In the North, a pond has to be deep enough for the heat exchanger to be at least two feet below the ice all winter. This is usually six to eight feet. Photos courtesy of AWEB Supply.
George Harvey
Many people seem to be confused by heat pumps. The fact is that nearly all of us have them in our homes and cars. A refrigerator has a heat pump, extracting what heat it can from the inside of the unit and delivering it into the kitchen. Air conditioners do the same thing, taking heat from a warm place and releasing it into another that is warmer. But it seems odd to be taking heat out of a freezer.
In a common refrigerator, the action of a heat pump starts with compressing a gas, which makes it hotter and denser. Then the heat is removed, so the gas is closer to room temperature but still dense. Then the pressure is released, which cools the gas far below room temperature. Then it is put through a heat exchanger for the refrigerator, which warms it up but makes the refrigerator cold.
A home heating and cooling system can work on the same principle. The really nice thing about this is that it uses far less energy to pump heat than it does to create it. A resistance heater, such as an ordinary space heater, operates at nearly 100% efficiency, in terms of converting electricity to heat. But a heat pump can heat just as much using a third of the amount of electricity or less, making it much less expensive than nearly all other ways to heat a home. It may boggle the mind, but it is true. And it can also run the other way to cool a building in the summer.
There are a number of different ways to run a heat pump. One is to extract heat from the outside air, which is how air-source heat pumps work. That is a good solution, compared to most other heating systems. It is like running an air conditioner backwards. It has the flaw that the outside temperature can drop below the heat pump’s limits, which it will do at temperatures between -10°F and 20°F, depending on the unit. (Inexpensive heat pumps that mount in windows are not good for low temperatures.) Another failing of air-source heat pumps is that there are very much more efficient ways of extracting heat than taking it from outside air, which is not all that good at transferring heat under any circumstances.
Geothermal heat pumps address the major issues of air-source heat pumps. They extract heat from the ground or water. These sources are not just warmer than the air on a bitter cold night; they are also much better at moving heat.
There are a number of ways to set up geothermal heat pumps. The heat exchangers on the outside of a building can be buried below the ground surface, which means a large area has to be excavated. Or they can be in drilled wells. Both of these solutions are rather costly, but for those fortunate enough to have it, there is an alternative.
An alternative solution to costly drilling is to put the outside heat exchanger into a body of water. Of course, a pond or river used for this purpose has to be large enough, and the question of whether it is or not should best be answered by someone who can do the calculations involved.
In areas of the South where the major load is cooling, a shallower pond that does not freeze solid can be sufficient.
Most solutions to water-based geothermal heating pumps involve long stretches of flexible pipes that are looped over and over, lying on the bottom of a pond. To be flexible, these pipes need to be made of some sort of plastic, which is not very good at transferring heat, and this is why they need to be so long.
Another approach to water-based geothermal heating was developed by Alan Watts of AWEB Supply, which has been installing its systems since 1995. This was first reported in Green Energy Times in the issue of April, 2018 (http://bit.ly/GET-AWEB).
AWEB Supply sells SlimJim® heat exchangers, made of stainless steel, and Geo Lake Plate®, made of titanium. These materials transfer heat far more efficiently than plastics. This means that the amount of piping needed for the heat exchanger can be greatly reduced, allowing for a rather compact system.
AWEB Supply’s heat exchangers can be used for any geothermal-style system near a sufficient body of water. For a small house, that might mean as little as one-third of an acre, providing the pond is deep enough – perhaps six to eight feet. The systems are connected to heat pumps at the buildings they heat and cool by buried pipes, through which water flows. The systems are not exposed to freezing temperatures, so no other chemicals are needed.
AWEB systems can also be used on much larger systems. For example, one of the larger systems AWEB installed is for Disney Barracks, one of the largest buildings at Fort Knox. The fort built a pond for this just to provide the water.
Anyone who lives on a pond or river might do well to think about having a water-based geothermal system from AWEB. While AWEB does not sell directly to consumers, the company is happy to refer customers to contractors in their areas who can undertake installation. Chris McCaskill, one of the owners of AWEB, told us, “It’s worth giving us a call.” He can be reached at Chris@awebgeo.com, or by calling (225) 928-2630. AWEB’s website is www.awebgeo.com.
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