Posted By mtrentw on 20 Aug 2014 07:33 AM
Heat capacity of the ground is significantly better with only 2' of pipe per foot of trench with a racetrack as opposed to 6' of pipe per foot of trench with slinkies.
While slinkies require less trench, they require more pipe. If excavation is cheap (or free) and real estate isn't a problem, a racetrack may be the better value.
Do you have any data to back up your statements? The heat capacity of the ground does not change, what changes might be the surface area for heat exchange. I would argue that every single design, wether it is slinky, racetrack or straight trenches, can be made to perform equally depending on the design. Your heatpump does not know where the water comes from. It comes down to who can install the best performance for the best overall price, including excavation, material costs, pressure drop and labor (time).
Having a job with more expensive prevailing labor rates might change the approach, where you invest more into the material.