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from the issue of September 16, 2004
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New chillers will keep us cool, even in winter
BY MATT STREFF, BUILDING SYSTEMS MAINTENANCE
Although September can still bring us some warm days, soon operators at the UNL utility plants will fire up massive boilers that produce the steam that heats UNL's campuses.
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| | | This high-efficiency water chiller, recently installed on East Campus, is one of four installed at UNL over the summer. The chillers will help keep UNL cooler year-round.
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Using this energy wisely and efficiently is one of the major concerns for UNL Facilities. Strangely, one process that has been very inefficient in the past is cooling during the winter. NUCorp, the Nebraska Utilities Corp., is fixing this problem by installing four new high-efficiency water chillers, two at East Campus and two at City Campus.
Air conditioning and heating systems in each UNL building use cold water and steam piped in from the utility plants to cool or heat the air. Cold water is needed for cooling even in the winter to help control humidity and to regulate temperature in areas that need to be cooler than the rest of a building, such as computer labs. But obviously, that need is much smaller in the winter than during the summer.
Efficient winter cooling was difficult with the old large chillers, which are meant to handle the enormous need for cold water in the summer. The four new chillers are compartmentalized, which allows them to operate economically in times when the need for cold water is minimal. New technology and the advanced design of these chillers make them significantly more energy efficient. In fact, regardless of the season, the new chillers generally use 20-25 percent less electricity than UNL's existing chillers to offer the same amount of cooling.
These chillers provide another great benefit during the summer. In addition to operating at a much lower cost, they add a substantial reserve capacity to the amount of cooling available. On the hottest days in summer, keeping the university cool is often a tricky task for UNL's utility operators. Large cooling towers remove heat from the chillers, while the chillers create the cold water that is circulated throughout campus (see diagram at right). If the cooling towers don't remove enough heat from the chillers, one of the chillers could overheat and shut down. The old chillers, especially, are difficult to start and stop, and if one of the old chillers does shut down, air conditioning could be mostly lost on a campus for hours. So, to prevent a shutdown, a careful balance must be kept between the heat removed by cooling towers and the cold water produced by the chillers.
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| | | Water chillers take the heat out of the water that circulates throughout campus. They move that heat into water that is pumped to cooling towers, which transfer the heat to the air.
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Because the new chillers are smaller and compartmentalized, they can approach the cooling towers' maximum ability to remove heat with a smaller chance of a shutdown. This is like filling a glass with ice from a bag. You can fit a few big chunks into the glass, but if you want to fill the whole glass, you'll need smaller chunks. These new chillers are small enough to "fill in" the cooling capacity of the towers.
Though the new chillers are smaller, they contribute significantly to the university's total cooling capabilities. The efficiency of the chillers saves money as UNL grows, and they ensure that each campus has the capacity to handle growth for years to come.
UNL Facilities Management and Planning has a number of projects under way to reduce campus energy costs. For more information or to make a suggestion, contact Matt Streff at 472-4846 or mstreff2@unl.edu or Kirk Conger at kconger2@unl.edu.
About this series
This story is one in a regular series spotlighting campuswide efforts to conserve energy and save money.
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