Improve Energy Efficiency – Indoor Air Movement Can Help You Save Money

1. Provide an overview
The thermal comfort of man and beast can be greatly influenced by air movement. On a hot summer day, a breeze can make a big difference in one’s thermal comfort. Recent strategies for improving building energy efficiency attempt to account for the cooling effects of natural ventilation air movement. Local air flow is held below 40 ft/min while the building envelope is closed for air conditioning. This ignores the possibility of increasing air movement in air-conditioned spaces to reduce cooling energy consumption. This paper looks into ways to save energy by taking advantage of the effects of indoor air movement.Do you want to learn more? Visit

2. Savings on cooling energy in air-conditioned spaces due to increased air speed
Increased local air speed allows for limited increases in summer thermostat temperature settings, according to the current edition of ANSI/ASHRAE Standard 55-2004 Thermal Environmental Conditions for Human Occupancy (ASHRAE, 2004). Figure 1 is based on Standard 55-2004’s Figure 5.2.3.

The upper limit of the comfort zone (PMV= +0.5) is used to reference the curves of equal heat loss from the skin for combinations of operative temperature and air movement. Sedentary activity has been set at 160 beats per minute and 5.4 degrees Fahrenheit, with a success rate of 1.0 to 1.3. Owing to broad individual variations in desired air speed, occupants must have personal control of air speed in 30 ft/min increments.
It is permissible to interpolate between these curves, according to the Standard. When the mean radiant temperature is higher than the mean dry bulb air temperature, air speed is more effective at offsetting temperature increases.

It should be noted that Figure 5.2.3 of the Norm includes two errors. There is a scaling error between the fpm and m/s scales, and the “18°C” should read “18°F.”
Temperature differences of -18°F, -9°F, 0.0°F, +9°F, and +18°F between mean radiant temperature, tr, and mean dry bulb air temperature, ta, are accommodated by five separate curves. For 1.0 met to 1.3 met and 0.5 to 0.7 clo, the writer fitted equations to the portion of the curves limited to sedentary activity of 160 fpm and 5.4°F.

The portion of the curves for activity beyond the sedentary limits was also fitted with equations by the author. For these equations fitted to curves in Figure 5.2.3 in the Standard 55-2004, the cooling effect limits were 300 fpm and 8°F.

2.1 tr – ta = 0.0 K curve
For tr – ta = 0.0°F, a thermostat fixed point increase of 4.4°F is possible with a 160 fpm air speed for moderate sedentary activity (1 to 1.3 met) and 0.5 to 0.7 clo.
1.85 V = 40 + 6.8”t (1)
Where V is the cooling effect in °F and t is the mean relative air speed in fpm.
The temperature of the wall, ceiling, and floor surfaces of most thermostatically controlled air conditioned spaces is similar to that of the air. That is, tr – ta = 0 degrees Fahrenheit. Spaces with poorly sealed windows, walls or ceilings where the outside surface is exposed to direct solar radiation, or cold winter conditions are examples of cases where tr — ta is not zero.