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  1. #1
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    Nov 2005
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    Chiller Rob Smardt question

    I am hoping you can answer a few questions I have. I am running into some problems with low suction pressure. I have an account with a couple of 240 ton air cooled machines. I am trying to find out if my problem is refrigerant, weather, or component related. I notice the problem on start ups and when the chiller is under heavy load. The unit will go into suction limiting mode. I have verified the flow at 480gpm. When the problem occurs the Kiltech says the demand is @ 70%, the eev is 10% the delta is at 10 degrees, the approach is high around 7. Most of the time the chiller runs great, 1.3 degrees approach, 10 degrees delta, 100% eev, 18% liquid level etc. I have the condensing temp set to 85.

    I am curious what you might think.
    Am I @ capacity?
    low on charge?
    liquid level sensor failure?

    I was having some issues with the eev and the sporlan driver board about 6 months ago. I replaced them both.
    I STARTED WITH NOTHING, AND I STILL HAVE MOST OF IT!

  2. #2
    Join Date
    Nov 2005
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    I STARTED WITH NOTHING, AND I STILL HAVE MOST OF IT!

  3. #3
    Join Date
    Sep 2007
    Location
    Bay Area California
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    Hello allstar,
    if its a startup issue, i would increase the exv start percentage, or perhaps the minimum exv percentage to help with the approach. i would also look at your hot gas settings and bump that a bit...

    what I think may be happening is on an inverted startup, the chiller is holding from loading because of operating on the choke line. as soon as the compressor comes into the operation map, it probably is racing to the moon as it can now load, this results in low evap problems, once the cycle of limiting on suction starts the problem can compound...

    what may help also is bumping your condensing temperaure setpoint a few degrees. this will give you more room to load and maybe find the problem...

    lastly, refrigerant leak check the chiller again. i dont put alot of confidence in the level control 18 number without context data but that sounds low...

    it would also help if i knew what the ambient temperature is when this happens...

    you may also want to download the data logs from the kiltech and take a closer look at the sequence of whats happening on your inveted start conditions...

    good luck...

  4. #4
    Join Date
    Jan 2009
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    Not in Iran
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    i would do what Rob said.,
    also i am thinking low ambient.,
    no signature blast'em man blast'em
    !!!KILL THE TERRORIST!!!

  5. #5
    Join Date
    Nov 2005
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    Quote Originally Posted by chiller rob View Post
    Hello allstar,
    if its a startup issue, i would increase the exv start percentage, or perhaps the minimum exv percentage to help with the approach. i would also look at your hot gas settings and bump that a bit...

    what I think may be happening is on an inverted startup, the chiller is holding from loading because of operating on the choke line. as soon as the compressor comes into the operation map, it probably is racing to the moon as it can now load, this results in low evap problems, once the cycle of limiting on suction starts the problem can compound...

    what may help also is bumping your condensing temperaure setpoint a few degrees. this will give you more room to load and maybe find the problem...

    lastly, refrigerant leak check the chiller again. i dont put alot of confidence in the level control 18 number without context data but that sounds low...

    it would also help if i knew what the ambient temperature is when this happens...

    you may also want to download the data logs from the kiltech and take a closer look at the sequence of whats happening on your inveted start conditions...

    good luck...
    .

    Thanks for the help by the way.
    I will bump up the condensing temp.
    I will increase the exv position on start up.
    The ambient temp is between 40-50.
    What do you mean by inverted start?
    I down loaded the logs already. The only thing I question is the liquid level verses exv position.
    I STARTED WITH NOTHING, AND I STILL HAVE MOST OF IT!

  6. #6
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    Nov 2005
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    1,350
    I read my post and I missed a 0> the EXV is @ 100% when the problem is happening.
    I STARTED WITH NOTHING, AND I STILL HAVE MOST OF IT!

