Two Stage Regeneration of Liquid Desiccant Using Solar Energy for Fresh Air Dehumidification System

摘要

Energy for all and control of greenhouse gas emissions are two contrary goals to be achieved and thus the solution needs a paradigm shift. Energy demand for air conditioning is significant, so there is urgent need to diversify the sources of energy for the same. Liquid desiccant (LD) based air conditioning system is an important alternative technology for air conditioning. This technology is very promising because it is adaptable to renewable sources of energy like solar energy and has valuable feature of high density energy storage at near ambient conditions. Low COP, high parasitic power consumption, corrosion and longer paybacks are the challenges against acceptance of this technology. Certain measures like two stage regeneration, low flow rate of LD and air and higher regeneration temperatures can address above issues. Due to hardware limitations, most prototypes in literature lack one or more of the above features. In present work, a novel heat pipe based evacuated tube solar collector, ETC, developed at the Heat Pump Laboratory at IIT Bombay, HPL_IITB, is used as high temperature regenerator, HTR. HTR regenerates LD to an intermediate concentration. A separator at the outlet of the HTR separates and redirects the steam to the low temperature regenerator, LTR for enabling further regeneration of LD. High LD, aqueous solution of KCOOH, concentration change allowed use of low solution flow rate which was catered to using a 40 W pump. LTR is a rotating disk type diabetic contacting device where steam from the HTR heats the LD as it regenerates into a small ambient air stream used as the scavenging air. High surface density, lower pressure drop and low flow rate of air through LTR are some of the salient features of this device. A prototype two stage LD regeneration subsystem for 3 TR solar fresh air dehumidification system is fabricated installed and tested at HPL_IITB. During low solar insolation, the system can be operated as a single stage regeneration system. Single stage dehumidification COP of around 0.86 and two stage dehumidification COP of 1.03 was recorded during initial trials. The COP can be further improved by running the system at near design flow rates. The improvement of effectiveness of solution heat exchangers and reducing flow rate of air through LTR can help to achieve COP exceeding 1.5 for Mumbai, India outdoor design conditions. The system developed in current work certainly has potential to provide clean and highly energy efficient solution for fresh air dehumidification.