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Beyond Temperature ControlGetting the Most from Your Integrated Control SystemYour greenhouse environment is under constant attack from external forces. Ever changing light levels, sun angles, cloud cover, air temperatures, pressures, humidity, and precipitation events are constantly working to destabilize your environment. These shifting external forces can play havoc with internal greenhouse conditions. They can tax even the most well designed heating and cooling equipment. No matter how you choose to control your greenhouse environment the challenge is the same: how can we maintain a stable climate against the dynamics of everyday weather?Early control equipment such as electric thermostats and humidistats were an attempt to provide better temperature and humidity regulation automatically. In a way they acted like safety valves. Fans would turn on, heaters would be fired up, or vents would open in an attempt to dissipate a problem. They did a great job of protecting against dangerous extremes, and provided a limited amount of control between the coldest and warmest climate temperatures and the maximum or minimum humidity levels. However, the type of equipment control was usually limited to full on or full off and separate devices had to be used for each problem. They also had to be manually offset in their response so that the heating and cooling equipment didn’t work against each other. True setpoint control was limited at best. To solve the problems of using independent ‘full off’ or ‘full on’ control devices, step controllers were invented. They added the ability to provide a number of discrete equipment operation steps to help meet a climate problem. For example, a series of exhaust fans could be turned on as needed, and vents could be opened and closed in increments.Later on, the power of computer processing was added to provide full span control for modulating devices such as roof vents and hot water mixing valves. And most importantly, the integrated control of several equipment systems was accomplished so that they could be made to work with one another rather than independently. Today, integrated control systems offer the best possibility of achieving a stable climate against anything the weather can throw at you. Of course, there are always limitations. Regardless of the type of control system you are using, it cannot compensate for insufficient venting capacity, an undersized boiler, or a poorly designed heat distribution system. Likewise, a control system cannot provide horizontal air circulation if you do not have HAF fans. Don’t laugh. We sometimes forget that equipment ability and control capability go hand in hand. They are real physical constraints that impose a limitation on any control strategy. Because of their processing power, computerized control systems offer many more possibilities than simple temperature or humidity control. Here are some ideas you may be able to take advantage of with an integrated control system.Conserving EnergyOnce again, everyone is preoccupied with energy costs. Over the years, many numbers have been tossed around regarding the potential energy savings when using automated control systems. Some growers have reported fuel savings of up to 30%. However, the actual amount you may save will depend upon how inefficient your existing control methods are, whether you have the equipment systems in place that can take advantage of precision control, and tolerances you wish to achieve with an automated system. A number of energy conserving ideas are discussed below. There are two perspectives to energy conservation and you can use your integrated control system to help achieve both of them: Minimize Inputs: This is what we usually mean when we talk about energy conservation. It involves finding ways to cut down on overall energy use. Many of the ideas discussed below are aimed at minimizing input costs.Maximize Outputs: You also conserve energy when you find ways to produce more with the same amount of inputs. Better crop uniformity, lower losses, and shorter cycle times are more attainable if you have precision control over your resources such as heat, water, and nutrients. Integrated control systems can help you achieve this. Better Temperature and Humidity ManagementWith better control precision you may be able to lower your heating setpoint without a noticeable difference in crop timing or quality. This is because the control system will maintain a more accurate average air temperature and will do a better job of avoiding wasteful heating overshoots. Use the computer control system to track your minimum, maximum, and average daily temperatures. This will provide you with a better indication of the crop conditions for timing and temperature management purposes.For growers in milder, more humid regions, dehumidification costs can be considerable. With an integrated system you can control the amount of heating resources that you want to apply to a humidity problem. If you have good air circulation and precision humidity sensing, you may be able to tolerate slightly higher humidities without running the risk of disease or reduced crop quality. On the other hand, you may decide that you need to allocate a lot of heating resources to humidity management. Even though better humidity control may cost more money, the improvement in output as mentioned earlier may well be worth it. Thermal CurtainsThermal or energy curtains are one of the most effective methods for reducing heat loss on cold nights and reducing cooling demand on hot days. Like all conservation investments, the higher energy prices climb, the faster the payback. If you have roof and wall curtains, use your control system to operate them in a manner that is both sensitive to the needs of the crop while at the same