HVAC demand factors

[jimport]

I was asked a question about demand calculations for multiple PTAC units like in a hotel. I know there are demand load adjustments for dryers and ranges , but do not remember the same for HVAC units. Can someone please enlighten me. Small commercial is not my area.

 

[ActionDave]

The last time I worked on a similar project it was adding PTACs to an apartment building and the design work was done on the back of an envelope. We came up with 125% for the largest unit and 100% of the rest. I can't remember it my boss found a code reference or we just went with it because it made sense. Inspector signed off on it and the building is still occupied.

 

[drcampbell]

HVAC is different than laundry & cooking. It needs to be designed for the hottest day/coldest night of the year. If it's sized correctly for the thermal load, it will run continuously.

In a hotel, you might be able to get away with a diversity factor for less than 100% occupancy, unless peak tourist season coincides with the hottest/coldest week of the year. But not an apartment building.

 

[electrofelon]

The last time I worked on a similar project it was adding PTACs to an apartment building and the design work was done on the back of an envelope. We came up with 125% for the largest unit and 100% of the rest. I can't remember it my boss found a code reference or we just went with it because it made sense. Inspector signed off on it and the building is still occupied.

Yeah this gets to the issue of adding up all the MCA's and over-counting because you are counting every unit at 125%. For feeder and branch, You only need to count the largest. I think 430.24 is the reference.

As far as diversity factors, I dont believe there are any allowances for this. The NEC really doesnt have that many diversity factors, just for a few specific things.