Solar Heating and Cooling System with Absorption Chiller and Latent Heat Storage – A Research Project Summary

A reliable solar thermal cooling and heating system with high solar fraction and seasonal energy efficiency ratio (SEER) is preferable. By now, bulky sensible buffer tanks are used to improve the solar fraction for heating purposes. During summertime when solar heat is converted into useful cold by means of sorption chillers the waste heat dissipation to the ambient is the critical factor. If a dry cooler is installed the performance of the sorption machine suffers from high cooling water temperatures, especially on hot days. In contrast, a wet cooling tower causes expensive water treatment, formation of fog and the risk of legionella and bacterial growth. To overcome these problems a latent heat storage based on a cheap salt hydrate has been developed to support a dry cooler on hot days, whereby a constant low cooling water temperature for the sorption machine is ensured. Therefore the need of a wet cooling tower is avoided and neither make-up water nor maintenance is needed. The same storage serves as additional low temperature heat storage for heating purposes allowing optimal solar yield due to constant low storage temperatures. Four pilot installations between 7 kW and 90 kW nominal cooling capacity were equipped with latent heat storages between 80 kWh and 240 kWh energy content. Annual in situ measurement data shows a positive effect on the seasonal energy efficiency ratio (SEER) for cooling up to 11.4. Furthermore simulation results under different climatic conditions indicate raising efficiency up to 64% compared to a system with solely dry re-cooling. Long-term test bench measuring data concerning performance and durability as well as a new approach for a state of charge detection for latent heat storages are presented as well.