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Thread: Defrost Problem

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    Defrost Problem



    Hello Guys,,

    We have 1700 cubic meter freezer cold store @ -20*C, this freezer have been installed 8 months ago, and it was running perfectly, b4 3 weeks, we've started to problem of not achieving temp. (Possibility of undersized units is not there coz the before 2 months the amb. temp. was 46 and now adays it is 40), when i went there i found too much of ice on the evaporator coils. so i did the following:

    1- i have increased the deforst stop temp. to be 25 and have an override from the defrost stop time.

    2- i have decreased the time between two defrosts.

    3- i increased the drainage time to 10 minutes.

    the temp. there now is -12, and it is not bringing the design temp. except night times, i've checked if there is any possible location that the out side humid air will go through but there is not, also the box door is opened to an air conditioned space..there is still ugly frost on the coil,, the coil heaters are running properlly !!

    any ideas.

    regards..


    Too Much Of Something Is Bad Enough

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    Re: Defrost Problem

    Is this a single compressor system, or part of a multiple compressor rack system?

    Have you checked evaporator and condenser airflow, liquid line subcooling, and TXV superheat?

  3. #3
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    Re: Defrost Problem

    Is there a lot of ice round the door?

    It could be that the prv is jammed and not equalising properly

    Cheers

    Richard

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    Re: Defrost Problem

    Iv'e found in the past that increasing defrost times and durations tends to mask the real problem and make things worse. Start by checking that the liquid solinoid is operating correctly and the tev is operating as it should . then check the integrity of the cold store.

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    Re: Defrost Problem

    Hi again,,

    Dear gray.. the room is cooled by means of 4 split systems each giving 16 KW.. i.e. 64 KW Refrigeration & -25*C.. 4 friga-bohn coolers inside.. for the airflow for both it is excellent, and the expansion valve is working properly, and the 4 systems are facing the same problem, all the suction pressures are going close to 0 psi !! thats ofcourse due to the frost accumulating,, it is insulating very well and poor heat transfer as u know... thx man..


    rbartlett.. what do u mean that it is jammed? there is now frost around the door, please tell me how do the prv coz this problem? thx..


    dill .. u mean that the solenoid is partially closed when actuated ? the expansion valve is working propely.. there are 4 valves for the 4 systems.. and the room was operating with worst ambient conditions (46*C) without problems before this problem... we have the worst climate in the world here man ..
    Too Much Of Something Is Bad Enough

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    Re: Defrost Problem

    sorry rbarlett .. i meant to say there is NO frost around the door..
    take care..
    Too Much Of Something Is Bad Enough

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    Re: Defrost Problem

    Hi Mahmoud
    The fins spacing, is it for freezers evaporators? Say, minimum of 7mm?
    Can you give the evaporator exact model?

    Chemi

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    Re: Defrost Problem

    Hi Mahmoud,
    is the heat load the same in the cabinet like earlier?
    same kinda goods inside?(another thread somewhere in this forum about plastic packaged meat ---> less moisture in the air)

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    Re: Defrost Problem

    Mahmoud, finally made and founs some time to help (perhaps)
    What type of Friga Bohn is used and also type of compressor?

    Is there an internal perforated distributor plate inside the original Friga Bohn distributor?

    Perhaps mositure in the system that comes free now because temperature is going up. The warmer the liquid, the less water it can contain or hold in solution
    .
    You sometimes reach a certain temperature whereby the moisture in the system (in the compressor varnish and the filter which was previously hold in solution or hold in the dryer silicagel, the POE oil,...) comes free at a sudden as free water and freezes in the orifice of the TEV.
    What doest he sightglass say, altough only the right color isn't a precise indication.
    Is it easy to change all the dryers? This is a cheap and fast solution.
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

  10. #10
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    Re: Defrost Problem

    Peter

    the original poster say's it reaches temperature at night but not during the day

    does moisture know the difference??

    there are 4 separate systems all having ice build up problems therefore it's a room fault not a refrigeration one.

    so it's either doors left open too much, prv not operating correctly, product overload, incorrectly stored, not frozen prior to entering etc etc

    cheers

    richard

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    Re: Defrost Problem

    I have to admit, I hadn't read this, you're right Richard.

    Perhaps the problem is slowly 'growing' during the day (icing of the orifice) and till the evening it has frozen completely.
    Just thinking loud.

