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.

中文翻译：

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太阳热力系统防冻保护系统的长期性能

在适度的暂时性气候中，为防止太阳能热系统中的室外管道和集热器冻结，通常使用防冻液。在这种气候下，几乎没有使用不含任何添加剂的水作为太阳能热流体的经验。基于这些发现，为填补知识空白，本文介绍了使用以水为太阳能热流体的热管真空集热器的太阳能供热系统的热性能和防冻保护的长期结果。在波兰南部分析了该系统在实际条件下的运行情况，历时五年。每年的日照量为839至近1000 kWh / m ²。从3月到10月，太阳能集热器的月度效率通常高于25％，最低的是11月至1月。防冻保护系统每年消耗设备中集热器产生的热量的7％至13％。在冬季，支持建筑物中集中供热系统的运行大大提高了太阳能收集器的效率。结果表明，在适度的短暂气候下，可以使用不含任何添加剂的水作为太阳能热流体。