Evaluation of the optimum insulation thickness of building external walls and roof based on human thermal comfort criterion

The need to save energy in the buildings is a key priority, as buildings consume the largest share of energy and have the greatest potential for energy savings. A large amount of this energy consumed, is used for heating and cooling of the buildings. One of the measures that contributes substantially to energy savings in housing is the appropriate thermal insulation material of the exterior walls and the building envelope in general. However, determining the optimal insulation thickness (OpIT) based on economic indicators, such as net present value or pay-back period, has high degree of uncertainty due to the impossibility of accurately predicting future energy prices. In addition, considering one set-point temperature for the winter and another for the summer season does not ensure thermal comfort inside the dwelling. In the present study, a criterion based on the human thermal comfort index was used, to determine the optimal thickness of the insulation of the external walls and roof. Thus, a dynamic thermal simulation of a typical house, using hourly weather data of Athens-Greece and Larnaca-Cyprus was performed, and an optimization algorithm was used to determine the optimal insulation thickness for the roof and for each wall individually. In addition, for the calculation of the outdoor heat transfer coefficient, the wind speed and direction have been taken into account. For the considered typical house and the corresponding climatic data, the OpIT was found to range from 2.9 cm to 13.9 cm for Athens and from 3.2 cm to 14 cm for Larnaca for the east wall and roof respectively. This new approach to determine the optimal insulation thickness showed that proposed method can be utilized ensuring a comfortable and pleasant environment inside the building, for 8512 h and 8506 h during the year for Athens and Larnaca respectively.