    If doors are left open, then you should find snow, not ice.

    If theres ice on the evaporators, then this moisture is entering the freezer from somewhere.
    Is there a siphon on the drain?

    Heaters working together with the cooling? Don't laugh, seen this already.
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

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    Re: Defrost Problem

    In case




    Regards
    Engineering, sciences, math, physics and my brain will generate "not responding " soon

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    Re: Defrost Problem

    Do you have commisioning data? How does it compare to the date you have now? Ie suction / discharge presures, Evap temps , air on/ air off. What refrigerant is in the systems. When did the problem start? All of a suden or gradualy??

    Honestly I think rbartlet may be onto something here...If all four are seperate systems and with same problem, It does seem to point towards a room problem. But the figures should give us more insight

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    Re: Defrost Problem

    Thx All for the support,,

    i'll answer and summerize all the replies:

    1- Fin Spacing is 6.35mm (Friga-Bohn Model : SKB-15 C), matched with DWM-Copeland Discus Condensing unit model (V6-4DL-1500 DC)

    2- Room Loading: Actually the room was loaded extreamly after commessioning but didnt have that kind of problem on extreme conditions.

    3- Type Of product: Carton and plastic packed beef and chicken and it is totally freezer before entering the freezer.

    4- preforated plate distributer: am not sure about this, and need to know how this part can cause a problem, i know that for smaller range we can find these, and the spanish KOBOL coolers equivalent to the Friga-Bohn SKB range i think it is without preforated plate distributer, can u explain what could happen there ?

    5- system dryness: actually the sight glass shows dry, but after the problem happened, i advised to change all filters, vacum and charge again, but with no use !!

    6- CCPRV or EPRV: both are not installed.

    7- Heaters functioning: all the heaters are functioning properly.

    8- Commessioning data: actually i dont have the commisioning data, coz my job is to layout, design, estimate, select the refrigeration units with all accessories, design the control panel, supply, and installation if requested, for this job i dont have the commission data, and am here to support the contractor as the after sales servise..but i believe that the contractor was getting the propper suction and discharge readings at the first commissioning, and the room was running properly for months even during the worst ambient conditions..

    9- i know it is going more complicated but for the door openings .. it is not that much door openings, and also there is plastic strips on the door..

    10 - as i explained earlier, we have a low suction pressure, thats ofcourse coz of the existing frost on the cooler,, but we tried to defrost an evaporator completly with sufficient drainage time.. and tried to charge more R22 to overcome the low suction pressure.. but the system had enough charge and started to cut on HP, then we reduced that charge to have a continious operation..

    i know it was quit along explanation ..

    the best..
    Last edited by Mahmoud; 21-09-2005 at 05:19 PM.
    Too Much Of Something Is Bad Enough

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    Re: Defrost Problem

    Hi Mahmoud,

    Are the four systems independent of each other?

    Does each system have a thermostat controlling a liquid line solenoid valve for pump down? If this is true, what is the cut out pressure for the low pressure switch? It should be set for a pressure higher than 0 psig.

    Where are the thermostat bulbs placed?

    Does the freezer construction have a pressure relief port installed?

    If there is a pressure relief port; is it heated and not frozen open? Is it wired?

    Do the drain pan lines have a trap installed outside of the freezer compartment?

    Do all four system have head pressure controls that flood the condenser with liquid refrigerant during cold weather?

    You mentioned the product is frozen before it is placed in the freezer. This freezer is only a storage freezer?

    You mentioned the TXV's were working properly. How did you determine this?

    An easy way to see if ice (in the refrigerant) is the problem is to completely defrost the coil. Then apply some heat to the refrigerant distributor. If the suction pressure is higher after this (or increases rapidly during the heating), but continues to decrease as the system runs, the distributor orifice is building ice.

    Since the system ran OK for several months in hot weather, water in the refrigerant is hard to believe. Unless someone has been charging the system after the four systems were commissioned.

    Also, if the four systems are totally separate from each other, the problem appears to be room related.

    Or, the freezer is now freezing a lot of product that has moisture in it. Usually found in unwrapped fresh product.

    It is hard to analyze a system without seeing it, so we will depend on you to supply details.

    Look forward to your reply.

    Regards,
    US Iceman

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    Re: Defrost Problem

    Mahmoud,

    More questions and some thoughts.

