4704 – Analysis and Validation of a Psychrometric Apparatus PDF

This article uses the analysis of variance as a tool to validate a calibration apparatus for temperature and relative humidity sensors. The validation procedure establishes the operational ranges for measurement of the dry-bulb (tdb) and wet-bulb (twb) temperatures and of the relative humidity of air (RH) for this particular apparatus. Analyses are carried out testing twb as a function of air speed ranging from 1.25 to 5.00 m/s and twb as a function of RH and also compares two environments to calibrate tdb: either in thermostatic bath or in the airflow of a test section. The results show that air speed on wet covered sensors within the tested range of 1.25 to 5.0 m/s does not change the measured twb, thus widening the range suggested in ASHRAE Standard 41.1-1974. However, for relative humidity of air within the studied range, significant differences are found, and these are close to the 2-3% indicated range. The use of different calibrated sensors for tdb result in different calculated RHc values in a controlled environment.

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