Effect of Design and Operating Parameters on the Performance of Two-Bed Sorption Heat Pump Systems

Abstract

The effect of design and operating parameters on the performance of closed-cycle, two-bed sorption heat pump systems were investigated. The parameters studied in this paper included the effects of bed switching frequency (i.e., the switching speed), the sorbent bed NTU, the thermal resistance within the sorbent, the contact resistance between the sorbent and the tube wall of the heat transfer fluid, the fraction of inert mass within the sorbent bed heat exchanger, and the amount of fluid resident within the heat exchanger. The results show that the performance of a sorption heat pump system is extremely sensitive to the switching speed. In fact, the value of the switching speed that optimizes the COP is different from the value that optimizes the overall cooling capacity. Such a performance characteristic allows the design of multispeed sorbent bed heat pumps to be operated in such a way to follow the load while still maximizing the system COP. However, operation of the system at switching speeds away from the optimum values can cause a dramatic deterioration in system performance.