Original Date: 06/05/2006
Revision Date: / /
Best Practice : Free-Cooling, Energy-Maximizing HVAC
In 1989 Rockwell Collins installed a heat exchanger and pump system combined with a series of valves that works in conjunction with the company’s existing cooling towers to reduce the load on its chiller plant during the colder months of the year. As a result of this facility modification, the company can shut down one additional 600-ton chiller whenever the outside temperature drops below 38×F, saving Rockwell Collins significant energy costs and prolonging the lifetime of the chillers.
Until 1989 all chilled water required by Rockwell Collins’ Cedar Rapids facility was generated by mechanical means of a series of electrical chiller plants. Chilled water for both process use and for comfort cooling flowed from this single source. This required a total of five chillers operating in the high-load summer season and three chillers operating in the reduced-load winter months, as the two largest chillers could be shut down during the winter months due to reduced need for comfort cooling on the campus.
Rockwell Collins elected to implement a free-cooling method to further reduce chiller operation during the winter months and take advantage of the company’s existing cooling tower infrastructure and the cold climate of Cedar Rapids. The company installed a heat exchanger and a dedicated pump to run a closed-loop system of water from the heat exchanger to the external cooling towers. A series of valves enables the Facilities Department to engage this system whenever the outside temperature drops to 38×F, effectively using the Iowa weather to cool water in the towers that in turn cools the Rockwell Collins plant water via the heat exchanger. This allows the Facilities Department to shut down one additional 600-ton chiller for as many as six months in a typical year. The direct savings of eliminating the 600-kilowatt electrical load of the mechanical chiller is estimated at $130,000 annually. At the time of installation of the closed-loop heat exchanger system, a 5-year payback was expected based upon this savings calculation. The Facilities Department rotates which chiller to shutdown to prolong the life of all the chillers.
Rockwell Collins is currently taking this project one step further as part of its overall energy management strategy by automating the switchover process from conventional to free cooling so that the decision point and execution of the switchover is software-controlled. The expected benefit is a more optimized use of the free-cooling concept and a faster changeover that can be executed at any time of the day.
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