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  1. #1
    Join Date
    Oct 2009
    Location
    Portage, MI.
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    Tandem Chillers (Carrier)



    We have a new 4 module Tandem chiller/Heat Pump. Made in Canada for Carrier. Geothermal Ground source. The water set point is 135 degrees for heating . I have never seen a DX chiller with a SP this high. Usually max out around 120. LEED *******s designed it. Burning up a Copeland 20 ton hermetic every six months. Am I wrong to think we are at to high of a water SP? Tandem and Carrier both seem to think it is OK. Copeland had no comment.

    Condensing pressures at that Saturation temperature are around 560-600 for 410a in heating

    HP cutout is 600psi

    My Trane multistacks 410a run around 117 SP for water and 400psi in heating.

    Thoughts?

    Thank You?


  2. #2
    Join Date
    Feb 2017
    Location
    New York
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    Making anything run right on the edge in my book is not a good idea. It puts a hell of a lot of stress on the components and leaves almost no margin of error. One oops and the system is down. I say it's too high.

    Stop, step back, relax and have another go at it.
    -----Stop, step back, relax and have another go at it.-----

  3. #3
    Join Date
    Feb 2010
    Location
    montreal
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    Mike

    I have done a LOT of recovery chillers I assume yours ain't different from the one I have seen.

    Don't get impressed by a high water out temp as it's not the main issue if the right compressor as been selected for the job.
    I have a multistack prototype running 170 fahrenheit. (it's still running)

    Mike if you want to know if the right compressor as been selected go on Copeland website get there selection software or ask Copeland the operating envelope of the compressor.
    On the chart you will see under which conditions your compressor should run. (based on saturated temp)

    The worst setup I have seen are the one like you have. Geothermal with high water out. That will bring a high compression ratio on the compressor and most of the time push the compressor to the limit of the envelope.

    The setup that work for geothermal are either cascade chiller or cascade compressor or you lower water out.


    Again don't get impressed by higher discharge pressure than we are used to its just a number meaning nothing without the big picture. And Mike make sure they keep the water extra clean and that you keep the heat exchanger spotless on condensing side once you lose the exchange you're gonna destroy compressor faster than you can replace them.

    Good luck!

  4. #4
    Join Date
    Feb 2017
    Location
    New York
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    Patpinet, on your chillers that run that high, what are you running on the low side? Are the compressors designed to run a much higher differential pressure or is the low side temp raised? I'm curious, I've never ran into units in this configuration. I am somewhat familiar with multi-stack units. Have a few in our area.

    Stop, step back, relax and have another go at it.
    -----Stop, step back, relax and have another go at it.-----

  5. #5
    Join Date
    Feb 2010
    Location
    montreal
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    BennyD,

    As explained in my first post the most important thing to look for is high compression ratio.

    Getting from a really low pressure(geothermal) and raise it to high condensing temp is really tough on the compressor.

    You need a higher evap temp more than a special brand of compressor to reach high condensing temp.

    If you go geothermal and want to have high condensing temp there should be 2 chiller in cascade or like the Multistack prototype I have ,two compressor in cascade.

    One chiller (or compressor) absorb heat from geothermal pit and reject the heat (at medium temp) in the evap of the second chiller.(compressor)
    From there the heat absorbed at an higher evap pressure can be raised to a much higher condensing temp .

    Basically you split the work load on two compressor instead of just burdening one.

  6. #6
    Join Date
    Feb 2010
    Location
    montreal
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    Look at the chart here to get a idea of envelope of operation of compressor.

    The dot is the operation of the compressor with 22 SST and 140 SST

  7. #7
    Join Date
    Feb 2017
    Location
    New York
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    To work like that, I would imagine the condenser and evaporators would have to be counter flow?

    Stop, step back, relax and have another go at it.
    -----Stop, step back, relax and have another go at it.-----

  8. #8
    Join Date
    Oct 2009
    Location
    Portage, MI.
    Posts
    22
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    Thread Starter
    Thanks for info. I requested a operating envelope from my local Copeland dealer. Should be similar to the one you sent. Should confirm that the compressors should handle load. Will be on upper edge. Unit does not short cycle. Compression rations can reach 4:1 on lower heating water flows. Today evap water was 45 degrees and heating water was 117 degrees and discharge temp of compressor was only 125 degrees on four compressors. One was 195 degrees. Doesn't add up. Delta T on condenser only 5 degrees with 100 hp of compressors running. Flow 160 gal/min.

    More will be revealed.

  9. #9
    Join Date
    Feb 2010
    Location
    montreal
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    Look to see if isolation have been installed.
    Tandem chiller I believe are modular unit.

    Without isolation valve, water will bypass some flow in all module and lower the reading of the condensor water out sensor on the master controller. (colder water will mix with your water that as been heated by the module running )
    Will do the same at the evap.

  10. #10
    Join Date
    Oct 2009
    Location
    Portage, MI.
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    Thread Starter
    Has isolation valves. Would not explain 1 compressor having such a higher discharge temp. I received the curve from Copeland and we are in spec, right on the edge @71% Isentropic Efficiency. Seems odd to run on the edge. Thanks for your help

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