Modeling and Assessment of ice Storage for Air Conditioning 1999-01-2719
A characteristic of any electric or thermal storage technology is that it is easy to qualitatively describe the benefits, but it is very difficult to quantify the benefit and how a storage system should be best operated since operation is both site specific and requires forecasts of future electric, heating or cooling demand. Ice storage has the advantage of being able to absorb or release heat at a constant temperature of 32 F by using the abundant mass of water as the storage medium. There is no comparable substance that is available for constant temperature storage of space heat. Thus heat storage is typically done much less effectively by sensible heating or cooling of water. Thus, storing cold is more practical than strong heat. Thus, ice for air con-ditioning has been installed at several locations and has been proposed for the expansion of the chiller capacity at Union College to meet the increased demand from two new buildings. The purpose of this project was to research ice storage techniques that are available and operating options and then to develop a model and methodology for evaluation. The mathematical model was developed of the cooling supply in terms of chilled water and cooling tower temperatures, storage and building load requirements. Hourly data of temperatures and demand were obtained from the central process computer that controls the heating, ventilation and air conditioning equipment and the temperatures and ventilation in the buildings throughout the campus. The resulting model and data was then used to evaluate the hourly electric power demand and cost for air condition-ing for three defined cases. One case was with no storage, the second case was with storage and constant operation of the central chillers and the third case was with the chillers operating at four times the average demand for six hours each night when the electric power rates may be lower. The operating cost, required chiller and ice mass versus time was calculated for each of these cases and will be presented in this paper.