Hi Viewers I am Afreen Ali . i bring this video for basic chilled water pump  head for primary pump / head for secondary pump. Kindly Subscribe my channel AfreenAli

Head for primary pump / head for secondary pump

Head for primary pump = chiller friction losses + pipe losses for longest pass + fitting losses

Head for secondary pump = pipe losses for longest pass + fitting losses + last equipment in the longest pass ( FCU or AHU )

there is tow way to calculate the pump head

1- equivalent length method and you may found it in carrier handbook.

2- k factor you will find it in ASHRAE.

the main concept for calculation and sizing

pipe size < = 2" -----> Max velocity = 4 fps

pipe size > 2" --------> max friction losses 4ft wg / 100 ft

there are many programs for pump head calculation like

H-sym (Elite) , Trane pipes , pipe flow expert

Example mention below with details

There is a difference between the pressure required from pump which is generated by the pump itself (dP)and the hydrostatic pressure generated by elevation

the fist one, we considered it for moving the fluid but the second one we considered it for determining the max. working pressure inflicted upon pipes, pump's parts (casing , mechanical seal ,....)and all the elements in network

example:

If we calculate dP=5bar required from pump to move the water with the required flow rate.

these 5bar may be from 1bar to 6bar

and may be from 15bar to 20bar

The 2 cases have the same dP (friction losses and fittings ,....) but not the same max. working pressure

Such as (Example), the maximum pressure the chiller would see, if on the bottom floor, is approximately 900 ft (due to elevation) + 140 ft (due to pump shut off pressure, which is basically the TDH provided by the pump during operation and the shut off pressure of the pump) for a total static pressure of 1040 ft (450 psi) per Solution A. This would exceed the rated pressure of the described fitting/chiller.

If the chiller is on the top floor (Solution C), then the total pressure the chiller would see would be 65 psi. This would be within the pressure rating of the fitting/chiller. The pump is still contributing 140 ft to the pressure, but because of the difference in elevation, the static effect is much less.

In this case you would specify fittings/pipe with higher pressure ratings on the lower floors and decreasing ratings as you went up. You would locate the chiller at a level where the pressure does not exceed its maximum pressure.

I hope that helps.

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