Four methods for judging the flow of chilled water in a chiller

Aug 13, 2021

Generally speaking, when buying a chiller, you will have questions. I don't know how to judge the chilled water flow rate of the chiller? From what aspects should the chiller water flow be considered? Here is a brief talk.

The detection of the return water temperature and the outlet water temperature of the chiller should be carried out in the normal state of the unit:

After 30 minutes of starting up, check the system or the chilled water system inlet and outlet thermometers through the unit's control system parameters, and the inlet and outlet water temperatures of the unit can be read when the unit is running. The difference must be about 4-6 degrees. If the temperature difference between the inlet and outlet water is too large, it means that the water flow of the water system through the plate is too small, which may cause the unit to fail to operate normally or be damaged.

Water pressure detection of the inlet and outlet pipes of the unit

Through the detection of the return water pressure and the outlet water pressure value, check the water flow rate of the chiller under the pressure difference between the inlet and outlet water pressures in the random manual of the unit. By referring to the water flow corresponding table or diagram of the unit in the manual, So as to judge whether the water system is normal; and through this difference to judge which section of the water pipeline has a large resistance value, and make corresponding rectification plans and actions.

Compressor copper pipe suction temperature detection only needs to be carried out during refrigeration operation

If it is detected that the suction temperature of the compressor is lower than 0 degrees after the refrigeration chiller is turned on for 30 minutes, it means that the water flow in the water-side heat exchanger is not enough, which causes the evaporation temperature and the evaporation pressure to drop, and causes the Freon to flow in the evaporator. The suction pipe of the compressor is still evaporating and absorbing heat, which will cause the suction temperature of the compressor to be lower than 0 degrees; in addition, it is necessary to exclude the drop in evaporating pressure and evaporating temperature caused by the too low water temperature set point; The low water temperature unit can be considered normal as long as the compressor has a suction superheat of 6~8℃. Therefore, under normal water flow, the suction temperature of the compressor will generally be greater than 0°C, and water system problems should be eliminated if it is lower than this value.

The current needs to be detected when the pump is running

By detecting the running current of the chiller water pump and comparing it with the rated current, it can be judged whether the actual water flow is larger or smaller than the rated water flow of the pump. A comprehensive judgment can be made with the previous parameters to obtain an accurate water system detection analysis and judgment. Report.

The water selection pump is generally centrifugal, so it is a problem to determine its flow and head.

Determination of pump flow:

We can calculate the energy balance of the chiller as a system. The heat entering the system includes: the cooling capacity plus the motor power, the heat removed from the system, the heat carried by the cooling water and the heat dissipated in the environment, and the heat transferred to the environment is omitted. According to the process requirements (inlet water temperature and outlet water temperature), the flow of circulating water can be obtained. For example, the total maximum cooling capacity of a centrifugal refrigerator and a screw refrigerator is 2637+1231=3947kw, The motor power is: 467+256=723kw, and the total heat (cold) generated by 4670kw needs to be removed. If the cooling water passes through the cooling tower to change from 37°C to 32°C according to the design requirements, the amount of heat it brings out is The water volume should be: 4670÷1.163×1000÷(37-32)=803.1m3/h

, (1.163 is the conversion coefficient between kilowatts and kcal), so that the flow rate of the pump should be determined, generally consider two pumps operation, one pump standby mode, in order to facilitate operation in the high temperature period.

The second is the pump head. It should calculate the resistance loss based on the flow rate of the water in the pipeline (determined by the size of the pipeline), the length of the pipeline, the local resistance (the condenser in the chiller (can be found in the manual), and the control parts. Cooling water is a circulating system, you don’t need to consider the height difference, just add the height difference of the cooling tower. The pipe flow rate is generally about 1m/s, you can press: (pressure drop per meter of pipe mpa/m) i= Calculate with the formula 0.0000107×v×v÷d^1.3, where v is the average flow velocity (m/s), so the pump head is also determined.

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