Calculating ROI to Correct Poor Performing Chilled Water System

[BronYrAur]

I don't know what this designer was thinking. Please look at the attached flow diagram for a chilled water system. The chilled water flow is primary/secondary, but there are 3 decoupling bridges. Those devices (that look like the letter Y laying on its side) are just regular circuit setters. There are no control valves in the bridges, so water flows through all 3 bridges all the time.

So, needless to say, secondary return water blends with cold primary water through any bridges with non-operating chillers. As a result, all chillers are operated all the time (so I'm told) in order to not lose supply water temperature to the air handlers. Perhaps there are times when they live with blended water.

I have proposed changes to the bridge piping, but it is not cheap. The piping is very high in the air, etc. Upwards of $100,000 to correct the problem. They have inquired about the ROI.

I'm not sure where to begin with that calculation. I doubt they have energy readings and other information that would be needed. Any recommendations on how to do the ROI?

 

[MintJulep]

I guess that what the designer was thinking was that they weren't thinking.

With no records you'll need to model a typical cooling year with the current arrangment and again with your proposed changes to identify the difference.

 

[ProcessHVAC]

A rough approximation of the comparative savings could be modeling a properly designed and upgraded system and manually calculating separately having the pumps running all the time.

 

[LittleInch]

Where is the inefficiency?

Chillers cannot be working "all the time" without temperature falling to a too low level and freezing.

SO you need to figure out operation as is and some mysterious "ideal operation with your mods.

Looks to me like it only need three motorised valves to shut off flow in the bridges if the chillers aren't needed?

How can than be $100,000?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[BronYrAur]

I had not consider motorized valves. I was figuring to re-work the 3 bridges into 1. Difficulty due to pipes being very high. Figured control changes would be needed also since I suspect the original programming has been abandoned.

I like the idea of valves instead.....

 

[LittleInch]

On a quick view it looks like something needs to work out when to turn those chiller banks on and off. Then when you only need two sets turn one off and isolate that bridge?

How does the VFDs on the secondary change flow?

I'm sure it's not as easy as that, but worth a look?

Remember - More details = better answers
Also: If you get a response it's polite to respond to it.

 

[nglty]

You need to have a single decoupler piping arrangement (not three). The SCWHP are getting water from other decouplers when other chillers not in use.
cost just the same as adding large control valves.

 

[AdrienneGC]

What about a straight forward engineering economics analysis. F/P [find Future given Present ($100,000)] vs F/A [find Future given a reoccurring expense(maintence + energy + etc)] calculation? Here's a calculator:

https://www.adicotengineering.com/present-future-value-calculator

As far as the A, reoccurring expenses, you will have to make some educated guesses on this.