Results 1 to 32 of 32
  1. #1
    Join Date
    Nov 2006
    Location
    Manila
    Age
    72
    Posts
    14
    Rep Power
    0

    Smile Replacement fo CO2 Bulk Tank refrigeration unit



    Good Day to all! I have this problem for a Coca-Cola
    bottling plant. Hope i could have some of your advice
    on this matter..The CO2 bulk tank holds 50 tons..
    the existing refrigeration unit is Russel condensing unit
    with a 10TR Copelametic Discuss Compressor and *****22...
    The compressor recently failed...they management want
    us to retrofit...either to 134a or R404a or some ozone friendly
    refrigerant...
    The CO2 unit was locally manufactured with the
    evaporator inside...With a compressor replacement
    with the same refrigerant there would be no problem.
    With a different refrigerant .. let's say 134a, do i have to change
    my condenser & evaporator coils?Do i have to increase or decrease
    the capacity of the compressor?...any special retrofit procedures
    to eliminate the mineral oil from the system, especially from the evaporator..
    Any inputs from all of you guys will be appreciated... thanks in advance..
    Last edited by pabs_ref; 24-11-2006 at 01:32 AM.



  2. #2
    Join Date
    Feb 2001
    Location
    Tampa Florida
    Posts
    1,086
    Rep Power
    19

    Re: Replacement fo CO2 Bulk Tank refrigeration unit

    The evaporator should be fine with any HFC refrigerant. You might want to do an oil change after a day or two of running to get a high proportion of Polyolester oil in the system. How cold will you be maintaining the CO2? You would probably be in great shape using the same compressor model and using R404a. Of course you would have to change the TEV. Suction line size could be a consideration since suction lines generally tend to be larger with R404a than with R22.

  3. #3
    Join Date
    Aug 2005
    Location
    USA
    Posts
    5,327
    Rep Power
    20

    Re: Replacement fo CO2 Bulk Tank refrigeration unit

    It's been a while since I've worked on one of these but will offer some comments .

    Are you sure the compressor is 10 Tons, and not 10HP? If you know what the suction pressure was running at before the compressor quit, you can very easily match up a new condensing unit with the new refrigerant.

    Most of the systems I have seen used R-502, which tells you how long it has been since I have worked on these.

    I might be more inclined to use R-507, not R404a to get rid of the temperature glide with R-404a (among other problems with charging).

    My recommendation would be to remove the old condensing unit and TXV and blow out the evaporator coil with low-pressure nitrogen to remove all of the oil (or at least as much as you can).

    Install a new R-507 condensing unit, TXV, and oversized liquid line filter-drier and also install a suction line filter.

    If you match up the old system capacity to the new one with R-507, the only remaining problem should be changing the oil & filter-driers after a week or so.

    Following this approach, the new condensing unit will have an adequately sized condenser for the compressor and heat rejection load.

    The evaporator capacity should be matched up since the replacement condensing unit should have the same capacity as the old one.

    Problem solved and you make a few $$'s.
    Last edited by US Iceman; 24-11-2006 at 03:17 AM. Reason: spelling

  4. #4
    Join Date
    Mar 2005
    Location
    USA
    Age
    71
    Posts
    639
    Rep Power
    14

    Re: Replacement fo CO2 Bulk Tank refrigeration unit

    Like above, my refrigerant of choice would be R507 since it is an azetrope and not a blend like the 400 series refrigerants. The conditions will be too cold for R134a to be successful.

    You will need to change out the cores, a good oil flush and the TXV needs to be checked.

    Best bet is a new condensing unit designed to run on R507.

    Ken

  5. #5
    Join Date
    Nov 2006
    Location
    Manila
    Age
    72
    Posts
    14
    Rep Power
    0

    Re: Replacement fo CO2 Bulk Tank refrigeration unit

    Thank you all for the replies:

    @Dan

    The CO2 pressure should be maintained at 300psig
    during no bottling periods.. set point for the ref
    unit is at 290psig cut-in and 250psig cut-out.. CO2
    pressure...With F22 the suction is 20-25psig and
    liquid line at 210-230psig at 85-95F ambients..
    The old compressor is rated for *****12-22-502..
    model is 3DB-1000-10HP/7.5KW..Using 404a, with
    suction length of 35ft. do i have to resize the suction
    lines? thanks...

