Asymmetric radiant fields and human thermal comfort




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De Montfort University


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Peer reviewed


The main purpose of this thesis was to develop a first principles model for predicting human local thermal comfort responses to asymmetric radiation environments. The research deployed state-of-the-art computer simulation techniques to model in detail inhomogeneous short-wave and long-wave radiative heat exchanges of standing and sedentary humans. Detailed 3D human geometry models, simulation software incorporating advanced, voxelbased ray techniques and statistical regression analysis were used to accurately model human local geometry-related characteristics, i.e. projected area factors with respect to both direct and diffuse solar radiation, and view factors for individual parts of the human body. The local projected area factors with respect to direct short-wave radiation (fp,dir) were presented as functions of the solar azimuth angle (a) between 0 0< a < 3600 and the solar altitude (jJ) angles between -900 <fi<+90o. In case of diffuse solar radiation from the isotropic sky the local human projected area factors (fp,dij) were modelled as a function of the ground albedo (pg) ranging between 0< pg <1. The functions were validated against available experimental data and showed good general agreement with projected area factors measured for both the human body as a whole and for local quantities. The view factors of individual body parts were modelled as functions of local projected area factors. This technique makes it possible to predict view factors between individual body parts and surrounding surfaces for almost any arbitrary geometrical configurations. ?Validation showed good agreement with available experimental data for both standing and sedentary humans. The detailed projected area factors and view factors developed were used in conjunction with the IESD-Fiala multi-node model of human heat transfer and thermal comfort to predict thermal responses of subjects exposed to various asymmetric radiation conditions. The extended model showed good agreement with available measured data obtained for frontal, lateral, horizontal and vertical thermal radiation asymmetries as well as for direct solar radiation. A new comfort model was developed using physiological parameters which predicts human local responses to asymmetric radiation in terms of percentage of dissatisfied due to local discomfort. Both local cold discomfort (LCD) and local warm discomfort (LWD) which are based on different physiological principles - were modelled as two separate responses. LCD was found to be a function of the sensitivity-weighted local skin temperature as related to the actual general thermal state of the human body described by the mean skin temperature. LWD was modelled as an exclusive function of local influences, i.e. the (sensitivity-weighted) local skin temperatures and the corresponding local setpoint values (referring to skin temperatures in a thermo-neutral environment of 30?C). The new model was verified and validated using various experiments in which the subjects were exposed to different types of asymmetric radiation conditions. The test showed good/acceptable level of agreement with measured data regarding the percentage of dissatisfied due to local discomfort, the location on the body where discomfort was perceived, as well as the dynamics of the local response (Le. time dependence). The new comfort model was linked with a building simulation program to predict thermal comfort conditions in buildings. A computational procedure was developed to enable this in conjunction with ESP-r which is one of the most well known building simulation programs. The new link enables researchers to perform detailed thermal comfort analysis and occupant implications of the dynamic climate conditions in buildings with daily, monthly, seasonal and annual statistics, and facilitates to quantify the thermal comfort implications of different building designs and individual constructions.





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