ZNEH - Zero Net Energy Housing - Energy Modeling

Zero Net Energy Housing - This is a home that generates as much on-site renewable energy as it consumes in one year.  Using grid-tied photovoltaic (PV) panels that generate electrical energy from the sun, wind or micro hydro turbines they generate power from alternative means - feeding surplus energy back into the electrical grid when available, and drawing power from the grid during evening hours and calm days when no renewable energy is available on site.  The houses are super-insulated to minimize energy losses, and utilize passive solar techniques to maximize direct solar gain for space heating through proper building orientation and optimum distrubution of south-facing glazing.  Carefully designed roof overhangs shade the south facing glass during the summer to minimize cooling loads.

In December of 2012 we completed a 10-week online course "Zero Net Energy Homes" Building Energy 13 Master Series with Marc Rosenbaum, PE as the instructuctor.  We covered such building science topics as:  Heat Transfer, Heat Loss Calculation, Vapor Diffusion, Air Barriers, and Thermal Bridges.  Wall and roof construction strategies and high-R value windows necessary to achieve high performance building envelopes were discussed in detail.  State-of-the -art heat recovery ventilation (HRV), heat pump domestic hot water heaters, air-to-air mini-split heat pumps, solar thermal, and photo-voltaic products were reviewed.  And finally, we learned how to perform energy modeling for a final design project that aimed at reaching the goal of a net zero energy home.

The images above show our design for a 2,300 square foot two story home with R-44 double stud exterior walls, R-75 blown-in cellulose attic insulation, carefully air-sealed to keep infiltration measured by a blower door test to 0.05 CFM50 per square foot of building shell.  Space heating is provided by a single 18,000 BTU electric mini-split heat pump that can meet the heating load down to -5˚F.  Domestic hot water is provided by an electric heat pump water heater with a COP of 2.5.  And finally, to meet the zero net energy target for the year, all the domestic electrical needs of the home plus charging a plug-in hybrid-electric vehicle, there is a 9.8 kW photovoltaic array on the roof of the south facing shed dormer.  In the event of a power outage, backup heat may be provided by a sealed-combustion, bio-mass pellet stove.