General exergy models on conventional district cooling system (DCS)

natural water-cooled DCS and air-cooled DCS were presented based on the first and the second law of thermodynamics. A commercial building district in Shanghai was discussed as a case study. Dynamic energy and exergy analysis models of three kinds of DCS using the TRNSYS software were developed. And

exergy loss，exergetic efficiency and COP on an hourly basis of three kinds of DCS were analyzed. Furthermore

a method to determine the longest pipeline length from natural water source to chillers of natural water-cooled DCS was presented when natural water-cooled DCS is better than the other two kinds of DCS based on COP and exergetic efficiency. The results of the case study show that the exergetic efficiency of natural water-cooled DCS is the highest

air-cooled DCS the second

and conventional DCS the lowest. The exergetic efficiency for the three kinds of DCS is 16.52%

15.05% and 12.12% respectively

and the exergy loss per unit of cold energy is 0.289

0.323 and 0.414 respectively. In addition

the COP of natural water-cooled DCS is the highest

conventional DCS the second

and air-cooled DCS the lowest

with the values of 2.52

2.32 and 2.2 respectively.