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Refrigeration Efficiency


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#1 RAM1975

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Posted 05 August 2013 - 05:29 AM

We have Brine chilling plant from YORK refrigeration system

This plant works in cascade system

 

The capacity of the plant is 40TR for (-45◦C ) & 100 TR for (-18◦C)

 

No. Of booster compressor  ONE

Booster compressor capacity is   40TR.

Booster compressor operation is (-45C) Evaporative temp.

                                                (-18C) Cond. Temp.

Refrigerant is   Ammonia

 

No. of high stage compressor is ONE

High stage compressor capacity is 153TR

High stage compressor operation is (-18C) Evaporative temp.

                                                     (38C) Cond. Temp.

Compressor speed       2950rpm

 

 

I am unable to prove how the booster compressor is 40TR and highstage is 100TR .

Can any one help me .



#2 Art Montemayor

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Posted 05 August 2013 - 12:44 PM

 

Our forum can help.  But first, we need CORRECT and applicable basic data and background information.  A process sketch or even a simple PFD, with temperatures and pressures indicated would be a great help in your explanation.

 

A ton of refrigeration is a unit of power used to describe the heat-extraction capacity of a refrigeration system.  A refrigeration ton is approximately equivalent to 12,000 BTU/h or 3,517 W.  When two stages of compression are used in a refrigeration cycle, it is the 1st stage of compression that is assigned the duty of defining the tons of refrigeration applied to the system’s evaporator (where the heat is extracted).  The capacity of the 2nd stage depends on the type and size of refrigeration system employed.  That is why it is essential for you to describe your system in detail and in a sketch.  Otherwise, we don’t know the work that the 2nd stage is doing.

 

Your submitted data is incorrect.  Note that you state that “High stage compressor capacity is 153 TR” and then you further state “…and high stage is 100 TR”.  So, which is correct and WHAT tonnage are you referring to?

 

Also, you don’t even tell us the TYPE and model size of York compressor you are using.  (I suspect you are using screw compressors)  Why don’t you refer to York to tell you the ratings of both compressors and under what conditions?  York should tell you the rated capacities of each compressor at the running speed.



#3 RAM1975

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Posted 06 August 2013 - 06:59 AM

Sir,

 

Its great to see your reply to my topic.I am sorry for the mistakes. 

 

I prepared the hand sketch as i understood for my system.

 

The high stage capacity is 153TR The model size is RWF II 134 .

 

As given on the template the swept volume is 999Ft3/Min and the rpm of the compressor is 4500.The compressor are screw comp.

 

I am trying to attach the PFD prepared but i am not getting the attachment option in the toolbar

 

 

 

  



#4 Art Montemayor

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Posted 06 August 2013 - 02:10 PM

Is the attached literature descriptive of what you are operating?

 

If so, you can obtain the screw compressor's rated Bhp directly from the supplied tables in the brochure.  Note that your compressor is a Frick model and not a York.

 

I await your PFD.

 

Attached File  Compresores_Tornillo_Frick_RWF_II.pdf   124.85KB   87 downloads

Attached File  Frick Rotary NH3 Screw Compressors.pdf   865.55KB   77 downloads

 



#5 RAM1975

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Posted 06 August 2013 - 11:26 PM

Sir,

 

Thanks for the attachements. this explains a lot.York has type with frick in INDIA so i said it's york compressor.

 

I am attaching the PFD here.(It is sketch )

 

I tried to calculate The TR as below but the last value coming is wrong.

 

The swept volume of the compressor for twenty four hrs 59940 Ft3.

 Considering 30% of losses  so 59940-17982.= 41958 FT3 in 24 HRS

 Suction Pressure 28.44 PSI

Volume of the NH3 at 0 Degree centigrade and above pressure ---------10.221 FT3.

 So the effective displacement of the compressor 41958/10.221=4105.077 lbs of ammonia circulated 24 hrs.

The latent heat of ammonia at 28.44 PSI =557.9

So 4105.77*557.9.=2290222.4583 BTU

These BTU absobed by ammonia in passing from liquid to gases state.

 

But it seems something is wrong there.

 

ajay

 

 

 

Attached Files

  • Attached File  PFD.doc   223KB   58 downloads


#6 Art Montemayor

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Posted 07 August 2013 - 10:29 AM

 

ajay:

 

Johnson Controls owns York, who they acquired together with Frick refrigeration.  Their York division sells industrial refrigeration packages that include both York centrifugal compressors as well as the Frick screw compressors.  You obviously have a skidded unit that was bought through the Johnson Controls office in India.  Am I correct?

