Shell Building Load Calc

[Jey-L]

Hello all,

I'm preparing my first shell building design with 10 office spaces - approximately 9000 SQFT. I've seen numerous threads on here using a watts/square foot method and rules of thumb (say 20 w/sqft for an office, 30 w/sqft for a restaurant). What I haven't seen, though, is how to actually put together a load calculation. I cant imagine multiplying 20 w/sqft by total sqft would fly. Is this right?

I was thinking of using VA/sqft numbers from article 220 for general lighting loads and receptacle outlet loads, and making a guess regarding show window lighting, general appliances, HVAC, water heating. This all goes into my load calc table on the plan. Is this how it's normally done? Looking for a bit of guidance here.

Thanks.

 

[petersonra]

The code has no provisions for you to guess at loads. Put down what the code says in your calcs. Worry about what it ends up being later when it happens.

 

[Jey-L]

The code has no provisions for you to guess at loads. Put down what the code says in your calcs. Worry about what it ends up being later when it happens.

Appreciate the reply. Unfortunately, as a shell building there are no loads inside this building - no ceiling, no lights, not even a slab. Each tenant will build out their space as desired and they will then prepare a load calc. In the meantime, I need to size a service for the entire building, meaning some guesswork. Just wanted some guidance on how this is usually done.

 

[brantmacga]

20va/ft is pretty close. I’m reading is as ten 900 sq/ft spaces, correct?

You should have hvac loads from the mechanical engineer, figure a water heater for each space, general lighting load, show window receps, sign circuit, and I would assume 35-40 receptacles at the most for each space.

A building this size for professional use (based on my experience building these) would typically have an 800/3 208Y/120v service, and each tenant space would have a 225/3 panel, plus a 100/3 house panel for exterior lighting and a recep for irrigation timer. Also assuming electric heat and water heaters on that service size.

For the load calc on your drawings, you show what you know but size the main to what you expect.


Edit to add….. I’m in the south with a mild climate. I priced a couple of shell buildings a few weeks ago further north with a cold winter climate, and they specified a 480Y/277v service and 277v unit heaters in all of the spaces connected to a house panel. I assumed that was to keep the plumbing from freezing until the spaces were built out? They’re still on 2017 NEC there so each space got it’s own meter and disconnect straight from the padmount xfrmr, and an empty conduit for future panel in the tenant spaces. Those buildings were for retail and a space in each was assumed to be a future restaurant. Anyway, just throwing that out there because I don’t know where you are .


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[Jey-L]

Yes, 10 spaces approximately 900 sqft floor area.

This is great information, and thanks much. I'm just dipping the toe into the commercial side of things - bulk of my experience is on the industrial side. Would never imagine theoretical loads would fly.

 

[hillbilly1]

20va/ft is pretty close. I’m reading is as ten 900 sq/ft spaces, correct?

You should have hvac loads from the mechanical engineer, figure a water heater for each space, general lighting load, show window receps, sign circuit, and I would assume 35-40 receptacles at the most for each space.

A building this size for professional use (based on my experience building these) would typically have an 800/3 208Y/120v service, and each tenant space would have a 225/3 panel, plus a 100/3 house panel for exterior lighting and a recep for irrigation timer. Also assuming electric heat and water heaters on that service size.

For the load calc on your drawings, you show what you know but size the main to what you expect.


Edit to add….. I’m in the south with a mild climate. I priced a couple of shell buildings a few weeks ago further north with a cold winter climate, and they specified a 480Y/277v service and 277v unit heaters in all of the spaces connected to a house panel. I assumed that was to keep the plumbing from freezing until the spaces were built out? They’re still on 2017 NEC there so each space got it’s own meter and disconnect straight from the padmount xfrmr, and an empty conduit for future panel in the tenant spaces. Those buildings were for retail and a space in each was assumed to be a future restaurant. Anyway, just throwing that out there because I don’t know where you are .


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Probably to keep the fire suppression from freezing in the space’s that are unoccupied.