An experimental evaluation of HVAC-grade carbon-dioxide sensors - Part 3: Humidity, temperature, and pressure sensitivity test results

This is the third paper in a four-part series reporting on the test and evaluation of typical carbon-dioxide sensors used in building HVAC applications. Fifteen models of NDIR HVAC-grade CO₂ sensors were tested and evaluated to determine the humidity, temperature, and pressure sensitivity of the sensors. This paper reports the performance of the sensors at various relative humidity, temperature, and pressure levels common to building HVAC applications and provides a comparison with manufacturer specifications. Among the 15 models tested, eight models have a single-lamp, single-wavelength configuration, four models have a dual-lamp, single-wavelength configuration, and three models have a single-lamp, dual-wavelength configuration. The sensors were tested in a chamber specifically fabricated for this research. A description of the apparatus and the method of test are described in Part 1 (Shrestha and Maxwell 2009). The test result showed a wide variation in humidity, temperature, and pressure sensitivity of CO₂ sensors among manufacturers. In some cases, significant variations in sensor performance exist between sensors of the same model. Even the natural variation in relative humidity could significantly vary readings of some CO₂ sensor readings. The effects of temperature and pressure variation on NDIR CO ₂ sensors are un-avoidable without an algorithm to compensate for the changes. For the range of temperature and pressure variation in an airconditioned space, the effect of pressure variation is more significant compared to the effect of temperature variation.