Geothermal Heating Systems

About Geothermal Heat pumps

Not all heat pumps are the same, the most common type is an air-to-air style that extracts heat from the air.   The most efficient heat pumps extract heat from  below the earth’s surface…..geothermal heat pumps.

When temperatures dip below 38–degrees an air–to–air heat pump is operating at a descending point of efficiency and the  heat strips are activated. Some systems even have  an outside sensor that disables the heat pump function when the set-point is reached and switches over exclusively to the electric heat strips.  This reduces the strain on the heat pump.  Cost savings are eroded as the electric meter spins recording the greater energy consumption as the system seeks to maintain the specified comfort dictated by the thermostat.

Claims of 30% to 70% heating cost savings with geothermal however are very inviting. Heat is extracted from the ground through a thermodynamic process. From about four–feet below the frost level,  temperatures are consistently about 50–degrees. The most reliable source of high quality consistent heat is from the ground not the air which varies with the weather.

Geothermal heat pumps or ground source heat pumps extract heat from the ground rather than the air, like a standard heat pump. Ground source heat pumps are considerably more efficient since they extract heat from the warmer sub-surface soil.  Standard heat pumps (air–to–air) extract heat from the air that fluctuates with weather changes. When outside temperatures drop below the set point of an air–to–air heat pump, efficiencies are reduced and back–up heat is activated to maintain heat levels.


There are two basic styles of geothermal heat pumps and ground field systems. The direct expansion (DX) method uses freon enclosed in copper tubing as its heat transfer medium  energy savings. Water based systems use a water/antifreeze mixture.

In the water based system, water/antifreeze mixture is pumped through  plastic tubing in the ground field and  then to the heat exchanger. At this exchanger, Freon absorbs heat and is pumped to the coil in the furnace.  Air from the blower passes over the coil transferring heat through-out the system.

The DX method is more  efficient since  Freon is considerably more effective as a heat transfer medium than water.  The elimination of a pump for the water  mixture circulation adds to the efficiency by reducing energy consumption.

When cooling is required , the two systems vary there too. Other ground source heat pumps are designed to   transfer heat into the ground rather than into the air like the Sub Terra system.   Trying to transfer  heat to the ground is a very real problem since soil  is a poor conductor of heat.  Where  air conditioning  requirements are high  The dirt  adjacent to the tubing quickly becomes saturated with heat and doesn’t readily make the the ground resulting in the compressor experiencing higher operating head pressures and reduced efficiency and higher operating costs.   In areas with a high water table or  short and intermittent air conditioning needs  the ground has time to recover  and  the system  does work.  Systems that do work  in areas with high air conditioning needs often must rely on evaporation to cool the tubing.  A system to provide water for evaporation becomes a necessary component to this kind of system.  Most of these systems by their very nature are  subject  to failure depending upon soil conditions.


The ground receives and stores heat from the sun on a daily basis. There is no need to “replenish” the heat removed from the earth.


Actual field tests show the ground is reset to the “normal” temperatures after a few weeks of heat extraction inactivity. The balance of nature continues with the sun doing its part to balance the loss of heat during the heat extraction cycle. This is a phenomenon that is easy to verify with simple refrigeration pressure gauges.

Remember: refrigerators and freezers, two common examples of heat transfer, use freon rather than water.

Contact:            503.267.6034 

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