NOTTINGHAM, England — The University of Nottingham is developing a solar air conditioning system that is said to have the capability to cut electricity consumption by up to 50 percent compared to conventional vapor compression (VC) systems.
Dr. Jie Zhu, from the Department of Architecture and Built Environment at The University of Nottingham, and Professor Tingxian Li, Shanghai Jiaotong University, China, are conducting this research supported by the Royal Society.
The two institutions are investigating a new air conditioning technology, powered by solar energy, whose features include:
• The ability to condition the air and control humidity independently.
• A sorption thermal battery that combines heat and cold energy storage in one unit and has the ability to achieve thermal energy storage with controllable temperature.
Zhu said, “A VC cooling system adopts a condensation dehumidification method to handle both sensible and latent heat loads. This means the system has to operate under lower evaporation temperatures, which results in lower cooling capacity, lower coefficient of performance (COP), and sometimes a reheating process is required to meet supply air requirements.
“We are proposing a temperature and humidity independent control technology to solve this problem. This system can save 25-50 percent electrical consumption and COP increases about 40-60 percent, thus greatly reducing operating costs, compared to the conventional VC system.”
Thermal energy battery storage plays a key role in the use of solar energy for heating and cooling due to solar's inherent fluctuation and the lack of year-round sun in many countries.
The solid-gas sorption thermal battery has the capability to store both heat and cold energy at a controllable temperature in a single unit. The heat energy is used to power the dehumidification subsystem, while the cold energy is used to cool the air circulating in the indoor environment.
The proposed system consists of heat-powered membrane liquid-drying dehumidification and solar sorption thermal battery units. Two sorption thermal battery units are used to ensure the system continuously operates.
To remove moisture and latent heat from the incoming supply air stream, the air conditioning system uses a liquid desiccant material which attracts and holds water vapor. During the regeneration process in the dehumidification unit, the desiccant solution is heated by the sorption heat of the battery and then flows into the regeneration cabin where the warmed desiccant solution will remove moisture from the air.
Afterwards, as the air reaches a water-air cooler, it is cooled by chilled water produced by the evaporation heat of refrigerant from the sorption thermal battery. This cyclical process ultimately generates the dry and cooled supply air which is released into a space.
The proposed research is investigating new composite sorbents, thermal energy storage capacity, heat and mass transfer properties, and will assess economic and environmental impacts using theoretical and experimental measures.
A small scale prototype system will be designed, constructed, and tested to evaluate the proposed system performance on cooling, dehumidification, and energy storage.
“Solar air conditioning is one of the promising technologies to alleviate the huge demand for energy resources. It has the potential to provide a viable alternative to conventional air conditioning systems,” said Zhu.
