Ceiling fan
A ceiling fan is a mechanical fan mounted on the ceiling of a room or space, usually electrically powered, suspended from the ceiling of a room, that uses hub-mounted rotating blades to circulate air. Ceiling fans typically rotate more slowly than other types of circulating fans, such as electric desk fans. They cool people effectively by introducing slow movement into the otherwise still, hot air of a room. Fans never actually cool air, unlike air-conditioning equipment, they in fact heat the air due to the waste heat from the motor and friction, but use significantly less power (cooling air is thermodynamically expensive). Conversely, a ceiling fan can also be used to reduce the stratification of warm air in a room by forcing it down to affect both occupants' sensations and thermostat readings, thereby improving climate control energy efficiency.
Hashem Akbari
The UHI group in LBNL have monitored buildings in the California central valley with lightly colored, more reflective roofs and found that these buildings used up to 40% less energy for cooling than buildings with darker roofs. In a study funded by the U.S. Environmental Protection Agency, they carried out a detailed analysis of energy-saving potential of light-colored roofs in 11 U.S. metropolitan areas, with resulting estimated savings potential of about $175 million per year (1998 USD) for the 11 cities. Extrapolated national energy savings from air conditioning was estimated at $750 (1998 USD) million per year. The savings from shade trees and vegetation is also estimated at $1B per year. The impacts of savings in health and lost work time owing to a projected 12% O3 reduction are three times larger than that cited for air conditioning above. Heat island mitigation technologies apply all around the world in both developed and developing countries. They estimate that the potential energy savings and health benefits from a worldwide implementation of heat-island mitigation technologies can save over $10B per year. They are working with manufacturers of roofing and paving materials to develop ‘colored’ solar-reflective materials for the marketplace, including both dark and light-colored cool shingles with reflectivity of up to 60%.