WHAT IS GEOTHERMAL?

Geothermal systems heat and cool your home, school, or office by utilizing the near-constant ground temperature in the earth. In Wisconsin, below about six feet the ground is about 50° throughout the entire year. Geothermal systems (also called GeoExchange, Ground Source Heat Pumps, or just ‘Geo’ Systems) use heat pumps to absorb heat from this 50° earth during the winter and then expel heat to this earth in the summer.

The design of your geothermal system will depend on the particular site of your building. But there are many other important factors affecting the cost and performance as well – the thermal conductivity of the ground and the heating and cooling requirements of your building have a large impact on the system design. Contact a WGA member today to learn about a design for your specific application.

HOW IT WORKS

In the winter, a compressor in the heat pump unit absorbs heat from the ground loop (when the ground is much warmer than the outside air) and transfers it into the air in your building at a much higher temperature. A fan then circulates this hot air just like a typical heating system. Or, if a radiant floor is installed, the heat pump transfers this energy to the fluid that is running in the floor.

In the summer, the compressor operates in the other direction and absorbs heat from your building’s air, transferring it to the ground loop (when the ground is much cooler than the hot summer air). Conventional air conditioners operate similarly, but must reject the heat to the hot summer air, lowering their efficiency considerably.

COMPONENTS

The heat pump unit is connected to a loop and operates as explained above. Heat pumps have become a common piece of mechanical equipment, and are made and sold by many of the heating and cooling companies that supply conventional equipment. 

The ground loop is made of conventional polyethylene pipe, with thermally fused joints for reliability – most carry 50-year warranties!

The fluid, often including a non-toxic antifreeze (propylene glycol), is pumped through this ground loop by a small circulating pump. It is this fluid that transfers the heat to/from the ground and your building. 

LOOP SYSTEMS

The ground loop can come in several different configurations.

Unlike conventional heating and air conditioning systems that use the outside air to absorb and release heat, geothermal heat pumps transfer heat to and from the ground. They do that through closed loops of plastic pipes buried either horizontally or vertically in the ground below the frost line where the temperature is consistently between 40° to 80° F depending on where you live. These pipes are called ground loops, which are sealed tight and connected to the geothermal heating and cooling system inside the building. Water circulates through the piping allowing for heat transfer between the fluid and the earth.

Commonly used when adequate land area is available (the home should sit on 1/2 acre, at least). Loop installers use excavation equipment such as chain trenchers, backhoes, and track hoes to dig trenches approximately 5-8 feet deep. Trench lengths range from 100 to 250 feet per ton, depending on the loop design and application. Directional bore machines can also be used.

Used mainly when land area is limited in new construction or retrofit applications of existing homes. A drilling rig is used to bore holes at a depth of 150 to 250 feet per ton. A U-shaped coil of high-density pipe is inserted into the bore hole. The holes are then backfilled with a sealing solution.

This loop style is an option if a large body of water is available within approximately 200 feet of the home. A ½ acre, 10 to 12-foot deep body of water is needed to support the average home. The system uses coils of pipe typically 300 to 500 feet in length. The coils are placed in and anchored just above the bottom of the body of water.

This loop type can be installed if an abundant supply of high-quality well water is available. A typical home will require a well producing 4 to 8 gallons of water per minute. A proper discharge area such as a river, drainage ditch, stream, pond, or lake must be present. Check for local restrictions before selecting a specific discharge method.