Constant volume chilled water system

[Bobfd7dbf]

Hello dears,

In the constant volume chilled water system , why it's essential to add 3 way valve with bypass on each coil instead of coils without any valves except the balancing valve to ensure that every coil will take the flow needed ?

I dont see any advantage of using this 3 way valves and using the bypass.
For example, when the coils are 50% load the flow of water will leave the coil at a lower temperature therefor decreasing the return water temperature to the chillers . Even if the coils have no heat load the fan can be shut off and water will enter and leave the coil with exact same temperature.

So why it's essential to add 3 way valves and bypass??
Thank you

 

[nuuvox000]

I assume that's so you don't have to keep the pipe size at full-size all the way to the end of the loop. If you use three-way valves then you can decrease the pipe size as you go along. Who says it's essential?

 

[Bobfd7dbf]

Pipe size becomes smaller either with 3 way valves or without . it's amount of water distributed to different coils and corresponding recommended pipe diameter for the amount of water needed for each coil.
Can you explain your point clearly please?

Who says it's essential ?
I see in every design of constant volume chilled water system they use 3 way valves , of courae it offers advantage over leaving the coil without it.

 

[nuuvox000]

The pipe can't get smaller if you're using 2-way valves (open/close) and constant volume. If the volume is 500 gpm constantly all day long and all of the 2-way valves are closed then you can't squeeze 500 gpm into a 1" supply pipe, right? If this is for comfort cooling then you're not going to want chilled water to the coils 24/7. If this is for industrial processes and the coils need to be providing cold air 24/7 then I suppose it could work.

For comfort cooling systems, we typically use variable volume systems with 2-way valves at the coils and a bypass valve at the end of the loop.

 

[immsk]

The 3 way valves modulate to maintain a supply air temperature setpoint. The coil entering air will almost always be cooler than what the system was designed for, therefore without any means of control such as a 3 way valve you'll end up with air that's too cold leading to occupant complaints.

 

[Bobfd7dbf]

Nuuvox000
You got me wrong sir , i am not saying i want to change the 3 way valves with 2 way valve. I am asking about just use balancing valves on coil to maintain the amount of water needed for each coil and not using any valve for part load control . Now please read my question again i am sure you will understand what i mean . Speacial thanks to your interaction.

 

[Bobfd7dbf]

Immsk
Thank you sir i got it now

 

[Bobfd7dbf]

Immsk
Thank you sir i got it now

 

[BronYrAur]

The 3-way is what gives you constant volume. The unused water bypasses the coil and returns to the chiller. It is a major contributor to "low delta-T syndrome", but it delivers constant flow to the chillers. Otherwise, the chillers may get knocked offline due to low flow.

variable volume systems are much better for this reason, but you don't have much choice if your chiller needs constant flow.

 

[Bobfd7dbf]

BronYrAur
I know well that 3 way valve is good for maintaining constant flow in the system and why it is used with constant flow system over 2 way valve which is normally used with variable speed pumps.

My question is not about this issue , i am asking if no control valve is added in constant flow volume system and what is the problems to do this ?

By the way i got the answer from ( immsk )
we control the air temperature leaving the coils by controling the flow rate of water through the cooling coils , if it is loaded all the time with the same flow rate , the temperature of the leaving air will decrease at part load conditions to a value under my setting and desired temperature.
I think this is the answer i needed Sir to understand (why) , your efforts are appreaciated , thank you.