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  1. #1
    Join Date
    Oct 2002
    Location
    Lexington, NC
    Posts
    5,144

    Rigging up a walk in cooler

    My gosh, I have to ask this. I am hoping to intrigue Poodle Head or some of the older techs here that have seen it all.
    I have a farmer friend of the family that sells produce. He is trying to rig up walk in cooler, and when i say trying, I mean he has already done it. He has an 8 x 10 utility building with R13 insulation and drywall nicely finished. The door is sealed up pretty decent. He has a concrete floor, couple shelves.
    Now here is the kicker. He is using a 5,000 btu window air conditioner to cool this contraption. Of course the a/c unit only goes down to 60, but it is maintaining 60 except the other day when it got up to 95 outdoor ambient he said it got up to 70.
    So he is asking me if I can make the unit cool lower than 60, preferably around 45, but 50 would be ok, but really he wants 45. I said I would have to have a medium temp stat and cycle the compressor with it. Of course I will have to have a coil temp of about 25 to get 45 if I recall, and my biggest worry is that if I can get it down to 45 with this A/C unit is how low will it take the humidity down, because you don't want low humidity with produce. Oh and I told him when it got to 95 he would probably need to have a fine mist of water spraying on the condensor coil.

    For the time being I moved the temp sensor of the a/c away from the coil, so maybe it will drop a couple more degrees. I know this is kind of funny, but you got to give the guy props for trying, and he is a farmer so I am wanting to help him out some if I can. Now I haven't done a load calc on a cooler in about 3 years, so I am wondering what btu removal is required to cool a structure like this down to 45 degrees. Again it is 8 x 10, probably 8 foot celing, R13 insulation with drywall, something like wood sheathing sideing. I don't know if we can use the U values from manual N on a refrigeration calc, but don't see why not.
    He just asked me right now if the 5000 btu is enough. maybe I could plug the numbers in on my load calc program with a 55 degree TD. Wow, that sounds like it would take a lot of btu's. Kind of interesting, but mostly entertaining this is. I am really hoping that he had this building already constructed for another purpose and just decided to try this out. I am pretty sure he is willing to buy a bigger A/C unit to get it to work though.
    The main thing is to keep the main thing the main thing!

    If "the grass is greener on the other side", it likely has been fertilized with Bull$hit!

  2. #2
    Join Date
    Sep 2008
    Location
    Western PA
    Posts
    25,563
    I think you will run into icing problems. Close fin spacing on the window shaker will cause it to bridge the fins as it gets colder.

  3. #3
    Join Date
    May 2011
    Location
    New York
    Posts
    307
    You are going to DEFINATELY run into icing problems. The evap isnt large enough, the UIQ (Unit In Question) will need more air through its evap at a slower rate than a typical 5000 btu window unit blower moves.
    Extended dehydration is the key

  4. #4
    Join Date
    Jul 2000
    Location
    Guayaquil EC
    Posts
    10,325
    A quick load estimate for a box like this gives me about 7200 Btuh for a 45F box. (For produce, you really should be figuring on a design temp closer to 35F however, which would put you up to around 8200 Btuh.)

    A 5000 Btuh high temp unit will only do about 3000 Btuh at the lower evap temp required, so you can see right off the bat, this ain't gonna cut it.

    As others have said, the coil will ice up quickly and game over. These window shakers probably have 16 fins per inch or more whereas a typical medium temp evap will have 6 FPI...and even then they need the compressor to cycle off long enough between run periods to defrost the coil.

    I have to say I have seen this done, but the only time it has half a chance of success is if the window unit is grossly oversized. I'd never recommend it because it'll be your fault when it doesn't work. In this case, that might call for something like an 18-24,000 Btu unit whch would have shorter runs times and even then, there's no guaranty of what you'd get for humidity. For produce, it needs to be about 90%RH at 35F. Lower than that, the product loses moisture, thus losing weight (and quality) and the farmer ends up losing money.

