Modelling of heating and ventilation levels in buildings

Solar Gain Factors

Solar gain factors for glazing combinations are often required by computer software for the modelling of heating and ventilation levels in buildings. These can be derived from a knowledge of the shading coefficients, short wave (SWSC), long wave (LWSC) and total (TSC).

Solar gain factors for glazing combinations are often required by computer software for the modelling of heating and ventilation levels in buildings. These can be derived from a knowledge of the shading coefficients, short wave (SWSC), long wave (LWSC) and total (TSC).

Solar gains through windows arise due to:

  • Part of the solar radiation absorbed in the window which is transmitted to the environmental point
  • Transmitted solar radiation absorbed on internal room surfaces which also appears at the environmental point

Where internal shading devices are considered, there is an additional convective load realised at the air point. As steady state conditions are rare in buildings, it is more common for conditions to cycle on a regular daily pattern. Such cycles can be considered in two parts, a 24 hour mean (or average) and a cyclic variation about the mean. Cyclic (or alternating) solar gain factors will differ between building types, depending on whether the construction is lightweight or heavyweight.

By reference to the equations in the table below, the tabulated values of shading coefficients can be used to derive the solar gain factors for a particular window design. These have been taken from section A.5 of the CIBSE Guide, Volume A (1986). To view the table below in a separate window please click here.

Solar Gain Factors