On-site testing of VOC detectors for Indoor Air Quality assessment

An increasing number of metal oxide semiconductor (MOS) gas sensors and sensor systems are in use to determine indoor air quality and/or support control of HVAC systems. One benefit of these low-cost MOS gas sensors is, that they are sensitive to a myriad of different volatile organic compounds (VOC). One drawback is that they also react to other gases. Furthermore, chemical properties of many chemical sensors can change during operation due to reversible or irreversible reactions, so drift and poisoning may downgrade the quality of the VOC detector output.

At the start of their operation, VOC detectors will typically work within the manufacturer’s speci­fication and deliver reliable results. But how reliable are the results after months or years of operation under a wide variety of atmospheric conditions? This can only be determined through testing.

Typical calibration procedures require sophisticated and expensive lab equipment, several gases/gas mixtures and many hours or even days. This is neither suitable for end users nor for installed VOC detectors, e.g. in HVAC systems. This paper suggests some test procedures for VOC detectors to check their performance in the field ranging from very simple “alive tests” to more elaborate “VOC release tests” that can provide a relative or, with more effort, even a quantitative assessment for one or more gases at fairly well-defined concentrations even in the field.

This paper is intended as a basis for discussion and exchange of experiences between VOC detector manufacturers, researchers and end users and can be extended to include further test protocols.