Optimizing the Mass Flow and Temperature Difference in a Cooling System for Energy Conservation

Abstract

Conventional wisdom in recent times has been to raise the chilled water temperature to conserve chiller power. This is an effective and well-proven conservation strategy; however, it may be less optimal than other available alternatives. Reducing the fan speed and therefore the amount of circulating air in most cases is more energy efficient than raising the chilled water temperature. Either alternative is viable only if the system was originally over-designed or the refrigeration load has been reduced by alteration such as reduced illumination. The removal of energy from a space or product is typically the function of a mass flow times a temperature difference. To reduce the rate of heat removal either the mass flow rate or temperature difference I can be diminished. In most applications, greater energy savings are associated with reducing the mass flow rate. This is the result of the inefficiency associated with fans and pumps compared with the relatively good efficiency (C.O.P.) of a chiller. This paper develops an optimization strategy for specifying the mass rate and temperature difference for given heat loads to minimize energy consumption.