The invention relates to an economical operating method of a central air-conditioning
system, comprising the following steps: cold accumulation operation, i.e. a
control system controls the closing of a valve at the inlet end of a fan coil, valves at two ends of a cold accumulation groove are open, refrigerating water comes out of the
evaporator of a refrigerating main
machine and enters the cold accumulation groove through a valve, the refrigerating water and cold accumulation medium in the groove undergo heat exchange, and the refrigerating water subject to the heat exchange is jointed at the collector
pipe of the cold accumulation groove and is conveyed to the
evaporator of the refrigerating main
machine by a refrigerating water pump for purpose of temperature reduction, thus the cold accumulation circulation is completed; and cold supply operation, i.e. a monitor of a
control system is used for monitoring the environment temperature and the air-conditioning load change and calculates which working condition of the compressor of the refrigerating main
machine leads to the highest energy efficiency, a frequency converter is used for changing the rotation speed of the
centrifugal compressor so that the compressor can work in the optimum working condition, the cold accumulation groove provides cold load for the sake of sufficient cold load, and surplus cold is stored in the cold accumulation groove. The invention causes the refrigerating main machine of the central air-conditioning
system to keep operating with the highest efficiency, without being influenced by the change of the
outside air temperature or the air-conditioning load, and the invention causes the refrigerating main machine of the central air-conditioning
system to save energy to the maximum extent.