The present study has three objectives, i) to investigate the temperature reduction in polymeric collectors by passive ventilation, ii) to demonstrate a built-in, temperature triggered mechanism to initiate the ventilation process iii) to present a simplified method for determining the temperature dependent heat loss coefficient and the heat capacity of glazed polymeric solar collectors from stagnation measurements. All measurements are performed under stagnation conditions (no heat carrier in the absorber). Central issues for the investigations in the present work are:

• Non-selective absorbers of polymeric materials (low temperature performance plastics);

• Building integrated installations;

• Solar heating system design: non-pressurised, water as heat carrier, drain-back function;

• Simple control system design, self-protective overheating control;

2.1. Polymeric collector

For the design of a polymeric collector it is important to have a high system performance, which is competitive with conventional collector systems. Due to the overall system design, the present system is not operative for absorber temperatures typically above ~90 °С, the heat carrier drains back to a drain-back reservoir and the absorber is filled with air. The present absorber material is a modified PPE/PS blend [12] and studied e. g. in [13, 14].

Here, the maximum temperature reduction due to ventilation is studied, however not whether the reduced stagnation temperature is suitable for a long service life of the polymeric absorber. Still it can be indicated that the stagnation temperature in the present collector should be significantly below 130 °С; the system design should be such that this temperature is only reached during short periods of time.