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One of the traditional “weak links” that is exposed during expansion plans is the central cooling plant, which provides air conditioning for campus buildings.
At California State University, Dominguez Hills (CSUDH), where the existing central cooling plant was not able to maintain adequate comfort for the current campus, let alone allow for expansion, a solution was found. Two new, natural gas-fired absorption chillers were installed as part of a complete modernization of its central plant.
Tidal wave coming“We’re getting our central plant ready to handle what’s being called ‘Tidal Wave II’ in student enrollment,” said Steve Slimp, assistant director of physical plant at CSUDH. Planning began at CSUDH seven years ago with feasibility studies that looked at three options: direct-fired absorption, electric, and hybrid.
The university chose direct-fired absorption. At a cost of about $7.2 million — partially offset by an incentive from Southern California Gas Co. (SoCalGas) and a bond measure passed by the state in 1996 — CSUDH replaced two 1,400-ton steam turbine-driven centrifugal chillers with two l,000-ton direct-fired, double-effect McQuay (Minneapolis, MN) absorption units.
“We’re finding we have more cooling capacity, more efficiency, and less energy usage, but with double capacity,” Slimp said. “And we’re promoting an environmentally friendly policy on campus.”
The chillers simultaneously produce chilled water and hot water for all space cooling and a portion of the heat for the campus’ nine major buildings, which cover 700,000 sq ft.
“We have three buildings coming on-line over the next several years, including a new information technology building,” said Slimp. “By taking steps now to upgrade our system, we will not have to increase the size of our central plants for at least 10 years. At present, we have full redundancy and only need to operate one chiller to meet the full cooling load.”
CSUDH will celebrate its 40th anniversary next year with an enrollment of more than 12,000 students. Serving communities across the South Bay and South Los Angeles, it expects to continue growing, so it cannot afford obsolete equipment.
“Our two chiller units were in dire need of repair. The cost to change out the refrigerant to be in environmental compliance would have been high,” Slimp said. Another consideration was the existing electrical system on the campus. Since the central plant only has a 480-V system, it would have been expensive to run the necessary power to an electric chiller. Changing to a 4,160-V system was considered, but also was found to be expensive.
“I was able to justify the upgrade on an environmental basis,” Slimp said. The new units use no CFCs, but rather rely on distilled water as the refrigerant.
The absorption process operates similar to an electrical system in that it uses a cycle of evaporation and condensation of a fluid or refrigerant to produce cooling. However, instead of a CFC refrigerant, the absorption cycle uses a working fluid that is mostly water and lithium bromide in solution.
The other major difference is that the absorption cycle cooling differs from the vapor compression cycle by using heat as a thermochemical compressor rather than a motor- or engine-driven compressor.
In addition to the new chillers, other aspects of the central plant and chilled water distribution system were upgraded. The original chilled-water piping was a single-loop, constant-flow system with about 20 total miles of pipe routed to all nine of the campus’ major buildings.
Decoupling the loopThe modernization of the system decoupled the distribution loop, or secondary loop, from the primary chiller pumping loop.
With the installation of two-way control valves at each building, the new Systecom pumping package provides variable chilled water flow to the buildings and constant flow to the chillers, which should significantly reduce pumping power requirements.
A new Tower Tech cooling tower has been installed on grade adjacent to the central plant building. This cooling tower has two cells with a common sump. Since the sump water level is maintained at about eight feet above grade, it was possible to use less expensive horizontal condenser water pumps.
Since both tower fans have variable-speed motors, the tower controls can be set to optimize performance using smart technology that coordinates the operation of the cells and fans to reduce overall power requirements.
Water treatment for the chiller water loop is done using a “fully smart” automatic system that monitors the water condition and adds chemical treatment as required.
The existing plant had little in the way of automation and was primarily manually controlled. A Johnson Controls Metasys® automation system was installed about five years ago, but was controlling a very small percentage of the plant. However, with the new chillers and other upgraded systems, the Metasys system is being greatly expanded.
“The design of the plant upgrades,” according to Slimp, “was to have a plant that does not need an operator.”
The university also gets more hours of operation with the new system, without increasing the amount of natural gas consumed. “Having gone through our first summer with the new system continuously running, I can say we were able to greatly improve the environment for our students and instructors,” said Slimp.
“This project is significant, not only because it represents one of the largest natural gas cooling projects in California, but also because it illustrates a healthy, head-to-head competition between the gas and electric markets in the big-tonnage commercial air conditioning market,” said Randall Higa, senior market consultant at SoCalGas.
“An engineering consultant study, co-funded by SoCalGas and Southern California Edison, pointed to gas air conditioning as the most economical alternative for the campus’ central plant renovation project,” said Higa.