The Overlooked Energy Source:
Bringing Geothermal Close to Home
We all look to renewable energy sources to help us cure ourselves of our addiction to foreign sources of fossil fuels. Such sources include hydroelectric, nuclear, wind, solar, ocean waves and geothermal. Much is written about each, but geothermal seems to get less attention than the rest, and what we do get usually refers to major projects to tap existing pools of superheated steam or efforts to create very large new man-made, single-location sources of hot water or steam. Both are used to generate electricity for use elsewhere.
Often overlooked (as a subset of geothermal energy)
are geothermal heat pumps designed for use in individual homes or commercial buildings, and which provide both heating and cooling. This article will explain broadly how they work and why they should be an increasingly important part of the solution to our problems.
Energy From Elsewhere Most Is Wasted
As we have heard, roughly half the fossil fuels used in this country are used to heat and cool buildings, both residential and commercial.
Given the cost, the pollution impact and the limited availability of these fuels, such consumption is increasingly foolish, damaging and unsustainable. Unlike vehicles, which carry substantial fuel quantities with them, buildings usually sit still and can therefore take better advantage of local sources. So, we should ask whether fossil fuel consumption for heating and cooling buildings makes any sense at all.
Electricity, generated in renewable ways, can be used directly to heat or cool a building, but the large amounts needed cause transmission losses and such high costs that this approach rarely makes sense, except perhaps near to large hydroelectric projects.
But there is essentially unlimited energy directly below virtually all the buildings we build and use, and all it takes is a bit of electricity to access it.
Enter the Geothermal Heat Pump
A few dozen to a few hundred feet beneath almost every place where man wants to live or work there is usually an aquifer that comprises water at about 60 degrees Fahrenheit. These aquifers are the source of most of the water we use for our daily needs. Generally speaking, the water is replenished by the natural flow of rain and snow back to earth. It is deep enough that the temperature is governed not by the climate at the surface, but instead by the virtually limitless energy stored in molten rock in the core of the earth. Where there is no aquifer, there is at least a subsurface temperature that offers similar opportunities for extracting energy.
But how can we use an unlimited supply of water (or rock) at 60 degrees to heat a house to 70 degrees? This is where the ideas get clever.
Think about your refrigerator or your air conditioner. Both of them are heat pumps. One is pumping heat out of the fridge into the house. The other is pumping heat out of the house into the surrounding air. But how can heat be "pumped"? Here is how:
Any compressible fluid, like air or Freon, heats up when it is compressed, and cools down when it expands. So, if we compress Freon, making it hot, then extract the heat from it by running it through coils cooled by an exhaust fan, and then release the pressure, the Freon will be a great deal colder than before, providing a source of cool air for the fridge or the bedroom. So, while the device is cooling one area, it is heating another.
Heat in Winter
Now extend that concept to an aquifer’s steady supply of water at 60 degrees: Expand some gas so that it is cold, say 40 degrees, and then run it through some coils submerged in 60 degree water until the gas is back to 60 degrees. Then re-compress the gas and it will heat up to say 100 or 120 degrees which provides a steady source of warmth in the winter. Since the aquifer, or the subterranean rock, is generally 60 degrees F, the expanded gas that is to be passed through the aquifer must be colder than that for it to absorb heat from a material that is "only" 60 degrees. Of course, both 40 and 60 degrees are "hot" compared to absolute zero which is minus 460 degrees F. (Absolute zero is the temperature at which there is no more energy in the form of heat left in a substance.) So the expanded gas needs to be cooler than the heat source, but not so cold as to cause problems from freezing something.
Cool in Summer
When it is too hot outside, reverse the process and use the well water to remove heat from the compressed gas, offering a source of cool air in the summer. So we are exchanging energy with the earth below the surface, using it sometimes to absorb energy, and other times to supply it.
How can we take advantage of this? When a house or commercial building is being designed and built, or refurbished, especially if the water will be supplied from an individual well, allow for the heating and cooling to be by geothermal heat pump. The original cost can be twice that for fossil fuel equipment, but the payoff in reduced energy consumption provides a handsome return on investment, especially in this period of sustained high fossil fuel costs.
Many will ask, "Since I still need electricity, where are the savings?". True, electricity is still needed to drive the system, but only about 20% of what would be needed to heat the building directly. And electricity is the form of energy that is most likely to result from exploiting the various renewable sources listed earlier.
So, using a renewable to take advantage of another renewable sounds pretty good to us. Savings of 30% to 70% in heating and cooling costs are not uncommon; the benefits in reduced reliance on foreign sources are substantial, and the carbon emissions are nil.
To find local suppliers of this technology, Google "well water heat pumps" or "geothermal heat pumps" together with names of nearby towns or cities. And you can harvest links from Wikipedia to use in locating vendors.
- Douglas Ayer