residential demand calculation

[drwill]

im helping a buddy whos building a duplex. Im doing a service calculation, to confirm both sides can be run off of 1 200 amp service.Both combined are 1100 sq ft, 2 4Kw water heaters, 2 10Kw heater, no laundry facilities to be installed. (1) lighting load = 3300 (2) small appliance circuits = 6000 (3) demand on above =(ist 3000 at 100% = 3000)+ (3001- 120000 at 35%= 2205)= 5205 (4) larger of a/c or heat 10kwX2 =20Kw. (5) clothes dryer at 5Kw. this is where my question lies, on part 2 above you can omit the laundry circuit if not installed, however i see no such exception to dryer circuit .(6) 2 ranges at demand factor of 11Kw.(7) total =44205 w/o dryer, =184 amps or 54205 = 226 w dryer. we want to save money and not go up to the next size service but we don't want ot burn up the 200 amp panel. this calculation doesnot include the refrigerators or vent hood or vent in the bathrooms. should these be included in the calculation or not.

thanks for any help will Dalrymple

 

[gndrod]

Re: residential demand calculation

Will, there is additional info needed to give you better numbers. First, a standard calc applies because of under 4 units for multi-family. Each unit is calculated separately as one family optional method. In answer to
Launtry...not required
Cl Dryer...can still install in each unit but calculations must be 5kva or NPR.
Hot water heater is 4.5kw standard each unit with small 40 gal
Good news is your 11 kva range is calculated at 8kva derate unless over 12 kva.(each apt.)
Refrig, vent hood, and bath vents are included under General L + R.
Vent fan is required in bath without open window.

The big question is what Climate Zone requirements exist in your area for energy heating. (in Seattle area it is 5-8 watts/sf.in lower zone 1) A 3 ft. baseboard will heat a 10 x 10 bedroom real easy. That's 750kva.

Cutting down on the heating load may help. Right now the figures for one unit with a dryer is hitting 106.5 amps demand for 125A panel. Without dryer=85.7A per unit for 100A.

These are basic figures knowing what you've mentioned.

rbj, Seattle
Add: Don,t forget Bath GFCI, Bedroom AFCI w/detectors

[ January 22, 2005, 04:47 AM: Message edited by: gndrod ]

 

[gndrod]

Re: residential demand calculation

Will, You can also wire a single bathroom with a 20A Branch Circuit for combined light-vent fan and GFCI receptacle on same circuit per 210.11(C)(3)Exception.
Also note that Smoke detector circuit has an outlet hookup in the bedroom(s) that is required to be on the bedroom AFCI circuit. Check local AHJ on that requirement.

rbj, Seattle

 

[gndrod]

Re: residential demand calculation

Note also using 220.30 (C)(6) allowing 40% of NPR if 4 separately controlled space heaters are used, then for each unit... (using 8 w/sf example) assuming of course:
550sf x 8w= 4400 w heating,
40% 4400= 1760 w heat derating
plus general L+R 4650
plus appl(incl dryer) 9.5 kva
with 10kva 40% reduction
sum is 11,660 + 1760
13,420 over 240V = 55.9A per unit
Check out 220.30 recipe and plug in Climate Zone heating needed for similar result.
Good Luck
rbj, Seattle

 

[1793]

Re: residential demand calculation

Originally posted by gndrod:
[QB]Will, You can also wire a single bathroom with a 20A Branch Circuit for combined light-vent fan and GFCI receptacle on same circuit per 210.11(C)(3)Exception.

How do you interpret 210.23(A) Exception?

This is one of those situations that trip me up if I think to hard about it. Any input would be welcomed.

Norb

 

[gndrod]

Re: residential demand calculation

Good observation Norb, There definitely are limitations to utilization equipment included in the related 210.23(A)(1) and (A)(2) compliances. The 50% max on the BC rating does restrict additional continuous load usages like fixed 1500 kva heater-vent units in conjunction with vanity lighting in this particular instance. (I.e. The fixed light-vent load NPR with remaining bath lighting must fall within the limit of the BC requirement in consideration of other potential cord and plug loads such as a 1250w hairdryer used on the same circuit.)

I can see where an 80% rating allowed for cord and plug can not be controlled regardless of NEC restrictions after a final. The rationale of this exception is not fully clear to me either.

rbj, Seattle