Performance Evaluation of A Stratified Chilled- Water Thermal Storage System

In countries with hot climates, air-conditioning forms a large proportion of annual peak electrical demand, requiring expansion of power plants to meet the peak demand, which goes unused most of the time. Use of well-designed cool storage can offset the peak demand to a large extent. In this study, an air conditioning system with naturally stratified storage tank was designed, constructed and tested. A new type of diffuser was designed and used in this study. Factors that influence the performance of chilled water storage tanks were investigated. The results indicated that stratified storage tank consistently stratified well without any physical barrier. Investigation also showed that storage efficiency decreased with increasing flow rate due to increased mixing of warm and chilled water. Diffuser design and layout primarily affected the mixing near the inlet diffuser and the extent of this mixing had primary influence on the shape of the thermocline. The heat conduction through tank walls and through the thermocline caused widening of mixed volume. Thermal efficiency of stratified storage tanks was as high as 90 percent, which indicates that stratified tanks can effectively be used as a load management technique.

Authors:

• M. A. Karim

Keywords:

• Cool Thermal Storage
• Diffuser
• Natural Stratification
• Efficiency Improvement
• Load management.

References:

[1] Karim, M. A, Musa, M. N and Ghazali, N. M. Design procedure of
stratified chilled water storage air-conditioning system. Malaysian
Science and Technology Congress, 1995, pp. 212-220.
[2] Guyer, E.C. and Brownell D.L. Review of heat storage materials. EPRI
report, EPRI, EM-3353, December 1983.
[3] Wildin, N.W., and Truman, C.R., Evaluation of stratified chilled water
storage techniques. EPRI report, EPRI, EM-4352, December 1985.
[4] Wildin, M.W., and Truman, C.R. Performance of Stratified Vertical
Cylindrical Thermal Storage Tanks, Part I: Scale Model Tank. ASHRAE
Technical Data Bulletin 1989; 5 (3).
[5] Dorgan, C. E. and Elleson, J. S. Design guide for cool thermal storage,
American Society of Heating, Refrigerating and Air-Conditioning
Engineers, ASHRAE, Atlanta, Ga. 1994.
[6] Hudson, H.E, Uhleer, R. B and Bailey, R. W. Dividing flow manifolds
with square edged laterals. Journal of Environmental Engineering
Division, ASCE, vol. EE4 (August): 745-755.
[7] Baines, W. D., Martin, W. W, and Sinclair, L. A. On the design of
stratified water thermal storage tanks. ASHRAE Transactions 1982; 88
(2): 426-439.
[8] Cole, R. L., and Bellinger, F. O. Thermally stratified tanks. ASHRAE
Transactions. 1982; 88 (2):1005-1017.
[9] Gross, R.J. An Experimental Study of Single Medium Thermocline
Thermal Energy Storage, ASME paper 82-HT-53;1982.
[10] Yoo, J., Wildin, M. W., and Truman, C. R. Initial Formation of a
Thermocline in Simplified Storage Tanks. ASHRAE Transactions. 1986;
92 (2): 280-292.
[11] Mackie, E. I and Reeves, G. Stratified Chilled-Water Storage Design
Guide, EPRI, Final report, EPRI, Pleasant Hill, CA. 1988.