air filtration

To study the impact of the filtration efficiency level on the particle concentration in a rural school equipped with a balanced ventilation system with heat recovery, measurements of indoor and outdoor particle concentrations have been carried out by using three different efficiency filters. The tested filters are respectively classed G4, F7 and F9 according to NF EN 779 (2012).

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. 

The thermal dynamic behaviour of buildings is solved by different methods; one of them is based on simulation by means of thermal node models. Computed results of the internal air temperature or the surface temperature are influenced by the used method, by the model for a solved problem situation, and by input values of model elements. The influence of the particular model element can be found by means of a sensitivity analysis.

The need to separate impurities from air or other gases has increased as regards both the degree of separation and the necessity to separate finer particles. An 85% efficiency filter is a prerequisite for the correct functioning of ventilation systems and to improve indoor air quality (IAQ).

Ventilation filters composed of electrostatically-charged fibers, also referred to as electret filters,are know to have the potential to decrease in filtration efficiency with use. However, little datahave been available on whether such decreases are seen in actual applications.

It is recommended to keep the ventilation filters dry. However there are manyventilating systems that cannot fulfil this requirement all the time. It is then interestingto know the state of filters in use, and how they perform during extreme wetconditions, especially at the end of their lifetime.This investigation includes used filters collected at the time of normal change offilters.The used filters absorbed a different amount of humidity. The particle filtrationefficiency was nearly the same as for unused filters (comparing only filter classF7/EU7).

k order to determine the amount of micro-organism present before and after the filters ofHVAC systems, 6 systems in 5 buildings were monitored every 2 weeks for one year. Measurementswere taken in triplicate and simultaneously before and after the filters using a sixstage Andersen sampler.

This paper presents ozone removal efficiencies, measured over an extended period of time, inthree different settings: a test plenum, an air handler providing outdoor air to a Class 100cleanroom, and a plenum downstream of an air handler providing outside air to a second, smallerClass 100 cleanroom. In each of these settings, the initial ozone-removal efficiencies werecomparable. After 8 years of service, the charcoal filters servicing the first cleanroom wereremoving about 60% of the ozone in the airstream.

Emissions from dust collected in air filters have been investigated using in situ and chambermeasurements. Two air filters (class F6 and F8/9) were exposed to outdoor air for a period ofsix months, after which measurements were carried out during continuous and intermittentoperation. Air samples were taken upstream and downstream of the filters and analysed forseveral substances, including VOCS, formaldehyde, microbial VOCS (MVOC), vital microorganisms,ergosterol and endotoxin.