June 2021 - 24

STRUCTURES & EQUIPMENT
" If there is flexibility in delivering the quality
and yield expectations, then growers also have
some flexibility in the controls and control
systems that need to be incorporated in their
production facilities. Some growers will be
able to incorporate low-tech environmental
control suited for the production system
selected with less precision control as long as
buyers and/or consumers are satisfied with
the product quality. "
THE IMPACT OF LOCATION
The environmental control strategy and
systems used are going to be different to meet
crop requirements for the environment and
operations depending on location.
" The Southeast states including Florida,
Georgia and the Carolinas have hot and humid
climates, " explains Kacira. " In the Southwest
states, including Arizona and Nevada, the
temperature is hot and the air is dry during the
summer and cool and dry during the winter.
In Arizona, growers are able to cool their
greenhouses effectively with evaporative cooling
systems, including fan-and-pad systems, except
during monsoon season. These types of systems
may not be able to function as effectively in more
humid locations like Florida because the capacity
to cool the air and to lower the humidity is more
difficult during hot, humid weather.
" Growers may need to look at alternative
cooling systems, including natural ventilation
with high volume and tall greenhouses with
vent openings. Growers can install some type of
shade covering and screening material that help
to reflect the portion of the solar light spectrum
that causes heat buildup in the greenhouse.
They can also incorporate a control strategy that
meets environmental control expectations. "
PLANTS - THE GREAT INTEGRATORS
Kacira says every plant has optimal
temperatures that are needed for physiological
activity and metabolic activity leading towards
optimal yields and quality.
" Even though there are optimum
temperatures, growers need to remember that
plants are great integrators of their environment,
meaning that plants can respond to the
maximums and the minimums for a short period
of time, " he says. " At the end of the day plants
respond to the accumulated conditions during a
given time period such as a day or several days.
" There are sophisticated environmental
control strategies that consider this time or
temperature integration. These controls can
aim for an average temperature over a period
of several days or weeks rather than precisely
trying to maintain a set point temperature for
a very short time. These types of advanced
control applications are used towards energy
24 JUNE 2021 GPNMAG.COM
Regardless of whether you're using a low-tech or high-tech greenhouse,
the crop you're growing should be one of the main considerations when
choosing an environmental control system.
(Photo: Eric Hanson, Michigan State University)
More sophisticated environmental control systems
can collect, interpret and analyze the data and
make the necessary adjustments.
(Photo: A.J. Both, Rutgers University)
and resource savings. A control system's
capabilities should be considered when selecting
the greenhouse hardware/technology and the
control strategy. "
BALANCING CONTROLLABILITY AND
AUTOMATION
Kacira says there needs to be a balance in
terms of the amount of controllability and
automation that growers want and are willing to
pay for.
Growers need to consider a cost-benefit
analysis. " Growers can have less sophistication,
but in that case growers need to do some of the
analysis, monitoring and control. They can look
at collected data, interpret it, make sense of the
data being collected and then determine if they
need to adjust the environmental settings, "
says Kacira.
" There is a semi-automation mode which
is going to be less costly, but growers then
need to do their own analysis and then adjust
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June 2021

Table of Contents for the Digital Edition of June 2021
