VICKSBURG, Miss. - The U.S. Army Engineer Research and Development Center (ERDC) is supporting Army installations as they seek to reach net zero energy requirements. At the same time, ERDC’s laboratories are also working toward reducing energy consumption. To test new energy planning software jointly developed by the Construction Engineering Research Laboratory (CERL) and the Information Technology Laboratory (ITL), ERDC launched a study of ITL’s facilities. ITL, located in Vicksburg, Miss., is ERDC’s largest energy consumer.
Energy Planning Tool
Installation-scale energy planning is a difficult, highly coupled problem; incremental projects that are individually optimal are not necessarily part of the most strategic master plan. It requires simultaneous analysis of hourly heating, cooling, and electric loads, a firm grasp of the possible utility rate structures, and robust cost and performance models of existing and potential energy conversion and energy storage equipment. To meet these challenges, CERL and ITL developed the “Net Zero Planner” software, which suggests energy solutions at the installation scale that comply with legislative or mission requirements. The tool automatically examines non-intuitive solutions while providing faster turn-around than manual, expert analysis.
Using “Net Zero Planner” at ITL
ITL consumes roughly 40,500 megawatt-hours per year, about half of the consumption at ERDC’s Vicksburg campus. ITL’s site includes 70,000 square feet of office space, the 10,000 sf Joint Computing Facility, and the 10,000 sf High-Performance Computing Center. The HPC, with its high supercomputing and associated cooling loads, consumes half of the electricity at ITL. These loads are likely to grow quickly as processor density increases. As such, the planning scenario assumed 10 times the current HPC computing load and a corresponding increase in cooling, pump, and blower requirements. With the almost entirely fixed, 24/7 load, the daily load profile was initially thought of as flat..
Since energy security is a dominant planning goal, and since uninterruptable information technology loads are increasing, more on-site generation could offset the cost of additional backup diesel generators, but the heating load alone is too small to justify cogeneration. The cooling and electric loads are well matched, however, prompting investigation of cogeneration with recovered heat driving absorption chillers. Net Zero Planner was used to examine this issue while incorporating all of the characteristics and constraints discussed.
The optimization algorithm examined combinations of many options for natural gas reciprocating and turbine engines, chilled water storage, and absorption and electric chillers. It determined that any possible cogeneration scheme was not life-cycle cost optimal. The best solution made use of high first cost, high-efficiency, electric mag-lev chillers, an outcome that validated recent decisions at ITL. Surprisingly, given the mostly flat cooling demand profile, the optimum also included a small amount of chilled water storage. On closer inspection it was clear that, given the daily variation in load for the office portion of the cooling, a small amount of storage could defer the purchase of an additional chiller. Since the load profile was formerly thought of as “flat,” this result would not have been considered in a purely manual analysis.
To validate the Phase I optimization results, ERDC performed manual analysis for several combinations of absorption chillers and on-site natural gas generators, as well as for the grid-powered, highly efficient electric chillers. This analysis arrived at an energy solution similar to that of the Net Zero Planner, but with a slightly higher cost due to its failure to examine every possible combination.
Phase II dug deeper into the chilled water storage issue. This study used isolated HPC loads and changed the rate structure from the blended rate that ITL is billed to the marginal rate plus demand charge that ERDC pays, allowing for even more chilled water storage opportunities. Despite the fact that ITL’s load profile is very nearly flat, it shares a substation with the rest of the campus and a large portion of its electric load can be inexpensively “stored” as chilled water; that is, it has a major opportunity to offset the peak loads from the rest of ERDC’s facilities by delaying chiller operation. When Net Zero Planner was run with the more sophisticated utility structure, it recommended chilled water storage twice as large as in Phase I.
Another interesting outcome of Phase II was a result of the new redundancy constraint enforced; due to HPC’s reliability requirements, the optimization was constrained to specify solutions with chilled water capacity 25% in excess of the peak. Without tedious, manual analysis of specific combinations, the algorithm was able to determine that maintaining, but not regularly dispatching, three of the existing air-cooled chillers and decommissioning the remaining one, rather than over-sizing new chillers, provided this redundant capacity at the lowest life-cycle cost.
Both phases validated ITL’s current plan to switch to highly efficient chillers, and manual analysis using well established techniques verified optimization outputs. In addition, the unique capabilities of the optimization revealed that the true life-cycle cost optimum includes some unexpected increases in chilled water storage.
Net Zero Planner 1.0 was released in September of 2013. It has been demonstrated at Fort Leonard-Wood, West Point Military Academy, and Portsmouth Naval Shipyard, Waterways Experiment station, and Fort Hunter Liggett.