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  1. #1
    Join Date
    Sep 2012
    Location
    northern Ohio
    Posts
    106

    high head pressure

    I have recently replaced a 5h80 open drive compressor, tube in shell evap, and expansion valves on a industrial chiller. a 500 micron vacuum was pulled (took four days) h-48 drier cores (2) were changed and system is charged with r-507. system brings glycol down to 0deg. set point, but my head pressure is always well above ambient + 30deg. my sub cooling (before sub cooler) also goes up/down with outdoor temp. i think there may be non-condensables as there does not seam to be a lot of heat rejection at the condenser. i also seam to be pumping about 1/3 of the oil thu the system all the time. my compressor holds just under 6gallons and i had to put 9 gallons in to keep the level at 1/2 sight glass. my superheat stabilizes at 6deg after about 10 min running from a restart, and as long as the ambient stays below 80 deg my head pressure is below the 400# safety lockout. all my condenser fans are running and the coil is very clean, even sparying water on it does not seam to do any good. i have changed the oil/driers once since putting this back n service but that did not seam to help either. what should i look for next?

  2. #2
    Join Date
    May 2012
    Location
    Los Angeles
    Posts
    31
    i also seam to be pumping about 1/3 of the oil thu the system all the time.
    This could be your issue. The condenser may look clean from the outside but the inside may be so coated with oil that your not able to transfer the heat.

  3. #3
    Join Date
    Jul 2005
    Posts
    5,380
    Sounds like its grossly overcharged and possibly poorly designed.

  4. #4
    Join Date
    Nov 2004
    Location
    up in the hizzy
    Posts
    1,375
    Quote Originally Posted by refrigeration johnny View Post
    I have recently replaced a 5h80 open drive compressor, tube in shell evap, and expansion valves on a industrial chiller. a 500 micron vacuum was pulled (took four days) h-48 drier cores (2) were changed and system is charged with r-507. system brings glycol down to 0deg. set point, but my head pressure is always well above ambient + 30deg. my sub cooling (before sub cooler) also goes up/down with outdoor temp. i think there may be non-condensables as there does not seam to be a lot of heat rejection at the condenser. i also seam to be pumping about 1/3 of the oil thu the system all the time. my compressor holds just under 6gallons and i had to put 9 gallons in to keep the level at 1/2 sight glass. my superheat stabilizes at 6deg after about 10 min running from a restart, and as long as the ambient stays below 80 deg my head pressure is below the 400# safety lockout. all my condenser fans are running and the coil is very clean, even sparying water on it does not seam to do any good. i have changed the oil/driers once since putting this back n service but that did not seam to help either. what should i look for next?
    was the chiller converted to r-507? have you checked the RPM's? it may be pumping too much, too fast exceeding system capacity,thats my wild guess.

  5. #5
    Join Date
    Mar 2010
    Location
    Morgan Hill Ca.
    Posts
    1,219
    Do you have a discharge oil separator? Have you inspected the float?

    Is the oil weight/viscosity appropriate for your system?
    If a day goes by and you have learned nothing, I hope you got a lot of sleep.

  6. #6
    Join Date
    Sep 2012
    Location
    northern Ohio
    Posts
    106
    thanks everyboy, i have thought that adding an oil seperator would be a good idea. i will talk to the owner monday, and yes it has been converted from 408a to 507 as per the manufacturer of the replacement evaporator. when the system ran with the old refrigerant it had a charge of 220#. I have only put about 170# of 507 in to date. The oil was also changed from alky to poe. I have tried adjusting the unloaders but the loss of cooling capacity is an issue, i also have no way of slowing down the rpm of the motor, yet.

