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  1. #14
    Join Date
    Jul 2000
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    Guayaquil, EC
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    Regardless of which defrosting method used, the evaporator and all of its electrical would still need to be rated as "explosion proof". There are a number of different NFPA/NEC ratings for hazardous locations, so it would behove you to find out which would be required for this job.

    Going to hotgas would eliminate the heater elements, but the remaining electrical components located inside the box would be about the same. Single compressor hot gas defrost great if it's designed, installed and maintained by someone who know what their doing. If you can get somebody with those attributes to handle this, then by all means go with HG defrost. Otherwise, let Heatcraft provide the necessary hardware and controls for electric defrost.

    An electrical contractor qualified and experienced in explosion proof installation would be needed too.

  2. #15
    Join Date
    Jun 2006
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    You can actually do the -40 with a 404a system running at a near vacuum SST. Depending upon the speed the load will be introduced will determine the size unit you are going to need.

    Not sure about the stepper motors and explosion proof but other than the fan motors everything else can be done outside the box.

    One other significant item for consideration, if there are going to be flammables inside the box there are significant design requirements such as a blowout panel etc. The fact that you are being asked to redesign the mechanicals is a HUGE red flag that the entire system has not been designed and approved by a professional engineer which is a very big concern for your liabilities. NFPA 68 and Factory Mutual have a LOT to say about explosive environments and you might be better off to RUN.

    Other than that, yes, about 12 hp units are available off the shelf and are in use everyday to hit 40 below and they are single stage units. Your customer needs to understand that it is going to run about 70k before explosion proof requirements are met to cool that space to that temp. Notably that is with about 60 foot of line set.

  3. #16
    Join Date
    Mar 2003
    Location
    haciendia heights
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    141
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    Thread Starter
    solvents to remove pot oil must be -40

  4. #17
    Join Date
    Jun 2006
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    Not sure why -40 is hard to explain, it can be and is regularly done 6 hp is a little light unless there is a lot of time to cool the solvent before use.

    Using a 14 by 14 freeze to store and cool the solvent that will warrant significant design requirements so it does t blow up and significant safety enhancements if it does, none of which can be ignored.

    If this is some backroom get the THC oil out of weed attempt by amateurs you really need to run away from it. Have you even been asked for a COI? I would expect them to want one in the 2 to 5 million range.

  5. #18
    Join Date
    Sep 2002
    Posts
    26,351
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    have you given any thought to reverse cycle defrost I have heard good things about using it on evaporators requiring defrosting which all freezers do if they are used continuously then just the fans would have to be explosion proof and the defrosts are really quick which increases the number of hours in the refrigeration day did you even think about using that and only two pipes but I would use an accumulator anyway


    Quote Originally Posted by bob1420 View Post
    have spoken to several mfg box must be explosion proof heatcraft has special heaters and fans and termination box for elect others say hot gas defrost with 3rd line heatcraft says lots of compressor prob with hot gas cond unit ground level 30 foot line set any thoughts
    PHM
    --------
    The conventional view serves to protect us from the painful job of thinking.

  6. #19
    Join Date
    Mar 2008
    Location
    kansas
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    1,614
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    https://www.dwdinternational.com/about/
    See if these guys can help or refer you to someone
    After reading this again I’m a little confused I’ve worked on -50f using Carlyle compoud cooling used for epoxy. That was about the limit of 404 it was a finicky . So the lights and everything your working on is class1 div2?
    Honeywell you can buy better but you cant pay more

    I told my wife when i die to sell my fishing stuff for what its worth not what i told her i paid for it

  7. #20
    Join Date
    Jan 2008
    Location
    LEHIGH VALLEY, PA
    Posts
    680
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    Installed a low temp box , for storing Artillery Shells , for testing there use in sub zero temps , a compound compressor got us to -40c . hot gas defrost . including drain pan , liquid line run through the drain . evaporator fan motors remote from the room on long shafts . the only electrical item was the lighting and it was explosion proof .

  8. #21
    Join Date
    Jul 2012
    Location
    WA
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    I work on a -40 walk in. It uses 404A and two stage Bitzer compressors. Suction runs a slight vacuum when approaching set point. It’s in a plasma donation facility with locations around the country. I’ve been told that they tried hot gas defrost in some locations and had problems caused by the hot gas hitting such a low temp coil.

  9. #22
    Join Date
    Jun 2006
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    Have had good luck with the bitzer set ups too but no hot gas concerns at all, in fact other than a damaged 4 way valve on the one I installed about a month ago the hot gas hasn't given any problems. I talked to Master bilt about them and other than when folks try and cheat the vacuum they have proven to work well, even tiny bits of moisture have given a lot of eev problems. It was a slow process hitting 500 microns with the second unit holding the box temp. Got it to 350 and only rose to 430 in 3 hours but took 18 hours to get there.

    Previous installs did 3/4 wall insulation, I did 1 1/2 to help with the condensation issues they were having on the other systems.

    I am not too keen on those new PE valve 4 ways, it was a real pain to replace, I am not sure what motivated them to move from the sporlans but I know after it took almost 20 days to get one they may be rethinking that one.

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