    pabs

    @US Iceman

    You are right... thought it's 10TR... checked the
    model and it's 10HP/7.5KW...The main problem is
    there is no available unit using new refrigerants
    available with our dealer (Copeland) they have
    only R22 units...Import request will probably be
    the fastest is by early 2007...Our dealer for Bitzer
    Germany may have a unit... will check with them..
    one more thing, do i change the capacity of the
    of the condensing unit? or i'll go for the same
    capacity with regards to the old evaporator?
    (havent' used 507 so far will have to check
    it's pressure/temp behaviour)...thanks... will
    follow your advice...

    pabs

    @TXiceman

    thanks for the advice... i have this renewable
    filters for both suction and liquid line filters so
    no problems there...The old condensing unit is old
    anyway having not far away from the from the
    cooling towers for the a/c unit and the chems
    coming from the vapor drift from the cooling tower
    water has made the aluminum powdery... so it
    should be a new condensing unit....

    pabs

  6. #6
    Join Date
    Feb 2001
    Location
    Tampa Florida
    Posts
    1,086
    Rep Power
    19

    Re: Replacement fo CO2 Bulk Tank refrigeration unit

    You are right... thought it's 10TR... checked the
    model and it's 10HP/7.5KW...The main problem is
    there is no available unit using new refrigerants
    available with our dealer (Copeland) they have
    only R22 units...
    In deference to the icemen, their advice is better than my briefer offering. Purging the oil out of the evaporator would be prudent simply because it is so easy during a unit change. I don't feel as strongly regarding the differences between R404a and R507. Both are remarkably similar. R404a is often called a "near azeotrope" which means that it's propensity to fractionalize and glide is for all practical purposes quite small compared to the temporary trinary blends such as HP80, etc. Condenser and evaporator sizing differences are less than 5% for the same performance, from memory when I was concerned about such things.

    In my opinion, an R22 unit would work fine with R507. Have you looked to see just what is different from an R22 unit and an R507 unit? Oil, pressure relief valves. I haven't noticed any differences in the valve plates or condenser sizing. I stand to be corrected.

    Icemen, am I missing something?

  7. #7
    Join Date
    Mar 2005
    Location
    USA
    Age
    71
    Posts
    639
    Rep Power
    14

    Re: Replacement fo CO2 Bulk Tank refrigeration unit

    The 400 series are merrily blends and will fractionate and also operate with a glide. For commerical applications, in tight systems they will work. R507 is a true azetrope and is more of an industrial refrigerant.

    If you are having problems with the fins on the existing unit condenser, I would go ahead and repalve the condensing unit in total. Get a unit with the E-coated coil or hav it Heresite coated to minimize corrosion problems.

    For a unit that is a bit better than the run of the mill commerical units and can be obtained with either a Bitzer or Copeland compressor and coated condenser coil, contact http://www.rae-corp.com

    I have worked with both the 400 and 500 series refrigerants and do prefer the 500 series. R22 is scheduled for phase out on new equipment here in 2010 and as a service replacement in 2020. Where you run up on problems with R22 to R507 is the oils and elastomers in the compressors ( and in some the motor winding varnish).

    Ken
    Last edited by TXiceman; 25-11-2006 at 01:46 AM.

  8. #8
    Join Date
    Aug 2005
    Location
    USA
    Posts
    5,327
    Rep Power
    20

    Re: Replacement fo CO2 Bulk Tank refrigeration unit

    If the CO2 pressure needs to be maintained below 300 psig (20.6 bar g), which seems normal, the evaporating temperature of the coil in the CO2 tank would need to be about 0F to -10F (-17.8C to -23.3C). These evaporating temperatures will match the approximate suction pressures you gave for R-22.

    If the CO tank is rated for a design pressure of 300 psig, I would probably use a slightly lower suction temperature on the compressors to ensure the CO2 pressure is around 250 psig (17.2 bar g).

    If you use a suction pressure cut-in of 27 psig (1.8 bar g with R-507) and a cut-out of 22 psig (1.5 bar g with R-507) that translates into an operating evaporating temperature range of -8.5F to -14F (-22.5C to -25.5C), which should place the CO2 tank pressure about 250 psig (17.2 bar g or close to it). That should keep the relief valves on the CO2 tank from lifting.

    Now, if the old R-22 system was a 10HP unit then find out what the Copeland compressor capacity was at 25 psig suciton pressure (with R-22) and the condensing temperature you were normally running at. This capacity is what you want for the new unit.

    It's probably around 5-6 Tons, if it's that much. That's my guess, but please check the compressor capacity from Copeland.

