Derate A/C units for feeder load calc.?

[Clint623]

I'm looking in article 220 for service calculations and I see that in a dwelling unit A/C's are supposed to be sized at 100%. I'm currently working on a commercial building that has decided to put in (4) 5 Ton split units. The A/C condenser will be fed from downstairs. The heater coil and air handler will of course be up in the attic. I'm trying to figure out my total KVA for the floor so I can size my feeder and cannot find anything for derating units for commercial use. Also, Art. 440 doesn't reference any derating or at least that I'm noticing.

This is what all the units will be. I'm also a little confused (which is easily done) about the Min Circ. Ampacity and Max OCPD. Shouldn't they be listed by from 208/240V? Things just really don't seem kosher from what I'm looking at. I called the A/C guy today and he said that he needed (2) 60A breakers for the air handler..... I'm pretty sure he was wrong lol.

The Air Handler model # is WH1T6021STANJA

Heater Model #	Heater kW (208/240V) (480V)	PH/HZ	No. Elements kW Per	Type Supply Circuit Single Circuit Multiple	Circuit Amps.	Motor Ampacity	Minimum Circuit Ampacity	Maximum Circuit Protector
RXBH-1724A15J	10.8/14.4	1/60	3 - 4.8	SINGLE	51.9/60	4.1	70/81	70/90
RXBH-1724A15J	3.6/4.8	1/60	1 - 4.8	MULTIPLE CKT 1	17.3/20	4.1	27/31	30/35
RXBH-1724A15J	7.2/9.6	1/60	2 - 4.8	MULTIPLE CKT 2	34.6/40	0	44/50	45/50

 

[hbiss]

Looks like it can be configured two ways. All the heating elements plus the blower motor on one circuit or one heating element plus blower on one circuit and the remaining two heating elements on another. I'll assume that since the HVAC guy is quoting two breakers that it is the latter.

And yes, for 208/240V you would use the first numbers given in the minimum circuit ampacity and maximum circuit ampacity columns. I'm seeing a 30 and a 45 not two 60s. The minimum circuit ampacity would be 27 and 44A respectively.

-Hal

 

[augie47]

As far as KW, what I see is 10.8 on 208 or 14.4 on 240.
They guy is wrong on (2) 60-s. Again, depending on your voltage, 208 a 30 & a 45; 240 a35 and a 50

 

[Clint623]

As far as KW, what I see is 10.8 on 208 or 14.4 on 240.
They guy is wrong on (2) 60-s. Again, depending on your voltage, 208 a 30 & a 45; 240 a35 and a 50

To me that doesn’t make sense though because I was always taught that the higher the voltage the lower the amps. Regardless I’m still using the same breaker sizes for 208 or 240.
Also, is there a way to derate the 14.4KW because right now I’m looking at 240A for all 4 units. Like there is for plugs or lighting
EX.
first 10kw at 100%
next 17kw at 45%
remainder at 35%

 

[david luchini]

To me that doesn’t make sense though because I was always taught that the higher the voltage the lower the amps. Regardless I’m still using the same breaker sizes for 208 or 240.

It's the same heating element, so you get less wattage at a lower voltage. The wattage is 14.4kW at 240V and 10.8kW at 208V. That's 60A at 240V and 51.9A at 208V.

With the unit motors, I believe you are looking at a minimum of 258A for all 4 units.

 

[augie47]

It's the same heating element, so you get less wattage at a lower voltage. The wattage is 14.4kW at 240V and 10.8kW at 208V. That's 60A at 240V and 51.9A at 208V.

With the unit motors, I believe you are looking at a minimum of 258A for all 4 units.

I agree for 240v
If we happen to be dealing with 208v I think it's around 225 amps

 

[Clint623]

It's the same heating element, so you get less wattage at a lower voltage. The wattage is 14.4kW at 240V and 10.8kW at 208V. That's 60A at 240V and 51.9A at 208V.

With the unit motors, I believe you are looking at a minimum of 258A for all 4 units.

That makes sense. I don’t know if I have that much accessible power for 240V though.. I’ll have to go look at the XFMR size and do a load check for the first floor.

 

[augie47]

Keep in mind you have 4 units. If you have a 3 phase supply you can "share" the load somewhat.

 

[Dennis Alwon]

If you know the kw at 240v then multiply by 75% and you will get close to the kw at 208V

Conversely if you know the wattage at 208V then divide by 75% to get the wattage at 240v

 

[Dennis Alwon]

Are you sure those are the correct specs. If the hvac guys says 2 circuits then perhaps you don't have the correct KW. Usually 2- 60 amp circuits is a 20kw unit