Monday, November 17, 2008

All a bit abstract?

Wondering what the gear looks like? In the background of this shot (courtesy of the Canberra Times) you can see the 'blower door' or... fan depressurisation, air leakage analysis equipment. In the foreground you can see the thermal imaging camera. The large fan draws air out of the house causing the air outside, at higher pressure, to flow in through all the unsealed cracks and gaps in the building envelope. In this photo, you can see the hot air flowing in through the gaps above the glass doors, in the thermal image.

Using accurate pressure gauges and special software we quantify the air infiltration rate of the building in terms of air changes per hour (ACH) at particular pressures. The international standard for comparison is ACH at 50 Pascals. The majority of homes (old and new) we have tested so far have been greater than 20 ACH at 50 Pa. At normal pressures (4 Pa) this equates to 4-6 ACH ie. every 10-15 minutes the entire volume of air in the house is leaking out through unsealed gaps... no wonder our homes are so expensive to heat and cool!
(In Europe and North America they aim for just 1.5 - 3 ACH at 50 Pa - this means their houses are so air tight and energy efficient that they need to use mechanical ventilation to ensure air quality is maintained.)

As the fan depressurises the house we investigate with our camera, locating all the areas of air leakage as well as the gaps in insulation and areas of moisture build up.

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