EGEE 102
Energy Conservation and Environmental Protection

Ground Source (Geothermal) Heat Pumps


Ground-source or geothermal heat pumps (GHPs) are similar to the air-source heat pumps, except that the source of heat is the ground instead of outdoor air.

Instructions: Where does the heat in the ground come from? Press the “play” button and then answer the questions that follow.

Geothermal Heat Pumps

Click here to open a text description of the geothermal heat pump activity.

Geothermal Heat Pumps

Where does the heat in the ground come from? Picture a house in the middle of a yard with the Sun in the background. As the Sun's rays hit the yard, heat is absorbed into the ground. The heat is stored several feet below the frost line and a fairly constant temperature (40 to 80 degrees Fahrenheit depending on location) is maintained throughout the year, due to the natural insulation of the ground.


1. Where does the heat in the ground come from?

  1. Coal


  2. Natural Gas


  3. The Sun


  4. Uranium


2. Does the heat in the ground remain constant throughout the year?

  1. Yes
  2. No


1. C: The Sun

2. A: Yes

As you observed in the animation, the earth absorbs and stores energy from the sun as heat, resulting in underground temperatures that range between 40–80ºF, depending on the location. These temperatures, which are located below the frost line (which is generally 4–5 feet in Pennsylvania), remain constant throughout the year.

The geothermal heat pumps (GHPs) use the earth as a heat sink in the summer and as a heat source in the winter, and therefore rely on the relative warmth of the earth for their heating and cooling production.

Through a system of underground pipes, they transfer heat from the warmer earth to the building in the winter, and take the heat from the building in the summer and discharge it into the cooler ground. Therefore, GHPs do not create heat; they move it from one area to another.

Operating Principle

The GHP system operates much like an air-source or air-to-air heat pump, except that:

  • The outside tubing is buried to extract or discharge the heat in the ground;
  • The compressor/condenser unit is inside rather than outside the house.

The GHP system also has additional valves to allow heat-exchange fluid (refrigerant) to follow two different paths: one for heating and one for cooling. The GHP takes heat from a warm area and exchanges the heat to a cooler area, and vice versa.

Instructions: Press the play button to see how a geothermal heat pump operates.

How a Geothermal Heat Pump Works

Click here to open a text description of how a geothermal heat pump operates.

How a Geothermal Heat Pump Works

Water in the ground loop is circulated and warmed by the earth. That heat energy is transferred to a series of coils circulating the heat exchange fluid. The fluid is warmed further by another heating unit and the use of a compressor and expansion valve. The second heating unit circulates and heats the air within the house through a series of ducts.