    Once you have the capacity of the Copeland compressor, that is the capacity you need from the new Bitzer condensing unit with R-507.

    If the capacity of the old system kept the CO2 tank pressure within adequate limits, the new R-507 unit with the same capacity should also work.

    Capacity is capacity, only the refrigerant has changed. The compressor discharge temperatures should also be lower for R-507 than R-22 at these operating conditions.

    Your last message had an interesting comment. If the drift from the cooling towers is causing the condenser fins to rot away, then you should really be looking into some type of protection for the air-cooled condenser coil. I completely agree with TXiceman on the use of a coil coating.

    Unfortunately, the coating will also increase your waiting time as the coil dipping process adds time to the order.

    As I mentioned before, the units like this I worked on used R-502 for the lower temperatures. R-507 is a reasonable replacement for R-502 from the info I have seen.

    Here's a link for pressure/temperatures for various refrigerants.

    http://www.parker.com/rs/PDFS/Ref_Temp_Chart.pdf

    I hope that helps you out. Any questions???
    Last edited by US Iceman; 25-11-2006 at 03:33 AM. Reason: added some of those nice SI units

  9. #9
    Join Date
    Aug 2005
    Location
    USA
    Posts
    5,327
    Rep Power
    20

    Re: Replacement fo CO2 Bulk Tank refrigeration unit


  10. #10
    Join Date
    Nov 2006
    Location
    Manila
    Age
    72
    Posts
    14
    Rep Power
    0

    Re: Replacement fo CO2 Bulk Tank refrigeration unit

    Thank you all again for the replies!

    @Dan

    Thanks for the info...In our country we are a long
    way from the changes....Most of the CO2 units i
    have come across still uses the old reliable *****22,
    being the least expensive... Five years ago we
    tried a retrofit with HP80 with 5TR Copelametic
    unit, but the cost of the refrigerant is 6-7 times
    than F22...(only to find out that HP80 is also
    not a long term alternative)...and with expensive
    refrigerant, CO2 migration to the evaporator is
    costly. I have seen also some Bitzer condensing
    units here stamped for 404a/507 used with R22
    because most contractor will assure owners that
    R22 will still be usable up to 2030?...you are right
    that R22 could be used in 404a/507 units and
    404a/507 can be used in R22 units...

    pabs

    @TXiceman

    Thanks for the info... I'll check with the link you
    suggest and endorse the coated condensing unit
    to the management.. It's interesting to note also
    the problems you mentioned that might arise in
    using 404a/507 to old F22 compressors...

    pabs

    @US Iceman

    Thanks for all those info....I forget to mention that
    the CO2 tank's relief valve is set at 375psig..enough
    to compensate for a 2-3 days no bottling period in
    case the refrigeration system went bad, with the
    system running it stabilize the pressure most of the
    time, rises only a few psig everyday on high
    ambients. The plant has 3 50Tons CO2 tanks
    on rotation daily during bottling periods..
    I noticed that the units never cycle off/on the
    system's pressure control as what you have mentioned,
    but cycle off/on with a pressure switch connected
    to CO2 pressure...Maybe using R507 will have a better
    operating temperature than R22...
    especially lower evaporating temperatures,
    thus might add to less operating cost in the long
    run...

    Checking the old compressor specs, with R22 it's
    capacity at 0F is 5tons, even lower to 4tons at
    -10F at 100F condensing temps... so i'll go for
    a R507 condensing unit with the same capacity..

    I guess the contactor who installed the units did'nt
    forsee the outcome after condensing units are
    exposed daily to water with chems from the cooling
    tower & evapco units..I will recommend to them
    the condensing units suggested by TXiceman...

    Thanks also for the links you gave me... I'll
    download it and i know it will be an interesting
    reading...Again thanks a lot!

    pabs
    Last edited by pabs_ref; 25-11-2006 at 02:23 PM.

  11. #11
    Join Date
    Feb 2001
    Location
    Tampa Florida
    Posts
    1,086
    Rep Power
    19

    Re: Replacement fo CO2 Bulk Tank refrigeration unit

    Figure 2: New product specifications and changes after 80% loss by vapour leakage.

    Changes in component concentrations were only observed to result from vapour leaks and when charging the system with refrigerant in vapour form.
    Solkane is clearly slanting the facts to promote R507. Recharging an 80% refrigerant loss with vapour is nonesensical. When you look at cop's 507 has a small but not all that significant advantage over 404a: 0.1 btu per watt advantage according to Copeland's calculator.

