Decoupler Pipe 2

[umairzz]

Hello,

I need help in calculating the Size of Decoupler pipe in my project. I heard the pipe size should be the size of header of the chiller which is 8" for my project. And also do i require to install any kind of control valve, if yes, what type of valve it should be, and from which point it gets input for mudulation. Also do i need to install a check valve.
My project consists of 8 chillers each 400 tons with dedicated pump (60 ft,1000 gpm Vertical Inline) for each chiller and one set of secondary pumps serving to 4 sets of secondary pumps to 4 buildings.
And also if there are any notes or study material for decoupler piping , please share.

 

[317069]

You heard, did you search?

 

[umairzz]

Yup, I was told by a friend i mean. Even i searched it.

 

[EnergyProfessional]

Get one of these

, it also includes your air and dirt separation and makes for very clean installation. they are pricey, but if you figure separate dirt/air separation and added piping, they actually are cheaper.

Each pumps needs check-valve. No need for valves (although I'm not sure what you try to do... I assume normal primary/secondary loop?)

 

[DRWeig]

Some general reading on the topic:

http://www.kele.com/WorkArea/linkit.aspx?LinkIdentifier=id&ItemID=4814

http://www.kele.com/WorkArea/linkit.aspx?LinkIdentifier=id&ItemID=4942

http://www.kele.com/WorkArea/linkit.aspx?LinkIdentifier=id&ItemID=4796

http://www.kele.com/WorkArea/linkit.aspx?LinkIdentifier=id&ItemID=4812

Best to you,

Goober Dave

Haven't see the forum policies? Do so now: Forum Policies

 

[EnergyProfessional]

just saw my link wasn't complete: [URL unfurl="true"]http://www.spirotherm.com/products/hydraulic-separators[/url]

 

[umairzz]

Hi,

Yes its a normal Primary-Secondary setup. As per the theory i have referred authors are suggesting a Modulating valve in Decoupler pipe for a Variable Primary systems only ( it is understood that to keep minimal flow through chiller in low load conditions a modulating valve is installed ), whereas in Constant- primary, variable secondary systems, they suggest not to install any valve in the decoupler pipe.
My question
1. In the university project where i am working , other buildings have the same Primary Constant- Variable Secondary systems, yet they installed a modulating valve in a decoupler pipe, is that correct ?

 

[EnergyProfessional]

the decoupler has nothing to do with the primary loop being constant or variable flow. it has to do with the fact that you need separate pumps in primary loop, because it de-couples the secondary loop. For small boilers we use primary/secondary loop with this exact decoupler and the newer boilers have variable pump control for primary pump.... the decoupler doesn't.

What you mean by variable primary flow is only having one loop, with a fake primary loop and dp sensor and valve to allow flow through boiler/chiller. For that you cannot use a decoupler. Because decoupling would not make this work.

think exactly about the meaning of decoupling and you will understand. You basically make whatever happens in sec. loop irrelevant for primary loop - you decouple them.

 

[cry22]

Heard and seen both, with and without control valves in the decoupler. My opinion, keep it simple, NO valve in decoupler for the secondary pumps. I've seen also designs with bi-directional flow meters in the decoupler.

The whole thing is how do you intent to use the valve? or the flow meter? most rely on the information to stage the chiller/boiler plant, when to bring the next chiller/boiler ON or OFF, combined with Delta T reading.

The idea behind the control valve is to insure that the secondary flow does not exceed the primary flow when running with only one chiller/boiler and avoid mixing of water.

An asymmetric plant design tends to correct that - asymmetric = different size chillers/boilers.

As for the decoupler size, it is never the main pipe size, you should look into partial load figures and size accordingly. In your case of 8" main - 6" decoupler will definitely do the job, 4" will likely do the job.

 

[EnergyProfessional]

I'm not sure why the flow in primary and secondary would matter at all. That is why you decouple. you can have 100 gpm in secondary and 0 in primary and vice versa. Obviously flow on each side will be determined by load, temp and equipment needs... but totally irrelevant for the other loop. Hence DE-COUPLER