On the best coefficient of performance and specific heating or cooling power combination for adsorption refrigerators and heat pumps

Abstract

The performance parameters of adsorption refrigerators or heat pumps are the coefficient of performance (COP) and the specific cooling power (SCP) or specific heating power (SHP), respectively. Higher COPs are associated with the longer cycle times required for more complete desorption and adsorption processes, resulting in a lower number of cycles per unit time and consequently in lower SCP or SHP, unless large masses of adsorbent material are used. The inverse situation occurs for shorter cycle times, associated with smaller COPs and higher SCP or SHP. This behavior leads to a relevant question: what is the combination of COP and SCP or SHP corresponding to the optimal performance of adsorption refrigerators or heat pumps? Although this question is recurrent in literature, its objective answer is still lacking. This work proposes an objective criterion to answer this question, setting the best balance between the COP and the SCP or SHP of adsorption refrigerators or heat pumps, as corresponding to the minimum unit cost of the obtained useful effect. The proposed criterion allows obtaining the cycle time that corresponds to the searched optimal performance. The dependence of the COP and the SCP or SHP on the cycle time can be obtained from numerical simulations for an adsorption system. Once these dependencies are known, it can be identified the cycle time leading to the minimum unit cost of the obtained useful effect, which corresponds the best balance between the COP and the SCP or SHP.