An experimental evaluation of HVAC-grade carbon dioxide sensors -Part I: Test and evaluation procedure

Carbon-dioxide sensors are widely used as part of a demand controlled ventilation (DCV) system for buildings requiring mechanical ventilation, and their performance can significantly impact energy use in these systems. Therefore, a study was undertaken to test and evaluate the most commonly used CO₂ sensors in HVAC systems, namely the non-dispersive infrared (NDIR) type. The procedures presented here provide a methodology to test and evaluate NDIR CO₂ sensors for accuracy, linearity, repeatability, hysteresis, humidity sensitivity, temperature sensitivity, and pressure sensitivity. The test and evaluation procedures presented in this paper are all inclusive in that they range from procuring the CO₂ sensor to comparing the performance of the sensors. Specifically, a procedure is presented to both procure CO₂, sensors from the manufacturers and to maintain quality control by controlling the storage and handling of the sensors. Further, it describes the apparatus and instrumentation. along with test conditions, used to test the sensors. Additionally, it outlines a detailed experimental procedure to evaluate the accuracy of the sensors. Finally, a discussion is presented on analyzing and comparing the performance of CO₂ sensors by using the test data. Partial results of the accuracy test and evaluation of the CO₂ sensors and the results of the linearity, repeatability, hysteresis, humidity sensitivity, temperature sensitivity, and pressure sensitivity evaluation are included in this paper. The full test results will be presented in a later publication.