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Discovering Geo-Thermal heating and cooling

Strictly speaking, this page should also be called "EARTH", but I chose "WATER" because it begins my love-affair with water as the ideal thermal transport media.  But I'm getting ahead of myself.  Let's talk heating and cooling.


We can all think of several ways to heat a house.  Since passive solar is dealt with on the SUN page, we'll ignore it here.  OK, let's list some of the ways.. 

  • Burn fossil fuels (coal, oil, gas, etc.)
  • Burn renewable fuels (wood, methane, etc.)
  • Resistive heat from electric elements (Power generated in a variety of green/not-so-green ways).
  • Heat Pump

As an Applied Physics Grad, all of these except the last one seem pretty crude to me.  The first three are all less than 100% efficient.  No matter how you cut it, energy costs money, so the less efficient your heating system is, the more it will cost.  Heat pumps on the other hand can be more than 100% efficient.  "How can that be?" you ask.  Well it's simple.  Heat Pumps don't generate heat, they pump it. When a heat pump operates in a suitable environment, it can be up to 400% efficient.  

So how come heat pumps get such a bad rap, especially in cold winters?  That's easy too.  When it's 70 Degrees inside the house, and 25 Degrees outside the house, heat pumps have a really hard time pushing heat from the outside to the inside (kinda like a sump pump trying to pump water up a 45 foot rise).  It's all a matter of differential.  

When the difference between the outside temperate and the inside temperature is only about 20 Degrees, heat pumps are extremely efficient.  

And that's what Geo-Thermal Exchange systems are all about. Underneath your yard is an unlimited supply of constant temperature, perfect for a heat pump.  All you need to do to tap into that constant temperature, is sink a long length of tubing beneath the ground, and circulate water through (in essence).  Then, instead of trying to pull heat from the sub-zero air outside your house, you now pull heat from the earth beneath your yard.  The units that do this for you are called "Ground Source Heat Pumps" (or GSHP).

There are many different tubing configurations, and the best one to use depends on your personal situation.  One manufacturer of  Geo-Thermal systems is Water Furnace, and they have a great tutorial for those interested in the specifics. 


Well, the most popular way to actively cool a home in the USA is with a heat pump.  Some desert locations may use evaporative cooling, or even ICE, but these don't really work in humid climates.  Once again, the normally high efficiency of a heat pump is effected by the temperature differential that the pump must overcome.  In raging summers, this difference may be as high as 30 Degrees, which is luckily still within the operational range of a modern heat pump.

But look what happens if you once again use the earth as a constant temperate source.  Now the heat pump is pushing heat from an inside temp of 75 Degrees, down to a nominal 55 Deg Earth temperature through those same in-ground coils.  Since the heat already wants to go from hotter to colder, the heat pump is operating in an ideal environment.  The highest possible efficiency is guaranteed here.

Other Benefits of Geo-Thermal exchange.

  • Ok, so burying the earth loop is a hassle, but so is burying power lines, but we do it.  Why? Well, from then onwards, the system is invisible, silent and low maintenance (no noisy fans outside, and no motors exposed to the elements etc.).
  • Since the Geo-Thermal heat pump is already dealing with one water loop, why not go all the way and replace the interior forced air system with an in-floor radiant heat system fed directly from the heat pump.  Now interior noise has also been reduced, and space isn't taken up with heating ducts. (Great for locations that don't have a cooling requirement)
  • Some Geo-Thermal heat pumps are also capable of supplying the household hot water service with heat.  Since the cost of heating water for cleaning and bathing is a significant component of any home's heating bill, the efficiencies of the Geo-Thermal heat pump can have a considerable cost saving
For the technically inclined, here are two great diagrams showing the refrigeration cycles for Ground Source Heat Pumps.  For more information, check out the great Geo-Heat Center reference site at the Oregon Institute of Technology.

Design Concepts
Earth - Sun - Water - Hybrid

© 2000-2018, Phil and Lisa's relaxed lifestyle home.
An exercise in Energy Smart, Not So Big living. -


This site is all about building a cool, energy efficient house, that makes maximum use of earth sheltered design, passive solar heating and cooling, geothermal exchange energy management, and right sizing of the house for it's designated use. The home's placement is on a south-facing hillside in Deep Creek Lake, Maryland. This site describes the design process, the technologies used and the expected results. We also have a comprehensive Links Page for anyone who is also interested in designing a similar project.