Improved predictive ability of climate-human-behaviour interactions with modifications to the COMFA outdoor energy budget model

The purpose of this paper is to implement current and novel research techniques in human energy budget estimations to give more accurate and efficient application of models by a variety of users. Using the COMFA model, the conditioning level of an individual is incorporated into overall energy budget predictions, giving more realistic estimations of the metabolism experienced at various fitness levels. Through the use of VO₂ reserve estimates, errors are found when an elite athlete is modelled as an unconditioned or a conditioned individual, giving budgets underpredicted significantly by -173 and -123 W m^-2, respectively. Such underprediction can result in critical errors regarding heat stress, particularly in highly motivated individuals; thus this revision is critical for athletic individuals. A further improvement in the COMFA model involves improved adaptation of clothing insulation (I_cl), as well clothing non-uniformity, with changing air temperature (T_a) and metabolic activity (M_act). Equivalent T_a values (for I_cl estimation) are calculated in order to lower the I_cl value with increasing M_act at equal T_a. Furthermore, threshold T_a values are calculated to predict the point at which an individual will change from a uniform I_cl to a segmented I_cl (full ensemble to shorts and a T-shirt). Lastly, improved relative velocity (v_r) estimates were found with a refined equation accounting for the degree angle of wind to body movement. Differences between the original and improved v_r equations increased with higher wind and activity speeds, and as the wind to body angle moved away from 90°. Under moderate microclimate conditions, and wind from behind a person, the convective heat loss and skin temperature estimates were 47 W m^-2 and 1. 7°C higher when using the improved v_r equation. These model revisions improve the applicability and usability of the COMFA energy budget model for subjects performing physical activity in outdoor environments. Application is possible for other similar energy budget models, and within various urban and rural environments.