Experimental and Theoretical Investigation of Unglazed Transpired Air Collectors in a Multicomponent Solar Thermal System

Unglazed Transpired Air Collectors (UTC) are a simple and cost-effective technology to heat up ambient air, typically used in open solar air systems, e.g. for space heating of production halls. A new application is the air assisted preheating for district heating nets in the former Soviet Union. Due to the unusual operating conditions in this application an existing numerical model has been extended. The thermal performance of the UTC is modelled as a matrix of energy balance equations. The model has a wide area of application, since it covers already known standard applications as well as specific constructional and technical features of the collector. Furthermore, convective losses from the collector to the surrounding, the dependency of the absorption coefficient on the angle of incidence and the capacity of the building wall are considered. The presented model was implemented in the simulation environment TRNSYS and has been compared with measurement data