A Comparison of WGT Measured by a Modified Botsball and WBGT in a Hot, Dry Environment

Abstract

Wet globe temperatures (WGTs) measured by a modified Botsball were compared to wet bulb globe temperatures (WBGTs) measured by an electronic meter in a hot, dry environment. Three repetitions of measurements were made by the two instruments and an unmodified Botsball in an environmental chamber under 12 thermal conditions that included two levels of radiant heat, three levels of air velocity, and two levels of relative humidity at a constant dry bulb temperature of 39° C. Temperatures were compared by analysis of variance, regression analysis, and stepwise linear regression. The geometric mean of the WBGT, 31.3° C, was significantly greater than the geometric mean WGT measured by the modified Botsball of 28.7°C, which was significantly greater than the geometric mean WGT of 25.7°C measured by the unmodified Botsball. WGT measured by the modified Botsball was highly correlated to WBGT (r = 0.960). Stepwise linear regression for each of the indices using radiant heat, relative humidity, and air velocity as independent variables found that WBGT was most affected by radiant heat, and the unmodified Botsball was most affected by air velocity and relative humidity. The effect of these parameters on the unmodified Botsball was intermediate to the other two instruments. Modification of the Botsball resulted in WGT values that more closely approximated WBGT than those of the unmodified Botsball; however, the differences were still significant. It appears that additional reduction of the evaporative cooling area of the Botsball will be necessary to obtain WGT measurements that are closer to WBGT in hot, dry environments.