Devens (Harvard), MA Residence
MassDevelopment put out a request for qualifications for developer/builders to design and build net zero energy homes at its Devens residential community. The 8 team submissions were narrowed down to 4 to submit proposals. The Transformations team was chosen to build 8 single family net zero energy homes.
During the build-out, a family approached Transformations to customize one of its standard saltbox designs. They wanted a first floor master bedroom with two additional bedrooms on the second floor. It was important for them to be able to send their two children to the Harvard public school system which has consistently ranked among the highest in the state.
We increased the size of the 1500 square foot standard plan to about 1800 square feet and added a screened in porch, customized the kitchen, changed to bamboo floors on most of the first floor and added a media center.
The large portion of the roof was aligned to face south. We were able to fit 78 Canadian Solar 235 watt panels for a total system size of 18.33 kW. This helped our Energy Star rating to come in at a -21. The home is projected to produce about 10,200 kilowatt hours more than it consumes over a 12 month period. This is enough electricity to power a Nissan Leaf for 30,000 miles, year after year!
The home has a heat recovery ventilation system that distributes fresh air to the bedrooms. Three mini-splits (two on the first floor and one on the second floor) supply quiet heating and cooling to the home.
A 98% efficient Navien 180 instantaneous propane gas hot water system supplies ample hot water for the home.
The walls are 12" double studded 2x4's with a 5" gap between the two walls. The R-Value of the low density foam that fill these walls is 45. The attic has 18" of cellulose on the flat for an R-Value of 63. The R-20 basement walls have 3.5" of closed cell foam and a sheetrock fire protection assembly. The slab has 2" of rigid for a R-Value of 10. The R-5 windows are triple glazed and filled with krypton gas.
The home received an Energy Star Tier 3 certification in Massachusetts and construction was completed in the spring of 2012.