Horizontal Ground Heat Exchanger
Horizontal ground heat exchangers are usually the most cost-effective when adequate area is available around the building and trenches are easy to dig. Figure below shows different configurations of horizontal GHE that can be constructed. The horizontal GHE has become increasingly popular due to its low cost and ease of installation. For instance in Canada, about 55% of direct geothermal installations use horizontal GHEs (CGC, 2011). Nevertheless a horizontal GHE requires a large area of ground to lay the pipe network. This problem can be alleviated to some extent by employing a slinky loop arrangement of the pipes. Slinky arrangements are coils of overlapping piping, which are spread out and laid either horizontally or vertically. This GHE’s ability to focus the area of heat transfer into small volume reduces the length of the trenches by 20-30% of those for single pipe configuration (Wu et al., 2010). The slinky coils can have different lengths per unit length of trench depending on the pitch spacing of successive coils. The performance of slinky coils is similar to straight pipes with an equivalent total length (IGSHPA 2011).
Different configurations of horizontal GHE (from IGSHPA (2011), Philippe et al. (2011) (Note: the pipes in red are not to scale for better visibility)