Birds need to lose heat to control their body temperature at the desired level of 40-41oC. Therefore, we must reduce the temperature in the house to compensate for the heat production in the birds.
It is not always possible to lower the temperature sufficiently to remove enough heat, especially if the birds are growing at a fast rate and outside condtions are warm and humid. If this is the case, we can increase the air velocity over the birds, which will increase heat loss. In this way, we lower the so-called effective temperature for the bird.
Although there are some discussions in the literature about how much the effective temperature is influenced by a certain air velocity, it is in general accepted that if air temperature is 32oC, the effective temperature is dropped with 5oC to 27oC if air velocity is increased from 0 m/s towards 1 m/s.
As a guideline, the following figures can be used for estimating effective temperatures:
At air temperature of 32oC
if air speed is 0 m/s, then effective temperature is 32 oC
if air speed is 0.5 m/s, then effective temperature is 28 oC
if air speed is 1.0 m/s, then effective temperature is 25 oC
if air speed is 1.5 m/s, then effective temperature is 23 oC
if air speed is 2.0 m/s, then effective temperature is 22 oC
Normally, we consider an air speed of 2 m/s to be maximum for a flock of broilers. At this air velocity, the effective temperature will be approximately 24oC, so approximately 10oC below the actual air temperature.
Air velocity for cooling should not be applied when the birds are too young, approx younger than 12-14 days, as the birds will be chilled easily.