Tons to amps
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Re: Tons to amps
rattus,
I am sorry that I wasn't clear enough. I typed it so quickly that I made an error. The formula to convert tons refrigerant to volt-amps (VA) is as shown below. I am using volt-amps (apparent power) because we are considering this in a three-phase power installation.
VA = (#tons) x (12,000 BTU/hr/ton) x .239 VA/BTU
--------------------------------------------
.8 x 1.7320 x 208 volts
all the units cancel out when you multiply the above variables and you are left with amperes (in case this doesn't come out clearly, the formula is a fraction, with [(#tons) x (12,000 BTU/hr/ton) x .239 VA/BTU] as the numerator and [.8 x 1.7320 x 208V] as the denominator). The ".8" represents an assumption of 80% efficiency. 1.7320 is the square root of 3, a factor that must be used when working with three-phase power. Also, I am calculating the current for a 208/120 three-phase system.
This is the exact formula to use, based on universally accepted conversion formulas. It is, to the best of my (and many colleagues) knowledge, correct. It is offered for your use in an effort to help. If you find an error, please describe what you feel is incorrect and I will appreciate and evaluate your criticism.
Thanks.
rattus,
I am sorry that I wasn't clear enough. I typed it so quickly that I made an error. The formula to convert tons refrigerant to volt-amps (VA) is as shown below. I am using volt-amps (apparent power) because we are considering this in a three-phase power installation.
VA = (#tons) x (12,000 BTU/hr/ton) x .239 VA/BTU
--------------------------------------------
.8 x 1.7320 x 208 volts
all the units cancel out when you multiply the above variables and you are left with amperes (in case this doesn't come out clearly, the formula is a fraction, with [(#tons) x (12,000 BTU/hr/ton) x .239 VA/BTU] as the numerator and [.8 x 1.7320 x 208V] as the denominator). The ".8" represents an assumption of 80% efficiency. 1.7320 is the square root of 3, a factor that must be used when working with three-phase power. Also, I am calculating the current for a 208/120 three-phase system.
This is the exact formula to use, based on universally accepted conversion formulas. It is, to the best of my (and many colleagues) knowledge, correct. It is offered for your use in an effort to help. If you find an error, please describe what you feel is incorrect and I will appreciate and evaluate your criticism.
Thanks.
Re: Tons to amps
Thirdbase, that looks better. I had just gotten on ronaldrc's case about his units, and this one threw me. I would think however that the SEER ought to be included as a parameter unless it is thought that wiring and OCP should be sized for a minimum SEER.
BTW, shouldn't it read, 0.239 VAH/BTU? Too many "hours"!
[ February 27, 2005, 09:47 PM: Message edited by: rattus ]
Thirdbase, that looks better. I had just gotten on ronaldrc's case about his units, and this one threw me. I would think however that the SEER ought to be included as a parameter unless it is thought that wiring and OCP should be sized for a minimum SEER.
BTW, shouldn't it read, 0.239 VAH/BTU? Too many "hours"!
[ February 27, 2005, 09:47 PM: Message edited by: rattus ]
Re: Tons to amps
You do need to be careful when applying the 1.5kva to AC loads. I have had AC units with electric heat blow my load calculation. Also, I just did a job where the AC units have "heat exchangers. Those work out to about 3.7 KVA per ton.
And one AC unit still baffles me: a 5 ton unit has 208V 3 phase and 36 amps. That works out to 2.6KVA per ton. But it has an option called a "Humidi-MiZer", and I suspect that accounts for the extra 5KVA.
Rattus:
I was just wondering what you call the grey fuzzy furball?
You do need to be careful when applying the 1.5kva to AC loads. I have had AC units with electric heat blow my load calculation. Also, I just did a job where the AC units have "heat exchangers. Those work out to about 3.7 KVA per ton.
And one AC unit still baffles me: a 5 ton unit has 208V 3 phase and 36 amps. That works out to 2.6KVA per ton. But it has an option called a "Humidi-MiZer", and I suspect that accounts for the extra 5KVA.
Rattus:
I was just wondering what you call the grey fuzzy furball?
natfuelbill
Senior Member
It is not Tons to Amps but I have the following explanation on Tons to kw from Tech Resources, Inc., do you concur?
It depends on the electrtical efficiency of your heat pumps which is usually measured by an efficiency ratio. SEER (Seasonal Energy Efficiency Ratio) measures how efficiently a residential central cooling system (air conditioner or heat pump) will operate over an entire cooling season, as opposed to a single outdoor temperature. EER (Energy Efficiency Ratio) measures efficiency at a single peak operating point, usually at 95? F. Most commercial air conditioning units are rated in EER. As a general rule of thumb, the EER number is about 1 point lower than the SEER number. SEER varies depending on what region in the country the cooling system is operating in, and EER is the same value regardless of the location.
