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How to find total head for primary or secondary Pump in the Chilled water systems? Give any thumb rules to select head

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Question added by Muhammed Arshak
Date Posted: 2016/04/22
chetan sharma
by chetan sharma , Senior project engineer , trinity engineering services

There is no thumb rule for this you can only calculate it based on friction losses in pipe by equivalent length method and for fittings k factors from the various supplier of the fittings ashrae k factors are old they tend to change according to various suppliers.

 

All suppliers for the fittings have to have the k factors according to prove there manufacturing according to designated area code of practice.

 

 

Sherif Mohammed Ibrahim
by Sherif Mohammed Ibrahim , Senior Mechanical Technical engineer , Al-Latifia Trading & Contracting Company

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 

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