Infiltration

Air-tightness testing has been a requirement of the Building Regulations for new and refurbished properties since 2006. In an air-tightness test a fan is attached to an opening in the building envelope and used to pressurize the building up to 50 Pa above atmospheric pressure. The curve of volume flow rate against pressure together with the area of the envelope is used to determine an air permeability value, Q₅₀/S_p [m³ h⁻¹ m⁻²]. For industrial buildings such as factories and warehouses 10 m³ h⁻¹ m⁻² represents good practice and 3.5 m³ h⁻¹ m⁻² represents best practice, according to CIBSE TM23:2000. Atkinson Science can convert the air permeability to an effective leakage area, ELA [m²]. From a survey of the building we can say reasonably accurately how the leakage area is distributed over the building envelope (often at the roof and floor lines and around doors and windows). Then from calculations of wind pressure and the stack effect we can estimate the leakage flows into or out of each opening. These leakage flows can be included in a CFD calculation of the internal environment to see how well the air-conditioning system copes with the infiltration. Sometimes the infiltration can overwhelm a perfectly well designed air conditioning system. If the environment in a building is uncomfortable, it is important to determine whether the source of the problem is infiltration before embarking on a costly programme of retrofitting. Click on the links below to see how Atkinson Science has calculated the leakage flows in a building and used CFD to determine their effect on the internal environment or contact Atkinson Science to discuss a problem involving infiltration. Contact us.