Improved Flat Plate Collector with Heat Pipes for Overheating Prevention in Solar Thermal Systems
Abstract
Heat pipes in solar thermal collectors can reduce thermal loads in the solar circuit by using the physical effect of dry out limitation. By avoiding high temperatures and vapor formation, simplified, more reliable and cost effective solar thermal systems can be designed. The paper presents a theoretical study on different heat pipe and manifold designs for flat plate collectors. The focus is on high thermal efficiency in the operating range and significant temperature limitation in stagnation mode. Furthermore, the selected design should provide for a suitable integration in a typical collector housing. A prototype collector is manufactured and experimentally investigated by means of indoor performance measurements. Thereby a conversion factor of 73 % is achieved, which represents an increase of 4 percentage points compared to the efficiency of a previous prototype. During stagnation we report a maximum fluid temperature lower than 130 °C in the manifold, which drops quickly below 100 °C close to the collector connections.