Charles Anderson

Angular-dependent optical properties of low-e and solar control windows—: Simulations versus measurements

Abstract The angular-dependent optical properties of low-e and solar control glazings have been investigated in a European project, ADOPT, within the Standards Measurements and Testing programme. The object of the project has been to identify reliable ways of predicting the angular dependency without having to perform measurements or detailed calculations. Two new predictive algorithms have been developed and validated. For the investigated coatings the accuracy of these predictive algorithms is mostly within 1% of the value obtained by measurements or Fresnel calculations. This is an improvement over previously used algorithms, which have failed to distinguish between different types of coatings. The improved accuracy is of importance in energy simulation of buildings and makes improved product specification possible.

Measurement and prediction of angle-dependent optical properties of coated glass products: results of an inter-laboratory comparison of spectral transmittance and reflectance

The European Union ADOPT project has been concerned with the accurate determination of the optical properties of coated glass products, describing reliable procedures for angle-dependent measurements and the development of predictive algorithms to enable accurate angle-dependent performance characterisation based upon near-normal values only. An essential element of the ADOPT project was the inter-laboratory comparison of transmittance and reflectance measurements for commercially available glazings. Thirteen European and three USA laboratories participated. The selected samples represent major categories of coated glass products used in buildings. Each participant received a set of samples and measured the angle-dependent spectral transmittance and reflectance under appropriate polarisation conditions for incident wavelengths within the solar spectral distribution. Calibrated mirrors were also provided for reference purposes. This paper presents the results of the inter-comparison which show that near-normal solar, visible and spectral transmittance and reflectance can be measured with an uncertainty of better than ±0.02. The inter-comparison illustrates the difficulties still experienced in making accurate oblique incidence measurements. The predictive algorithms, which require near-normal input data only, are capable of predicting the angle-dependent transmittance, reflectance and total solar energy transmittance for double and triple glazed windows to an accuracy which enables reliable calculation of the annual solar heat gain through windows.

Angular-dependent optical properties of coated glazings: validation of two predictive algorithms

The angular dependent optical properties of low-e and solar control glazings have been investigated in a European project, ADOPT, within the Standards Measurements and Testing programme. Two new predictive algorithms have been proposed and tested. One algorithm is based on an empirical formula and the other is based on a hybrid equivalent model, which approximates the actual coated glass. The validation procedure has included measurements as well as Fresnel calculations. The algorithms allow the user to calculate the solar heat gain coefficient versus angle of incidence for any transparent window combination without having to perform time-consuming measurements. For the tested window configurations the precision is mostly within one percentage point as compared to measured results.