Stumped by HVAC

T

TealHeals

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Location
Oregon
Occupation
journeyman electrician & licensed signing supervisor
Which values am I taking from this HVAC unit for my calculated load? It will be run on a single phase 120/240 volt system. The compressor motor is rated for 230 volts. My drafters/engineers are adamant about using 230 instead of 240 volts.
1. To get my VA for the total calculated load for my feeders, would I use the FLA from the heater package? Or the RLA from the electrical ratings?
2. Since the unit is operating on 240 real world volts, I should use 240 for my calculation, correct?
 

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Just follow the nameplate. It says unit will run on 197-253 volts. Use the MCA for wire size and the MOCP for fuse or breaker.

It has electric heat so the only decision is to weather you run 2 circuits 1 for the compressor and motors and 1 for the electric heat or 1 circuit for both following the valves given on the name plate.

You don't have to do any calculations with HVAC it is on the name plate. You only decide (1) circuit or (2) circuits, size the wire per the MCA and the breaker or fuse per the MOCP
 
Eddie702 said:
Just follow the nameplate. It says unit will run on 197-253 volts. Use the MCA for wire size and the MOCP for fuse or breaker.

It has electric heat so the only decision is to weather you run 2 circuits 1 for the compressor and motors and 1 for the electric heat or 1 circuit for both following the valves given on the name plate.

You don't have to do any calculations with HVAC it is on the name plate. You only decide (1) circuit or (2) circuits, size the wire per the MCA and the breaker or fuse per the MOCP
Click to expand...
I think that he's asking about a calculated load for more than just this unit.
 
Eddie702 said:
Just follow the nameplate. It says unit will run on 197-253 volts. Use the MCA for wire size and the MOCP for fuse or breaker.

It has electric heat so the only decision is to weather you run 2 circuits 1 for the compressor and motors and 1 for the electric heat or 1 circuit for both following the valves given on the name plate.

You don't have to do any calculations with HVAC it is on the name plate. You only decide (1) circuit or (2) circuits, size the wire per the MCA and the breaker or fuse per the MOCP
Click to expand...
Wire size and breaker sizing have been fine/easy.
However, some of our design drawings have been bounced back from state permitting lately because my drafters/engineers have not been looking at the possibilities of 220.60 noncoincident loads. Nor have they been looking at all the motors in the small commercial spaces they're designing.
We need to show the calculated load VA for permitting, and I'm having a hard time justifying what I *think* is correct.
 
TealHeals said:
Yes, Rob. Somehow, this number is getting more chaotic to pin down.
What do you think? Am I pulling 77 amps from the MCA and using 240 volts?
Click to expand...
77 amps is the MCA which already has 25% added to a portion of the load so does that number actually work? I would use 240 volts in the calculation since most of the load is resistive and the load will be higher at 240 volts that at the listed nameplate voltage of 230. Not sure if anything in Article 220 would require that.
 
For load calculations, MCA is conservative, because it includes 125% of the largest motor.

I always just add up all the RLA's and FLA's and multiply the total by the nominal voltage.

Compr. 15.6
O/D Fan 2.0
I/D Fan 2.3
Heater 40.0
Total 59.9A

(59.9A x 230V)/1000 = 13.8 kVA (This assumes it's a heat pump, where compressor, O/D fan and Heater can all run at once. YMMV.)

If you had used the MCA, it would have come out to 17.7 kVA, which is less perfectly accurate.
 
I see what you mean I misunderstood you first. I am assuming the heat and AC do not run at the same time so you would take the larger of these two loads which is the heater.

I don't know whether your required to do this, but the heater will have a higher output on 240volt than at the name plate rating at 230 so you may want to calculate that and add the two motors into the calculation.

I would use 10,018kw for the heater and 2.625A Plus 2.1A for the two motors @240v

So you max load for calculation is 46 amps @240
 
don_resqcapt19 said:
220.5(A) specifies the voltage to be used for load calculations.
Click to expand...
I *knew* there was a published "why" in there! ThankYouThankYouThankYou.
I just got myself an NFPA Link subscription, and yet I still missed this. In the spirit of continuous learning, I'll never forget it after today ;)
 
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