Architectural Record BE - Building Enclosure

From the Ground Up

Geothermal-heat exchange is a great concept, but inefficiency can quickly turn a heat sink into a money pit.
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From GreenSource
Tudor Van Hampton
Continuing Education

Learning Objectives - After this course, you should be able to:

  1. Understand the concept of geothermal heating and cooling.
  2. Explain the benefits and drawbacks of geothermal systems.
  3. Discuss the various types of geothermal systems.
  4. Identify the necessary components of these different systems.


1 GBCI CE Hour


On Oct. 25, 1948, a short article appeared in the back of LIFE magazine entitled the "Fireless Furnace." There, postwar America witnessed the emergence of a futuristic technology that Lord Kelvin, the King of Cold, only dreamed about nearly a century earlier.

The fireless furnace ran water through coils in the ground, and then sent it through a heat pump to eliminate burning fossil fuels. But the technology was too expensive-about $3,000 installed-and too new to gain acceptance. "However, as the efficiency of getting heat from the earth improves, it is almost certain that eventually the heat pump will be able to compete successfully with conventional heaters in most localities," said the story.

Read a related story about "green" refrigerants by Tudor Van Hampton »

Sixty years later, geothermal-heat pumps (GHPs) and related systems are competing. If designed efficiently, the systems can produce more energy than they consume-three to five times as much on average-yielding a positive coefficient of performance (COP). They tap the natural heating and cooling properties of the earth by "pumping," or extracting heat from it. Homes and commercial buildings in the southern United States have been "recycling" this ambient heat for years using what are called air-source heat pumps (ASHPs).

As soil is a more stable heat-exchange medium than air, so-called "ground-source" heat pumps (GSHPs) are becoming a more attractive option. Nearby bodies of water can provide green sources of heating and cooling as well, using "water-source" heat pumps (WSHPs). The medium is different-earth vs. water-but the mechanics and components are basically the same. However, not all geothermal systems require heat pumps, and as such are even more efficient than GHPs.


Illustration by Alan Kikuchi


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Originally published in GreenSource