Page 1 of 2 12 LastLast
Results 1 to 13 of 14
  1. #1
    Join Date
    Jul 2007
    Location
    regina saskatchewan
    Posts
    257
    Post Likes

    sizing walk-in cooler?

    Have a 6800 BTU compressor.How do I size the evaporator/txv?I know the txv are rated by ton.Just starting to get into installs and want to be informed before I proceed.Any good info will be greatly appreciated!!
    Artificial Intelligence is no match for Natural Stupidity

  2. #2
    Join Date
    Feb 2004
    Location
    Medford Oregon
    Posts
    807
    Post Likes
    the design TD of a cooler can be 10 to 20 depending on usage
    at 10 TD a 6800 btu coil will do (general storage)
    at 15 TD a 4500 coil will do (beer cooler)
    at 20 TD a 3400 coil wll do (met prep room)
    (most coils rated at 10 TD)

    you can get all the info you need from Heatcraft's Engr Manual, though it will take a bit of study, it will explain above TD examples (no simple answers)
    it's free, download link:
    http://www.heatcraftrpd.com/resource...H-ENGM0806.pdf

  3. #3
    Join Date
    Jul 2000
    Location
    Guayaquil, EC
    Posts
    14,209
    Post Likes

    Walk-In Equipment Selection...

    To add to what rocket posted...

    Since you are just getting into this and want to learn more about it, i suggest studying the Heatcraft Engineering Manual. It's an excellent resource which takes you from sizing the box load through equipment selection.

    First however, just as in HVAC work, it's always advisable to run a load calc before installing or changing out a system. Use the manual's accompanying Load Estimate Form and do the calculations longhand. This will give you a better feel for where the numbers come from and will establish your box load for selecting the proper equipment to do the job. There are free load calc programs available, but initially doing it by hand will make those easier to understand and use later on.

    Once you get your box load, you'll need the compressor and evaporator manufacturer's performance ratings which you will use for equipment selection to achieve proper system balance. This info is readily available online from the major manufacturer's websites. Many wholesaler's catalogs have all the necessary data included as well.

    A basic example for equipment selection might be a typical general storage walk-in box where the design box temp is 35F and the ambient for the condensing unit is 90F and let's assume the box load comes out to 6500 Btu/Hr. Starting on p.21 of the manual, you will find that you first need to determine the proper evap TD for this application...let's say it's 10F. Since the TD = T (box) - T (evap), then the evap temp in this case would be 35F - 10F = 25F.

    Now to get the design saturated suction temp for the compressor you have to take into account the line losses between the evap and the compressor, which are typically equivalent to about 3F. That would place your compressor suction at 22F, but for simplicity let's just round it off and call it 20F. Then go to the condensing unit's expanded performance ratings chart for 90F ambient and select the unit that will give you 6500 Btu/Hr or slightly greater at 20F SST (Saturated Suction Temp) which uses the refrigerant you prefer. Let's assume then that it's R404A and the compressor capacity is 6800 Btuh @ 20F/90F.

    Now go to the evaporator data and select a unit that will give you the closest to 6800 Btu/Hr at a 10F TD. Note that all manufacturers use 10F TD as their "nominal" performance rating. To calculate for a different TD, just divide the nominal rating by 10 and multiply by the actual TD.

    Finally for the TEV selection, the quick way is to use nominal tons. In this example that would be 6800/12000 = .57 tons. Pick a valve for the refrigerant your using (R404A) with a thermostatic element charge suitable for the temperature (+20F) and a capacity equal to or slightly greater than .57 tons. Also, the coil manufacturers often have quick selection charts for TEVs to match their evaps. However, the proper method (and good learning experience) of TEV sizing would be to go to the manufacturer's data like Sporlan Bulletin 10-10 and do a longhand selection.

    That's about it in a nutshell. Let us know how you make out.

  4. #4
    Join Date
    Feb 2008
    Location
    Southern Indiana
    Posts
    83
    Post Likes
    Icemeister said everything and I can't add to it except for warning you that you are "green" and dangerous to yourself on this so far.

    You need to check everything through the engineers at the place you're buying the box from. Pay attention to their questions and make sure you come away with the educational experience, sell this one, then sell some more on your own doing what Icemeister says and make some better money.

    Nothing is free. Its just another four-letter word.

