Determining NEC Service Capacity/Size

[RAF7]

Slightly different type question.

Church Service Size Question

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We are doing a church and several of us have a “discussion” going relative to the service size. The loads are as follows:

LOAD KVA Connected "Estimated" KVA Demand


Lights 43 43
Rcpts 61 25
HVAC 320 250
EWH 8 8
Ranges (2) 16 16
RV hookups (3) 18 12
=========================================
466 KVAc 354 KVAd
1305 Ac 991 Ad

Thus provide a 1000A service. (?)

The HVAC's are heat pumps. We used for demans 100% of the heat pumps and 65% for the AHU's (strip heat). Frankly, I think that's on the high size, IMHO.

The code doesn’t specifically help for this type occupancy. We used various pieces of the code to come up with the estimated demands above. Based on experience, they are “reasonable.” Heat pumps are used. The ranges are part of a "warming" kitchen.

It's just under 15,000 ft sq. The sanctuary takes 21 kw of the light load. Plus, I generally round up when sizing lighting circuits.

The sanctuary is on the "bright" side and it does have a dimmer system.

It also has church offices, nursery, class rooms for all ages, a warming kitchen, a kitchenette, etc.


Proposed service would be an I-Line 1200A panel with outside disconnect sized at 1000A. There is additional "discussion" to make the service 1200A. The downside is that two doors would then be required in the room where the 1200A pnlbd is located, but doable, just a PIA.



Anything larger than 1200A bumps cost way up as we need to go to a switchboard. Even splitting things up into two I-Line panels adds to the cost.


As you can imagine, there’s a significant cost difference involved in the two service sizes. We obviously want to provide an adequate service but also don't want to tack on un-necessary costs.


Comments?



What have you used as a guide to determine service size for an occupancy as this?

Thanks in advance.

 

[wareagle]

#4 02-24-2008, 10:47 PM
bob
Senior Member Join Date: Feb 2003
Posts: 1,392



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Your Quote:
Lights 43 43
Rcpts 61 25
HVAC 320 250
EWH 8 8
Ranges (2) 16 16
RV hookups (3) 18 12
=================================
466 KVAc 354 KVAd
1305 Ac 991 Ad
Thus provide 1000 amp service?
end Quote
466kva/(.208 x 1.73) = 1295 amps not 1305 amps.
The NEC does not allow you to size a main panel on Amps Demand. It is calculated per the code requirements.
The AC units should be calculated at 100%. Section 220 will give you factors for the recpts and ranges.
Using your figures
and 100% for the A/C the load is 1295 amps + 25% for the largest A/C. unit. You are estimating 991 amps and you haven't added the 25% for the largest motor. The calculation
may be on the high side but thats not your decision to make.
I assumed 208/120 volts 3 phase. May want to consider 480 volts.

 

[waross]

I would take a close look at the HVAC. This is the major part of the load and the major part of the demand reduction.
The Canadian code does not allow any demand factors to be applied to air conditioning.
For heating, if the heat pumps are arranged to shut off when the strip heaters come on, you need consider only the greatest load. Typically the strip heaters.
In a church, more so than many other types of occupancies, there is a high probability that most of the building will be kept quite cool when unoccupied. When an event is about to start, you can expect all the thermostats to be turned up and the connected heating load to be 100%.
I would consider the possibility of a very cold day when all the heating may be on simultaneously. You could be without heat and light on the coldest day of the year.
Trying to justify a smaller service may end in disaster and much greater future costs.
Possible solutions:
Is there any way you can justify two services? Possibly 480 volts at 400 amps for the HVAC and a 200 single phase panel for the rest of the loads?
Can you run a 600 amp 480 volt service and use a 50 HVA dry type transformer for the non heating loads?
Have you considered a load monitor to cycle the heating so as to limit the maximum current?
If the smaller service is selected, I strongly suggest making provision for the future addition of load control and switching equipment. If a disaster does ensue you will have a fairly easy solution.


Bill
--------------------
"Why not the best?"
Jimmy Carter

 

[RAF7]

wareagle: (Auburn, obviously. My son went there.


The code does allow us to size services, thus main panels on demand. Lots of examples in Appendix D which is where We derived out demand figures.

DId I miss something?

 

[wareagle]

RAF7
You son must be very good looking, intelligent and a
gentleman.
My demand comment referred to your figures
466 KVAc 354 KVAd. I assume you mean 466 kva calculation
and 354 kva demand. You can use all of the adjustment factors given in Article 220. For instance table 220.42.
However, look at 220.18(A) which requires the additional 125% of the largest motor for the load of the service.
220.51 requires electric heat to be calculated at 100%.
220.82 allows for a 65% factor for the electrical heat associated with a heat pump but this is for a dwelling unit.
I think you need to recalculate the load using the factors
listed in Article 220. 1200 amp may be too small. Again I
think you should consider 480 volt service.

 

[BJC]

Whats the square footage of the building? There are various "Sanity checks" you can use.
The local utility may have some as well.
6-8 watts/ Sq-ft is not unreasonable.
Any other simaler size churches about? Get in you car and go on a tour. You can usually get the trasformer size even if you can't get the switchbaord isze.
The local utility may give you the load history of simaler buildings.

 

[DonPhillips]

For lighting, you may want to use the energy code, 2006 IECC Table 505.5.2:

Dining: Family 1.6
Dormitory 1.0
Office 1.0
Religious Building 1.3
School/University 1.2

These are allowable watts per square foot.




Don Phillips

http://worthingtonengineering.com

 

[itsmoked]

Remember last years thread on a church's gymnasium that went all pear shaped..

Keith Cress
Flamin Systems, Inc.-

http://www.flaminsystems.com

 

[wareagle]

BJC
Your suggestion may be used to get an idea of the estimated
load at this new church but it can not be used to size the service main. The NEC does provide a method to use an existing demand from the utility, 220.87, when there is added load to an existing building.

Don,
Table 220.12 lists 1 VA/sqft for churches.

RAF7
Why don't you put up your load and calculations and let look
at what you have. Where is the church located?

 

[EEJaime]

In addition to those items listed by the various posts, keep in mind that you must also include an additional 25% of your LCL, (long continuous loads), which are all loads that may operate continuously for 3 hours or more. Different AHJ's will include lighting, signage, and any non-cyclic mechanical loads, if there is a possibility that the electric heat could be all started simultaneously and operate for this much time before cycling off, your AHJ may include this in his LCL calc.

All in all, I have found that anytime the choice occurs between a minimally sized service and one which will definitely serve the facility for the long run, it is a good investment to provide for the future. Next year you may get a project to add a classroom on site, or a carnival panel or any number of things. I would recommend to the owner that they invest for the long term.