Feasibility study on a novel freeze protection strategy for solar heating systems in severely cold areas

• A new anti-freezing strategy for a solar heating system was presented.
• The control principle of the strategy was described in detail.
• The anti-freezing effect was analyzed during winter nights.
• The concentration of the antifreeze fluid could be significantly reduced.
• The anti-freezing strategy has better economic performance by comparison with that of conventional measures.

In severely cold areas, the freezing of outdoor pipes and collectors is one of the most serious problems, which, to a certain degree, limits the utilization of solar energy and decreases the system economic performance. To solve this issue, a novel anti-freezing strategy using the remnant thermal energy in solar collector as the heat source was proposed to prevent the freezing of the solar collecting system in winter nights and overcast days. The strategy was investigated and analyzed experimentally under different weather conditions to verify its anti-freezing effectiveness. The results indicated that the concentration of antifreeze fluid could be reduced from 50% to 20% or even lower due to the anti-freezing strategy. The economic feasibility of the strategy was also analyzed and compared with two conventional anti-freezing measures, which indicated that the proposed strategy was the most economical. The strategy presented in this paper can successfully resolve the issue that the initial cost of antifreeze fluid was high when all-glass evacuated tube collectors are used in solar heating systems in severely cold areas. It also can provide a key reference for the design of solar heating systems, especially for the selection of the concentration of antifreeze fluid required in severely cold areas.