A Novel Solar-assisted Membrane-based Liquid Desiccant Air Conditioning System for Hot and Humid Climatic Conditions
Liquid desiccant dehumidification, solar air conditioning, membrane dehumidifier and regenerator, Hot and humid climatic condition
1. Introduction According to the energy statistics of India, building sector consumes 40% of electricity out of which nearly one third is consumed by heating, ventilation and air conditioning (HVAC) systems . Currently, more than 90% of the HVAC systems are of vapor compression refrigeration type which are energy inefficient for humidity control . Therefore, it is desirable to meet such HVAC demands using an alternative system which is not only energy efficient, but can also utilize the low grade energy sources such as solar or waste heat. The liquid desiccant system is one such prospective alternative which can utilize the solar energy for its desiccant regeneration. Such systems are classified as direct contact-packed bed system and indirect contact-membrane system. The latter is preferred to avoid problems associated with the desiccant carryover. The conventional membrane-based liquid desiccant air conditioning system (MLAC) contains adiabatic dehumidifier and regenerator. The temperature of the desiccant to the dehumidifier is maintained in such a way as to simultaneously cool and dehumidify the air. However, it cannot cool and dehumidify the air to the desired level due to resistance for heat and mass transfer in the intermediate membrane and the exothermic heat that is generated during absorption. Present study proposes a novel MLAC with an additional air cooling heat exchanger. Performance analysis of such a novel solar assisted MLAC is carried out for the hot and humid climatic conditions prevailing in the city of Chennai, India. 2. Methodology and Description The main components of MLAC are dehumidifier and regenerator. They are modelled and validated with the reported experimental data. The MLAC is designed to provide air conditioning for a room having low sensible heat factor (SHP) with loads of 3 kW sensible and 2 kW latent. Aqueous solution of lithium chloride is used as desiccant. Evacuated tube solar collector is used to harvest solar energy. Storage tank with three mixing zones and aspect ratio (L/D) of 4:1 is used. The year round performance of the MLAC is evaluated in terms of the room temperature, specific humidity and coefficient of performance. 3. Conclusions Results of the present study conclude that the proposed solar assisted MLAC is able to achieve better indoor conditions (24°C and 0.0097 kg/kgda) at approximately the same COP of the conventional MLAC. The recommended range of inlet desiccant temperature to the dehumidifier and regenerator are 16-19°C and 45-50°C respectively. The results of the present study are expected to be useful in optimum design of MLAC for the hot and humid climatic conditions. References 1. A technical report of energy and buildings by Centre for Science and Environment. Available at < http://www.cseindia.org/userfiles/Energy- and -% 20 buildings. pdf > [Accessed 5.6.2017]. 2. Alternatives to Vapor-Compression HVAC Technology, ASHRAE Journal Article. Available at < https://www.ashrae.org/File%20Library/docLib/.../2014Oct012-023_ Goetzler. pdf > [Accessed 15.12.2017].