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Power gets messy because horsepower has several definitions. Mechanical horsepower, 745.6998716 W, is the one quoted on car specifications, and it descends from James Watt's estimate of what a draft horse could lift per minute. Metric horsepower, or PS, is smaller at about 735.5 W, and electric horsepower is 746 W. The gaps are small enough to ignore in conversation and large enough to matter in a specification.
Air conditioning is sold in a different unit again. One refrigeration ton is 3,516.85 W, which is 12,000 BTU/h, and it is not a weight - it is the rate at which a ton of ice would have to melt in a day. A 3-ton air conditioner therefore delivers about 10.5 kW of cooling.
| W | kW | MW | hp | BTU/h | TR | |
|---|---|---|---|---|---|---|
| 1 W | 1 | 0.001 | 1.0000e-06 | 0.001341 | 3.412142 | 0.000284 |
| 1 kW | 1000 | 1 | 0.001 | 1.341022 | 3412.141633 | 0.284345 |
| 1 MW | 1.0000e+06 | 1000 | 1 | 1341.02209 | 3.4121e+06 | 284.345164 |
| 1 hp | 745.699872 | 0.7457 | 0.000746 | 1 | 2544.433578 | 0.212036 |
| 1 BTU/h | 0.293071 | 0.000293 | 2.9307e-07 | 0.000393 | 1 | 8.3333e-05 |
| 1 TR | 3516.8525 | 3.516853 | 0.003517 | 4.716177 | 11999.998833 | 1 |
How many watts is one horsepower? 745.6998716 W for mechanical horsepower, the figure used for cars and machinery. Metric horsepower, or PS, is about 735.5 W, roughly 1.4% less, which is why a European and an American rating of the same engine can differ slightly.
How many BTU per hour are in a ton of refrigeration? 12,000, which makes one refrigeration ton 3,516.85 W. It is the unit North American air conditioners are sized in, so a 3-ton unit is a 36,000 BTU/h unit.
How many watts are in a kilowatt? 1,000 by definition. A kilowatt is also about 1.34 mechanical horsepower, which is why a 100 kW electric motor is roughly a 134 hp engine.
What is the difference between kW and kWh? kW is power, the rate at which energy is used; kWh is energy, the total amount used. A 2 kW heater running for three hours uses 6 kWh - and that is the number that appears on the electricity bill.