Calculate demand load for dryers in apt building

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resistance

Senior Member
Location
WA
Why are you calculating your demand factor on 12 dryers when there are 14 total?

also there are 12@5kw and 2@2kw
You can only take a demand for the 12. The other two are considered commercial, and no demand allowed for the two dryers located in the shared laundromat. Note: I thought I seen the two at 5Kw ea.. Sorry. So to refine: 31.6va :happyyes: This will be your answer.
 

97catintenn

Senior Member
Location
Columbia, TN
You can only take a demand for the 12. The other two are considered commercial, and no demand allowed for the two dryers located in the shared laundromat...
Interesting twist. I tried finding the code reference that says the commercial units will be at 100% but cant find anything. Where is it? and thanks for commenting
 

david luchini

Moderator
Staff member
Location
Connecticut
Occupation
Engineer
Interesting twist. I tried finding the code reference that says the commercial units will be at 100% but cant find anything. Where is it? and thanks for commenting
220.14(A) says that the load for an appliance shall be calculated based on the ampere rating of the appliance served.

220.54 applies to dryers "in dwelling units. The two dryers in the common area are not "in dwelling units" so the demand factor would not apply to them.
 

97catintenn

Senior Member
Location
Columbia, TN
David (and others), what if it is a three phase system? Do you still calculate it based on 12 dryers at 5kw? Which would be 4,4,4 and the two commercial units? as per 220.54

So then I would have 16 dryers at 5kw calculated at 42% = 33.6kw

33.6kw plus the common area which is 4kw = 37.6kw
 

david luchini

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Location
Connecticut
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Engineer
David (and others), what if it is a three phase system? Do you still calculate it based on 12 dryers at 5kw? Which would be 4,4,4 and the two commercial units? as per 220.54

So then I would have 16 dryers at 5kw calculated at 42% = 33.6kw

33.6kw plus the common area which is 4kw = 37.6kw
For three phase, you would still use the "twice the maximum connected between any two phases" method described in 220.54. See Example D5(A) in the annex for an example of how to apply that method.

I think you would take 8 dryers (not 16) at 5kW each and apply the demand factor in T220.54. 8*5kW=40kW @ 60% = 24kW. You would then multiply that by 1.5 (or divide the 24kW by 2 phases and multiply be 3 phases - see the example D5(A)) to get 36kW.

36kW plus the common area (4kW) = 40kW demand.
 

jumper

Senior Member
For three phase, you would still use the "twice the maximum connected between any two phases" method described in 220.54. See Example D5(A) in the annex for an example of how to apply that method.

I think you would take 8 dryers (not 16) at 5kW each and apply the demand factor in T220.54. 8*5kW=40kW @ 60% = 24kW. You would then multiply that by 1.5 (or divide the 24kW by 2 phases and multiply be 3 phases - see the example D5(A)) to get 36kW.

36kW plus the common area (4kW) = 40kW demand.
that is where i always screw up this calc.:dunce:
 

97catintenn

Senior Member
Location
Columbia, TN
For three phase, you would still use the "twice the maximum connected between any two phases" method described in 220.54. See Example D5(A) in the annex for an example of how to apply that method.

I think you would take 8 dryers (not 16) at 5kW each and apply the demand factor in T220.54. 8*5kW=40kW @ 60% = 24kW...
If it's not sixteen, then in a case with 13 dryers, it would be arranged on phases as 4 4 5, so the max between two phases would be 9. Is that right? So, you don't take twice the max?
 

david luchini

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Staff member
Location
Connecticut
Occupation
Engineer
If it's not sixteen, then in a case with 13 dryers, it would be arranged on phases as 4 4 5, so the max between two phases would be 9. Is that right? So, you don't take twice the max?
Huh, :?

You have twelve dryers in the dwelling units. 4 will be connected between A&B, 4 will be connected between A&C and 4 will be connected between B&C. So the max between any two phases is 4. Twice that is 8.

If you had 13 dryers, then the max between any two phases would be 5. The demand would be based on 10 dryers.
 
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