An Inexpensive Retrofit Technology for Reducing Peak Power Demand in Small and Medium Commercial Buildings

This article describes a low cost retrofit technology that uses collective control of multiple rooftop air conditioning units to reduce the peak power consumption of small and medium commercial buildings. The proposed control uses a thermal model of the building and air conditioning units to select an operating schedule for the air conditioning units that maintains a temperature set point subject to a constraint on the number of units that may operate simultaneously. A prototype of this new control system was built and deployed in a large gymnasium to coordinate four rooftop air conditioning units. Based on data collected while operating this prototype, we estimate that the cost savings achieved by reducing peak power consumption is sufficient to repay the cost of the proto-type within a year. Moreover, it is possible to reduce the cost of this proto-type technology by a factor of at least six and thereby create a retrofit package that pays for itself within two months of operation.