Can Table 220.84 apply to multiple HVAC units in a hotel?

[HelioElectric]

Greetings,

I am at a loss (and my local building department is no better off) to find information related to derating multiple HVAC (typical hotel window/wall units rated 9,000 BTU [2.64 kilowatts] each). There are 72 rooms with two rooms per 30 amp, 208 VAC breaker and each breaker carrying a maximum of 25.4 amps on #10 THWN-2 wire derated to 70%, or 28 amps. As I have 36 breakers at 25.4 amps maximum each, there is a potential draw of 914 amps of power at 208 VAC if every unit was turned to the maximum rating. As this is never likely to be the case, I am certain there must be a table that tells me how much I can derate. Table 220.84 almost makes sense, as it would derate 62 or more units to a 23% demand factor, which is 210 amps, a much more workable number from distribution and load center standards.

Would anyone who has experience loading hotel HVAC units onto panels please send me in the proper direction? My building department thinks I should be using Table 220.44, but I feel as though that formula is way too liberal, requiring 481 amps of power for these units.

Regards - Baran

 

[Smart $]

Similar questions have been asked here before. The general consensus is that no demand can be applied directly per NEC. You cannot look to 220.84 as Part IV. Optional Feeder and Service Load Calculations cannot be applied to commercial units. Additionally, 220.44 does not apply either as that is for receptacles covered under 220.14(H) and (I)... 220.14(A) supercedes (H) and (I):

(A) Specific Appliances or Loads. An outlet for a specific appliance or other load not covered in 220.14(B) through (L) shall be calculated based on the ampere rating of the appliance or load served.

That said, the AHJ is permitted to allow you to apply a demand factor for such (I don't recall the section offhand), but you have to prove, "As this is never likely to be the case, ...".

I will offer this as justification: the NEC has no way of determining whether your units are properly sized, oversized, or undersized in their performance, nor that efficiency will not diminish over time. Just looking at initial performance, if undersized, all units operating at their maximum IS LIKELY to occur. If properly sized, that one-in-a-million chance of all units max'd is a possibility that must be considered. If oversized, prove it... that the units will NEVER operate max'd simultaneously... and even if you do, how many will operate max'd simultaneously???

 

[iwire]

I agree with smart, and will add that in a hotel people tend to do wasteful things like crank the heat but leave the window open, instead of being happy at 68 like they are at home were they pay the bill they crank it up etc.

We have done hotels and while I did not see the calculations the services where very large, 2000-4000 amps at 208Y/120.

 

[jumper]

Smart, are you thinking of 220.60 Noncoincidental loads?

I gotta go with Iwire and Bob, I see no allowable demand factor for the units.

I do not know hotels, but I do know dorms-which are similar-and the HVAC loads were always very large.

 

[Smart $]

Smart, are you thinking of 220.60 Noncoincidental loads?

Perhaps. May also have been an unfounded impression... :huh:

 

[jumper]

Perhaps. May also have been an unfounded impression... :huh:

Okay, I am dense as usual-What does "an unfounded impression" mean?

 

[Smart $]

Okay, I am dense as usual-What does "an unfounded impression" mean?

In this case, it means I thought it was in the NEC, but it is not.

 

[Fulthrotl]

Greetings,

I am at a loss (and my local building department is no better off) to find information related to derating multiple HVAC (typical hotel window/wall units rated 9,000 BTU [2.64 kilowatts] each). There are 72 rooms with two rooms per 30 amp, 208 VAC breaker and each breaker carrying a maximum of 25.4 amps on #10 THWN-2 wire derated to 70%, or 28 amps. As I have 36 breakers at 25.4 amps maximum each, there is a potential draw of 914 amps of power at 208 VAC if every unit was turned to the maximum rating. As this is never likely to be the case, I am certain there must be a table that tells me how much I can derate. Table 220.84 almost makes sense, as it would derate 62 or more units to a 23% demand factor, which is 210 amps, a much more workable number from distribution and load center standards.

Would anyone who has experience loading hotel HVAC units onto panels please send me in the proper direction? My building department thinks I should be using Table 220.44, but I feel as though that formula is way too liberal, requiring 481 amps of power for these units.

Regards - Baran

well, you can't control what people do, and get a derating as a result of that bound up in the code....

now.... there is a new little widgit, just coming on the market. i saw it demonstrated two weeks ago,
it's an insane money saver for the hotel industry.

i'd upsell your customer. it's been shown to drop the hvac power consumed by 60%, and AC is the
biggest expense in a lot of hotels

it consists of a smart plug that goes into the outlet for the AC
and a dual mode occupancy sensor/thermometer that looks like a smoke detector, ceiling mounted, wireless
and a door limit switch, wireless.

the AC tstat can be set at 68, and not have to be turned off by housekeeping when the room is vacant,
or turned down to cool the room before check in.

when nobody is in the room, the AC is turned off.. the t stat / motion sensor is preset at 78 to keep the room
from going to 90.

when the door is opened, the door switch closes the smart plug, so the AC is running when you walk in the room.
whatever you set the T stat for is where the temp goes.

while you are in the room, the motion sensor keeps the ac running.

15 minutes after you leave, the AC is turned off, till someone re enters the room.

all wireless, peel and stick components.

 

[iwire]

If you walk into a newer hotel room and the T-stat is modern looking there is a very good chance it has an occupancy sensor built in and is networked to all the t-stats in the building and a PC at the front desk. So the front desk can get a signal when someone is in the room when it should be empty along with temp control.

I priced putting in a system like that, it was made by Mitsubishi to work with their split systems.

 

[kwired]

What happens if you do not allow for enough load and on the hottest day when nearly all the units are in demand the load goes over the demand factor you used? A/C units are not like ranges. They don't cycle as frequently, and when cooling demand is high they often don't cycle at all.