Solar hybrid air-conditioning system for high temperature cooling in subtropical city K.F. Fong * , C.K. Lee, T.T. Chow, Z. Lin, L.S. Chan Division of Building Science and Technology, College of Science and Engineering, City University of Hong Kong, 83 Tat Chee Avenue, KowloonTong, Kowloon, Hong Kong, China article info Article history: Received 18 November 2009 Accepted 24 February 2010 Available online 21 March 2010 Keywords: Adsorption refrigeration High temperature cooling Radiant cooling Solar air-conditioning Desiccant dehumidification abstract Although solar energy is able to power the heat-driven refrigeration, its contribution is quite limited due to the conventional cooling requirement. In building air-conditioning, it is common to supply low temperature chilled water, usually in 5e7  C. If this temperature can be elevated, it would enhance the effectiveness to harness solar energy and minimize auxiliary heating. Solar refrigeration would then be more effective through high temperature cooling, by providing 15e18  C chilled water instead. In such provision, radiant ceiling cooling can be coupled to handle the space cooling load, particularly space sensible load. And the space latent load and ventilation load are handled by a separate dehumidification provision, like the heat-driven desiccant dehumidification. Therefore, a solar hybrid air-conditioning system is formulated, using adsorption refrigeration, chilled ceilings and desiccant dehumidification. In this study, the year-round performances of the proposed solar hybrid air-conditioning systems were evaluated for two typical office types. The performance metrics include the solar fraction, coefficient of performance, solar thermal gain, primary energy consumption and indoor conditions. Comparative study was conducted for the hybrid air-conditioning system worked with the three common types of chilled ceilings, namely the chilled panels, passive chilled beams and active chilled beams. The solar hybrid air-conditioning system was also benchmarked with the conventional vapour compression refrigeration for office use. It is found that the proposed solar hybrid air-conditioning system is technically feasible through high temperature cooling. Among the three types of chilled ceilings, the passive chilled beams is the most energy-efficient option to work with the solar adsorption refrigeration for space conditioning in the subtropical city. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction The demand of air-conditioning is increasing due to the effect of climate change and global warming. If we still rely on the conventional electric air-conditioning but electricity is generated from fossil fuels, the greenhouse gas emission would continuously worsen global warming, in turn the demand of air-conditioning would be further increasing. In the subtropical cities, air-conditioning is a standard provision for buildings. However, air-conditioning would commonly take up half of building electricity consumption. More and more evidents show that the climate change is getting worse. The changes of global surface temperature, global average sea level, snow and ice over 1850 to 2000 are reported [1]. The increasing trend of the environmental temperatures would affect the future air-conditioning requirements [2]. Therefore it is urgent to minimize the consumption of fossil fuels and promote wider use of alternative energy, particularly in refrig- eration and air-conditioning. Application of solar cooling is a feasible way to replace the electric refrigeration machines for building air-conditioning. In the recent years, more reviews have been made about the feasibility of wider application of solar cooling technologies [3e5]. Especially the solar thermal technologies, they are getting mature for refrigera- tion and air-conditioning purposes. A number of demonstration projects have been launched to study the design and operation of the solar refrigeration and air-conditioning [6e8]. It is fit to apply solar energy in air-conditioning for office and commercial build- ings, since the major cooling demand is coincident to the time of solar energy supply. In a centralized air-conditioning, it is common to supply 5e7  C chilled water for cooling and dehumidification purpose. If this temperature can be elevated, it would enhance the effectiveness to harness solar energy. Solar refrigeration is more effective to provide 15e18  C chilled water for high temperature cooling, * Corresponding author. Tel.: þ852 27888724; fax: þ852 27889716. E-mail address: bssquare@cityu.edu.hk (K.F. Fong). Contents lists available at ScienceDirect Renewable Energy journal homepage: www.elsevier.com/locate/renene 0960-1481/$ e see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.renene.2010.02.024 Renewable Energy 35 (2010) 2439e2451