Geothermal + Solar = Efficiency

By George Harvey

When Don and Judy Jordan decided put build a house, they wanted to share it with Judy’s parents, who are in their mid-80s. This meant addressing some unusual needs for warmth, as they had spent twenty years in Florida, and special consideration for potential special needs. Given four adults and a potential for visiting grandchildren, they allowed 3325 square feet of space. These issues meant making some careful choices on how to achieve efficiency and comfort without breaking the bank.

The Jordan house, showing its solar array.

They contacted Prudent Living, a division of Biebel Builders, of Windsor, Vermont, to help them with the project. This choice gave them some guidance with some very technical issues.

They did not decide to be fancy and go for LEED certification, or even to be entirely free of fossil fuels. Nevertheless, they achieved some very impressive results, in terms of green performance, because they were trying to get comfort, warmth, and economy, goals that can be achieved through green means.

Insulation and sealing are, of course, essential. Even if your heating is great, it does no good if you are using it to heat the great outdoors. R-60 insulation was specified for the ceiling, and above-grade walls were R-40 and R-30. Below grade walls were specified at R-20, with insulation under the slab at R-10. The house was buttoned up, and GDS Associates of Manchester, New Hampshire, tested for infiltration.

The Jordans’ ground-source, or geothermal, heat pump.

All told, the house would get a HERS Index of 42, if it were rated without consideration for renewable energy generating capacity. This means it uses only 42% of the energy needed to power a typical new house of the same size.

Given a good start on insulation and sealing, the Jordan’s went for a ground-source heat pump, or geothermal heat, to provide both house heating and hot water. This provides heat at just about the lowest possible price heating in a house that is not actually passive solar. It also makes possible use of the same equipment for cooling, as needed.

One result of the choice of ground-source heat pump is that the overall cost of heat has dropped below the cost of lighting. This is despite the fact that all the lighting is Energy Star compliant.

Offsetting the electricity load, the Jordans opted to have solar PVs generating about 70% of the power they need. This reduces their HERS Index to 12, meaning that their net usage is only about 12% of what might be normally be expected. Adding in service charges and a very small amount of propane used for cooking and drying clothes, their cost for 2013 was estimated at less than $1000 for all power and fuel, and their carbon emissions were a good deal less than half a ton.

The Jordans’ house got a confirmed Energy Star certificate of “Five Stars+”. We at Green Energy Times wish to congratulate them and Prudent Living on a fine effort.