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Study Examines Fan Efficiency in HVAC Systems

By CP Editorial Staff September 2007 - Energy Efficiency

A new study finds that despite common perception, parallel fan-powered air-terminal units, which are used to distribute cooled or heated air in HVAC systems, may not be more efficient than series fans.

The study from ASHRAE and co-funded by Air-Conditioning Engineers and Air-Conditioning and Refrigeration Technology Institute, was conducted by investigators at Texas A&M University’s Energy Systems Laboratory.

Tests found considerable air leakage from parallel fans’ back-draft dampers and terminal box seams, greatly reducing their efficiency. Leak rates for tested parallel fan terminals were found to be, on average, between 10 percent to 20 percent, and in some cases higher than 30 percent.

When no leakage occurs, the parallel fan terminals are more efficient, consuming 17 percent less energy than series fan terminals; however, tests showed that when leaks are present, series fans appear to outperform parallel fans. When a 20 percent leakage rate was introduced, the series terminal unit outperformed the parallel unit and used 5.5 percent less energy.


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