  5. #5
    Join Date
    Oct 2002
    Location
    Lexington, NC
    Posts
    5,144
    Yeah, I told him that I was afraid the run times would be long and that he would be loosing the humidity. I figured the freezing and defrost would be like a food prep station. He said 45, and really I don't think he stores the product long. He picks probably on Thursday evening and Friday, maybe a day or two before that if it is really needing to be picked, and he always sells on Saturday, so long storage times isn't really what he is looking for, I don't think. I don't know though, he was telling me that egg plant gets soft in about a day. Anyone know if it has a higher aspiration rate than other vegies?
    The main thing is to keep the main thing the main thing!

    If "the grass is greener on the other side", it likely has been fertilized with Bull$hit!

  6. #6
    Join Date
    May 2008
    Location
    brooklyn ny
    Posts
    103
    will like to know what is the out come of this set up keep me a head up sound very insterting

  7. #7
    Join Date
    Dec 2007
    Location
    houston, texas
    Posts
    3,787
    Quote Originally Posted by icemeister View Post
    For produce, it needs to be about 90%RH at 35F. Lower than that, the product loses moisture, thus losing weight (and quality) and the farmer ends up losing money.
    How do you accomplish that combination, by driving down the temp as quickly as possible so not so much moisture is removed?
    I'm not tolerating Political Correctness anymore, from now on it's tell it like it is.

    Veto Pro Pak - The best tool bag you'll ever own






  8. #8
    Join Date
    Jul 2000
    Location
    Guayaquil EC
    Posts
    10,325
    A refrigeration evaporator (technically called a unit cooler) runs very high aiflow of around 2000 cfm/ton, a low TD (T room - T evap) of 8F-10F, has a large face area of approximately 3-4 Sq Ft/ton and wide fin spacing like 6 FPI.

    At 35Fdb / 90%RH the dewpoint of the air is about 32F. The coil would be running at around 25F-27F at that condition. That evap temp is determined by the balance of the equipment during selection of the condensing unit capacity relative to the evaporator capacity. A lower TD = higher RH and a higher TD = lower RH.

    Check out this past thread about equipment selection and system balance:

    http://hvac-talk.com/vbb/showthread....=balance+curve

  9. #9
    Join Date
    Dec 2007
    Location
    houston, texas
    Posts
    3,787
    Thanks for the link, now I have the copeland manual stored away.

    What is part 1 and 2 pertaining to? Do you possible have links to them as well
    I'm not tolerating Political Correctness anymore, from now on it's tell it like it is.

    Veto Pro Pak - The best tool bag you'll ever own






  10. #10
    Join Date
    Jan 2008
    Location
    LEHIGH VALLEY, PA
    Posts
    162
    GOOGLE COOLBOT, and further discusion i would take to pro section .

  11. #11
    Join Date
    Jul 2000
    Location
    Guayaquil EC
    Posts
    10,325
    Quote Originally Posted by Texas-Tech View Post
    Thanks for the link, now I have the copeland manual stored away.

    What is part 1 and 2 pertaining to? Do you possible have links to them as well
    There are 5 Copeland manuals actually.

    HVAC-Talk member Powell has them (and a few more) all conveniently listed on his website, www.hvacrinfo.com

  12. #12
    Join Date
    Mar 2007
    Location
    Madison, Wisconsin
    Posts
    2,260
    If I were to try "rigging" something, here is what I would do:

    Take a two ton AC condenser (junker 10 seer) and set it outside the building/shed . Take 1/2 copper pipe(just use type M and flush it), and use it to make a "coil" that that basically looks like radiant piping and hang it from the ceiling. Use a TXV and there you go. I know for a fact that this type of thing works, and no worry about loss of humidity. The coils will frost up, but will drip off during off cycle. I have seen an a very old Ice house that had an ammonia chiller that worked like that. You might have to play with the design a bit, say like using a header and multiple circuits to get better balance and so on.
    I r the king of the world!...or at least I get to stand on the roof and look down on the rest of yall

  13. #13
    Join Date
    Jun 2010
    Location
    Miami
    Posts
    257
    Me thinks there might be better ways to go. I understand the guy is looking to save money but electrical costs are part of that picture. With a little looking around you might find something used....scrap yards....places that have upgraded to newer refrigerants...etc. Typically nobody wants the old equipment. Bound to be a 40 year old R12 system getting torn out somewhere A compressor here....an evap there.

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