PICV for HVAC system

[Wayne _ Lunar]

Hi All!!

I am working with Danfoss PICV valve for a Chiller system. I have a question and hope you can help me by explaining it to me. Thank you so much!

Photo of the DN25 PICV as bellow link:

https://www.danfoss.com/media/eyljd...20x747.jpg?anchor=center&mode=crop&width=1050

With the size bigger than DN 32, they have 3 ports to measure P1,P2 and P3, which P1 is inlet pressure, P3 is outlet and P2 at the pressure control valve. I use Delta P1-P2 to count for the water flow. But with model DN25, there is only 2 port, and I cannot know it is for Delta P1-P2 or Delta P1-P3 measurement?

 

[LittleInch]

Maybe I'm missing something here but those two valves look identical to me.

Please sketch out what you're doing or provide a link to a more detailed diagram.

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

 

[Wayne _ Lunar]

Hi LittleInch

Please see the schematic for FCU with a PICV as attached.

 

[LittleInch]

Thanks, but that doesn't really help answer your question about P1,2,3

PICVs just control flow to a set figure. That's all. I'm not able to see what your issue is.

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

 

[MintJulep]

If there are only 2 test ports they must be p1 and p2.

But the document could be more clear.

 

[Wayne _ Lunar]

Hi MintJulep
If you look at the attached photos, you can see there are 2 holes, one at the inlet and one at inside the PICV chamber, not the outlet, so I also assumpt that there are P1-P2.

 

[LittleInch]

I think there's an error in the manual and when they say differential pressure they mean p1-p3 as there are only two ports on the valves as far as I can see.

The manual is consistent as saying delta p is p1-p3.

What exactly p2 is is not wildly clear, but looks like the minimum pressure point in the venturi chamber. I don't see any port with which to measure this, but the diagram doesn't match the valve. Can you post the actual diagram of your actual valves please?

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

 

[HVAC-Novice]

What are you trying to accomplish?

Those pressures are NOT for measuring flow. At best they confirm flow, but not how much flow.

You should review the manual or contact their support for specifics of THERIR valves.

 

[LittleInch]

HVAC - they are used to measure flow.

See this

https://assets.danfoss.com/documents/latest/283199/AM322356127863en-010203.pdf

As far as I can see you just use the differential pressure from the two test ports. It is a bit odd that the smaller valve uses a different nomenclature.

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

 

[HVAC-Novice]

interesting. In the old day si used Honeywell PICV and they didn't publish the flow/pressure data. they stated those ports are not for flow measurement. I don't know how that is today.

Anyway, it isn't clear what P the 2 ports are and where to get the third measurement.

Maybe look at a complete manual only for those specific valves? what was linked is only a partial manual and covers multiple devices. There must be more information. they call it "flow-checker". I don't even see a reference that being a PICV.

 

[LittleInch]

The complete manual pointed you towards this document. It is also just as confused about P1, 2 & 3.

What is clear though is that there are only two ports to measure flow so just use them....

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

 

[Wayne _ Lunar]

Hi LittleInch

Agree! I will use them for water flow measurement.

Thanks!

 

[WD42]

It does depend a bit. Those ports can be used to measure flowrate through the PICV, however, the accuracy is typically around +-10%. For critical applications, the best practice is to include an orifice metering station downstream of the PICV to measure flowrate during commissioning.

 

[LaciHudson]

When there are just two ports, it’s usually measuring Delta P1-P2 for the water flow, even though it feels weird compared to the bigger valves with three ports. Manuals can sometimes be a bit confusing, but that’s typically how these smaller ones work.