Insights into the impact of wind on the Pulse airtightness test in a UK dwelling

Requirements for measuring the building airtightness have been proposed and included by many countries for national regulations or energy-efficient programs to address the negative effect of poor airtightness on building energy performance, durability and indoor environment. The methods for measuring building airtightness have continuously improved and evolved over a number of years. At present, the well-established and widely accepted method for quantifying the building airtightness is the fan pressurisation method (blower door being the most well-known), which can be implemented by pressurising the test building to a range of high pressures (usually in steps across 10–60 Pa range) and measuring the corresponding fan flow rate. As an alternative method, the Pulse technique can be utilised to measure building airtightness at low pressures (typically at 4Pa) by rapidly releasing a 1.5-second pulse of air from a pressurised vessel. It is known that the outdoor weather condition and in particular wind velocity can significantly influence building airtightness measurement. For example, ISO 9972 suggests a meteorological wind speed limit of 6m/s and 3m/s at ground level for the fan pressurisation test. However, limited studies have been conducted to evaluate the performance of the Pulse technique under windy conditions. In this study, a series of tests were carried out to measure the building airtightness of a five-bedroom house located at the University of Nottingham, UK using the Pulse technique under various wind conditions. A Pulse unit with a 58.5-litre air tank was employed to measure the building airtightness while an ultrasonic anemometer, located 12 metres away from the building perimeter, was used to obtain the outdoor wind speed at the height of 2.2 metres above ground level. Tests were conducted in March 2019 in a range of wind speed up to 10m/s. Experimental results demonstrate the viability of the Pulse technique for delivering airtightness measurements under certain wind conditions, although analysis has also identified conditions where the test result becomes invalid. This study provides insight into those conditions, which adversely affect the result produced by the Pulse technique and discusses possible areas of improvement to the measurement and calculation process to mitigate such effects. Based on the 423 Pulse tests undertaken, it is recommended that the Pulse tests should be performed when the wind speed is lower than 5m/s (with relative percentage difference of ±10%) in calm conditions and 7.4m/s (with relative percentage difference of ±20%) in windy conditions at the height of 2.2 metres above ground level to minimise the wind impact. If tests are to be carried out when the wind speed is above this limit, multiple Pulse tests should be carried out in order to reduce the wind impact on building airtightness measurement.