In December 2013, an ice storm caused an extended power outage in Maine, leaving many residents scrambling to keep their pipes from freezing. But even with no utility electricity for five days, below-freezing temperatures, primarily overcast conditions, and no supplemental heat, the homes at Belfast Cohousing & Ecovillage (BC&E) lost only 2°F a day, on average, for a total drop of 8°F to 10°F. Nearby homes, by contrast, were below freezing after 24 hours.
How did they do it? Passive House design, passive solar orientation, and a small building footprint.Small, Smart Design
The super-efficient ecovillage homes are heated largely by passive solar gain. Despite Maine’s cold winters and relying on electric space and water heating, a 900-square-foot BC&E home can approach net-zero energy with a 3.5-kilowatt PV system, and a 1,500-square-foot home can zero out with a 4.5 kW system.
Although the homes aren’t certified, the Passive House Institute US standards guided the design process. A southerly orientation; generous south-facing glazing; triple-pane windows and doors; lots of insulation; airtight construction; and a compact footprint resulted in a 90% reduction in the energy used for space heating compared to the average house. The homes share walls, reducing the exterior surface area and heat loss to the outside.
When designing the ecovillage homes, architect Matthew O’Malia of GO Logic used the Passive House Planning Package (PHPP), a spreadsheet-based design tool for architects and designers. “The Passive House standard is revolutionary in that it has spawned a new way of thinking around high-performance buildings,” says Gibson. The PHPP energy model spreadsheet is used to determine a building’s energy gains and losses. “You have a section of wall with certain properties, and the program can calculate how much heat is going to move through that wall over time. If you determine every way a building can gain or lose energy, you come up with a comprehensive model for how a building is going to perform.”
However, Gibson points out, PHPP has its limitations. The software was designed in Europe and has been very accurate in predicting how the building will perform, but doesn’t accurately model household electricity use in U.S. homes. “We use a lot more electricity than Germans do,” he says. “And you can’t predict occupant behavior, such as how someone might set their thermostat.”
Even so, Gibson estimates that a 1,500-square-foot ecovillage home (without a PV system) uses $300 for heating each year (2,000 kWh at $0.15 per kWh), while a standard Maine home costs more than $2,500 to heat, using an estimated 680 gallons of fuel oil.
What makes the homes so energy-efficient is the attention to details, like insulation and air-sealing. The outer walls are a hybrid system: blown-in cellulose in 2-by-4 framed interior walls and 8.25-inch structural insulated panels (SIPs), achieving R-45. The load-bearing portions of the slab are 12 inches thick, with 4-inch-thick floors. The concrete slab is insulated with 6 inches of EPS rigid foam, slowing heat loss to the ground, and the ceilings have 24 inches of loose-fill cellulose for R-80. The house-wrap seams were taped to complete an air barrier, significantly reducing heat loss due to infiltration.
The triple-glazed wood-aluminum Unilux windows have an SHGC of 0.5 and a U-factor of 0.09. The R-7 windows and doors help keep the homes virtually airtight, and promote ventilation and summer comfort when open. The windows can swing inward on two hinges or be hinged on the bottom to tilt inward, opening at the top. The latter offers draft-free ventilation and prevents rain from entering the home.
Despite being clustered, the ecovillage houses shade each other very little, and only in the early morning and late afternoon. All of the homes are oriented either due south or within 30° of south, making them well-suited for PV and solar water heating systems.
Most of the homes have enough roof space for a grid-tied PV system large enough to offset the home’s electricity using net billing. Some roofs also have room for a couple of solar collectors for water heating. The roof pitches vary—30° on the smaller units and 40° or 45° on the larger units. These angles are well-suited for year-round PV system performance and ease of winter snow removal. All of the homes are PV-system ready, with a junction box on the roof, concealed conduit running from the roof to the load center, and dedicated breakers in the electrical panel. To date, 22 of the 36 ecovillage homes have PV systems installed. One home also has a solar water heating system.
