Evaluation of the optimal thermal insulation thickness for an office building in different climates by means of the basic and modified cost-optimal methodology

Energy consumption for heating and cooling of Italian office buildings is growing. In particular, there is an increase in the demand for electricity for cooling in the summer. Thermal insulation on the external side of the buildings is a very usual strategy to reduce energy demand for air-conditioning systems. However, a too high thickness of insulating material, even if complying with current legislative requirements, can be disadvantageous in buildings characterized by great internal thermal loads and/or located in climatic contexts with mild winters and hot summers. In this paper, the energetic and economic influence of external thermal insulation is evaluated by using energy simulations under dynamic conditions (DesignBuilder software) for a case study. The analysis is performed for various cities (Palermo, Milan and Cairo) and for different values (10, 20, 30 W/m(2)) of internal thermal loads. According to the recent and innovative cost-optimal methodology, optimal insulation thicknesses are derived, and the results demonstrate the need to avoid excessive insulation of buildings to obtain the highest energy saving. Finally, an integration of the cost-optimal methodology is proposed considering also the topic of thermal comfort; this modification allows to obtain other optimal solutions compared to the basic calculation procedure.