Results 1 to 13 of 13
  1. #1
    Join Date
    Nov 2007
    Location
    singapore
    Age
    38
    Posts
    24
    Rep Power
    0

    Thumbs up hi iam new to RE please clear my doubt



    How to calculate the tonnage of a compressor if the name plate doesnt show any details bcoz most of the unit in my site are very old and they doesnt have any name plate is it possible to calculate the tonnage by measuring the consuming amps of the compressor?pls anybody can clear my doubt based on the compressor how to design the condenser and evaporator and refrigerant pipings
    Last edited by balaji; 16-11-2007 at 04:11 PM. Reason: i want more details about this



  2. #2
    Join Date
    Nov 2007
    Location
    singapore
    Age
    38
    Posts
    24
    Rep Power
    0

    Re: hi iam new to RE please clear my doubt

    tonnage of the unit is based on compressor or size of the unit i mean size of condenser coil,evaporator coil etc

  3. #3
    Join Date
    Apr 2006
    Location
    Not so sunny coast (BC Canada)
    Age
    35
    Posts
    1,646
    Rep Power
    17

    Re: hi iam new to RE please clear my doubt

    ((3.14*R^2)*L*N)\1728)*RPM = CFM
    R=Radius
    L=length of stroke
    N=Number of cylinders
    RPM=Compressor speed

    Once you know the CFM you can calculate it based on the refrigerant your using. other then that there is no way.

  4. #4
    Join Date
    Nov 2007
    Location
    singapore
    Age
    38
    Posts
    24
    Rep Power
    0

    Re: hi iam new to RE please clear my doubt

    thanks for your reply but i need more information about thisaccording to you if we calculate the CFM how to convert it in tonnage and i hope there must be some other way to calculate the tonnage that means how they are designing a compressor for the required tonnage pls clear my doubts

  5. #5
    Join Date
    Apr 2006
    Location
    Not so sunny coast (BC Canada)
    Age
    35
    Posts
    1,646
    Rep Power
    17

    Re: hi iam new to RE please clear my doubt

    well you find the refrigerants specific volume at the temp you plan it to evapourate then figure out how many pounds the compressor will circulate then figure out the BTU per pound then devide that figure by 12,000.

  6. #6
    Join Date
    Feb 2007
    Location
    North Carolina, USA
    Posts
    53
    Rep Power
    11

    Re: hi iam new to RE please clear my doubt

    double tap
    Last edited by ultralo1; 17-11-2007 at 03:26 PM. Reason: impatient fingers

  7. #7
    Join Date
    Feb 2007
    Location
    North Carolina, USA
    Posts
    53
    Rep Power
    11

    Re: hi iam new to RE please clear my doubt

    MG Pony,
    I have similar question, How do you calculate the compression ratio when the suction runs in a vacuum?

    example: suction pressure= 15 inches vac
    Discharge pressure= 120 psi

    Thanks.

  8. #8
    Join Date
    Apr 2006
    Location
    Not so sunny coast (BC Canada)
    Age
    35
    Posts
    1,646
    Rep Power
    17

    Re: hi iam new to RE please clear my doubt

    Good question, I'd wager you convert it to psi Absalute and do it as normal?

    The whole focus of the course has been you simply do not go into a vacuum!

  9. #9
    Join Date
    Jul 2006
    Location
    USA
    Age
    67
    Posts
    708
    Rep Power
    18

    Re: hi iam new to RE please clear my doubt

    Quote Originally Posted by ultralo1 View Post
    MG Pony,
    I have similar question, How do you calculate the compression ratio when the suction runs in a vacuum?

    example: suction pressure= 15 inches vac
    Discharge pressure= 120 psi

    Thanks.
    Compression Ratio is allways calculated by absolute pressures.

    For example;
    5" Vacuum (Apx 2.5lbs.), 150lb head
    Add 14.7 lbs to Suction=12.2 lbs.
    150 divided by 12.2=Compression Ratio 12.3

    Hope I got the math right and no time to convert to SI Units. (on the way to work). But you get the idea.

  10. #10
    Join Date
    Sep 2007
    Location
    New Zealand
    Age
    73
    Posts
    54
    Rep Power
    11

    Re: hi iam new to RE please clear my doubt

    Compression ratios should always be calculated in absolute units. The swept volume per rev = Cylinder area x piston stroke. Volume x number of cylinders x rev/second = gross swept volume per second . Multiply this by the specific volume mass per unit volume , i.e. kg/m3 of the refrigerant , obtained from tables at the suction condition. neglect superheat at this time . A previous calculation using tables or charts will deterring the refrigeration effect in tonnes or kW's obtained per unit mass of refrigerant . This value multiplied by the previously calculated compressor swept volume mass will give you the gross compressor capacity. Then determine the actual compression ratio. Discharge Pressure in (ABS) divided by the Suction Pressure in (ABS).
    This will allow the determination of the Volumetric efficiency of the system. Some examples. CR. 3.0 = Vol. Eff 81%. CR. 4.0 = 77% CR. 5 = 72% . CR. 6.0 = 68%. CR. 9 = 55%. If you multiply the CR. by the previously determined compressor gross capacity will give you the actual refrigeration capacity of the compressor at the operating conditions. There is another method if you calculate back using input power by using a factor called Entropic Efficiency but I will not describe it here as it could be more confusing. It is certainly much easier to use makers data or software to undertake this type of work. The (calculated refrigeration load + the motor power) x 20% will gve a reasonable determination of the condenser capacity required. The actual condenser would be selected based on local ambient conditions and the type intended to use.

  11. #11
    Join Date
    Feb 2007
    Location
    North Carolina, USA
    Posts
    53
    Rep Power
    11

    Re: hi iam new to RE please clear my doubt

    I did not know that inches of vacuum could be converted to PSI.

    Learn something new everyday.
    Thank you.

  12. #12
    Join Date
    Apr 2006
    Location
    Not so sunny coast (BC Canada)
    Age
    35
    Posts
    1,646
    Rep Power
    17

    Re: hi iam new to RE please clear my doubt

    Quote Originally Posted by ultralo1 View Post
    I did not know that inches of vacuum could be converted to PSI.

    Learn something new everyday.
    Thank you.
    PISa the a is very important as it is an absalute

    0 inches vac = 29.92inches absalute = 1atm = 14.696 PSIa

    so 15 to PSIa = (29.92-15) / 2.03 = 7.349 PSIa

  13. #13
    Join Date
    Jul 2010
    Location
    usa
    Age
    33
    Posts
    16
    Rep Power
    0

    Re: hi iam new to RE please clear my doubt

    thanks to your concern

Similar Threads

  1. hoe do you clear domestic blockages r134a etc.
    By john squibb in forum Domestic
    Replies: 27
    Last Post: 04-11-2009, 12:13 PM
  2. R134a Blockage
    By frank in forum Technical Discussions
    Replies: 25
    Last Post: 13-09-2006, 08:15 PM
  3. Without a doubt
    By Deejey in forum Chit Chat & Service Stories
    Replies: 1
    Last Post: 24-04-2006, 11:15 PM
  4. Clear sightglass. Vapor or liquid?
    By Sparkplug in forum Trouble Shooting
    Replies: 5
    Last Post: 28-02-2006, 09:37 PM
  5. Let This Message Be heard loud and Clear
    By Abe in forum Legal-Business-Marketing
    Replies: 8
    Last Post: 21-12-2005, 09:26 PM

Posting Permissions

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