At present, the cold water supply and return water temperature in the air conditioning project is generally 7 ℃ / 12 ℃, the temperature difference is 5 ℃. And the hot water supply and return water temperature is 60 ℃ / 50 ℃, the temperature difference is 10 ℃. About twice the temperature difference between them.
The heat load of air conditioning in winter in the southern region is smaller than the cooling load in summer in the cold region; the heat load of air conditioning in winter in the cold northern region is larger than that in summer. In addition, the resistance of the steam-water heat exchanger or water-water heat exchanger commonly used in winter is much smaller than the resistance of the evaporator of the chiller. Therefore, only when the ratio of summer load to winter load is 0.5, the amount of chilled water in summer and the amount of hot water in winter will be equal, and then a group of circulating domestic water pump can be shared in winter and summer.
When the flow of hot water in winter is much smaller than the flow of cold water in summer, if a group of circulating domestic water pumps are shared in winter and summer, some circulating water pumps can be put into operation in winter, but at this time, in order to ensure the flow of the user system, the outlet valve of the small pump needs to be closed. After throttling, the pipeline characteristic curve moves up and the pump head increases.
If you keep the pump head unchanged, you need to increase the flow, that is, small temperature difference, large flow operation. In this case, no matter what kind of operation mode the water pump adopts, it will cause a waste of electric energy in winter operation. Therefore, cold and hot domestic water pumps should be installed separately.
For small air-conditioning projects, in the two-control water system, chilled domestic water pumps can be used as hot water pumps in winter, but at this time, it is necessary to check whether the pumps are working in the high-efficiency area under heating conditions and determine the appropriate number of pumps to run. When necessary, the speed of the water pump can be adjusted to meet the flow and head requirements of winter heating conditions.
For district two-control and four-control water systems, cold and hot water are independent systems, and cold and hot domestic water pumps are set separately.
(1) Setting of primary cold domestic water pump
The number and flow of chilled water pumps (primary pumps) should correspond to the number of refrigeration units and the required flow, that is, the "one machine and one pump" operation mode, generally no equipment pumps. There is no hard-and-fast provision in the design code for whether the air-conditioning system that operates throughout the year is equipped with a backup pump.
(2) Setting of secondary cold domestic water pump
The setting of the secondary cold domestic water pump should be determined through technical and economic comparison according to the size of the cold water system, the degree of difference in pressure loss of each parallel loop, use conditions and adjustment requirements. The secondary pump is generally not used for equipment, but it should not be less than two, so that when running at a small flow rate, it can be rotated to facilitate maintenance. The secondary pump should be equipped with frequency conversion speed regulation device.