Hi everyone,
I would like some input regarding a project I may be building for a family in Salisbury, MA. This family would like to go to net zero energy use if possible. It is a Deltec round home,
www.deltechomes.com built on a radiant frost protected shallow foundation slab. The house is 2500 square feet, 10' walls rising to perhaps 16' in the center with a loft in the center. We are looking at a slab insulated to about R30 underneath and up to the edge of the exterior walls, and R10-20 around the perimeter. We will use closed cell sprayed polyurethane to R40 in the exterior walls, and R70-80 in the ceiling, so there will be little if any air infiltration. Windows will have a u value of .08 to .12, depending on location, and shgc of around .55, again depending on location. Windows are oriented mostly to true south with shading, so there will be a significant passive solar contribution. In addition, there may be solar photovoltaics with net metering feeding back into the grid.
My question mainly deals with the HVAC: I have received quotes of $40,000 for a 3 ton geothermal system with 2 drilled wells, including heat in the radiant slab, with 3-4 zones, a desuperheater to provide domestic hot water for 4 people, high velocity central air via a split system, and a heat recovery ventilator. For heating alone, I show an approximate total heat loss of 8,000 - 10,000 btuh. For 4 people, I believe the load would be a fair amount more for domestic hot water than for heat. I know HVAC types propensity to oversize for safety's sake. However, 3 tons worth? And I know the northeast is higher priced, but $40,000 strikes me as a bit high.
What do you think? I would appreciate any and all input.
Thanks much,
Ronald Sauve
[email protected]