Agriculture Reference
In-Depth Information
There is a trend in current housing systems for meat birds to be raised in totally
enclosed mechanically ventilated structures. This is also true of most swine
breeding, gestation, and nursery facilities. Swine grow-out buildings and some
dairy housing facilities are naturally ventilated or use a hybrid system that uses
mechanical ventilation in some extreme conditions, and natural ventilation in other
conditions.
A key feature of environment control, whether via natural, mechanical, or hybrid
control systems, is the provision of a more uniform environment near the thermoneu-
tral zone for the animals (Hellickson et al., 1983; Pratt et al., 1983; Scott et al., 1983;
Albright, 1990). This is the range of environment conditions (temperature, humidity,
air velocity) for which animals are most comfortable and for which they expend the
least amount of energy for maintenance requirements. Accordingly, thermoneutral
conditions also result in the most efficient feed conversion efficiency and thus the
least feed cost for production. However, in extreme climates, there is a substantial
energy penalty associated with “tight” temperature control, which has resulted in
some unique control systems that may be characterized as environment modifica-
tion rather than direct control. As an example, in extremely hot conditions it is gen-
erally not considered economically feasible to provide air conditioning via direct
expansion refrigerant systems, and instead reliance on various forms of evaporative
cooling to modulate external extreme temperature is traditionally used. It is quite
common for interior environment conditions to greatly exceed thermoneutral limits
for the animals housed within; this is a design and operational decision made in
a balance between energy costs, capital equipment costs, maintenance costs, and
potential improvement in production efficiency.
8.2.2 L
IGHTING
S
YSTEMS
Providing and controlling light intensity and simulated day length is critical because
light is closely tied to reproductive and hormonal responses of animals. The sim-
plest automated lighting systems use a 24-h timer that controls lighting circuits to
provide the desired amount of “day” and “night.” Required light levels are often
rather low, ranging from 5 to 50 lx for chickens, 10-100 lx for turkeys (http://www
.omafra.gov.on.ca/english/engineer/facts/06-009.htm#2), 250-360 lx for swine
(http://www.thepigsite.com/pighealth/article/111/light), and 100-300 lx for dairy
cattle (http://www.omafra.gov.on.ca/english/engineer/facts/06-007.htm). By com-
parison, light levels on sunny days outdoors can be up to 80,000 lx. For installa-
tions where fixed light intensity is acceptable, incandescent bulbs have long been
the favored light source with recent adoption of fluorescent bulbs and, in the past
few years, light-emitting diode (LED) bulbs. For installations requiring a change
in light intensity, all three light bulb types have been used although incandescent is
still the preferred means of dimming, using simple rheostats or solid-state dimmers
to reduce the voltage to the bulbs. Cold cathode fluorescent bulbs have achieved
some recent acceptance and are dimmable using properly designed dimmers. LED
bulbs, although very new to this market, offer substantial opportunities for spectral
quality control as well as basic light intensity but are still undergoing development
and testing.