    Regardless, R507 is an excellent refrigerant. In Florida, we have more than a thousand systems operating with some sort of combination of R502, R22, R507, R404a, HP80, et al. A virtual witches brew from hasty changeovers and charging what is available to keep the ice cream hard. Surprisingly, they all seem to work together happily.

    I wonder, now, why the manufacturer of R404a chose to use the R134 component.

  12. #12
    Join Date
    Aug 2005
    Location
    USA
    Posts
    5,327
    Rep Power
    20

    Re: Replacement fo CO2 Bulk Tank refrigeration unit

    Quote Originally Posted by pabs_ref
    I noticed that the units never cycle off/on the
    system's pressure control as what you have mentioned, but cycle off/on with a pressure switch connected to CO2 pressure
    All of the units I have seen operated off of a low-pressure refrigerant switch, but in hind sight, by using the CO2 tank pressure the refrigeration system would be more responsive I believe.

    Quote Originally Posted by pabs_ref
    with the system running it stabilize the pressure most of the time, rises only a few psig everyday on high
    ambients.
    This may be caused in part by this...

    Quote Originally Posted by pabs_ref
    I guess the contactor who installed the units did'nt
    forsee the outcome after condensing units are
    exposed daily to water with chems from the cooling
    tower...
    or, in combination with the condensing unit be being sized with insufficient capacity.

    If the CO2 tank is designed for 375 psig, the relief valves are set at this pressure (or should be). Most relief valves will start to "weep" (a highly technical term that means the relief valves can start to open slightly ) at a lower pressure than their design setting).

    Quote Originally Posted by pabs_ref
    ...with the system running it stabilize the pressure most of the time, rises only a few psig everyday on high ambients.
    That tells me the system is a little under-sized for the required operating conditions.

    If the refrigeration system runs a lot of the time, this might also suggest the unit capacity is insufficient.

    Without seeing the installation and having more facts available, my suggestion is to look at a condensing unit (operating at -10F to -15F) that would have about 5 Tons capacity AT a condensing temperature suitable for your location. 100F seems a little low...

    What is the design air dry bulb temperature in your area? Almost every condensing unit I have seen is normally rated at 110F to 120F condensing temperature. Sometimes higher....
    Last edited by US Iceman; 25-11-2006 at 05:51 PM. Reason: spelling

  13. #13
    Join Date
    Aug 2005
    Location
    USA
    Posts
    5,327
    Rep Power
    20

    Re: Replacement fo CO2 Bulk Tank refrigeration unit

    Quote Originally Posted by Dan
    I wonder, now, why the manufacturer of R404a chose to use the R134 component.
    My guess is they used a percentage of R-134a to help control the discharge temperature.

  14. #14
    Join Date
    Jul 2006
    Location
    USA
    Age
    68
    Posts
    740
    Rep Power
    20

    Re: Replacement fo CO2 Bulk Tank refrigeration unit

    Good Morning US Iceman. Hope you survived the Holiday without discomfort.

    Having a bit of trouble getting that nice balloon around the selected quoted text. Am sure someone can tell me how to do it correctly.

    At any rate you said;
    "Most relief valves will start to "weep" (a highly technical term that means the relief valves can start to open slightly ) at a lower pressure than their design setting)."

    I do not disagree with that. My question is why. The valve is designed so that once it opens the area under the seat is larger. This causes the closing pressure to be higher than the opening pressure, in affect creating a "snap action" valve.
    Is the lessening of the spring pressure pushing down on the seat causing this or is it a more complicated issue?
    I notice this most of all on Screw Packages.
    Is there any Mfgs info on this?

    I believe we are only coming to notice this problem using NH3 now that we have alarms on the relief valve lines. The cheap aluminum valves used on some compressor packages have always been a problem.
    Fortunately we now have rupture disks available which eliminate this as a problem.

    I once saw a R-22 plant losing hundreds of pounds a week through seeping relief valves. I would suggest rupture disks on all Industrial Plants.

  15. #15
    Join Date
    Feb 2001
    Location
    Tampa Florida
    Posts
    1,086
    Rep Power
    19

    Re: Replacement fo CO2 Bulk Tank refrigeration unit

    My guess is they used a percentage of R-134a to help control the discharge temperature.
    That's as good a guess as any. My other guess is that R404a was marketed before R507, thus your guess makes some sense.

