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Electrical Multifamily Dwelling Residential Demand Factors

I am designing the electrical system for a high-rise residential tower.  Per NEC 220.84, I can apply a demand factor to my main switchboard, depending on the number of dwelling units that are being fed by the switchboard.

 

Unfortunately, Revit seems to have no way to calculate demand loads in this manner.  Revit can calculate demand loads by quantity of fixtures, or by load, but not by quantity of dwelling units.  For now, I have to use Excel to create my switchboard panel schedule.

 

It would be useful for Revit to have the ability to assign demand loads to electrical equipment, instead of electrical fixtures (at the user's discretion).  If this were the case, then I could assign my dwelling unit panelboards with a "Dwelling Unit" load classification, and the switchboard would be able to count the number of "Dwelling Unit" panelboards, and apply the right demand factor, rather than incorrectly passing the "receptacle" or "lighting" demand factors down to the main switchboard.

Comentarios
Collaborator
Collaborator

As a workaround, we have an invisible load family where we put all the loads. It does the demand calculations necessary for the unit loadcenter and feeder and we have a tag that displays all that information in a demand load box. The load family passes the undiversifed load on to the meter center (or panel) with a Load Classification of "Residential", then applies the 220.84 factors accordingly. This means that our unit loadcenters are not technically connected to anything - only the load family.

Observer
Observer

I know this is a year old post. I am trying to do this exact thing did  you ever figure something out?  Also the workaround that was posted here , how do you go about doing it this way.

 

Collaborator
Collaborator

If you're doing your dwelling unit calcs per NEC 220.84, you can create an electrical fixture with parameters for all of the inputs (sqft, small appliance circuit qty, heat & air, etc.). Then create a calculated parameter to do the calc as required by 220.84.  If you make them all shared parameters, you can build a fixture tag to create a demand load schedule to put on your sheet. To apply Table 220.84, just give the fixture a load classification of 'Dwelling Unit' and build out the demand factor to match the Table. Make a Type for each dwelling unit type and put one in the project for each dwelling unit and connect them to your meter centers as required. It will calculate correctly.

I've done similar for hotel units.

Observer
Observer
I am trying to follow what you explained. Do you create a panel in each unit and connect all the devices in each unit to its panel and let it do normal calculation of the unit ? And then take the total of the unit panel and create a fixture with that load and connect just that device to the main.

Thanks
Collaborator
Collaborator

No; there is a unit within the panel and each device within the unit is connected to the panel, but this is really for circuit number and panel information only. Don't show load info on the panel - turn it off in the Panel Schedule Template. The panel is unconnected (no load info is transferred from it to the overall building system) because it can't do calcs based on 220.84.

 

Create a separate electrical fixture that does the 220.84 calcs and connect that fixture to your meter center.

 

I don't have a good working example to share with you right now or I would.

 

It's not a quick-and-easy thing to set up but it is possible.