The University of Nottingham is developing a solar air-conditioning system that cuts electricity consumption by up to 50 per cent compared to the conventional vapour compression (VC) system.
This innovation could have major savings for the environment and people’s pockets, particularly as air-conditioning accounts for a significant portion of total energy use around the world.
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 supported on this research by the Royal Society.
The two institutions are investigating a new air-conditioning technology with sorption thermal battery for temperature and humidity independent control (THIC), powered by solar energy.
Its innovative features include:
• Conditioned air temperature and humidity to be controlled 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
Dr Zhu, from the Fluids and Thermal Engineering Research Group at Nottingham, 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 per cent electrical consumption and COP increases about 40-60 per cent, 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 its inherent instability and the lack of year-round sun in many countries.
Design innovations
The solid-gas sorption thermal battery has the ability to store both heat and cold energy at a controllable temperature in one unit. The heat energy is used to power the dehumidification sub-system, while the cold energy is used to cool the air that needs to circulate in indoor environments.
The proposed system consists of two units: heat-powered membrane liquid-drying dehumidification and solar sorption thermal battery units. Two sorption thermal battery units are used to assure the system continuously operates.
To remove moisture and latent heat from the incoming supply air stream, the air-con system uses a liquid desiccant material which attracts and holds water vapour.
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 working 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 room.
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.
Benefits to industry
On completion, the system could be of huge value to industries including Heating, Ventilation, and Air-Conditioning (HVAC), building services, environmental engineering and component manufacture.
“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,” explains Dr Zhu.
“The proposed system will focus on THIC and sorption energy storage to improve air-conditioning energy-efficiency. We hope this will be a step change in thermal energy storage technology and strengthen renewable energy application in the building sector.”
The collaboration will be mutually beneficial to both the UK and China and will encourage knowledge transfer between two universities, providing a background for the development of new energy efficient means of controlling the building internal environment.
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Notes to editors: The University of Nottingham has 43,000 students and is ‘the nearest Britain has to a truly global university, with a “distinct” approach to internationalisation, which rests on those full-scale campuses in China and Malaysia, as well as a large presence in its home city.’ (Times Good University Guide 2016). It is also one of the most popular universities in the UK among graduate employers and was named University of the Year for Graduate Employment in the 2017 The Times and The Sunday Times Good University Guide. It is ranked in the world’s top 75 by the QS World University Rankings 2015/16, and 8th in the UK for research power according to the Research Excellence Framework 2014. It has been voted the world’s greenest campus for four years running, according to Greenmetrics Ranking of World Universities.
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