airforceblue
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How many amps are pulled by a 12 ton HVAC unit(208v, three phase)? Is there a formula to figure this out?
12 Ton HVAC unit
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websparky
Senior Member
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- Cleveland, Ohio
Re: 12 Ton HVAC unit
Here is the one I use;
Google > name of Manufacturer > model number > specs.
Here is the one I use;
Google > name of Manufacturer > model number > specs.
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- Lockport, IL
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- Retired Electrical Engineer
Re: 12 Ton HVAC unit
The question is similar to asking, ?How many amps does a 25 horsepower pump draw?? There is a way to convert the unit ?horsepower? to ?watts,? and from there you can calculate amps. But a pump does not draw current, the motor does. Before you can calculate motor amps, you need to know the efficiency of the pump, the motor, and the combination of the two. Only the manufacturer can give you that information.
?1 Ton? of air conditioning is equivalent to a cooling capacity of 12,000 BTU/Hr. It is the cooling capacity of one ton of ice under certain standard conditions. A ?BTU/Hr? is a unit of power, and can be converted into ?watts.? But that value is the output of the mechanical device. There is an efficiency factor to consider, and it depends on the specifics of the machine.
The bottom line is that the other two answers are true. You need to get the information from the manufacturer.
The question is similar to asking, ?How many amps does a 25 horsepower pump draw?? There is a way to convert the unit ?horsepower? to ?watts,? and from there you can calculate amps. But a pump does not draw current, the motor does. Before you can calculate motor amps, you need to know the efficiency of the pump, the motor, and the combination of the two. Only the manufacturer can give you that information.
?1 Ton? of air conditioning is equivalent to a cooling capacity of 12,000 BTU/Hr. It is the cooling capacity of one ton of ice under certain standard conditions. A ?BTU/Hr? is a unit of power, and can be converted into ?watts.? But that value is the output of the mechanical device. There is an efficiency factor to consider, and it depends on the specifics of the machine.
The bottom line is that the other two answers are true. You need to get the information from the manufacturer.
Re: 12 Ton HVAC unit
I assume you are just trying to get a rough estimate (maybe to get a preliminary service size, or to bid a job.) I often have to do this before our HVAC engineer has selected a unit. And when jobs go out for bid, it is still possible the for any of several manufacturers to supply the unit.
I often see units in the 2-5 ton range draw 1500 - 2500 watts per ton. For your larger unit, I would guess at about 1500 watts per ton. For a 3 phase 208 volt unit, that comes out to about 50 amps. You may want to add a 20% margin for error which gives about 60 amps.
A note of caution: using the direct conversion Charlie B mentioned, a ton of refrigeration is equal to 3517 watts. So I'm not really sure how a unit gets a ton of refrigeration from 1500 watts. It sounds impossible, but I just checked the numbers for two smaller units, and they both use less than 2500 watts per ton.
Steve
I assume you are just trying to get a rough estimate (maybe to get a preliminary service size, or to bid a job.) I often have to do this before our HVAC engineer has selected a unit. And when jobs go out for bid, it is still possible the for any of several manufacturers to supply the unit.
I often see units in the 2-5 ton range draw 1500 - 2500 watts per ton. For your larger unit, I would guess at about 1500 watts per ton. For a 3 phase 208 volt unit, that comes out to about 50 amps. You may want to add a 20% margin for error which gives about 60 amps.
A note of caution: using the direct conversion Charlie B mentioned, a ton of refrigeration is equal to 3517 watts. So I'm not really sure how a unit gets a ton of refrigeration from 1500 watts. It sounds impossible, but I just checked the numbers for two smaller units, and they both use less than 2500 watts per ton.
Steve
Re: 12 Ton HVAC unit
Steve66,
The seemingly impossible efficiency of heat pumps is possible because it only "lifts" heat from one temperature to another. Remember, heat and power is the same thing. If you use metric units, Watts are used for both. The aircondition takes heat from the inside of the building, lifts the temperature to something above the outdoor temp and dumps the heat on the outside of the building. You need to add electrical or mechanical power to drive the fans and compressors but that is small compared the amount of power (heat) it takes from the indoor air.
The bigger the difference in temperature, the more power you need to add.
Steve66,
The seemingly impossible efficiency of heat pumps is possible because it only "lifts" heat from one temperature to another. Remember, heat and power is the same thing. If you use metric units, Watts are used for both. The aircondition takes heat from the inside of the building, lifts the temperature to something above the outdoor temp and dumps the heat on the outside of the building. You need to add electrical or mechanical power to drive the fans and compressors but that is small compared the amount of power (heat) it takes from the indoor air.
The bigger the difference in temperature, the more power you need to add.
caosesvida
Senior Member
Re: 12 Ton HVAC unit
watts converted to btu's will give you the answer of how many btu's per watt of electric heat as btus is a heat quanity measurement. THe problem is that at peak efficiency a heat pump can give 4 or 5 times the btus per watt as compared to electric heat. But at 30 degrees or so a heat pump is equal to or less efficent than electric heat. Also a ton of refrigeration specified on a unit, is at ton at " 85 degrees and 70% humidity (more or less)" At 90 degrees you will not get a ton of refrigerant from that unit. The best rough estimate might be find out what size compressor is popular in a 12 ton unit and go from there, add some amps for the fan motor. hope this helps a bit.
watts converted to btu's will give you the answer of how many btu's per watt of electric heat as btus is a heat quanity measurement. THe problem is that at peak efficiency a heat pump can give 4 or 5 times the btus per watt as compared to electric heat. But at 30 degrees or so a heat pump is equal to or less efficent than electric heat. Also a ton of refrigeration specified on a unit, is at ton at " 85 degrees and 70% humidity (more or less)" At 90 degrees you will not get a ton of refrigerant from that unit. The best rough estimate might be find out what size compressor is popular in a 12 ton unit and go from there, add some amps for the fan motor. hope this helps a bit.
sceepe
Senior Member
Re: 12 Ton HVAC unit
The problem of how to design something that depends on the nameplate when you don't even know which manufacturer will be used on the job.
One way to do the design before you see the nameplates is to have the mechanical engineer state that: "the basis of design is (insert manufacturer). Any required electrical changes to use other approved equipment are the responsibility of the mechanical conractor."
You can then go to one manufacturer and base your electrical design on that. You will still need to check the shop drawings for the mechanical equipment that is actually installed.
Also caosasvida said
The problem of how to design something that depends on the nameplate when you don't even know which manufacturer will be used on the job.
One way to do the design before you see the nameplates is to have the mechanical engineer state that: "the basis of design is (insert manufacturer). Any required electrical changes to use other approved equipment are the responsibility of the mechanical conractor."
You can then go to one manufacturer and base your electrical design on that. You will still need to check the shop drawings for the mechanical equipment that is actually installed.
Also caosasvida said
You also need to find out the strip heat size. A 12 ton heat pump may have 40-50kw of strip heat.
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