Trane Liquid Chillers RTHD Models 200tr

[rmarcelo61]

I hope you can help me. I'm a civil engineer working in the Engineering Department of a mall here in the Philippines. I've been doing research on our ACU system which seems to be consuming more power than they were designed for. We have in-place 3 x 200 ton Helical Rotary Liquid Chillers made by Trane USA. Two (Chiller 1 and 2) out of the three chillers register Condenser Approach Temps of 5 to 7 deg F even after swabbing and descaling the condenser tubes. The local Trane technicians cant explain the high readings. They have checked the sensors and they were working fine. They've pointed out high chiller water flow (900gpm as against 480gpm design) as "maybe" causing the problem but i'm not convinced. Water Ph is between 7 and 8. We regularly clean our cooling towers and treat our waters. My concern is why is it that one chiller performs better than the other two given that all factors are constant for all three chillers? Chiller 3 registers below 4 deg F cond appr temp. Thanks.

[maxster]

what are your chilled water setpoints,and are the off chiller isolated in lag modes?what are the subcooling readings at full load per chiller?

[Nuclrchiller]

What is meant by "chiller water flow"? Is that chilled water through the evaporator or condenser water through the condenser? Either way, doesn't that contradict your statement "all factors are constant for all three chillers"? Higher water flow will cause a higher approach, so try decreasing the flow. Make sure you use one gauge (moving it back and forth from the entering tap and the leaving tap) to prevent gauge error from affecting your measurements.

[rmarcelo61]

Thank you very much to maxster's and nuclrchiller's reply to my queries. To maxster : my chilled water setpoint is 44 deg at full load. And yes all the off chillers are isolated (if that means i only use one chiller at a time and the other two are off. Sorry but my knowledge on HVAC is very limited). I have to get back to you re subcooling readings since i got off work 2 hours ago and i'm sending this from home.

To Nuclrchiller: Yes, chilled water is evaporator water. By saying "all factors are constant", i meant that all chillers have 900gpm fed through them (Chilled water and Condenser water). All the pump's motors (CHW 25hp and CW 15HP) rotate at 1750 rpm. Trane technician said is should limit CHW flow to 480gpm and CW flow to 572 gpm as designed. If what you say is true, then you may have just solved my problem. I'll just trim entering and leaving water flow rate by adjusting the butterfly valves, is that correct sir? Or should I do something with the pumps (reduce impeller diameter size?). Also, I read from Trane that the min and max flow rates for this model is 289 to 11040 gpm. Does that affect approach temps directly proportional sir? One last thing that puzzles me - evap approach temp for 1 chiller read zero while its condenser approach is 6.9. Is that possible? Again, thanks for the help!

[GT Jets]

rmarcelo61,

As a quick experiment, you could open the chilled water valves to a second chiller and flow the same rate through each with only one machine running in cooling.

This should theoretically cut the water flow through the cooler in half putting you at closer to 450GPM.

As for the solution to the water flow adjustments, around here it is most cost effective to install a VFD (Variable Frequency Drive) on the chilled water pump, or to do the math and have the impeller trimmed....The VFD option more than likely will actually save more energy. I will go out on a limb and say there are probably no triple duty valves on your chilled water pumps...Sounds like a little design oversight.... Again around here, we call that "Value engineered".

Good luck...

GT

[Nuclrchiller]

I'm concerned that all three chillers appear to have high flow rates, yet only two are showing the effects of it. How were the actual flow rates determined?

[Nuclrchiller]

I'm like GT Jets- I would not be surprised if there are no triple duty or balancing valves. However, my next choice would be to use an isolation valve to adjust water flow. In fact, it's possible that was done originally. Then , after someone completed their service that required shutting those valves, they opened them back up all the way fully open, having forgotten (or failed to notice) that they were adjusted to some mid position. I believe this happens quite a bit. Whichever valve you use, make sure it is not between the gauge taps you're using to measure the pressure drop across the vessel you're checking. And I would not be concerned with the difference in the approaches on that one chiller (between evaporator and condenser) until the flow issue is resolved (if, in fact, that proves to be the problem). If I recall, the accuracy of those sensors is plus or minus one degree F.

