Passive stack ventilation.

The adequate ventilation of houses is essential for both the occupants and the building fabric. As air-tightness standards increase, background infiltration levels decrease and extra ventilation has to be designed into the building. Passive stack ventilation has many advantages - particularly when employed in low cost housing schemes - but it is essential that it performs satisfactorily. This paper give the results from monitoring two passive stack ventilation schemes. One scheme was a retrofit into refurbished local authority houses in which a package of energy efficiency measures had been taken and condensation had been a problem. The other series of tests were conducted on a new installation in a Housing Association development. Nine houses were monitored each of which had at least two passive vents. Measurements were taken over periods of three weeks in each dwelling and included; wind speed and direction, internal and external temperatures, humidity, and air velocity in the ventilation duct. The data were recorded every quarter hour. The results show air flow rates by the passive ducts equivalent to approximately 1 room air change per hour. The air flow in the ducts was influenced by both, internal to external temperature difference and wind speed and direction. An important finding was the need to site the vents in the correct location. In those houses where the vents were installed on the roof slope facing the prevailing wind, a location not recommended in current guidance, the air flow was in the reverse direction for the majority of the time due to the design of the terminal. However, in those houses with correctly sited vent terminals of recommended design, reverse flow was negligible.