Physical Model

Figure 1. Schematic diagram of the cavity.

As solar radiation strikes the glazing, a percentage of the solar radiation is reflected, some percentage is absorbed and the rest is transmitted to the interior of the cavity. The solar radiation reflected to the outside by the glass and the solar control coating is considered that it does not contribute in the processes of heat transfer inside the cavity. The solar radiation absorbed by the glass implies heating the glass and the solar control coating. The solar radiation that is transmitted by the glass and solar control coating goes to the wall 2 and it is absorbed, without causing heating of this wall, since it is considered at constant temperature.

As consequence of the temperature difference between the external surface of the glass and the air of the environment, the heat is transferred by convection (qc) and radiation (qr) to the ambient air. In a similar way, the interior solar control coating surface transfers heat from the glazing to the interior air and to the interior surfaces of the cavity. Inside the glass, the heat is transferred by conduction.