Introduction to Passive Houses

The term “passive house” originates from its German counterpart “passivhaus.” It is among most stringent standard in building energy efficiency today, with a typical carbon footprint 20% that of a conventional building. The passive house is accomplished by, among other things, the implementation of dedicated heat transfer ventilation systems and super insulation that significantly reduce heat transfer through walls, windows, flooring, and roofs. Passive houses require a very small amount of space heating and cooling because their tight envelopes preserve relatively constant indoor air psychrometrics. In effect, a passive house can cut down the need for active heating and cooling, which, is by far the greatest source of energy consumption within a building.

The Passive House movement has been around in Europe for about two decades and is just starting to take off in the United States. The slow adaptation is partly due to the 10 to 15 percent higher construction cost due to the need to import specialized European parts. As of 2010, an estimated 25,000 passive houses were present in Europe while there were only about a dozen in the US. By 2021, a European Union directive will come into effect where the passive house will become the construction standard for every European building. Although its name suggests a residential undertaking, the passive house standard can be implemented in institutional and commercial buildings such as high-rises, and supermarkets as well as institutional buildings such as college dormitories.

The passive house standard necessitates that a building fulfills certain conditions. It must consume under 4.75 kBtu per square foot of floor area annually in both cooling and in heating energy; the total primary energy consumption must be less than 38 kBtu by the same measure; and the number of air changes per hour in the building space must be below 0.6 while pressurized to 0.2 inches of water column. In addition, there are comfort criteria that must be met where indoor surface temperature variations must be kept to specified minimums. Having met such standards, a passive house can typically eliminate the need for a conventional heating system. Instead, the passive house can be sustained with a reduced-sized supplemental furnace or heat pump whose warmth is distributed by a continuously running, low-flow heat recovery ventilator system (HRV).

A passive house is designed so that most of the air exchange with the outdoors is accomplished by controlled ventilation through an air-to-air heat-exchanger in order to curtail indoor temperature changes during unfavorable weather conditions. Humidity is carefully controlled by sealing all joints, ductwork and wall penetrations. In addition, low energy ground source heat exchangers can pre-cool or pre-heat incoming air to temperatures closer to those of the exhausted air, as well as to provide frost protection for the HRV unit in the wintertime. Passive houses are characterized by having the same indoor temperature throughout due to HRV registers installed in most rooms. Furthermore, air quality is always remarkably clean due to air filtration in HRV units.

The need for an extreme level of air tightness requires a passive house design to incorporate with the architectural planning and conceptualization phases rather than as an add-on to existing buildings. In addition to walls, windows used in passive houses are manufactured with remarkably high R-values and thermal properties. It is customary for the windows of a passive house to lose the same amount of heat (very low) to the outdoors as its super insulated exterior walls, while being able to trap heat from the winter sun. To accomplish this, a triple-pane insulated glazing filled with noble gases, with air seals around thermally broken frames, are used. With passive solar gains and waste heat from household appliances and electronic devices, occupants can be comfortable in the winter in a passive house without a heater. Furthermore, indoor air temperature changes due to the opening of windows and doors are resilient and are quick to return to previous levels.

The passive house will undoubtedly assert itself in the American commercial and residential real estate market in the coming future. The energy crisis may be grim, but with the billions of dollars already saved in energy costs in Europe with the passive house standard, there is hope for sustainability in the future. Give us a call today at (347) 470-7090 if you are interested in implementing the passive house standard for a future project or if you would like to upgrade your existing facility with energy efficiency measures.

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