condo design

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bwyllie

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Any opinions on the following: when designing a multi-story condo/apt building is it better to have a 480V bus duct thru the building and feed off the bus duct to a step down transformer and then feed meter modules for the unit metering or install one large transformer in the basement level and install a 208Y/120V bus duct thru the building to feed the meter modules. I know there are alot of variables in this questions, such as transformer sizes, bus duct sizes, etc, by I am just curious for general opinion & ideas on design.

Thanks
 
Re: condo design

I seem to remember that 500kva is the break even point. If your load is <500kva than go with the lower voltage without transformers. If it's >500kva than use the 480 volt riser(s) with transformers for 120/208.
 
Re: condo design

Suggest you check with the utitlty regarding the metering. I see nothing wrong with 208 volts so long as the designer specs 208 volt A/C, WH
Dryer, Range and other similar equipment.
 
Re: condo design

TO my memory all of the condos that I have worked on had the step down transformer in the basement then feed the busduct. These were at least 6 story condos with 8 units per floor.
 
Re: condo design

There are a lot of ways to do it and in Indiana, the law requires each power user to have their own meter. </font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">We have used 120/240 1? for most condos.</font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">120/208 1? is also used for larger buildings.</font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">There is a new building downtown that is served with 480Y/277 and we are going to give up to 125 ampere services @ 480 1? to each apartment and the customer will have a transformer to get 120/240 1? @ 200 amperes each.</font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">We have some where feeders are run to the floors and meter centers are installed in the electrical closets.</font>
  • <font size="2" face="Verdana, Helvetica, sans-serif">If the building is large enough, primary conductors are taken into the building and large transformers are installed every 15 floors or so (we don't have any installations like that but you will see them in New York, Chicago, etc.)</font>
<font size="2" face="Verdana, Helvetica, sans-serif">The bottom line is that you will need to work with the serving electric utility to see what they are willing to do and they should know what the law is concerning individual metering (in Indiana, it was part of energy legislation). :D
 
Re: condo design

Originally posted by hardworkingstiff:
IMO, 208/120 is an inappropriate voltage for a residential structure.
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Why do you think that/ As long as customers know what the voltage is (maybe a big sign on their panelboard) and the equipment that might normally be 240 single phase is purchased as 208 3 phase (or 208 L-L if there is such a thing).

It might even be somewhat less expensive to wire and even to operate.
 
Re: condo design

Originally posted by hardworkingstiff:
IMO, 208/120 is an inappropriate voltage for a residential structure.
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Why? :confused:

That is the only voltage to be found in this area for larger apartment buildings.
 
Re: condo design

A range, water heater, dryer, etc.(the normal 240-volt found at stores) operating at 208 volts is less efficient. The customer will have to pay more for an appliance designed for this voltage and will have a much smaller selection. Chances are even if 208-volt equipment were installed originally, a homeowner would probably replace it with one from Sears, Lowe's, Home Depot, etc. These units will probably be 240-volts.

You could still use a 3-phase distribution system, just when you put in transformers, pick 2 phases to feed a 480 to 240/120 transformer and wire conventionally.
 
Re: condo design

I have also seen most condo projects having the 208/120 voltage to the individual units. what is the reasoning behind the location of the transformer. I would think the larger transformer in the basement would be better because then the electrical rooms would be smaller on the floors and thus the landlord will be happy since there is less floor space being taken up by a transformer.
 
Re: condo design

What is the reasoning behind the location of the transformer.
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Voltage drop.

By the way, a 240 volt range will generally work on 208, an electric dryer will generally work on 208, and an electric water heater will work on 208. Name the appliance and most are listed for either 240 or 208. Keep in mind that it just takes longer to come to heat and then it will cycle on and off just like at 240 volts and the electric motor on a dryer is 120 volts just like the controls. :D
 
Re: condo design

I'd think it would also be better to have the individual customer transformers or floor transformers rather than one big mother in the basement. I'd hate to see one bad xfmr take out the whole place.
 
