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Geothermal HVAC SystemsDots

Geothermal HVAC systems, also called ground source heat pumps, are among the most energy efficient systems available. Depending on the situation, typical energy savings are from 25% to 70%. According to the U.S. EPA, these systems have the lowest life cycle cost of any HVAC system. Although they usually cost more to install, they generally require less maintenance and repairs. Depending on the local conditions, the time required to recover the installation expense can be pretty short.

What Is It?

The basic geothermal system consists of three parts - the loop system, the heat pump, and the duct system.

Loop System

There are two main types, open loop and closed loop systems. These systems carry either water or a water/antifreeze mixture. Open loop systems are commonly called "pump and dump" systems. They pump water from a well to the system then return it to another well or discharge it on the surface. They are not very common and many local codes do not allow this type. Closed loop systems are the industry standard. These loop systems use a sealed water system where the water is used over and over instead of being dumped.

Heat Pump

The next part of the system is the actual heat pump. They work like a typical heat pump operating, but the main difference is that their heating and/or cooling capacity and efficiency do not change as much because the ground temperature is relatively constant. The unit uses a reversing valve to change the direction of refrigerant flow. This determines whether heat is added or removed from the air in the home. In addition to heating and cooling the home, most of the units can provide a good portion of the homes hot water requirements. In these systems, hot water is only produced when the home requires heating or cooling.

Duct System

The final part of the forced air geothermal system is the duct system. This is similar to a conventional duct system, although the ducts are typically bigger.

How is it Installed?

There are three basic ways these systems are installed. The first way is a series of plastic pipes buried in trenches about four feet deep. This is called a horizontal loop system. It is an economical solution where sufficient land area is available. In the vertical loop system, the pipes are buried in a series of holes drilled down around 200 feet. The holes are filled with a material called grout. This ensures good heat transfer between the pipe and the ground. This method is usually more expensive to install due to the specialized drilling required. But, much less land area is required, so it is a more common solution in smaller cities and towns. The last method involves submerging the loop system in a pond or lake. Usually the loops are placed on a rack and submerged. The earths' temperature at the depths of these loops stays relatively constant all year. In the U.S., it is about 45-55 degrees all year. In the warmer parts of the world, the temperature can be as high as 70 degrees. But even at that temperature, they can still provide superior cooling capacity.