Experimental Investigation and Mathematical Modeling of a Low Energy Consuming Hybrid Desiccant Cooling System for the Hot and Humid Areas of Pakistan

Abstract

This experimental and simulation study investigates the potential of using a solar assisted hybrid desiccant cooling system (SHDCS) for air conditioning applications for Pakistan. A review of literature reveals that compared to the conventional vapour compression cycle this cycle could offer saving in overall primary energy. Since the cycle is based on supply of conditioned ventilation air it has significantly lower environmental impact. A gas fired hybrid desiccant cooling test rig has been installed at the Energy Conservation Laboratory NED to study the performance of various components. These experiments enabled understanding of the system and helped develop effect of individual components on the system performance. Important parameters of system components established from the experiments were used as input to the TRNSYS simulation model. The simulation studies have been based on a well established transient energy software TRNSYS. Specific to this work a mathematical model of Modified Cooler was prepared from basic principles and added as module to TRNSYS. Addition of this component resulted in an increases of the COPp-s by a factor of 1.065 for the weather of Lahore. Besides COP; all system parameters showed an improvement due to the addition of this component. Six case studies based on SHDCS have been performed for Karachi and Lahore. The results so obtained established that the advantage of using SHDCS depends on the climatic conditions. SHDCS offers considerable promise for Lahore i. e., it shows that of the seven month summer cooling season the desiccant cooling system alone suffices for three month – April, May and October. However for Karachi summer, characterized by high humidity, SHDCS does not provide acceptable temperature and humidity conditions without auxiliary air conditioning. The source of thermal energy needed for regeneration plays an important part in the overall success of the desiccant cooling scheme. To reduce the use of conventional energy, in this case natural gas, a solar collector has been included in the study. Micro analysis of the flow and heat transfer phenomenon taking place inside inclined solar air collector was studied using CFD software, which demonstrated that low heat transfer between air and absorber can be improved by using staggered fins. It was also shown that the fin configuration coupled with low flow velocity helped increase heat transfer in the absorber duct by increasing heat transfer area, mixing and residence time. Energy, economic and environmental impact of the solar collectors was also studied and payback periods for energy, Carbon emission and monetary investment have been found to be 1.5 years, 1 year and 14 years respectively. The success of the desiccant cooling system is strongly associated with cost of the thermal energy. Combined heat and power systems offer an opportunity of providing this energy at no additional cost. The latter study has been suggested to be taken up as future work.