    Are the liquid line driers replaceable core types?

    Have they been recently replaced on all four systems?

    Sometimes when the air humidity is high, and during a drier core replacement, the drier shell will sweat after pump down and when it is opened.

    This may explain how moisture could get into all four systems at the same time, or in a similar time frame.

    If the cooling loads and type of product have not changed, we are looking for something that happened to the refrigeration systems at the same time, OR, a room problem.

    Regards,
    US Iceman

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    Re: Defrost Problem

    Quite often you will find that on these evaporators the tev will bi inside a lump of ice.
    When the tev is completely coverd in ice the tev will not open and the capacity will go down resulting in not reaching temparature.
    Make sure both sides off the evaporator are totaly ice free and the defrost end sensor is at that special place where the last bit of ice will melt.
    (I know this takes a long time of observation but a lot off coffee and patiance will do the job)
    People tend to give 4 times 24H a defrost, witch will result in very short defrost periods, where the evaporator does not get time to make the sides and tev (often draintray) ice free.
    In such a large storage area once a day, often once every 2 day a defrost is more than enough.
    with modern regulators it is posible to give a maximum defrost time of 60 min, this wil stop when the evaporator has reached the selected defrost end temp, and will start the selected drain time.
    make the drain time at least 15 min so the rest heat of the heaters has time get the whole evaporator (sides and drainpan) above freezing point.
    when done in the middle of the night a long defrost period will not give product damage.

    Let us hear what you found

    Victor

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    Re: Defrost Problem

    This need some further explanation why ice around the TEV will close the valve
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

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    Re: Defrost Problem

    Dear all again ..

    thx all again,, actually i got intrested more and more 4 such comments and ideas, i'll comment on the notes:

    US ICEMAN

    1- Solenoid Valve: yes man, each system have it's own thermostat and solenoid, the pressure setting for LP is around 5 psi for the pumpdown, i've mentioned zero to give you an indication how low pressure the system is operating on while the pull down not the pump down... we have a situation of very low pressure .. the refrigerant is evaporating at -35 instead of -25..

    2- Sensors: both sensors are located correctly (Return air, and coil temp.)

    3- PRV : yes it have a prv heated and functioning properly.

    4- Trap: the trap is inside the room.

    5- Head pressure : no head pressure controls, besides we dont have cold climate here all year round

    6- Storage Freezer : yes it is a storage freezer of already frozen products.

    7- TXV Functioning: The txv is correctly sized and installed, 4 o'clock bulb position, also the pressure and temp. difference is alright around the valve.

    8- Filter Drier : the driers are hermatic ones.


    CoolMan

    1- The TXV is free of ice ..

    2- defrost sensors is correctly located.


    Peter

    Peter, lets say the PRV is iced how this will effect on the humidity inside?

    Regards all..
    Too Much Of Something Is Bad Enough

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    Re: Defrost Problem

    Hi Mahmoud,

    OK, this is getting very interesting now.

    Can you provide some digital pictures of the evaporator coils during operation? I would like to see how the coils appear.

    Can you provide a PDF with a flow diagram of the system and components installed?

    Are the coils covered in heavy frost, or ice? These are of course different and sometimes caused by various problems. Frost grows, ice accumulates.

    Sorry about the question for head pressure controls. I forgot where you were located.

    My questions about the drain pan traps and PRV: I was thinking there could be some additional air infiltration into the freezer (extra water to freeze on the coils and greater cooling loads).

    Did all four system start to develop the problem at the same time, or has this been a gradual process (loss of temperature control)?

    The way this looks to me is:

    Four systems that worked well in hot weather for approximately 8 months. 3 weeks ago something happened and temperatures started to rise.

    During the day, the temperature is too high. At night they are acceptable and within the desired range. This indicates something different is occurring at night. NO door openings to allow moisture or air into the freezer!

    You said the door opened into an air conditioned space. Air conditioned spaces can still hold a lot of moisture. Is there any cooking/washing process close to the freezer that started within the last few weeks?

    It is hard to believe that something happened simultaneously to all four systems causing the same effect. Are all of the systems operating the same?

    Is the PRV located close to the coils? Constant door openings during the day could allow sufficient moist air into the room to allow rapid frost growth. More door openings during the day would require more frequent pressure equalization within the freezer.

