Understanding Ventilation in Occupied Case Study Dwellings with Trickle Vents and Mechanical Extract Fans
Jessica Few, UCL Energy Institute
Ventliation influences indoor air quality and the energy use of a building. In recent years, new buildings have become more airtight as part of the effort to increase energy efficiency and reduce the carbon emissions associated with buildings. However, sufficient ventilation must be attained for good indoor air quality; UK building regulations require new buildings to provide adequate ventilation for the people in the building. Four ventilation system types are recognised as sufficient to meet this requirement. Three of four of these systems utilise trickle vents: small closeable vents often found in window frames. There are relatively few studies on the effectiveness of trickle vents for providing adequate ventilation in occupied buildings, but most of the existing literature suggests they are not effective. This research focuses on four occupied dwellings with trickle vents and continuous mechanical extract ventilation. This research will compare the in-situ ventilation rates in these dwellings to the design ventilation rates put forward in the Approved Documents to the Building Regulations to understand whether the ventilation is adequate in practice.
Ventilation is influenced by weather conditions and occupant behaviour relating to use of windows, doors, fans and other ventilation technologies. Despite this, extended measurement campaigns which address the variability of ventilation rates and the influence of occupant behaviour are lacking. For this project, the ventilation rate will be measured using the tracer gas concentration decay technique with metabolically generated CO2 over several seasons. The windows and doors will also be monitored and this will support the insight into how ventilation rates are manifested in occupied dwellings, and how this ventilation rate varies in time and in different locations in the dwellings. This will allow a detailed understanding of the adequacy of the ventilation over time and space, rather than a ‘snapshot’ of the conditions.
The research also aims to understand how and why occupants engage with the building in ways which affect the ventilation. This includes their use of internal doors, windows, trickle vents and fans. Trickle vents are of particular interest because their sole purpose is to provide ventilation and they have been designed into newly built dwellings specifically to provide adequate ventilation in response to increased airtightness. The stated intention in ADF is that they are left open all the time, but previous examples in the literature have often found them closed. Detailed semi-structed interviews will be conducted to support understanding of how and why the occupants behave in particular ways and the effect these behaviours may have on ventilation rates.
The research will provide understanding of the sociotechnical issues around ventilation; in which the design of the building, its ventilation system, weather and occupant actions combine to result in adequate or inadequate ventilation conditions in occupied dwellings with trickle vents and mechanical extract fans. This ventilation strategy is extremely common and this kind of understanding will help to identify whether the system is adequate and whether and how it might be improved.