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  1. #1
    Join Date
    Oct 2002
    Location
    Denali Park, Alaska, McMurdo Station, Antarctica
    Posts
    114
    I've got a puzzler. One of our crew had to do an install down on the Palmer penninsula about 64 degrees south lattitude on a coastal site. He ahd to install the condensing units outside, and basically had to shovel snow off of the cabinets to access the equipment to run lines and such (wet, cold damp climate). The question is with the piping running from outside to the inside where the walk-in environmental rooms are. How would you get a decent vacuum on the systems at start up? What he did after consulting with a supply house in Anchorage was to tent and heat the condensing unit and get the crankcase heaters online and then ran the vacuum pump on it for a full 24 hrs to get it down to a 28" vac., There was not a vacuum guage on site. So the question is any one have any other suggestions? As of this post the equipment is still running fine. We have some engineering issues to sort out as well but that is another story.... Thanks

  2. #2
    Join Date
    Sep 2001
    Location
    Rochester, New York
    Posts
    1,385
    If it's -10ºF or 70ºF, get the comp. heater online, and tell him to buy a micron gage.

  3. #3
    Join Date
    Oct 2002
    Location
    Denali Park, Alaska, McMurdo Station, Antarctica
    Posts
    114

    Agreed there

    Yeah that is pretty much the nutshell, we're in-house mutts so we are stuck with what they got but progress is being made, we keep ordering and they keep sayin not enough money this go round. Some are happy with the status quo and some aren't.

  4. #4
    Join Date
    Jun 2004
    Location
    Eugene, Oregon
    Posts
    1,018
    You should be able to pull a vacuum regardless of the temp. The issue is that the moisture won’t vaporize at such low temps unless a very deep vacuum is obtained. If it’s a new installation and good installation practices were used there shouldn’t be too much moisture in the system. I would do a triple evacuation and make sure driers are installed with a sight glass and moisture indicator.
    "The bitterness of poor quality remains long after the sweetness of low price is forgotten". --Benjamin Franklin
    "Don't argue with an idiot, they will drag you down to their level and beat you with experience". --Mark Twain
    http://www.campbellmechanical.com

  5. #5
    Join Date
    Dec 2002
    Posts
    603

    Talking

    Cold traps are used to remove water vapor and other contaminant rich air streams of those things that can cause difficulty when introduced into the vacuum pump. In principle cold traps in general work by sublimating a gas molecule, This means that the molecule transforms from a gas phase to a crystalline phase bypassing the liquid phase.I used to use dry ice and F 11,but now it's recommended you use dry-ice and alcohol which is combined to produce a slurry in the 3-quart trap well. When used in line with a rotary vane or small diffusion pump, complete trapping of water vapor and condensable gases is achieved, as well as a lower base vacuum..For more info go here:
    http://www.hyvac.com/Products/Filt_T...20Overview.htm

  6. #6
    If you pressure tested the system once it was sealed shut, you should be alright with a vacum of any kind and then keep an eye on your driers.

    I hate to talk like this ... but what else can you do when your employer wont provide the tools you need to do your job correctly?


    There is a way around this dilema, but I wouldnt want to say it in public. Contact me if your game.


    "Vee have vays of dealing vith dare kind...."

  7. #7
    Join Date
    Oct 2002
    Location
    Denali Park, Alaska, McMurdo Station, Antarctica
    Posts
    114
    I think that is basically how it went. When he contacted us over in McMurdo his main concern was getting it dry enough, in below freezing temps. We suggested after conferring with the brainy guys at RSD in AK, that he build a tent around the condensing units and apply some heat with a space heater, and energize the crankcase heaters for awhile and pull a good long deep vacuum on the system, and let it run overnight on the final evac.
    The main drag is not having any input in the project ordering, we basically don't know what we're into till we get there and open the box and if you're lucky there will be enough stuff in there, and then tools are a whole nother guessing game, vintage, condition, or even if they are all there. A little input could save them big $$. But thats our engineering dept for you. Too used to cost plus I guess. Thanks for the feedback guys, this site and the collective experience are what it is all about.
    Remember the lowest bid isn't always the best deal.

    To err is human, to really screw things up requires an electrical engineer.

    If brute force and ignorance isn't working for you, you probably aren't using enough.

    What would you expect from a defense contractor- your money's worth?

  8. #8
    Join Date
    Dec 2004
    Posts
    56
    if your in alaska why are you bothering with refrigeration just hook up a stat to a motorized dampewr and fan and screw the vacume.

  9. #9
    Join Date
    Dec 2004
    Location
    Mid-west
    Posts
    567
    Heating the condenser up above 60F is the only way to do it. Even in a deep vacuum below 60F you won't get the moisture out. I don't have the technical reason but I have for many years seen this to be true here in Michigan where water cooled condensers are popular on w/i freezers.

  10. #10
    Join Date
    Oct 2002
    Location
    Denali Park, Alaska, McMurdo Station, Antarctica
    Posts
    114
    Wish it was up home , there you have resources and more options and less engineering interference. These units are for laboratory environmental rooms, temps running from freezing to around zero. Down at south pole they do use, a glycol heat exchanger and an outside coil to cool the walk-in but stay with vapor compression for the walk-in freezer. Here in mcmurdo, and at palmer there is too much variation in ambient temps to make it viable to use heat exchanger or outside air- too dusty when it is real warm(have had almost 3 weeks of above freezing temps-lows, and lots of intense solar gain.. well you can figure it from there.) Water cooled condensers use to much water, all station water is RO from sea water, or snow melting (S. Pole and flying fuel in is unrealistic to use in that case) So we still have to run with a more consistant operating system.
    Thanks for the ideas.
    Remember the lowest bid isn't always the best deal.

    To err is human, to really screw things up requires an electrical engineer.

    If brute force and ignorance isn't working for you, you probably aren't using enough.

    What would you expect from a defense contractor- your money's worth?

  11. #11
    Join Date
    Dec 2004
    Location
    Calif
    Posts
    1

    Lightbulb controled envolope

    use a humidifier Place inside box For walk-ins use a heat strap or juice up defrost element with a standard thermostat from a domestic refer , dont forget to keep evaparator fans running

    [Edited by fiotiga on 12-29-2004 at 06:16 PM]

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