Case studies of passive stack ventilation systems in occupied dwellings.

A possible alternative to mechanical extract ventilation for kitchens and bathrooms is passive stack ventilation (PSV). BRE has carried out work on this type of system in a test house under controlled conditions. To find out how well they worked in practice, four occupied dwellings were monitored over a period of 2 - 3 weeks each. Each dwelling had two ventilation ducts. Air flow rates within the ventilation ducts were measured, together with humidities, temperatures and climatological data. The results show that the risk of problems due to condensation can be reduced by the use of this type of ventilation system. The systems were found to have been poorly installed and where possible the faults were corrected as part of the study. Nevertheless the systems successfully kept down moisture levels below 70% RH for all but a small proportion of the time. The design and performance of the systems is discussed and advice given on how these could be improved. This study demonstrates the need for clear and simple guidance on PSV systems to enable them to work to maximum efficiency.