Aircon Chilled water Expansion Tank

[nicole10g]

I have a Chiller system installed at the basement floor with the chilled water expansion tank installed at the roof top at 37.4m height relatively to the chiller unit. The highest chilled water pipe is at 32m. The expansion tank is gravity fed to the chilled water pipe system. There is a bypass valve from a pressurized water supply of 25psi at the expansion tank for maintenance purpose of fast filling the chilled water.

I have noticed that during the normal chiller operation with the bypass valve on, the chilled water will be further pressured from 59psi to 74psi with an increase of 5psi (reading taken from the chiller unit at the basement) from the pressurized bypass. However, the chiller operation efficiency seem to be increased by 10%.

My question is can I left the bypass on all the time to have the increase chiller performance?

 

[trashcanman]

QUOTE: "However, the chiller operation efficiency seem to be increased by 10%. "

Please explain how this increase in efficiency was determined or calculated, and please define what you mean by "operation efficiency". Usually chiller efficiency is determined by Tons refrig/KW input.

 

[IRstuff]

If you're bypassing, then you are using less water from the chiller, are you not? So your "increased chiller performance" is simply that it's not supplying all the water in the system. Is this an open system, i.e., the used water is not recirculated?

TTFN
faq731-376

 

[KiwiMace]

So you are saying that if you flood your expansion tank, you get better chiller efficiency? 10% improvement because the water is pressurized more?

I would start by checking the data.

That type of expansion tank is supposed to be vented to the atmosphere.

 

[nicole10g]

What I am saying is if I am bypassing the make-up chilled water from the expansion tank and directly feed the make-up water from pressurised water inlet, which indirectly increase pressure of the closed loop chilled water circulation system by 15 psi. This is to say the expansion tank is no longer connected to the chilled water system.

The centrifugal chiller panel will show an average of additional 10% unloading.

 

[ChasBean1]

It’s an interesting observation. There shouldn’t be a chiller performance benefit by increasing water pressure at the chiller from 59 psig to 74 psig, so far as I know. Either way, with the chiller in the basement and your make-up and expansion devices 37m higher, there should not be risk of air binding or cavitation. I think if you are really seeing a performance benefit there is more to the story, somewhere, that may not be obvious… I’m first curious as to why you may have felt the need to open the make-up water bypass valve while the system was alreay full and operating…

 

[nicole10g]

The bypass was left open by accident or rather forget to be closed after a major retrofit.

Anyway, I think the improve in performance could be due to the increased in water pressure have totally eliminated the air binding or cavitation in the system. However, I am interested to know if there is no expansion tank connected (literally) but with the bypass valve open, what untoward impact will it happen to the aircon system that I should take note?

 

[ChasBean1]

Are you sure it is a gravity fed expansion tank? Meaning the expansion relies on the weight of the water column, the tank is about half full (or half empty, depending on your outlook on life), and makeup water is based on a float switch if the level in the tank gets too low?

If not, and if your system is like 90+ percent of the systems today (a bladder tank with basically an air bag with a factory pre-charge of 12 psig) you have a leaking bladder. Please don't take this personally. Just call Taco (or whomever sold you the tank) and replace it.

 

[nicole10g]

The makeup expansion tank is fed by the same pressurized bypass water system through a float valve. What I am saying is that the expansion tank in turn feed the aircon chilled water system through gravity.