I've often been asked what configuration of GHX is better...a horizontal or slinky? They both work well, but there are differences in the way they work over the year. A horizontal GHX is closer to the earth's surface. Outdoor air temperature and precipitation have a much greater impact on a horizontal GHX because the piping is close to the earth's surface...usually within 5 to 10' (1.5 to 3 m). Cold air temperatures drop the GHX temperature during the winter and the hot sun warms the earth by the end of the summer. How quickly the air temperature affects the temperature of the heat transfer fluid depends on the thermal properties of the soil and the depth of the piping,
The piping in vertical boreholes is buried much deeper...boreholes 400' to 600' (120 to 180 m) are common. It takes much longer for the outdoor air temperature and precipitation to influence the temperature of the soil. Heat rejected to a vertical borehole doesn't dissipate very quickly...energy doesn't move very quickly through rock and soil unless there is ground water movement in the ground. The soil and rock tend to act as an energy storage medium, while heat rejected to a horizontal GHX dissipates fairly quickly to the air a short distance above it. A designer can take advantage of the storage capacity of vertical boreholes, storing waste energy in the soil. A project in Okotoks, AB illustrates the storage capacity of a vertical GHX. 52 single family homes are connected to a vertical GHX that is used to store solar energy all summer for use the following winter.
A designer can also take advantage of the much quicker heat dissipation or heat absorption of the shallow piping in a horizontal GHX. If the building loads are cooling dominant, for example, a horizontal GHX will dissipate the energy rejected to the ground through the winter. There is much less chance of heat build up in a horizontal GHX.
In my blog I'll be expressing my opinions about what I've the learned about ground coupled heat pump (GCHP) systems over the last 30 years. I've been very fortunate to work with many interesting people who are passionate about this technology...engineers, geologists, mechanical contractors, drillers, excavation contractors...in different parts of the world. I've learned a lot from them and will be using this forum to pass on some of the things I've learned and feel are important. Please feel free to use this information if you feel it's worthwhile...hopefully you can avoid some of the same mistakes I've learned from.