Saving Energy with Indoor Air Movement

The cooling effect of indoor air movement from circulator fans has been discounted in many strategies for increased energy efficiency. Standards such as ASHRAE 55-2004 clearly provide thermostat offset guidance for indoor air movement to maintain the comfort of sedentary occupants. The Standard is ambiguous on the cooling effects of air movement for non-sedentary activity. US utility company Exeloncorp, has indicated that each 1C increase in summer thermostat setting will save 5.4% to 7.2% of cooling costs. Another study has shown that a residential air conditioner costs 11 times more to operate than ceiling fans. In winter, air movement that thoroughly mixes indoor air can save 20% to 30% of heating costs. A study in Thailand has quantified cooling effects of air movement for velocities up to 3 m/s and relative humidity from 50% to 80%. The US Naval Medical Command published relative cooling effects of air speed over man from 0.2 m/s to 10.9 m/s. Air movement is widely used in livestock barns to cool dairy cattle, pigs and chickens. Gusting air flow can significantly enhance the cooling effect at low velocities. It is concluded that strategies for energy efficiency that discount the benefits of increased indoor air movement forfeit significant energy savings. Further research on the cooling effects of indoor air movement for higher velocities, lower clothing insulation and higher activity levels is needed.