Influence of transmission models for special glazing on the predicted performance of commercial buildings

A new improved model has been developed to calculate the radiation transmittance, absorptance and reflectance values for glazing with optical thin films and/or tinted glass layers. The model is based on the optical behaviour of radiation in thin films and substrates. Simulation studies examined the thermal consequences of using glazing properties calculated using the improved method rather than properties calculated by applying the conventional Fresnel-based calculations for clear glass to special glazing. Two glazings (one heat-absorbing and one coated) which had the same basic window properties (U-value and total solar energy transmittance) were studied using a commercial building, located in either a temperate, or an extreme continental, climate. The heating and cooling loads predicted by using the improved model differed from those using the conventional approximations by up to 19%. The results also demonstrated that conventional total solar energy transmittance values do not accurately reflect the thermal differences between glazing systems. Therefore, effective total solar energy transmittance values have been introduced which correctly represent the imposed heating and cooling effects of glazings. They permit more accurate predictions of heating or cooling loads from simplified (steady-state) calculation methods.