Integrated Control Systems
Part 1
Choosing a Greenhouse Control System
Unless you’re the sort of person who just can’t get enough ‘hi-tech’ in
your life, you probably need a good reason to invest in complex greenhouse
equipment. Remember how computers were going to make our lives easier? Remember
how they were going to eliminate paper? Well OK, maybe those early promises were
a bit off the mark, but there really are a few things that computers do very
well. The best news is that integrated greenhouse control computers don’t have
to complicate your job. In fact, they can make managing a sophisticated growing
environment a lot easier. Greenhouse control systems, particularly integrated
systems, are now a standard feature in many modern facilities.
Throughout the
world, computer systems are busy managing the day-to-day climate, irrigation,
and nutrient equipment activities of large and small commercial greenhouse
operations, research institutions, and conservatories. They have enabled an
unmatched degree of precision that has resulted in better crop uniformity,
higher energy efficiency, less crop disease, and a host of other
benefits.
But before we get carried away it’s important to emphasize that computer
control systems are not a replacement for growers or managers. They can’t do
your thinking for you (at least not yet!). Like any other tool, integrated
control systems work best in the hands of someone experienced and knowledgeable.
If you can produce top quality crops in greenhouses with no control equipment,
then automated controls will simply extend and expand your capabilities. They’ll
enable you to produce higher yields of better, more uniform crops, and to manage
multiple climates and irrigation systems without having to be in several places
at once.
What
Computers do Best
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What Humans
do Best
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| They carry out our instructions
precisely (even the wrong ones!) |
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Research the latest crop
information and recommendations
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| Make large numbers of
calculations every minute without getting bored |
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Decide which instructions to
give the computer Analyze the results of those calculations and use them
in management decisions |
| Maintain the correct setpoints
within the capabilities of your equipment |
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Choose the setpoints and
setpoint modifiers
Choose equipment that will provide the most uniform effect (heating,
cooling, irrigation etc.) |
| Make precision sensor
measurements of all current greenhouse conditions |
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Determine the best location for
making representative measurements |
| Collect, store, and summarize
data on the status of controlled parameters |
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Analyze recorded data to
confirm proper climate status and decide upon changes |
| Monitor conditions 24 hours per
day, 7 days per week, 365 days per year and signal alarms when things go
wrong. |
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Monitor the status of
greenhouse conditions
Prepare in advance for emergencies
Determine exactly which conditions constitute an alarm, and what the
computer should do if it detects one.
Analyze the cause of malfunctions and take corrective action |
| Provide remote control
capabilities |
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Check in on greenhouse
conditions from remote locations while getting on with your life |
Control Alternatives
There are plenty of choices in greenhouse control, ranging from manual, where
you make all the adjustments by hand, to fully integrated, where a computer
control system coordinates the operation of all major climate control,
irrigation, and nutrient delivery equipment. In between there are simple
mechanical and electronic controls such as thermostats and clock timers, analog
“step” controllers, and computer zone controllers. All have their place, but
with today’s increasing trend towards building ever more complex greenhouses
(with shade/blackout/thermal systems, evaporative cooling, recirculating
nutrients, water treatment, supplemental lighting, CO2, heat storage, root zone
heating/cooling etc.,) it’s getting too complicated to effectively manage all
this equipment without some form of automated control.
Integrated Control - All the Bells &
Whistles
An integrated system is like the ‘Mission Control’ of your greenhouse
operation. With everything managed from a single source, the control system is
able to coordinate the activities of each piece of equipment, performing
sophisticated operations that are nearly impossible to accomplish by other
means. You define how your equipment should be controlled, how it should
coordinate with other systems, and how you want it to respond under various
conditions.
