scope:

INTRODUCTION

This is part four of a four-part series of papers reporting on the test and evaluation of typical CO₂ sensors used in building HVAC systems. In this study, fifteen models of NDIR (non-dispersive infrared) HVAC-grade CO₂ sensors were tested and evaluated to examine the affects of ageing on sensor performance. To compensate for sensor ageing, some sensors automatically reset the baseline value (normally 400 ppm) according to minimum CO₂ concentration observed over a time period. This technique relies on the fact that many buildings experience unoccupied periods during which CO₂ levels drop to outdoor levels. Other techniques used to compensate for the sensor ageing include dual-lamp, single-wavelength and single-lamp, dual-wavelength configurations. The working principles, physical construction, advantages and disadvantages of NDIR CO₂ sensors are well documented in the literature (Raatschen (1990), Emmerich and Persily (2001), Schell and Int-House (2001), Fahlen et al. (1992)).

Among the 15 models tested, eight models have a singlelamp, single-wavelength configuration, four models have a dual-lamp, single-wavelength configuration, and three models have a single-lamp, dual-wavelength configuration. In all, 45 sensors (three from each model) were evaluated. The tests were designed to assess the performance of the sensors while they operated under typical building conditions for a one-year period.