Energy Efficiency at the Sir Wilfrid Laurier School Board

An informational and awareness website

Geothermal Heating

A geothermal heating system consists of three main components:
1- A cold water loop, usually containing a blend of water and antifreeze that circulates in hoses
    buried underground;
2- A heat pump;
3- A hot water loop that circulates water throughout the building (in radiators and ventilation
    systems) to provide heat.

Geothermal heating uses the energy available underground to heat buildings more efficiently than conventional methods. The temperature of the soil below the frost line (about six feet below the ground) remains fairly constant (roughly 8C) throughout the year. The sun is the most significant source of heat to the ground, though the magma at the center of the Earth provides some heat at greater depth. This is a free, renewable source of energy.

To retrieve the energy from the ground, the cold fluid must be circulated in underground heat exchanging pipes. The cold fluid leaves the heat pump where it has been cooled to a lower temperature than the ground and circulates through the buried hoses.  It is slowly heated to a temperature approaching that of the surrounding earth and then returns to the heat pump. The heat pump extracts the available energy from the fluid while cooling it again for another circuit underground.  The extracted heat is redirected into the hot water loop. The electricity consumed by the heat pump is also transformed into heat that is sent to the hot water loop.

The total heat transferred to the hot water loop is the sum of the electrical energy consumed by the heat pump and the free heat recovered from the ground.  This makes geothermal systems one of the most energy efficient and sustainable ways to heat buildings. A geothermal system will typically provide the same amount of heat as fully electric heating at 1/3 of the cost.  The other 2/3 of the energy is the free energy recovered from the ground.

A heat pump works on a similar cycle as a refrigerator.  The main difference is the side of the cycle that we use.  A refrigerator cools down the food it contains by rejecting the heat out the back, whereas the heat pump uses this heat. You can see this at home by feeling the air behind the refrigerator!  Notice that it contributes to the heating of the kitchen all year long, an advantage in the winter, but a disadvantage in the summer.

Figure 1
   The underground piping of a geothermal    
   system can be vertical (many wells up to 150m
   deep) as seen in figure 1, or horizontal as seen in  
   figure 2.  Both options are equally efficient but ground
   characteristics and space around the building (clay,  
   rock, etc) will dictate the most appropriate solution.

  Back to the Measures Summary

Figure 2