Performance assessment of solar water heating system using CO2 under various climate conditions.

[Display omitted] Water heating without greenhouse gas emissions is indispensable for sustainable development in low sun regions. The integration of solar energy in domestic water and space heating systems is a sustainable pathway. Kyoto and Montreal protocols have already banned the use of chlorofluorocarbons and hydrofluorocarbons and granted a time limited permission to hydrochlorofluorocarbons. Synthetic refrigerants outperform natural refrigerants, yet 196 countries agreed on phasing out these refrigerants under Paris Accord in 2015. Industries, researchers and policy makers are retrofitting existing heating and cooling systems to integrate natural refrigerants worldwide. In this regard, an evacuated glass tube solar water heating system is simulated in Transient Systems Simulation Program (TRNSYS®) using low global warming potential (GWP) refrigerants. Parametric analysis is carried out to determine optimal sizes and configurations of solar collectors, heat exchangers, tank volumes and heights for annual performance assessment of solar water heaters. The optimized model was dynamically simulated under diverse weather conditions of Pakistan (Karachi), Australia (Melbourne) and China (Beijing). Our results show an optimal selection of solar water heating system parameters using 6 m2 collector area, 0.42 m3 tank volume, and 1.2 m tank height fulfil single family dwelling heating demands. Moreover, use of low global warming potential hydrofluoroolefins (HFOs) R-1234yz and R-1234yf refrigerants shows even superior thermal performance. The highest annual solar fraction values were recorded for CO 2 (0.720289) and R-410a (0.723428) under various weather conditions. Our findings show that use of synthetic refrigerants slightly improves the performance of system, however, giving weightage to environmental benefits the natural refrigerants take precedence over synthetic refrigerants. This research work recommends an adoption of natural refrigerants as an environmentally superior and sustainable option. [ABSTRACT FROM AUTHOR]