[Otis221]

Is there a rule of thumb to determine amperage of an HVAC Roof Top Unit (RTU) when voltage, phase and tonage is known?

 

[green light]

Is there a rule of thumb to determine amperage of an HVAC Roof Top Unit (RTU) when voltage, phase and tonage is known?

Read the nameplate

 

[jrsparky]

I would check nameplate data or check manufacturer specs.

 

[Otis221]

This is for estimating purposes. I'm taking the information given to me from the HVAC drawings. At this time the nameplate is not available.

 

[green light]

This is for estimating purposes. I'm taking the information given to me from the HVAC drawings. At this time the nameplate is not available.

Are you bidding off of a set of prints?

 

[Wirenuting]

Is there a rule of thumb to determine amperage of an HVAC Roof Top Unit (RTU) when voltage, phase and tonage is known?

Without a type & model number you can't estimate amperage.
The best you could do is be on the same block as the unit but not close enough to be in the ball park.

 

[Otis221]

Yes. There is no information given on the electrical drawings for the RTU's (no equipment schedule or panel schedules).

 

[green light]

Yes. There is no information given on the electrical drawings for the RTU's (no equipment schedule or panel schedules).

Good luck... RFI

 

[Wirenuting]

You can try this. http://www.kylesconverter.com/power/horsepower-to-tons-of-ait-conditioning Let us know how well it works.

edit: then convert HP to Amperage.

 

[wildleg]

put a WAG in, and qualify it on your bid

 

[480sparky]

Yes. There is no information given on the electrical drawings for the RTU's (no equipment schedule or panel schedules).

Submit a Request For Information.

 

[CopperSlave]

An old timer told me once to figure 10A per ton but, I've found that it doesn't always work out.

 

[Meadow]

If you know the size of the space and the building you are working with its possible to guestimate. But in all effort ask the customer, if your bidding Im sure 10 others are asking the same question.

 

[cdslotz]

When I am budgeting a job with only tonnage given, I use 2200 watts/ton, then divide by the voltage x 1.732

 

[cdslotz]

I might add that most units today are more efficient, and that figure is closer to 1700 watts/ton.
I still use 2200 just to be covered..

 

[MechanicalDVR]

Stand facing the prints, take all the 'rule of thumb' formulas you've been given and toss that crap out and request more info.

 

[cdslotz]

Stand facing the prints, take all the 'rule of thumb' formulas you've been given and toss that crap out and request more info.

When you get a written design narrative it usually gives you a list of RTU's..
It might say...provide power to 6-15 ton, 3-12 ton, 3-7 1/2 ton RTU's at 480V, 3ph.....

That's it...I thinks that's the kind of info the OP has received..