A human thermal model for improved thermal comfort

Energy efficient very low-energy houses, passive houses and nearly zero-energy houses have a significantly lower heating power demand than traditional buildings. Therefore, the typical design and dimensioning criteria of conventional structural and building service system concepts need to be verified to avoid problems concerning the thermal sensation and comfort of the building users. Fanger’s Predicted Mean Vote, PMV-method is traditionally used for estimating thermal sensation and comfort. The PMV method is based on a heat balance model, also referred to as a “static” or “constancy” model. While assuming that the effects of the surrounding environment are explained only by the physics of heat and mass exchanges between the body and the environment, heat balance models do not take into account the human thermoregulatory system but view the human being as a passive recipient of thermal stimuli. According to previous research results, the PMV method progressively over-estimates the mean perceived warmth of warmer environments and the coolness of cooler environments. It is therefore valid for the prediction of thermal comfort only under severely restricted conditions. To accurately estimate thermal sensation and comfort in transient conditions, the calculation method should take into account the natural tendency of people to adapt to changing conditions in their environment by means of the human thermoregulation system. Human thermal models represent the human body from a thermokinetic point of view and they have been used for modelling the thermoregulation system. Over the last hundred years, numerous human thermal models have been developed. The utilization rate of these models has been low due to the complexities of the models and the difficult determination of calculation variables. This thesis presents the first approach, where a human thermal model is implemented in a building simulation environment: the Human Thermal Model (HTM). HTM can be used for predicting thermal behaviour of the human body under both steady-state and transient indoor environment conditions. It is based on true anatomy and physiology of the human body. The connection with the building simulation environment enables defining the external boundary conditions such as surface temperatures and radiation heat transfer more accurately than with the previous human thermal models. The thermal sensation and thermal comfort estimation methodology presented by Zhang is integrated in HTM. HTM tissue heat transfer, thermal sensation and thermal comfort calculation has been successfully validated under various steady-state and transient indoor environment boundary conditions comparing the simulation results to measurements made with real human beings. The simulated thermal sensations with the HTM method showed a better correlation with measured values than the Fanger’s PMV method. The boundary conditions for a good thermal comfort were estimated by studying the effects of various internal and external parameters on human thermal sensation. According to the simulation results, the operative temperature, metabolic rate and clothing are the most dominant boundary conditions for the human thermal sensation and comfort. As a module of the VTT House building simulation tool, HTM can be used for estimating the effects of alternative building structures, as well as building service systems, on occupants under different conditions more accurately and easily than before. This integrated method enables quantitative analysis of the significance of both external (structure insulation level, heating/cooling system) and internal (clothing, metabolism) boundary conditions on thermal sensation and comfort. The realistic thermal comfort of the user can be used as a design parameter for designing better thermal environments in new and renovated buildings. The various utilization possibilities of HTM were represented by two realistic case studies: effects of alternative energy renovation measures and heating distribution systems on thermal sensation and comfort.