Leakage tests measure the total crack area in a building, or part of a building. The building is pressurised and depressurised using a powerful fan, and the airflow through the leaks at a series of different pressures is measured. Relatively straightforward analysis then yields the leakage area, and can also give an idea of whether those leaks are via many small holes or a few relatively large ones. This gives a good indication of how tightly constructed the building is, an important piece of information if, for example, a ventilation heat recovery system is to be used successfully. The main air leakage paths can also be identified during the test, using a smoke tube to search for airflow, which is greatly emphasised by the action of the fan.
We carry out all our tests in accordance wih the Building Research Establishment recommended procedure:
Determining the air tightness of buildings by the fan pressurisation method: BRE recommended procedure
The equipment that the Energy Monitoring Company uses to carry out these tests was designed and built by ourselves. It features a very high quality flow measurement device, and an electronic motor controller. This allows us to consistently produce high quality results.
Once the total leakage through a building enevlope has been determined it is often of interest to see how this is apportioned between the different elements of the structure. This can be done using a technique known as 'reductive sealing' - a rather grand name for the simple process of successively sealing up sources of leaks. For example, if the proportion of the leakage occuring around the building windows is required the windows are all sealed (usually with masking tape and polythene sheet) and the measurement repeated. Any reduction in leakage observed is the contribution from the windows. Here the use of a high quality flow measuring device becomes very important. As with any subtractive technique the results can be very sensitive to measurement error. With our equipment we have consistently found that we can obtain good results in this type of test.
In some situations it may not be feasible to seal a particular type of leak. A good example is when testing a house in a terrace: you may be interested only in leakage to outside, but it is not feasible to seal every air path into the adjacent buildings. In this situation the very close control that we have over our fan motors allows us simultaneously to pressurise the adjacent buildings, giving a 'guarded pressure test' and measuring only the leakage to the outside.
Study bedrooms in a student residence building were proving impossible to keep warm. Leakage testing revealed that the rooms had four times as much air leakage as the average UK building. The leaks causing this were identified, and a series of measurements made as they were progressively sealed.
|Source of leakage||Contribution|
|Composite wall structure||39%|
|Storage shelf alcove||29%|
To the building operators' surprise the majority of the leakage turned was not around the poorly fitting windows, but through the external wall structure and a storage area at the far end of the room. Suitable sealing measures were recommended.
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