An evaluation of the effect of adsorbent properties on the performance of a solid sorption heat pump

Solid sorption heat pumps can improve the effectiveness with which energy resources are used for heating and cooling. The research presented here evaluates the effect of adsorbent material properties on the performance of a thermal wave solid sorption heat pump. In order to evaluate these effects, a numerical model of the thermal wave heat pump was developed. This model incorporates not only the effects of the adsorbent properties but also the effects of the refrigerant properties, application parameters, operating parameters, and bed geometry. For a typical air conditioning application, the model was used to study the influence of material properties on the COP for systems using both water and ammonia as refrigerants. For each set of material properties, operating and geometric parameters were adjusted to determine the best COP that could be achieved subject to capacity constraints.; The results of this research indicate that COP increases with saturation adsorption level and exhibits an optimum with respect to the adsorption equilibrium coefficient. The results also indicate that increasing the thermal conductivity of the adsorbent to approximately 1 W/mK can improve COP. Beyond this value, heat transfer is limited by the thermal resistance associated with convection within the heat exchanger tubes and the contact resistance at the adsorbent/tube interface. The results also illustrate that for solid sorption heat pump systems using ammonia as a refrigerant, the performance is impaired by vapor flow restrictions if the adsorbent permeability is less than {dollar}rm1.5times10sp{lcub}-11{rcub} msp2.{dollar} For systems using water as a refrigerant, vapor flow restrictions are significant at even higher values of the permeability. If high values of the permeability can be maintained while increasing the thermal conductivity of the adsorbent to 1 W/mK and the contact heat transfer coefficient to 180 W/m{dollar}sp2{dollar}K, then COPs as high as 0.75 can be achieved for the system described here.; Improvements in adsorbent materials and system design will be necessary to achieve further increases in performance. The research presented here provides insight into the influence of adsorbent properties and provides a numerical model that can be used to investigate other design characteristics.