|Fig. 1: A heat-map exemplifying the drastically low heat loss from a passive house (right) as compared to an ordinary building (left). (Source: Wikimedia Commons)|
Almost 75% of Germany's domestic energy consumption goes towards heating and cooling for houses. While the number may seem staggering, it is not much different from the consumption patterns of most Northern European countries. Enter: the Passive House (or Passivhaus, in German).
The passive house is an ultra energy-efficient design for houses that utilizes very little energy for heating and cooling spaces. Using a combination of special construction supplements, and knowledge of conduction of heat, passive houses can cut the energy consumption of an average home by up to 85%, as exemplified by the most recent trials.  The passive house project began in Germany in 1990, and there are currently between 15,000- 20,000 passive homes in the world, with the closes to us being in Menlo Park. 
In order to become a designated passive house, certain construction standards must be met. For central Europe, these standards are :
The building must not have an annual heating and cooling demand of more than 15 kWh/m2 each.
Total primary energy consumption (energy for heating water, electricity etc.) must not be more than 120 kWh/m2.
The building must not leak more air than 0.6 times the volume of the building each hour.
|Fig. 2: One of the original passive houses, built in Germany in 1990. (Source: Wikimedia Commons)|
The buildings are designed to maximize solar gain, to reduce energy consumption for heating. However, for more temperate months, unwanted solar gain is reduced using techniques ranging from gardening strategies to shade windows, to using tools such as green roofs (rooftops covered in vegetation). In addition, the houses are designed with super-insulated walls, i.e. insulation material and techniques that reduce heat transfer between rooms, and to the exterior of the building.
While natural ventilation is a key component to the Passivhaus design, some builders also install earth warming tubes that are generally 8 inches in diameter.  These use the earth's natural subterranean temperature to heat or cool the ventilation taken in by the building. This form of ventilation, coupled with sophisticated window design, helps use as much of natural resources as possible, limiting the need for further energy consumption. Passive houses also sometimes have a dual-purpose heating and cooling unit, designed to keep the heating load under 10 W/m2.
Passive Houses are not built like other energy-efficient houses (such as the zero-energy building). The underlying idea is that these houses will use and misuse as little energy as possible, as compared to other initiatives, where houses generate their own energy from solar or wind sources, only to utilize that while not really reducing their carbon footprints. Conservation is at the very core of the passive house design, and it requires superior engineering that asks the important questions about energy efficiency, and optimal utilization.
© Nadiv Rahman. The author grants permission to copy, distribute and display this work in unaltered form, with attribution to the author, for noncommercial purposes only. All other rights, including commercial rights, are reserved to the author.
 E. Rosenthal, "No Furnaces but Heat Alenty in 'Passive Houses'," New York Times, 26 Dec 08.
 M. Gröndahl and G. Gates, "The Secrets of a Passive House," New York Times, 25 Sep 10.
 W. Feist et al., "Climate Neutral Passive House Estate in Hannover-Kronsberg: Construction and Measurement Results," Passivhaus Institut, 2005.