Saturday, September 11, 2010

Blower Door Test

Yesterday Building Diagnostics performed the blower door test.
This test measures the air leakage of the house.  At 50 pascals the leakage was 658 cubic feet per minute.  That sounds like a lot, but it's really pretty good.  The total house volume, including basement and attic, is about 23,000 cubic feet, which translates into about 1.7 air changes per hour (ACH).  According to the "blower door test" link above, less than 5 ACH is tight, 5 to 10 ACH is moderate and more than that is leaky.
I wanted to see how much the heat recovery ventilator (HRV) added to this number.  The HRV has two 6" diameter ducts, one intake and one exhaust, going through the outside wall.  I took a piece of newspaper and put it up to the intake.  The air going in the HRV intake hood held the paper in place.  The CFM reading went down by about 10 percent just from this.  I would guess that, if the opening was sealed, there would be about 15 to 20 percent less infiltration.  However, the purpose of the HRV is to allow ventilation.  About 75 percent of the energy which would otherwise be lost can be recovered when it passes through the HRV.

When I took the photo above, I had the camera angled down, which skewed the perspective.  I decided to fix that, which is pretty easy with photo editing software.
The mat inset into the tile and the bench both factor into the final LEED rating.  It is recommended that dirt and contaminants be contained rather than tracked into the house.  The purpose of the walk-off mat is obvious.  The bench is a spot to sit down and remove your shoes.

Building Diagnostics will take the infiltration information, along with other information regarding insulation levels, HVAC equipment efficiencies and other factors including the capacity of the photovoltaic solar system and will use this to calculate a Home Energy Rating System (HERS) score.  This score indicates how much energy this house uses compared to a code minimum house.  Then that number will be translated into a point score that will factor into the final LEED score.

1 comment:

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