Need a Valve to Prevent CHW Vaporization in a High Rise Building

[eqkimball]

I have a 9-zone building, one on each floor, redesigning for a variable secondary with a 2-way control valve on each AHU. Because the primary feeds 2 other secondaries, I must keep the pressure at the return node to the primary circuit low (around 10 psi).
As a result, I am having vaporization issues on the top 2 floors 170' and 110' elevation.

I am considering using a balancing valve of some sort to stay above vapor pressure at these levels.

Does anyone know of a valve that would throttle the flow, holding a MINIMUM pressure on the upstream side? This would be the opposite of a pressure regulator in my mind.

Thanks.

 

[willard3]

There's not enough information here to help. Do you have a diagram with elevations and flows?

 

[KiwiMace]

Sounds like a standard Pressure Reduction Valve or Pressure Regulator application to me, but you're forgetting that the secondary pressure control is done with the VFD pumps.

You have a known low pressure to achieve on the downstream side. You don't want to drop below a given static at the the top of the sec loop, so you control your secondary pump/s to provide this pressure, and let your PRV or regulator take care of the return.

Although I would have to question why your primary static pressure can't be increased to take care of this problem? Nine storeys should be easily managed with normal pipe.

 

[ChasBean1]

You don't need to keep pressure low unless devices can't handle high pressure. Somehow you have a pretty substantial conceptual error involved. You need to post more detail.

 

[MintJulep]

Reducing pressure reduces the boiling point.

 

[coldmaster]

Sounds to me like you need to increase the pressure to get some water up to the top stories...

 

[mauricestoker]

Instead of a throttling valve, maybe you need a differential pressure sensor to run the VFD on each secondary. Or, if still at design, use a variable primary pumping system and eliminate the secondaries.

 

[walkes]

Are you sure you just haven't bled all of the air out of the system?

 

[eqkimball]

Thanks for all the replies. Attached pdf is a screenshot of the Pipeflo model.
Concept: The location of the flow restriction is placed at a point to keep the water above it from falling below vapor pressure.
The pressure downstream (not shown) has been "set" to 5 psi, because that is the desired primary loop pressure.
The idea is, restricting a section of the riser that flows a low volume of water will minimize the energy loss in the system.
A manual balancing valve could work, but the location will be physically difficult to access.
This is why the automatic balancing valve came to mind, if such an animal exists for this purpose.

Thanks again for all the help!