Decoupling - EagleEye

[dsirdah]

Hi guys, does anybody know about the decoupling system used in chilled water systems, and what is the EagleEye valve?

[keepyoucool2003]

Based off pipe size, and balancing, from my non-engineering, control guy mind. Unless your doing a temp reset for the secondary loop I'm not aware of any reason to have a valve. Typcially with chilled water there is a flow station to determine the load on the plant.

[r755jake]

This system is used for large plants with multiple chillers. It consists of a primary chilled water loop with bypass and pumps a secondary loop with the multiple chillers in parallel. Each chiller has its own pump and can be valved into and out of the chiller loop based on the demand accross the primary loops bypass flow. If the flow is negative (low demand in the primary loop) chillers are subtracted from the system and vice versa. The issue of the eagle-eye valve is a new one for me, could this be the trade name? The valves on the system I have experience with are Rotork and we always call them this rather than the "chiller" valve??

[dsirdah]

so for me as a control guy, how will i control the system? what is the sequence of operation for such system? attached you will see the drawing where it shows the the Decoupled system.


Any clue??

[r755jake]

I'll take a look at the drawings and give this a think. If you can get a copy of Trane's chiller plant engineering document they have several control strategies for large plants built into their software. I don't know what control company you're using but this may give you some good ideas. Just at first glance I'm thinking the eagle eye setup is for detecting flow direction??

[controlgeek]

Looks like flow meter to indicate how much water is being used by the system vs how much is being bypassed back to the chiller(s) unused.

[r755jake]

Yep. Made by Rosemount, found it on their site, it's there for exactly that function. I'm going to assume that the secondary loop is monitored, normally a diff pressure xducer and the secondary pumps will have variable speed drives. As the secondary loop flow demand drops the back flow through the decoupling loop to the chillers will indicate that chillers can be subtracted from the primary loop. The flow values time delays etc. to add or subtract the chillers will depend on the dynamics of the chilled water system. I didn't take a close look at the flow sensor but as a note it will be required to measure forward and reverse flow. The terms primary and secondary loop seem to vary job to job, I will clarify here the secondary loop is the one going out to the facility and the primary has the chillers.

[keepyoucool2003]

so for me as a control guy, how will i control the system? what is the sequence of operation for such system? attached you will see the drawing where it shows the the Decoupled system.


Any clue??

A bit... over your head? Engineer didn't provide a sequence? If you have the sensor to know your GPM flow yoy can use % to stage the chillers since you know the rated GPM of each chiller. It's been awhile, don't quote me. As someone else said, bring on more secondary pumps as the DP can't make set point and VFDs are maxed. You have 10 chillers? I see 10 primary pumps. Sounds like an awful big job to be designing from scratch, if these are big secondary pumps they may not want to run two pumps at 100 when its more efficient to run 3 are 60. Same as chillers, there is an awful lot of questions I'd be asking to someone with some letters after their name.

[adrianfromoz]

The following Trane engineers newsletter gives a good overview of decoupled systems:

http://www.trane.com/commercial/libr...8_2/en18_2.pdf

The Eagle-eye is a flow sensor and needs to be able to provide both flow and direction as the direction will tell you whether the operating chillers are meeting the load.

In my experience decoulped systems work excellently for large distributed systems (shopping centres, casinos, large office buildings) as long as the decoupler line is long enough, straight enough and well positioned enough to provide a good decoupling effect. Unfortunately mechanical contractors can take what looks great in a schematic and turn it into a nightmare by not properly considering the effect of poor pipework design.

Cheers