The solar response factor for the dynamic response of buildings to solar heat gains

The contribution of the solar heat gains to the cooling load is usually calculated through accurate procedures implemented in several simulation programs. Some simplified methods, such as the ASHRAE method, are also available for hand calculations, but they are based on tabular data that apply only to specific conditions. This paper discusses a newly introduced parameter for the evaluation of the cooling load due to the solar radiation incident on the glazed surface of a building. This is the Solar Response Factor (SRF): it is a complex number, and can be rigorously defined and calculated as a combination of the thermal and the optical properties of walls and glazing. In particular, the usefulness of the SRF is twofold. First, it allows to classify the response of the enclosure to the solar radiation by means of a couple of parameters (amplitude and phase), which makes it easy to perform comparisons amongst different envelope solutions. Then, it allows an easy analytical estimation of the cooling load in dynamic conditions, starting from the decomposition of the cyclic solar gains in a series of sinusoidal functions. The paper discusses how the Solar Response Factor depends on the main thermo-physical and geometrical properties of the opaque and the glazed envelope. Moreover, an example is discussed to show how the use of the SRF allows evaluating the effectiveness of a series of solutions to limit the cooling load. The outcomes of this analysis provide very useful information for a conscious design of buildings, oriented to the limitation of the cooling load and the overheating of indoor spaces.