  5. #5
    Join Date
    Jul 2007
    Location
    regina saskatchewan
    Posts
    257
    Post Likes
    Thread Starter
    Thanks for the info guy's.I have no problem with the repair side of refrigeration,but want to get in to the install side.1\2 ton txv is aprox 6000 btu's right?I will read the links you guy's provided.But for quick reference should everything match with respect to btu's?6000btu compressor,1\2 ton txv,6000 btu evap coil?I have a customer that want's a evap coil installed in place of a gravity feed.I haven't got the spec's on the coil he has yet and wnat to know what I can get away with if it is over or under sized.
    Artificial Intelligence is no match for Natural Stupidity

  6. #6
    Join Date
    Feb 2008
    Location
    Southern Indiana
    Posts
    83
    Post Likes
    Cretan; you have problems and you are hanging on to high-temp memories. Do not keep your assumptions when doing refrigeration work. Do more reading of refrigeration fundamentals, compressor ratings, valve sizing, and other related material, before losing your way down the wrong path.

  7. #7
    Join Date
    May 2000
    Location
    Monmouth Junction-NJ-USA
    Posts
    6,121
    Post Likes
    You may have a match and you may not. You are working this backwards. Must know the load of the box first. Make sure you know the composition of the box. If you don't want to take the time and do the load long form (highly recommened to know the whys and how tos) the go to a site like keeprite refrigeration and download the load program. Start at the begining not the end of the equation. You also need to know if the exixting condensing unit is High Temp or Med temp. Good Luck and remember that Knowledge is Power.
    Last edited by rayr; 06-01-2008 at 06:17 AM.
    If you really know how it works, you have an execellent chance of fixin' er up!

    Tomorrow is promised to no one...

  8. #8
    Join Date
    Jul 2007
    Location
    regina saskatchewan
    Posts
    257
    Post Likes
    Thread Starter
    double post.
    Last edited by cretan; 06-01-2008 at 01:33 AM. Reason: double post
    Artificial Intelligence is no match for Natural Stupidity

  9. #9
    Join Date
    Jul 2007
    Location
    regina saskatchewan
    Posts
    257
    Post Likes
    Thread Starter
    Looks like it's time to read some more.Went to see the customers evap coil and looks oversized.It's a keeprite R775.Thanks for all the info guys.
    Artificial Intelligence is no match for Natural Stupidity

  10. #10
    Join Date
    Jul 2007
    Location
    regina saskatchewan
    Posts
    257
    Post Likes
    Thread Starter
    Is a keeprite R775 a good match for a 6800 btu compressor?
    Artificial Intelligence is no match for Natural Stupidity

  11. #11
    Join Date
    Jul 2000
    Location
    Guayaquil, EC
    Posts
    14,209
    Post Likes
    Quote Originally Posted by cretan View Post
    Is a keeprite R775 a good match for a 6800 btu compressor?
    To state that the compressor you have can do 6800 btu's doesn't really mean anything unless you define the operating conditions...ie, suction & discharge pressures and what flavor of refrigerant you're using.

    Give us the compressor or condensing unit make and model numbers, the refrigerant, the design box temperature and then maybe we can help further.

    BTW...The Keeprite R775 is rated for 7900 Btu/hr at a 10F TD.

  12. #12
    Join Date
    Jul 2007
    Location
    regina saskatchewan
    Posts
    257
    Post Likes
    Thread Starter
    Sorry I didn't give more info.Walk-in cooler.The compressor# is rsn40100cav215.it is being used with a static coil right now.He wants to change to forced air.he has a keepright r775,but I thought it is too big.I did not look over the system that much.just got some of the numbers.Someone answered a question I asked about the compressor and said it was a 502 system.I know that 408 is a drop in.What else would be in there?How would someone tell what refrigerant is in a system if not marked?
    Artificial Intelligence is no match for Natural Stupidity

  13. #13
    Join Date
    Jul 2000
    Location
    Guayaquil, EC
    Posts
    14,209
    Post Likes

    Rsn4-0100-cav...

    I can't find performance data for that model in any Copeland info I have...even in my dusty old books from more than 20 years ago. It doesn't show up in anything but an old Copeland electrical handbook.

    There's an RSN4-0075-IAV which is R502 medium temp, but no RSN4-0100-CAV. I believe the RSN4 was available with both a 1 hp and .75 hp motor at one time and the larger one was dropped. The RSN4 designates the pump style and displacement so the capacity curves should be roughly equal for both.

    I have attached the performance tables for the RSN4-0075-IAV which shows at +25F/120F a capacity of 8180 Btu/hr with R502, so with a 35F box and the Keeprite R775 you'd have a TD of about 10.4F.

    Assuming my performance data assumptions are correct, I therefore assume you have a good match.

    (Maybe Powell has an old set of Copelaweld curves listing that 1 horse pump.)

Page 1 of 2 12 LastLast

Posting Permissions

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