Raising Evaporative Cooling Potentials Using Combined Cooled Ceiling and High Temperature Cooling Storage

Evaporative cooling is able to generate the cooling medium at a temperature approaching to the ambient wet bulb temperature. In this paper, a low-energy air conditioning strategy is proposed, which is a combination of cooled ceiling (CC), microencapsulated phase change material (MPCM) slurry storage and evaporative cooling technologies. The assessment of evaporative cooling availability and utilization is done for five representative climatic cities, including Hong Kong, Shanghai, Beijing, Lanzhou and Urumqi in China, and the energy saving potential of the proposed air conditioning system is analyzed by using a well validated building simulation code. The results indicate that the new system offers energy saving potential up to 80% under northwestern Chinese climate and up to 10% under southeastern Chinese climate. The optimal sizing method of the slurry storage tank is also proposed based on the slurry cooling storage behaviors and cooling demand variations of the ceiling panels. INTRODUCTION In the past decades, CC systems are increasingly used for cooling in the commercial office buildings. A displacement ventilation system is usually used to provide the fresh air at a minimum ventilation rate for a room when a CC system is applied for the cooling load removal. Since a CC system operates at relatively high cooling water temperature, usually around 14-20C [Feustel and Stetiu 1995], depending on the areas of the ceiling panels, it offers the opportunities to use the cooling water generated by evaporative free cooling [Niu and v.d. Kooi 1995] and reduces the energy requirement of the vapor compression refrigeration system. By integrating the cooling tower model into a dynamic thermal analysis program, energy saving potentials of combined system of CC and evaporative cooling tower were evaluated for different climates by different researchers [Niu and v.d. Kooi 1995, Vangtook and Chirarattananon 2007], and the simulation results revealed significant energy saving potentials of combining evaporative free cooling with CC system for both the European countries like the Netherlands and the Asian countries like Thailand. In recent years, a new kind of thermal energy storage medium was proposed, in which a phase change material (PCM) was microencapsulated with plastic shells and suspended into water to form solid-liquid MPCM slurry [Yamagushi et al 1996, 1999]. The heat capacity of the slurry is then significantly increased with the presence of MPCM particles. Due to the wide temperature availability of PCM, MPCM slurry also offers the flexibility of wide range of working temperatures. The purpose of this study is to investigate the energy saving potential of a hybrid system which is a combination of CC, MPCM slurry storage and evaporative cooling technologies. The MPCM slurry is used to store the cooling energy generated by the Eleventh International IBPSA Conference Glasgow, Scotland July 27-30, 2009