Testing of a lab-scale four-bed adsorption heat pump

A lab-scale adsorption heat pump with four adsorbers was tested. The core structure of the adsorber is aluminum alloy finned tubes. Water was the adsorbate (refrigerant) and a fine silica gel granule was the adsorbent. At the regeneration temperature of 77.5 °C, a maximum SCP value of 93 W/kg silica gel was found. The corresponding optimum cycle time is 11 min and the COP value is 0.31. The COP value considerably increases with the cycle time. At the cycle time of 35 min, the COP value reaches a maximum of 0.54 and the corresponding SCP value is 73 W/kg silica gel. In the adsorption process, the evaporation rate of the liquid refrigerant in the evaporator was found to be much smaller than the vapor adsorption rate of the adsorbent in the adsorber. This resulted in a slow adsorption process and thus a descent of the maximum SCP value.