Sizing a sub panel and feeder for multiple air conditioning/ heating units.

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Deepick

Member
Location
Buffalo, New York, USA
Hello all I am currently working on sizing a sub panel and feeder that will feed (18) individual PTAC units. Each unit contains AC, a heat pump and a backup electrical heater. I can perform the calculation to determine the total connected load based on the specs I was provided. Where I’m stumped is wether or not I would be able to apply any demand factors to the total connected load or if I need to use 100% of it. I don’t believe these units to be a continuous load since they cycle on and off as needed. These units will be installed in a elderly retirement facility. The rooms where they will be installed do not have provisions for cooking equipment so I do not believe they would be considered a dwelling unit. Im truly stumped and would appreciate Any clarification or guidance. Thanks!
 
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Deepick

Member
Location
Buffalo, New York, USA
Additional thoughts

Additional thoughts

After reading through 220 again I think I’m wanting to use demand factors that are meant for a service calculation to a feeder calculation. So I’m probably barking up the wrong tree I probably need to take the load at 100%. But still if anyone can help I’d appreciate it.
 
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topgone

Senior Member
Deepick said:
Hello all I am currently working on sizing a sub panel and feeder that will feed (18) individual PTAC units. Each unit contains AC, a heat pump and a backup electrical heater. I can perform the calculation to determine the total connected load based on the specs I was provided. Where I’m stumped is wether or not I would be able to apply any demand factors to the total connected load or if I need to use 100% of it. I don’t believe these units to be a continuous load since they cycle on and off as needed. These units will be installed in a elderly retirement facility. The rooms where they will be installed do not have provisions for cooking equipment so I do not believe they would be considered a dwelling unit. Im truly stumped and would appreciate Any clarification or guidance. Thanks!
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Heaters do have demand factors depending on the number of heaters and size. And A/C units are considered "continuous" loads. You have to use 125% for continuous loads, not 100%, IMO.
 
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Deepick

Member
Location
Buffalo, New York, USA
topgone said:
Heaters do have demand factors depending on the number of heaters and size. And A/C units are considered "continuous" loads. You have to use 125% for continuous loads, not 100%, IMO.
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Topgone after more research and reading I’m agreeing with you that the a/c units should be considered continuous loads. I’ve read that the manufacturers specs of MCA and MFS actually include the additional 25% for a continuous load. So it seems that if I take 100% of the stated specs I should be good to go. I’m gonna read up some more though. Thank you very much for your response.
 
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Deepick

Member
Location
Buffalo, New York, USA
ActionDave said:
We did this at an apartment building a long time ago and settled on 125% of the largest unit and 100% of all the rest. I can't remember where the boss and the powers that be came up with that.
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Thank you sir for your response. I’m definitely leaning away from using any demand or diversity factors. I’m actually reading through 220 right now and 220.18(A) says basically what you posted. So that may be the source.
 
kwired

kwired

Electron manager
Location
NE Nebraska
If they have resistance heat the heating load is likely larger than cooling load you should only need to account for the larger of the two unless they can operate simultaneously.
 
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Deepick

Member
Location
Buffalo, New York, USA
kwired said:
If they have resistance heat the heating load is likely larger than cooling load you should only need to account for the larger of the two unless they can operate simultaneously.
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The PTAC units do contain a heat pump and a back up heater. I will be using the heat load for my final calculations. Thanks for your response.
 
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