These facts lead to further recommendations concerning energy conservation
1.It is generally unnecessary and often wasteful to convert heat into power and then back into heat again. An example of this is generating electricity at a power plant, as above, and then delivering it to buildings, where through electric resistance heaters, it is converted back to heat. As seen in the examples, only 30 BTUs of the original 100 BTUs in the fuel is used, whereas 80 BTUs would be available if the heat was used directly. There are sometimes other advantages to using electricity directly for heating (convenience, control), but the energy conservation aspects should always be considered.
2.If heat is converted into power, the remainder of the heat that cannot be converted into power should be used for heating and not wasted, if practical. This is the basis for total energy systems, to be discussed later.
Some other effects related to energy conservation, also explained in Chapter 2, are summarized here:
3.Friction causes loss of useful energy and should be minimized, especially in pipe and duct flow.
4.Rapid expansion of fluids causes loss of useful energy and should be minimized. An example where this may occur is in pressure-reducing devices.
5.Mixing of fluids at different temperatures causes loss of useful energy. This occurs in dual duct and thee-pipe systems and should be minimized.