“It was nice to work on a project where there are a large number of folks who are interested in solar power,” says John Luft of ReVision Energy, which installed the first 11 systems. Homebuyers were given the option of a PV system as part of the homes’ feature selection process, and the option of including the system cost in the mortgage. GO Logic provided estimates of energy usage and a variety of solar options drafted by ReVision Energy that were customized to each home based on house size and number of occupants.
In the summer of 2014, residents organized a collective purchase for 11 additional PV systems, which were installed by Capital City Renewables (CCR). To receive wholesale rates on the PV modules and components, all of these systems used Axitec 250-watt PV modules with Enphase microinverters. The systems range in size from 2 to 5 kilowatts. Two BC&E members were trained and helped install the systems with the CCR crew.
With so many PV systems, Central Maine Power was concerned that the transformers couldn’t handle the back-feed, and the utility required BC&E to commission a study. It was determined that numerous PV systems could be supported without upgrading the transformers, although CMP imposed a limit—no more than 150 kW of PV capacity. There was also concern about the “resiliency” of BC&E’s all-electric homes when the utility grid goes down, considering that all the PV systems are grid-tied without battery backup. But so far, residents have—literally—weathered the winter storms with relative ease. Even without mechanical heating during a winter snowstorm and several-day utility outage, indoor temperatures remained relatively constant.
The ecovillage homes are all electric, in part because the 36 units are clustered on 6 acres of a 42-acre site. “There were a lot of discussions of whether or not to have wood heaters,” says Alan Gibson, a principal for GO Logic. Because of air-quality issues and the heating loads of the buildings being so low, it made sense to install inexpensive electric-resistance baseboard heat.
Gibson estimates that using electric baseboards in every room, controlled by individual thermostats, instead of a conventional oil-fired forced-air central furnace, saved $15,000 in each 1,500-square-foot home, although other energy-saving techniques—such as the heat-recovery system ($3,000; see “Heat-Recovery Ventilation” sidebar); increased insulation ($17,000); and triple-pane windows and doors ($8,000)—added to the construction costs.
The mission of the ecovillage includes sustainability, so solar energy was part of the initial vision as a major source of energy for the community. “We didn’t want to truck in deliveries of fossil fuels, so oil and propane were out,” says Gibson. “If you can afford a PV system to meet all of your annual electricity needs, [electric heat in a super-efficient house] can be a greener alternative.”
Maine’s net-metering program allows customers to bank credit for surplus solar electricity for up to one year. Ecovillage homes have no air-conditioning and, in general, low electrical loads—so they usually earn credit from April to October. Once heating season rolls around, they can draw on the credit, as heating with electric baseboards drives up the electricity usage. Residents still pay a monthly fee to the utility for distribution; thus, the lowest electric bills are about $9.74. The energy credit appears on the electricity bill, further motivating homeowners to conserve energy to reach net-zero goals. All of the PV systems include access to MyEnlighten, an online monitor which includes historical and real-time energy production.
BC&E homeowner Penny West has numerous ways that she reduces her energy use to achieve her net-zero goal with her 4.3 kW PV system, such as using only a 6-cubic-foot refrigerator with no freezer. “I also take advantage of the fact that the breaker panel is in the entryway. I turn on the water heater in the morning before I take a shower and turn it off when I’m done.”
One ecovillage member placed a bulk order for 400 LED lights, reselling the discounted 3.5 W bulbs to residents who were interested in replacing the 50 W halogen bulbs that came with the original track lighting systems. Some members installed low-flow showerheads that use 1.25 gallons per minute (reducing water use and water-heating loads), forgo a clothes dryer, or put timers on their water heaters to reduce standby loss. When the common house is complete, shared group dinners will reduce individual cooking energy consumption.
Although nobody has moved forward yet, there is interest in installing PV systems on the garage roofs to offset electric-vehicle charging. The garages have moderate solar potential, with orientation up to 30° off of south and some shading from houses. With downtown Belfast just 2.5 miles away, electric vehicles are a viable transportation option for ecovillagers.