Design of a thermochemical process for deep freezing using solar low-grade heat

Abstract

A deep-freezing process has been designed and experimented to cool a cold box down to about −30 °C using only low-grade heat produced by simple flat plate solar collectors operating at 70 °C. The original process involves two cascaded thermochemical systems using BaCl 2 salt reacting with ammonia. It works discontinuously, with one day phase of regeneration at high pressure and one night phase of cold production at low pressure. A global dynamic model allows the simulation of the different system components functioning depending on the hourly weather conditions. It takes into account the transient periods and shows the temperature changes of the components, the chemical reactions in the system and its performances. This system will cover the cooling needs of a 560 L cold box at −20 °C during the 3 sunniest months of the year and provide more than 60% of the total yearly cooling needs of this box for the weather conditions of Perpignan (South of France). The prototype is expected to show a system coefficient of performance (COP) of about 0.07 over the 10 sunniest months of the year, and a net solar COP of 0.05, taking into account the collectors efficiencies.