Application Potential of Solar-driven Ejector Refrigeration System for Space Conditioning in Buildings

Project: Research

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The Hong Kong Government has started to launch a tangible target of renewable energy application, it is 1 to 2% of the electricity consumption by 2012. Solar energy has the highest potential of wider application among various types of renewable energy in Hong Kong, in which the total global solar irradiation of 4.70 GJ/m2 is received annually. According to the latest energy end-use data of Hong Kong, airconditioning and refrigeration consumed 48% electricity in office buildings in 2007, so it would be sustainable to make use of solar energy for driving the refrigeration cycle. In recent years, solar cooling is widely blooming in the Western Europe under the statutory policies and financial incentives, which are still not available in Hong Kong yet.Solar cooling can be broadly classified as solar-electric cooling and solar-thermal cooling. The former seems straightforward and applies photovoltaic (PV) panels to produce electricity and drive the conventional refrigeration equipment. However, the high initial cost of PV causes a very long payback period, usually longer than the equipment life if there is no financial subsidy. Therefore opportunities are still emerging for solar-thermal cooling. The market of solar thermal collectors is growing rapidly, China has the largest total capacity in operation in 2007, about 3.8 times more than the second largest country United States. The application potential of solarthermal cooling becomes more economically viable due to both technical advancement and mass production of solar collectors. From the recent studies of the Principal Investigator (PI), solar absorption refrigeration system using evacuated tubes is the most feasible option in Hong Kong among various types of solar-thermal cooling systems. The PI has also found that the year-round primary energy consumption of solar absorption refrigeration is lower than that of the medium-scale electric-driven refrigeration equipment by 37.5% for office use. Therefore it is worthwhile to have development of solar absorption refrigeration for space conditioning.In this proposal, ejector design is incorporated into the absorption refrigeration cycle in order to improve the overall system performance. Ejector is a fluid compression device without power input. Various designs have been proposed and constructed by others, but the system effectiveness is dependent upon the refrigerant properties, climatic and loading conditions, therefore it is necessary to explore the application potential in Hong Kong. Office buildings are targeted in this study, since the solar availability is generally coincident with their occupancy. To evaluate the year-round performances of the solar-driven combined ejector and absorption refrigeration system, a number of performance metrics are used, including solar fraction, coefficient of performance (COP), heat gain factor, solar thermal gain, primary energy consumption and exergetic COP. The entire study would be conducted by means of plant and energy simulation. It is expected that the research outcomes will promote wider applications of solar energy and alleviate the electricity demand for space conditioning. The results will not only beneficial to Hong Kong, but also to the adjacent hot and humid cities. We believe the findings will also be a good foundation to attract the research funds from the Government, like GRF (General Research Fund) and ECF (Environment and Conservation Fund), for in-depth and long-term studies in solar-thermal cooling.


Project number7002555
Grant typeSRG
Effective start/end date1/05/1028/03/13