1.) How are environmental control computers important in raising a crop?
In addition to controlling humidity and temperature, they can manage shade systems and supplemental lighting, control CO2 concentration, schedule and sequence irrigation valves, and control the pH, EC and temperature of the irrigation water. Because they integrate these functions into a single controller, environmental computers can manage the interactions between these elements, giving the grower a tool to optimize production.
2.) Do they respond to both the greenhouse and outdoor environments?
Yes, they monitor wind speed and direction to protect vents from damage. Many can use wind speed, outdoor temperature, and light level to anticipate heating and cooling demand, and to control the firing of boilers. By measuring outdoor humidity, they can compute whether dehumidification of the greenhouse is possible.
3.) How can they minimize energy costs?
Computerized environmental controls help minimize energy costs by closely controlling the environment, and by integrating and coordinating the use of all the climate control equipment in the greenhouse.
4.) Is there a way to reduce the amount of chemicals used on crops?
Yes, by using an environmental control computer humidity can be controlled, reducing mildew and cutting down on the amount of fungicides needed. Some systems offer pesticide programs that guarantee the environment will be closed for the necessary dwell time, then ventilate for safe reentry of personnel. "DIF" programs can reduce or eliminate the need for growth regulators.
5.) Can labor be reduced through an environmental control system?
Yes, in many ways. Environmental control computers can create a model of how the environment should be controlled, dramatically reducing the manual intervention needed from the grower and staff to maintain desired conditions.
6.) Can an environmental control computer change crop quality?
Because they monitor and control temperature, humidity, and light intensity constantly, environmental control computers create the most uniform conditions possible. This leads to increased uniformity in the crop. "DIF" programs are easy to implement with computers, and have been proven to be effective in producing compact, well-branched plants that sell more readily or for higher prices.
7.) Does the computer keep records and how can they be used?
Environmental control computers keep records of their sensor readings and equipment usage. This allows the grower to monitor past conditions, and events on nights and weekends. This data can be carried over from crop to crop and used as a tool in crop timing and quality control. Equipment usage records can also help in planing maintenance schedules.
8.) Can the computer help in plant modeling?
The data from most environmental control computers can be fed directly into manual or computerized graphical tracking programs. In many cases the data can be passed automatically to computerized tracking systems, without the need for re-keying.
9.) How does the computer acquire data from the greenhouse?
Sensors in the greenhouse send an electrical signal (either voltage or current) that varies as the quality measured varies. To use this data, the computer converts it to a number that its program can process. An environmental control computer uses a device called an analog-to-digital converter for this purpose.
10.) How does the computer control the equipment?
An environmental control computer must be able to operate the equipment that heats, cools, or otherwise alters the greenhouse environment. It usually does this by turning relays on and off, or by sending voltage or current signals to the equipment.
11.) Does the computer generate alarms?
An environmental control computer will generate alarms when it detects conditions that threaten the crop. Examples of alarm conditions include high and low temperatures, power failure, and any failure of the computer to operate properly. If you have equipment that operates on three-phase power, consider a computer that can detect phase failures, and generate an alarm to protect your equipment.
12.) How will the computer respond during a power failure?
Environmental control computers retain all your settings during power failures that last several hours. It is not essential that the computer itself continues to operate through an outage, since the equipment it controls cannot respond. If your stand-by generator doesn't have enough capacity to operate all the equipment, consider a computer that can selectively shed load while on standby. When power returns, be sure your computer will gradually turn on the equipment that's needed: turning everything on at once can stall a generator, or trip the overload protection on your electrical service.
13.) What are the advantages of a centralized single system?
A single central computer consolidates all control and supervisory functions at one location. Information and control functions that are common to all zones in a greenhouse range, like weather data or boiler control, need not be communicated between multiple computers. Because only one computer is needed, a single central unit can be the most economical choice.
14.) What are the disadvantages of a centralized single system?
In a single computer system, if there is a problem with the computer, it affects the whole greenhouse range. Also, wiring of sensors can become complex. Either all the wiring must be brought to the central computer, or brought to concentrators that send and receive signals from the central control. A single central location can be distant from some zones, and therefore less convenient. Furthermore, for a large range, a powerful enough computer may actually be more expensive than multiple smaller computers.
15.) What are the advantages of a multiple computer system?
In case of a problem with one computer, other computers in the greenhouse range are unaffected. Multiple computers can be located near the areas that they control. This can reduce cost and complexity of wiring and improve convenience of use.
16.) What are the disadvantages of a multiple computer system?
Multiple computers require a communication link in order to share information about weather or equipment common to zones controlled by more than one computer. Because you are buying more than one computer, it may be more expensive than a single, centralized unit. In practice, many greenhouses need only one unit of a multiple computer type system and they do not gain the benefit of the multiple system.
