Operational envelope and performance enhancement of a two-bed adsorption cooling system

Highlights: • Optimized passive heat recovery strategy with improvement in COP of up to 42%. • Operational envelope enhancement of up to 56% through two-stage strategies. • The theoretical upper limit on desorption temperatures for multi-stage operations. Along with the measures to improve the design of the adsorption cooling systems, the operating strategy selection plays an equally important role in their performance enhancement. Though several strategies such as heat recovery, mass recovery, multi-staging, etc., have been reported in the literature, their implementation in the more popular small-scale two-bed systems has not been given due attention. The present study highlights the performance enhancement of a two-bed single-stage silica gel-water adsorption cooling system through novel interventions in the operating cycle. A facility has been developed for testing a 10 kW water-cooled adsorption chiller. Passive heat recovery and two-stage operational strategies have been proposed for the enhancement of performance and operational envelopes through modifications in the chiller's valves sequencing. An improvement of 23–42% in coefficient of performance (COP) is observed with an optimized passive heat recovery strategy, while maintaining the water level in the hot water tank. Two kinds of two-stage operations viz., conventional two-stage and reheat two-stage, show potential for performance improvement under extreme conditions, resulting in an operational envelope enhancement up to 56%. A theoretical approach based on the thermodynamic analysis of adsorbent limits has been presented to assess the maximum desorption temperature limits.