Material selection and exposure
After a market analysis, which included all major distributors, a selection of 58 collector glazing types were chosen in the beginning of this long-term investigation (1984). An overview of tested samples is given in Table 1. These glazing types cover a variety of different material and plate types. Although the selection was made in 1984, the results still provide important information regarding the materials currently available on the market.
|
Table 1. Summary of the tested materials with the corresponding solar transmittance values.
|
Two exposition sites with different climatic conditions were chosen (see Table 2.); Rapperswil representing a sub-urban location is home of the SPF institute. The alpine site of Davos is characterized by higher irradiation and lower temperature and air pollution.
Table 2. Main climatic parameters of the exposition sites.
|
|
|
Altitude
Total annual insolation Annual UVA insolation Annual UVB insolation Yearly mean temperature Site character Air pollution sources
417 AMSL
1093 kWh/m2 per year 60.7 kWh/m2 per year 2.08 kWh/m2 per year
9.3 °C Suburban
Train station and industries
Five samples of each glazing type were exposed at the two sites. Each sample covered a “mini collector” [1] which consists of a non-insulated box of solar selective coated stainless steel facing south at an inclination of 60°. One sample from each type was collected, analyzed and stored following 40 days, 1, 3, 10 and 20 years of exposure.
