Just remembering my Muller lectures.
I can remember asking these questions a long time ago and having no answers. So here they are:
1 Horsepower = 746 W
1 W = 1 joule/sec
1 kW = 1.34 hp = 3412 BTU/hr
Energy per unit time, as mentioned, is power. Units of power in common use
are horsepower (hp) for work, Btu/hr for heat, and Watt (W) for
electricity. As you expect these units are related. It is due to
historical precedent that terms other than W are used. In the metric
system, we can express all the above in Watts.
In any case, by referring to table of conversions, you will see that one
horsepower is 746 W and 2545 Btu/hr.
To summarize:
Power can be expressed in terms of horsepower, Btu/hr, or Watts. Energy,
which is power multiplied by time, is expressed, correspondingly, in lb-ft,
BTU, and Joules.
In particular, 1 W = 1 Joule per second. I BTU=1055 Joules.
Example: You turn on a 1000 W (=1 kilowatt) electric heater for one hour.
The power of the heater is, of course, 1000 W =1.34 hp = 3412 Btu/hr.
The energy used or the heat produced is commonly referred to as one
kilowatt hour = 1000 W x 3600 seconds = 3600 kilo Joules = 3412 Btu.
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