 

If you bought the unit, did you buy it NEW or USED?  Did you buy it directly from Johnson Controls in India?  If you did, then you should have full customer service from them in India and they can furnish you with all the information you need for the unit – such as the operating and maintenance manuals, the PFD and the P&ID for the process you have, and all available calculations for the refrigerating duty you specified when it was purchased.  Go to:  http://www.johnsonco...al_cooling.html

 

It is next to impossible to interpret your “sketch”.  I am having to generate a reasonable version of what you depict, but your drawing is terrible.  You cross process lines (where did you study engineering?  It is a Cardinal Rule to NEVER CROSS process lines in an engineering drawing) and your notation is very difficult to read.  Since you photographed the sketch, I cannot zoom it up and have sharpness on the letters you wrote.  Anyway, your product is not of any use the way you drew it.  I have to literally re-draw it myself in Excel (the way you should have done it in the first place) and will post it here when I finish it.

 

Please answer my questions so I can understand what you are trying to do.  You have not addressed my first question: “Why don’t you refer to York to tell you the ratings of both compressors and under what conditions?  York should tell you the rated capacities of each compressor at the running speed.”

 

Also, please use engineering units.  What do you mean by kg/cm2 or psi???  Always designate if your pressures are absolute or gauge.  This is needed because we can’t read minds.

 



#7 RAM1975

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Posted 08 August 2013 - 12:31 AM

I accept the mistake of me.

 

The unit is skidded and bought new here.

 

I have communicated in the johnson control and recieved their response.

 

The pressure i gave are absolute..

 

 

 

Ajay

 



#8 RAM1975

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Posted 08 August 2013 - 11:03 PM

Sir,

I am attaching the P &ID recieved from Frick.

 

I want your guidelines and suggestion to me .

 

I will be thankful to you if you answer .

 

AJAY

Attached Files



#9 Art Montemayor

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Posted 09 August 2013 - 02:41 PM

 

Ajay:

 

Thank you for the P&ID.  Unfortunately, it is a very poorly organized and even more poorly colored and printed.  The lettering in bold red, blue and green is unreadable in the PDF – even when I zoom it up to 400%.  You must have copied your version from it.

 

Attached find my workbook that responds to your queries.  Note that I calculate that your brine cooling loads are, indeed, the 100 and 40 Tons of Refrigeration that your P&ID show.

 

What you have is not the conventional, single brine cooling load.  What you have is TWO (2) brine cooling levels that the High Pressure Compressor is handling plus the duty in the intercooler and the economizer.  The Booster Compressor is handling the load on the low temperature brine cooler-evaporator (@ -45 oC).  That is why the HP compressor has twice the load of the Booster.

 

If you want to find the required compressor capacities for both of your machines at the rated TRs, you have to obtain the information that I have outlined in the workbook (in YELLOW cells) in the worksheet titled Ajay’s Design Basis.  There, you will find also my load calculations.  You need that information to make a complete heat and material balance of your system.  Unfortunately, from what I can deduce, you seem to have bought a very cheap or low-priced engineered version of a packaged chiller.  Your system lacks any means to detect the critical temperatures and pressures in the ammonia process.  The designer/fabricator that sold you the unit saved themselves the money needed to furnish the temperature and pressure gauges indicated in my yellow cells.  If you could come up with that data, a heat and material balance could be generated which would tell you the amount of ammonia vapor that has to be handled by the compressors.

 Attached File  Ajays Ammonia Chiller System.xlsx   866.66KB   78 downloads



#10 RAM1975

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Posted 12 August 2013 - 06:12 AM

Sir,

 

Thanks for the reply i have filled the information required to make a complete  heat and material balance in the ex-cel sheet given by you.

 

I am attaching here with auto cad copy of layout for your information.

 

I studied the other sheet attached in the ex-cel file.In the chiller flow digram i seen suction drum .this could be helping to accumolate vapours coming from evaporator and can be hold .this is not there in my system.

the other problem we are facing is the discharge of HP compressor is going high as near to 13.25Kg/Cm2 a

and this is creating the back pressure on the compressor discharge and not allowing the compressor to further load .in this machine the high pressure discharge is set to pressure of 13.50kg/cm2 a and as soon as this pressure goes near to this it  unloads the compressor and does not allow it to go on full load.

