Transient analysis of a variable-mode adsorption chiller

Adsorption cooling has high potential as a technology for saving energy and reducing greenhouse gas emissions. It can also be driven through low-temperature levels obtained from solar thermal collectors or waste heat. However, it has low relative performance at high ambient or re-cooling temperature as compared to its performance at lower temperatures. Adsorption cooling has a high heat rejection rate from the condensation and adsorption processes; due to this reason, it becomes difficult to maintain a low re-cooling temperature with an air-cooled adsorption system. Therefore, the concept of variable-mode adsorption chiller was proposed to evaluate the chiller output at different re-cooling temperatures. For performance evaluation of the proposed adsorption chiller, transient re-cooling temperature conditions were employed along with four proposed modes; single-stage mode, short and medium recovery modes, and variable mode which represent a combination of these modes. In addition, the cycle stability during shifting from one mode to another was investigated. The modeling results showed that the proposed chiller needs one cooling cycle to reach the steady-state after shifting from single-stage mode to mass recovery mode and three cooling cycles while shifting from mass recovery mode to single-stage mode. Furthermore, the variable-mode chiller has the highest averaged annual cooling capacity compared to other modes at Dubai weather conditions, while the single-stage has the highest averaged annual COP followed by variable, short and medium mass recovery modes respectively at same conditions.