Massachusetts Ranch House Gets Solar Thermal Heat
By SETH MASIA
Jennifer and Bill Marrapese bought an inefficient 1977 ranch house out of foreclosure, in chilly Massachusetts. They planned a deep energy retrofit. Jennifer, as executive director of the Northeast Sustainable Energy Association (an ASES chapter), had access to a panoply of resources and experts. Beginning in the spring of 2012, general contractor Sean Jeffords of Beyond Green Construction jacked up the house in order to replace the soggy concrete slab. A new slab, covering 1,350 square feet, was poured over four inches of blue-board rigid foam. The slab was also designed to accommodate four loops of 5/8-inch PEX hydronic tubing, about 900 linear feet in all, installed by Beyond Green Construction.
Donavin Gratz of DA Gratz Solar installed the solar thermal system, the heart of the home’s cold-weather performance. Six Stiebel-Eltron collectors, 168 square feet in all, feed a 50-50 glycol mixture to a 160-gallon SBB 600 storage tank, with a two-stage heat-exchange system. The heated water goes to the domestic water system and, at 105°F, through the radiant coils in the floor. Two loops are laid in a tight pattern close to the perimeter of the house, and two in a loose pattern across the interior. Back-up heat comes through a 20-kilowatt Hydro-Shark electric boiler.
The whole system is controlled by a Steibel Eltron SOM controller/SolarWave DL-2 remote monitoring circuit, and a Nest Labs thermostat system, which senses motion in the rooms and directs heat where it’s needed. When outside air temperature dips below 15°F, the heating system kicks into high gear. Construction was completed in December; the house stayed warm through January’s bitter cold snap. Cost of the electric back-up heat totaled about $100 a month over the heating season.
Gratz estimates his crew put about 85 head-hours into the heating system, in two stages: rough-in on the new clerestory to take building-integrated collectors, and plumbing the tanks and controls before the walls were closed.