During colder months of the year, the blades of top HVLS fans can run in reverse to break up pockets of warm air near the ceiling of a warehouse or manufacturing center and bring the heat down to the occupied space. Air settles into layers with the warmest air at the top. HVLS fans reclaim this warm air by pulling it off the ceiling and returning it to the occupied space.
How HVLS fans’ airflow patterns change by season
Despite what many think, an HVLS fan (or a regular ceiling fan, for that matter) does not actually lower the temperature of a room; it creates airflow that cools down the building’s occupants by speeding up the natural human cooling process, which involves the evaporation of moisture from the skin.
Similarly, in cooler seasons, an HVLS fan doesn’t warm a space up by increasing its temperature. When you run an HVLS fan in reverse, it pushes the warm air trapped at the ceiling outwards and down the walls into the lower areas of a building where it mixes with denser, cooler air. This mixing of air creates a process called thermal equalization which makes the temperature of a large room or building consistent.
These ideas aren’t mutually exclusive: HVLS fans achieve thermal equalization during both the summer and winter seasons. During the summer, the fan is run in the forward direction, thoroughly mixing the air and delivering a cooling breeze to the building’s occupants. In the winter, the fan runs in reverse to mix the air – breaking up the heat layers – without creating a perceivable breeze.
The seasonal energy use of HVLS fans
HVLS fans are primarily designed for cooling, so they do move more air in the forward direction than in the reverse direction. At a high enough speed, both directions will mix the air, destratifying the space. So why does running your fan in reverse deliver better climate control results in the winter? If you want to destratify your space in the forward direction, you will need to run your fan at a speed that will generate a perceivable breeze. Reverse direction redirects the airflow away from building occupants, delivering undetectable airflow to mix the air in the building. Running your fan in reverse allows you to save money by reclaiming warm air without impacting the comfort of those inside your building.
Last word on seasonal use of HVLS fans
Thermal equalization and the generation of a cooling breeze are the two main reasons that HVLS fans exist today. Be sure to choose a well-designed HVLS fan built by a manufacturer who understands how to optimize airflow for year-round climate control.