    I have a lot of questions, but I do hope this helps lead us to an answer.

    US Iceman

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    Re: Defrost Problem

    Erm, To be honest I might be tempted to open all tev's by 1/4 turn, and watch it for an hour, You can always put it back, Just a meer hunch, but I have come across valves "wearing in" and in the proces the super heat setting has shifted after afew months of operation, Probably way off the mark but it is something I would try if I were up against it. If you can get your guage on the suction line directly after the coil to rwead the evap pressure and take temp to check superheat this is good also.

    If all else fails try the old suck it and see aproach..

    last resort... kick it.

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    Re: Defrost Problem

    Hy all
    I did't understand the defrost time is independent for each units ?
    Regards

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    Re: Defrost Problem

    Another question: what material is the floor made?

    If you have ice building up, then there's moisture entering. The only quesiton is: where?

    I suggest you do a pressure test on the freezer.

    If it's a technical problem with the refrigeration system, we need all the needed values(temperatures and pressures) to determine a possible cause.
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

  24. #24
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    Re: Defrost Problem

    For the good understanding: this is a test that has always to be done for an ULO room.
    It don't has to be always a pressure but it can also be an underpressure.

    A Belgium poster - see other threats about 'Air tightness freezer' - did it for two -70°C rooms according to the method I gave him and this gave amazing results.
    Last edited by Peter_1; 04-11-2006 at 09:18 AM.
    It's better to keep your mouth shut and give the impression that you're stupid than to open it and remove all doubt.

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    Unhappy Re: Defrost Problem

    Greetings All

    PLease bear with me, I am new at this.

    Not long ago I was troubleshooting Cold Chambers used to test cars , trucks , etc.... etc.. ( @ -29 C ).
    There were many problems , one them being the moisture in the air ( from an air cond. space ) entering the chamber before and after every test.

    If the door of the chamber was kept open too long , frost and then ice was formed on the coils, floor, walls, ceiling , ....etc ....etc.. Instantly.

    Going back to the defrost problem , I think that if the four independent units in the system are acting the same , I would look for a common problem . The ice.

    If the door of the refrigerated room is open even to an air conditioned space , there are many grains of moisture at that temperature that will end up on the coils.

    I have seen Plastic and Air Courtains installed in similar systems to stop this problem. ( While the door is open )

    One thing I would do to start with,
    is to turn the System on with the door closed and the original control settings and watch it dive to the set point , while checking suction pressures , temperature drops across the coils , defrost cycles,..etc...

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    Re: Defrost Problem

    Going on the data in your posts Mahmoud I would have to agree with richard thats it is more than likely a room problem rather than a system problem especially as all units are affected the same. if it's none of the things that Richard said "doors left open too much, prv not operating correctly, product overload, incorrectly stored, not frozen prior to entering etc etc" then I would suggest the vapor barrier had been compromised in some way and the insulation is wet. This will happen due to condensation inside the wall when the vapor barrier is ineffective
    100% is possible 100% of the time

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    Re: Defrost Problem

    Dear all,

    somethings have improved here... problem solved partially..

    i went to the site yesterday, i have noticed the following:

    1- it seems that owner for a reason or another have switched off the four systems one by one i donno why, and then he start it randomly with a random sequence, when we went there 3 weeks ago the defrost was taking place for the 2 evaporators having a 20m distance between, but one of them was leading less than 2 minutes only, so i didnt consider that important coz less than 2 minutes is not that much.

    2- it seems that the client after we left for the first inspection was switching and switching off, these facts we knew after along investigation with ppl woring at site, the client dont want to show his mistake and want to deduct or embaress the contractor.. any way the system was mesirable, totally mesirable... while one cooler is frosting the other one is throwing air on it !!!!! and vise versa.. that is also the same for the other 2 coolers !!!....,

    3- for each 2 evaporators facing each other (20m distance between) i've set the defrost for them to work in synchronization. then the beautiful result shown... no frost on the ice .. very small quantity but nothing compared to the last situation.. and the room temp. started to go down to -15 instead of -10.

    4- now we have the following situation .. the actual room temp measured by the client (2 meters from the floor is -20) but on the thermostate it reads -15 !! that means that cold air still down, anyway i hope that the room will stablise withen a day and we'll read that temp.

