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Airtightness and non-uniformity of ventilation rates in a naturally ventilated building with trickle vents

Jessica Few, David Allinson, Clifford Elwell, 2019
ventilation | airtightness | measurement | indoor air quality | building regulations.
Bibliographic info: 40th AIVC - 8th TightVent - 6th venticool Conference - Ghent, Belgium - 15-16 October 2019
Languages: English Pages (count): 10

Infiltration is an uncontrolled contribution to ventilation in a building and can contribute significantly to the total ventilation rate, particularly in older, leaky, dwellings which can rely on infiltration to provide adequate indoor air quality. However, as explored in this paper, using a whole house airtightness metric to characterise ventilation rates can fail to identify low ventilation rates in specific rooms. 

Measurements were undertaken in autumn and winter for a dwelling with an airtightness (by blower door) of 15.1 m3/hr/m2@50Pa. The dwelling was built in the 1930’s: semi-detached, suspended timber floors, cavity walls and retrofitted throughout with double glazing incorporating trickle vents.  

The whole dwelling ventilation rate (by CO2 tracer gas decay) with the trickle vents closed was  0.7 ach, and 0.8 ach with the trickle vents open. However, the ventilation rate (by CO2 tracer gas decay) in a single room with its internal door closed under different weather conditions was only 0.17 ach (standard deviation = 0.06 ach, number of measurements = 34), and with trickle vents open 0.32 ach (standard deviation = 0.13 ach, number of measurements = 40). This is  below the 0.5 ach required for good indoor air quality. This is likely related to the closed internal door reducing cross-ventilation and the non-uniformity of air leakage paths in the dwelling. The leakage paths were investigated using smoke pens during a pressurisation test and significant air leakage paths were observed in other rooms: through the under stairs cupboard, around services in the kitchen and bathroom, and through the ceiling into the loft. 

Low air change rates have been observed in a building with very low airtightness, typical of older stock in the UK. The dwelling was retrofitted with double glazing, which is likely to have significantly affected the airflow, but still left the dwelling with low total airtightness. The double glazing had trickle vents, but these did not provide adequate ventilation. Inclusion of trickle vents in replacement windows is ‘good practice’ according to English building regulations, but not compulsory if there were no vents in the previous windows. Similarly, undercuts are required for doors in new dwellings, but are only required for existing buildings in new wet rooms; the tested dwelling had undercuts half the size required for ventilation regulations in new buildings. 

The difference in ventilation rates at different spatial scales is rarely discussed, but this research shows that there can be major discrepancies. This paper discusses the implications of this for appropriate measurement of ventilation, and the implications for ventilation regulations and guidance as well as the need for further research into the complexity of the manifestation of ventilation in occupied buildings. 


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