THERMODYNAMIC ANALYSIS OF VAPOUR ABSORPTION HALF EFFECT SOLAR DRIVEN WATER LITHIUM BROMIDE SYSTEM FOR SPACE COOLING

Abstract

Nowadays Solar Cooling systems are becoming popular to reduce the carbon footprint of air conditioning. The use of an absorption unit connected to solar thermal panels is increasing. The need and importance of solar based cooling system can play a very prominent role in attenuating energy crisis by the use of solar energy. Two types of the absorption systems, the single and half effect cycles, can operate using low temperature hot water. The unique characteristic of the half-effect absorption cycle is that its running capability at lower temperatures in comparison to the single effect vapour absorption system. The COP of half effect system is almost half to that of the single-effect cycle but it is operated at lower temperature to that of single effect. The system functions with the principle of absorption refrigeration cycle having water as a refrigerant and Lithium Bromide as an absorbent. In the present work, thermodynamic analysis and simulation of vapour absorption half effect cooling system using flat plate solar collectors as source of energy, for an office space has been done and the system performances were analyzed parametrically by using EES. The cooling load calculation of an office space was carried out on 21st of June located at Dehradoon, Uttarakhand India (Latitude 30°N). The estimated capacity of the office space (Qe), comes out to be 25 kW (approx). The evaporator temperature is maintained constant at 7°C and condenser temperature is varied from 30°C and 46°C and generators temperatures are varied from 65 to 85 °C. For a given condenser temperature (say 38°C) there is an optimum generator temperature for which the total area flat plate collector is minimum. This optimum generator temperature comes out to be 80°C. This generator temperature gives the maximum COP and exergetic efficiency of the absorption cooling system. There exists an optimum intermediate pressure corresponding to which COP and exergetic efficiency are maximum. The optimum intermediate pressure comes out to be 4.935 kPa. (for TC = Tal =Tah = 38°C, TE = 7°C and Tgh = Tgl = 80°C). For the same input parameters the maximum COP obtained is 0.4158 and the maximum exergetic efficiency is about 7.36%. The ultimate goal in the long term would ideally be to reduce the consumption of electricity used for refrigeration and air conditioning, hence saving money and reducing the stress on our electricity generation and distribution networks. The cost analysis of the half effect system is done by comparing it with the conventional vapour compression refrigeration system (VCRS). Based on the cost calculation of two systems, the payback period of the half effect system is calculated and it comes out to be 2.8 years.