Super efficient geothermal heating
Q:Dear Jim: My old electric furnace is on its last legs and has needed service lately. I was considering installing a geothermal heat pump this time. With its higher installation cost, does this make sense for me? - Paul G.
A: Dear Paul: A geothermal heat pump is probably the most efficient heating and air-conditioning system available for any home today. In the heating mode, the heat blowing out of the registers is often warmer than with a standard air-to-air heat pump so comfort during the winter is better.
Throughout its life, installing a geothermal heat pump usually makes economic sense for the average home, but always have your contractor do a computerized payback analysis for you. If your house is extremely energy efficient and already has low utility bills, even cutting them in half with a geothermal heat pump may not justify its higher cost.
A geothermal heat pump both heats and cools your home like a common air-type heat pump, but that is where the similarities end. In the heating mode, a geothermal heat pump pulls free heat from a ground loop, well water, lake water, etc. for super high efficiencies. For example, with a coefficient of performance (COP) of 4, it produces an extra $3-worth of free heat for each $1 on your utility bills. During the summer, the energy savings can be as much as 60 percent. Some geothermal models have efficiencies as high as a seasonal energy efficiency rating (SEER) of 22 as compared to an old central air conditioner at about 8. The dehumidification factor is also often better for improved indoor air quality, less allergic problems and better comfort. When operating in the air-conditioning mode, most geothermal heat pumps offer the option of using a desuperheater device. This device takes the waste heat from your house that is normally exhausted outdoors and diverts it to your water heater for free hot water during the summer. Some of the newest geothermal models use ozone-friendly R410A refrigerant instead of standard freon. Geothermal heat pumps are so energy efficient because they use the earth as the source of heat during the winter; and during the summer, they exhaust indoor heat to the earth. Since the ground temperature several feet below the surface stays relatively constant year-round, a geothermal heat pump uses less electricity to heat and cool your house. Using constant-temperature water from a deep well also provides the same efficiency benefits. During the winter, even though it feels cold out-
James Dulley is a mechanical engineer who writes on a wide variety of energy and utility topics. His column appears in a large number of daily newspapers.
Copyright 2001 James Dulley
18 ILLINOIS COUNTRY LIVING • DECEMBER 2001
doors when it is 30 degrees, there is still heat energy in the air that a standard heat pump can "pump" into your house. At the same time, the ground temperature may be 55 degrees. It makes intuitive sense that it is easier to pull heat from the ground at 55 degrees than from the air at 30 degrees. The colder it gets outdoors, the greater the benefit of a geothermal heat pump becomes.
The efficiency and comfort improvement when cooling during the summer with a geothermal heat pump can be even more dramatic. If you plan to use water, in particular well water, with your geothermal heat pump, consider a model with an additional water-type heat exchanger. Often, the incoming water is often cold enough to cool your house without having to run the compressor.
To install a typical ground-loop system, a series of small pipes is placed in deep narrow trenches dug in your yard with a back hoe. Drilling deep vertical holes can be used instead. The pipes are connected to a heat exchanger inside the heat pump. An antifreeze solution runs through the pipes to capture heat during the winter or exhaust heat during the summer.
Another efficient design (called DX) does not use an antifreeze solution in pipes or a heat exchanger. Instead, thin copper tubing is placed in the ground and the actual refrigerant (freon or R410A) runs directly through it. This requires less overall ground loop length and is ideal for smaller yards. The inefficiencies of using an extra heat exchanger are also eliminated.
Since a noisy outdoor condenser fan is not needed, most geothermal units are located entirely inside your house. There are designs to fit utility rooms, basements or attics. This makes servicing them easier. If you have a gas or oil furnace that still works, new outdoor geothermal heat pump units are also available so you can still use the existing furnace.
For ultimate comfort and efficiency, select a two-stage model with a variable-speed blower. This allows it to constantly fine tune the heating and cooling (and electricity usage) to the varying needs throughout the day.
Write for (instantly download - www.dulley.com) Utility Bills Update No. 644 - buyer's guide of 13 single/two-stage geothermal heat pump manufacturers listing efficiencies, heat/cool outputs, features, fuel cost comparison chart and ground loop details. Please include $3.00 and a business-size SASE. James Dulley, Illinois Country Living, 6906 Royalgreen Dr., Cincinnati, OH 45244.
DECEMBER 2001 • ILLINOIS COUNTRY LIVING 19