On-Site Particle and Gas Filtration Efficiencies of Air Handling Unit Filters in Industrial and Non Industrial Building

Air handling units are used to provide a mixture of fresh and recycled (recirculated) air to buildings. They include general ventilation filters for the removal of particles and gases in order to protect the components of the air handling units and to provide clean air to occupants. Standardised test methods exist for the laboratory performance assessment of particulate filters - EN 779 (2012) in Europe and ANSI/ASHRAE Standard 52.2 (2007) in USA - and gas phase filters - ANSI/ASHRAE Standard 145.2 (2011) in USA and draft International Standard ISO/FDIS 10121-2 (2012). Test results enable the comparison of filters against each other but they cannot be used to predict their in-situ performances because the laboratory loading pollutants are not necessarily representative of real pollutants. The EUROVENT 4/10 recommendation (2005) describes the measurement of the pressure drop and the filtration efficiency of HVAC filters on site (this may be one filter or a bank of filters depending on the size of the air handling unit) along with the airflow rate of the installation. It can then be verified that the efficiency of the filters is as expected and that the filters are correctly installed with no leakage or bypass. Results also give an idea about the particulate filter replacement frequency depending on their pressure drop. The EUROVENT 4/10 recommendation was used as a basis for the development of the ASHRAE Guideline 26 (2008) and the draft International Standard ISO/DIS 29462 (2011). For gas phase filters, no document covers the on site determination of the filtration efficiency.  This paper presents examples of results obtained in-situ for both particulate and gas phase general ventilation filters (an original method is presented for gas phase filters) and shows that the methods used are suitable for the inspection of the air handling units in relation to their filtration function.