[GT Jets]

I'm like GT Jets- I would not be surprised if there are no triple duty or balancing valves. However, my next choice would be to use an isolation valve to adjust water flow. In fact, it's possible that was done originally. Then , after someone completed their service that required shutting those valves, they opened them back up all the way fully open, having forgotten (or failed to notice) that they were adjusted to some mid position. I believe this happens quite a bit. Whichever valve you use, make sure it is not between the gauge taps you're using to measure the pressure drop across the vessel you're checking. And I would not be concerned with the difference in the approaches on that one chiller (between evaporator and condenser) until the flow issue is resolved (if, in fact, that proves to be the problem). If I recall, the accuracy of those sensors is plus or minus one degree F.

Just to add to this....I am not comfortable with reducing the flow by half with just a butterfly valve. But to see what's going on it would be a great tool. Butterfly valves IMHO are not real consistent when it comes to balancing...I know it is done often, but from my experience rarely to reduce the flows by 50%..

GT

[Nuclrchiller]

Just to add to this....I am not comfortable with reducing the flow by half with just a butterfly valve. But to see what's going on it would be a great tool. Butterfly valves IMHO are not real consistent when it comes to balancing...I know it is done often, but from my experience rarely to reduce the flows by 50%..

GT

I won't argue with any of this . I have balanced, and seen balanced, many water flows using butterfly valves, but always as a last resort. And I couldn't begin to tell you what the worst case (highest excessive flow) was. I simply don't remember. But I do remember at least one where the noise through the throttled down valve was objectionable. Don't remember what the owner's final decision was. This also got me remembering that, usually, when flow rates were that excessive, then a triple duty valve was installed. So maybe there is hope in rmarcelo's case.

[rmarcelo61]

Thank you all for the posts and recommendations you gave me. It was, to say the least, very very gratfying!!

I'll be sure to inquire about the triple duty valves GT and Nuclrchiller mentioned here. As far as the VFD is concerned, I, along with a Mechanical Engineer-friend, actually recommended this system to the mall owners as early as a month ago (i've been doing this study since september). I believe you GT when you say its the most cost effective method for the mall. I even told them to install VFD's for the AHU's. (and around here we also call them value engineering .) The cost of it isn't peanuts, however, but I'm trying to convince them to look at the long term. But you know how it is - a civil engineer talking about things not associated with his profession can't make believers out of them

I am very grateful for all your inputs. I'm going to try it out tomorrow when I report for work and I hope it will do the trick! (lemme try the butterfly valve trick first and then the two chiller-one cooling next as GT suggested.

I'm gonna post the results as soon as possible. You have all been so much help!! Thank you very much!!

If there's anything more you can think about then i'd be glad to hear from all of you again.

[rmarcelo61]

I'm concerned that all three chillers appear to have high flow rates, yet only two are showing the effects of it. How were the actual flow rates determined?

Nuclrchiller hi! Trane technicians were the ones who took the reading by attaching a flow meter (or volumeter, i dunno what they call them) in one of the service ports along the pipes. Thanks!

[Nuclrchiller]

Hi rmarcelo. I've never used a flow meter, so I don't have an opinion about them (don't know how easy or likely or even if possible to make a mistake). I prefer measuring delta P and comparing to design, or manufacturer's curve. That's just my personal preference. And you're welcome for any help I may be able to offer. I think you'll find this site to be informative and helpful. There are many here more helpful than I. GT is one. Billy.

[rmarcelo61]

Yes Nuclrchiller i can maybe do that too - measuring delta P and comparing to design. I have the manufacturer's curve in the manual I'm reading. And you are definitely right! I'm learning so much from this site! I plan to print this thread and include it in my report. Never thought this field of engineering could be this exciting!