DRV plus ISOLATION VALVE on pump discharge line

[moideen]

This is a project submittal for the variable chilled water pump, and I've noticed a suggestion from the consultant to include a balancing valve (DRV-double regulating type) alongside a butterfly isolation valve (BV). My concern lies in the following points:
The DRV concept seems to conflict with the variable flow concept, potentially resulting in unnecessary energy loss.
If the DRV is solely for isolation purposes, it raises the question of the necessity of the BV.
I would greatly appreciate your further insights and comments on this matter. Thank you.

The problem with the world is that intelligent people are full of doubts, while stupid ones are full of confidence.
-Charles Bukowski-

 

[LittleInch]

Is the variable flow due to turning pumps on and off or variable speed of the pumps?

Is the valve there to balance flows from each pump?

Parallel operation of even "identical" pumps is difficult to balance without control devices, so this seems like a good idea.

A bit more explanation would be good.

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[mk3223]

The purpose of the BV at the discharge line is the on-off isolation valve to isolate the line for the maintenance of the DRV if needed.

 

[LittleInch]

Also what exactly is that DRV?
DRV means?
Why is it looking like a ghost picture and just hanging in mid air?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[TenPenny]

The BVs are necessary if maintenance is ever needed on the pumps, so no matter what else is in the system, the BV should be there. And it is a poor practice to use an isolation valve to balance the line.

 

[georgeverghese]

https://www.cranefs.com/product/balancing-valves/dm931/

If pressure drop at a given flow is too high, you could ask the consultant to use a larger DRV?

 

[moideen]

@LittleInch, the DRV-double regulating valve, which is used to balance the flow rate of chilled water pumps during commissioning It helps adjust flow if the actual head is less than the selection head.
These distribution pumps adjust their flow based on the building's needs. The VFD in the automation system adjusts the pump speed according to the signal it receives. But if the VFD keeps the speed locked to the design flow rate, we might question why we still need the DRV in a system where the flow isn't constant. Using the DRV like this could waste energy.
When the DRV is fully open, it causes about 2.5 meters of head loss. And as we decrease the flow by turning the DRV clockwise, the pump's BEPmoves to the left, which can increase energy consumption. For example, let's say the pump's design flow rate is 59 l/s (940 GPM) with a head of 50 meters (164 fthd). If the actual head is 40 meters instead of the selected head of 50 meters, the DRV will increase the head while closing to regulate the flow. However, using the VFD to regulate the flow as per design will not increase the head and will allow it to run almost at the BEP region. Thanks


The problem with the world is that intelligent people are full of doubts, while stupid ones are full of confidence.
-Charles Bukowski-

 

[RVAmeche]

Is a DRV used to avoid having a pressure transmitter and PID loop controlling the VFD? It seems odd to me unless you have a "standard" pump you use for buildings and that helps cover the differences.

 

[georgeverghese]

"The VFD in the automation system adjusts the pump speed according to the signal it receives."

So what signal does this VFD for each pump operate on? Pump flow or pump differential pressure or pump discharge pressure? This info would be on the P&I D and in the process control narratives.

 

[moideen]

@RVAmecheump’s VFD is controlled by the index loop differential pressure.

The problem with the world is that intelligent people are full of doubts, while stupid ones are full of confidence.
-Charles Bukowski-

 

[shvet]

Maybe this will help

https://www.eng-tips.com/viewthread.cfm?qid=501898

 

[mk3223]

moideen,
It’s correct that the DRV may waste the energy in the system as the operations you described.

First, it seems no sense to operate the VFD pump at fixed speed to defeat its purpose for a prolonged time period. The DRV is only to be functioned as a manual instrument valve to adjust the flow but will sacrifice the pressure head. Or, to add some flow controller to automate the DRV to balance the pressure head.

 

[georgeverghese]

"If the actual head is 40 meters instead of the selected head of 50 meters, the DRV will increase the head while closing to regulate the flow."
From what we can see on the brochure, the DRV is a manually set valve, not automated.
If the piping around the pumps is well done, then the % close of the DRV on each pump will be minimal in order to keep the flows balanced.