Ambient air filter efficiency in airtight, highly energy efficient dwellings – A simulation study to evaluate benefits and associated energy costs

Highly energy efficient buildings such as ones built to the Passive House standard, require a very airtight building envelope and the installation of a mechanical ventilation with heat recovery (MVHR). MVHR systems incorporate ambient air filters, which reduce the introduction of particulate matter (PM) from outdoor sources into the dwelling. However, indoor PM sources, e.g. cooking, can also contribute substantially to occupants’ exposure and need to be accounted for when designing ventilation or deriving recommendations for filter classes. 
This simulation study investigates which ambient air filter class is a reasonable choice in terms of indoor air quality and energy use for highly airtight residential housing. It considers outdoor and indoor generated size-resolved PM, while comparing different cooktop ventilation concepts. Results confirm that a F7 filter according to EN 779 (or equivalent) is a reasonable choice for low or short-term moderate ambient air PM concentrations, as total PM exposure will be dominated by indoor sources and higher filter classes will therefore not provide a substantial exposure reduction. For locations with high outdoor PM concentrations, the use of a high-class filter like F9 is advisable, as it will further reduce the exposure. In locations with low ambient air pollution, cooking emissions could likely contribute a substantial or even dominant fraction of the total PM exposure, if no measures, like an effective cooker hood system, is used. Here, the use of an extracting hood shows clear advantages over a recirculating system. However, for cases with elevated ambient concentrations, the use of extracting kitchen hoods (with unfiltered make-up air) will increase the total PM exposure for cases with low or moderate cooking intensities.