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Function and selection of water pump in refrigeration and air conditioning system

Frozen water pump:

A device that drives water to circulate in a chilled water loop.As we know, the end of the air conditioning room (such as fan coil unit, air treatment unit, etc.) needs cold water provided by the water chiller, but the frozen water will not flow naturally due to the restriction of resistance, which requires a pump to drive the frozen water to circulate in order to achieve the purpose of heat transfer.

Cooling water pump:

A device that drives water to circulate in a cooling water loop.We know that the cooling water takes away part of the heat from the refrigerant after entering the chiller, and then flows to the cooling tower to release this part of the heat.And the cooling water pump is responsible for driving the cooling water in the unit and the cooling tower this closed loop for circulation.The appearance is similar to that of a chilled water pump.

Pump:

The device used for air conditioning water replenishment is responsible for injecting the treated softened water into the system.The appearance is the same as the above water pump. The commonly used water pump is horizontal centrifugal pump and vertical centrifugal pump. They can be used in the chilled water system, the cooling water system and the water replenishment system.Horizontal centrifugal pump can be used for large area of the machine room, and vertical centrifugal pump can be considered for small area of the machine room.

Water pump model introduction, example: 250RK480-30-W2

250: inlet diameter 250 (mm);

RK: heating and air conditioning circulating pump;

480: Design flow point 480m3/h;

30: Design head point 30m;

W2: Pump mounting type.

1. When choosing multiple pumps, we should consider the attenuation of flow, and generally add a margin of 5% ~ 10%.

2, the pump should not be more than 3 in parallel, that is, the selection of refrigeration host should not be more than three.

3. Cold and hot water circulating pumps should be set up respectively in large and medium-sized projects.

In general, the number of chilled water pump and cooling water pump should correspond to the refrigeration host, and consider a standby.The supplementary water pump is generally selected in accordance with the principle of one use and one standby to ensure the reliable water replenishment of the system.

The nameplate of the pump is generally marked with parameters such as rated flow rate and head (see pump label).When we choose the pump, we need to first determine the flow and head of the pump, and then determine the corresponding pump according to the installation requirements and the site situation.

(1) Calculation formula of flow rate of frozen water pump and cooling water pump:

L (m3/h) =Q(kW)×(1.15~1.2)/(5℃×1.163)

Q- refrigerating capacity of the main engine, KW;

L- Flow rate of refrigerated cooling water pump, m3/h.

(2) Flow rate of supply water pump:

The normal replenishment water is 1% ~ 2% of the circulating water of the system. However, when selecting the replenishment water pump, the flow of the replenishment water pump should not only meet the normal replenishment water of the above water system, but also consider the increased replenishment water when an accident occurs. Therefore, the flow of the replenishment water pump is usually not less than 4 times of the normal replenishment water.

The effective volume of the replenishment tank can be considered according to the normal replenishment water volume of 1 ~ 1.5h.

(3) the composition of the head of the frozen water pump:

Refrigeration unit evaporator water resistance: generally 5~ 7MH2O;(Please refer to product sample for details)

End equipment (air handling unit, fan coil unit, etc.) table cooler or evaporator water resistance: generally 5~ 7MH2O;(Please refer to the product sample for the specific value)

The resistance of backwater filter, two-way regulating valve, etc., is generally 3~ 5MH2O;

Water resistance of water divider and water collector: generally one is 3MH2O;

The resistance and local resistance loss of the water pipe in the refrigeration system are generally 7~ 10MH2O;

In summary, the head of the frozen water pump is 26~ 35MH2O, generally 32~ 36MH2O.

Note: the calculation of the head should be based on the specific situation of the refrigeration system, do not copy the empirical value!

(4) the composition of cooling pump head:

Refrigeration unit condenser water resistance: generally 5~ 7MH2O;(Please refer to the product sample for the specific value)

Cooling tower nozzle spray pressure: generally 2~ 3MH2O;

The height difference between the water tray and the nozzle of the cooling tower (open cooling tower) is generally 2~ 3MH2O;

The resistance of backwater filter, two-way regulating valve, etc., is generally 3~ 5MH2O;

The resistance and local resistance loss of the water pipe in the refrigeration system are generally 5~ 8MH2O;

In summary, the head of the cooling water pump is 17~26mH2O, generally 21~25mH2O.

(5) Head of supplementary water pump:

The head is the rich head of the distance between the constant pressure point and the highest point + the resistance of the suction end and the outlet end of the pump +3 ~ 5MH2O.

 


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