Green Homes With Passive Heating Emerge in US

The super-insulated solar home in New Hampshire. (image: buildinggreen.com)

Popular in Europe, especially in Germany, where it’s been practiced for nearly two decades, passive house technology is just beginning to catch on in the US. A recent article in Newsday talks about a home on Long Island that a local firm is rebuilding as a passive house. The project is part of a local fundraiser for muscular dystrophy, but it’s also intended to showcase this emerging green technology.

Typically, passive construction starts from scratch, but whether you’re building from the ground up or just remodeling, the concept is a radical one. It aims to create a structure so energy efficient, it doesn’t require a conventional heating system, even in cold regions. It accomplishes this amazing feat by maximizing conservation and use of the sun’s heat, as well as that given off by a home’s lights, appliances and even its live occupants. Humans give off the heat equivalent of a 100 watt bulb.New construction begins with a passive solar design. Passive buildings tend to be compact in shape to reduce surface area, with windows oriented towards the sun. The windows themselves are new triple-pane insulated glazing with low-emissivity coatings, argon or krypton gas fill between the multiple panes and ‘warm edge’ insulating glass spacers with air-seals and specially developed thermally-broken window frames. In Europe, where they are in extensive use, when windows like these are oriented toward the sun, heat gains, even in winter, are greater than losses.

But once you’ve collected that free solar heat, you’ve got to keep it in. Passive homes are “super-insulated,” significantly reducing heat transfer through the walls, roof and floor. Passive home construction calls for extremely high R-values (a measure of thermal resistance) and low U-values (or measure of heat transference). Achieving this can require thermal insulation material up to 13 inches thick in the wall and 20 inches thick in the roof.  Special attention is given to eliminating “thermal bridges,” places where heat escapes in conventional structures. A passive house also calls for nearly airtight construction. Fully forty percent of heating costs go to combating air infiltration, otherwise known as drafts.

A feature in Environmental Building News on the Building Green website details the construction of a super-insulated home in New Hampshire which according to the article has “about the lowest energy consumption of any house in the United States”. The house was built to be airtight as well.

The tighter the house, the more heat efficient it can be. But you still have to breathe. Some passive homes, including the New Hampshire house, incorporate heat recovery ventilations systems, to provide air exchange with the outside without sacrificing heat.

An article in Popular Mechanics magazine details how such a system works. Stale, but warm, indoor air, and fresh, but cold outdoor air are handled in separate streams, while a heat exchange core in the system transfers the heat from the outgoing, old air to the incoming, new air. Ingenious!

Diagram of a recovery ventilation system. (image: popularmechanics.com)

Depending on how it cold it gets in the area, or how frequently the sun shines,  passive homes sometimes include a backup heating system which might depend on electricity, a woodstove, oil or natural gas burners.

Building a basic passive solar home can be expected to cost at least 10 percent more than a conventional one, and maybe more than that, depending on how much energy saving technology is employed. But while a fully independent passive home, with heat exchangers or other sophisticated equipment will cost more initially, these costs will be quickly recouped in energy savings.

There are as yet very few passive homes in the US, but as green construction and remodeling gain popularity, builders are gaining expertise and accreditation. Prospective green homeowners can locate accredited builders through organizations like the Green Building Council which administers LEED (Leadership in Energy and Environmental Design program.)