Many multi-family development projects that are tied to tax credits must meet strict energy efficiency standards. We have worked on several projects that had to score below HERS 50 and we are currently working on one that will be HERS 0.
EVERY UNIT within the building must meet the required HERS score so a major challenge has been air leakage testing. In most units there is quite a bit of air leakage from unit-to-unit or from the unit to a conditioned hallway. Since this air leakage is from conditioned space TO conditioned space, it doesn’t have the energy penalty associated with air leakage to the outside. However, there may be other reasons to seal these leaks like odor control, sound transmission, stack effect, etc., but for these projects we are focusing on the HERS score.
Reduced air leakage, combined with ventilation per ASHRAE 62, is necessary to achieve a low HERS score. Most apartment units we test are in the 5-12 ACH50 range and we are now trying to reduce that to 2-4 ACH50. We suspect that most of the leakage is coming from conditioned space so we have been experimenting with different testing techniques.
Our first attempt took place in a 4-story new construction apartment building. We performed semi-guarded testing where we set up blower doors in 3 adjacent units, testing the middle unit while depressurizing the 2 adjacent units to -50 pascals. This testing resulted in ONLY a 3-5% reduction in air leakage compared to normal, unguarded testing.
In our latest attempt, we performed a Whole Building Air Leakage on a 3-story 44 unit multi-family new construction project. We first tested 7 units, unguarded, and the air leakage ranged from 9.3 to 14.2 ACH50. We then depressurized the entire building to -50 pascals using commercial blower door fans. While the building was at -50 pascals, we used 4 technicians with individual blower doors to test each of the 44 units. This Whole Building Guarded Test resulted in air leakage rates of 1.9 to 4.5 ACH50.
The Whole Building Air Leakage Test allows us to demonstrate the air leakage from each apartment unit to the outside, while neutralizing air leakage from conditioned space to conditioned space. The reduced air leakage rates we demonstrate significantly impact HERS scores.