Investigation of the Effect of Radiant Heat Flux on Thermal Sensation and Thermal Comfort

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Although radiant heating systems - especially floor heating - have gained great popularity, the evaluation of thermal comfort of these systems through simulation is still based on models, which do not account for a precise representation of radiant heat exchange between the human body and its thermal environment. This might become an issue when significant radiant temperature asymmetries occur due to larger differences in surface temperatures of an indoor space. This could particularly be the case when planning a new heating system during renovation of older, less energy-efficient buildings with only medium-insulated exterior walls or windows. Existing comfort models either focus on convective heat transfer with simplified radiation terms or show other shortcomings (no physiological parameters, not applicable for asymmetrical conditions, etc.).Against this background, the objective of this proposal is to enhance an existing thermal sensation and comfort model – the Berkeley Comfort Model – by including a more detailed sub-model for radiant heat exchange between human body parts and their thermal environment. This sub-model will be developed by correlating subjective (responses from human subjects) and objective data (physical measurements), collected from experiments in a climate chamber under steady/uniform, steady/asymmetric, and transient/asymmetric thermal conditions using a newly developed device for measuring radiant heat exchange with single body parts. The enhancement will consider the Berkeley model's four partial models – local sensation, local comfort, overall (whole-body) sensation and overall thermal comfort – and will be based on statistical analysis, using different mathrmatical approaches for an optimal fit. For measuring the radiant heat exchange a new apparatus will be designed and built, which is composed of a modular radiant panel and a telescopic arm. The modular panel will consist of eight movable parts of the same size. Their front surfaces will be directed towards the respective body part and each module includes a heating element (copper electrical conductors), which creates the heat flux by the Joule effect.Validation of the enhanced Berkeley Model will be done with experimental data from further experiments with human subjects under thermally asymmetric conditions in a climate chamber. After that, as a prove of readiness, the enhanced thermal sensation/comfort model will be used to assess radiant heating systems under realistic boundary conditions in buildings. For this purpose, a case study scenario will be designed and a parametric study will be performed investigating thermal comfort in a room with varying insulation levels and thus surface temperatures of the exterior building parts as well as different surface temperatures of the radiant heating system (floor, ceiling).