  16. #16
    Join Date
    Aug 2005
    Location
    USA
    Posts
    5,327
    Rep Power
    20

    Re: Replacement fo CO2 Bulk Tank refrigeration unit

    Hi NH3LVR,

    Yep, I survived. It was a good day. I hope yours was also.

    My best answer on the relief valve weeping is that the valves are manufacturered with a tolerance. Some of the rupture discs (the industrial ones, not the ones by Hansen, Henry, etc.) can be purchased with different tolerances.

    If you order an industrial /process rupture disc you can get them with I believe a 2%, 5%, or 10% tolerance. The higher tolerance (2%) means the disc will not rupture until the disc is exposed to 98% of the design pressure. They are very tight.

    The lower tolerance disc (10%, if I remember my numbers properly) means the rupture pressure is 90% of the disc rating.

    Mechanical relief valves are similar (although I don't remember the exact numbers right now . but I think the tolerance for a relief valve is 10%). When the operating pressure gets to within the tolerance of the valve it starts to simmer. Essentially, the way I read this is the disc in the valve floats a little, which causes the valve to weep some vapor.

    Quote Originally Posted by NH3LVR
    I believe we are only coming to notice this problem using NH3 now that we have alarms on the relief valve lines. The cheap aluminum valves used on some compressor packages have always been a problem.
    I think you are right. Before (back in the good ole days ) the relief valves were essentially forgotten until they let go.

    I'm assuming you are talking about the Rego valves for the underlined text?

    Rupture discs are a good idea, but you have to de-rate the relief valve capacity if a rupture disc is used upstream.

  17. #17
    Join Date
    Jul 2006
    Location
    USA
    Age
    68
    Posts
    740
    Rep Power
    20

    Re: Replacement fo CO2 Bulk Tank refrigeration unit

    Do not mean to let this thread wander off course but I think this is important.
    I think most of the Mfgs of mechanical relief valves used in industrial applications are 5%. I hope I am right. Never having blown one personally (although I have seen it done) I do not want to find out.
    We are required to change reliefs every 5 years. Few of the Regos make it.
    Now the admission of guilt. As a serviceman, I know the valve has to be derated 5% (which is the usual figure) when installing a rupture disk. Rather than modify a vessel (which requires retesting), I will most likely install it anyway. One Mfg admitted to us lately that they have has a problem with valve weepage. I have to keep the Customer operating. When his plant shuts down on a alarm, I have to make it operate.
    I know I have done wrong.

  18. #18
    Join Date
    Aug 2005
    Location
    USA
    Posts
    5,327
    Rep Power
    20

    Re: Replacement fo CO2 Bulk Tank refrigeration unit

    I don't think you are taking this off course as the relief issue is pertinent to the CO2 vessel being discussed also.

    If the valve has to be de-rated due to the installation of a rupture disc, then the replacement valve should have a 5% greater capacity. That's it.

    The key thing with this is the relief pressure is lower than the design pressure. The problem arises when you back out the tolerances to the maximum working pressure of the system (not maximum design pressure).

    If you condense at 180 psig in normal conditions, the tolerance below the relief valve setting puts you very close to the weeping pressure of the valves. If you add in some non-condensables and dirty condensers or high wet bulb temperatures you get very close to the weeping pressure in operation. Now it becomes a problem.

    If we used 300 psig design pressures instead of 250 psig, we would be in better shape I believe.

    I need to refresh my memory on the exact figures...
    Last edited by US Iceman; 26-11-2006 at 02:50 AM. Reason: editing

  19. #19
    Join Date
    Nov 2006
    Location
    Manila
    Age
    72
    Posts
    14
    Rep Power
    0

    Re: Replacement fo CO2 Bulk Tank refrigeration unit

    That tells me the system is a little under-sized for the required operating conditions.

    If the refrigeration system runs a lot of the time, this might also suggest the unit capacity is insufficient.

    Without seeing the installation and having more facts available, my suggestion is to look at a condensing unit (operating at -10F to -15F) that would have about 5 Tons capacity AT a condensing temperature suitable for your location. 100F seems a little low...

    What is the design air dry bulb temperature in your area? Almost every condensing unit I have seen is normally rated at 110F to 120F condensing temperature. Sometimes higher...
    You are right about the unit being undersized...
    or a combination of facts that the condensing
    unit was subjected to extreme elements.. It was
    installed 12 years ago....I was just accredited
    by them 3 years ago...