 Hence this gives me feeling of Heat and material not balanced .

 

I am trying to uoload the autocad copy but but error is coming.

 

Ajay

Attached Files


Edited by ajaykarkhane, 12 August 2013 - 06:15 AM.


#11 Art Montemayor

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Posted 12 August 2013 - 09:48 AM

Ajay:

 

Your problem in keeping the discharge pressure of the HP compressor BELOW the maximum 13.5 kg/cm2A (13.4 barA) is that your evaporator condenser is not giving you enough condensing capacity.  You are condensing the Ammonia discharged from the HP condenser at a temperature of 34.3 oC (93.7 oF).  This is a very hot ammonia condensate and is probably beyond what the York people designed the unit for.  By setting the maximum discharge pressure of the HP stage at 13.5 kg/cm2A, York is telling you that you must condense the ammonia discharged from the HP stage at a temperature LESS THAN 34.3 oC.  If York supplied (and designed) the Baltimore Air Coil unit, then something is going wrong with that evaporative condenser.  Your humidity might be too high (Where in India are you located?) or your tubes in the condenser might be fouled.  Are all your condenser fans working at designed conditions?

 

You should have stated and explained this problem with the unit at the very first description in your first posting.  This is your FIRST priority problem to resolve.  You must make it available for the HP condenser to NOT reach the 13.5 kg/cm2A value.  And to do this, you must condense at a lower temperature than 34 oC.   Clean or modify the condenser or get a bigger condenser.



#12 RAM1975

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Posted 14 August 2013 - 06:01 AM

Sir,.

 

I am trying to recieve the yorks design conditions for condensor.

 

We are located at Aurangabad in INDIA the very fameous place from here is AJANTA & YEllORA CAVES.

 

I checked and found the condensor fans are correctly working.The other thing i must note is the HP discharge is at 80 oC and the condensor is cooling this to 34 oC .This condensor is supplied by EVAPCO. 

 

I am thinking if the discharge pressure from the compressor it self is very high or it is experiancing back pressure from reciever ?

 

If you give any idea to me to know what should be the flow of ammonia across the PHE for -10 oC and -40 oC tnen i could try to balance the system. 

 

As mentioned by you in previous post i must try to balance this system. for which i should calculate the ammonia flow from evaporator to

compressor actually the temp and pressure condition.

 

Thanks

 

Ajay



#13 Art Montemayor

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Posted 14 August 2013 - 01:18 PM

Ajay:

 

The way to directly improve your refrigeration efficiency is to lower the temperature of the condensed, liquid ammonia coming out of your condenser.  When you lower this temperature, the discharge pressure of your HP ammonia compressor will also be lower.  This is so because the only major back pressure the compressor is going against (with the exception of the pipe and fittings resistance) is the pressure at which the ammonia is condensed.  If you reduce the saturated condensing pressure by reducing the condensing saturated temperature, you automatically reduce the HP compressor discharge.

 

The lower is the pressure of the saturated liquid ammonia coming out of the condenser, the lower will be the temperature, and consequently, the efficiency of converting the condensed liquid ammonia into a low temperature refrigerant will be higher.  This is because you reject your heat of compression to a lower heat sink (the cooling water in the evaporative condenser.  Therefore, you can see now that the importance of the operation of the evaporative cooler is very important.  The evaporative cooler is designed to produce cool water and spray this cool water over coils that carry your hot ammonia gas.  Two major things that can negatively affect the good operation of your evaporative condenser are:

  1. The coils carrying the hot ammonia gas get “fouled” – they get covered with carbonates, other substances, or just plain algae.  This fouling prevents the effective heat transfer to take place between the cooled water and the hot ammonia gas.
  2. The humidity of the locality (Aurangabad, Maharashtra, India) is very high and the evaporative condenser can’t cool enough.  The Annual mean temperatures in Aurangabad range from 17 to 33 °C and I know that the elevation is 568 meters.  But I don’t know how the humidity ranges in that locality.

What I recommend is that you obtain the design conditions for the evaporative condenser and compare the specifications with how the unit is performing - especially the outlet condensed ammonia temperature.



#14 RAM1975

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Posted 16 August 2013 - 05:51 AM

Sir,

Condensor is fully fouled and it requires cleaning or change.

 

I have one more question the minus fourty Booster compressor is showing -0.30 kg/Cm2 A  suction pressure( At Compressor).This is negetive suction pressure.

