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  1. #1
    Join Date
    Nov 2005
    Posts
    6

    Hot gas defrost in commercial refrigeration

    Hello, experts
    I'm looking for information about hot gas defrost system.
    I know some theory, but never seen real system.
    It would be great to see working system photo.
    Has anyone tried an hot gas defrost system for low temperature islands, how did it work out?
    What world's manufacturers use it?
    What advantages and disadvantages hot gas defrost system in comparison electrical defrost system?
    Thanks for any advance or link.

  2. #2
    Join Date
    Sep 2002
    Posts
    12,195

    Hot gas is excellent - if you have multiple evaps ganged together, but

    For a single system it is less good. Especially in the winter. You tend to run out of hot gas unless you can keep adding heat via the non-defrosting evap coil.

    The far better and cheaper way to get all the benefits of hot gas defrost without any of the downside is to install a four-pipe reversing valve at the condensing unit and a check valve in parrallel reverse flow around the TXV.
    PHM
    --------
    The conventional view serves to protect us from the painful job of thinking.

  3. #3
    Join Date
    Dec 2002
    Location
    Tampa, Florida
    Posts
    706

    info here..

    go to this web site, plenty of information--

    www.sporlan.com

  4. #4
    Join Date
    Sep 2002
    Posts
    12,195

    Oh; sorry -

    The advantage to using warm refrigerant vapor rather than electric is that it's operates at lower cost and melts the ice off the coil much faster.

    Of course done the normal way it costs more to install.

    Done my way I think it costs about the same. <g>
    PHM
    --------
    The conventional view serves to protect us from the painful job of thinking.

  5. #5
    Join Date
    Sep 2007
    Location
    Denver , Co.
    Posts
    109
    Was it Hussman that had the "Cool gas" Defrost they would take it off the Drop leg of the Condenser instead of the Discharge >??
    Outlaw guns? only outlaws will have guns
    Those who live by the sword are SHOT by us who don't.

  6. #6
    Join Date
    Aug 2006
    Location
    Vancouver , Canada
    Posts
    297

    Cool Gas

    Quote Originally Posted by IceVicious View Post
    Was it Hussman that had the "Cool gas" Defrost they would take it off the Drop leg of the Condenser instead of the Discharge >??
    IV:
    I haven't worked on a rack for a while, but yes, Hussmann used cool gas and a 2 pipe system - gas from the top of the reciever goes through a slide valve, down the suction line to the evap, and condenses - then through a checkvalve around the TXV, and back into the main liquid line. The main liquid line was shut off, and the condensed refrigerant fed the other systems.

    Typical low temp defrosts were less than 20 minutes, but only one system at a time could be on defrost. Advantage to Cool Gas was it was only a 2 pipe system and there was not as much expansion / contraction as hot gas due to the cooler temperatures. The latent heat was what did all the work - worked great!
    Superheat and subcooling tell it all !

  7. #7
    Join Date
    Mar 2005
    Location
    burlington county n.j.
    Posts
    9,704
    only hot gas defrost i had ever seen ariund here was Kramer thermobank units.

    never did any rack or big market work so don't have a clue about that stuff.

    thermobank unit would defrost a coil in a big @ss hurry as long as water level in the thermal bank was good.

  8. #8
    Join Date
    Aug 2007
    Location
    Oregon
    Posts
    19

    Hot is great

    I have never installed or built a system that didn't use hot gas defrost. Most of our systems were designed as low temp IQF freezers. The brine freezers or Refrigerated Sea Water systems also have hot gas defrost options on them. The purpose of the hot gas is the speed at which we can get the system back in operation as a freezer. It takes about 5 to 8 minutes to defrost an evaporator with hot gas and that leaves at least 50 or 55 minutes of freezing time per hour. Some systems only go into defrost once every 5 or 6 hours while others have to be defrosted every hour. It isn't expensive and I absolutely don't recommend any type of three or four way valve. If you use separate valves you will quickly be able to solve any valve problems in the future and with manual stems it really makes it easy. And, before you ask, we use a hot gas option on brine freezers and chillers systems to clear a frozen coil if it should happen. A hot gas loop also has the advantage on some systems of allowing the system to be restarted with minimal power if it has shut down under some unusual condition. The one thing to remember here is that I have never built or installed a system under 5 hp and if it doesn't have a sight glass, I don't touch them.

  9. #9
    Join Date
    Apr 2007
    Posts
    6,285

  10. #10
    Join Date
    Jul 2005
    Location
    FLORIDA
    Posts
    1,163
    ever been in an ice machine and watched it harvest the ice its hot gas in action
    once you think you've seen it all
    (THINK AGAIN)
    I would rather work for free than be look upon as a thief!!!!!

  11. #11
    Join Date
    Sep 2002
    Posts
    12,195

    CB reminded me - with hot gas the compressor HP can be smaller too -

    Anything with a coil which frosts does not work in a world with 24 hour work days. It's working day hours are shorter by the amount of time spent defrosting.

    Like when you have to sleep and can't work? Well, frosting coils have to defrost and can't work during that time.

    So where a full refrigeration ton-day would be 288,000 BTU's moved in 24 hours and require about 1 HP - a frosting coil refrigeration day may be 18 hours and so require 15,000 BTU's to be moved each available working hour instead of 12,000. This would require about 1 1/3 HP instead of 1 HP.

    So far as I can tell - electric defrost only has the benefits of simplicity and lower first cost. I think reason number two is the reason for it's apparently widespread popularity. <g>

    What really the pluses to using electric defrost? Can anyone list them for me?
    PHM
    --------
    The conventional view serves to protect us from the painful job of thinking.

  12. #12
    Join Date
    Sep 2005
    Location
    florida
    Posts
    5,501
    I cant think of any pluses to using electric. I like hot gas myself but kool works to with less stress on the system.
    I love the smell of phosgene first thing in the morning:

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  13. #13
    Join Date
    Dec 2004
    Posts
    509
    Quote Originally Posted by Poodle Head Mikey View Post
    Anything with a coil which frosts does not work in a world with 24 hour work days. It's working day hours are shorter by the amount of time spent defrosting.

    Like when you have to sleep and can't work? Well, frosting coils have to defrost and can't work during that time.

    So where a full refrigeration ton-day would be 288,000 BTU's moved in 24 hours and require about 1 HP - a frosting coil refrigeration day may be 18 hours and so require 15,000 BTU's to be moved each available working hour instead of 12,000. This would require about 1 1/3 HP instead of 1 HP.

    So far as I can tell - electric defrost only has the benefits of simplicity and lower first cost. I think reason number two is the reason for it's apparently widespread popularity. <g>

    What really the pluses to using electric defrost? Can anyone list them for me?
    1. Electric defrost can operate with a lower head pressure.
    2. Electric defrost requires less sophisicated equipment and is cheaper to maintain
    3. Diagonostics are easier

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