Re: condo design

I like mdshunk's idea of having a transformer on each floor, serving that floor for it's electrical needs. If they have the room, I would go for a transformer on each floor, instead of one big transformer feeding the entire building. It certainly gives you more flexibility. I would put a Square-D distribution panel in the basement, with a fused switch feeding each transformer on each floor. I really like this idea, rather than one big transformer feeding the entire building.
 
Re: condo design

I think it depends on where the meters are located and what the serving electric utility's rules are for this type of situation. In Indiana, the units are required to be separately metered but the association or building owner is permitted to do that only if the sub-metering is used to split the bill. In other words, the power can not be resold for a profit.

By the way, we usually have a single transformer and don't seem to have a lot of problems, what is really wrong with a large transformer in the basement (you don't loose all you diversity that way and one larger transformer costs less than several smaller ones)? :D
 
Re: condo design

I am at a loss to understand why anyone would want a 480 service to a residential building?

It would have to be very large residential building before we would contemplate a 480 volt service. We have installed up to 4000 amp 208Y/120 services in residential buildings. The up front costs are not the only thing to consider.

No one wants to give up rentable floor space for transformers nor do any of the building owners want the future maintenance of these transformers.

Let the power company maintain one large transformer. :D

By the way, just currious as I have not seen this done, how does the power company feel about the unmetered power wasted at each trnsfomer? :confused:
 
Re: condo design

I also like the idea of 208v service to the building, but in some cases there have been 480V service and I have seen some designs with one large transformer in the basement and some on the floors and was wondering is this a cost driven decision, a design issue, or a floor space decision. I have seen it mentioned on VE items from peer reviews to install transformers on the floors in lieu of one large transformer.
 
Re: condo design

Ok, time for some more lessons for me. I will state a concept I have and wait for others to educate me.

Resistance heat (like range, water heater, dryer, etc.) spends x amount of energy pushing current through an element before the actual heat is generated (useable heat). If you operate a unit at 208 that is designed to operate at 240, you will get useable heat out of the unit. The way I understand it is most of the energy you would get from the extra 32 volts at 240 would be converted into useable heat. Therefore, it is a tremendous waste of energy to operate these units at 208 since a much smaller % of the used energy is actually converted into useable heat. It will cost more per unit of heat used (not power consumed, there is a difference) and move us farther away from being an energy efficient nation.

IMO, a 208 service to a residential building is a poor installation.
 
Re: condo design

HWS any heat from the electric element is 'usable' heat.

Perhaps you are thinking of a incandescent lamp and the wasted heat vs the usable light?

In a water heater the only change will be the recovery time. The element will run longer but end up using close to the same KWh.

If you have an electric range go take a look at the tag (its on the front) I will bet you it is rated at both 208 and 240, mine is 8 KW or 11 KW depending on voltage. Water heaters are also dual rated, my dryer is not.

All that said, when I lived in a 208 volt apartment I thought about a buck / boost for the stove as it did not boil water as fast as I was used to. :D
 
Re: condo design

iwire,

If you were to put 120 volts on a range element, would it heat up? How about 50 volts? 25?

At some point, there will be amperage flowing through the element that will not generate useable heat.

My argument is based in energy efficiency, not cost of installation. We really are entering a crisis when it comes to energy (not just in this country, but the world) and we need to do everything we can to conserve.
 
Re: condo design

Originally posted by hardworkingstiff:
iwire,

If you were to put 120 volts on a range element, would it heat up? How about 50 volts? 25?
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120, 50, 25 volts, sure, depending on what you call hot.

Any current used by an electric element is converted into usable heat. If that heat is 'enough' to do anything with is another matter.

But we are not talking about running a 208-240 rated element at 25 volts. We are talking about running a 208-240 rated element at 208 volt.

All the current consumed by that element is converted into usable heat. There is as little or as much efficiency at either voltage.

IMO This would stay true until the voltage is reduced to a point where the heat produced is less than the heat needed, at that point the element runs 24/7 and you never reach the desired temperature.

Originally posted by hardworkingstiff:
My argument is based in energy efficiency, not cost of installation.
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I understood that, we just do not agree if the efficiency changes or not. :)
 
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