We recently finished a conversion of two-story home in Honeoye Falls from propane space and potable water heating to geothermal space heating and cooling (i.e. air conditioning) and potable hot water heating.
We located the horizontal ground loop in a field adjacent to the back lawn, approximately 150ft from the basement. Only a narrow – 2-foot wide – path across the lawn would have to be reseeded in the Spring.
The inside was a bit more of a challenge. Space heating had been by baseboard fed by a boiler and air conditioning was non-existent. Adding to the challenge, there was a bonus room over the garage which did not share an attic with the main house.
After doing a room-by-room heat load analysis and comparing to the amount of heat that each room’s baseboard would provide at 140F (the maximum water temperature achievable by a Geostar Aston Optiheat heat pump, designed as a solution to boiler replacement), we were ready to design the forced-air portion of the system.
Except the family room, which was walled off on three and half sides, the first floor was fairly open with no walls separating the living room, kitchen, and dining room. As luck would have it, the family room had an abundance of baseboard (for 180-200F boiler water) and needed very little second stage heating from forced air. For this situation, a single ductless air handler could do the job of second stage – supplemental – space heating and complete air conditioning for the first floor.
The second floor was compromised of 4 bedrooms and a common bathroom. Based on our calculations, every room would require forced-air heating to supplement the baseboard whenever outside air temperatures dipped below approximately 30F. Individual ductless air handlers for each room would have been prohibitively costly and overkill in terms of heating capacity. Instead, we decided to install a centralized ducted air handler in the attic space and run duct work laterally to the rooms where we installed ceiling grilles to provide supply and return air – again, both supplement heating and complete air conditioning.
As previously mentioned, the bonus room adjacent to the main house second floor was not accessible from the attic, so the central air handler could not service it. Here we were able to find a rather tortuous path for two lines of insulated ¾-inch oxygen-barrier pex tubing from our buffer tank adjacent to the heat pump in the basement to a ductless air handler in the bonus room, with only a minor amount of drywall repair required.
Given the high water temperature capability of the Optiheat heat pump, we had the capability to provide 100% of the household’s potable hot water needs using an indirect hot water tank configured as an addition zone with “priority”. Then the question was one of economics: does the energy savings warrant the additional costs of an IDHW tank and special controls which can easily exceed $2500? If the homeowners were empty nesters, probably not, but they still had two teenage sons at home, so their hot water consumption and, more importantly, potential energy savings was high enough to result in a fairly short payback on the additional cost of this feature. (“Priority” in this context means that when potable hot water heating is called for, the heat pump briefly ignores any requests for space heating or cooling to attend to potable heating needs.)
With a hydronic system design in hand that addressed all of the homeowners’ functional needs and delivered an attractive return on the cost of the conversion, we were ready to begin installation.