reverse engineering help

[hvacer2]

Hi all.....

I am a Mech Eng with no HVAC experience, but have been asked to help with a 25yr old Glycol chiller. System has been "badgered" over the years, and documumentation is almost non existant. I have been trying to reverse engineer the thing, but have a few questions. First - what I do know:

Continental NUPAC air cooled chiller (w remote condenser)
9 ton (nominal) capacity
R134a
fluid: 40% EG
flow rate: 50gpm
Ent temp: 15 deg F
Lvg temp: 10 deg F
Ambient Temp: 65 deg F

OPTIONS:
Low Ambient to -20 deg F
hot gas bypass
suction accumulator
oil seperator
head pressure control + 2 speed condenser fan

My first thought was to get into the pressure enthalpy diagram. Is a good assumption for the design high pressure side to be:

65 + 30 = 95 deg F - corresponds to 129 psia

What is a good assumption for the low pressure side design temp/pressure? Would it be 10 deg F (leaving glycol) minus some standard # for the evaporator?

I have dug up alot of information on all of the individual components in the system. Just not the "nominal" operating conditions. Any suggestions or help with a "plan of attack" would be much appreciated....

Just FYI - the system is not meeting spec, and I have been asked if I can figure out why not.

[klrogers]

Hi all.....


Continental NUPAC air cooled chiller (w remote condenser)
9 ton (nominal) capacity
R134a
fluid: 40% EG
flow rate: 50gpm
Ent temp: 15 deg F
Lvg temp: 10 deg F
Ambient Temp: 65 deg F

Are these the specs. or the present operating conditions ?

[hvacer2]

these are numbers i found on an old spec sheet......

[wolfdog]

klrogers is asking a good question. At first glance your GPM is way high.

[Heavyevans]

I would need more info on the refrigeration circuit to be certain. Pressures, superheat, subcooling, etc...
I would probably take a close look at a 25 year old chiller using 134a. I don't remember 134a being used until the early 90's.

[hvacer2]

50 gpm was the spec....

I have measured (with several different methods) and get numbers in the mid 40s...

If I am not mistaken, 50gpm x delta 5 deg F x S.H. of EG is approx 9 ton

[hvacer2]

ahhh yes... my first small victory!

when I was handed the folder, I was told "25yr old system". I just looked at the date on the original spec sheet and see it was built in 93.

Sorry - my bad.

As for Pressures, superheats, subcooling, - well, these are what I am trying to figure out (well - at least what they should be).

The only thing I could find was that the TXV was set at 13 deg F (factory). The system has a reciever in it if that helps (subcooling wise).

[wolfdog]

..

[Heavyevans]

Unless I can put my hands on it, I'm usually no help. Try here http://www.air-conditioning-and-refr...d-chiller.html

[gasnowman]

Evaporator approach defined is 10 degrees colder than your leaving medium. Have you checked the specific gravity of EG? Is this system capable of running? If so we would need more trends.

[wolfdog]

If you are looking for Continental chillers....http://www.continentalteam.com/index.html

If they are like some other process chiller manuf. they will have a file on the original design/build for this one.

[hvacer2]

The system produces chilled glycol at ~45gpm right now..... That glycol is pumped to three seperate circuits. Two of them have AHUs and the third is to pipes embedded in the floors and walls.

The glycol flow is not really the problem (I don't think). The chiller does not seem to be able to get down to the specified temperatures (even when removing much less than 9 tons).

[mrhvacmechanic]

Please correct me if I'm mistaken, but due to the weight of the glcol solution you need a higher flow rate than the 2.4 gpm for water.

You said the system is 25 years old. What is the present condition of the solution?? Has it been chemically maintained over the years? If not, you may be pumping more of a jel than a solution? You may not get the heat transfer you should be getting.