  7. #7
    Join Date
    Dec 2005
    Posts
    1,908
    Quote Originally Posted by refrigeration johnny View Post
    I have recently replaced a 5h80 open drive compressor, tube in shell evap, and expansion valves on a industrial chiller. a 500 micron vacuum was pulled (took four days) h-48 drier cores (2) were changed and system is charged with r-507. system brings glycol down to 0deg. set point, but my head pressure is always well above ambient + 30deg. my sub cooling (before sub cooler) also goes up/down with outdoor temp. i think there may be non-condensables as there does not seam to be a lot of heat rejection at the condenser. i also seam to be pumping about 1/3 of the oil thu the system all the time. my compressor holds just under 6gallons and i had to put 9 gallons in to keep the level at 1/2 sight glass. my superheat stabilizes at 6deg after about 10 min running from a restart, and as long as the ambient stays below 80 deg my head pressure is below the 400# safety lockout. all my condenser fans are running and the coil is very clean, even sparying water on it does not seam to do any good. i have changed the oil/driers once since putting this back n service but that did not seam to help either. what should i look for next?
    So what is the subcool at the TXV ?
    and sub cool prior to the sub-cooler ??

    It did not have oil separator before. And I don't think POE make the situation differ.
    6 degrees super heat is also low in my opinion.

  8. #8
    Join Date
    Apr 2002
    Location
    most of the time in the Philippines
    Posts
    1,211
    It sounds like this system began life as an R502 system. Before chasing your tail, take a look at your pressure/temperature chart and compare the condensing pressures of R502 to R507. Example- at a 125*F condensing temp, R502 is 301 psig where R507 is 344 psig. Makes me wonder about the condensor capacity. How was your blankoff test after you reached 500 microns? If it went well, I doubt that you have non-condensables. Slowing down the motor will decrease the pumping rate of the compressor, same thing as unloading. I don't think it will help. Does this system have a receiver? Tell us more about the subcooler. Is it a separate coil, maybe a refrigerated heat exchanger? This system sounds like some I've seen in juice plants where they made juice concentrates like OJ, Lemonade and what not. However they were not as cold as 0*F; the product had to be slushy so they could fill the containers, then they put them in a drive in freezer.

  9. #9
    Join Date
    Dec 2008
    Location
    Dixiana, AL
    Posts
    2,609
    What's the subcooling AFTER the subcooler - not before....

    Superheat doesn't sound bad on a -10° or -15° coil and 0° space temp as long as it's taken at the coil. If it's being taken at the compressor, then that may be why you have an oil circulation issue. 3 gallons of oil in circulation is serious. If compressor suction superheat is correct and you don't have an oil management system, it's time to think about one (this assumes that you don't have a compressor problem creating the oil loss). I also agree with checking the original specs of your condenser for TRH (total heat rejection) capability. Arbitrarily changing refrigerants on existing equipment can create some interesting situations.

    Also agree with GT: double check the oil specs for a system of your type

  10. #10
    Join Date
    Sep 2012
    Location
    northern Ohio
    Posts
    106
    i revisited the unit Momday to change the oil and liquid driers. i removed just under 6 gallons of oil from the compressor, and maybe another quart came out with the drier cores. it was a little dark but i have seen much worse. After puting 5 and a halve gallons of oil back in the comp. and three new drier cores i restarted the unit and recorded the following when the glycol temp' was within 5 deg. of set point. suction press. 18#, discharge press. 280#, glycol at +2 dgf outdoor/condenser ambiant air at 55degf. liquid leaving the condenser at 55df, at txv it was 37df. suction at exit of evap at -8df at the comp it was +17 df. the oil level in the comp. seems to stay at just under 1/2 the sight glass. ther are bubbles in the liquid line sight glass, and the operator using the glycol has told me the temps have stayed between +10 and -2 while running product. the liquid enters a reciever after leaving the condenser, then goes thru a sub-cooler, drier, sight glass, and solinoid valve before splitting the line for two txv's. The suction gas leaves the evap, goes into an accumulator then the sub-cooler before it gets to the compressor. the compressor oil has a cooler that uses liquid taken between the drier and s valve, goes thru a solinoid valve and txv, sub-cooler and reenters the suction line between the evap and accumulator. When the outdoor temp. goe above 75df my head press. has been over 400# enough to shut the system down on lock-out. the oil temp. and glycol temps also get warmer but thw oil pressure seems to always be at least above the safty setting. I hope to get this staightend out before the weather gets warm again.

