The purpose of this study is to develop an improved human radiation exchange model for use by planners and researchers. Although applicable for all environments, emphasis will be on urban areas. All processes of radiation exchange between the human body surface and surrounding environments were investigated through human body area factors (effective radiation area factor, feff, and projected area factor, fp), existing human thermal exchange models and three-dimensional (3D) computer simulation models with collected microclimatic data. For new body area factors, a sample of standing contemporary Canadian adults in normal-weight (male: 31 persons, female: 40) and over-weight (male: 48, female: 20) body mass index (BMI) categories were analyzed. A 3D mean body model was created for each category. Only very small differences in feff and fp were found between genders and BMI categories. Differences in feff and fp values between this study and previous studies were very large, up to 0.101 and 0.173, respectively. Another common body posture, walking, was also studied for the normal-weight male and female BMI categories. 3D computer walking body models at four stride positions were created. The directionless fp values for walking posture had minor differences between genders and positions in a stride. However, the differences of mean directional fp values between azimuth angles were great enough (up to 0.072) to create important differences in modeled radiation receipt. When both standing and walking postures are considered, the mean feff value of standing (0.826) and walking (0.846), 0.836, could be used. However, fp values should be selected carefully because differences between directional and directionless fp values were large enough that they could influence the estimated level of human thermal sensation. A new human radiation exchange model was developed using the new body area factors and compared with five existing models and one method (Burt, COMFA, MENEX, OUT_SET* and RayMan models and the six-directional method) using collected microclimatic data observed in Guelph, Ontario, Canada. Most differences between models came from absorbed solar radiation, especially absorbed direct beam solar radiation because of differences in fp* (=fp×feff) and feff or some missing components (feff or view factors). The lowest differences between the new model and the RayMan model alter the net all-wave radiation estimate up to 29 Wm-2, which can be significant in the human thermal exchange model. For 3D computer estimation, a new human-urban radiation exchange simulation model was developed combining the new human radiation exchange model and improved urban area factors (i.e., albedos and view factors of sunny and shaded building, ground and vegetation surfaces). The results of the new computer model were compared with microclimatic data collected in Nanaimo, B.C., Canada and Changwon, Republic of Korea as well as with two other 3D computer simulation programs, RayMan Pro and ENVI-met 3.1. The differences between the collected data and the new model were very small. Their correlation was very strong, over 0.99 for total radiation. RayMan Pro and ENVI-met 3.1 programs had larger differences, and their correlations with measured data were weaker than the new model’s. Accurate meteorological and urban setting data should be obtained for better results. The new model will give planners and researchers a simple tool to estimate accurate radiation effects in complex urban areas. / Graduate