Strategic Response
One advantage of an integrated system is that it can provide a coordinated
response to a specific control situation. In other words, you can use several
equipment systems to deal as effectively as possible with a single problem. For
example, you may want your equipment systems to automatically adjust pipe
temperatures, thermal curtains, mixing valves, snow melt pipes, and CO2 burners
in response to a snow storm, and to return to normal once the threat of a snow
load has passed. Without an integrated system this sort of automated response is
difficult to achieve, and lacking in the ability to make seasonal or other
setpoint changes with ease. Integrated controllers allow you great flexibility
in modifying your heating, venting, irrigation, and equipment strategies based
upon sensor values, logic-based parameters, and changing seasonal conditions.Intelligent Equipment Control
Integrated controllers can also produce a sophisticated response in a single
equipment system. For example you might want to define multiple conditions to
manage your fog system. You can define how the time of day, temperature, light,
humidity, and ventilation levels should affect its operation. Equipment
programming using several input decision sources is easy to configure with
computerized control but very difficult to do otherwise.Record Keeping
One of the added benefits of computer control is the ability to record the
conditions in the greenhouse and outside. Sensor information and equipment
states can be recorded and summarized providing you with valuable information
about the performance of your operation and it’s equipment systems. Historical
information can be archived and compared to previous years. You can even keep
track of energy use and equipment wear. Monitoring and Alarms
With the ability to monitor and control so many simultaneous conditions, many
integrated control systems also allow you to set up alarms to let you know when
there are problems. Not all alarm conditions have to be emergencies. Some
systems allow you to configure sophisticated ‘smart’ alarms. For example a
greenhouse heating failure may not be a serious problem in the summer, but it’s
a real emergency on a cold winter night. You could use a smart alarm strategy to
simply note a heating failure in mild weather so that someone will attend to it
when they get to work, but to press the panic button if it’s freezing outside.
This way, you’ll only get called out of bed for true emergencies!What About Manual Control?
In a way, integrated systems have brought greenhouse control full circle.
Although they provide for intelligent, fully-automated operation, the remote
manual control features of integrated systems allow you many of the same
hands-on capabilities that you could only previously accomplish by being there.
Surprisingly, it’s not so much the automated control (everyone takes this for
granted) but the human control that growers rate so highly about integrated
systems. You can irrigate, open vents, turn up the heat, or do anything else
that is controlled from the system. The convenience and efficiency of
consolidating all your major control points under one interface often makes this
one of those ‘how-did-we-ever-get-along-without-it’ improvements. From a
single source, you can see just about everything that is happening at your
operation and you can make all the adjustments you need, whether you are in your
greenhouse office, at home, or dialing in from a remote PC anywhere in the
world.Selecting an Integrated Control System
Unless you have an intimate knowledge of computer control systems, it’s easy
to get lost in technical specifications. Concentrate instead on performance
specifications. What exactly do you expect the system to do? Try to list all the
things that you want controlled and measured in each part of your operation. If
you can, provide a sketch showing the physical layout of your growing zones and
mechanical rooms showing where all the equipment is located.Too much or too little control - both will cost you money!
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Don’t make a wrong choice in
either direction. Sophisticated computer controls aren’t for everyone or
every application. Study and compare the features and limitations of the
available systems and make sure that you and your operation will actually
benefit from the level of control provided.
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Don’t be in a rush. Check
references and talk with other growers. Look for a system designed for
greenhouse control and greenhouse conditions, and a vendor with greenhouse
control experience. A greenhouse is not the same as a warehouse or an office
building. It has a far more complex climate and changes happen much faster.
Other industrial control systems may claim to be capable of greenhouse
control, but if they can’t supply the specialized programs tailored to
greenhouse equipment operation such as thermal curtains, CO2, irrigation,
nutrient monitoring, etc., they are of limited use.
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Ask the manufacturer or dealer
how they tackle environmental control problems. Many advanced integrated
control systems use ‘feed forward’ control intelligence to predict the
level of control response based upon changing conditions. They do this by
looking at current conditions and reacting to changes that will result in
errors if not corrected. In many situations this works better than simpler
feedback strategies where the controller waits for a deviation to occur
before making changes.
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One of the most useful
applications of feed forward control is in energy balance equations. Good
integrated control systems accurately predict the energy balance
requirements for a climate, and preemptively manipulate the heating/cooling
to maintain this balance.
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Make sure the company provides
good after-sales service. If you’ve ever bought a home computer from a
store that doesn’t service (or even understand!) their products, you’ll
know what we mean.
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Ask about flexibility. Unless
you expect to be growing the same crops in the same way forever, you’ll
need the option to change the way you manage your equipment.
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Make sure the system can expand
and grow as you do. Find out what it’s going to cost to make future
changes and upgrades to your system. Again, references and advice from other
growers will help you here.
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