Abstract
In a moderate, transitory climate, to prevent freezing of outdoor pipes and collectors in solar thermal systems, anti-freezing fluids are commonly used. There is little experience of using water without any additives as a solar thermal fluid in such a climate. Based on these findings, to fill the knowledge gap this article presents the long-term results of thermal performance and anti-freeze protection of a solar heating system with heat pipe evacuated tube collectors with water as a solar thermal fluid. The operation of this system under real conditions was analysed for five years in southern Poland. The annual value of solar insolation ranged from 839 to almost 1000 kWh/m2. The monthly efficiency of the solar collectors from March to October was usually higher than 25%, and the lowest was between November and January. The anti-freeze protection system consumed annually from 7 to 13% of the heat generated by the collectors in the installation. Supporting the operation of the central heating system in the building during the winter season highly improved the efficiency of the solar collectors. Results show that it is possible to use water without any additives as a solar thermal fluid in a moderate, transitory climate.
Highlights
Energy is an essential commodity in many aspects of human life and industrial production, in both developing and developed economies
Measurements of the intensity of solar radiation acting on the solar collectors (SCs) surface, which are necessary to
Annual solar insolation for 2012 is not Measurements of the intensity of solar radiation acting on the SC surface, which are necessary marked, because full measurement data for this year was not collected
Summary
Energy is an essential commodity in many aspects of human life and industrial production, in both developing and developed economies. To reconcile the economic growth with the ever-increasing global demand for energy, energy-efficient and environmentally-friendly solutions are being sought in various branches of human activity. For this reason, equipment using renewable energy sources is becoming more and more important. SCs can be classified into concentrating (e.g., compound parabolic collectors) and non-concentrating (e.g., flat plate collectors, ETCs) [2]. Another important criterion for the division of SCs is the type of solar fluid used (i.e., liquid or gas) [5]
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