Geothermal Loop Systems: An Overview

To regulate temperature within a home or other building, geothermal systems use a looped arrangement of pipes to exchange heat energy. Loop systems vary in layout orientation, space requirements and the medium of energy exchange. Each system described below delivers a high level of energy efficiency:

Open Loop Systems

This system uses water rather than earth to exchange heat energy. It requires both an adequate well or pond, and an appropriate discharge field. Water pumped in from the source enters an exchanger contained within the system’s heat pump. The water trades heat energy with the system’s refrigerant, either drawing away or delivering heat, before being discharged outside. The water doesn’t return to the exact same source, however. Possible discharge fields include a separate well.

Advantages of open loops include greater efficiency over an earth-exchange system, and lower costs for installation and setup. However, environmental regulations may restrict the use of ground water in some areas, permits may be required and discharge methods must ensure that ground water and other sources won’t be contaminated. The quality of the water is another consideration, with mineral and other content potentially causing corrosion in the geothermal system, possibly resulting in increased maintenance issues.

Closed Loop Systems

All other loop systems are considered “closed,” in that no outside substance circulates through the system to interact with the refrigerant. Instead, the refrigerant travels through the external loops to exchange heat energy with the ground or with water.

Closed-loop systems can run through wet or dry ground, as well as water, and be either vertical or horizontal in orientation. The type used and the size of the system depend on a variety of factors, such as available space, soil type and whether an extreme climate affects soil temperature.

Vertical Loop

Chosen in rocky soil conditions, extreme climates or where little land space is available, vertical systems install pipes with u-shaped connections into the ground through deep boreholes, anywhere from 30 to 40 meters down. Bentonite grout is commonly added to the holes to increase the heat exchange, to prevent ground-water seepage and to prevent the borehole from collapsing. In some cases, a special lining may be required to prevent collapse.

The depth of a vertical-loop installation provides several advantages: The more stable ground temperature means more efficient operation; with greater efficiency, often less pipe is needed; and with less chance of disturbance, there is less chance of pipe damage. Among disadvantages, high water tables may cause problems; a full survey may be needed to avoid utility lines. Each of these can add to costs, on top of the special drilling equipment needed for vertical installation.A typical 3 ton installation takes a vertical bore hole of 7 x 16 meters.

Horizontal Loop

This system positions the pipe loops horizontally in a shallow, back-filled trench, less than a couple of meters deep. Standard pipes may be laid over a space 100 meters or more in length, which often limits this setup to rural areas with adequate space. Pipes are usually u-shaped, although new technologies are currently being developed in loop pipe configurations.

Given the simpler digging requirements, horizontal systems are more economical to install than vertical systems.

Horizontal loops can also use a pond or other water body of adequate size and depth for the energy exchange, if it’s located within approximately 60 meters of the building. Slinky coils are anchored at the bottom of the pond, while a horizontal land-trench contains the pipe connection between the water loop and the building. Pond systems take advantage of water’s greater thermal-exchange capabilities, and the closed system ensures that the source water and ground are not contaminated. With one of the simplest installations, pond loops are an efficient and economical geothermal solution but your pond does need to meet a certain minimum size requirement.

Related pages: Geothermal Heating Systems