Estimating Black Globe Temperature Based on Meteorological Data

Abstract

An automatic weather station, comprising of temperature and humidity sensors, a pyranometer, an anemometer, and a thermocouple inside a black globe, was installed in a grassed area at the University of the State of Bahia-UNEB, Juazeiro County, Bahia State, Brazil. Half of the data collected at this station was used to generate models (simple or multiplicative) for estimating the Black Globe Temperature (BGT). Model performance was evaluated by using the second half of the data. Statistical precision and accuracy indices and statistical errors were used to analyze the collected data and the Student`s t test was used to evaluate the significance of the model parameters. Two models to estimate the BGT using meteorological variables were obtained: BGT d = [1.360 T air d-2.358]⋅[0.075 ln(Rs)-0.562] and BGT n = [0.942 T air n ]. One model was elaborated for daytime BGT d), when the air temperature (T air d) and solar radiation (Rs) were combined to generate a multiplicative model (R 2 = 0.877), and a second model was developed to determine the BGT values for night-time (BGT n) based on the night-time air temperature (T air n) (R 2 = 0.962). The models developed resulted in great performance to predict the black globe temperature, allowing the estimation of bioclimatic indices to assess the conditions of the environment, to accomplish regional studies, and to indicate best house designs for animals.

Accuracy of Mean Radiant Temperature Derived from Active and Passive Radiometry

“…The required input T mrt may be derived, assuming that it is a linear function of t a [51,52], i.e., radiant flux densities are only estimated. In more recent approaches, T mrt is explicitly derived from readily available standard meteorological data that include the above-mentioned data from active radiometry (e.g., [24,34,53,54,67]). Here, T mrt,r,BG can be calculated for a black globe by means of Equation (3) using f p = 0.25 and α sw,Sk = 0.95.…”

“…Then, Equation ( 7) is solved for T g by iteration or by using empirical/polynomial methods. As this study found, it is advantageous for such empirical approaches to differentiate during the daytime between conditions in which the black globe is sunlit or is shaded [50] and to address separately nighttime data that are more closely linked to t a (Figure 4a) [54,69]. From the correlation of modeled against observed t g [49,50,54] and from the difference T mrt,Tg,BG − T mrt,r,KMM as a function of t g [70], it is apparent that the observed t g exhibits the same problem as seen here, especially under sunny conditions (see Figure 4a,b, Table 4).…”

“…Figure 4 examines some of them and their implications for the derived T mrt,Tg,BG . It is also closely related to frequent attempts to predict t g based on standard meteorological measurements [34,[49][50][51][52][53][54]. Figure 4a relates t g ( • C) to t a ( • C), where t g is split into three bins of radiant conditions: (i) at nighttime, i.e., sun is below the horizon, at daytime dependent on the value of E I : (ii) cloudy, i.e., E I < 120 (W/m 2 ), no sunshine according to WMO [14], and (iii) sunny, i.e., E I ≥ 120 (W/m 2 ).…”