Use Of Inexpensive Psychrometers To Estimate WBGT

Generation of Models for Estimation of WBGT Using Mannix Digital Psychrometer and Manual Sling Psychrometer

Here’s how this calculator’s calculation of WBGT, based on weather data from a digital psychrometer or a sling psychrometer, was worked out:

1.  233 measurement sessions were carried out between June 26 and Sept 7, 2003. Devices used included industrial heat stress monitors ($2000) (2), and a variety of consumer psychrometers: Aspirated psychrometer ($170) (1), digital psychrometer ($105) (2), and sling psychrometer ($70) (2).

2.  Measurements were made according to the manufacturers’ directions, at intervals of no less than 20 min. (Median sampling interval = 33 min.)

3.  For each device type, Discomfort Index (DI) = (Dry Bulb Temp + Wet Bulb Temp)/2 was calculated, to approximate WBGT. These “raw” DI’s were then modeled to optimize correlation to measured WBGT. The results were subjected to statistical analysis, expressed as Mean Error (WBGT-DI) ± standard deviation.

4.  The results were as follows: Mean WBGT = 85 ± 7°F (Range: 59-95°F). Aspirated psychrometer error: Raw = 2.2 ± 2.0°F, modeled = 0 ± 1.2°F (N=233); Digital psychrometer error: Raw= -0.3 ± 2.0°F, modeled = 0 ± 1.8°F (N=357); Sling psychrometer error: Raw = 2.2 ± 2.7°F, modeled = 0 ± 1.7°F (N=328).