Heater Calculations

[Sparky_1]

Hello,

Im calculating a house that would be moved to a job site for housing.
There is going to be 4 bedrooms, each having there own bathroom, water heater
& heating / AC unit. The water heaters are 1650 watt 120 volt each and
the heating unit is 3500 Watts 240 Volt. The kitchen, living area
would have two of these heaters and one 1650 watt water heater.

If they are able to establish the house as a single family dwelling,
can I use th optional calculation for single family dwelling, where
I can calculate all of the load and take the first 10kva at 100%
and the rest at 40%? Im thinking I can add all of the heat/ac units
and the water heaters together. With everything else in the house, (range
laundry, dishwasher, small app circuits & sq footage watts I come up with
120 Amps.

Now that being said, I'm thinking the house will be considered a motel, each bedroom
will be seperated from each other and have there own entrance. Then
I calculated the heating /AC units and the water heaters at 100%
That would put me at 243 Amps.
At any given time there could be six heaters going along with five water heaters and
someone using the oven, that would put it over the 200 amp mark.
I'm thinking of putting in a 300 Amp service to accomdate this load.

Can I get some input on this,

Thank You.
Sparky

 

[hurk27]

Is this some kind of modular or purpose built housing?

to me it sounds more like a boarding type house with common area living and cooking spaces and common laundry.

The problem I see is even though the NEC allows for devarcity factors to be used to reduce the caculated load as a housing unit at the location of a single job site, depending upon the work hours it sounds like if every tennet is going to work and getting off at the same time your going to have many of the loads at the same time such as water heating and such, the NEC is bare minium but if your demand turns out higher then the NEC caculated allowance there will be over load problems if you dont size for it.

Now can you make a list of the loads and the square footage, because with just what I figured for the water heating and regular heating you are over 100 amps with just that alone?

Heres what I have:
5*1650 = 8200 5 water heaters
6*3500 = 21000 6 wall heaters
"heater load larger then AC load since both wont run at the same time you take the larger of the two"
3*1500 = 4500 2 SABC's and one 20 amp laundry circuit
1*5500 = 5000 1 electric dryer
1*1250 = 1250 1 dishwasher
1*8000 = 8000 1 12kw range
total = 47950/240= 199.8 amps
and this doesn't include your 3va per sq. ft.?

I don't know but to me applying any demand reduction that might be allowed could result in an over loaded service with the workers all getting off work at the same time?

 

[Sparky_1]

Hurk,

The sq ft is 1200,
Garbage Disposal also.
The water heaters are 120 Volt, I see in my calculations that I took the
wattage of 8250 and divided by 120 V, instead of adding the 8250 to my
total wattage, then divide by 240.
I come up with a total of 49750 Watts / 240 = 207 Amps

To close for 225 Amp service or should I bump it up and be safe at a 300 Amp?

Thanks for the input
Sparky

 

[hurk27]

Hurk,

The sq ft is 1200,
Garbage Disposal also.
The water heaters are 120 Volt, I see in my calculations that I took the
wattage of 8250 and divided by 120 V, instead of adding the 8250 to my
total wattage, then divide by 240.
I come up with a total of 49750 Watts / 240 = 207 Amps

To close for 225 Amp service or should I bump it up and be safe at a 300 Amp?

Thanks for the input
Sparky

Around here I have never seen a 300 amp service, the next size up for us would be a 320 meter and it is common to just run two 40 circuit 200 amp main breaker panels off it that gives us so many extra breaker spaces, but then electric heat anything is also un common as our utility rate is one of the highest in the US, all our appliances are natural gas, and the avarge demand load on a three bedroom house with garage here is about 65 amps which is a good thing when a customer wants to add a whole house generator.

I must say I have never heard of bringing a house to a job site before:happyno:

I know in Alaska they use those stackable modular units for portable housing at the oil well camps, back in the "70s" a friend and I went up there to see about jobs on the APL and they were renting shipping crates for 400 a month for housing, and everything else was sky high.