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Types of Geoexchange Installations

The active component of a geoexchange system that actually transfers energy between the ground and the heat pump is called the ground heat exchanger (GHX). The GHX is the configuration of ground loops located outside or underneath the structure. The individual ground loops are where the energy will be absorbed or released. The underground pipes used in the GHX can be a closed loop or an open loop system and can be buried either horizontally or vertically.

The sizing of a GSHP is critical for proper functionality, and ultimately, customer satisfaction. Building size, construction and location will be factors in determining the size of heat pump. A heat loss and heat gain calculation should be performed to select the best unit for a given application. Once the heating and cooling loads have been determined, a ground loop can be designed. The factors used in designing the ground loop will include the building load, land area, building use, local geology and local climate. The size and type of system that will best serve a particular site will depend upon the amount of land and/or water available, and the type of soil and rock at the site. There are two different configurations for ground loops, open and closed, both relatively equal in operating efficiency.

Open and Closed Loops

1) Closed loops: The most common type of installation, these circulate water or a water and antifreeze solution continually through the pipes of the GHX. The fluids inside the pipes never come into direct contact with groundwater, surface water, or soils. Figure 3 shows three common ways to install a closed loop system in a pond, horizontally, or vertically, respectively.

Figure 3 – Three Different Types of GHXs

2) Open loops: Though similar in principle to the closed loop system, the key difference is that water is taken from a well, piped directly through the heat pump, and then discharged into a second well or discharge field. An open loop system can only be installed where there is an adequate supply of useable water and open discharge is feasible and permitted. See Figure 4.

Figure 4 - Open Loop - Commercial Building

Types of Installations

1) Vertical installations: These systems use a variety of drilling equipment to install vertical loops inside boreholes. They can be more expensive to install than either a horizontal or pond loop, but are ideal where land is scarce. These installations can operate with either closed or open loops, but usually closed loops. Installation of the vertical loop involves drilling holes into the ground and then inserting a U-bend loop, which is then attached to a header pipe and then trenched to the building. Drilling depth averages about 200 to 400 feet, and several holes will need to be installed depending upon the total square footage of the conditioned space. See Figures 5 and 6.

Figure 5 - Vertical Closed Loop Residential

Figure 6- Vertical Closed Loop Commercial

2) Horizontal installations: Heavy equipment is used to excavate a sufficient area or series of trenches to depths of at least 6 feet and install the GHX loops horizontally. The loop fields or trenches are then returned to grade. These installations can be less expensive than vertical installations due to elimination of drilling costs, but require significantly more land area. See Figures 7 and 8.

Figure 7 - Horizontal Closed Loop Commercial

Figure 8 - Horizontal Closed Loop Residential

3) Pond systems: For installations close to bodies of water, less than 100 yards, which do not freeze solid in the winter or evaporate in the summer, a pond or lake style system provides yet another option which eliminates most of the trenching. Great for cottages or houses on a lake, the application involves weighing down loop coils which sit on the bottom of the lake or pond. Energy transfer is just as efficient as other loop systems. See Figures 9 and 10.