How Geothermal Heat Pumps Work

Definition of a 'Heat Pump'

 Simply stated a heat pump is an electrically driven mechanical device which absorbs heat energy at one location and transfers it to another. Geothermal heat pumps use the natural heat storage ability of the earth or the earth's groundwater to heat and cool your home or business.  'Heat pump' is only another manner of saying 'refrigeration device'. We are all familiar with air conditioners, home refrigerators, dehumidifiers, and ice-cream coolers, these devices could also be correctly termed 'heat pumps' since the principle of operation is to remove heat from one place and transfer it to another.  

The History of the Heat Pump

The principle of the "heat pump" or 'refrigeration machine' was discovered during the 18th century by Lord Kelvin, a prominent British scientist.

In 1834, Jacob Perkins, an American engineer, designed an apparatus which artificially produced ice and was the forerunner of our modern vapor compression systems.

In 1918, Kelvinator Company marketed the first automatic refrigerator and in 1926, General Electric introduced the first "hermetic'' or sealed compressors, a design which is still in use today.

Economics of a Heat Pump 

A heat pump can move 3.5 to 4.5 times more heat to or from a building than the energy required to operate it.  The energy efficiency of heating equipment can be compared by looking at the rated COP or Coefficient of Performance of the unit.

The COP of an electric furnace is 1, since each watt of electricity put into it produces the equivalent of 1 watt of heat energy out. The COP of a NORDIC unit is 3.5 or greater. Each watt the heat pump uses to run its transferring mechanism enables it to draw 2 or more from the earth thus giving a total of 3 or more units out for every 1 unit put in. The heat pump supplies more than 2/3 of your energy requirement from free energy stored in the earth and reduces your heating cost by at least 66%.

Bonus: FREE Hot Water

One of the innovative features of the NORDIC unit is its ability to provide "free" hot water during summer operation. Btu output actually increases during hot water making cycles and the recovery rate is similar to that of a 40 gallon electric hot water heater. Hot water is also provided during winter operation at a saving of 65-70% less than the cost of heating the water with an electric hot water heater. A typical homeowner can expect this feature alone to save him 20 to 30% of his/her present electric bill.

Where does the energy come from?

There are two common sources of energy from which a heat pump could transfer energy:

• The AIR around us.
• The EARTH beneath us.

Efficiencies of Heat Pumps

The efficiency of a heat pump depends upon the temperature at which it finds its heat (source temperature) and the temperature at which it discharges this heat (sink temperature). The greater the difference between the source temperature and sink temperature, the more work is done by the compressor in the heat pump; and consequently, the more cost. In other words, as the source temperature declines, so will the efficiency of the heat pump. The prospective buyer will naturally choose the type of heat pump (air source vs. ground source) which gets its heat from the source that remains at the highest temperature for most of the year. During the heating season in our part of Canada (Atlantic Provinces), our mean ground water temperature will remain 47°F (8°C) where the mean winter air temperature is approx. 12°F (-10.4°C). It is for this reason that seasonal efficiencies of a ground source heat pump are much higher than an air source. 

Glossary of Terms  

It is quite helpful to become familiar with the following terms upon introduction to Geothermal heating & cooling:

• Heat Pump - A heat pump is any device that moves heat from one place to another.
• Heat Source - The area where heat is taken from. (Water, air, etc.)
• Heat Sink - The area where heat is deposited. (Inside a home, etc.)
• Evaporator - The heat absorbing mechanism in a heat pump.
• Condenser - The heat rejecting mechanism in a heat pump.
• COP - The coefficient of performance of a heating system is a ratio of the heat we get out divided by the heat we put in electrically.
• SCOP - The SEASONAL COEFFICIENT OF PERFORMANCE is the average COP over the entire heating season.
• EER - The ENERGY EFFICIENCY RATIO is the ratio of Btu's of cooling divided by total watts used.
• SEER - Average EER over entire cooling season.
• Degree day - The number of degrees that the mean temperature for that day is below 65° F. (eg. mean temp. of 40 for the day--65-40=25 degree days)
• CFM - Cubic feet per minute of air flow.
• KWH - Kilowatt Hours
• BTU - British thermal units (method of measuring a quantity of heat). The amount of heat required to raise one pound of water 1° F.
• BTU = WATTS * 3.413
• 1 WATT = 3.413 BTU'S