filter

Ventilation filters are classified according to the results from standard laboratory tests. These tests, however, produce information which may be insufficient for estimating the true filter performance. The properties of a ventilation filter in the ambient air conditions may be quite different compared to filter behavior in the standard test. The disagreement may be especially strong in the case of electrostatically charged filters. The loss of electrostatic removal mechanism can lead to a significant decrease in the efficiency.

There has been lack of fact based knowledge for design and operation of supply air jilter for general ventilation. An Invent multi-component project was started in 1994 to tackle this problem area. The paper describes the basic performances of air filters and requirements to be included in the Design Guide Handbook, managed by Invent, Finland.

Samples of 31 different air filters, representative of the designs and efficiency range of those used in general ventilation, were tested at constant airflow. The complete array of ASHRAE Standard 52.1 tests was run on these filters, plus particle-size efficiency tests and tests measuring the reentrainment of dust from the filters when subjected to ultra-clean air flow. Additional samples of the same filters were then subjected to the same test array, except that VAV flow was simulated.

In this study, the odor generation of various components of air handling units was investigated. Results how that air handling system really can deteriorate the perceived air quality of the supply air. Almost all components seem to be sources of pollution, but differences between the components were significant. Used fiber filters seem to be the worst. A major reason for the pollution seem to be oily, dusty, and dirty surfaces.

Ventilation systems may in some cases be a major contributor to indoor air pollution. Several studies have shown that the pollution mainly originates from the filters. Microbial growth in the filters is seen as a cause for this pollution. The sensory pollution from a standard glass fiber filter and a glass fiber filter treated to inhibit microbial growth (both EU7) were compared. No clear pattern was found in the influence of the filters on the sensory air quality. The differences between the two tested filters were not significant.

Concerning artificial ventilation of interiors, microbial processes on air filters are assumed to cause pollution of the supply air with possible damage to the exposed persons' health. Therefore, the reaction of microorganisms on air filters was analysed in this project. The analysis focused on the influence of air temperature, relative air humidity, the filter medium and service life as determinants for microbial growth on air filters. The experiments showed that the parameters air temperature, filter medium and service life had no significant influence on microbial growth.