Recent developments in adsorption heat pumps for heating applications

Abstract

Adsorption heat pumps (AHPs) have gained noticeable attention in recent years. The review discusses significant research in the domain of adsorption heat pumps focusing on heating applications, the working principle, adsorption equilibrium and kinetics, the design of adsorbent beds, physical models, operating parameters, and physical and thermodynamic characteristics of adsorbents. A comparison is presented among AHPs and traditional heating technologies and systems for AHPs that certain market participants have created. The review focuses on the most appropriate conditions for each measurement technique and the constraints of the modeling processes that are an essential element for the comprehensive performance evaluation of adsorption cooling units. For adsorption bed applications, it is suggested to use various bed designs and heat exchanger structures. Moreover, significant literature gaps and constraints in designing AHPs for heating applications are identified and analyzed. The heat and mass transfer resistance should be reduced by developing novel adsorbent materials and an improved interface among the duct wall and the bed, where heat transfer fluid circulates to increase adsorption heat pump system performance. Furthermore, optimum operational modes for the intended application might significantly enhance system performance.

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“…Their study shows that depending on the temperature lift, the COP of such systems is, respectively, ceiled at 1 and 0.5 for ideal single-stage AHP and AHT. Conversely, the literature also reveals coefficients of performance for AHP up to 1.6-1.7 [177,178], where the low-temperature heat source was the ambience and, therefore, not considered in the energy balance. Riaz et al [178] present an extensive review of AHPs used for heating applications, presenting different adsorbant-adsorbate working pairs such as zeolite/water, silica gel/water, activated carbon/methanol, and activated carbon/ammonia.…”

“…Conversely, the literature also reveals coefficients of performance for AHP up to 1.6-1.7 [177,178], where the low-temperature heat source was the ambience and, therefore, not considered in the energy balance. Riaz et al [178] present an extensive review of AHPs used for heating applications, presenting different adsorbant-adsorbate working pairs such as zeolite/water, silica gel/water, activated carbon/methanol, and activated carbon/ammonia. If expected COPs vary generally between 1.3 and 1.6 depending on the working pair and, therefore, temperature levels, this study also highlights the COP deterioration of about 18% between commercial or experimental plants and theoretical studies.…”