The accessible energy must be employed appropriately, as there is a high requirement for electrical energy creation and circulation. Around 40 – 45% of electric power in every household is used to function refrigeration, heating, ventilation and air conditioning schemes. All these systems reject a tremendous quantity of heat to the environment as waste. Therefore, proper reclamation of this unused heat could also expand the COP of such structures and their minor adverse effect on the surroundings. Incorporating a desiccant structure with a vapour compression refrigeration system can distinctly eliminate latent and sensible load under hot and humid climates. It also increases COP and decreases the energy consumption of a vapour compression refrigeration system. Incorporating a desiccant scheme with a vapour compression refrigeration system will also lower desiccant regeneration temperature from (70–80)°C to (50–60)°C. Thus, the heat excluded by the condenser can contribute to renewal of desiccant in dehumidifier.
Desiccant based air conditioning units have shown numerous benefits than that of conventional arrangements for dehumidification and cooling. Thus, their usage is also scattering for tertiary and domestic structures, mainly when renewal of desiccant can be acquired via utilizing accessible unused heat. Increasing of occupant comfort demands are leading to rising requirement for air conditioning, but deteriorating global energy and environment crisis are starving for energy saving and environmental protection. The need to come up with the new energy saving as well as environmentally friend air conditioning systems has been more urgent than ever before. The liquid desiccant dehumidification systems integrated with VCS driven by low-grade heat sources can satisfactorily meet those needs; meanwhile, they provide an ideal area for the application of waste heat discharged from local factories brings less damage to environment.
The working of comfort desiccant dehumidifiers
The incoming room air is heated through electric heater to the required temperature and then humidified through a humidifier. After that, hot and humid air is blown over process segment of the rotary desiccant wheel. When processed air streams over the desiccant exterior in the adsorption segment, its vapour pressure is higher than that of the desiccant outward due to the more humid air state, which generates a significant difference. Thus, adsorption sector takes away water vapour from moist air. This water vapour is adsorbed on the exterior of the desiccant and is condensed above it. Hence, adsorption occurs. Then the air passes over the vapour compression refrigeration system’s cooling coil and is sensibly reduced to an ideal temperature.
In the regeneration sector, when restoration air streams over the desiccant exterior in the restoration segment, it heats the desiccant surface. It increases its vapour pressure which upturns the vapour pressure difference within regeneration air and desiccant surface. Therefore, restoration air evaporates the moisture from a desiccant layer. Thus, regeneration occurs.
The desiccant used in rotary dehumidifier may also get regenerated by use of heat recovery carried out waste heat expelled by the VCR (Vapor Compression Refrigeration) condenser as shown in figure 1. This results into amelioration of cooling performance of solid desiccant-based hybrid comfort space cooling system as well as efficient cooling of the condenser. Thus, reactivation heat requirement of dehumidifier used in solid desiccant-based vapour compression integrated hybrid cooling can also be provided by use of VCR condenser exhaust heat otherwise it is expelled to open atmosphere. This proves that the utilization of waste heat for dehumidifier reactivation not only achieves better energy savings but also marginal reduction in running cost of the system that results into economical feasibility of the system.
Benefits of comfort desiccant dehumidification over conventional VCR system
The comparison between comfort desiccant dehumidification and conventional VCR cooling for electrical energy utilization has been depicted in figure 2. To provide a more tangible comparison, the hourly electricity consumption of desiccant dehumidification integrated cooling system and conventional vapor compression cooling system are integrated over the entire summer cooling season for tropical hot and humid climate. Using desiccant dehumidification and cooling system, substantial reduction in electrical energy consumption could be obtained as compared to the conventional vapour compression cooling system. Thus, results provide fascinating insight into the significant energy saving potential of desiccant dehumidification and cooling system in a tropical and subtropical humid climate.
Conclusion
The use of desiccant dehumidification system in modern air conditioning in energy saving and green cooling approach in building comfort cooling can be an innovative approach towards sustainable cooling. Desiccant based hybrid cooling systems can achieve substantial energy savings by use of waste heat for reactivation of desiccant material used in rotary dehumidifiers – used in the system to make the hybrid cooling system more cost effective. It can also help in alleviating the peak supply of electrical power demanded by the conventional vapour compression air conditioning system by use of waste energy harvesting.
Dr. (Prof.) D.B. Jani received Ph.D. in Thermal Science (Mechanical Engineering) from Indian Institute of Technology (IIT) Roorkee. Currently he is a recognized Ph.D. Supervisor at Gujarat Technological University (GTU). He has published more than 180 Research Articles in reputed International Conferences and Journals. He has also published 5 reputed books in the area of thermal engineering. Presently, he is an Associate Professor at GEC, Dahod, Gujarat Technological University, GTU, Ahmedabad (Education Department, State of Gujarat, India). His area of research is Desiccant cooling, ANN, TRNSYS, and Exergy.
