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November 2007 | TEC 25

Circulating Fans for Summer and Winter Comfort and Indoor Energy Efficiency

Richard Aynsley

Circulating fans are defined as a class of axial propeller fans, generally without an enclosing housing, and used for circulating air in a space. The energy-efficiency of circulating fans tends to increase with their size and reduction in their operating speed.

In summer, air movement from circulating fans can have a significant cooling effect on exposed skin, using less than ten percent of the energy used by an air conditioner to cool the air to achieve a similar effect. The cooling effect of airflow can be calculated from differences in standard effective temperature (SET*) using readily available computer software.

In winter, rising warmed air accumulates near the ceiling. Circulating fans can be used to mix this warmer air with the remainder of air in the room to provide a uniform temperature, providing warmer air in the occupied zone closer to floor level, and thus increase energy efficiency. Energy required to provide thermal comfort for people in a heated space is reduced, saving 3 per cent for each metre of ceiling height proportional to the heat released in the space.

Note: This paper includes a glossary at the end.


Airflow, circulating fans, destratification, fans, standard effective temperature, SET, thermal comfort

Click here to go to paper

Related EDG note: Natural ventilation in passive design by Richard Aynsley

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