3 way bypass

[rimide]

Chilled water a/h replacement, 2" feed, 1 1/4 at a/h, I'm putting in a strainer, a 3 way valve and a circuit setter, I was going to install a
1 1/4 3 way valve, boss ordered 3/4, I say circuit setter will take care of flow through a/h and would be better at 1 1/4, there is a major issue in build with bypass, right or wrong?

[pecmsg]

Depending on the CV rating of the valve. 1 1/4" would by my choice with that information. Correct in letting the circuit setter do its job!





With that said always refer to rule #1!

[hvac69]

Even with the circuit setter properly sized, if the valve CV is too large there could be an issue with hunting if the valve is modulating. Especially if the controlled reference is discharge air. But like pecsmg stated info supplied doesn't give much to go on.

[chander]

Do you have the old 3 way valve, if you do what manufacture and what numbers are on the valve? Do you know the specs on the new coil GPM ,etc ? Hopefully WAYNE or one of the other TAB guys see this, they could help you out better.

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[WAYNE3298]

You need to know the flow and some information on the chilled water system. hvac69 is on the money because if the control valve is oversized hunting will occur. The control valve has to sized to supply design flow to the coil. Oversized circuit setters can also be closed enough to cause premature failure of the circuit setter and result in inaccurate flow readings.
Without more information we can't tell you more than to make sure the valve is properly sized. How did the old valve function?

[71CHOPS]

If its a new ahu, you should have all the design data needed to properly size the valve and circuit setter.

How was the replacement AHU selected?

[Thunder Chunky]

I read an article once that discussed how circuit setters are only needed when the valve is two position. If a 3 way valve is modulating the circuit setter doesn't need to be there. It seems to make sense to me. Thoughts?

[WAYNE3298]

You need a circuit setter on both ports. One reason is to balance the pressure drop to assure flow control to the load and return.

[gbfromsd]

And . . . you need to consider the sum of all the three-ways in the loop. The total flow of all should be above the chiller's minimum flow requirements.