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Thread: Watts per square feet in buildings

  1. #1
    Join Date
    Nov 2004
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    Post Watts per square feet in buildings

    Does anybody know where to find tables with total electrical watts per square feet for different kind of buildings? I am using 15 W/sq.ft for office buildings and 30 W/sq.ft. for restaurants. But what should I use for new hospital building or some other buildings??
    Thanks,
    Mike

  2. #2
    Join Date
    Dec 2004
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    Fort Collins, CO NEC: 2014
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    See 220.12.

  3. #3
    Join Date
    Nov 2004
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    Question Watts

    NEC 220.12 addresses how to account for loads when planning show windows and/or track lighting....

    I am talking about "rule of thumb" for basic sizing.. I know for table 220.3(a) but it calls for basic lighting load and 1W/sq.ft for general receptacles... I am asking for complete load (HVAC, equipment, lighting etc..) for different building types when you do not work on detail design. Sometimes we are working just on shell building and future tenants will do detail design. But still you have to provide correct amount of power to that space and whole building..
    Thanks,
    Mike

  4. #4
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    Jun 2004
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    Tenents can vary quite a bit, and so could the bid if you go by who is using it.... A "medical building" can be pretty vague. Who knows what type of equipment they will use once they sign a lease. An MRI machine could be huge electricaly. In most base builds we ask what type of market the owner is looking to lease to, and advise the largest service possible for it reguardless. Tell 'em it is a selling point for most buisinesses, and it is... The more that is available per unit the better time they will have leasing it without immediately up-grading it for a TI build-out. Most will opt for this... The largest service available with-out recalc'ing POCO, common lighting, F/A, HVAC, and over-sized conduit only for feeders to each area. When the tenent signs the lease, they hire out a contractor for the TI build-out who pulls the conductors for the unit at what they need. (The first one in will usually rob all the power. :rolleyes: ) Or, split it out for 200, or 200x2 for each. If you go by sq', the service will often be too small for end-use. (plus all of thier equipment) The code is the minimum.

  5. #5
    Join Date
    Jul 2004
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    Ca and Wa
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    Hi miodrag,
    Welcome to MH's forum and a bunch of good people who know a lot more than I do. I have specialized in residential and have worked in energy management to know that keyiing in to local and state energy codes are a major prerequisite to setting up load minimums for taking both lighting and HVAC into consideration. Even with a shell design, principle enforcement of both spec and prescriptive energy minimums come from the driving Code enforcement requirements at the building department. If the structure is made of heavilly glazed wall fenistrations, you must include the conditioning that requires either passive or active environment compensation. So starting at the permit specification stage and the building department will be a great source of expertise in electrical loading design. (i.e. Regional zone minimums such as type of structure, watts per sf lighting, btu's per sf heating, etc. vary determinatly by climate.) I have not found any tried and true rule of thumb without starting at the planning department.
    rbj, Seattle...Safety is a Professional Courtesy.

  6. #6
    Join Date
    Feb 2003
    Location
    Missouri
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    Below is what I normally figure for a service size on commercial buildings when square footage is the only thing given to me.

    Basic Electrical Mechanical (1,500 to 2,000 Watts/Ton)
    BldgType Watts/SF SF/Ton
    Data Center 50, As Needed
    Detention Facility 6, 300
    Educational 6, 350
    Hospital 20, 200
    Hotel 6, 350
    Medical Building 7, 300
    Office Building 7, 300
    Public Building 6, 300
    High Rise Residential 4, 400
    Retail 4, 300
    Warehouse 2, 500


    Note: No Electric heat. If electric heat then add approximately 30btu/sf.

    I hope you can read this it looks good and in columns when I type it on the previous page but when I post the reponse it removes all of the spaces between the columns.


    Hope this helps.
    -Ed
    Last edited by ed downey; 08-14-06 at 02:48 PM.

  7. #7
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    Feb 2003
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    Florida
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    it has been a standard on office space for the owner to fugure 6.5 watts per square foot in tenant usage and this is a figure used in most lease agreements. anything in excess of this can be charged back to the tenant including the necessary metering equipment. however this figure is probibly twenty years old, and most tenants don't use half of this estimated wattage due to the higher efficency office equipment. one particular tenant (motorola) went to a three shift schedual when developing the nextel telephone and the building owner made them purchase and install a certified metering system and pay all electrical costs in excess of 6.5 watts per square foot. the metering system cost $66k and the extra electrical costs were very high.

  8. #8
    Join Date
    May 2003
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    Maryland
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    There is no "rule of thumb" as electrical useage can vary greatly. It would be nice to replace all of article 220 with a "rule of thumb" but it ain't going to happen.
    There are no shortcuts. Any shortcut that is attempted will turn around an bite you. Do the article 220 calculation. Make the owner or general contractor provide the informatiuon needed to do a proper calculation or let someone else make a fool of themselves.

  9. #9
    Join Date
    Feb 2003
    Location
    Missouri
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    You would be surprised how close the actual service size comes in most buildings while doing preliminary budgets with the information I listed above. We do not build from these calculations but we do budget the electrical based upon these rules of thumb when we have nothing to go off of except for building type and square footage.
    We negotiate about 85% of the work that we do as a general contractor and the clients rely on a good budget for financing purposes early on in the process which means using many rules of thumb that I have developed over the years.
    -Ed

  10. #10
    Join Date
    Aug 2006
    Posts
    13
    For lighting, you may also want to look into International Energy Conservation Code (IECC) and find out what energy code your state follows.
    They have free programs on their website called COMMcheck (commerical applications) and REScheck (residential appilcations) to help with calculations.

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