220.30(c)

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tedge

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Would electric baseboard heat be considered 230.30(c)(3) or (5) + (6)? They are designed to run at full nameplate value so I would think (3) but I'm not sure.

Been invited to bid on a renovation in a house with 18,200w of existing baseboard, as well as two ranges, water heaters, dishwashers, etc. Basically a duplex with no separation between the units. They want to add 7500w more heat plus some sq. footage and a second dryer. This puts the standard load calculation at 253A for a 200A existing service. With the optional method, I might get away with it if the heat is taken at 40% [220.30(c)(5)+(6)]

Anyone have an opinion on whether or not I should use the optional method to force the numbers this way? Money isn't necessarily a problem for these people, so should I go with the standard method and upgrade to 320A meter socket/disconnect to be safe? I have a hard time accepting that the two methods can be so far off from each other. :D

[ February 14, 2005, 01:59 AM: Message edited by: tedge ]
 
Re: 220.30(c)

Okay, here's the reference so you don't have to dig out your books (2002 BTW). Any input would be appreciated.

220.30 Optional Calculation- Dwelling Unit

(C) Heating and Air Conditioning Load The largest of the following 6 selections shall be included:

...(3) 100% of the nameplate ratings of electric thermal storage and other heating systems where the usual load is expected to be continuous at the full nameplate value. Systems qualifying under this selection shall not be calculated under any other selection in 220.30(C)

...(5) 65% of the nameplate rating(s) of electric space heating if less than four separately controlled units.

(6) 40% of the nameplate rating(s) of electric space heating if four or more separately controlled units.


As I read this for the umpteenth time, it makes sense that they would be under (5) and (6). Which brings me back to my second question. How can both the Standard and Optional calculation methods be so far apart, but still perfectly acceptable? Was the optional method developed just for a case like this with lots of electric heat?
 
Re: 220.30(c)

I don't think #3 would apply. I wouldn't expect baseboard heaters to run constantly. They list "storage systems" as a type of system #3 applies to. When they say "storage system", I visualize something like a heat pump running all night to cool a large tank of water. Then the water is circulated around the building all day. So the heat pump runs all night long with no break.

Baseboard heaters have thermostats, so it seems pretty likely that they will cycle on and off. I would use the 40% factor if you have more than 4 units.

If you bid the job with a 320 A service, and someone else bids it at 200A, won't they get the job? (As an engineer, I'm glad I don't have to bid jobs :) )

So I would say if you can legitimately get the numbers under 200, then that's the way to go. After all, the POCO will probably size their transformer for about half of your calculated load. (Unless maybe they expect to add load in the near future - like maybe a pool or spa. Then maybe you can convince them that now is the time to upgrade the service).

Steve
 
Re: 220.30(c)

If you have the handbook see example D2(a). They do an optional calcualtion for a dwelling with "9KW of electric space heat installed in 5 rooms". They apply the 40% factor to the heating load.

Steve
 
Re: 220.30(c)

Steve,

You're right I probably would lose the bid if someone else did it with the existing 200A service. That would be okay with me if I thought I was in the right. I will concede that the heaters should have the 40% demand factor applied (as there are probably ten t-stats). I just have this vision....

The people come in from a long day sailing on their 100' boat. It's October, so the temperature has dropped 20degrees since they left in the morning. They go around and turn on a majority of the heat. They take showers in both ends of the house causing the water heaters to kick on. As it gets darker they turn on the lights, and begin to cook their dinner. Their clothes got wet so they throw them in the dryer and POP! I get a call asking me why this happened, and what I was going to do about it.

Far fetched? Maybe. Out of the realm of possibility? No. Using the standard calculation would leave no question. The optional...well...I don't know.
 
Re: 220.30(c)

Went to the house today and gathered all the info. Calculations came out as follows:

Standard: 277A
Optional: 167A
230.31(B): 163A

That's a pretty big difference, all caused by taking the heat at 40%. Am I the only one who has a hard time with that? :confused:

I guess what I'll do is bid with existing service then try to up-sell the service upgrade for future expansion.
 
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