Mar 152011
 

Photovoltaic Net Metered Electrical System at Amstutz Woodworking, Upper Jay, NYBy design, timber frame homes are already much more energy efficient than traditional stick-built homes. But as an energy conscious timber frame builder, I have always entertained the dream of building a Net Zero timber frame home. Net Zero buildings produce as much or more energy than they require to operate. Last week I attended a conference to learn more about making the dream home a reality: the Northeast Sustainable Energy Association Conference in Boston.

The conference features professionals in sustainability and whole system thinking and included daily sessions and presentations and an impressive trade show of building materials, mechanicals, etc. The sessions were organized around 9 thematic tracks such as Renewable Energy Technologies, Germany and Upper Austria, Regional Models for Sustainability (because these folks are way ahead of us), and the one I focused on: Residential Buildings Retrofit and New.

Integral to the presentations in the residential track was Net Zero buildings. Nationally, our residential buildings consume a very large portion of our energy usage, and as energy costs continue to rise and the availability of oil and gas, which are after all limited resources decreases, we need to couple new technologies with sound building practices to build more efficient structures. I saw presentations on dozens of houses that have been built in the last years in the Northeast that meet this specification. Our timber frame homes have always been better insulated than standard stick framed homes, but this is new territory.

Achieving net zero in a home requires excellent design and engineering modeling and an interesting mix of building techniques and mechanical systems. Firstly, size matters {like to modest-sized homes post}, so reducing the size of homes to what is really needed is the first order of business. Secondly, getting a handle on the energy consumption habits of the homeowners and reducing that load is very important. Next, and probably to my eye, most important, is the insulation of the envelope. It is not uncommon for designers and builders to craft homes with R 50 in the walls and R 80-100 in the roofs. These R values (i.e. measure of resistance to heat loss in a wall or roof or window) may seem excessive compared to our New York State energy code of R 26 in walls and R 40 in the roof, but pushing the envelope to this degree of insulation dramatically reduces the heating system needs. Integral to this envelope is also the absolute reduction of air infiltration and thermal bridging (which refers to structural components of the house, such as wood framing members bridging through the insulated envelope from the inside warm wall to the outside cold wall, and as such transferring heat from inside to outside). In short, with proper design and construction, superb envelopes can be built, and heating needs become very, very low indeed.

Most of the houses presented had their own net-metered solar photovoltaic system for producing electricity. In the ìnet meteredî system, a photovoltaic array is designed to produce of the kilowatt hour needs of the house for an annual cycle. Rather than use storage batteries, electricity produced in excess of the house’s need in the more solar summer months is banked in the electrical grid and considered as a producer credit to be used in the darker winter months. We have had such a system since 2004.

With heating needs substantially reduced, one presenter noted that his house could be heated with 2 hair dryers and an 80 watt bulb–which was hardly fictitious. Some homes also utilized ground source heat pumps, i.e. systems in which the heat from water in a well or in underground tubes is harvested and warmed further through a reverse refrigeration process (i.e., a heat pump) to heat the home. And integral to such tight homes is the use of heating recovery ventilators (HRVs) that ventilate these homes but avoid heat loss in the air exchange.

The resulting homes were well crafted and attractive structures that elevated the concept of energy efficiency to amazing heights.

What was exciting for me as a timber framer was to learn how we could quite easily boost the R value of our envelopes and to establish contacts with design and engineering professions who could make the net zero Timber Frame home a reality. Now, we just need to find some interested clients..