Quote:
Originally Posted by bernard
Thank you bmxeroh,
I am not interested in knowing why do these two values differ, but how they can be compared (without interfering with costs).
Indeed watt is watt.
But upper "4" is 4 kWh of electric energy.
While upper "5" is 5 kWh of thermal (?) energy.
These two can not be compared, as they are different types of energy.
Or did I get this wrong?
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Those two can be directly compared. They are essentially defined amounts of heat energy. Btu's are also a raw amount of heat. As with all physical systems, the heat you put in is greater than what you get out. No matter what, some will be lost.
For example, the transformer that feeds your house might be 99% efficient. For every 99 kWh of energy that flows through your meter, 1 kwh is lost at the pole transformer. This value can be directly converted into btu. In the same sense, a gas furnace may be 80% efficient. For every 80 btu of usable heat, 20 btu is lost as waste heat, mainly up the chimney.
I believe your questions lie within the bulk value of raw energy and the relationship with time and rate. A watt is a rate (joules per second), as is horsepower. This translates directly to units like lbf/sec, btu/sec, kcal/min, etc. The raw heat value is determined by multiplying by time to get watt-hours or kWh. A definite number of kWh equals a converted number of btu, kcal, joules, foot-pounds, etc. This conversion of energy between forms (electrical, thermal, mechanical, chemical, nuclear, etc.) is one of the gears that drives science. It is a well-travelled path. Power is a rate, energy is a bulk quantity.
Did I completely miss the point here?