Ventilation in washrooms and kitchens in high-rise residential buildings

Ventilation provisions in kitchens and washrooms in high rise residential buildings in Hong Kong are under a great concern, after the SARS outbreak incident. In this study ventilation rate in kitchens and washrooms in typical high-rise residential flats was estimated by injecting SF6 tracer gas inside. An air-change of 3.1 ACH was determined, when the washroom window was opened and all other openings were closed. When the exhaust fan was switched on and all other openings (include the window) were closed instead, a lower air-change of 1.7 ACH was measured. The result leads to a re-consideration on the adequacy of the contemporary sizing of typical exhaust fans in residential washrooms. In addition, when the re-entrant window in kitchen was opened, SF6 concentration was found to be fluctuating for 20 minutes after the injection, showing that the air was trapped in kitchen and re-entrant region. By comparing with the smooth decay observed when only mechanical exhaust was used in the same flat, opening the re-entrant window would be less preferable than using exhaust fan. This shows the importance of adequate sizing of the exhaust fan.