Jack Bingham’s house in Barrington, NH (Jack Bingham)
Wes Golomb
Jack Bingham’s house is a direct result of the research he conducted at the University of New Hampshire on how heat pumps can make greenhouses usable in the winter. Most greenhouses are either shut down in winter or are inefficiently heated with fossil fuels to keep them going in cold weather. Despite the cold, on a sunny day in February the temperatures in a greenhouse can rise to the high 90°F range.
Jack’s research centered on installing heat pumps to remove heat from his greenhouse and store it in insulated water tanks.
There was one problem, however. Because glass is such a poor insulator, the greenhouses ran out of heat by 3 a.m. That got Jack thinking. Suppose he built a greenhouse attached to a very well-insulated and air-sealed home. He could capture the heat with a heat pump and store it in a water tank to heat his house. And that is what he did! Jack designed a house with a greenhouse on the front, a heat pump, and a storage tank.
An abundance of boulders made it cost prohibitive to build a basement, so an Alaskan Slab, also known as a floating slab was used. The entire foundation is wrapped by foam insulation.
The walls are constructed of structural insulated panels (SIPs) produced by Foard Panel in West Chesterfield, NH. The SIPs are made of foam insulation sandwiched between two pieces of oriented-strand board (OSB). They are made in eight-foot-wide panels and splined together. Laminated in a vacuum press, together they become an impermeable structural component that offers continuous insulation and greatly limits the conductive heat loss experienced in most typically framed houses.
In standard framed houses, the electric wiring runs through the walls. This often compacts the insulation, making it less effective. To avoid this, the inside of the SIPs is strapped with 2×4’s, which allows space for wiring.
Heat pump on second floor of the greenhouse (Jack Bingham)
The design challenge in this house was to keep the heat in rather than letting it escape. To achieve this, the greenhouse walls, like the rest of the house, were well insulated and air-sealed.
At $50,000, double-paned glass was cost-prohibitive, so Jack looked into other materials. There are two factors to evaluate when installing glazing—how much light the glazing will let through (its emissivity) and how much heat the glazing will let out (its conduction). These two factors are inverses. With thicker material, the insulation is better but less light gets in. With thinner material, more light gets in but more heat gets out. Jack chose the middle option—a three-quarter inch triple-walled polycarbonate.
One of the key features of this design is a means for storing heat after it is collected from the greenhouse. This is accomplished by installing an 800-gallon tank buried under the floor of the greenhouse. The storage tank is contained within a wooden crate made from pressure-treated wood. The tank is insulated to R-28 on the sides and bottom, and R-40 on top. As a result, the hot water stored in the tank holds its heat for a very long time.
The greenhouse is specifically designed to capture the sun’s heat and store it for use at a later time. The mechanism used to accomplish this is two air-to-water heat pumps installed on the second floor of the greenhouse. Using the same concepts as an air conditioner, the heat pump takes heat from the air in the greenhouse and transfers it to water via a heat exchanger and refrigerant.
On a sunny winter day, it is common to find the greenhouse’s temperature at 90ºF or higher. At this temperature, heat pumps are extremely efficient. Jack calculated that for each unit of electricity used by the heat pump, it generated a heat equivalent of up to eight units of electricity! What an incredible ratio: an input of one unit of energy (electricity) produces an output of eight units of energy (heat)! It seems like magic, but it’s physics.
When the average person’s energy consumption is calculated, a car is the second largest energy consumer after a home. Jack’s net-zero home is designed to generate enough energy to run the family’s Nissan LEAF all-electric car in addition to the home.
In the first years of occupancy with 9.5 kW of solar installed, the cost of electricity was under $500 a year which included charging a car. Last year Jack added 4.6 kW of PV and a second heat pump.
The system is net-metered, so when the solar array produces more energy than is needed, the excess is put back onto the grid. This runs the meter backwards and builds a credit so no on-site battery storage is required.
With the added solar and second heat pump, Jack expects this house to be net-zero and may possibly be net-positive, (generating more electricity than it uses) this year.
Jack’s house is indeed one of the most unusual I have investigated. The synergy created by the tight envelope, extremely efficient heating system, and photovoltaic array provides all the needed electricity to power the house and car.
We energy geeks tend to focus on cool technologies and design but perhaps what is most impressive is that Jack’s wife, after long suffering with asthma, has had no attacks since they moved in. This is an excellent example of the power of these technologies to allow us to live in a comfortable, healthy and resilient way without generating pollution.
Wes Golomb is a long-time clean energy and climate advocate from Deerfield, NH. Wes is the author of the Warm and Cool Homes book and videos.
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Very interesting article. Thanks for publishing it.