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Heat gain in computer server room

JUGHNE Member Posts: 8,312
Room is 12 x 8 surrounded on all sides by 70-72 degree conditioned space. Ceiling is at least r-30.  The electrical load in this room is less than 26 amps X 250 VAC which equals 6,500 watts X 3.414 = 22,191 BTUH of heat gain from electrical equipment.  Would 30,000 BTUH cooling be adequate?  I'm just the electrician on the job, but this has sparked my interest.  A 42,000 btuh Mr Slim mini-split is to be installed and the results should be interesting.  I know the inverter system will ramp down to low speed, but is there a limit of oversizing that this may not work for.  Meanwhile I keep quiet and again the local yocal knows nothing. Will we have the "cold and clammy" feeling??


  • icesailor
    icesailor Member Posts: 7,265
    Smart Rooms:

    Sounds like you are the smartest guy in the room.

    I had a bank, built in 1970 that had AC for the summer in the main lobby. Heating was the main issue. It worked fine. 20 years later (1990), they were dying in the offices, the air was foul and the main lobby was so hot that they had to open the windows. When I was there on a heating issue because they were blaming something wrong with the heat, I tried to show then that there was nothing wrong that they needed to run the AC in the winter. HORROR'S What a fool. AC in the winter? I told then that in 1970, they had no computer terminals at each teller station. Now, they had 12 VDT and servers at each station. Plus the ones in the offices. That's where the heat was coming from.

    Later, when workers complained of feeling sick and having to go home, they hired a consultant to figure out the problem. The consultants found lethal levels of CO2 in some offices and work rooms. Solution: AC for the entire building and a complete ventilation/heat recovery system.

    All became good. It cost a lot of money for that information.

    That Mini-Split is the nuts but it needs to re-circulate air if people are going to work in there. It can become a dangerous thing.
  • Hot stuffy little room

    Is there any way to exhaust that air in the summer, and reuse the heat in the winter?

    When we had an overheating computer room, we put a kitchen exhaust fan, with a filtered makeup air vent in the wall to equalize the air movement. As long as the temperature does not get over 80 degrees, the equipment is happy. The room must be close to the outside as those Mr Slim line sets are pretty short.--NBC
    JUGHNE Member Posts: 8,312
    edited February 2014
    Server room

    No one works in the server room for any length of time.  Yes the waste heat would be a good idea to capture.  But the equipment is installed there already (waiting for the electrician) and there are mind sets not to be changed.  Does my heat gain formula seem logical concerning the electrical input being the actual heat gain ??  This is a bank I'm around a lot and will be able to observe in the future this, what I believe to be oversizing unit will, operate like.  Thanks!!  PS:  the building has numerous roof-tops that I assume allows fresh air.  Line set is probably about 25-30 foot run.  By the way there are complaints that the server room might reach 80 degrees,  the whole world of work places are overcooled. 
  • SWEI
    SWEI Member Posts: 7,356

    Normally everything in a data center is redundant, either 2N or N+1 depending on budget and size.  What about future growth?  Blade servers can spew phenomenal amounts of heat -- I've worked on data centers designed to 900 BTU/sq ft.  I'd probably recommend three 12k units or perhaps two 20-24k ones.
    EBEBRATT-Ed Member Posts: 8,961

    It will be fine. I think your electrical load is accurate. You have some room for future expansion.
  • Canucker
    Canucker Member Posts: 678

    Could they use the waste heat to help with DHW? Sounds like this would be a good application to use it.
    You can have it good, fast or cheap. Pick two
  • Techman
    Techman Member Posts: 2,144
    Server Room

    Are there humidify/dehumidify concerns?
    JUGHNE Member Posts: 8,312
    Server room waste

    DHW needs are minimal--4 restrooms & 1 break room.  Humidity might not be a factor as the entire building surrounding this room is conditioned year around.  Headed there today so might get more info.  I'm not the hvac guy on the job.  Just the electrician.
  • M Lane
    M Lane Member Posts: 123
    Heat capture

    Most computer rooms I have built had some seriou Liebert CRAC units. They used condenser water to dissipate the heat. I suppose you could use a heat exchanger to transfer heat to cold fill of a domestic water heater to increase recovery efficiency. But the condenser water only runs at about 90* F.
  • Harvey Ramer
    Harvey Ramer Member Posts: 2,217
    It's a wonder

    they don't start building water-cooled PC's and servers.

    Or maybe they already do?

    It would be a lot easier and more effective. Plus the opportunities to reuse waste heat.


