Preferred Air Velocity and Local Cooling Effect of desk fans in warm environments

Common experiences, standards, and laboratory studies show that increased air velocity helps to offset warm sensation due to high environmental temperatures. In warm climate regions the opening of windows and the use of desk or ceiling fans are the most common systems to generate increased airflows to compensate for higher environmental temperatures at the expense of no or relatively low energy consumption.

When using desk fans, local air movement is generated around the occupant and a certain cooling effect is perceived. The impact of the local air movement generated by different air flow patterns, and the possibility to keep comfortable conditions for the occupants in warm environments were evaluated in studies with human subjects.

In an office-like climatic chamber, the effect of higher air velocity was investigated at room temperatures between 26°C to 34°C and at constant absolute humidity of 12.2 g/kg. By a thermal manikin the effect of direct air movement generated by a personal desk fan at 26 °C, 28 °C, or 30 °C room temperatures and the achievable thermal comfort was also analyzed.

Results show that it is possible to offset warm sensation within a range of indoor conditions using increased air velocity. Besides, higher air velocities and personal control increase the acceptability of the indoor environment at higher air temperatures with a limited energy consumption compared to full air conditioning during summer seasons in warmer countries.

Comparing the study with Danish subjects with previous findings with Chinese subjects showed that subjects used to warmer climate could accept higher air velocities and felt less uncomfortable.