If sufficient land area suitable for drilling or trenching is available, horizontal loops may be the most economic.

A horizontal system will use a number of horizontal trenches. Piping system designs range from a single pipe to multiple pipes, arranged vertically in a narrow trench to multiple pipes in a wider trench.

Examples

Some examples, depending on system size, of typical horizontal ground heat exchangers are:

• Single 1.25- to 2-inch pipe, series water flow, 350 to 500 feet per ton nominal length, buried four to six feet deep.

• Two-pipe using 1.25- to 2-inche pipe, series water flow, 210 to 300 feet of trench per ton with 420 to 600 feet per ton nominal length, buried four to six feet deep.

• Four layer using 0.75- to 1-inch pipe with 1.25- to 2-inch headers, parallel water flow, 125 to 200 feet of trench per ton with 500 to 800 feet per ton nominal length, buried six feet deep with 12-inch spacing.

Piping systems

The ground heat exchanger may be either series or parallel piping. Each has both advantages and disadvantages.

Series system

Advantages include:

• Single flow path and pipe size

• Higher thermal performance per foot of pipe, since a larger diameter pipe is required.

Disadvantages include:

• Larger water or antifreeze volume of larger pipe

• Higher price per foot of piping material

• Increased installed labor cost

• Limited length due to fluid pressure drop and pumping costs

Parallel system

Fabricated from smaller diameter pipe, which is generally less costly, special care must be taken in flushing to get all the air out of the piping loop.

Advantages include:

• Lower cost pipe

• Less antifreeze required

Disadvantages include:

• Special attention to assure air removal

• Attention to balanced flow, within plus or minus five percent, in each parallel path is required