Ben Rush likes the idea of a ground-source heat pump, despite their reputation for higher cost than other heating and cooling alternatives.
A ground-source heat pump (GSHPs) requires heat-exchange tubing buried in the ground or inserted in a well or pond. The excavation required to bury the lines (or drill an extra well or two) helps to make GSHPs more expensive than air-source units. In addition, the equipment itself tends to be more costly. In all, GSHPs suffer a significant disadvantage when it comes to cost.
Even so, Rush thinks they make sense, and he wonders if he’s put his finger on a way to bring down the cost of installing a new system.
“To address the first issue, could the ground loop go under a basement floor?” he asks in a Q&A post at GreenBuildingAdvisor. “Would any additional excavation be required? How much? Would 2 or 3 inches of sub-slab foam insulation be enough to separate the conditioned basement from the year-round +/-55F (Climate Zone 5) soil? Bottom line: would this be an inexpensive — yet effective — way to install the ground loop?
“I really like the idea of GSHPs,” he continues, “for two theoretical reasons, and one practical one: A) In zone 5, the soil is cooler than the air in summer — and warmer than the air in winter. Why would I want to put heat into 90° F. air or take heat out of 10° F. air? B) The volumetric heat capacity of soil is about 1000 times that of air; and C) in Chicago, occasionally it might be too cold to heat with a minisplit (not sure if that’s three times a year — or once every three years — but it could happen), but it will never be too cold to heat…