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  1. #1
    Join Date
    Nov 2004
    Location
    Hollywood, FL
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    365

    cooling a small server room

    I have a small, rather dense server room that I need to cool. The total watts I have in there now is approx 12,000, plus the need to cool another unit that has a 2800 btu rating.

    I would like to be safe and be able to cool 17,000 watts of computer equipment. My question is, what is the smallest unit I can put in that will hold me over for now, and what is the size unit I should put in to allow for my gowth.

    humidity is not a problem b/c my systems can all operate between 10 and 90%

    I have gotten conflicting quotes anywhere from 3 to 5 ton, two speed and one speed systems. What would you suggest?

    I also have an Inergen fire supression system in there, just so you know

    Thanks for the help

  2. #2
    Join Date
    Oct 2004
    Posts
    43
    You should contact an area HVAC contractor. He will perform a load calculation, (Manual N) which will include heat gains from walls, roofs, windows and doors. That info along with the equipment, lighting, people load, and desired temp they will be able to select the proper system for you. There are way too variables to provide you with the size needed based off of the little information you have provided.

  3. #3
    Join Date
    Nov 2004
    Location
    Hollywood, FL
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    365
    I wish it were that simple....I have had 3 of them come in, never saw any "load test" they all come and gather information and then tell me what I need.

    I feel that 3.5 ton is good for now, but not so good for future growth. 5 Tons I feel will be sufficient for my growth.

    here's how I came up with it

    12,000 btu = 1 ton
    my calculations came out the 3.4 btu is necessary to cool every watt (I have seen calculation on the Internet as high as 3.7)

    my projected equipment will be 15730 watts which would need 53482 btu which is about 4.5 tons, so if my raw calcs are correct a 5 ton unit would be perfect for me

    I heard a little about sensible vs lightened heat....The server room will be locked and we will only enter if necessary, so it should primarily be only sensible heat. Based on that, the one company I personally talk to say that my 3.5 ton unit will be suffice to grow into. My walls are drywall and my ceiling is acoustic tiles that are caulked.

    is a 3.5 ton two-speed system possibly enough for me to grow into? Is it plausible?

    Thanks for the help, I'm just a computer guy trying to make sure I get what I need


  4. #4
    Join Date
    Nov 2001
    Location
    East Texas
    Posts
    897
    This is not something you want to play around with. I take care of a com room. Get an experienced engineering company to size it correctly. Then you will need equipment designed for this application, such as Liebert,etc. In the future if you expand you can add another unit which will also provide you with a secondary unit for when one of the two fails. And trust me they all will have failures. The ambient temp can get over 100 very quickly you have a unit that is down.
    You must pm these units on a weekly basis.

  5. #5
    Join Date
    Oct 2004
    Posts
    43
    It's unfortunate that your area contractors couldn't provide you with better service. How about a mechanical engineer? They may be a little expensive but how important is the equipment you are trying to cool or the data they store and transmit.
    Something to consider if your real comfortable with your own calculations. If 53482 is all sensible than you need to find a system(s) that will provide you with that sensible capacity. A 5-ton will provide you at best 60,000 BTu total, but of that only 38000 to 39000 btu of sensible, the rest is latent capacity.
    You may want to call your area Leibert supplier. They specialize in computer room a/c. As much as we don't like it, alot of them sell direct to owners, and recommend a contractor to do the work.

  6. #6
    Join Date
    Sep 2007
    Location
    Newark, Ohio
    Posts
    112
    Quote Originally Posted by airtoo View Post
    It's unfortunate that your area contractors couldn't provide you with better service. How about a mechanical engineer? They may be a little expensive but how important is the equipment you are trying to cool or the data they store and transmit.
    Something to consider if your real comfortable with your own calculations. If 53482 is all sensible than you need to find a system(s) that will provide you with that sensible capacity. A 5-ton will provide you at best 60,000 BTu total, but of that only 38000 to 39000 btu of sensible, the rest is latent capacity.
    You may want to call your area Leibert supplier. They specialize in computer room a/c. As much as we don't like it, alot of them sell direct to owners, and recommend a contractor to do the work.
    I am having trouble understanding the sensible/latent capacity of the A/C. Can someone explain how this is determined?

  7. #7
    Join Date
    Jan 2007
    Location
    Charm City--the city that bleeds
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    2,790
    If understood correctly, Daikin has a variable refrigerant flow line of product which even can charge itself with refrigerant, as well as can vary the output of cooling to 50% of rated output. (could cool for 2 ton load upon demand while being a "4 ton" system.)

    Bet Mr. Slim is going to put up the "prevent D".
    It's great to be alive and pumping oxygen!

  8. #8
    Join Date
    Apr 2005
    Location
    where the beer flows like wine
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    2,871
    chuck,

    Sensible heat removal refers to the type of heat a regular thermostat measures for example heat gains from sun light, lamps, equipment, people etc, latent loads refers the removal of moisture or the condensation of water vapors on the coils surface.

  9. #9
    Join Date
    Sep 2007
    Location
    Newark, Ohio
    Posts
    112
    I understand the difference between sensible and latent but why is the 60,000 BTH unit only capable of 39000 BTU of sensible and the rest is latent?

  10. #10
    Join Date
    Apr 2005
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    where the beer flows like wine
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    2,871
    Quote Originally Posted by Chuckg222 View Post
    I understand the difference between sensible and latent but why is the 60,000 BTH unit only capable of 39000 BTU of sensible and the rest is latent?
    A unit could be engineered to provide a given sensible to latent heat removal ratios. I dont think a generic DX unit right out of the crate will have a set ratio, it would float all over the place depending on the space conditions.

  11. #11
    Join Date
    Jan 2007
    Location
    Charm City--the city that bleeds
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    Quote Originally Posted by Chuckg222 View Post
    I am having trouble understanding the sensible/latent capacity of the A/C. Can someone explain how this is determined?
    I'm way down the totem pole on the total explanation but let's continue the conversation anyway...

    Latent heat is not as much of a factor in most server rooms, when proper room seals/vapor barriers are applied. The heat load from many if not all of today's servers is more sensible--approximately 90%/10% sensible-latent as opposed to typical cooling ratios which have more latent heat. Latent heat has more to do with moisture content in the air.

    Computer rooms have a "higher density" heat load or concentration than you will typically find in comfort cooling, and so computer rooms need more airflow to change the air while cooling that load. On the other hand, in typical cooling, the number of air changes per hour can be reduced, which will subsequently remove more of the moisture. Hence, we slow the blower speed in dehumidification, even in some server rooms.

    But the lion's share of cooling in server rooms/phone rooms/computer, etc. is removing sensible heat which in these rooms is more dense.

    In certain places, such as switch rooms for cell phone providers, for example, at close of business day, the room will heat up more rapidly than at non-peak times of cell usage, because people get in their cars, shout "yabba dabba doo", and pick up the cell phone. Thus, the heat load in a phone room there will increase in direct relation to the computer processing. But not to get too far off the beaten path....
    yes, but it's a dry heat.
    It's great to be alive and pumping oxygen!

  12. #12
    Join Date
    May 2002
    Posts
    9,564
    Liebert is overkill for this application 10-90% RH.
    How about your temperature restrictions? Can it be 75F in the room?

    What's the size of the room? Ceiling height? Square foot of outside wall? Windows? Size of windows?

    Then go with something smaller and when you add more equipment add another unit and then you have redundancy and neither unit will short cycle.


  13. #13
    Join Date
    Nov 2004
    Location
    Hollywood, FL
    Posts
    365
    let me get that info....I don't have the exact specs....I don't remember off hand

    my head is spinning from all these numbers

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