    5- there is a little frost now on the distributer.. !! why now ?!!

    US ice man.. i couldnt take photos .. but the systems is simple enough (Diagram) .. (Condensing unit-filter drier, sight glass-shut-off valve-solenoid-- cooler, etc..) the usual spli system..

    Peter.. the floor is two layers of polyurethane panels covered with concret..

    US ICE MAN, chillu, Cooling magic, O'Brian, peter, victoria man , Deejey , and all thx 4 the support, it is getting real joy hearing your comments..

    please advise for point 4 & 5 guys ,,

    Partially solved partially relieved..
    Too Much Of Something Is Bad Enough

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    Re: Defrost Problem

    Hi Mahmoud,

    Glad things are looking better, If the end user is switching units off at times its possable they are missing their defrosts also. Just an after thought.

    This whole thread though does highlight one thing.. There is no such thing as " a usual system" all systems are diferent and once we assume things about a system design and running conditions, we could and most often do muiss the most obviose, User error!

    Good exercise though
    Last edited by Peter_1; 04-11-2006 at 09:22 AM.

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    Re: Defrost Problem

    Hi Mahmoud,

    It sounds like the main problem was the client!

    I suspect he was having high energy bills (or at least what he thought was too much) and was shutting them down to save energy. Just a guess.

    A deliberate act of shutting the systems down to put your contractor in a bad situation is a terrible thing to do, if this is what happened? If this could be proven, I would not work for the client again.

    item 4) If the room temperature is being measured at -20C, you could be reading the air discharge temperature off of the evaporators. The -15C air temperature could be closer to the actual room temperature with all of the additional help you have had running these systems (the client I mean).

    item 5) There should be a little frost on the distributor. If none before, I would attribute it to the earlier probelms you presented (the client).

    Quote Originally Posted by Chilly
    This whole thread though does highlight one thing.. There is no such thing as " a usual system2 all systems are diferent and once we assume things about a system design and running conditions, we could and most often do muiss the most obviose, User error!
    Well said...

    The first thing that should have happened is that someone should have verified all systems were even operating!

    Quote Originally Posted by Mahmoud
    while one cooler is frosting the other one is throwing air on it !!!!! and vise versa.. that is also the same for the other 2 coolers !!!....,
    Quote Originally Posted by Mahmoud
    for each 2 evaporators facing each other (20m distance between)
    I question the placement of the evaporators. These should have been located in a staggered position to prevent this. Or possibly, located down the center of the room with each fan discharge blowing in an opposite direction to provide uniform air circulation.

    Any any event, I'm glad the problem is getting resolved.

    Regards,
    US Iceman

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    Re: Defrost Problem

    Thx 4 the support !!
    Too Much Of Something Is Bad Enough

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    Re: Defrost Problem

    Hi,
    we also facing such a problem in our -20 cold storage. The large quantity of ice get block the coil. every thing was fine.
    Please check the slope of the drain pipe also check the drain heater.
    clean the block coil with hot water. don't depend on the coil heater to clear the coil fully

  32. #32
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    Re: Defrost Problem

    It is important for HVACR man to notice the possible effects of surrounded circumstances ,human and others. some times human effects is the worst,sometimes ,on the contrary,the notices that comes from those responsible in the site shorten the way to the experit and faciltate solving the proble.But I think in all cases it is the DUTY of the HVACR man to good evaluate all that and not look only for the technical causes ,if not you always go astray!

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    Re: Defrost Problem

    Quote Originally Posted by Mahmoud View Post
    We have 1700 cubic meter freezer cold store @ -20*C, this freezer have been installed 8 months ago, and it was running perfectly, b4 3 weeks, we've started to problem of not achieving temp. (Possibility of undersized units is not there coz the before 2 months the amb. temp. was 46 and now adays it is 40), when i went there i found too much of ice on the evaporator coils. . . . .
    If i may ask:

    1) Have you seen how the following were installed:

    1.1) cold room sub floor &/or vents (or floor heater)
    1.2) insulated wall & ceiling panels
    1.3) floor insulation, vapor barrier.
    1.4) sealant, door, door heater, relief port.

    2) Have you checked where in the cold room (other than the evaporator) there are frosting or ice build up?

    3) What is the evaporator capacity? how much capacity it has compared to design load.