    Sorry I was not posting the exact specs of the
    the condensing unit but from the compressor
    specs found in a Copeland compressor databook.
    Guess i choose the lowest condensing temp as a guide...
    You are right about the condensing unit
    specs could be in the 110-120F temperature range...
    The unit tag was erased by the chems from the
    cooling tower and no datas were available from there
    engineering dept.

    Our dry bulb temperature ranges from 90-95 with
    relative humidity of 85-90%....

    I will look for a condensing unit with the design
    specs you mentioned...I still have to check
    the cost of R404a & R507 with regards to
    F22...With our government invironmental
    agencies on our backs about the Montreal
    Protocol Agreement...we'll soon say goodbye
    to F22...(InshaAllah!!!.. as what my friends in
    the Middle East says.... Guess I would be
    lucky if i lived to see that day!)

    Thanks a lot
    Last edited by pabs_ref; 26-11-2006 at 03:02 AM.

  20. #20
    Join Date
    Aug 2005
    Location
    USA
    Posts
    5,327
    Rep Power
    20

    Re: Replacement fo CO2 Bulk Tank refrigeration unit

    Quote Originally Posted by pabs_ref
    I was just accredited by them 3 years ago...
    Keep asking the right questions and doing a good job. I'm sure you will be working there for a long time.

  21. #21
    Join Date
    Jun 2001
    Location
    N.Ireland
    Age
    45
    Posts
    1,632
    Rep Power
    19

    Re: Replacement fo CO2 Bulk Tank refrigeration unit

    Hi

    Henry make a rupture disc and relief valve assembly together, probably for accurancy and reduction of refrigerant loss

    Kind Regards Andy
    If you can't fix it leave it that no one else will:rolleyes:

  22. #22
    Join Date
    Nov 2006
    Location
    Manila
    Age
    72
    Posts
    14
    Rep Power
    0

    Re: Replacement fo CO2 Bulk Tank refrigeration unit


    I don't think you are taking this off course as the relief issue is pertinent to the CO2 vessel being discussed also.

    If the valve has to be de-rated due to the installation of a rupture disc, then the replacement valve should have a 5% greater capacity. That's it.

    The key thing with this is the relief pressure is lower than the design pressure. The problem arises when you back out the tolerances to the maximum working pressure of the system (not maximum design pressure).

    If you condense at 180 psig in normal conditions, the tolerance below the relief valve setting puts you very close to the weeping pressure of the valves. If you add in some non-condensables and dirty condensers or high wet bulb temperatures you get very close to the weeping pressure in operation. Now it becomes a problem.

    If we used 300 psig design pressures instead of 250 psig, we would be in better shape I believe.

    I need to refresh my memory on the exact figures...
    Keep asking the right questions and doing a good job. I'm sure you will be working there for a long time.
    @US Iceman
    About the topic of rupture disc and relief valves...

    I have seen equipments emptied of refrigerants
    due to high pressure switch failure and rupture
    discs releases the charge... Especially in the
    Middle East where ambients reach 120-130F....

    And CO2 relief valve lifting could be more
    disastrous especially when more vapor than
    liquid is in the tank(1/4full)....

    Aside from the failsafe design you mentioned
    coupled with good preventive maintainance
    procedures, as far as invironmental concerns
    about venting to the atmosphere of gases
    which cause ozone depletion and global warming
    is there any other way or system design to
    to avoid such disaster?

    Thanks! Hope you can give me you insight about
    this and or this is not out of topic...

    pabs
    Last edited by pabs_ref; 26-11-2006 at 09:37 PM.

  23. #23
    Join Date
    Aug 2005
    Location
    USA
    Posts
    5,327
    Rep Power
    20

    Re: Replacement fo CO2 Bulk Tank refrigeration unit

    We commonly use and accept design pressures that are applicable to a wide range of normal operating conditions, or, a common design pressure because it's what everyone uses.

    A common design pressure does not mean it's applicable to all cases. Each case should be reviewed to ensure the design pressure is correct for that specific application.

    In IIAR-2 (it's similar to the ASHRAE Standard 15 - Refrigeration Safety Code for the US), they have a recommended practice.

    For air-cooled systems the design pressure is determined by taking the 1% design dry bulb temperature and adding 30F (16.7C) to that 1% design dry bulb temperature. The equivalent refrigerant pressure at this temperature is the design pressure.

    (The 1% means the design dry bulb temperature will be seen or exceeded for 1% of 8,760 hours of the year. It's a nice figure to consider, but we all know the dry bulb temperature always gets hotter than the design conditions.

