Modelling and Mapping Thermal Comfort Conditions with Solar Radiation: Comparison of Steady-State and Dynamic Indexes

AIM AND APPROACH Short-wave solar radiation may have a great impact on the indoor thermal sensation of occupants, especially in highly glazed buildings. The dynamic nature of the phenomenon suggests that steady-state approaches such as Fanger’s could be not completely suitable to analyze the performance of building design configurations or management and control strategies. This paper investigates the impact of solar radiation on some commonly used thermal comfort indices. In particular this study contrasts the steady-state PMV with dynamic indices (TSENS, TSV and DTS) based on Pierce’s thermophysiological model. Solar irradiation on the subject has been taken into account by means of an adjusted value of the mean radiant temperature according to La Gennusa et al. (2005) approach, which was originally proposed to correct Fanger’s PMV. The evolution of comfort conditions is mapped on a grid of reference points, which allows us to pay special attention to the irradiated area, closer to the glazing. The indexes capability of describing critical conditions is contrasted. SCIENTIFIC INNOVATION AND RELEVANCE Despite the use of highly glazed facades has become more and more common, the most used thermal comfort models do not account explicitly for solar radiation. The availability of a reliable and computationally efficient approach to include solar radiation contribution in thermal comfort metrics is of great importance for improving indoor environmental conditions either in the early design or during the operation optimization phases. In this work, the effects of short-wave solar radiation contribution have been included into different thermal comfort models by adjusting the mean radiant temperature (MRT) of the environment. The solar-adjusted metrics and the original ones are calculated in an open plan office of 100 m2 with a large window on the South façade, equipped with shading devices and a heating and a cooling system. The environmental variables are obtained by thermal simulation of the space in EnergyPlus. The results are then fed into an original simulation code implementing the traditional and the solar-adjusted comfort models in several reference points inside the space. The comfort conditions and their evolution are presented in detailed comfort maps, to contrast the capability of the solar-adjusted metrics to describe the quality of the thermal environment and highlight the main criticalities. PRELIMINARY RESULTS AND CONCLUSIONS Although under abrupt variations of the environmental conditions steady state indices such as PMV are far from being accurate in describing the occupant sensation, there is little difference between steady and non-steady approaches when considering the typical conditions inside a conditioned space. The four comfort indices, PMV, TSENS, TSV and DTS, seem to be equally suitable to assess the evolution of thermal sensation in conditioned buildings when warm sensation is prevailing and no solar radiation is to be included. Nevertheless, TSV requires a suitable calibration, being very sensitive to the choice of the reference mean skin temperature in the thermally neutral and steady state Tsk,0, and its scale must be resized with reference to the other comfort metrics. TSENS is the less affected by the mean radiant temperature correction when considering cooler conditions. In this respect, either PMV, DTS or calibrated TSV succeed in highlighting criticalities arising from specific positions of the occupants and time of day. In the current implementation, TSENS appears to be insensitive to cool environments. Further investigation is needed. MAIN REFERENCES Cappelletti, F., Prada, A., Romagnoni, P., & Gasparella, A. (2014). Passive performance of glazed components in heating and cooling of an open-