Understanding the relationship between electric horsepower (hp) and tons of refrigeration (TR) is essential for engineers who design HVAC, refrigeration, and industrial power systems. Both units measure power, but they originate from different industries and have distinct historical contexts.
Electric horsepower (hp)
Electric horsepower is a unit of mechanical power commonly used in the United States to rate electric motors and other rotating equipment. One electric horsepower is defined as exactly \(746\,\text{W}\). It is a convenient size for many industrial applications, from pumps to compressors.
Ton of refrigeration (TR)
A ton of refrigeration represents the rate of heat removal required to melt one short ton (2000 lb) of ice at 0 °C in 24 hours. This is equivalent to \(12{,}000\,\text{Btu/h}\) or approximately \(3.517\,\text{kW}\). The TR unit is standard in the HVAC and commercial refrigeration fields.
Use hp when selecting electric motors, drives, and generators.
Use TR when sizing chillers, cooling towers, and evaporative condensers.
Converting between the two helps compare motor power to cooling capacity, especially for compressor‑driven refrigeration systems.
Horsepower (Electric) to Ton of refrigeration Conversion Reference Table
Horsepower (Electric) (hp)
Ton of refrigeration (TR)
0.1
0.0212
0.5
0.1061
1.0
0.2121
2.0
0.4242
5.0
1.0606
10.0
2.1212
20.0
4.2424
50.0
10.6061
100.0
21.2122
500.0
106.0608
1000.0
212.1216
Step‑by‑step conversion example
Convert 10 electric horsepower to tons of refrigeration using the factor \(1\,\text{hp}=0.21212164294752406\,\text{TR}\).
So a 10‑hp electric motor can theoretically drive a refrigeration load of about 2.12 TR.
The exact factor is \(1\,\text{hp}=0.21212164294752406\,\text{TR}\). This value is derived from the definitions of hp (746 W) and TR (3.517 kW) and provides a direct way to translate motor power into cooling capacity.
No. Mechanical (or shaft) horsepower is defined slightly differently (≈ 745.7 W) and is used for engines and non‑electric drives. The conversion factor above applies only to electric horsepower, which is the standard rating for electric motors.
"On fait la science avec des faits, comme on fait une maison avec des pierres ; mais une accumulation de faits n'est pas plus une science qu'un tas de pierres n'est une maison." "Science is built up of facts, as a house is built of stones; but an accumulation of facts is no more a science than a heap of stones is a house." — Henri Poincaré (French Mathematician, Theoretical Physicist & Mining Engineer)