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unit conversion: ton of refrigeration to horsepower

unit conversion: ton of refrigeration to horsepower

I'm trying to find the unit conversion as mentioned above.  

Generally speaking the conversion was 12,000 btu/hr to 5.2 hp.  There was also a boiler hp conversion that was really different.

I think I should be using 1 ton refrig = 12,000 btu/hr = 5.2 hp.

Can someone verify this and if you have an idea as to why the boiler hp is a different conversion I'd be interested as well.


RE: unit conversion: ton of refrigeration to horsepower

Huh.  What I get is:

1 ton = 12000 Btu/Hr = 3517.2 Watts = 4.713048 HP.  

Keep in mind this is relative to only conversion factors and has nothing to do with actual HP=tons.  

RE: unit conversion: ton of refrigeration to horsepower

Hi MarauderX,

Thanks for your response.

I was at this website;

and I was converting 1 ton refrigeration (UK), I'm in Canada.  When I use 1 ton refrigeration (US), I get 4.7hp per ton refrig as you mention in your response.

However, I not sure that I understand your last comment about a direct conversion between hp and tons refrig.  Would you mind explaining a bit further?

Thanks again.

RE: unit conversion: ton of refrigeration to horsepower

1 motor hp = 2545 btu/hr
1 boiler hp = 33475 btu/hr

cooling tons is normally not converted to hp using 12000/2545 = 4.89.
Instead the KW compressor input is used and if desired converted to hp. The compressor does not transform elect to cooling tons. Instead the compressor is used to transfer heat from one medium (air or water) to the refrigerant and then reject the heat absorbed in cooling + the compressor heat equivalent power input to either air (air cooled condenser) or water (cooling tower or evaporative cooler). For air cooled kw/ton is approximately 1.2 so hp/ton is 0.9, say 1 hp including condenser fan input. For water cooled, kw/ton is about 0.6.

RE: unit conversion: ton of refrigeration to horsepower

Thanks lilliput1.

RE: unit conversion: ton of refrigeration to horsepower

Thanks to the both of you.

I was incorrectly thinking that the hp conversion gave me the motor hp required to turn a chiller/compressor for a given "tons of refrigeration".  I was using this logic against a household a/c unit and could see something wasn't right.

Thanks again!

RE: unit conversion: ton of refrigeration to horsepower


When I use 1.2 kw/ton and convert it to hp/ton, I do not get 0.9, which is what I read in your response dated 7/12/04.  Instead, I get 1.61 hp/ton.

The following is how I performed the conversion:

1 hp = 745.7 watts = 0.7457 kw

(1.2 kw/ton)*(1 hp/0.7457 kw) = 1.61 hp/ton

Am I missing something?

RE: unit conversion: ton of refrigeration to horsepower


The boiler horsepower is the output capacity of the boiler in kilowatts divided by 10.  ie.  A boiler that has an output of 170,000 btuh or 50 kw (170,000 * .293 / 1000) has a boiler horsepower of 5.  
The same conversion can be used for a chiller plant.  
This information can be found in the Power Engineers Act for your province.  

RE: unit conversion: ton of refrigeration to horsepower

The theoretical HP/TR values for the isentropic work of compression vary according to the refrigerant used and the evaporator/condenser temperatures at saturation. For example, data from the literature for some typical refrigerants, with the same degree of superheat at compressor's suction:

range=>      +40F/100F   +5F/85F     -30F/100F


R-11               0.63           0.94            1.81  
R-12               0.67           1.00            1.91
R-22               0.69           1.02            2.05
R-113             0.63           0.97            1.76
R-114             0.67           1.02            1.82
Actual overall compression efficiencies for small machines of around 50-65% may almost double the above figures.

RE: unit conversion: ton of refrigeration to horsepower

There is no direct conversion from TR to HP. But its TR that is the abortion, not HP.  TR is a quantity of heat moved from one place to another and can be done without Horsepower input as long as the temperature difference is in the right direction...Refrigeration only gets involved when the T_D is in the wrong idrection, so it makes sense that the bigger the contermanding TD, the more effort it takes to make a unit of move the "wrong" way...

To oversimplify:  How muach power will I expend pumping a thousand gallons of water up a hill?  Depends: How high is the hill?

RE: unit conversion: ton of refrigeration to horsepower

Can someone tell me where boiler horsepower comes from. We don't use this in the UK and I am curious to know where it first used and how/why?

Friar Tuck of Sherwood

RE: unit conversion: ton of refrigeration to horsepower


Simple answer is that it was used to match boiler steam output to steam engine power output.  An engine that produced 5 HP output needed a boiler of 5 boiler HP to keep up with it.

RE: unit conversion: ton of refrigeration to horsepower

From what I could gather from the net: "boiler horsepower" is unrelated to the above units and born in America.

The earliest such measure was simply based on the boiler's heating surface. Each 10 square feet of surface would represent 10 boiler horsepower. Because boilers varied greatly in design and efficiency, this inadequate way of rating them was quickly replaced.

The Committee of Judges in the 1876 Centennial Exhibition in Philadelphia, considering the reported results of testing boilers and engines of the time, called it "developed boiler horsepower" and defined it as the ability to turn 30 lb of water at 100oF to steam at 70 psig in one hour.

To somewhat rationalize the above value, the present one was adopted by ASME in 1884 to define the power it takes to boil 34.5 lb of water per hour at 212oF and 1 atmosphere of pressure. So defined the boiler horsepower equals 9,809.5 W (PERRY), namely 34.5*970.3 ~ 33,475 Btu/h.

Who uses it nowadays ? I guess nobody does.

RE: unit conversion: ton of refrigeration to horsepower

The way I read this question is:

How much horsepower is needed to turn the compressor per ton (12,000 BTUH, cooling) of refrigeration capacity?

The old rule of thumb is one horsepower per ton. Most modern systems do better, especially those with larger capacity. If the EER rating is known, it can be used as the number of BTUH per watt of electric power consumption.

Where did the term "ton" come from? If a ton (2000 pounds) of ice at 32F is converter to water at 32F, it will provide 12,000 BTU's of cooling per hour for 24 hours.

RE: unit conversion: ton of refrigeration to horsepower

ROT for ammonia refrigeration that I found in the literature:

For "air" condensation at about 120oF:

HP/TR = 2.1444 - 0.02668x + 0.000152x2

For "water" condensation at, say, 106oF:

HP/TR = 1.6952 - 0.02657x + 0.0001373x2

where x : evaporation temperature, oF.

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