سطوح کارآمد انرژی در ساختمان ساندویچ پانل - یک مدل شبیه سازی پویا

The choice of building envelope is critical for the energy performance of buildings. The major part of the energy used by a building during its lifetime is used for maintaining a suitable interior thermal climate under varying exterior conditions. Although exterior heat radiation properties (i.e. total solar reflectivity and long wave thermal emissivity) have been well accepted to have a large impact on the need for active cooling in warmer climate, the effect of a reduced thermal emissivity on interior surfaces on the building thermal energy flux is rarely studied. This paper addresses the sensitivity of the thermal energy flux through a sandwich panel, by systematically varying the surface thermal emissivity (both interior and exterior) and total solar reflectance of exterior surface, for three geographical locations: southern, middle and northern Europe. A model is introduced for calculating the effect of both interior and exterior optical properties of a horizontal roof panel in terms of net energy flux per unit area. The results indicate potential energy saving by the smart choice of optical properties of interior and exterior surfaces.

The energy required to maintain a desired indoor climate in buildings is usually larger by roughly an order of magnitude compared to the energy needed to provide the building materials [1]. A smart choice of material and sustainable design can trench the energy demand and contribute to less heating or cooling usage. Among building materials, the sandwich panel has earned its reputation due to short construction time and cheaper labor cost. It can be used in a wide range of applications; new constructions, extensions and refurbishments. Sandwich panels usually consist of two coil coated steel sheet profiles, which are tightly pressed and glued to an insulation core. They can be manufactured even without trans-sectional supports to avoid thermal bridges. Coil-coated steel is profiled and utilized in sandwich panel as the shield. Since the shield is also interface between indoor and outdoor environment, it is considered for both climatic exposure and aesthetic aspects. Continuous development of paint, used in coil-coating has nowadays made it possible to improve both durability and energy performance of such materials. For the panel's exterior, coatings with high solar reflectance can contribute to lower surface temperatures and consequently reduce the thermal stresses and mechanical strains. The lower temperatures prolong the panel's life time and minimize buckling and other mechanical problems.

The magnitude of exterior surface solar absorbtion and thermal emission varies differently compared to each other over the varying seasons as well as between day and night. Our results indicate that, in tempered climates, there can be a benefit of optimizing both the total solar reflectivity and the thermal emissivity of a building exterior surface to minimize the total energy use. Naturally, a combined “Cool Roof”-measure, e.g. the Solar Reflective Index would be insufficient as a sole definition of the exterior surface optical properties for use in dynamic building energy simulations and in the design of energy efficient buildings. By varying the interior radiation temperature and the thermal emissivity of the interior surface, the trends seen here in the total heat flux strongly indicate the benefit of using low emissive interior surfaces when maintaining an anisotropic radiation temperature distribution, e.g. with large temperature differences between interior surfaces.