It’s much easier to answer this question for residential applications. The price is composed of three pieces: the drilling cost, the loop field installation including underground piping to/from the building, and the HVAC system installation. Many times the driller is also the installer, but not always. Sometimes the mechanical contractor controls the overall bid. In general, here in the SE PA area prices for the geothermal installation are running between $12/ft to $14/ft. There is another $1600 in the trenching, penetration, backfill, grading & re-seeding. So, for a typical 2500 sf home, one might expect to pay around $15,000. The extended range (4 ton) heat pump installation, circulator, water/methanol fill, and commissioning might add $8000 for a total price to the owner of $23,000. This could be higher or lower based on the thermal conductivity of the site and how easy or difficult it is to drill and contain the spoils.
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Commercial geothermal installations are another beast altogether. Here you are dealing with the composite bid from many subcontractors: driller, mechanical, electrical, controls, likely overseen by the general contractor. I’ve heard bids ranging from $23/ft to $32/ft for the geothermal closed loop installation piece of it. These are assumed to be paying prevailing wage under Davis-Bacon. The issue, in comparing such a bid to other geothermal installations that might utilize, e.g. standing column wells (SCW), is how do you translate the cost basis from $/ft to $/ton, the latter reflecting the owner’s bottom-line interest.
In an earlier blog, I mentioned that SCW offers a factor of 2X better heat transfer to the ground than grouted loops on the premise of the same water temperature. The design choice of ft/ton (fpt) is dictated by the measured effective thermal conductivity of the drilled formation. So, if a particular site allows 100 fpt for SCW, then a true comparison will dictate 200 fpt for the closed loop design. The drilling & SCW installation expense for a nominal 1200’ deep SCW can vary significantly depending on where the project is located: $30/ft to $100/ft (cities such as Boston, NYC). The former price reflects what ARB Geowell has developed for its projects.
So, let’s take a look at a typical 100 ton commercial project, carrying the price all the way through and including the building heat exchanger and the submersible pump controls. The Pie Chart below is a summary of the total geothermal project pricing, which ranges from $2600 to $3100 per ton installed. Note that the drilling portion is approximately 50%, the SCW installation 25%, and the remaining 25% captures the HVAC, electrical and controls subcontract value.