Experimental evaluation of evacuated tube collectors with heat pipes to avoid stagnation loads in a domestic hot water system

摘要

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 thennal systems can be designed. The paper investigates a newly developed evacuated tube collector based on optimized heat pipes able to limit the temperature loads at the manifold up to a desired value. On the basis of efficiency measurements on a prototype heat pipe collector, we determine the annual yield of a collector field in a domestic hot water system compared to an identical system with direct flow collector according to ISO 9459-5. The results are validated by simulations with TRNSYS and show no significant difference between the performances of the two systems. By means of extensive outdoor stagnation tests on the same fields, we report a maximum temperature of 125 °C in the solar circuit of the heat pipe system, which is 95 К lower compared to temperature measured in the reference system.