ton to horsepower

[Alwayslearningelec]

Is there a rough conversion when converting motor in tons to hp. Someone I work with said 1 ton equals about 1.5hp. THanks.

 

[cowboyjwc]

I think there is a way, though I've never figured it out, but I would think with the new higher efficiancy motors that the 1 ton=1.5 HP isn't really true anymore.

 

[infinity]

I don't think that you'll find a conversion that actually works. Given different SEER ratings of equipment the ratio can vary. Here's a photo of the nameplate of a 3 ton unit. The compressor motor is 17.9 RLA which is about 3 HP @ 230 volts. The second photo is from a 4 ton unit. If you look closely you'll see that the compressor motors are almost the same size. (17.9 vs. 19.9)

 

[charlie b]

• One ton equates to 12,000 BTU/Hr
• One watt equates to 3.412 BTU/HR
• One horsepower equates to 746 watts
• Divide 12,000 by 3.412, and divide again by 746, and I get one ton equals 4.7 horsepower.

Do keep in mind that this is a pure unit conversion. If you are looking for the size(s) of the motor(s) that would be associated with a cooling system with a capacity of one ton, that is a different matter entirely.

 

[Alwayslearningelec]

• One ton equates to 12,000 BTU/Hr
• One watt equates to 3.412 BTU/HR
• One horsepower equates to 746 watts
• Divide 12,000 by 3.412, and divide again by 746, and I get one ton equals 4.7 horsepower.

Do keep in mind that this is a pure unit conversion. If you are looking for the size(s) of the motor(s) that would be associated with a cooling system with a capacity of one ton, that is a different matter entirely.

Thanks Charlie . What do is the difference between the two?

 

[kwired]

Thanks Charlie . What do is the difference between the two?

The difference is the efficiency factor. With no losses the conversion factors would be true all the time.

If you know how many ton the unit is and what the efficiency is you should be able to get a lot closer with horsepower, remember that will be horsepower of the motor at full load rating.

 

[Alwayslearningelec]

The difference is the efficiency factor. With no losses the conversion factors would be true all the time.

If you know how many ton the unit is and what the efficiency is you should be able to get a lot closer with horsepower, remember that will be horsepower of the motor at full load rating.

When he says " size of motor associated with cooling system would be completely different" that's what I'm rferring to. Thanks

 

[jumper]

When he says " size of motor associated with cooling system would be completely different" that's what I'm rferring to. Thanks

Are you talking about a compressor or a fan motor?

 

[Alwayslearningelec]

Are you talking about a compressor or a fan motor?

Ok so is this how works. An HVAC peice of equipment will have either a fan motor or compressor? What about a pump? THat is just a motor. Anyway, how do you figure/convert for a compressor and a motor? THanks Jumper

 

[renosteinke]

I don't know; just how much does a horse weigh? Are we talking Shetland ponies or Clydesdales?

 

[al hildenbrand]

Anyway, how do you figure/convert for a compressor and a motor?

Horsegoer, regrettably there isn't an single answer to your question.

Start with Charlie B's answer, above. That is the theoretical, "calculated" answer. It is absolutely accurate, but hidden behind the simplicity of it is a huge assumption. The theoretical answer "assumes" that the motors are 100% efficient (no windage, bearing loss, hysteresis, resistance in wires, reactive impedance, etc), and that the refrigeration cycle is also 100% efficient.

So, a theoretical motor uses 746 Watts to deliver 1 Horsepower, but a "real world" motor will have to have around 1000 Watts to make up for the losses, as well, before a "real" usable 1 Horsepower is delivered to the turning shaft. Some types of motors can be made that use less than 1000 Watts to make a real world HP, other types of motors may need more than 1000 Watts.

The refrigeration cycle is similar, but it is more widely varied. The variation from one piece of HVAC equipment to the next is shown by the SEER rating. The larger the number that is given as the SEER, the more efficient the refrigeration cycle is, so the piece of HVAC equipment can deliver One Ton of cooling with fewer Watts of electricity.

To be clear, a Ton, in refrigeration, is the amount of cooling required to take a ton of liquid water that is at 32 degrees Fahrenheit, and turn it into a ton of ice at 32 degrees Fahrenheit. For water to go from liquid to solid, at the freezing temperature, a chunk of heat has to be pulled out of the water. This, at least, is fixed. The amount of heat removed from the freezing water is something that is a fixed amount. The machine that moves the heat, however, is going to be better than some but less efficient than other machines.

So, I'll guess that you want to size your wiring for a piece of HVAC equipment. Regrettably, the cost competitive answer (avoiding oversizing your wiring) requires that you get the nameplate information of the specific HVAC unit that will be wired, because the current required from one model to the next can vary a lot.

 

[GeorgeB]

When he says " size of motor associated with cooling system would be completely different" that's what I'm referring to. Thanks

Charlie is way ahead of me in intelligence, but the CONVERSION is about energy equivalence. When we run an HVAC system, whether cooling (one direction) or heat pump (both directions), we MOVE energy from one location to another. The power to do that varies with many things, one of which relates to source and sink temperatures, another to efficiencies. The SEER (Seasonal Energy Efficiency Ratio) makes lots of assumptions for these to come up with a number such that systems may be compared.

The (horse)power of the (compressor, a/k/a condenser) motor may be approximated by electricity consumption rate (if single phase, V*A*pf*eff) and the 746 Watts/hp. It will be larger for a lower SEER unit, all other considerations ignored.

If we were "creating" the energy (whether adding or removing heat), the conversion factors by Charlie apply. Resistance heat is exactly that; I know of no simple equivalent for cooling ... we would be talking about "negative" energy, I think.

 

[Alwayslearningelec]

Thanks a lot guys, I really appreciate the insight.

 

[charlie b]

I just had a long chat with my mechanical engineering colleague. It took a bit to work out the physics of the situation, but in the end it turned out that I had had the right general idea. So here is what I meant, when I said that a simple unit conversion will not tell you what sizes of motors will be needed, as the key components of a 1 ton air conditioning system.

In an immersion heater (think electric tea pot), all of the electrical energy is used up in causing cold water to become hot water. In an electric baseboard heater, all of the electrical energy is used up in causing the heating element to become hot, allowing it to transfer heat to the surrounding air.

But in an air conditioning system, the role of the electric motors is to move fluids from one location to another. They are not directly involved in causing a hot thing to become cold, or a cold thing to become hot. You have fans blowing air across an evaporator and across a condenser, and this is what moves the heat from one location (e.g., your living room) to another location (e.g., the outside world). So a very little amount of horsepower can physically relocate a significant amount of heat.

This process would not work, without the services of a much larger motor (the compressor). The rule of thumb that the ME remembers is that one ton of cooling equates to approximately one horsepower (not far off from the OP?s 1.5 HP). But what that rule of thumb refers to is the size of the compressor needed to support the overall cooling process.

Thus, if you had a 100 ton cooling system, you would need a compressor motor of about 100 HP, along with a pair of fan motors of about 3 HP each. The three motors add up to only 106 HP for a 100 ton system, whereas the HP equivalent (i.e., unit conversion, like feet to inches, or like ounces to pounds) of 100 tons is 417 HP. How can there be such a discrepancy (106 HP versus 417 HP)? Well it is not because of motor efficiencies. It is because the electrical energy is used by the motors to move fluids, not to change the temperature of fluids. The function of the entire cooling system is not so much to change the temperature of air, but to physically move heat energy from one location to another.