Installing the heat exchanger for the gethermal heat pump

Here is a sequence showing how we installed the heat exchanger and tubing for our geothermal heat pump (GHP). Two 1.25" poly tubes circulate a mixture of water and methyl alcohol from the unit in our basement out underground to the stainless-steel heat exchanger submerged in the pond. For cooling, the GHP extracts heat from the house and puts it into the fluid where it is "dumped" into the pond via the heat exchanger, and returns cooler. Since the water is already fairly cool, this is very efficient, even if the GHP uses refrigeration methods to augment the cooling.

For heating, the fluid picks up heat -- albeit at perhaps only 36-40F in winter -- from the pond water, and then extracts heat from it using much the same principle as a refrigerator in reverse. The GHP needs to raise the temperature from the fluid temperature to whatever our thermostat is set to -- say 75F. Unlike a conventional furnace where combustion heats the air quite substantially, the GHP hot air flue is only somehat warmer than the setting, and relies on exchanging a lot of slightly-warmer air to reach the desired temperature. This means there is much more air exchange, but since it is not so hot, the humidifier works much better, and the whole system reduces the tendancy to have hot and cold areas in the house during the heating season.

As a side benefit, the GHP is plumbed in to an electric water heater, and excess heat from the system's operation is run through a "superheater" to provide hot water. In the shoulder season -- when we are not using much of either heating or cooling, the water heater functions normally by electricity.

Eric Fletcher