 

Where as in the charts given by you For this evaporation temparature there should alwayes be positive Pressure at compressor inlet. 

 

The surge drums expansion valve is in closed condition and the pressure over surge drum is 2.0Kg/CM2G

 

is it possible the compressor suction pressure could go in negative also ?

 

The  atmospheric condition are as below

 

                                                           Summer                         Mansoon                               winter

 

                                                            0.4%                                 0.4%                                  99.6%

                                                          DB       MCWB                  WB    MCWB                         DB MCWB

AURANGABAD                                   40.3       22.1                   26.3     36.2                         10.6   8.2

 

 

This place is not humid.

 

Thanks

Ajay

 



#15 RAM1975

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Posted 27 August 2013 - 03:41 AM

Sir,

 

I am trying to evaluate the present TR genrated by the system and the values i recieve are very less to that of plant design.

 

The -10 plant is producing only 30TR against 100TR and the -40 plant is producing 25TR against 40TR.

 

This looks to me some serious operational mistake is happining .

 

As discussed in past post the pressure above the surge drum is 0.5 Kg/cm2 A for -40 oC plant and suction pressure at the compressor is -0.4Kg/Cm2 A.and for -10 plant the pressure above surge drum is 2.5Kg/Cm2 A for -10 oC and suction pressure at compressor is 1.8Kg/Cm2 A .

I am unable to understand How should i run the compressor so that i can take this plant to maximum of its efficiency.

 

If you could give any book for operation of this plant.

 

Thanks

Ajay



#16 Art Montemayor

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Posted 28 August 2013 - 02:36 PM

Ajay:

 

If your condenser is “fully fouled”, then it is probably the reason you can’t condense the ammonia at a design pressure.  As I’ve stated before, you must try to keep the condensed ammonia as cool as you possibly can.  You certainly can’t do that if your condenser is fouled.  You either clean it out or replace it.

 

Please refer to the attached workbook Rev2 in the ammonia saturated Properties Tab to see the thermodynamic properties of the refrigerant in various locations within your cycle.  Note that the suction of the Booster Compressor is always going to be in the partial vacuum range if it is to maintain its evaporator at -45 oC.  Also note the quality of my sketch as compared with the P&ID you submitted.  You can clearly read and understand my sketch because of its layout and the clarity of the symbols and values.  That is the quality of sketch that I expected from you since you are the one soliciting the help.

 

Use my sketch to indicate what you mean by “surge drum” and place the values of the temperatures and pressures in “call-outs” that are readily available in Excel.

 

Your local atmospheric conditions show that you should have no trouble in obtaining good cooling from your ammonia condenser – and consequently good efficiency from your system.

 

What do you mean by “-10” and “-40” plant?  Please be concise and clear in your descriptions.  As I stated, simply show your pressure and temperature inputs on my PFD in the workbook – and title the workbook with the next Rev number.

 

Your Booster compressor should be having a suction pressure of approximately 0.5 kg/cm2A and that is what you report, so your unit is supposedly working as designed.  I don’t know how you are making your efficiency calculations or where you get your information.  Now that you have a legible and simple PFD to work with, you should be able to communicate the various process values with ease and accuracy.  I will await your information.  This thread has already surpassed 15 posts and that is excessive writing.  This is all due to your lack of communicating with the proper, legible, clear, and concise information on a decent PFD.

 

I await your response.

Attached File  Ajays Ammonia Chiller System Rev2.xlsx   1.14MB   32 downloads



#17 RAM1975

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Posted 29 August 2013 - 06:24 AM

Sir,

 

Thanks i really understood the flow easily in the attached file by you.

 My problem of writing as -10 and -40 plant is wrong.This is high stage and booster Compressor respectively.

 

As i said you there is some thing wrong in the operation of compressor as i presume because the set point over the machine for booster compressor Suction pressure is -0.45Kg/Cm2 A.Will this cause the compressor to do more work and not allow the evaporator PHE to do the desired work ?

 

The same can be problem in high stage compressor also ,as i understand the high stage compressor should suck the vapor only above the 2.0 Kg/Cm2 A. and it should try maintaing the same pressure as that in the evaporator (Surgedrum) for -10 oC.

 

The pressure and temp mentioned in the attached File are actual taken today and written .

I am unable to understand what should be approximate ammonia quantity .

