Air pressure testing is one of the many names given to an Air Tightness test. This one is slightly less favourable as it can be miss-conceived. Air pressure testing means exactly the same as Air Tightness Testing and Air leakage testing. But these two name are much more accurately describing the job in hand. Air pressure testing is still relevant to the job role due to the fact that pressure is obviously involved in an Air Test.
The figures used to calculate the final outcome of and Air Leakage test are all measures of pressure. When we are Air Pressure Testing, there are two key figures we are interested in. The first of which is building pressure. This very simply measures the pressure either being drawn from the building or increased within the building (Dependant if the test is a depressurisation test or a pressurisation test). For example, in a depressurisation test, the fan isn’t “Blowing air out of the property” it is actually dropping the building pressure 50 pascals below the pressure outside, surrounding the buildings outer shell. This then causes a rush of air back through any open gaps and cracks in the buildings outer shell to try and level the building building pressure back out, to be equal with, the outside air pressure.
The other figures we are interested in are Fan pressures. Very important whilst Air Leakage Testing. Fan pressure is simply as it sounds, this is the air pressure running over the fan whilst the test is underway. It is then from this figure and the building pressure we can work out the final Air Permeability score at 50 pascals (Whether it is a pass or a fail). To work this out, it is all done by the Air Pressure Testing equipment now a days. But the maths is actually very simple. A line graph is created to plot the readings. So one plot would be at 50 pascals (Building pressure) the fan was running at 165 pascals (fan pressure). That is then plotted on a graph with the remaining figures. A line of best fit is then added to the graph. This line has to be as tight as possible to all of the points, if not, the test becomes invalid and the test must be re-run. So this is how we make sure the test is a valid test. (It is a little more complex than this, with a few more boundaries and figures certain readings cannot exceed)
Then to actually work out the final Air permeability score, you simply Take the flow at 50 pascals, (So the fan pressure when the building pressure was at 50 pascals), then divide this figure by the envelope area of the development you tested (Envelope area is the area of all walls, floors ceilings and roof space making the outer shell ONLY of a building). This then gives your result to your Air Pressure Test. These scores are allowed to be between 0 and 10. Usually these days, most tests are set a target of 5.00 and achieve 3.00. Passivehaus and houses with MVHR can, and usually must be, lower.
So through all of this information, and this is the very basics, you can get an idea of where the name Air Pressure Testing came from. Air Leakage Testing and Air Tightness Testing are must more direct into describing what is going on during the test. Air Pressure Testing describes whats really going on within the test.
A little bit of background about the name Air Pressure Testing
(Image attached is not owned or claimed to be owned by Anglia Air Testing)