Power, Lighting, and HVAC allowed watts/sqft

[CurrentCrusher]

Hi All,

Can anyone help with a good reference either in NEC or Energy code, what is the allowed watts/sqft for power, lighting, and HVAC, also does HVAC require Watt/sqft for both heating and cooling or it doesn't matter? this is for a commercial building, I'm not sure if it matters if the building is commercial or residential. Industry newbie here ..any input is appreciated. Thanks!

 

[tom baker]

Lighting loads are in Art 220, some areas have lesser loads per state nec changes
Not sure you you are asking about power.
HVAC is the connected load of what the mechnical designers specify , typically the larger of hearing or cooling
And yes it matters if resi or non tesi
Receptacles are 180 VA per strap, check Art 220 for demand allowances

 

[brantmacga]

Lighting loads will be calculated based on occupancy type listed in Art 220. Receptacle loads are 180va per strap and for non-dwellings it’s the first 10kva at 100%, and the remainder at 50%.

See tables 220.3, 220.12, 220.42, 220.44. I’d recommend you just read all of 220.


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[suemarkp]

There may be rules of thumb in your area for sizing HVAC by square footage, but it is difficult. Much depends on how well it is insulated, how much sun the area gets and whether there is large glass or not, and the design temperature. Energy codes add a further wrench into the design. Even if you know the HVAC size, the nameplate can vary, especially in commercial sized units.

 

[tom baker]

Energy code is per state. you’ll need to look into that

 

[mtnelect]

California has the strictest energy code it is called Title 24. No more "Rule of Thumb" like 400 square feet equals a ton. As an example, you have 2,000 square foot house, so you divide 400 into 2,000 and wa-lah you have a 5-ton unit. Not anymore, you must do a "Heat Load" engineering study to prove your size of unit. Then you must conduct a "HERS" independent 3rd party inspection of your installation.

See attached letter from a HERS provider explaining the problem California is having on HVAC contractors not filing permits.

 

[topgone]

There may be rules of thumb in your area for sizing HVAC by square footage, but it is difficult. Much depends on how well it is insulated, how much sun the area gets and whether there is large glass or not, and the design temperature. Energy codes add a further wrench into the design. Even if you know the HVAC size, the nameplate can vary, especially in commercial sized units.

Sizing HVAC is quite a steep curve for others. Using rules of thumb does not apply especially if the locations are totally different from the scenario where the ROT is based upon.
Best to do it the way the mechanical guys do it, where they calculate the cooling and heating loads of the space to be conditioned.

 

[JoeStillman]

Watts-per-square-foot calculations should only be used in the early stages of a project, when you are filing the paperwork to get the attention of the POCO. Eventually, you need to do an NEC load calc based on real connected loads. The energy code does not apply to your service-sizing calculations. If you are calculating energy usage, that's different. Department of energy and ASHRAE have some helpful resources for that. There are lots of solar vendors that offer an energy use calculator for estimating the payback on you alternative energy design.

For load calcs here in my region (mid-Atlantic), we use 20W/ft² for commercial/retail, 30W/ft² for restaurants and 15 kW per apartment (which includes the house loads like elevators, corridor lights, &c.) YMMV, for example, we try hard not to use electric heating, and somebody needs to make a decision about gas or electric cooking.

 

[Knightryder12]

You have to check what energy code your state has adopted and go by that. You can look it up through the states/county/cities building department and you can also try muni-code as well. This is for commercial projects. Residential has some energy code restrictions, but not many.

 

[mtnelect]

Additional information.

 

[CurrentCrusher]

Watts-per-square-foot calculations should only be used in the early stages of a project, when you are filing the paperwork to get the attention of the POCO. Eventually, you need to do an NEC load calc based on real connected loads. The energy code does not apply to your service-sizing calculations. If you are calculating energy usage, that's different. Department of energy and ASHRAE have some helpful resources for that. There are lots of solar vendors that offer an energy use calculator for estimating the payback on you alternative energy design.

For load calcs here in my region (mid-Atlantic), we use 20W/ft² for commercial/retail, 30W/ft² for restaurants and 15 kW per apartment (which includes the house loads like elevators, corridor lights, &c.) YMMV, for example, we try hard not to use electric heating, and somebody needs to make a decision about gas or electric cooking.

This is really useful information thanks for your input

 

[mtnelect]

One example of a Heat Load Engineering Study