Consider a heat engine working between two temperatures "T"H and "T"a. With "T"a we have ambient temperature in mind, but, in principle it may also be some other low temperature. The heat engine is in thermal contact with two heat reservoirs which are supposed to have a very large heat capacity so that their temperatures do not change significantly if heat "Q"H is removed from the hot reservoir and "Q"a is added to the lower reservoir. Under normal operation "T"H > "T"a and "Q"H, "Q"a, and "W" are all positive.