Microencapsulated phase change material (MPCM) slurry provides a good kind of medium for thermal energy storage due to its thermal properties, especially proper working temperature, which is appropriate for maximized utilizations of nature cooling sources. In this study, a novel MPCM slurry storage system is investigated by combining MPCM slurry storage with a nocturnal radiative cooling system. The cooling energy consumption and the effect of energy-free nocturnal radiation application were simulated using the energy simulation code ACCURACY and MATLAB model based on hour-by-hour calculations in five typical cities across China. It can be concluded that MPCM slurry appears to be a good medium for the combined application of passive cooling technology in air conditioning system. The results showed the energy saving potential in Lanzhou and Urumqi can reach 77% and 62% for low-rise buildings, which exhibits strong attractions for building energy conservation and emission reduction. Hong Kong has the weakest effect in the five typical cities under the same operating condition due to the hot and humid climate condition. The present hybrid system is recommended to be used in northern and central China cities where the weather is dry and the ambient temperature is low at night. (C) 2012 Elsevier B.V. All rights reserved.