Chilled 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, air treatment unit, etc.) needs the cold water provided by the chiller, but the chilled water will not flow naturally due to the restriction of resistance, which requires the pump to drive the chilled water to circulate to achieve the purpose of heat transfer.
Cooling water pump:
A device that drives water to circulate in a cooling water loop. As we know, the cooling water takes away some heat from the refrigerant after entering the chiller, and then flows to the cooling tower to release this heat. The cooling water pump is responsible for driving the cooling water to circulate in the closed loop between the unit and the cooling tower. The shape is the same as the chilled water pump.
Water supply pump:
Air conditioning water refill device, responsible for the treatment of the softened water into the system. The shape is the same as the upper water pump. The commonly used pumps are horizontal centrifugal pump and vertical centrifugal pump, which can be used in the chilled water system, cooling water system and water refill system. Horizontal centrifugal pump can be used for large room area, and vertical centrifugal pump can be considered for small room area.
Introduction to the water pump model, for 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.
Parallel operation of water pumps:
|
Number of pumps |
flow |
Value added of flow |
Flow reduction compared to single pump operation |
|
1 |
100 |
/ |
|
|
2 |
190 |
90 |
5% |
|
3 |
251 |
61 |
16% |
|
4 |
284 |
33 |
29% |
|
5 |
300 |
16 |
40% |
As can be seen from the above table: when the water pump runs in parallel, the flow rate attenuates somewhat; When the number of parallel stations exceeds 3, the attenuation is particularly severe.
It is suggested that:
1, the selection of multiple pumps, to consider the attenuation of the flow, generally additional 5% ~ 10% margin.
2. The water pump should not be more than 3 sets in parallel, that is, it should not be more than 3 sets when the refrigeration host is selected.
3, large and medium-sized projects should be set up respectively cold and hot water circulating pumps
In general, the number of chilled water pumps and cooling water pumps should correspond to the number of refrigeration hosts, and one should be used as a backup. The water pump is generally selected in accordance with the principle of one use and one backup to ensure the reliable water supply of the system.
Pump nameplates are generally marked with parameters such as rated flow and head (see pump nameplate). 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) Flow calculation formula of chilled water pump and cooling water pump:
L (m3/h) =Q(Kw)×(1.15~1.2)/(5℃×1.163)
Q- Cooling capacity of the host, Kw;
L- Flow of chilled cooling water pump, m3/h.
(2) The flow of the supply pump:
The normal recharge water volume is 1% ~ 2% of the circulating water volume of the system. However, when selecting the supply pump, the flow of the supply pump should not only meet the normal recharge water volume of the above water system, but also consider the increased recharge water volume in the event of an accident. Therefore, the flow of the supply pump is usually not less than 4 times of the normal recharge water volume.
The effective volume of the water supply tank can be considered according to the normal water supply of 1 ~ 1.5h.
(3) Composition of chilled water pump head:
Evaporator water resistance of refrigeration unit: generally 5~7mH2O; (See product sample for details)
End equipment (air handling unit, fan coil, etc.) table cooler or evaporator water resistance: generally 5~7mH2O; (Please refer to product sample for specific values)
The resistance of backwater filter, two-way regulating valve, etc., is generally 3~5mH2O;
Water separator, water collector water resistance: generally a 3mH2O;
Cooling system water pipe along the resistance 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 situation of the refrigeration system, can not copy the experience value!
(4) Composition of cooling pump head:
Condenser water resistance of refrigeration unit: generally 5~7mH2O; (Please refer to product sample for specific values)
Spray pressure: generally 2~3mH2O;
The height difference between the water tray and the nozzle of the cooling tower (open cooling tower) : generally 2~3mH2O;
The resistance of backwater filter, two-way regulating valve, etc., is generally 3~5mH2O;
Cooling system water pipe along the resistance and local resistance loss: generally 5~8mH2O;
To sum up, the cooling pump head is 17~26mH2O, generally 21~25mH2O.
(5) feed pump head:
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 outlet end of the pump +3 ~ 5mH2O.
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Post time: Dec-03-2022
