At 30 F, latent heat from moisture in the soil freezing adds considerably to the capacity of the system, allowing very successful performance of the systems in northern climates. Not if a system is properly designed and installed. The three to four foot depth allows the sun to melt the frozen soil during the summer. Adequate length per ton capacity prevents objectionable soil movement. With the vertical installation, time varies with conditions at the site such as type and depth of the overburden, type and hardness of the bedrock, and the presence of aquifers.
Horizontal installations are simpler, requiring lower-cost equipment.
However, they require longer lengths of pipe due to seasonal variations in soil temperature and moisture content. Since a horizontal heat exchanger is laid out in trenches, a larger area is usually required than for a vertical system. If regional soil conditions include extensive hard rock, a vertical installation may be the only available choice. Vertical installations tend to be more expensive due to the increased cost of drilling versus trenching, but since the heat exchanger is buried deeper than with a horizontal system, vertical systems are usually more efficient and can get by with less total pipe. Your GHP contractor will be able to help you decide which configuration best meets your specific needs.