Patent US 4,742,865

A method is provided to control an energy recovery system to achieve an increase of the statistical average system recovery efficiency. The system includes at least one fluid accumulator tank (6, 20, 30) and at least one heat exchanger (10, 25) for waste process fluid or gas. According to the invention the flows through the primary or secondary side of the heat exchanger (10, 25) is at each time continuously controlled by a parameter being a function of both the actual temperature and the actual fluid volume in said accumulator tank (6, 20, 30).