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Chilled Water System Design
1. Selection principles and precautions
First of all, the flow rate and pump head of the highest operating condition must be satisfied, and the working state point of the water pump should be in the high efficiency range. The flow and head of the pump should have a margin of 10-20%. When the flow rate is large, multiple parallel operation should be considered, and the number of parallel connection should not exceed 3, and the same type of pump should be selected as much as possible. The circulating water pump in the heating and air-conditioning system should be equipped with a backup water pump. When selecting a pump, the influence of the static pressure of the system on the pump body must be considered, and attention must be paid to the pressure bearing capacity of the pump casing and packing and the influence of axial thrust on the sealing ring and shaft seal. When selecting a water pump, the static pressure value it should withstand should be indicated, and if necessary, the manufacturer will do special treatment.
2. Chilled water pump selection
Chilled water flow: The unit selected without considering the simultaneous utilization rate can be selected according to the value provided in the product catalog or calculated according to the following formula. If the simultaneous usage rate is considered, it is recommended to use the following formula for calculation. Q in the formula is the total cooling load of the building without considering the simultaneous utilization rate.
3. Composition of chilled water pump head
★Water resistance of the evaporator of the refrigeration unit: generally 5~7mH2O; (for specific values, please refer to the product catalog)
★Water resistance of surface cooler or evaporator of terminal equipment (air handling unit, fan coil unit, etc.): generally 5~7mH2O; (depending on the volume value, please refer to the product catalog)
★Resistance of return water filter, generally 3~5mH2O;
★Water resistance of water separator and water collector: generally one is 3mH2O;
★Resistance along the water pipeline of the refrigeration system and local resistance loss: generally 7~10mH2O;
To sum up, the head of the chilled water pump is 26~35mH2O, generally 32~36mH2O.
Note: The calculation of the head should be based on the specific conditions of the refrigeration system, and experience values cannot be copied!
4. When piping the pump, pay attention to the following points:
★Installation of flexible connecting pipes: Installing flexible connecting pipes on the suction pipes and discharge pipes connected to the water pump is beneficial to reduce and weaken the transmission of noise and vibration of the water pump.
★Check valve installed at the outlet: the purpose is to prevent the water pump from being damaged due to the reverse flow of water when the power is suddenly cut off.
★Inlet valve and outlet valve should be installed on the suction pipe and pressure outlet pipe of the water pump respectively; the purpose is to facilitate maintenance without emptying the water in the system when the water pump is not running.
★The outlet pipe of the water pump should be equipped with a thermometer and a pressure gauge to facilitate detection. If the water pump sucks water from the ground tank, a vacuum gauge should also be installed on the suction pipe.
★The height of the pump foundation above the ground should be less than 0.1m, and the ground should be provided with drainage ditches.
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