    For air conditioning systems, it just means the system looses some capacity during the hottest periods. If it does not shut down.

    On the other hand, refrigeration systems are more critical. They should never shut down, just because it gets warm outside.

    Myself, I look at the 0.4% design data and maybe even increase the safety factors a little more.)

    So, if the design dry bulb temperature is 130F and we add 30F to this, we find the design pressure would be equal to the pressure of the refrigerant at 160F. That's pretty high.

    But let's add a few mistakes to this. If the condenser were selected for a 30 degree TD, then the normal condensing pressure would be equal to the design pressure. Do you see a problem with this?

    When the design dry bulb temperature is seen in operation, the relief valves would be lifting and venting the refrigerant.

    Even if the condenser were selected for a 20 degree TD, the condensing temperature would be, 130F + 20F = 150F. That ends up being very close to the equivalent design pressure, so you can still have problems with relief valves weeping since the normal operating pressure is close to the design pressure and the tolerance of the relief valves.

    Rupture discs are not the only answer to this problem. The inherent problem is due to how the system was designed.


    In other words, when we select the design pressure of the system we need to be aware of the interaction of the components and the weather.

    What might be considered a good design pressure, might only be suitable for a limited number of applications (or countries).

    I don't consider this "fail-safe" design. I call it good design practice.

    PS. When I was using the 180 psig pressures I reverted back to ammonia systems, so the actual values change dependent on the refrigerant and condensing method.
    Last edited by US Iceman; 26-11-2006 at 10:18 PM. Reason: added post script

  24. #24
    Join Date
    Jan 2006
    Location
    Croatia
    Age
    63
    Posts
    2,141
    Rep Power
    24

    Re: Replacement fo CO2 Bulk Tank refrigeration unit

    Hi, all

    reading all your posts about relief valves, high pressure... one idea (not exactly mine) came to my mind...

    You know that we have shortcut lines to evacuate refrigerant from single unit (compressor, receiver, separator/s on multi unit plant) for service.

    What do you think about to connect relief valve discharge line to low pressure separator/s thus relief valve will act as bypass valve. We need only to reduce the pressure, without any need to lost refrigerant. Bypass valves are in common use...


    My colleagues and me discussed this many times in the past but without any proof it is good/possible or bad/impossible regarding regulations.

    Knowing also this is not good idea for refrigerant manufacturers because they are coming everyday with new refrigerant which is much better, the best... and advice us to retrofit.

    I believe it is possible (not releasing any refrigerant into nature (at least reduce it - being green).

    What do you think, maybe to patent this idea or it is too late

    Best regards, Josip

    It's impossible to make anything foolproof because fools are so ingenious...

    Don't ever underestimate the power of stupid people when they are in large groups.

    Please, don't teach me how to be stupid....
    No job is as important as to jeopardize the safety of you or those that you work with.

  25. #25
    Join Date
    Jul 2006
    Location
    USA
    Age
    68
    Posts
    740
    Rep Power
    20

    Re: Replacement fo CO2 Bulk Tank refrigeration unit

    Quote Originally Posted by Josip View Post
    What do you think about to connect relief valve discharge line to low pressure separator/s thus relief valve will act as bypass valve. We need only to reduce the pressure, without any need to lost refrigerant. Bypass valves are in common use...
    Best regards, Josip
    If I understand you are thinking of running relief valves back to another part of the system.
    This used to be common. I inventoried relief valves in a plant a couple of weeks ago and found some that way.
    Vilter piston machines do this internally.
    The problem you face is that the relief valve opening pressure becomes the difference between the pressure you are trying to relieve and where you are relieving to. In other words, if you have a relief valve set at 250lbs (17.2 BAR) discharging into a low pressure vessel with a 150lbs (10.3 BAR)relief the worst case conditions would mean a valve opening At 400lbs (27.6BAR).
    These would be extreme conditions, such as a fire, but this might be when you need them most.
    I also believe this might make the other reliefs undersize in the plant.

