A Method to Determine the Optimal Tank Size for a Chilled Water Storage System Under a Time-of-Use Electricity Rate Structure

In the downtown area of Austin, it is planned to build a new naturally stratified chilled water storage tank and share it among four separated chilled water plants. An underground piping system is to be established to connect these four plants together. This paper presents the method of determining the optimal tank size as well as corresponding optimal operating strategies for this project. Based on the analysis of the historical log data, utility rate structures, and equipment information, the baseline profiles of electricity fed to buildings, plant cooling load, and utility billing cost for each plant are generated. A simplified TES plus four plants model is built based on some assumptions. The results show that a 3.5 million gallon tank has the shortest payback time and the projected total capital cost is within the budget. The annual billing cost savings are $907,231 and the simple payback time is 12.5 years.