How to calculate head pressure of pump for a CHW system.

 How to calculate head pressure of pump for a CHW system. This is a question where almost all engineers ask while interviews.

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There are 2 types of heads

Static head which is due to height difference - second is Dynamic head which is due to the losses while flow like losses in pipe due to friction, bends and due to piping accessories like vaves coils etc.

As chilled water systems are closed loop so the static head is zero in the chilled water system (NOT FOR COOLING TOWR IF APPLICABLE BECAUSE CONDENSER PUMPS FOR COOLING TOWERS ARE OPEN CIRCUIT). 

So the pressure for CHW System will be calculated by adding all the piping in the maximum pressure drop route and add friction losses, bending and coil losses, losses in equipments etc thus adding all of them will give you the pressure head.

Example 

Two different pressures. All friction losses are for pump capacity sizing. Basically how much water the pump can pump. This would be the same if the same piping system is 900 ft high, or 900 ft wide. 

The static pressure depends on height and is important for selection of equipment, relief valves etc. so it doesn't "explode" at the highest pressure. You need to imagine the hydro-static pressure + the pump pressure at tha tlocation. Pump pressure at pump suction side is zero, at discharge the max what the pump can do (assume someone overrides the VFD).

Consider gravity of fluid. for water every 2.3 ft you increase by one psi. this will be less for lighter fluids, more for denser fluids.