17.) What types of temperature sensors are there?
Common temperature sensors include thermistors, thermocouples, and integrated circuit types. Thermistors are devices that restrict the flow of electricity in a way that varies with temperature. Thermocouples use two dissimilar metals welded together that generate a small voltage that depends on temperature. Integrated circuits vary a voltage or current that is supplied to them in a way that varies with temperature. Typically, thermistors and IC's are the preferred types, since they give accurate results with less expense than thermocouples.
18.) What kinds of humidity sensors are available?
Typical humidity sensors are capacitate, resistive, or wet bulb/ dry bulb types. Capacitate sensors absorb and give up moisture form the air as humidity changes, and vary their electrical characteristics in a measurable way. Resistive sensors also absorb and give up moisture as humidity changes, and restrict the flow of electricity in a varying way similar to thermistors. Wet bulb/ dry bulb sensors measure the temperature of a dry sensor and by a wet wick in an in a water reservoir. In dry conditions, the wet wick cools it sensor more than in humid conditions. The difference in temperature from the dry sensor can be translated to a humidity reading. Wet/ dry types are the "gold standard" of humidity sensors, offering the most reliable readings. However, they require routine maintenance of wicks and water reservoirs, and they don't work outdoors in freezing weather. Capacitate and resistive humidity sensors require no maintenance, but can readily be contaminated by chemicals in the greenhouse environment, requiring recalibratation or replacement. Resistive types appear to withstand the environment better than capacitate types.
19.) What are the common types of light sensors used with the computers?
Common light sensors include photodiodes and photoresistors. A photodiode is a device that generates electricity when exposed to light. A photoresistor changes the amount it restricts the flow of electricity according to how much light falls on it. Both photodiodes and photoresistors "see" wavelengths of light outside of photosynthetically active radiation (PAR), but can be filtered to limit the angle at which light strikes them, and it may be desirable to choose a type with a diffuser ("cosine corrector") for best accuracy early and late in the day.
20.) How can I measure wind speed?
Most wind speed sensors, or anemometers, are either generators or tachometers. Generators generate electricity when the wind turns their cups or propellers. Tachometers use a striped or slotted disk attached to a shaft that the wind turns. The disk interrupts a beam of light on a light sensor sending an electric pulse to the computer. The computer measures how quickly the pulses come in and translates the rate to the speed. Tachometers are potentially more sensitive than generators, but there is no practical difference in their suitability for use with environmental control computers.
21.) Are there different wind direction sensors?
Wind direction sensors include resistive types, and digital resolvers. As the wind vane turns on a resistive sensor, it moves a wiper on a circular resistor, analogous to the volume control on a radio. A digital resolver uses three of more light sensors to read a pattern of stripe printed on a disk attached to the wind vane. These patterns translate to wind directions. Resistive types offer higher resolution than resolvers do. In practice, available control systems report only the points of a traditional compass N, NNE, NE, ENE, etc.
22.) Are there different types of precipitation sensors?
Precipitation sensors may offer detection only, or they may measure the amount of precipitation. Detectors trigger when rain or snow closes an electrical circuit between two interleaved electrodes. Units that measure precipitation typically use a funnel to feed rainwater to a small cup balanced on a hinge. When the cup fills, it tips and empties itself, and momentarily closes a switch that sends an electrical pulse to the computer. Since the volume of the cup is known, the computer can measure rainfall by counting pulses. In greenhouse applications, it's enough to detect rain, since the amount will not affect indoor irrigation. Look for a detector with a heated grid to detect snow and drive off dew. Detectors should drive their electrodes with alternating current rather than direct current, which causes the electrodes to fail prematurely.
23.) Are there sensors that test pH?
Yes, there are sensors to test pH. These sensors work on a principle analogous to that of a car battery. They generate a voltage proportional to how acidic or basic the solution they are immersed in is. They also respond to the temperature of the solution, so the readings must be corrected for variations either by the computer or electronically. These sensors must either use special cables, or be amplified near where they are used to deliver a clean signal to the computer.
24.) Can the sensors test the EC?
EC sensors measure the flow of electricity between two metal probes. The more fertilizer present in the water they are immersed in, the more electricity flow. Like pH sensors, EC sensors also respond to temperature and must be corrected either electronically, or by the computer. Typical applications use redundant sensors, and compare the readings to check for sensor fouling or sensor failure.
25.) How can I learn to use my environmental control computer?
Computer environmental controls now include so many features and options that most users need some help in learning to use them. You can learn more about environmental controls by contacting your NGMA greenhouse or environmental control manufacturers.
26.) Where can I get more information about environmental controls?
Contact the NGMA office for a free copy of the Environmental Control Guidelines or download it off of the NGMA website.
 Back to FAQs
|
|