  7. #7
    Join Date
    Jan 2009
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    Quote Originally Posted by allstar08 View Post
    low suction pressure.
    I notice the problem on start ups and when the chiller is under heavy load. The unit will go into suction limiting mode. When the problem occurs the Kiltech says the demand is @ 70%, the eev is 10% the delta is at 10 degrees, the approach is high around 7. Most of the time the chiller runs great, 1.3 degrees approach, 10 degrees delta, 100% eev,


    I was having some issues with the eev and the sporlan driver board about 6 months ago. I replaced them both.

    from what i see, if ur under heavy load, the eev should be more than 10% i would think,
    double check the eev and the sensors that would control the device.,
    the reason the approach is 7 * shows a lack of refrigerant / heat transfer/ in the cooler.,
    no signature blast'em man blast'em
    !!!KILL THE TERRORIST!!!

  8. #8
    Join Date
    Sep 2007
    Location
    Bay Area California
    Posts
    321
    Inverted start is when your chilled water is warm and your evap pressure is higher than condenser pressure... Naturally the refrigerant stacks in the condenser thus starving the evap... So the settings I mentioned would help with that condition/ scenario...

    Leak check the chiller again, sounds like the unit is short on charge or your exv may be loosing time... Pay particular attention to the suction isolaton valves and sniff the little flappers under the capacitors on the compressors themselves... Nailing down a leak can be tough an we techs are so used to trace oil leading us to the problem... I always reference the motor cooling sight glass as you should always have a full column there except for a few bubbles on start...

    Question, does the unit run for prolonged periods of time? Like days on end or does the unit cycle daily on OSA or time lock... All of that comes to play in the exv timing analysis... Also does the exv control directly (4 wires) off the Kiltech I/O board or are you running a 0 to 10 vdc from Kiltech I/O analog output 4 to a Sporlan IB6 driver module and then (4 wires) to the valve...

    Point being, the Kiltech exv driver only has a certian amount of VA to drive the valve. Being that there is no oil circulating thru the refrigerant circuit the valves have a tendency to wear causing increased levels of friction in the valve body... Over time it takes more power to drive the valve... So it's possible the Kiltech is telling you the exv is 100% but actually it's 80% (example, the valve pulsed open 10 times but only 8 of those pulses moved the valve due to the increased wear VA)

    Keep in mind the valve position displayed on the panel is what is requested, there is no feedback position signal... With controls I always question 100% or 0% values... It usually means something is wrong...

    The Sporlan IB6Q driver board has a 24 volt 30 va power supply and is better suited to drive a EXV and solves a lot of problems... As far as the comment about he chiller cycling when off, on shut down the valve drives completely closed and ratchets... The panel knows its at 0% so the valve is essentially back in time... I have had some chillers that were 24/7 and after timing the valve by cycling the chiller, they would run just about 10 days till similar conditions you discribe would make my phone ring...

    Of course with your exv setup it's important to tune the control so the valve is not killing itself trying to maintain set point whether it's level control or suction superheat etc... Along those lines head pressure affects all of this...

    When everything is setup correctly, your trends on the Kiltech and the Turbocor monitor program should be flat and stabile... In your original post you mentioned flow at 480 which is 2 gpm/ ton and 10 degrees at 70% leading me to believe this is a variable flow application... Be careful with that as this also plays a big part with evap approach... I don't over commit to a diagnosis till ther are 5 things that all point to the same conclusion... Pulling the charge to weigh it for example...

    A few tid bits to chew on, hope that helps!

  9. #9
    Join Date
    Sep 2005
    Posts
    11
    Judging by the numbers you posted i would be more leaning to shortage of ref. What kind of float is used on this vintage of chiller, the black float style or the blue capacitance one? and what is your liquid level setpoint for the cond for the eev, as 18% is pretty low. There is usually enough gas in these chillers to overcome the inverted start issues. Dont know where you are located but in the colder climates the black motor cooling hoses are known to be bad leakers as well as well as the oring on the brass bornia style hot gas valve

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