Pulse tests in highly airtight Passivhaus standard buildings

Due to the minimal energy requirement, the Passivhaus standard has been widely recognised and adopted to deliver low carbon buildings. To achieve this standard, the thermal and physical properties of the building envelope have to meet a stringent criteria. It has set out the highest requirement for the building airtightness, which requires the envelope to achieve an air change rate less than 0.6 h-1 when the building is subject to a pressure difference of 50 Pa. Building an envelope with such a high level of airtightness can be extremely challenging. However, with careful planning and conscientious implementation, the required airtightness can be achieved regardless of the construction method. Airtightness measurement plays an important role in the journey of delivering Passivhaus standard building as it allows the construction team to quality check its airtightness at the key construction stages and ensures its airtightness level meets the predefined target.
Current standard approach for measuring building airtightness is the conventional steady fan pressurisation method, which establishes a pressure difference across the envelop by drawing air out of or blowing air into the building and measures the corresponding air flow rate to establish the leakage-pressure correlation. Differing from this steady-state method by maintaining the building integrity and delivering a dynamic measurement, the novel Pulse technique releases compressed air from an air tank into the building over a short period of time and simultaneously measures the building and tank pressure responses to achieve the same purpose but at low pressures. Alongside the steady method, the Pulse technique has been used to measure the airtightness of 11 Passivhaus standard properties to understand its feasibility in measuring highly airtight buildings. The results show that measured airtightness ranged from 0.29 m3/h/m2 @50Pa to 1.19m3/h/m2 @50Pa. The average difference between the two methods at 4Pa is 0.0003 m3/h/m2 @4Pa (11%) and 0.12 m3/h/m2 @50Pa (18%) at 50Pa when using the Power Law as a means of extrapolation.