EER is calculated based on the total rated amount of cooling (in Btu) the system will provide divided by the total number of watts it will consume:
EER = Rated Cooling Output, kBtuh / Rated electrical input, kW
A 12 EER unit delivers 12 BTUs of cooling for every watt of energy consumed. This can also be thought of as 1 kW per 12,000 Btu/h, where 12,000 Btu/h is the definition of a cooling "ton". Therefore, a EER rating of 12 (inverted) equates to 1 kW/ton. A 13 EER unit consumes 0.9 kW/ton and an 10 EER unit consumes about 1.2 kW/ton.
An ENERGY STAR commercial air source heat pump today has a minimum national standard of 9 EER, but a recommended level of 11 EER with 12 EER as "best available". A 12 year old commercial air source heat pump would probably have an EER between 8 and 10. For 3 ton units, a 10 EER would consume 3.6 kW, and the 8 EER would consume 4.5 kW.
kW/ton = 1 kW/ton * (12 EER ? Rated EER)
It depends on the electrtical efficiency of your heat pumps which is usually measured by an efficiency ratio. SEER (Seasonal Energy Efficiency Ratio) measures how efficiently a residential central cooling system (air conditioner or heat pump) will operate over an entire cooling season, as opposed to a single outdoor temperature. EER (Energy Efficiency Ratio) measures efficiency at a single peak operating point, usually at 95? F. Most commercial air conditioning units are rated in EER. As a general rule of thumb, the EER number is about 1 point lower than the SEER number. SEER varies depending on what region in the country the cooling system is operating in, and EER is the same value regardless of the location.
EER is calculated based on the total rated amount of cooling (in Btu) the system will provide divided by the total number of watts it will consume:
EER = Rated Cooling Output, kBtuh / Rated electrical input, kW
A 12 EER unit delivers 12 BTUs of cooling for every watt of energy consumed. This can also be thought of as 1 kW per 12,000 Btu/h, where 12,000 Btu/h is the definition of a cooling "ton". Therefore, a EER rating of 12 (inverted) equates to 1 kW/ton. A 13 EER unit consumes 0.9 kW/ton and an 10 EER unit consumes about 1.2 kW/ton.
An ENERGY STAR commercial air source heat pump today has a minimum national standard of 9 EER, but a recommended level of 11 EER with 12 EER as "best available". A 12 year old commercial air source heat pump would probably have an EER between 8 and 10. For 3 ton units, a 10 EER would consume 3.6 kW, and the 8 EER would consume 4.5 kW.
kW/ton = 1 kW/ton * (12 EER ? Rated EER)
- Location
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Standard compressors don't...scrol compressors do, and most of them do not come with a phase reversal relay.
Don
jwelectric
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- North Carolina
With this cooling unit we need not worry about the amperes we need only worry how strong the arm is.
Tons to Amps
Tons to Amps
Well, the correct way to do this is to consult the manufacturer's data sheet! If you are dealing with a new unit, you presumable have design data. For an existing unit, it presumably has a nameplate.
If you really need a rule of thumb: A large, new chiller will be down in the 0.5-0.7KVA/Ton range for a real high efficiency unit. A Window-shaker might come in at 1.8 or even 2 KVA/Ton. A run-of the mill rooftop unit or old chiller will run 1.2 to 1.5 KVA/Ton. We used to use 1.2KVA/Ton for rough estimating purposes if we didn't have any nameplate data yet, say for a budget square foot estimate.
--Lawrence Lile, P.E.
Tons to Amps
ronaldrc said:Another way
One ton of frig.=12000 BTU
1 watt=3.412 BTU
4 tons x 12,000=48,000 BTU
48,000/3.412=14,068 watts
14,068/208 volts=67.63 amps.
Ronald
Well, the correct way to do this is to consult the manufacturer's data sheet! If you are dealing with a new unit, you presumable have design data. For an existing unit, it presumably has a nameplate.
If you really need a rule of thumb: A large, new chiller will be down in the 0.5-0.7KVA/Ton range for a real high efficiency unit. A Window-shaker might come in at 1.8 or even 2 KVA/Ton. A run-of the mill rooftop unit or old chiller will run 1.2 to 1.5 KVA/Ton. We used to use 1.2KVA/Ton for rough estimating purposes if we didn't have any nameplate data yet, say for a budget square foot estimate.
--Lawrence Lile, P.E.
According to this site http://www.onlineconversion.com/power.htm
1 ton of refrigeration = 3 516.852 84 watt
1 ton of refrigeration = 3 516.852 84 watt
Bob NH
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"According to this site http://www.onlineconversion.com/power.htm
1 ton of refrigeration = 3 516.852 84 watt"
The reason that one ton of air conditioning is related to power is that the definition of one ton of refrigeration is not 12,000 BTUs; it is 12,000 BTUs per hour.
One ton comes from the fact that one ton of ice melting in one day corresponds to 2000 pounds x 144 BTU per pound = 288,000 BTU per day = 12,000 BTU per hour. The latent heat of fusion (melting) of ice is 144 BTU per pound.
