Building pressure adjustment is essential when conducting air tightness or pressurisation tests, especially when the tester’s location (inside or outside the building) affects the accuracy of flow pressure readings. This guide explains when and how to apply building pressure adjustment to ensure reliable results.
It is common that tests are performed with the building depressurised and the tester inside the building. This makes a lot of sense as the tester usually has easier access to power sockets, they can check that the temporary sealing inside the building has remained in place, leakage locations are easily identified by checking for drafts when a pressure is induced, the range plates and rings on the fan are the same side as the tester and they are keeping their gauges and laptop or tablet out of inclement weather.
However, there are occasions where pressurisation tests are undertaken, or the tester is located outside of the building for the duration of the test. Under certain conditions the flow pressure readings need to be adjusted to correct by the building pressure.
Example: When Building Pressure Adjustment Is Needed
Considering a flow pressure of -100 Pa the difference between the tester being inside and outside when pressurising using Energy Conservatory equipment is as follows:
Therefore, when pressurising and inside the building a correction must be applied to adjust the flow pressures to the correct value. This can be handled in one of two ways. The first is to apply a software adjustment to correct the flow pressure reading by the building pressure reading. The second is to connect an additional tube to the open port on the flow pressure channel and have the other end terminate outside the building.
For the tubing correction to the flow pressures the setup now changes as follows:
The flow pressures have now been corrected back to the correct values.
When using Retrotec equipment their software corrects the numbers as part of the calculation process. The numbers on the manometers are slightly different as they connect the fan to the reference port on the manometer channel rather than the input port as in the Energy Conservatory example above.
Considering a flow pressure reading of 100 Pa the difference between the tester being inside and outside when pressurising using Retrotec equipment is as follows:
Retrotec’s software then corrects the 150 Pa flow pressure when pressuring and the tester is inside by the building pressure reading on the blue pressure tap to reduce the flow pressure down to 100 Pa. The flow pressure numbers in the software remain the same but when the flow pressure is converted to flow from the calibration variables for the fan this is when the correction is applied.
If Retrotec’s software is not being used then a tube can be connected to the green pressure tap on the manometer with the other end terminating outside of the building. This will drop the flow pressure displayed on the manometer to 100 Pa.
Building Pressure Adjustment During Depressurisation
The corrections need to be applied, either by tubing or a software adjustment, when the building is being depressurised and the tester is located outside the building. In this instance you want to connect a tube to the open pressure tap on the flow pressure channel and have it terminate as close to the fans as possible without being influenced by the flows induced by them, such as in a nearby room.
The internal building pressure value should not be used as this may not be the same as the building pressure present near the fan. The further the distance that the building pressure tube is from the fan and the more convoluted the route the more likely it is that the building pressure by the fan will be greater than that at the geometric centre of the building due to pressure loss.
Which Building Pressure Adjustment Method Is Best?
In my opinion the tubing correction method is better as when depressurising and outside it allows you to use the building pressure by the fans for the correction whereas the software method assumes that this pressure is the same as the building pressure measurement even though it could be different.
