Results 1 to 9 of 9
  1. #1
    Join Date
    Aug 2009
    Location
    cambridge
    Posts
    13
    Rep Power
    0

    Low, Medium or High back pressure compressor?



    Hello all,

    I'm trying to spec a condenser section for a small (internal diam 1.85m x 3.55m x 1.35m ) fridge trailer I'm building. And looking for some advise on what sort of compressor would be best suited?

    Basically I built one and I rent it out as a portable cold store, mostly for weekend events and cold store break downs. Most of the time the required temperature is around +2 for fresh food and drink. But on the odd occasion I get asked for a freezer, so now I'm building a second trailer what should I do?

    Do I spec a frozen LBP unit capable of -18C and run it at +2 most of the time, what damaged could it do to the compressor if any, running outside of its parameters? Or spec a over duty MBP unit and on the odd occasion set it to run at -18C.

    The first trailer has a MBP open type condenser section and the unit is well over duty as the unit came up second hand at the right time and right price so I made it fit rather than spec'd it for the cold store. But it does all work well for how it gets used.

    Any advise or ideas welcomed.

    Thanks
    Last edited by frank; 03-02-2014 at 11:09 AM.



  2. #2
    Join Date
    Feb 2009
    Location
    telford
    Posts
    2,097
    Rep Power
    33

    Re: Low, Medium or High back pressure compressor?

    think you just answered your own question?

  3. #3
    Join Date
    Aug 2009
    Location
    cambridge
    Posts
    13
    Rep Power
    0

    Re: Low, Medium or High back pressure compressor?

    But if I want to be able to set the unit between -18 and +2 is there a option or which configuration is less likely to cause damage to the compressor?

    Or should I just stick with a chiller and not think about trying to provide a freezer option?

  4. #4
    Join Date
    May 2007
    Location
    Auckland
    Age
    74
    Posts
    3,362
    Rep Power
    37

    Re: Low, Medium or High back pressure compressor?

    Select for highest load condition, MBP and add an oil cooler or compressor cooling fan for low temp., stops frying compressor with low SST.

  5. #5
    Join Date
    Feb 2007
    Location
    UK
    Posts
    2,479
    Rep Power
    45

    Re: Low, Medium or High back pressure compressor?

    There are options, there are always options...

    Bypass valves, suction pressure regulators, oil coolers to name a few. This would mean designing the system as a freezer and "degrading" it to operate as a refrigerator but the running costs will be higher and the design as well as the controls will be more complicated.
    Might be worth looking in to how they do it in the Transport sector, there is probably a good reason why there is less than a handful of established manufacturers there but their kit normally do what you are asking for.


  6. #6
    Join Date
    Aug 2009
    Location
    cambridge
    Posts
    13
    Rep Power
    0

    Re: Low, Medium or High back pressure compressor?

    I have a transport refrigeration back round, working on Carrier and the usual direct drive suspects. Maybe that's why they all go through compressors.

    Like you say lots of different things can be added, if possible I like to keep it simple though, less to go wrong.

    What about a MOP expansion valve?

  7. #7
    Join Date
    May 2007
    Location
    Auckland
    Age
    74
    Posts
    3,362
    Rep Power
    37

    Re: Low, Medium or High back pressure compressor?

    Generally transport equipment is build like brick out house for multi- operational modes. Compact and lots of air over compressor, that has deep and finned sumps etc., for heat dissipation and oil cooling. The whole compressor has finning in castings.
    MOP TXV are OK but select for highest loading. Low temp conditions equals low vapour volumes and less cooling effect at compressor, hence need for extra cooling for compressor and particularly oil that cools compressor.

  8. #8
    Join Date
    Dec 2010
    Location
    devon
    Age
    52
    Posts
    837
    Rep Power
    24

    Re: Low, Medium or High back pressure compressor?

    for what our trailers run, they dont run long enough do do any long term damage i converted me first one in 2003 useing a caj2446z freezer comp the reason i used this was the biggest comp i could fit that would run well with a 16/13 amp supply i always fit a cpr to protect comp and the trailer runs chill and freeze i would always fit freezer kit as its a possible rental option if its out everyweekend overal that adds up to a total of 15 weeksrental so not a major issue we build one or two a year now and never fitted a comp yet, it really depends on your market our spot rentals are mainly chiller but when we have a commercial freezer go down its a real godsend

  9. #9
    Join Date
    Aug 2009
    Location
    cambridge
    Posts
    13
    Rep Power
    0

    Re: Low, Medium or High back pressure compressor?

    Thanks for that reply charlie patt, I was figuring the same, the hours it'll run per year are minimal compared to a static cold store. Think I'll go with that then.

Posting Permissions

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