OPTIMAL-CONTROL OF AN HVAC SYSTEM USING COLD-STORAGE AND BUILDING THERMAL CAPACITANCE

This paper presents a comprehensive analysis on the optimal control protocol to minimize the daily operating cost of an air-conditioning system in a 33 600 m(2) office building. The system consists of two chillers, one designated for cold storage charging, the other for direct cooling, an air-handling unit, a cooling tower, and water pumps. This analysis determines the optimal protocol for indoor temperature and humidity control as well as operating point settings for the chiller control considering two thermal storage sources: (i) the thermal capacitance of the building, and (ii) a cold storage facility. The analysis is based on the thermodynamic modeling of the air-conditioning system including the thermal response of the building structure. A discussion of operating cost savings is presented for several outdoor conditions and electricity rates. Furthermore, the load shift potentials are discussed for each storage source. The results of this analysis indicate significant savings can be achieved by precooling the building during hours of low electricity rates. The resulting load shifting can be augmented by utilizing cold storage equipment. The results are discussed in detail for Seattle climatic conditions and electric rates. A regional comparison of the results for the four US locations, Seattle, WA; Phoenix, AZ; San Diego, CA; and the island of Hawaii, is given.