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  1. #1
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    Trane rtac200 high approach

    Both circuits run an approach of about 13 degrees loaded. Glycol is ethylene 35%. Is this normal with this concentration on glycol.

  2. #2
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    Whats your Delta P compared to design spec ?
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  3. #3
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    In my experience this approach is too high. Have you logged the chiller? You might try logging, then go back and compare it to your previous annuals. I think you will catch the discrepencies.

  4. #4
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    This chiller is designed to have 239-875 gpm flow. I have 450 and I can go as high as 550 if I turn up the drive. It was set to run at 250 gpm but I turned up the drive when I tested it. It is maintaining setpoint and each circuit will do 5 degrees by it self. But this seems to be high. It would trip on low saturated evap temp once in awhile but not since I increased the water flow and and lowered the low saturation setpoint from 26 to 15. The manual says to set this at -5* with this solution but this seems a little low. Could this have too much oil in it? I checked the level according to the manual and it seems to be ok. I ask about this because I have ran into one of these being over charged on oil before.

  5. #5
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    what is your design flow and pressure drop at 35% EG? higher flow rates can cause higher approach temperatures. how do you know that you have 450 gpm? have you verified that the 450 gpm measurement is correct if it is from a flow meter or other device? 13F sounds high to me as well...have you verified the evaporator pressure transducer is very accurate? have you verified the entering and leaving fluid temperatures are accurate?
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  6. #6
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    Yes I verified the sensors, I checked the water flow with pressure drop. I can't find anything in the manual about flow design with 35% fluid. Or how much this de-rates the chiller.

  7. #7
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    how does the discharge temp look on each compressor? Have you verified your glycol concentration with refractometer? are liquid levels staying close to 0 inch and how far are exvs opening?

  8. #8
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    Quote Originally Posted by michael26 View Post
    Yes I verified the sensors, I checked the water flow with pressure drop. I can't find anything in the manual about flow design with 35% fluid. Or how much this de-rates the chiller.
    so....what was the pressure drop that you measured? you won't find any information on derating the chiller in the manual...it is all in Trane's engineering program. if you have a pressure drop, how do you know how to coordinate the pressure drop with the gpm? i have a program that helps me do that, but only if i have the design data.
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  9. #9
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    Post a complete log AT FULL LOAD including water temps, refrigerant pressures and temps, discharge superheat (oil temp on ch530 is the same as hot gas temp), liquid level, EXV position, GPM, amps, subcooling (using liquid line pressure with a gauge), oil level, %RLA, and anything else you can think of. Make sure your temp sensors are inserted all the way in the wells and are reading accurately. Older CH530 temp sensors are known to read high when they go out. Also check accuracy of pressure transducers. Also make sure oil scavanger line is not clogged up and working.

  10. #10
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    I've seen instances where water has gotten into the entering/leaving temp sensor wells and frozen over and over, slowly pushing the sensor out of the well and causing it to read high. This typically happens on machines that run low solution temps and high glycol percentages like yours.
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  11. #11
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    Quote Originally Posted by r404a View Post
    how does the discharge temp look on each compressor? Have you verified your glycol concentration with refractometer? are liquid levels staying close to 0 inch and how far are exvs opening?
    .
    Did not check discharge temp. Did check with refractometer, I checked the pressure drop across the evap and there is a chart in the manual that crosses foot of h2o diff to flow. Level is 0 to -0.1 and Rev is around 49% when compressor is at 90%

  12. #12
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    Quote Originally Posted by michael26 View Post
    .
    Did not check discharge temp. Did check with refractometer, I checked the pressure drop across the evap and there is a chart in the manual that crosses foot of h2o diff to flow. Level is 0 to -0.1 and Rev is around 49% when compressor is at 90%
    that chart is for water only...if you used that chart and you have glycol then your pressure measurement may have been accurate but your gpm calculations are wrong.

  13. #13
    Quote Originally Posted by michael26 View Post
    Both circuits run an approach of about 13 degrees loaded. Glycol is ethylene 35%. Is this normal with this concentration on glycol.
    I wouldnt be too alarmed at your approach with 35%. i have several rtac's running the same approach with the same concentration, all is fine. just double check your design gpm to your actual gpm. your one issue of tripping you corrected by lowering sat temp trip point, that should have been done at start up. running 250 gpm originally seems quite low, unless the system is designed for low flow. what tonnage was the chiller putting out fully loaded?

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