  • Techman
    Techman Member Posts: 2,144
    edited February 2014

    in a computer/server room helps prevent gold scavaging and silver migration of the circuit boards, or it used to anyway. Liebert taught us that in class,but that was back in 76'.
  • Techman
    Techman Member Posts: 2,144
    edited February 2014
    double print

  • meplumber
    meplumber Member Posts: 678
    Server room.

    We recently installed and started up the equipment in the largest data room in the state of Maine.  This system holds 1,100 lbs of refrigerant.  That doesn't count the chiller or the redundant CRACs.  That is only for the rack coolers. 

    The list of questions regarding this room are endless.

    Techman is correct.  You need to control humidity.  Outside air is a huge no-no in data rooms as moisture of OSA cannot be controlled.  If budget is an issue, I concur with SWEI to install (3) 12K units and put the setpoint one degree higher on each consecutive one.

    Good Luck.
    EBEBRATT-Ed Member Posts: 8,961
    server room

    Typical comfort cooling load is approx. 80% sensible and 20% latent heat. Not so In a server room the biggest load is the equipment which is entirely sensible load. As a result the equipment has no problem running enough to remove the humidity. If anything the room may be to dry and humidity will need to be added.

    We have a ton of small server rooms in our area and the small ones are typically done with ductless splits.
  • Very Low Sensible Heat Ratios


    Computer rooms and data centers are deigned for very high sensible heat ratios (SHR). The loads are typically 95% sensible, so the SHR = 0.95.
  • What to do with waste heat

    What a pity it is that Jugne cannot use this unwanted heat in his remote church project!

    We need to concentrate on the reuse of unneeded heat in one area, so as to make another area warmer, or with more hot water

    Easier said than done, but can we at least aim that way?.--NBC
    JUGHNE Member Posts: 8,312
    Heat gain revisited-corrected

    My first posting of energy use was based on the amp draw to that area panel and I assumed most of the load was in the server room.  (Again I'm not the HVAC contractor, only the electrician connecting equipment chosen by others so my assumptions don't matter in this situation.)   Now checking closer at the actual server load there are only 1570 watts flowing into this room.  1570 x 3.414 = 5360 BTUH.  This included the 240 VAC power supply conditioner/UPS for the single main rack plus a small 120 VAC UPS for the phone system and the single ceiling light fixture.   I'm impressed and educated by the number of responses to this posting.  By the way the AC tonnage was selected by the in house IT guru who said the equipment needed 30,000 BTUH to keep it cool and then thought it would be good to bump this up to be sure!  HVAC contractor went by this expert recommendation of 42,000 BTUH.  I'll keep you posted and thanks again for the info for future use.
  • Mark Eatherton
    Mark Eatherton Member Posts: 5,837
    Short life expectancy...

    Why is the IT guy considered the "expert"?

    Over sizing this equipment they he has will lead to excessive short cycling and a VERY short life expectancy.

    I think professor Silberstein would agree that the hardest thing a person can do to a compressor is to start it up. Once running, it will run forever, but that continuous starting is hard on windings, contractors, capacitors and everything required to get the train moving...

    The best you can hope for is that the cooling equipment is designed for soft start, and is variable speed compressor with VRF. Otherwise, expect premature compressor failures.

    Obviously, the IT dude doesn't know what he's talking about, so he's covering his butt through gross over sizing. Typical overkill that causes issues in the field that are then blamed on the manufacturer.

    It's not so much a case of "You got what you paid for", as it is a matter of "You DIDN'T get what you DIDN'T pay for, and you're NOT going to get what you thought you were in the way of comfort". Borrowed from Heatboy.
    JUGHNE Member Posts: 8,312

    it is the IT server room.  The actual reason I started this thread was to confirm my thoughts of heat gain from equipment (watts going into the room X 3.414) and adding building gain if any.  Again I'm just the electrician.  The Mr. Slim is a inverter/variable speed design.  This has been a very learning experience on the wall.  If I give myself the "dope slap" to the head because I'm not seeing something I will come back here and fess up.  Thanks again!
  • Jack
    Jack Member Posts: 1,045
    For Server Rooms

    the mini-split heat pump MAY be fine. Many of them are doing an excellent job in this application. If it is a really serious server room without a lot of back-up off site, redundancy is key. I don't think the mshp manufs actually support or recommend this type of application, but again a lot of them go in.

    As previously noted the Leibert system is the correct way to do this, but you can buy a lot of mini-splits for what you pay for the Leibert.
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