Help with HVAC for a green home in Grand Rapids, MI
I had a question regarding use of geothermal heating and cooling about for a green home I am getting ready to build in Grand Rapids, Michigan. First, my home is 1633 square feet on the main floor, 1424 on the second floor and 1633 in basement. The walls will be 2 x 6 with blown in fiberglass and 2 inches exterior Rockwool and the goal is to get the air changes per hour low (ideally 1 or under). Windows will be Energy Star U-factor 0.26. Foundation walls will have 2 inch foam interior against concrete and adjacent 2 x 4 framed with fiberglass bats in basement. The ultimate goal is to be net zero capable with 15kW solar panel system.
I was told the home was too large to heat and cool with air source heat pumps and be comfortable so was primarily looking at geothermal. I have been quoted by two HVAC companies, one told me the load calc came in at 50,797 btuh at 7 degrees outdoor temp and recommended a 5 ton heat pump (60,000 btuh). This company said their rationale was there would be a 9000 btu cushion and electric heat coil backups would kick in for any sustained subzero temps (rare, but not unheard of here). They felt 6 ton wasn’t necessary for heating and overkill for cooling. The second company did not give me their load calc but feels strongly I need two 3 ton heat pumps to be comfortable.
Also, I have a friend who is in HVAC and he feels strongly that I should have radiant tubing run in the basement to help with heating in winter and while I was at it I was going to run it in the mudroom, master bath and three season porch.
After reading some of the articles on GBA, I am coming to the conclusion that people are not really fond of geothermal or radiant heat which leads to several questions.
Is there a better alternative to geothermal if I want to have the potential for net zero? If I stick with geothermal is two 3 ton heat pumps overkill (its certainly more expensive)? Should I abort the radiant altogether?
Any insight is much appreciated. Thanks!
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