# watts per foot rule of thumb for Lab Generator load



## mshields (Jul 12, 2013)

If you were doing a core and shell for a building that would be filled with labs but for whom the tenants had not yet been established, what watts per square foot of lab space would you use as a safe number sizing your Optional Standby Generator or generator(s) which are to be provided under the base building?


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## north star (Jul 12, 2013)

*=** = **=*

Mike,

Some additional basic information would be needed for a proposed calculation.

How many "gennies" & the amperage of each to start with.

*= **=** =*


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## ICE (Jul 12, 2013)

That's a big horse their putting before the cart.


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## chris kennedy (Jul 12, 2013)

36Wft²

Based on 2000A 208y/120V for 20,000ft² building. Safe bet, maybe for optical lab, State Health Dept lab, ect. Landlord leases to printing operation instead you may want to use the same watt per ft² at 480y/277.


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## north star (Jul 12, 2013)

*= = =*





> "That's a big horse their putting before the cart."


I agree, but with some more information, we might givesome direction for him to go in, ...albeit "an inaccurate

load calc." based on the tenant space square footage

only [ i.e. - lighting loads, ...general use receptacles,

...motor loads, etc.......*RE:* Article 220, ...430, & 700,

in the NEC ].

*= = =*


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## north star (Jul 12, 2013)

*= = =*

Chris,

Thanks for the input !.......On behalf of the forum viewers and others,

may I please ask you to provide the pathways to which you arrived

at the " 36W per sq. ft. " amount ?.....Thanks !

The various Articles and calculations help me greatly !   :agree

*= = =*


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## chris kennedy (Jul 12, 2013)

NS, no arts to quote but based on experience a 20,000ft² lab for uses as I described above we usually will see a 2000A 208y/120. Soooo...

2000A×360=720,000va or loosely translated for this exercise watts (360 based on 208V×1.73 for 3Ø)

720,000w÷20,000ft²=36watts per ft²


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## north star (Jul 13, 2013)

*& - - - - &*



Thank You Chris for your input !   



Can we approach the topic with actual Articles from the NEC to

apply some sort of a calculated "guess-timate" ?.......Granted,

Mike will need to supply some more basic info.

No disrespect intended Chris, but rather than your experience,

...can the question be addressed by using the NEC and its various

Articles ?......*REASON:*  We code officials get asked some pretty

outlandish questions from developers,  ...contractors, ...home-

owners, ...colleagues  & everyone else in-between.......By having

at least some ideas of how to address the problem; from a

printed Standard, and in which direction to assist the customer,

...we haven't *(1)* left them with negative impression of our AHJ,

...*(2)* we have demonstrated a sincere effort to assist in their

problem, ...*(3)* we have promoted a desire to have a relationship

with that customer, however small or insignificant it may seem

at the moment, which "MAY" result in them having a business

located in our / your AHJ,  ...*(4)* we may actually learn something

from the exercise,  ...*(5)*  the customer may leave with a little

clearer understanding of the problem, ...what other questions

to ask, and who to go to find their answers, and *(6)* others who

visit this Forum and view this topic may also learn something,

...and maybe, just maybe, ...they too will want to join and

become a Sawhorse.

FWIW, ...I regularly get asked to "show me that requirement

or section in the codes !".........I already have an uphill battle in

interpreting & administering the various codes, so the more

[ accurate ] information I can provide, ...the easier it is for

me to have a legitimate position on the matter, and over time,

...to [ hopefully ] build a positive image for myself and my

AHJ !



*& - - - - &*


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## chris kennedy (Jul 13, 2013)

No way to even venture a guess at a 220 calc with the info Mike has given. Sorry NS, I understand where you coming from.


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## north star (Jul 14, 2013)

*& * * * * &*

Thank you Chris for your regular contributions !  

*& * * * * &*


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## mark handler (Jul 14, 2013)

What is the generator for? exiting? lighting? continuing lab operations? refrigeration? Hoods? filtering ventilation?


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## peach (Jul 14, 2013)

That was going to be my question too, Mark.. I just didn't scroll all the way down.  The emergency lighting should be picked up by the main generator.


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