Maintaining Minimim Chiller Flow using a Cla-Val

[BronYrAur]

I'm asked to resolve a problem where a chiller isn't receiving it's minimum flow at all times which is causing problems. The system serves several unit ventilators each with 2-way on/off valves. When the units aren't calling for cooling, the valves are closed.

The chiller has a minimum flow requirement of 119 GPM, and they want the chiller to operate even if only 1 unit ventilator is calling, which would be only about 6 GPM.

A 1-1/4" Cla-Val was installed about half-way down the piping system. It is a model 50-01, and from what I can find on their web site, it can pass a maximum continuous flow of 93 GPM.

This is obviously short of my required 119 GPM, but I don't understand how the Cla-Val operates. I'm not sure how it should be set to bypass flow when needed and not bypass it when the unit ventilators are calling. The system pump is rated at 160 GPM @ 80'.

Any suggestions on the best resolution? Should I increase the Cla-Val size? Should i add a second one? Should I do something else entirely? Where in the piping system should I put it?

Thanks for your help

 

[tys90]

The automatic valve is set to hold some upstream pressure. When the 2-ways on the unit vents. close, the pressure increases upstream and the automatic valve in the bypass opens to relieve the pressure back to the return side. This is assuming you are using a constant volume pumping system.

If that's the only bypass it just sounds like you are short on bypass. It's hard to tell you exactly what should be done without seeing a schematic of the piping. You could add a small bypass to the end of each unit ventilator loop with manual balancing valve and then reset your automatic valve so you are getting min. flow when all 2-ways are closed. Or you could put a bigger bypass in, that isn't going to be cheap though.

 

[imok2]

Chris, For a sequence of operation in graphic form go here

http://www.cla-val.com/animation.cfm

and find the 50-01 valve

 

[CH5OH]

I assume the minimum flow requirement from the chiller unit is caused by limited capacity control of the cooling compressor eg the amount of cooling produced by compressor/condensor needs to be counterplated by adding the same amout of heat to the system.By using a bypass system you can regulate the flow of your chiller water and keep it above minimum flow, however that doesn't help since the temperature of the return chiller water flow to the condensor will drop in temperature and stop the compressor.
I assume the wish is to prevent the compressor from start and stopping all the time at minimum load.Proposed solution:
1.mount an on/off bypass valve on each ventilator unit with an orifice.the delta P of the ventilator circuit with the on/off valve to be the same as the on/off bypass valve with the orifice.
2.improve the capacity control of the compressor by using a VFD or a two speed motor

 

[lurch17]

I always eliminate ClaValves. They are hard to adjust and keep repeatable. There are too many unknown variables here to respond with precision so I will shoot anyway.

Determine which units run the most until you get around 120 GpM worth. Outfit each of those with a correctly sized Hays Mesurflo (I have used thousands) and 3-way valves instead of the two-way. If no other units are running, you will have just enough to keep the chiller running.