Research On Characteristic And Operating Strategy Under Varying Heat Source For Adsorption Chiller Powered By Solar Energy

The silica gel-water adsorption chiller has the large potential of industrialization in the filed of waste heat and solar energy for being environment-friendly, energy-saving and low temperature-driving. In the past research, most researchers focus on the performance of adsorption chiller under stable heat source, while the performance under varying heat source is neglected. As a matter of fact, varying heat source is an unavoidable problem when adsorption chiller is utilized because of the instability and intermittence of waste heat and solar energy. The poor performance under varying heat source has been one of the bottlenecks of industrialization for adsorption chiller. The proper operating strategy is also destitute for the lack of insight into the performance of the components under varying heat source. Therefore, it is necessary to investigate the performance of the adsorption chiller under varying heat source.Because of the cyclical variation in parameters of the adsorption chiller, an intense fluctuation can be observed in heating power and cooling capacity. When the system is a multi-chiller system, the total fluctuation might be enhanced by the superposition of several fluctuations, which will degrade the performance of the refrigerating system. Therefore, this paper focuses on several parts:1) A dynamic model is developed for the silica gel-water adsorption chiller to predict its performance under varying heat source. The three layer heat exchanger model is adopted to consider the thermal capacity of metal and remained water in heat exchanger. Considering the ununiformity of temperature along the flowing direction, one dimension method is used to model the evaporator, condenser and adsorber. The condensate on the surface of condenser is also taken into consideration for its effect on the chiller performance. The validity of this model is verified by experiments, and the model shows great agreement with measured data in most working conditions with the relative error within 15%.2) A test rig is built to investigate the corresponding characteristic of the chiller under approximate linear heat source by typical experiments, and the dynamic model mentioned before is employed as well. We conclude that: the chiller performance is influenced notonly by the temperature of heat source, but also the variation rate of temperature. The chiller performance is degraded with the variation rate increasing, when the averaged temperature of heat source remains the same. When the variation rate varies from -0.2°Cmin-1 to 0.2°Cmin-1, the maximum difference of cooling capacity and COP can be 18% and 30%, respectively.3) An air-conditioning system powered by solar energy is built to explore the characteristic of heat source and its effect on the adsorption chiller. Some operating strategies are also put forward for different solar insolations. By simulation and experiments, we conclude that: when solar insolation is high (20MJm-2), the performance of open cycle is slightly better than that in closed cycle, but the electric based COP in closed cycle is about 35% higher than that in open cycle; when the solar insolation is low (13.7MJm-2), open cycle is much more suitable than closed cycle.4) By analyzing the variation in the performance for a multi-chiller system, the phase contrast method is brought forward to minimize the fluctuation in the performance of refrigerating system. It is proved that the system performance can be enhanced and its fluctuation can be decreased by choosing a proper phase contrast, which is called optimized phase contrast. The optimized phase contrast can be determined by working period of the chiller divided by the number of the chillers.