Prevention from thermal losses in buildings and using environmental potentials such as solar energy, are two fundamental strategies in designing buildings with the approach of saving nonrenewable energy resources. As a border between the interior space and the environment, the building envelope plays a determining role in approaching these strategies. It is expected from the building’s envelope to mitigate unwanted energy dissipations and protect occupants from severe weather conditions. At the same time, a well-designed building envelope should provide the occupants’ comfort using environmental potentials, and ideally it may even take part in fulfilling energy demands.
The importance of energy harvesting in building envelops is more recognized in metropolises in which the growth of high-rise construction causes an intense decrease in the ratio of sun exposed horizontal surfaces such as roofs or yards to the area of floors. However, on the height of building and the overall area of floors -and followed by them, demand for energy- increases, the area of vertical surfaces such as facades, increases in a more appropriate proportion. Additionally, installing solar energy equipment on horizontal surfaces with high potential of functionality, is usually an undesirable interference in architecture.
From another point of view, conventional insulating stops the wall from transferring solar energy to the interior spaces. This research aims to make a convergence between high thermal resistance and solar energy collection. To achieve this, different methods of solar energy collection was reviewed. Due to the large angles between the sun’s altitude and the normal vector of southern façades, especially in summer days, a significant part of solar radiation is reflected from the cover glass surface of flat collectors. Non-glazed collectors, because of large amount of heat loss, have a low efficiency and like the conventional flat collectors, do not transfer the light and ban the transparency. However tubular evacuated solar collectors, if installed horizontally on southern façade, represent a circular section which is always perpendicular to the rays of sun, regardless of the altitude of radiation. So, solar reflection from glass cover of the collector, will no longer depend on the sun’s vertical position in the sky in different seasons. Also, the relative vacuum -made possible according to tubular form- decreases heat loss to a minimum. According to these two facts, this type results in an appropriate performance, which enables the envelope to provide a part of heating load and indirectly, cooling loads by supplying an absorption/adsorption chiller or a desiccant cooling machine.
The concept of the proposed system is a combination between the idea of tubular evacuated solar collector and vacuum transparent insulation. It consists of aluminum blades covered with a selectively solar absorbing coating, arrayed like a louver, surrounded by an evacuated glass container with corrugated skin. The result is a modular façade panel, with a high thermal resistance, which efficiently takes part in solar energy collecting and at the same time, acts as a louver to protect the interior spaces from direct solar radiation, while providing a relative visual transparency and daylight transmission.