In most Army installations, the electrical demand charge equals more than one-third of the total electrical utility bill. For many installations, the demand portion is as high as 50 percent of the total bill (Sohn and Cler 1989). One effective way to reduce peak electrical demand and thereby to reduce electrical utility costs is through the use of storage cooling systems (Sohn 1992). Installation and use of chilled water storage systems as a way to meet cooling needs and reduce energy costs are well documented. An industry-wide design guide for storage cooling systems has been published by the American Society of Heating, Refrigerating, and Air Conditioning Engineers (ASHRAE 1993). The U.S. Army Corps of Engineers published a guide specification for military construction of storage cooling systems in 1996 (CEGS-15848; HQUSACE 1996).
A detailed analysis of end-use of electricity at Fort Hood, TX showed that cooling is responsible for 54 percent of the total peak demand of electricity (Akbari and Konopacki 1995). Fort Jackson is typical among Army installations, where summertime air conditioning accounts for a significant portion of electrical utility bills. During calendar year 1989 (CY89), the yearly electrical utility cost for Fort Jackson was $4.5M, the demand charge was $2.2M (49 percent), and the energy charge was $2.3M (51 percent). The demand portion of the bill, as well as the total cost of the electrical utility cost, kept on growing in the following years. By CY96, the demand charge was $2.7M, or 51 percent of the total electrical bill of $5.3M.
To curb the anticipated growing cost of the electrical utility at Fort Jackson, the engineers at Directorate of Public Works (DPW), Fort Jackson, decided in early 1990 to install a chilled water storage (CWS) cooling system for the Energy Plant No. 2, which serves more than half of the Fort's cooling load. The U.S. Army Corps of Engineers Construction Engineering Research Laboratories (CERL) conducted a feasibility study in 1990. The results showed a simple payback of a CWS cooling system less than 5 years (Sohn 1990). Based on the results of the study, the Army Energy Conservation Investment Program (ECIP) funded the project in fiscal year 1993 (FY93). The South Carolina Electric and Gas Company offered an incentive program for the thermal storage at Fort Jackson at a rate of $300/kW deferred (Memorandum of Understanding [MOU] 1995). The one-time incentive award shortened the system payback time to less than the time predicted in the earlier feasibility study.
The objectives of this study were: (1) to document the design, construction, and operational performance of a CWS cooling system at Fort Jackson, SC, (2) to provide a design, construction, and operation reference on CWS cooling systems for Army engineers, and as a result, (3) to assist Fort Jackson DPW engineers to further improve system operation.
A description of the project was made from the design and construction of the system to the operation and performance analysis up to the second year of operation. The system's economic performance was analyzed using monthly electrical utility bills from 1994 through 1997. The system energy performance was measured by the on-site instrumentation with the EMCS system at Fort Jackson. Actual system payback period was calculated by the total project cost spent and the annual savings in the electrical utility cost as reflected in the monthly electrical bills during the first year of system operation.
A summary of this work was presented to the U.S. Army Corps of Engineers 1998 Electrical and Mechanical Engineering Training Conference (Sohn, Fuchs, and Gruber 1998). It is also recommended that the information in this report be incorporated into the Corps of Engineers guide specification on chilled water storage cooling systems. For the U.S. Army installation engineers, this report can serve as a reference for project development and implementation of chilled water storage cooling systems.
Units of Weight and Measure
U.S. standard units of measure are used throughout this report. A table of conversion factors for Standard International (SI) units is provided below.
SI Conversion Factors | ||
1 in. |
= |
25.4 mm |
1 ft |
= |
0.305 m |
1 yd |
= |
0.9144 m |
1 sq in. |
= |
6.452 cm2 |
1 sq ft |
= |
0.093 m2 |
1 sq yd |
= |
0.836 m2 |
1 cu in. |
= |
16.39 cm3 |
1 cu ft |
= |
0.028 m3 |
1 cu yd |
= |
0.764 m3 |
1 gal |
= |
3.78 L |
1 lb |
= |
0.453 kg |
1 kip |
= |
453 kg |
1 psi |
= |
6.89 kPa |
_F |
= |
(_C x 1.8) + 32 |
1 ton (cooling) |
= |
12,000 BTU/hr |