Just how geothermal works seems like magic to me. Because the earth, at 300 feet down, maintains a steady temperature of 55 degrees, right there in my small front yard I have five times as much energy as is needed to heat my house.
“Instead of creating heat by using fossil fuels for combustion, the WaterFurnace is pulling heat from the ground and compressing it, which makes more heat,” says Laura Harris, a WaterFurnace spokesperson in Fort Wayne, Indiana. “What we are doing is moving energy that is in the ground. Given the opportunity, heat will always move to cooler area. That’s why an ice cube melts, and it’s what makes a geothermal heat pump possible.”
The simple explanation: the geothermal heat pump pulls heat from the earth and converts it to hot air. In the summer, with the flip of a switch that reverses the system, it cools the air in the house — sending the heat out to the earth.
Each of the two 300-foot holes in my yard has a pipe filled with a water-alcohol mix. These four polyethylene pipes have been spliced together. At six feet below the ground, they feed into two pipes (in and out, forming a continuous loop) that lead to my cellar and the heat pump.
Once inside, the pipes lead to the “flow regulation” center. The liquid exits through a smaller pipe that feeds into the heat pump. The liquid — still nearly 55 degrees — flows into a coaxial coil made of copper and nickel. Inside the coaxial coil is a smaller pipe with a refrigerant.
The two fluids — the water-alcohol mix from the earth and the refrigerant inside the smaller pipe — travel along side each other through the insulated coils, so that heat exchange can take place through the small pipe’s walls. As the fluid from the earth heats the refrigerant, the refrigerant turns to gas and feeds into the compressor.
The compressor raises the temperature of the refrigerant, which ultimately provides hot or cold air. (Remember the warm blast of air from under your refrigerator? With the heat pump in winter, that hot air flows into your house.)
The compressor raises the temperature of the refrigerant to 165 degrees. It goes through a valve into an air coil that looks like a radiator and has aluminum fins attached to the copper refrigerant tubing. When the heat is released from the refrigerant in the air coil, it is absorbed by the cool air from the return air duct. Then the now-warm air, from 95 to 105 degrees, continues its way through the duct system, spurred by a blower fan.
The cool refrigerant returns to the coaxial coil, where it can accept more heat from the loop fluid.
If the temperature gets extreme, as happened in the 2 degree weather in January, the WaterFurnace has a backup electric system.
In warm weather, when we change from heating to cooling, the valve reverses — and the liquid goes the other way.
All this magic happens inside the same size box as your old fossil fuel furnace.
There’s more. The same system has enough heat to help out the hot water heater by five to ten degrees. This doesn’t work in the “swing months” in the fall and spring when the system is not active, but it provides a big boost to the hot water heater in the summer and it offers some help in the winter.
I don’t have a houseful of teenagers, but once I did. Now they could take an unlimited number of long, hot showers.