Results 1 to 4 of 4
  1. #1
    Join Date
    Mar 2016
    Location
    Lithuania
    Age
    33
    Posts
    1
    Rep Power
    0

    Low back pressure compressor (LBP) in high back pressure system (HBP)



    Hello,

    I'm a newbie here, but was following this forum for quite some time. I'm an electronics engineer who somehow have an inexplicable attraction to refrigeration and HVAC in general.

    So the question:
    I'm planning to design a small power r134a heat pump (~250w) with capillary flow control. Evaporating temperatures (forced air flow) would stay around +10C (50F) and condensing temperatures around 50C (122F). By my understanding, in this situation the HBP compressor with 3,4 cub. cm should be used, BUT - If I used the LBP compressor with the 6 cub. cm displacement, but increase the superheat (by prolonging the cap. tube) to keep the current consumption of the compressor not to go over the designed nominal, would it be OK? Would the compressor lifetime expectancy be somehow altered? Because to my knowledge LBP compressor in HBP designed system would be overloaded and HBP compressor in LBP system would not get enough refrigerant flow to cool down the motor.

    The question why is pretty simple - LBP compressors are significantly cheaper. I understand that compressors quality vary immensely. But by general experience - if the "economy-class" compressor is rated for lets say 250w cooling power - is it real to expect it's lifetime to be at least 5 years while keeping it at nominal or just a bit over nominal power?

    By the way, I might still have a misunderstanding about the condensing and evaporating temps - am I correct that these are the mediums around the coils temperatures (lets say forced air)?

    Thank you for the answers.
    Last edited by Bushmenass; 03-03-2016 at 09:50 AM.



  2. #2
    Join Date
    May 2007
    Location
    Auckland
    Age
    67
    Posts
    3,362
    Rep Power
    31

    Re: Low back pressure compressor (LBP) in high back pressure system (HBP)

    hello
    I have this feeling you are pushing the proverbial up hill with a pointed stick.
    134a in an inefficient refrigerant on a good day and is pretty much banned and taken out of production, capillary is OK at high temps., but LBP compressors not, they rely on cold /cool vapour over the motor windings to keep itself cool, high suction, no saturation compressor will fail.
    Next good idea please. \

  3. #3
    Join Date
    Sep 2007
    Location
    Split Croatia
    Age
    51
    Posts
    6,075
    Blog Entries
    6
    Rep Power
    30

    Re: Low back pressure compressor (LBP) in high back pressure system (HBP)

    High suction superheat = high discharge superheat = compressor winding overheating!
    Now, when I am officialy citizen off EU, I am looking for decent job! For any job offer please check my profile!

  4. #4
    Join Date
    Aug 2007
    Location
    Russia
    Posts
    306
    Rep Power
    14

    Re: Low back pressure compressor (LBP) in high back pressure system (HBP)

    Shortly, it is no good idea to use a LBP compressor with +10C evap. temperature.
    http://www.refrigeration-engineer.co...or-application
    http://www.embraco.com/Default.aspx?tabid=194
    Last edited by narkom; 04-03-2016 at 06:32 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
  •