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Natural Home Heating: Air-Source vs. Ground-Source Heat Pumps

A reader comment on a previous post about home heating got my brain-hamster spinning his wheel about air-source versus ground-source (read: geothermal) heat pumps. What it boils down to is, when you’re choosing the proper heating/cooling system for your home, consider the local climate. The most energy-efficient system for one locale may not be the most energy-efficient system for another. Whereas in Orlando, Florida, an air-source system—where the heat-pump is placed outdoors—works marvelously, in a colder, wintry area—say, for example, oh, I don’t know…White River Junction, Vermont—geothermal might be where it’s at.

There are other considerations, of course, but here’s a quick overview of these systems.

The following is an excerpt from Natural Home Heating by Greg Pahl [1]. It has been adapted for the Web.

Heat Pump Systems

On the outside, heat pumps are unexciting; they’re rectangular metal boxes with pipes and wires coming out of them. It’s what’s inside the box that creates the magic. Not all heat pumps are created equal, and there are so many choices. The analogy to a Lego toy set is particularly appropriate when you’re combining elements to create an efficient and effective heat-pump system.

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Air-Source Systems

The two basic types of air-source heat pumps are one piece and two piece. A one-piece heat pump is self-contained in a single unit.This type of heat pump is often found in commercial settings, such as motel rooms, or is used where a relatively small area in a house or office building is being heated and cooled. One-piece units are often mounted on the roof or in a wall.

Two-piece systems consist of two main packages of equipment. One is installed in your home, often in the basement or utility room, while the second package is located outside, normally on a concrete pad on the ground. The inside unit looks similar to a gas furnace, while the outside unit looks just like a central air-conditioning unit. These two pieces of equipment, connected by pipes and electrical controls, transfer the heat in or out of your home, depending on the season.Two-piece systems are the design most frequently used in air-source home heating applications.

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Ground-Source (GeoExchange) Systems

Unlike an air-source heat pump, where one heat exchanger (and frequently the compressor) is located outside, a ground-source heat pump unit is located entirely inside your home, often in the basement or utility room. This is especially important in northern climates, where extremely cold winter temperatures and snow can have an adverse impact on heat-pump equipment located outdoors. Part of the heating system is located outside, however, and that is the underground piping that contains the liquid heat exchange medium.The type and configuration of the outside piping system is the main factor that differentiates various ground-source heat pump designs.