Demand factor too high !!!

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mdomran

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Im working on a Marina Hotel project in AbuDhabi in the UAE. Our concept design for TCLs and Maximum Demand figures was based on the commonly practiced figure of 0.8 to 0.9.

But the client says that these figures are too high, and that a 0.5 demand factor would suffice!

Now my team's challenge is to somehow JUSTIFY the demand factors of 0.8-0.9 for hotels, and i'm thinking statistics? or is there a procedure somewhere to calculate demand factors to some sort of precision?

P.S. We follow British Standards here, so your references to NEC codes (as is the case most of the time), will make us sadder!

Help!
:-?
 
mdomran said:
Im working on a Marina Hotel project in AbuDhabi in the UAE. Our concept design for TCLs and Maximum Demand figures was based on the commonly practiced figure of 0.8 to 0.9.

But the client says that these figures are too high, and that a 0.5 demand factor would suffice!

Now my team's challenge is to somehow JUSTIFY the demand factors of 0.8-0.9 for hotels, and i'm thinking statistics? or is there a procedure somewhere to calculate demand factors to some sort of precision?
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Get it in writing that you used 0.8 and he wants 0.5. Use the 0.5 and move on!! The client is always right...........
 
LOL!

I thought of doing just that, but then when the feeder melts, he'll just say
"Oh....how did THAT happen?"
and next thing you know, the Utilities have blacklisted me! the Design Engineer!
 
mdomran said:
Im working on a Marina Hotel project. . . . Our concept design for TCLs and Maximum Demand figures was based on the commonly practiced figure of 0.8 to 0.9.
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There is much that I do not understand about this question. For starters, are you talking about a marina (i.e., piers with power to boats) or about a hotel (i.e., plugs, lights, and appliances in rooms? Secondly, what does ?TCL? mean? Third, what do you mean by ?commonly practiced figure of .8 to .9?? Practiced by whom, and in what context?

As it is addressed in the book that you don?t want us to talk about (so as not to make you sad), the concept of ?demand factor? is a permissive thing. There is nothing to calculate; you use the demand factors that the book allows you to use. How the authors of the book came up with those particular numbers is beyond my knowledge or interest. If I come across a situation for which the book allows me to use a demand factor, I will probably take advantage of that opportunity.

Taking it back to the very basics, you can design the service, the feeders, and all branch circuits so as to have capacity for every single load in the entire facility to be energized at full load at all times. But that situation does not often take place. More often, some percentage of the load is turn off, and the loads that are on are not on at their highest setting. So ?our book? lets us design conductors for less than the total connected load. How much less? Less by whatever demand factors the book gives us. Our book gives us demand factors for marinas, and it gives us demand factors for dwelling units (of which a hotel is an example).

Now can I ask for a bit of clarification of your question? What exactly are you looking for?
 
I am also confused by your question. IF you are referring to Marina Wiring as in shore power for boats the demand factors that the NEC allows (sorry if that makes you sad, but it is the reference that must be used for wiring in most jurisdictions in the US, so it is the only standard that with which many of us are familiar) are found in 555.12, and are based on the number of receptacles served. If you refer to the FPN following 555.12 you will find that it says that the use of these demand factors may result in an inadquate installation if the Marina is located "in areas of extreme hot or cold temperatures". In effect this is saying "use these demand factors at your own risk". I assume that "AbuDhabi in the UAE" is an area of extreme heat. With this in mind I would hesitate to use ANY demand factor for this installation. We need much more information about what you are trying to accomplish to help you further.
 
I would imagine the type of Marina Hotel in the UAE that is being designed is quite extravagant, to say the least. I was invovled with some building over there and they are usually multi-use high rises with shopping and entertainment on the ground level; with hotel, apartments, restaurants etc, on the upper levels. Sounds like this one even has a boat (yaugt) pier or wharf attached to it.

NEC is completely irrelevant in the UAE. As stated by the OP, they use British and IEC standards, my recolection is they also use the International Building Code and International Fire Code.

I don't think there are going to be any written factors. Probably have to apply a lot of experience. Maybe look at each type of space individually, add them up, and arrive at some average.
 
Other than using standard demand factors from the appropriate code for your area you can only reference the demand factors for similar structures in your area. You would need peak usage numbers from other similar structures. On particularly complex structures you may need to survey different areas within the structure. Rooms might have a low demand while entertainment areas have a high demand.

Comparisons might be made with smaller dedicated purpose buildings. A similar quality restaurant to that planned for the hotel can give you an estimate for the hotel restaurant.

You may not be able to lower the demand for the entire structure but if rooms are lower in demand the customer might be happy saving money on them. I presume his true beef is the total cost.
 
I'm guessing that TCL is Total COntinuous Load.

If you are following the British ruleset, there are no defined diversity factors any more, there are no tables to consult; they are up to a "competent person" to assess. Such assessment should be documented with the as-built plans.

For a hotel wired the British way (assuming 240V), and if you are providing a ring per room, in my unqualified opinion I'd have thought 0.5 was over the top, let alone 0.9. Even a 20A radial per room would fit within 0.5 I'd have thought. How will you continuously burn 4KW per room on appliances? Obviously the hotel services (kitchens etc) you would rate at near 100% I'd have thought, as in these places all the stuff does get switched on at once.
 
charlie b said:


As it is addressed in the book that you don?t want us to talk about (so as not to make you sad.

Now can I ask for a bit of clarification of your question? What exactly are you looking for?
Click to expand...


Wow, great post. You got a beer coming on me.
 
well, its a mixed use development with a hotel, cabanas, 4 or 5 luxury
villas, and piers with power to boats.
By TCL i meant Total Connected Load.
A Demand factor of 0.8-0.9 is the commonly accepted figure for the
UK, the Commonwealth and most of the Middle East.

I agree with you, charlie, about simply using the figures given in books,
but like i said, my client does not want to use a demand factor that
we suggest to them because he doesnt want to spend money on more
MDBs and assoc. equipment.

The USPs here usually sign off on whatever the consultant( me ) has agreed to.
And if i agree with my client and install undersized feeders, then there
will be problems when the development is running at more than 50%
capacity.

Kingbp rightly implied that the client should simply be given what he wants. But
the consultants reputation is at stake when a design is not correct.

I also agree with dbuckley about 0.5 being OTT,but you never know,right?
As a competent practicing professional(supposedly), need to throw some calculations/statistics at the guy
with the money so he can get equipment that will make this thing work

What im looking for exactly, is how to come up with demand factors! Do we have US statistics by the NEC or the IEEE on it?
 
I know there exists, and have seen a chart, on demand factors for different buidling types. Unfortunately, I cannot remember what publication or if I have a copy where I might of stashed it. (Older age is creeping up, I presume). I will take a look this a.m. and see if I can locate it.

After looking I realized what I have is energy usage in watts/sqft. This would get you energy conservation, but then the demand factor is going to be higher, not lower.
 
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But these Watts/sft.values, are these official statistics / something that can be used as basis for a decision on demand factor?
 
One possible solution, and by "possible" I mean that it may or may not work, is to get a copy of "that book," perform the calculations it describes. If it gives you an effective demand factor that is lower than the 0.8 your client doesn't like, then you can certainly cite that book as the technical justification for using a lower demand factor.
 
In my experience as a utility engineer, we sized transformers at 50% or less of the design engineers calculated loads. Now in private practice, when checking demand loads on existing buildings, I seldom find a demand on a relatively new building to be as much as 50% of the service size.

If there are no rules, 50% might not be bad for service related equipment. Diversity decreases as you go out into the system.

Jim T
 
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