Pennsylvania Home Gets Direct Exchange

The owner of this new 3,000-square-foot home in Mechanicsburg, Pennsylvania, learned about direct-exchange geothermal heating/air conditioning systems on the Internet, as he was planning construction. Through research, homeowner Del Leese quickly became aware of the unparalleled efficiency, comfort and cost savings provided by such systems, and was impressed with the fact that direct-exchange geothermal systems require no fuel or energy beyond the small amount needed to operate the compressor.

At the start of the installation, the contractor calculated the home's load and determined that a 3½-ton heating unit and 14 copper earth loops, each 50 feet long, were required for this home.

Direct Exchange Components

Choosing the Appropriate DX Configuration

At the heart of direct-exchange geothermal systems is a series of copper earth loops and a copper manifold installed underground, outside the home. Copper earth loops can be installed in several different configurations, depending upon site specifications like soil characteristics, space availability and equipment costs.

Drilling Diagonally for Space Efficiency

For Del Leese's property, 14 holes were drilled diagonally at 30-degree angles in a circular configuration with a 6-foot diameter. Mechanical contractor Jeff Demme chose this setup because it consumes less surface space than others, so more property is free for planting.

Running the Copper Lines

After the holes were drilled, a copper earth-loop fabricated with 1/4" and 3/8" seamless Air Conditioning and Refrigeration (ACR) copper tube supply and return lines were fed into each hole. These lines circulate the refrigerant back and forth from equipment in the house to the earth loop field.

Backfilling the Holes

Once all the copper tubes were installed, sand was used to backfill the holes using a sand-water slurry.

Preparing for the Manifold Installation

Next, the centre of the circle was excavated to 4 feet below grade, where the earth's temperature is relatively constant.

Connecting the Copper Earth Loops to the Manifold

All of the copper lines are joined to a corresponding supply or return manifold, which provide a junction where the 14 earth loops converge, channelling refrigerant through return and supply lines that are connected to the compressor.

A Tunnel to the Home

A 4-foot-deep trench was dug from the manifolds to the house foundation to accommodate the house supply and return lines.

The Role of the Compressor

The copper supply and return lines were connected to a compressor, which pressurizes the refrigerant according to the need for heating or cooling, based on the thermostat setting. Heat energy released by the pressurized refrigerant may be either channelled to the air handler if heat is needed, or back to the earth for cooling indoor air temperature. The process is controlled by a reversing-valve.

Connecting the Air Handler

Copper tube was then run from the compressor to the air handler. The air handler is used to circulate the heat into the home, or extract it from the home by carrying it through ducts.

Water Heating Options

A water heater connected to the direct-exchange system can either use waste heat given off in the air-conditioning mode or ground-source heat generated by the heating mode to reduce water-heating costs by as much as 70 percent compared to electric-resistance heating.