Geothermal 101


The descriptions and pictures below are designed to foster a basic understanding of the parts of your geothermal system.  When you call for service, we hope they will help you to identify those parts of your system that may need service.  When you receive an invoice from us, we hope the information below will help clarify which parts and systems we worked on during our service visit.

There are two fundamentally different forms of geothermal heating – “Sun based” geothermal and “Hot rock” geothermal.

“Sun based” geothermal – the type we install, service, and rescue – is truly a solar energy machine – the heat from the Sun heats the first 30 feet of Earth in a seasonal fashion and the remaining 300 to 500 feet in an annual fashion.

“Hot rock” geothermal starts at about 1000′ and goes deeper and utilizes the heat generated by the radioactive decay of the elements in the interior of the Earth.  (Interesting to ponder that the Earth was so “hot” from radioactivity that life could not begin on the surface until at least a billion years of decay had elapsed!)

Because we are using the Earth and the Sun, we need to somehow connect our geothermal system to the Earth.  The mode of connection – closed loop with buried black plastic pipe, closed loop with buried copper tubing, open loop with supply and return water wells, pond source, and ocean source – are all discussed in our geothermal page in Products.  Here we will discuss the particular components of the geothermal system.

Fielder geo trench w geo ball slinkee rolled out Jan 2011


The geothermal field comes in many different types but one of the most common is the horizontal “slinkee” closed loop arrangement of black plastic pipe (same type of pipe as we use for buried water wells).





The geothermal loop circulator is the heart of the system that connects the outside geothermal field with the inside geothermal heat pump.  It needs to be large enough to handle the largest heating and cooling load that might be encountered during the winter or summer.





We use an air separator to remove air bubbles from the geothermal supply water, just like we do with boilers, solar systems, and hydronic heating systems.




We also use an expansion tank to accomodate the seasonal changes in geothermal supply temperature and the accompanying change in pressure.






Each geothermal heat pump is connected with the loop circulator and outside geothermal field via supply and return piping.





Each geothermal heat pump is connect to the supply and return piping with stainless steel flex connections (stainless braided hoses) that help to reduce the transmission of noise and vibration from the heat pump to the piping.





Most geothermal heat pumps are “water to air heat pumps” which means that they are connected to the geothermal “water” as a source for heating and cooling via the heat pump and to the “air” delivery system of ducts in the house as we would find in a furnace or air source heat pump.





The other common type of geothermal heat pump is the “water to water heat pump” which means that it is connected to the geothermal “water” as a source for heating and cooling via the heat pump and to the “water” delivery system of hydronic heat.  Typically the heat pump is connected to a radiant heating system – the water temperature limit of 120 F from a heat pump is fine for radiant floor heat but not high enough for baseboard fin tube or radiators.


In all geothermal heat pumps, there are two heat exchangers; the first one is between the Earth (geothermal water) and the refrigerant in the heat pump. (water to refrigerant heat exchanger)



copeland compressor


This heat exchanger is connected to the compressor which increases the temperature and pressure of the refrigerant.





The refrigerant is metered by the thermostatic expansion valve (TXV) which regulates the flow of refrigerant into the evaporator.






The flow of refrigerant can change direction, based on the position of the reversing valve.  This valve determines if the heat pump is in cooling mode or heating mode.





The contactor is the large relay that sends power to the compressor when there is a call for heating or cooling.




The control board determines the operation of all parts of the heat pump by interpreting the commands from the thermostat.




The refrigerant rejects or absorbs heat from the inside space through the refrigerant to air heat exchanger (also known as the evaporator coil or condenser)






The blower motor and blower wheel (squirrel cage) pull the air through the air filter and force it through the heat exchanger and back up to the living space.






The condensate pump is necessary to remove the collected water from the inside coil when in cooling mode.





The thermostat regulates the temperature of the living space by cycling the blower, compressor, and loop circulator on and off.  The latest heat pumps are able to modulate the speed of all three of these parts with the resultant increase in efficiency, comfort, and even temperature distribution.




The heat pump part of the geothermal system is usually powered by a double pole circuit breaker in the breaker box.  An extremely common cause of no heating or air conditioning in a geothermal system is a circuit breaker in the off position.



Our goal is to be Martha’s Vineyard’s premier plumbing and HVAC shop – we appreciate the opportunity to service, install, and “rescue” your geothermal system!