 

Thanks

 

Regards

Ajay

Attached Files



#18 Art Montemayor

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Posted 29 August 2013 - 12:35 PM

Ajay:

 

As I commented to you previously, please number the Rev Identity number on the workbook file title in sequence when you make a modification to it.  You are causing a lot of confusion when you don’t label the revision number accordingly because no one will know the sequence of the revisions and when they were made.  I have labeled you last submission as Rev3 and I am now submitting Rev4 here.

 

The temperature and pressure data you submitted in the Tab “Ajay’s Design Basis” is not correct and very suspect of being wrong.  Please submit your pressure as ABSOLUTE in value, and not as gauge pressure.  You should know your local atmospheric pressure and be able to compute the absolute value.  I can’t do that because I don’t know your location’s atmospheric pressure or altitude.  This makes a big difference in calculating the saturated thermodynamic values for ammonia.

 

As I recommended to you, you should use “call outs” to label the different process streams in the PFD I supplied.  See how I have done it and how simple it is to identify the streams and be able to tell if the stream values make sense or not.

 

If you truly are now condensing the HP ammonia at 30 oC (which corresponds to a pressure of 11.67 barA or 11.9 kg/cm2A) then you should have no problem obtaining the design tons of refrigeration predicted by York.  Of course, this is assuming that both compressors are displacing their predicted volumes.  You do not need to make a mass balance around the system to confirm if your unit is producing the design 40 tons for the booster and 100 tons for the HP compressor.  All you have to do is measure the brine flow rate in each of the brine coolers and calculate the tons of refrigeration there as I have done in the workbook.  All you need is the brine flow rate and the temperatures of the inlet and outlet brine – which you should have readily available to you.

 

To answer your specific questions:

  • It is impossible for you to have a suction pressure of -0.45 Kg/Cm2 A.  There is no pressure existing below 0.0 kg/cm2A.  You are reading or interpreting pressure wrongly.  Your booster compressor is designed to take -45 oC ammonia vapor at its saturated pressure of 0.545 barA (0.56 kg/cm2A) and that should be what you are producing approximately inside your -45 oC evaporator.  You must generate that low pressure in that evaporator to produce the desired temperature – and keep it there continuously.  This will NOT cause the compressor to do more work and not allow the evaporator PHE to do the desired work.  On the contrary, keeping the booster compressor suction at 0.56 kg/cm2A IS A REQUIREMENT if you are to achieve the design tonnage of refrigeration.
  • The same principle applies to the HP compressor and its -19 oC evaporator.  Here, the suction pressure should be approx.. 1.9 barA or 1.94 kg/cm2A in order to ensure that the evaporator is at -19 oC.

You have not commented further on the fouling found in the evaporative condenser and I hope this has now been cured and is no longer a problem.  Condensing at 30 oC (or lower) should be your goal because that sets the conditions for the rest of the refrigeration cycle.

 

Please fill in the correct and accurate field data in the appropriate call outs shown on the PFD and re-submit the workbook as Rev5.

Attached File  Ajays Ammonia Chiller System Rev4.xlsx   1.14MB   39 downloads



#19 RAM1975

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Posted 06 September 2013 - 02:02 AM

Sir,

I am on leave till 15th of this month for my problems .

Will come back on 15Th.

 

Ajay



#20 RAM1975

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Posted 20 September 2013 - 05:48 AM

Sir ,

 

Thanks i am back .

 

I have updated temp. at each point indicated in call-out.

 

Further more i recieved both PHE'S drawings and their area's from Alfa - Laval.

 

I tried to evaluate the area selection of PHE for the system but failed the alfalaval has supplied 44&23 Sq.M.PHE for(-)40 &(-)18  application.

 

Over the frick panel all readings were in BAR G hence i was reading them in negative this cleared the doubt.

 

I doubt their motor rating selection too .

 

Thanks ones again for your help to me.

 

Ajay

Attached Files



#21 jainisha

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Posted 23 November 2014 - 01:42 PM

hello friends,,

i m jainisha

plz help me i m stuck in some problem plz try to solve my problem n give  reply me

 

 

 

how to find power usage of screw  compressor in load and unload condition? when load of compressor is increased in chilling plant?

what is the reason behind this to increasing the load of compressor?????????



#22 Art Montemayor

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Posted 23 November 2014 - 08:50 PM

Jainisha:

 

Please start your own, specific thread dedicated to your specific topic.

 

This thread is already over a year old and it belongs to RAM1975.  Please do not try to skyjack this thread for your purposes.

 

I will delete your post here after a day in order for you to start your own thread.

 

Thank you.






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