Good write up on the Passive House standard in the Journal of Light Construction this month. See the original article [here].
“There’s no doubt that the Passive House approach works. Experience shows that buildings constructed to the standard do use dramatically less energy than conventional structures. They offer excellent air quality, resist excessive solar heating, and maintain comfortable levels of temperature and humidity with little effort on the part of their occupants. ”
It’s a long article, so I’ll repost it in 3 parts.
Passive House Seeks Broader Appeal The Passive House concept is an approach to energy-efficient building that – compared with conventional code-compliant construction – reduces energy use for heating and cooling by up to 90 percent. The “passive” part of the name is meant to emphasize that those savings are achieved through passive heat gain, building-envelope efficiency, and high levels of insulation, rather than through “active” strategies like on-site power generation or collection and storage of solar heat. While quite popular in northern Europe – particularly in Germany, where it was developed during the 1990s – the method has only recently drawn much attention from designers, builders, and homeowners in North America.
Some of that surge in interest can be traced to a December 2008 New York Times article that described Passive House as “part of a revolution in building design.” While generally accurate, the story did stumble a bit coming out of the gate – it was titled “No Furnaces, but Heat Aplenty in ‘Passive Houses’” – since most cold-climate Passive Houses do in fact include a heat pump, small furnace, or some other supplementary heat source.
Tight budget. The core of the Passive House concept is a clearly defined standard that holds structures to a strict energy budget based on their floor area: They must use no more than 15 kwh per square meter per year for heating and cooling, and no more than 120 kwh per square meter for all uses, including lighting, appliance use, and hot water. (The 120 kwh figure refers to primary energy, which accounts for energy lost in converting fossil fuels to electricity.) In addition, a Passive House must have an air-infiltration rate of no more than 0.6 ACH50, as measured by a standard blower-door test.
These numbers are inflexible with respect to latitude or climate zone. A structure in the Canadian interior, for example, is allowed no more energy for heating than one in a relatively mild climate, such as the Pacific Northwest. It’s up to each project designer to work out a site-specific construction plan that will hold energy to an acceptable level.
Potentially net zero, but not necessarily green. That one-size-fits-all approach doesn’t please everyone. The standard calls for levels of insulation that some critics find excessive. Particularly in cold climates, they argue, mandated R-values may be so high, and heat losses so low, that it would be more cost-effective to cut back on insulation, buy a few solar panels with the resulting savings, and use them to power a slightly larger air-source heat pump – since such a backup heat source is ordinarily required anyway – to compensate for the small additional heat loss.
Cold-climate Passive Houses do indeed use eye-opening amounts of insulation. One northern Minnesota Passive House, for example, sits atop 16 inches of rigid polystyrene foam. But to Passive House loyalists, the cost-effectiveness argument is shortsighted. Insulation, they say, unlike heat pumps and PV arrays, is immune to mechanical failure, should last for the life of the building without any maintenance, and once installed is unaffected by rising energy costs.
Its reliance on conservation sets Passive House apart from the much more flexible net-zero approach to energy-efficiency, in which there’s no limit to the amount of energy a building is permitted to burn through (as long as its consumption is offset by on-site generation from solar, wind, or some other renewable source). There’s no inherent conflict between Passive Houses and net zero, however: Because a Passive House’s energy use is so low, adding a relatively small PV array allows it to qualify as a net-zero building as well.
The Passive House community also seeks to distance itself slightly from “green” construction methods, perhaps because Passive Houses rely heavily on the use of materials like plastic foam. The excellent introductory text Homes for a Changing Climate: Passive Houses in the U.S. – published by the Urbana, Ill.–based Passive House Institute U.S. (PHIUS) – puts it this way: “When comparing the costs of conventionally built homes and Passive Houses, there is a need to distinguish between costs associated with energy efficiency features and costs associated with green features. Energy-efficient construction costs less than building green. … Construction costs for a house built to both Passive House and green standards will be significantly higher than construction costs for a house built to Passive House standards alone.” In short, while Passive Houses are generally thought of as green – and are green, from the standpoint of their ongoing energy consumption – they may or may not contain only green building materials.
Posted on February 17, 2011