condo design

[don_resqcapt19]

Re: condo design

hardworkingstiff ,
There is only a very small change in the efficiency of a resistance heating device when the voltage changes from 240 to 208. The only change in efficiency is the very small additional heat losses to the ambient air as a result of the longer time it will take for the element to heat the water to the desired temperature.
Lets look at some numbers. First we have to remember that for all practical purposes there will be no difference in the resistance of the heating element when the voltage is changed from 240 to 208. If you take a water heater element with a 3000 watt rating at 240 we find the resistance is 19.2 ohms. If we supply this same element with 208 volts we will have heating equal to 2253 watts. Water weighs about 8.3 pounds per gallon so a 40 gallon water heater would have 332 pounds of water. One BTU or 0.293 watthours are required to raise one pound of water 1?F. If the water supply is 50?F and the desired temperature is 120?F, then we need 6809 watt-hours to heat this water. With a 240 volt supply this will take 2.27 hours and with the 208 volt supply it will take 3.02 hours, but the total energy used remains the same.
Don

 

[tom baker]

Re: condo design

Electric heat is essentially 100% efficient, whether 120V, 208V, 240V. Due to ohms law, if the voltage is lower, the current will be higher. The reason that the higher voltages are considered to be "more efficient" is due to I (squared) R. As the current goes up with the same resistance, the current is squared. More current means greater voltage drop and larger conductors.

 

[infinity]

Re: condo design

Electric heat is essentially 100% efficient, whether 120V, 208V, 240V. Due to ohms law, if the voltage is lower, the current will be higher

I think that you meant that if the voltage is lower, the current is lower . Voltage and current are directly proportional in a purely resistive load.

 

[charlie]

Re: condo design

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

Bob, the building I am talking about is a hotel that is being served with 480Y/277V, 3?, 4w and the top few floors will be luxury apartments. This is what the customer wanted so they could use small feeders to the apartments and provide them with a standard 120/240V, 1?, 3w feeder. Being the absolutely great guys that we are, we said OK, we will bend to your desires (don't all electric utilities do that?).

 

[mdshunk]

Re: condo design

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

Plus, if the building is very big at all, the 480 is super nice for the elevators and the chillers.

 

[hardworkingstiff]

Re: condo design

Well Bob and Don, I think you guys are probably smarter than I, but...... I still would prefer the 240 volts, and would never buy a home (condo or otherwise) that had a 208 service.

Thanks for your lessons!

 

[don_resqcapt19]

Re: condo design

hardworkingstiff,
There are even subdivisions in this area where the utility supply to single family dwelling units is single phase 208/120. So check close before you buy.
Don

 

[hardworkingstiff]

Re: condo design

Originally posted by don_resqcapt19:
hardworkingstiff,
There are even subdivisions in this area where the utility supply to single family dwelling units is single phase 208/120. So check close before you buy.
Don

Don, where is your area?

 

[mdshunk]

Re: condo design

Originally posted by hardworkingstiff:

Originally posted by don_resqcapt19:
hardworkingstiff,
There are even subdivisions in this area where the utility supply to single family dwelling units is single phase 208/120. So check close before you buy.
Don

Don, where is your area?

There's residential places like that in my town. Anytime you have to install a 5th terminal meter can, you're on one of the 120/208 "network services".

 

[hardworkingstiff]

Re: condo design

So am I the only one that has a problem with 120/208 (2-legs) service to a residence?

 

[iwire]

Re: condo design

Originally posted by hardworkingstiff:
So am I the only one that has a problem with 120/208 (2-legs) service to a residence?

It seems possible.

I do not understand the problem with this.

The only issue I see would be the number of current carrying conductors for pipe job.

I don't think the average consumer knows or cares if their service is 208 or 240.

 

[don_resqcapt19]

Re: condo design

Illinois

 

[redfish]

Re: condo design

I second the 208Y/120 voltage. Three legs are better than two.

 

[hardworkingstiff]

Re: condo design

Originally posted by redfish:
I second the 208Y/120 voltage. Three legs are better than two.

But we are only delivering two legs to the premises.

 

[hardworkingstiff]

Re: condo design

And since we are delivering only 2 of 3 legs to a building, what about the "Oregon Fudge Factor"?

If you were in Oregon, wouldn't you have to upsize your 2/3 services by 15%?

 

[charlie]

Re: condo design

I second the 208Y/120 voltage. Three legs are better than two.

Actually, with 1?, you only get two legs of the wye service for each dwelling unit. The 5th terminal is just for potential so the meter will work correctly and is jumpered from the neutral position with a small conductor (we require a #10).