Vertical Loops

Vertical loops, illustrated in Figure 28.2c, are generally considered when land surface is limited. Wells are bored to depths that typically range from 75 to 300 feet (22.9 to 91.4 m) deep. The closed-loop pipes are inserted into the vertical well. Typical piping requirements range from 200 to 600 feet per system cooling ton (17.4 to 52.2 m/kW), depending on soil and temperature conditions. Multiple wells are typically required with well spacing not less than 15 feet (4.6 m) in the northern climates and not less than 20 feet (6.1 m) in southern climates to achieve the total heat transfer requirements. A 300- to 500-ton capacity system can be installed on one acre of land, depending on soil conditions and ground temperature.

There are three basic types of vertical-system heat exchangers: U-tube, divided-tube, and concentric-tube (pipe-in-pipe) system configurations.

• Advantages: Requires less total pipe length than most closed-loop designs; requires the least pump-

ing energy of closed-loop systems; requires least amount of surface ground area; ground temperature typically not subject to seasonal variation.

• Disadvantage: Requires drilling equipment; drilling costs frequently higher than horizontal trenching costs; some potential for long-term heat buildup underground with inadequately spaced bore holes.

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