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Three Blower Door Tests were conducted on ARC'08 over a 2-week period. A Blower Door Test measures the airtightness of a building and helps locate air leakages.
Doug Manthey of Conservation Technologies sets up the frame for the blower door. Contracting with MN Power, Conservation Technologies evaluates building performance. Results are compared with the Triple E Tier I or Tier II standards. In the case of ARC'08 we're aiming for achieving Tier II standards.
All known gaps are sealed and the building is depressurized using a “blower door.” The blower door lowers air pressure on the inside of the building by 2/10 of an inch on a manometer which is similar to a 20mph wind hitting the walls. Measurements are presented in a number of different formats, for the purposes of this article we are focusing on Air Flow and Air Changes per Hour.
Air flow
CFM50 is defined as the air flow in cubic feet per minute needed to create a 50-pascal pressure change in the building envelope. CFM50 is one of the most basic measurements of airtightness. The chart below shows how ARC’08 compares to average existing construction in MN, average new construction in MN and Energy Star Tier II Standards.
Air Changes per Hour (ACH) at 50 pascals
Air Changes per Hour (ACH) is a standard measurement used in blower door tests. One of the most common ways to normalize building airtightness is to calculate the number of times per hour that the total volume of the enclosure is changed, when the enclosure is subjected to a 50-pascal pressure difference. To calculate air changes per hour, the total volume of the enclosure is required in addition to the CFM50 measurement.
Passive House is the most aggressive set of energy efficiency standards in the world. An airtight shell, good insulation and use of passive energy sources are the primary components that minimize heat loss and generate heat. The Passive House standard requires airtight building shells of ≤ 0.6 ACH @ 50 pascal pressure. For more information on Passive House visit the Passive House Institute US
Peter Lofstrom of Evergreen Energy Audits checks for air leakage using neutral density smoke.
Although the blower door test is a good test of air infiltration it doesn’t give a complete picture of building performance. The openings in the house (windows and doors ) must have a good U/R rating. Insulation throughout the building must have as few flaws as possible. (ARC’08 has R-50 under the floor, R-50 side walls, and R-100 roof assembly).
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