closed loop chiller

Having problems with a closed loop chiller supplying cooling water for a plastic molding operation. With minimal demand while equipment heats up, coolant (glycol/water) reaches set piont (45 degrees) and maintains. Once production starts, chiller no longer maintains set piont temp even though demand still seems slight. Difference in coolant temp leaving chiller and returning from process is only 4 dgrees. Have checked refrigerant charge, water flow rates, coils are clean. What should superheat range be? Is this a heat transfer problem? Any info appreciated.

Is the coolant temperature 'bouncing' dramatically, like going from 6 deg. C to 15 deg C. in 5 mins, and pullling down to 6 deg. C. in 3 minutes when the chiller kicks in? If so, you most likely have a coolant flow problem - check the volume of coolant in the system, & make sure it's above the chiller manufacturer's stated minimum. Check that any valves, actuator, etc, are operating correctly.
Our TEV kit normally works on 6 C at evap. outlet, or 8 - 12 C where we actually have a schrader to connect to, or about 3.5 C if it has an electronic expansion valve. What's the pressure drop through the evaporator? Is that close to the design PD?
Hope this helps.

Hi, Bender:)
there may not be a problem with the fridge end of the process. Has the system a buffer tank fitted? This would take care of the peak load which could quickly overcome any system which has not been over sized to cope with it.
TEV superheat should be in the region of 6 Deg C, compressor inlet superheat will be higher than this and is dependant on if a suction liquid heat ex is fitted or not.
Regards. Andy.

Hi Bender

Is it possible to take off one of the water circulating hoses from the tank resorvoir and time the flow into a bucket?

If you can do this then by weighing the bucket you can determine the actual water flow per second/minute.

If the delta T is measured and the unit's capcity known then you can calculate everything from then on which will give you the answers to your problem.

let us know if this is possible. I had a very similar problem just 2 weeks ago!


Frank

Hi Bender,

Here is the information needed to properly evaluate the system:

Low side:

Evap water in temp
Evap water out temp
SST (saturated suction temp)
Suction line temp at evap
Suction line temp at compressor

High side:

Condenser air/water in temp
Condenser air/water out temp
SCT (saturated condensing temp)
Liquid line temp at condenser
Liquid line temp at metering device

With these temperatures, we should be able to determine the problem(s).

hey is the return mixing with the supply check the holding tank.
have you checked the level of gical it may be to high empty flush system w/descaler and refill w/ polly I would have them depose of the old stuff.

Hi Tony_Rich :)

Your observation regarding high glycol level is very sound advice. I would, as you suggest, dispose of esixting cooling solution, and recharge with the minimal amount of glycol required for freeze protection and corrosion resistance.

Glycol is a very poor medium for heat transfer. :)

Hi bender,

As ask by gary we do need more info.

Add the flow rate of the secondary coolant, and take the flow rate at different time if you do not have a buffer tank, because the flow rate can change depending on a many equipment you are feeding.

You said a closed loop therefore you probably do not have a water tank. I hope you have a expansion tank on the secondary coolant.

Hi Marc

Good to see you again. That guage is still on my desk, by the way.

Yeah, I can be sharp at times. Probably comes from having lived mostly on the highveld as a youngster! lol.
I'm looking forward to seeing Gary's figures too, in case there's more to it. The low flow idea is based on my experience, but until we have some figures, it's a best guess.
Bender, have you got any more info? Have you solved the problem?

I'm not surprised at S.A's improving our technology. When I moved back here, I was astonished how far behind the U.K. was! You couldn't even get a statement from a ATM machine! And as a kid, I had a watch that had 4 different games on it - I've never seen anything similar here. :D
And the killer is... The SADF's version of the Apache combat helicopter - tougher, meaner, faster, with longer range and bigger payload than the Apache Longbow. Just what you need to get around London! lol

You're right about the superheat, but we do find that we get some 'high' readings, due to the location of the suction schrader on some of our kit. As a general rule, if it's a screw, it's around 3deg. (as they've got EEV's) and if it's a recip, it's 4-8deg. (TEV control). Obviously that's dependant on load, etc.
When I was doing pack refrigeration, I was taught to take the superheat across the coil, not back at the compressor. It took a bit of mental gymnastics to get my head around the A/C way of doing it! lol. Oh well, I was a lot greener back then...

As to what's happening here this year - well, hopefully, this guage will be collected before it gets lost? ;)

HAPPY NEW YEAR EVERYONE!