Optimum furnace operation and demand control

Summary

In applying demand control to a furnace shop, the preferable procedure from a furnace operational point of view would be to have the control not interfere with the furnace operation. However, in the course of carrying out its functions it has to call for changes in furnace power level, changes which may not be in keeping with optimum furnace operation. The reduction in electric power billing must be weighed against the corresponding degree of interference with plant operation and the possibility of reduced production. Higher cost, more sophisticated controls can be expected to control within a smaller “acceptable” zone and to maintain control closer to the preset demand level without exceeding it. As the controls become more costly and more sophisticated this ability to improve on the performance of the next lower cost unit becomes more limited. The worth of the control should be based, therefore, on the return on investment versus cost for the difference between that control and the next lower cost unit. A large, high power furnace shop will find economic advantage in applying digital computer controls. The small furnace shop will find that a demand meter with auxiliary controls is economically justifiable; it may also find that more costly controls cannot be justified due to their ability to provide only limited additional return on investment.