Filter pressure drop control in balanced ventilation systems for dwellings

As a consequence of the energy and environmental issues, it is necessary to reduce the energy consumption of buildings. So, the air tightness of building envelopes is being improved and the air change rate due to infiltration is decreasing. It is then even more important than in the past that the buildings are equipped with well designed and working ventilation systems in order that the air renewal within buildings is ensured. In this context, the market of balanced ventilation systems with heat recovery for dwellings is growing. 
In order to maintain the air flows of the balanced ventilation systems and to control their electricity consumption (one fan on each air circuit), it is necessary to define a maximum pressure drop value for the filters above which they should be replaced. 
The objective of our study was to determine the pressure drop increase of commercially available filters in balanced ventilation systems for dwellings as they are continuously used for long-term (1 year) with real outdoor air. The efficiency by particle size as well as the mass of dust collected were also reported. 
A very popular filter for balanced ventilation systems for dwellings is the panel mini-pleated filter type and this is why it has been considered in our study. It has been decided to study G4, F5 and F7 panel mini-pleated filters. Some of the studied F7 filters have been tested with and without a prefilter (class G4) installed upstream. Choosing a filter for balanced ventilation systems if not only a question of class. It has been shown that from the energy consumption point of view, it is better to use a F7 filter protected by a prefilter installed upstream instead of the same F7 filter alone because the increase of pressure drop is lower. A G4 prefilter appears suitable for the protection of the panel mini-pleated F7 filters but a more efficient prefilter can be necessary if the efficiency of the fine filter is high. Regarding the popular panel mini-pleated technique, the pleat width is an important parameter that has to be high enough to prevent fast surface loading of the filter. So a pleat width smaller than about 5 mm should be avoided. 
Energy savings issues should not reduce indoor air quality. The efficiency of the filters has to be high enough to insure that the balanced ventilation systems will provide clean air to the building and its occupants (well being and health issues). 
Finally, the results of our study are of a great interest for the design of filters for balanced ventilation systems in the context of low energy buildings.