The closed-loop is the outdoor portion of a geothermal heat pump system. Basically, it is a continuous closed circuit made of polyethylene pipe. The pipe carries a water/antifreeze mixture to and from the indoor heatpump and into the ground. The process either removes or adds heat to the home's living area, depending on the season.
Generally, there are three common types of closed-loop systems — horizontal trench, vertical well and lake loop. Each type functions using the same operating theory, but the actual loop location is in a different area.
The horizontal system's piping is buried in a long trench, where it is looped back and forth. The depth of the trench needs to be about two feet below your location's freeze line. This method requires quite a large ground area to install, and often this is the most limiting factor.
A vertical system's piping is put in wells that are bored straight down into the earth. The wells are usually 150' to 200' deep. The number of wells required is dependent on the tonnage of the system — generally one well per ton. Even though the wells must be spaced about 10' from each other, this method requires less ground area to install than a horizontal. Restrictions can include tree lines, potable water or sewage lines and underground conditions. Some wells may require permanent casing or full grouting, which can add cost.
The lake-loop system is usually made of the same material and antifreeze, but a trench is made to a nearby pond or lake, where the loop is coiled and weighted down to the bottom. This system uses the stable temperatures of deeper water instead of ground temperature to transfer heat. The limiting factor of the lake system is proper water depth and distance from the lake to the dwelling.
The only way to really know which closed-loop system is best for a particular home is to contact a knowledgeable and trusted geothermal contractor in your area and have them visit your site and listen to your ideas and concerns. They will show you the pros, cons and restrictions of each type and help you make an educated decision.
This expert insight brought to you by Russ Scott, general manager of Scott-Lee Heating Co. and an Enertech Global LLC geothermal dealer.
Russ Scott has worked for more than 16 years at Scott-Lee Heating Co., and is now the general manager of the business his father co-founded. He received business and creative writing degrees from St. Louis University, is on the S.M.A.C.N.A. - St. Louis Board of Directors, is a Contractor Rep on the Local 36 Apprentice Committee and is involved with the local H.B.A. and A.C.C.A. chapters. Russ enjoys sharing his knowledge of all high-efficient HVAC systems, especially geothermal heat pumps.