High-volume low-speed fan for cooling of a large enclosed space

A ceiling fan is a commonly used mechanical device for promoting airflow inside an enclosed space, for thermal comfort purposes. However, it is difficult to clean and maintain, noisy and sometimes can be dangerous to occupants. Recently, a high-volume low-speed fan (HVLS) was introduced as an alternative device to provide better air movement at a lower energy cost. This study aims to compare the distribution of airflow velocity produced by a single HVLS fan and that produced by two ceiling fans inside a room, using computational fluid dynamic (CFD) method. Two simplified models of two similar rooms were developed using commercial CFD software. One is furnished with an HVLS fan and the other with two ceiling fans. Steady-state flow simulations were performed on the CFD models using a Spalart-Allmaras turbulence airflow model and adopting a moving reference frame (MRF) technique. The CFD models were validated based on experimental data obtained from the literature. It was found that for a single HVLS fan operating at a rotational speed of 140 RPM, the average airflow velocity on a horizontal plane at 1.1 m height from the floor is around 0.87 m/s. This value falls within the range stated in the ASHRAE-55 standard for good thermal comfort. For the room furnished with two ceiling fans operating at the same rotational speed, the average airflow velocity on the similar horizontal plane is around 0.19 m/s, which is outside the limit specified in the ASHRAE-55 standard. But when the two ceiling fans were operated at a rotational speed of 300 RPM, the average airflow velocity on the plane increases to 0.42 m/s, which satisfies the ASHRAE Standard-55 requirement. These findings suggest that a single HVLS fan would provide a more desirable air movement inside a confined space thereby would promote a much better feeling of thermal comfort to the occupants, as compared to the use of two ceiling fans operating at a much higher rotational speed.