    3.1) Can you take hold of the cooling load calculation made before the purchase of ref eqpt.?
    3.2) Can you check the infiltration/air change load that were considered?
    3.4) Also other loads e.g. Floor transmission load?

    Above question may lead to problem with the cold room construction.
    How can you check the heat load & air infiltration you are having from the floor?

    I hope this helps. . .

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    Re: Defrost Problem

    hi,

    1. Take a good sleep.

    2. Start from scratch.

    3. Chk evry parameter with a fresh mind.

    4. Do a heat load again.

    5. Observe the product and people movement for 2 days continuously.

    6. Observe the system for 2 days continously.

    7. You'll find where the problem is.

    8. Send me a thanks.

    9. Hv a gud sleep

  35. #35
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    Re: Defrost Problem

    undersized units
    Paul Paxson
    PAX Commercial Refrigeration
    pawpax@verizon.net

    "The early Bird get's the worm, But the second mouse get's the cheese"

  36. #36
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    Re: Defrost Problem

    As we know trouble shooting is a process of elimination so I suggest you do the following and check for infiltration.

    Infiltration by direct flow through doorways: Qt = 60 VA (hi – hr) prDt

    Where:
    Qt = average refrigeration load, Btuh
    V = average velocity, ft/min (60)
    A = opening area, sq ft (100)
    hi = enthalpy of infiltration air, Btu/lb (18.62 @ 50 degrees F db/10 degrees C, 47 degrees F wb/8.3 degrees C, 80% RH)
    hr = enthalpy of refrigerated air, (-3.26 @ -15 degrees F db/-26.1 degrees C, -15.15 degrees F wb/26.2 degrees C, 90% RH)
    pr = density of refrigerated air, lb/cu ft (0.089)
    Dt = decimal portion of time doorway is open (0.50)
    Equation with applied values: 60 x 60 x 100 x (18.62 + 3.26) x 0.089 x 0.50 = 350,518 Btuh
    Load components: 249,569 Btuh of sensible and 100,949 Btuh latent heat.

    The latent load is about 29% of the total. The latent portion of the load is actually visible in the form of condensation, fogging, and frost and ice buildup on coils, doors, ceilings, walls, and floors. The largest buildup of frost and ice occurs at the access doors and conveyor openings. High-speed doors and airlocks with strip curtains can be added to help prevent this infiltration.

    However, the movement of product will force open the door, conveyor, and strip curtains to allow air exchange. The temperature difference between the two areas causes warm, humid air from the loading dock to enter the freezer at the top of the access door, and cold air from the storage freezer to discharge at the bottom of the door along the floor of a loading dock.

  37. #37
    ehsanfadhil's Avatar
    ehsanfadhil Guest

    Re: Defrost Problem

    hi
    at night the temperature is reduced and no sun raditation .

  38. #38
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    Re: Defrost Problem

    Hi,
    Mahmoud,when i was in Saudi arabia i got a problem in my walk in freezer we done manythings til i found the problem is the Ventilation of the building,as you said at night it reach the tempture coz at night the ambient is lower.just check your ventilation.

    Hope you sort your problem,
    Cesar

  39. #39
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    Re: Defrost Problem

    Check the dates to the original post. It's almost two years old guys.
    If all else fails, ask for help.


  40. #40
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    Smile Re: Defrost Problem

    Gidday Mate
    1/ Is There An Chilled Loading Area And How Long Is This Door Being Left Open For? Watch It For A Couple Of Hours As The Customer Will Insist That Its Fine.

    2/are The Coils Getting A Good Pumpdown Before Defrost Initiation?

    3/is The Compressors Cycling During Derost?
    If The Liquid Line Solenoid Was "bypassing" And Continued To Feed Making Your Heaters Useless

    4/is The Condensor Efficiant ?

    5/dont Install Poxy Little ***** Systems Where Ammonia Should Be ! Hot Gas Hot Gas Hot Gas.the Most Important Thing Is Get Rid Of The Ice Before You Believe Refrigerant Levels Pressures Superheats Are Ok

  41. #41
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    Re: Defrost Problem

    Hi Mahmoud

    I am sure that you have checked all possible causes of air ingress into the chamber, but have you checked the condensate drains. Are they individually trapped, you will be surprised how much air is sucked up the drains especially with a +-60deg temp diff
    Cheers
    Shaun

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