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Purpose of the work
To which extent do leaky exhaust air dampers in extractor systems impact energy-efficient buildings?
To which extent do such dampers influence Blower Door tests?
Method of approach
Measurements at the test stand and calculation
Content of the contribution
Exhaust air dampers are part of an extraction system and a permanent penetration in the thermal building envelope, even though the vent is out of operation most of the time (about 23.5 hours per day). Exhaust air dampers with air leakages can cause considerable infiltrations resulting in significant heat losses. We used the MLM measuring system to detect leakages at different exhaust air dampers (masonry boxes). Depressurization and pressurization tests were carried out to determine the air leakage at each test specimen. The resulting air flow corresponds to the leakage of the test specimen plus the test stand. The test stand leakage is determined prior to each measurement by closing the test stand without the test specimen to conduct a “baseline measurement”. This baseline is then deducted from the results obtained when measuring the component. Several measurements were carried out for each damper at varying differential pressures ranging from 0 to 200 Pascal at the closed damper. Using a compensation function, the results were converted to the same condition to allow for a better comparability.
Results and assessment of their significance
The comparison was made at differential pressures of 5 and 50 Pascal, respectively. In this case, the low pressure of 5 Pascal is used as a reference for real operating conditions.
The leakage rate varied significantly at a differential pressure level of 50 Pascal. The variant "ventilation grille (bird protection)" constitutes a reference, since the building stock still has this variant. After having investigated all masonry boxes, two dampers from the DIY store stood out: These backdraft dampers were so leaky that they almost opened up fully during pressurization as soon as low differential pressures occurred. Test stand measurements attained a mere pressurization of up to approximately 10 Pascal, because a higher differential pressure was not feasible at the test stand fan due to this high leakage. A pressurization of 10 Pascal already indicated leaks ranging from 5 to 30 m³/h. When applying a differential pressure of 50 Pascal, the leakages at the other dampers were below 10 m³/h. Again, there were distinct differences between the dampers: A motorized damper had a leakage rate below 1 m³/, whereas another backdraft damper had a rate above 5 m³/h at 50 Pascal.
Leakage rates of all masonry boxes are below 5 m³/h at 5 Pascal. However, one backdraft damper from the DIY store and another more expensive backdraft damper had leakage rates of approximately 2 m³/h which are more than twice as high than the leakage rates of the other masonry boxes. Five of the nine investigated masonry boxes have leakage rates below 1 m³/h, three of the exhaust air dampers even below 0.6 m³/h. It is noteworthy that the closing mechanism does not seem to be a criterion for the quality of the leakage, because a spring-loaded backdraft damper was one of the three best dampers.
For further information please contact Søren Peper at: soeren.peper@passiv.de