Passive House design comes to Vermont
by Rolf Kielman, November 24, 2010
The Passive House: it sounds like some kind of strategic mind game for buildings. In actuality, this is a very positive development for designing better buildings.
In the quest for more knowledge about these passive houses, I spent last weekend with Marc Rosenbaum at the Yestermorrow Design-Build School. The course he was teaching dealt with the comprehensive process involved in the design of Passive House. The Passive House is a rigorous process for ensuring dramatically improved energy performance. This process has been stringently refined by (who else?) German design professionals. It is applicable to larger scale buildings as well, and many European structures are being built to these standards.
The continued increase in world-wide energy costs has led to higher performance expectations for the buildings we design. The Germans and the Japanese have established standards that mandate a low level of energy consumption per square meter of building area. These standards will soon be coming to North America. I would not be surprised to ultimately see performance criteria established for our buildings much as we already have mileage criteria for automobiles.
During the 1970s, I (and many others) designed low energy homes. These homes often had renewable energy collection systems and were either super insulated or double envelope houses. At the time, we did little to rectify air leakage or utilize much more than the crudest methods to measure building performance. Nevertheless, those buildings became the precedent structures that our design colleagues around the world are now emulating and improving on.
The principal behind the making of Passive House is simple: provide houses (or any building) with an exceptional thermal blanket. So exceptional, that all one might need to heat the house is a single candle or some form of minimally fueled heating device. The higher cost of fuel has spurred the European Communities to accelerate their quest for the more “perfect” building. Many of us in North America are again in quest of this perfection.
A Passive House is more than just an ultra thick blanket of insulation, however. The “blanket” must be designed to minimize air leakage, and as we all know, it can get stuffy under a blanket that doesn’t offer some modicum of ventilation. Enter an effective ventilation system that supplies fresh outdoor air. Ventilation is essential, but when we ventilate in our cold climate we dump lots of warm, stale air into the winter night. So, we ventilate with what is called an energy or heat recovery ventilator. In slightly more moderate climates (such as much of Germany), an ERV is about all that’s needed to heat a super-insulated and non-leaky home.
Here in northern Vermont we need a little extra heat, and this can be provided by an electric heating coil placed within the ductwork of the ERV. Or, if a little romantic bio-fuel is desired, one could install a pellet or wood stove, perhaps with a hot water coil on the back to provide supplemental hot water for showers and washing dishes. Increasing in popularity is a mini-split air-to-air heat pump. These devices extract heat from outside air and add it to your interior heating needs. The advantage to these little babies is that they can run in reverse in summer and help cool your house. This device runs on electricity as well. It should be stressed that the heat load, even in our climate, is minimal. For the electric heating coil or heat pump, a photovoltaic array on the roof would supply the electricity required for the coil/pump as well as supplying additional renewable power for your home’s lighting and electrical needs.
I believe the idea behind passive House is sound. Spend a little extra money on the building envelope and save money on the cost of a heating plant and distribution system. The Passive House has fewer moving mechanical parts and very high overall building performance. Save money on heating fuels (the cost is only going up), and dump less carbon into the air. All is good.
A couple of other points worthy of discussion: with a sound building envelope, fresh air supply and a modest heating source, we still need natural light to live and grow. While windows are vastly improved with regard to thermal effectiveness, they still fall far short of a well-insulated wall. So Passive House logically places windows on the south side with more modest amounts of glass on the east, west and north. A good window on the south side of our houses, even in the Vermont winter, is still a net heat gain, so this glazing contributes heat to the house’s needs.
Passive House is a great idea. The certification process looks complicated, but the design and calculation principals are sound. A good rule of thumb is keeping the shape of your home straightforward… even box-like. Think of our ancestors who populated much of the New England landscape. Their buildings were remarkably straightforward and often the more elegant for that simplicity. That simple beauty lies at the root of our building traditions and Passive House seems like an idea that New Englanders will embrace.