Ground Heat Exchanger (GHE) is the key to the efficiency of a Ground Source Heat Pump (GSHP). However, GHE is not standardized as other parts of the GSHP. It is basically a bunch of tubes that need to be properly sized and burred in the ground. Improperly sized GHE can lead to chocked flow and higher pumping cost or stagnate flow and less heat transfer.


Sizing methods and data of GHE are mostly scattered in installation manuals and other documentations, such as the International Ground Source Heat Pump Association Installation Guide and other literature. 

I have listed some general steps and references needed to size a Ground Heat Exchanger. I am also considering to build a webpage to facilitate the calculation.  Do you think if such a utility is useful? Do you know if there is already web based software to do this?  What do you wish such a sizing utility to do?  Please commentate here or at my website

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Since the ground loop is the biggest cost of having Geo installed it's critical to get this right for quickest payback time vs. a conventional HVAC system. Too small of a loop and you won't get the rated EER from the unit, too big and you overpay for installation costs. Reducing the installed cost (therefore payback time) is key to making geothermal a successful technology.

Does your calculator take into account the thermal mass of the ground?

The geo system may be designed for a peak load of 42,000 BTU/hr, but the average load may be closer to 480,000 BTU over a 24hr period (24,000btu/hr). The ground due to it's high thermal mass may only need to produce the average capacity instead of peak.

Does the calculator consider installed cost?

Installed cost varies wildly depending on site conditions and labor costs. Installing a larger loop might make sense at the time of construction since the digging equipment is already on site for construction of the building. There are no landscape considerations to worry about. Same may hold true on a rural farm where land is plentiful and labor costs may cost substantially less. In an urban area where installation costs are high, it might make more sense to size for cooling load and have backup heat strips pick up the rest on those really cold nights.


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