In the last installment of this series, I explained my rational for going geothermal.  In this portion, I will explain how a geothermal system works.
 
A geothermal heat pump system works by using the ground’s thermal energy to heat and cool your home.  There are several components to the system:

• First, a six inch wide hole was dug 420 feet straight down into the ground in front of my home.
• A closed loop of piping was inserted into the hole and back out, and then run into my basement.  (The piping is entirely hidden underground – you could be standing right on top of it, and you would have no idea.)
• From the ground, it enters my basement, where it connects up to a pump.  This pump pushes water deep into the ground, where it is always 55 degrees Fahrenheit, and then draws it back out.

 
The geothermal heat pump system takes advantage of the fact that far below the surface, the ground is always 55 degrees Fahrenheit.  Before I explain how the system works, we must first understand some basic thermodynamics.  All matter contains some amount of heat.  If you remove heat from matter, its temperature drops.  If you add heat to matter, it temperature increases.  For example, if I take room temperature water (75 degrees Fahrenheit) and apply heat to it, I can cause it to boil (212 degrees Fahrenheit).  Similarly, if I take room temperature water (75 degrees Fahrenheit) and use my freezer to remove the heat from it, I can cause it to become ice (32 degrees Fahrenheit).  A geothermal heat pump works the same way.  I’ll explain.
 
In the summer, the system pumps water into the ground.  The earth cools the water to 55 degrees Fahrenheit.  Or, put another way, the earth absorbs thermal energy from the water, lowering its temperature.  The cooled water is then pumped back out of the ground and run through the geothermal heat pump.  There, additional heat is removed from the water through the use of a heat exchanger (I wasn’t given enough of a work allowance to go into the details of a heat exchanger here).  The cool air that remains is then blown through the house.  The waste hot water that results from the process is put into the hot water tank to make the best use of all available thermal energy.
 
In the winter, the system works in reverse.  The earth warms the water to 55 degrees Fahrenheit.  Or, in other words, the water absorbs thermal energy from the ground, raising its temperature.  The warmed water is then pumped back out of the ground and run through the geothermal heat pump.  There, heat is removed from the water by using a heat pump.  This time, the warm air is blown throughout the house, and the cold water is returned to the ground to warm up, beginning the cycle anew.
 
Neat, isn’t it?
 
The whole system is controlled by a programmable thermostat, just like a conventional furnace/condenser unit (which is likely what most of you have in your homes).  Electricity runs the pump and blower inside the geothermal heat pump, both of which use far less energy than conventional HVAC systems.
 
This is more or less a crash course on how a geothermal HVAC system works.  I will discuss the logistics of installing a geothermal system in the next installment.

About the author:

Josh Goldfarb is the President of NetflowData LLC, a cyber security and network traffic analysis consulting firm.  He resides in Silver Spring, MD.