Sizing a water heater

[fauxfly]

Hi guys


Wiring two seperate water heaters in two of my buildings. First one I have 480, 3 phase available, the plumber tells me he'd like a thirty minute recovery time on this unit. The guy at the plumbing desk needs a KW rating from me. I don't really have a way to calc a KW rating do I. I know the plumber says its based on a fixture count but the guy at the front desk is giving me a ridiculous current rating for these.

My question is I'd like to feed the 480 volt heater with an existing circuit I already have there... 480, 20Amp. Is this a standard commercial water heater size , if not where do I go next.

Thanks all

Steve

 

[charlie b]

If you want to use the existing circuit, you have (480 x 20 x 1.732 x 80%), or about 13kW to work with. Give that number to the plumbing desk, and see what they have to offer. We can't tell you anything about recovery time, without knowing the volume of the tank.

 

[One-eyed Jack]

If you want to use the existing circuit, you have (480 x 20 x 1.732 x 80%), or about 13kW to work with. Give that number to the plumbing desk, and see what they have to offer. We can't tell you anything about recovery time, without knowing the volume of the tank.

Using the available kw you will have a recovery rate of approx. 90 gal per hr with a 60 degree rise.

 

[Cow]

Why isn't the plumber sizing the water heater? You could just tell him you have 20 amps of 480v available(13kW) like Charlie mentioned and have him figure the rest out.

 

[GUNNING]

Hypothetical equipement is mythical in nature.

Hypothetical equipement is mythical in nature.

Because most plumbers are rich idiots. There are two questions here. What size tank, & then calculate hook up parameters. I rely on the three rules of thermo dynamics. You cant win you cant loose and you cant get out of the game. If some engineer or architect has calculated the size of an existing electric water heater to be placed there for an existing need then Id say the existing circuit is going to be ok, unless something has changed. Tell the plumber to specify 3 phase 480 water heater elements to his supply house and get back to you on the total KW. Only then will you know if the circuit is the right size.
Have you thought about tankless? Sounds like that would be the way to go here.

 

[jumper]

I install a lot of 3 phase, 30amp, 480volt, 18,000w, 120gallon WH's. Recovery is good.

You can get a 54,000w, if you need it. Check Rheem and A.O. Smith.

3 days from the factory, till delivery, if expedited.

 

[One-eyed Jack]

Because most plumbers are rich idiots. There are two questions here. What size tank, & then calculate hook up parameters. I rely on the three rules of thermo dynamics. You cant win you cant loose and you cant get out of the game. If some engineer or architect has calculated the size of an existing electric water heater to be placed there for an existing need then Id say the existing circuit is going to be ok, unless something has changed. Tell the plumber to specify 3 phase 480 water heater elements to his supply house and get back to you on the total KW. Only then will you know if the circuit is the right size.
Have you thought about tankless? Sounds like that would be the way to go here.

There goes his existing circuit !!!

 

[jumper]

Tell the plumber to specify 3 phase 480 water heater elements

I assume you mean 3 480v single phase elements wired as AB-BC-CA. The number of sets can vary for total Kw output.