two pole airhandler load calc on three phase system

whofrankw

Member
Engineered speced out three phase airhandler equipment for a big gym im working on and during the estimate the equipment changed to single phase. im trying to figure out how much more amps the new equipment is going to put on the main panel. The specs so far are a 400 amp main 3 phase 4 wire 120/208v. The original equipment on the plans are 5 air handler units, 3 phase , 45 amp circuit breaker with a load of 4.2kva on each phase. The specs i have on the new 5 air handlers require two, two pole breakers. a 25amp and a 50amp which draw 17 amps and 35 amps. I want to know how much more if any are the new specs for the air hanlders going to draw. I could put this off on the engineer but i want to bring this up to the contractor first and talk it over with them too.

one more question. the original plans without the new air hanlders show a total demand of 343.91 amps on a 400 amp breaker. this is a gym and i was wondering if that load should be considered continuous and no more than 320amps
 

topgone

Senior Member
IMO, air handlers are treated like space heating equipment. As such, they are classified as continuous loads!
 

Dennis Alwon

Moderator
Staff member
It's the engineers job to redo his calcs and you may have to get the hvac system looked at again by the inspections. You can't just change plans once they were okayed by the jurisdiction
 

powerpete69

Senior Member
Who on Earth would approve single phase vendor prints for such large power drawing equipment?
Who ever approved that needs to pay for the new design and possibly the upcharge in copper if it will even work at all.
Also, don't single phase motors make a lot more noise than three phase? Yep. Don't three phase motors outlast single phase motors? Yep.
 

roger

Moderator
Staff member
I
It's the engineers job to redo his calcs and you may have to get the hvac system looked at again by the inspections. You can't just change plans once they were okayed by the jurisdiction
Who on Earth would approve single phase vendor prints for such large power drawing equipment?
Who ever approved that needs to pay for the new design and possibly the upcharge in copper if it will even work at all.
Also, don't single phase motors make a lot more noise than three phase? Yep. Don't three phase motors outlast single phase motors? Yep.
Agreed, if the Mechanical engineer approved this he/she left the Electrical engineer out of the loop and they need to be brought to the party, an EC can not make the changes on their own.

Roger
 

kwired

Electron manager
Who on Earth would approve single phase vendor prints for such large power drawing equipment?
Who ever approved that needs to pay for the new design and possibly the upcharge in copper if it will even work at all.
Also, don't single phase motors make a lot more noise than three phase? Yep. Don't three phase motors outlast single phase motors? Yep.
I agree that original spec'd equipment probably was not installed or updated electrical plans were never given to the electrician, but I have run into this a time or two myself, where they install single phase residential grade HVAC equipment because it cost less. The HVAC guy also often doesn't realize that 15 kW heat package is no longer 15 kW when applied on a 208 volt system, though the AC unit still produces same output at either voltage. But outside of those things they have multiple units with multiple supply circuits, simply balance load as much as you can and it probably won't be too big of a deal for the loading of the system. You may have ordered breakers and other items per plans and may be stuck with things you can't use as well as need alternate items to replace them with though, that is what change orders are for.

One trade changes the plans to save money doesn't necessarily save money when he creates hardships for other trades.
 

whofrankw

Member
Nothing was ordered yet.Just trying to get things straightened out. The plans say three phase Hvac equipment but the equipment is on the smaller size and not made in three phase. One was on the job site already. No electric will be done with proper approval. Basically just wanted to know how to calculate it for myself. I understand it’s the engines job.
 

roger

Moderator
Staff member
I agree that original spec'd equipment probably was not installed or updated electrical plans were never given to the electrician, but I have run into this a time or two myself, where they install single phase residential grade HVAC equipment because it cost less. The HVAC guy also often doesn't realize that 15 kW heat package is no longer 15 kW when applied on a 208 volt system, though the AC unit still produces same output at either voltage. But outside of those things they have multiple units with multiple supply circuits, simply balance load as much as you can and it probably won't be too big of a deal for the loading of the system. You may have ordered breakers and other items per plans and may be stuck with things you can't use as well as need alternate items to replace them with though, that is what change orders are for.

One trade changes the plans to save money doesn't necessarily save money when he creates hardships for other trades.
With the exception of the COR none of that has much to do with a contractor supplying something less than the customer thinks they are buying. In the end all items not approved through the submittal process will be replaced and all associated expenses incurred by others will be held in back charges to the offending party.

Roger
 

topgone

Senior Member
I agree that original spec'd equipment probably was not installed or updated electrical plans were never given to the electrician, but I have run into this a time or two myself, where they install single phase residential grade HVAC equipment because it cost less. The HVAC guy also often doesn't realize that 15 kW heat package is no longer 15 kW when applied on a 208 volt system, though the AC unit still produces same output at either voltage. But outside of those things they have multiple units with multiple supply circuits, simply balance load as much as you can and it probably won't be too big of a deal for the loading of the system. You may have ordered breakers and other items per plans and may be stuck with things you can't use as well as need alternate items to replace them with though, that is what change orders are for.

One trade changes the plans to save money doesn't necessarily save money when he creates hardships for other trades.
Agree.
What's more devastating to us is when client makes very big changes like changing the whole building floor use and leaving us electrical guys in the dark! It was easy for the CAD operator to cut and paste the structural plans and swap floors! It's damn hard work redoing the electrical side of things there!
 

kwired

Electron manager
With the exception of the COR none of that has much to do with a contractor supplying something less than the customer thinks they are buying. In the end all items not approved through the submittal process will be replaced and all associated expenses incurred by others will be held in back charges to the offending party.

Roger
When it has happened to me I'm pretty sure customer and HVAC guy talked and agreed on lesser price for the single phase equipment. Those projects had engineered plans but engineer wasn't ever coming to the site and assuring things were done to their design either, and even some of my electrical possibly gets customized on the fly. One project we did coordinate early on and change the service from three phase to single phase as the AC units were the only three phase load on original plans and it wasn't all that large of a facility to begin with.

We don't have all that strict of building codes out in the boonies, unless you are building an oil pipeline or wind farm :)
 
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