  26. #26
    Join Date
    Jan 2006
    Location
    Croatia
    Age
    63
    Posts
    2,141
    Rep Power
    24

    Re: Replacement fo CO2 Bulk Tank refrigeration unit

    Hi, NH3LVR

    Quote Originally Posted by NH3LVR View Post
    If I understand you are thinking of running relief valves back to another part of the system.
    This used to be common. I inventoried relief valves in a plant a couple of weeks ago and found some that way.
    Vilter piston machines do this internally.
    The problem you face is that the relief valve opening pressure becomes the difference between the pressure you are trying to relieve and where you are relieving to. In other words, if you have a relief valve set at 250lbs (17.2 BAR) discharging into a low pressure vessel with a 150lbs (10.3 BAR)relief the worst case conditions would mean a valve opening At 400lbs (27.6BAR).
    These would be extreme conditions, such as a fire, but this might be when you need them most.
    I also believe this might make the other reliefs undersize in the plant.
    About Vilter I do not know, seems good construction but I know some other piston compressors having similar system like protection against liquid stroke.

    I was thinking to relief high (condensing) pressure to low pressure vessel working at -20C/-30C/-45C even -10C and then maybe from that vessel relief valve to atmosphere.

    Best regards, Josip

    It's impossible to make anything foolproof because fools are so ingenious...

    Don't ever underestimate the power of stupid people when they are in large groups.

    Please, don't teach me how to be stupid....
    No job is as important as to jeopardize the safety of you or those that you work with.

  27. #27
    Join Date
    Jul 2006
    Location
    USA
    Age
    68
    Posts
    740
    Rep Power
    20

    Re: Replacement fo CO2 Bulk Tank refrigeration unit

    Quote Originally Posted by Josip View Post
    About Vilter I do not know, seems good construction but I know some other piston compressors having similar system like protection against liquid stroke.

    I was thinking to relief high (condensing) pressure to low pressure vessel working at -20C/-30C/-45C even -10C and then maybe from that vessel relief valve to atmosphere.
    Josip:
    I apologize as I believe I was unclear.
    I only mentioned Vilter as they are a example of internally relieving pressure that is considered acceptable. The function in the Vilter is too prevent high pressure in case the machine is started with the discharge valve closed. It doubt it would be of much use in a liquid slugging situation.
    My comments were directed to your post as I understand it.
    Again my apologies for being unclear.

  28. #28
    Join Date
    Jun 2001
    Location
    N.Ireland
    Age
    45
    Posts
    1,632
    Rep Power
    19

    Re: Replacement fo CO2 Bulk Tank refrigeration unit

    Hi
    both Sabroe and Grasso recips have this relief fitted

    If you are fitting PRV's to vent back to suction they have to be outlet independant, uneffected by the pressure at the outlet side, most common PRV's are not

    Kind Regards Andy
    If you can't fix it leave it that no one else will:rolleyes:

  29. #29
    Join Date
    Jul 2006
    Location
    USA
    Age
    68
    Posts
    740
    Rep Power
    20

    Re: Replacement fo CO2 Bulk Tank refrigeration unit

    Quote Originally Posted by Andy View Post
    If you are fitting PRV's to vent back to suction they have to be outlet independent, unaffected by the pressure at the outlet side, most common PRV's are not
    Andy;
    Do you have a example of a PRV that is not not outlet dependant? I have never seen one for refrigeration use. We have a job coming up soon (NH3) on which we could save a great amount of time and trouble if we could use them in a couple of places. I assume the other valves would have to be increased in size to accommodate them?

  30. #30
    Join Date
    Jun 2001
    Location
    N.Ireland
    Age
    45
    Posts
    1,632
    Rep Power
    19

    Re: Replacement fo CO2 Bulk Tank refrigeration unit

    Hi NH3LVR

    Herl make some (now owned by Parker) Danfoss has a range, using a pilot and main valve assembly.
    I will take a look at the Danfoss site and see if I can get a link.

    Kind Regards Andy
    If you can't fix it leave it that no one else will:rolleyes:

  31. #31
    Join Date
    Jun 2001
    Location
    N.Ireland
    Age
    45
    Posts
    1,632
    Rep Power
    19

    Re: Replacement fo CO2 Bulk Tank refrigeration unit

    Hi NH3LVR

    Please use the following linkhttp://www.danfoss.com/Products/Cate...972d837cf1a%7d

    Some link

    POV valve is the one

    Kind Regards Andy
    If you can't fix it leave it that no one else will:rolleyes:

  32. #32
    Join Date
    Jul 2006
    Location
    USA
    Age
    68
    Posts
    740
    Rep Power
    20

    Re: Replacement fo CO2 Bulk Tank refrigeration unit

    Thanks Andy!
    Learn something new here everyday!
    Will ship you some bottles of Homebrew!

Posting Permissions

  • You may not post new threads
  • You may not post replies
  • You may not post attachments
  • You may not edit your posts
  •