Experimental evaluation of stagnation-safe flat plate collectors with heat pipes for domestic hot water preparation in thermosiphon systems
Abstract
Overheating in thermosiphon systems, which represent the dominating solar thermal technology worldwide and are often installed in regions with water scarcity, can lead to significant water losses and to failures of the safety valve. The paper analyses the behavior of a prototype thermosiphon system, provided with a novel flat plate collector, by comparing it with a conventional system based on experimental investigations. The novel collector is equipped with specially designed heat pipes, offering an intrinsically safe solution to limit the stagnation load in the heat tank up to a desired temperature. The results of the performance tests according to ISO 9459-5 show, that the prototype system can achieve similar solar yields as the standard system (-2% to -4%, depending on the location). Stagnation measurements report a maximum temperature of 96 °C in the heat tank of the prototype. The conventional system reaches temperatures above 100 °C, which leads to a pressure increase of 3.4 bar.