Thermal performance of small low flow solar heating systems

摘要

Detailed measurements for a small low flow solar heating system for domestic hot water supply were carried out. A detailed mathematical model simulating the thermal behaviour of a small low flow solar heating system based on a mantle heat storage was validated by means of the measurements. It was investigated how the thermal performance of low flow system is influenced by variations of the solar irradiance caused by clouds. A figure showing the extra yearly thermal performance of low flow systems caused by these variations was prepared. First the yearly thermal performance was calculated with the model and the Danish Test Reference Year, which is based on average hourly weather data for all hours during the year. Then the extra thermal performance caused by variations in the solar irradiance was determined by means of the above mentioned figure. The thermal performances of low flow systems and of traditional solar heating systems have been calculated. Especially for small solar fractions an for small ratios between the hot water consumption and the solar collector area the extra performance of the low flow system compared to the performance of the traditional solar heating system is significant. By means of the validated mathematical model a number of calculations with different system designs were carried out. Based on these calculations figures showing the yearly thermal performance of differently designed low flow systems have been prepared. (AB).