  11. #11
    Join Date
    Mar 2010
    Location
    Morgan Hill Ca.
    Posts
    1,219
    Quote Originally Posted by refrigeration johnny View Post
    i revisited the unit Momday to change the oil and liquid driers. i removed just under 6 gallons of oil from the compressor, and maybe another quart came out with the drier cores
    This didn't raise an eyebrow or two?


    Quote Originally Posted by refrigeration johnny View Post
    it was a little dark but i have seen much worse. After puting 5 and a halve gallons of oil back in the comp. and three new drier cores i restarted the unit and recorded the following when the glycol temp' was within 5 deg. of set point. suction press. 18#, discharge press. 280#,
    16:1 CR? What is your discharge temperature?

    Quote Originally Posted by refrigeration johnny View Post
    glycol at +2 dgf outdoor/condenser ambiant air at 55degf. liquid leaving the condenser at 55df, at txv it was 37df. suction at exit of evap at -8df at the comp it was +17 df. the oil level in the comp. seems to stay at just under 1/2 the sight glass. ther are bubbles in the liquid line sight glass, and the operator using the glycol has told me the temps have stayed between +10 and -2 while running product. the liquid enters a reciever after leaving the condenser, then goes thru a sub-cooler, drier, sight glass, and solinoid valve before splitting the line for two txv's. The suction gas leaves the evap, goes into an accumulator then the sub-cooler before it gets to the compressor.



    the compressor oil has a cooler that uses liquid taken between the drier and s valve, goes thru a solinoid valve and txv, sub-cooler and reenters the suction line between the evap and accumulator.
    What oil temps are you maintaining?

    Quote Originally Posted by refrigeration johnny View Post
    When the outdoor temp. goe above 75df my head press. has been over 400# enough to shut the system down on lock-out. the oil temp. and glycol temps also get warmer but thw oil pressure seems to always be at least above the safty setting. I hope to get this staightend out before the weather gets warm again.

    It sure sounds like she is FULL of air to me....

    Get spell check or use Mozilla Firefox please, I felt like a third grade English teacher grading a paper...
    If a day goes by and you have learned nothing, I hope you got a lot of sleep.

  12. #12
    Join Date
    Sep 2012
    Location
    northern Ohio
    Posts
    106
    system scheduled to go off line next week. will be able to breakdown compressor, ect. will post update when i can, thanks for input,

  13. #13
    Join Date
    Mar 2010
    Location
    Morgan Hill Ca.
    Posts
    1,219
    Quote Originally Posted by refrigeration johnny View Post
    system scheduled to go off line next week. will be able to breakdown compressor, ect. will post update when i can, thanks for input,
    What will you be looking for when you do a tear down?

    I would pull an oil sample and get it analyzed then change it out, look for excessive mineral oil to POE ratio, this oil needs to be of the right viscosity. If not it will either experience foaming or be susceptible to excessive windage and be carried away..

    If the oil temperature is allowed to get to hot (say over 120*F) it will also be susceptible to windage and or foaming...

    Are you seeing all four stages of loading and is the amp draw changing in accordance with each stage? I am thinking you have problems other than the compressor, it is doing it's job quite well, maybe even too well.

    Any idea what your discharge temps run? Used to take care of an older wine vintner that had 5F40's, 5H40's, 60', 80's 120's and some 126's. Fairly bulletproof compressors, they either work, or they don't....

    The only time you really see excessive oil carry over is when you have major cylinder/ring damage or a broken/leaking oil line within the crankcase. Did this compressor ever destroy a rod or a piston?


    GT
    If a day goes by and you have learned nothing, I hope you got a lot of sleep.

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