Solar calorimetric testing of glazings and shading devices

Within the European project ALTSET (Angular-dependent Light and Total Solar Energy Transmittance) the angular properties of so-called complex glazings (i. e. glazings with special optical properties) and shading devices have been investigated. The scope of the project was

the comparison between direct calorimetric measurements and modeling from layer properties

— the important experimental factors for good interlaboratory comparison of results

— error analysis and evaluation procedure

— conclusions for and development of a testing procedure.

The results showed that using different approaches for apparatus design one can reach uniform results for well-defined reference conditions and the project team has developed a test procedure for this purpose. Solar calorimetry could be shown to be an indispensible methodology for all complex glazings like diffusing glazings, transparent insulation,

shading lamellae and switchable glazings and can be used for validation of optical-thermal glazing models. But also for conventional glazings the accuracy is comparable with standard testing techniques. [ 4]

In a German national project REGES this approach has been extended for shading devices (internal and external devices), and recommendations for testing have been given. [ 6]

The principle and advantage of solar calorimetric testing is that glazing plus eventually shading devices, the complete fagade structure, can be tested in a "black box” approach, i. e. no additional information on the layer properties or the internal heat transport (ventilation) is needed. There is no modelling involved which is always a problem for more complex fagade constructions. Only a general parameter model is being used which is parameterized using the information from the experiment and parallel optical measurements.

The second important advantage is that angular dependence can be measured with these test procedures.

Figure 2: View of the solar calorimetric test Figure 3: Test frame for internal solar

cabin of Fraunhofer ISE, with an external shading devices shading device mounted in front of the calorimetric plate