?Budgets are tight for many smaller universities. We needed to replace two older chillers and we needed to make the right decision fast.?

  This was the situation facing Capital University in Columbus, Ohio in late 1998, according to Frederick McKinney, the superintendent of buildings and grounds. Located in the suburb of Bexley, Capital is a private liberal arts college with a total enrollment of about 4,000. It features well-maintained brick buildings with ivy-covered walls and shaded grassy walks. The buildings on campus are heated by a central plant and most are also cooled by a central chilled water plant.

    The need to replace chillers had been developing for several years. The school had previously relied on a central chilled water plant with two single-stage steam absorption chillers, one a 650-ton and the other a 750-ton. The two machines were 33 years old and approaching the end of their useful life. The school had started to evaluate replacement options and retained ThermalTech Engineering of Cincinnati, Ohio to evaluate options.

   McKinney said the university had worked with ThermalTech on mechanical engineering and energy management projects for many years. The situation suddenly became more critical when the absorption chillers failed ? with little hope of repair ? right in the middle of the 1998 cooling season. The school temporarily rented chiller capacity to get through the cooling season and asked ThermalTech to accelerate it research on chiller plant options. The goal was to have replacement capacity online in time for the 1999 cooling season.

   There were about 20 potential scenarios for equipment replacement, initially. These were narrowed down to a smaller number of practical choices based on life-cycle economics. The engineer reviewed options that would be reliable, economical and could be installed by the beginning of the next cooling season.

   McKinney adds that the university and consultant wanted a system that would be viable well into the future. ?We needed a system that would meet our needs for the next 20-25 years.? He said that the school also was planning to build a new sports complex and this would increase the amount of chilled water required in the near future. ?That was a driving force in our being sure that the new system had extra capacity.?

   Based on the life-cycle analysis and its familiarity with the university?s situation, the consultant recommended installing electric centrifugal chiller capacity. However, ThermalTech also recognized that, with the absorption chillers being removed from service, the school risked higher natural gas costs because of the potential loss of an advantageous gas rate. This rate required the use of 30% of its total gas usage during the summer months. With this in mind, ThermalTech suggested consideration be given to an engine-driven centrifugal chiller fired on natural gas to meet at least part of the cooling load.

 GAS-POWERED OPTION ATTRACTIVE

The school decided to purchase a system with two 1,000-ton centrifugal chillers and an 800-hp natural gas engine-generator set that could supply either of the chillers at full load. The system selected was a Trane gas-powered CenTraVac (GPC) chiller package consisting of two Trane Model CVHF 1,000-tone two-stage centrifugal chillers with an accompanying Waukesha Enginator rated at 560 kW at 1,800 rpm.

   The Waukesha engine is a liquid-cooled V-12 design and the Kato generator delivers electric power at 460V. ThermalTech designed the system to allow the engine to supply energy to either of the chillers through a dual transfer switch. The switch also provided positive assurance that the chiller being supplied through the engine-generators was disconnected from the utility power supply. University personnel expressed concern with the engine initially. Their comfort was established through visits to similar operating sites, and by touring Trane and Waukesha factories with Trane representatives.

   The new chiller plant design incorporated a low-flow condenser water flow feature (2 gpm/ton) to minimize tower requirements and pumping energy. The design also features variable primary pumping to reduce pumping energy. Each campus building was retrofitted with an energy delivery station to optimize chilled water flows. The Trane chiller plant control system uses a BACnet interface with the university?s existing facility management system.

   With the removal of the old absorption machines, there was ample space for the new chillers. Unlike other systems that mechanically connect the engine and chiller, with the CenTraVac-Enginator combination the engine-generator unit can be located remotely from the chiller. In this case the engine was located in an adjacent room, which was remodeled to allow it to be acoustically isolated from the rest of the chiller plant. Another advantage of the remote location is that the generator can power either chiller if one is down for maintenance. Further, it can be used to provide backup electric power generation for other buildings in the event of a power failure.

 ACOUSTICS, DEADLINE CONCERNS

Acoustics was an important consideration in the project. The chiller plant is only about 150 feet from the university?s Conservatory of Music Building. ?We were concerned about acoustics,? McKinney said. ?That?s one reason we chose to use a hospital-grade muffler on the engine. Since we?ve started up there have been zero complaints about acoustics.?

   Another one of McKinney?s concerns had been getting all the equipment delivered and installed in time for the necessary spring startup. The university did not approve proceeding with the replacement until November of 1998. ThermalTech worked with Trane to pre-purchase all of the major components and expedite deliveries. By careful planning and use of expedited equipment deliveries, the engineer and manufacturers were able to achieve a fast-track schedule and assure that both proper design and commissioning could be performed.

   As it turned out, the plant was started up on schedule April 1, 1999, and has been operating smoothly since then. The two chillers alternated running on the engine through most of the summer of 1999. At present load levels, the campus can be carried on a single chiller on even the hottest days. With the projected completion of the new Athletic Complex in 2001 and extension of chilled water service into the few campus buildings not currently cooled by the central plant, it will be necessary to use both chillers on the hottest days. Even with these additions, McKinney is confident that the university has adequate capacity for the foreseeable future.

   Energy and control specialist Rex Fisk is responsible for running the plant. He notes that an additional advantage of the new system is that ?It can bring the chilled water system down to its operating temperature of 44 degrees Fahrenheit within 20 minutes.? This compares to a matter of hours for the previous system. This is a particularly valuable feature during the spring or fall months when there is a sudden need for chilled water on a warm day, Fisk said.

   The mechanical room containing the chillers features a window that looks into the engine room. This allows visual observation of the engine and its gauges without the need to enter this separate room. Two cooling towers on the roof of the plant building serve to cool both condenser cooling water and engine jacket water.

 ENGINE OPERATION

The engine-generator for the chiller is operated during most of the summer months. This has been the advantage of using the necessary proportion of natural gas fuel that allows the university to take advantage of the low gas rate. This use pattern also assures that summer electric peak demand is minimized.

   In addition, McKinney notes that the ability to run a chiller on either natural gas or electricity places the owner in a stronger and more flexible position in the future. ?On any given day, we can decide which energy source to use. We?re less at the mercy of changing future energy supplies or prices.? McKinney said it is unknown what effect future utility deregulation will have. ?But whatever happens, we?re in a better position with a choice of energy sources.?