page_title: Blower door
section_title: History
hierarchical_section_title: Blower door / History
caption_attribution_description: Blower-door-test_it, Kino, Wikipedia Germany, http://de.wikipedia.org/wiki/Bild:Blower-door-test.PNG
context_page_description: A blower door is a machine used to measure the airtightness of buildings. It can also be used to measure airflow between building zones, to test ductwork airtightness and to help physically locate air leakage sites in the building envelope.
  There are three primary components to a blower door: a calibrated, variable-speed fan, capable of inducing a range of airflows sufficient to pressurize and depressurize a variety of building sizes, a pressure measurement instrument, called a manometer, to simultaneously measure the pressure differential induced across the face of the fan and across the building envelope, as a result of fan airflow, and a mounting system, used to mount the fan in a building opening, such as a door or a window.
  Air tightness testing is usually thought of in residential settings. It is becoming more common in commercial settings. The General Services Administration requires testing of new US federal government buildings.
  A variety of blower door airtightness metrics can be produced using the combination of building-to-outside pressure and fan airflow measurements. These metrics differ in their measurement methods, calculation and uses.
context_section_description: Blower door technology was first used to measure building airtightness in Sweden around 1977.  This earliest implementation used a fan mounted in a window, rather than a door.  Similar window-mounted measurement techniques were being pursued by Caffey in Texas, and door-mounted test fans were being developed by Harrje, Blomsterberg and Persily at Princeton University to help them find and fix air leaks in homes in a Twin Rivers, New Jersey housing development.  Harold Orr has also been identified as a member of a group in Saskatchewan, Canada who was pursuing similar testing methods.
  These early research efforts demonstrated the potential power of blower door testing in revealing otherwise unaccounted for energy losses in homes.  Previously, air leakage around doors, windows and electrical outlets was considered to be the primary leakage pathway in homes, but Harrje, Dutt and Beya used blower doors to identify “thermal bypasses”.  These bypasses were air leakage sites, such as attic utility chases, that accounted for the vast percentage of air leakage energy losses in most homes.  Use of blower doors in home energy retrofitting and weatherization efforts became known as “house doctoring” by researchers on the East and West coasts.
  The blower door first became commercially available in the United States in 1980 under the name Gadsco.  Harmax started to sell units in 1981, followed closely by The Energy Conservatory in 1982. 
  While these blower door-testing efforts were useful in identifying leakage pathways and in accounting for otherwise inexplicable energy losses, the results could not be used to determine real-time air exchange in buildings under natural conditions, or even to determine average annual air exchange levels.  Sherman attributes the first attempt at doing this to Persily and Kronvall, who estimated annual average air exchange by:
   = Natural Air Changes per Hour [1/h]
   = Air Changes per Hour at 50 pascal [1/h]
  
  Further physical modeling efforts allowed for the development and validation of an infiltration model by researchers at Lawrence Berkeley National Laboratory (LBNL).  This model combined data derived from blower door tests with annual weather data to generate time-resolved ventilation rates for a given home in a specific location.  This model has been incorporated into the ASHRAE Handbook of Fundamentals (1989), and it has been used in the development of ASHRAE Standards 119 and 136.  Other infiltration models have been developed elsewhere, including one by Deru and Burns at the National Renewable Energy Laboratory (NREL), for use in whole-building performance simulation.
caption: Simplified schematic diagram of blower door pressure testing
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