why isn't heat energy usable?

Answer 1

Heat energy is usable as long as you have a relatively cold reservior to do work on. If everything is hot and at the same temperature, you won't be able to transfer any energy.

Example: You can use heat to increase the volume of gases to do work. But if the gas is already hot, you cannot heat it further unless your heat source is (relative to the gas) hotter.

Answer 2

Heat Energy is useable in areas where the climate
is cold to mild. If the climate is hot, probably the last thing you want is more heat, so it is usually vented into the atmosphere.

One way to use heat energy is to heat water for miscellaneous household purposes by making use of a heat exchanger.

If you had lots and lots of heat energy, and a suitable water source, you might use the heat to make steam to drive an electric generator or well water pumping system.

Answer 3

Any time you have a temperature difference between two systems you can use the heat flow from one system to the other to do work. So, heat energy is useful and is how most engines work. This process can never be more efficient than the Carnot efficiency - is this what you mean?

Answer 4

Heat energy is used in many ways, for example a nuclear reactor works by heating up water and turning it into steam which when pressurized turns turbines which produce electricity. Coal fired plants do the same thing by burning coal and using that heat energy to heat water.

Answer 5

It is usable, how do you think the energy in a piston is used to propel a car.

Answer 6

it's usually lost into the atmosphere so unless you have some sort of recovery system there's not much you can do.