a compressor. Because they take advantage of the stable, underground temperature of the earth (about 50 degrees Fahrenheit in Massachusetts), ground-source heat pumps are the most efficient heating and cooling system available. They are much more efficient than electric resistance (electric baseboard), oil, propane, or gas heating. They also provide highly efficient air conditioning.

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Heat Pump

Loop Field

Most ground-source heat pump systems feature an underground loop of piping that circulates an anti-freeze fluid (a mixture of water and non-toxic propylene glycol or ethanol) between the ground and a central heat pump unit. The central heat pump is usually located in the basement or mechanical closet of a house. It includes a refrigerant loop with a compressor, reversing valve, expansion valve, and two heat exchangers. One heat exchanger transfers heat between the outdoor fluid and the refrigerant. The second heat exchanger transfers heat between the refrigerant and the indoor distribution system, which brings heating and cooling to all the rooms. The indoor distribution system may consist of ducts for forced air, hydronic baseboards, or radiant floors. In addition to heating and cooling, some ground-source heat pumps can also provide domestic hot water.

Winter

Winter Mode

In the winter, anti-freeze fluid pumped through the ground loop absorbs low-grade heat from the ground (1). At the ground loop/refrigerant heat exchanger, the anti-freeze fluid transfers its heat to an indoor refrigerant loop, without any mixing of the two substances (2). The warmed refrigerant flows to the compressor where it is pressurized, causing it to heat up further (3). The reversing valve (4) directs the hot refrigerant to the refrigerant/ indoor distribution heat exchanger, where the heat is transferred to the air- or water-based distribution system that spreads the heating throughout the house (5). The refrigerant next passes through an expansion device (6), which makes it very cold. Because it is now colder than the temperature of the anti-freeze fluid in the ground loop, the refrigerant can again absorb heat from the ground loop to begin the cycle again (2).

Summer

Summer Mode

In the summer, the process is reversed. Anti-freeze fluid from the ground loop (1) cools the refrigerant at the ground loop/refrigerant heat exchanger (2). The refrigerant then flows through the expansion valve (3), which makes it even colder. At the refrigerant/indoor distribution heat exchanger (4), this cold refrigerant absorbs heat from the air or hydronic distribution system, cooling the interior of the house. The compressor then concentrates the heat in the refrigerant (5), and the reversing valve (6) directs the hot refrigerant back to the ground loop/ refrigerant heat exchanger (2), where the refrigerant easily releases the heat to the ground loop. The fluid in the ground loop is then cooled by the earth (1). Ground-source heat pumps work very well in four-season climates like New England’s. You are not limited to the temperature of the ground and you do not need a supplemental fossil fuel system to keep your house comfortable year-round.