The equivalence of 1 ton of refrigeration (12,000 BTU/hour) to 3516.85284 Watts is simply the result (12,000 BTU/hour)/3412.14 BTU/kWhr. That isn't talking about work; it is about energy equivalence.
An air conditioner with a SEER of 12 would requre 1 kW per ton if it were always operating at the seasonal average conditions. Since it is not always operating at those conditions, it is probably reasonable to estimate at about 1.5 kW per ton; then look at the specs or the nameplate.
HEAT PUMPS: A heat pump with a SEER of 2 will use 1 kW of electricity (3412 BTUs) to extract another 3412 BTUs from its heat source such as outside air, and discharge 6824 BTUs (the sum of the electrical + outside heat) to the heated space. Therefore, you get twice as many BTUs in the room per kWhr used as you would get from a resistance heater.
Since heat pumps don't work well below freezing, they usually add resistance heaters to add heat and keep the ice from forming on the evaporator coils. That resistance heating often requires more power than the compressor and fans.
1 ton of refrigeration = 3 516.852 84 watt"
The reason that one ton of air conditioning is related to power is that the definition of one ton of refrigeration is not 12,000 BTUs; it is 12,000 BTUs per hour.
One ton comes from the fact that one ton of ice melting in one day corresponds to 2000 pounds x 144 BTU per pound = 288,000 BTU per day = 12,000 BTU per hour. The latent heat of fusion (melting) of ice is 144 BTU per pound.
The equivalence of 1 ton of refrigeration (12,000 BTU/hour) to 3516.85284 Watts is simply the result (12,000 BTU/hour)/3412.14 BTU/kWhr. That isn't talking about work; it is about energy equivalence.
An air conditioner with a SEER of 12 would requre 1 kW per ton if it were always operating at the seasonal average conditions. Since it is not always operating at those conditions, it is probably reasonable to estimate at about 1.5 kW per ton; then look at the specs or the nameplate.
HEAT PUMPS: A heat pump with a SEER of 2 will use 1 kW of electricity (3412 BTUs) to extract another 3412 BTUs from its heat source such as outside air, and discharge 6824 BTUs (the sum of the electrical + outside heat) to the heated space. Therefore, you get twice as many BTUs in the room per kWhr used as you would get from a resistance heater.
Since heat pumps don't work well below freezing, they usually add resistance heaters to add heat and keep the ice from forming on the evaporator coils. That resistance heating often requires more power than the compressor and fans.
Minuteman
Senior Member
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Hold the bus!
Hold the bus!
Whoa - wait a minute. A ton of refrigeration represents the heat energy absorbed when a ton of ice melts during a 24-hour period. And a BTU is the amount of energy necessary to raise the temperature of one pound of water, one degree Celsius.
Having said that, you can't convert 12000 BTU's into motor amperage because most motor are 60% - 70% efficient. (I use 65% for most calculations)
But, single phase A/C units need 1 HP per Ton. One Horse Power is 746 watts.
So, 746 watts x 160% eff = 1230.9 watts needed to produce 1 HP of work. So, for the 4 Ton A/C unit that the OP asked about, we need a 4 HP compressor motor.
4 x 746 x 165% = 4923.6 watts and 4923.6 / 208 volts = 23.67 amps for the compressor motor Then we have the fan motor.
I believe most condenser fan motor are about 1/3 - 1/2 HP on a one ton. So I think a 4 ton would have about a 1 1/2 HP motor (I am guessing)
1.5 x 746 x 165% = 1846.35 watts and 1846.35 / 208 = 8.87 amps for the fan motor.
23.67 + 8.87 = 32.54 full load amps.
Edit: Had to get my facts strait
Hold the bus!
Whoa - wait a minute. A ton of refrigeration represents the heat energy absorbed when a ton of ice melts during a 24-hour period. And a BTU is the amount of energy necessary to raise the temperature of one pound of water, one degree Celsius.
Having said that, you can't convert 12000 BTU's into motor amperage because most motor are 60% - 70% efficient. (I use 65% for most calculations)
But, single phase A/C units need 1 HP per Ton. One Horse Power is 746 watts.
So, 746 watts x 160% eff = 1230.9 watts needed to produce 1 HP of work. So, for the 4 Ton A/C unit that the OP asked about, we need a 4 HP compressor motor.
4 x 746 x 165% = 4923.6 watts and 4923.6 / 208 volts = 23.67 amps for the compressor motor Then we have the fan motor.
I believe most condenser fan motor are about 1/3 - 1/2 HP on a one ton. So I think a 4 ton would have about a 1 1/2 HP motor (I am guessing)
1.5 x 746 x 165% = 1846.35 watts and 1846.35 / 208 = 8.87 amps for the fan motor.
23.67 + 8.87 = 32.54 full load amps.
Edit: Had to get my facts strait
Last edited:
Minuteman
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Thanks Steve, I was almost right.
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