time reducing heat loss. To prevent chilling injury, you can program the curtains to open gradually, avoiding sudden cold air spillage from above. To minimize heat loss you can program the curtains to close whenever the outdoor light levels have fallen below a beneficial level. For snow load protection set the curtains to open whenever snow is detected. This will direct heat to the roof for snow melting. Occasionally, growers have had problems with gutter heat pipes freezing while the curtains are closed. With an integrated control system you can maintain a minimum pipe temperature and circulation in the gutter heat pipes whenever the curtains are closed.Intelligent Lighting ControlSupplementary lighting is an example where an integrated control system can help you arbitrate between your energy conservation needs, crop requirements, and premature equipment wear. For example, to save money, it might be beneficial to operate your HPS lights only as needed, say when natural the light levels fall below a defined level during the day period. However, frequent on/off cycling of the lamps is very hard on the equipment and is not recommended by the manufactures. You can use your control system to set up threshold light levels and windowed times for the lights to be turned on, and them stipulate the minimum on and restart interval times to prevent excessive cycling. In this way, your lighting system will only be operated when the external light levels are too low, and at a cycling and restart frequency that is safe for the lamps. Heat StorageIf you use CO2 gases obtained from condensed boiler flu gases you should consider a heat storage and recovery system. Usually CO2 is required in the daytime, when the combustion heat may not be needed. Heat storage systems store this heat in a hot water reservoir for later use during the evening. The result is either free heat or free C02 depending how you look at it. An integrated control system can mange the somewhat complex operation of the heat storage and recovery system as well as CO2 extraction and dosing. CogenerationMany large and mid sized operations may have an opportunity to invest in cogeneration equipment to help offset rising heating costs. Basically, with cogeneration, you make electricity with a gas fired generation plant, and sell it to the utility. You then use the ‘free’ waste heat from the generator exhaust and cooling water to operate your greenhouses. If your greenhouse operation is located close to other greenhouse facilities there may be an opportunity to build a joint venture facility. You can use your integrated control system of manage cogeneration activities and equipment control. Standby PowerUsing cogeneration or standby power systems for your own electrical needs can be cost effective, particularly if you are paying a premium for electricity during peak demand periods. Depending upon the surcharge rates, you may be able to save money by generating your own electricity during these peak periods, whether or not you can benefit from the extracted heat. Your integrated control system can be used to manage these switchovers automatically. Allocating ResourcesYou can use the flexibility of an integrated control system to manage limited resources such as heat and water. For example, if your hot water heating system capacity is occasionally limited due to extreme weather conditions or sudden changes, you can designate certain zones to have priority when allocating central heating resources. Likewise, you can manage your irrigation system so that all zones are watered within the limits of your irrigation system capacity. You can also designate certain zones such as mist propagation zones for high priority watering. Equipment ProtectionWithin an integrated control system there are all sorts of ways to ensure safe operation of your greenhouse equipment. You can define the sequence of operation for each system and you can set alarms to warn you of many types of malfunctions. This is sometimes called ‘Management by Exception’ since the control system monitors all of the equipment constantly and only bothers you when it detects a problem. The potential applications are limited only by your imagination. For example, suppose you wanted to protect your irrigation pump from damage caused by running dry or deadheading. Both situations can result serious overheating of the pump and connected piping, and both would be an indication that no water is getting to the crop even though the pump is currently running - not good.A simple method of detecting these situations is to strap an inexpensive temperature sensor to the pump outlet. You then configure an alarm on the control system that will become active if the temperature sensor indicates an unusually high temperature at the pump outlet. This will indicate that the pump is either dry or deadheading. Depending upon your preferences, the alarm can be tied to the irrigation program as a failure indicator so that the pump will be shut down automatically (preventing damage), or you might want to configure an alarm that simply annunciates whenever there is a problem. This is just one example. There are other ways of detecting the above problem including the using a flow sensor, and there are hundreds of other ways you can use sensor based failure detection throughout your facility.Central and Remote ManagementComputers work with information. Input information is used to calculate an output response. In the process of doing this, the control system brings together tremendous amounts of useful information to a central place where you can review and evaluate it, and make informed decisions about your control strategies. Although many of our customers initially purchased their control systems for their obvious capabilities in equipment automation, many have told us that they only came to truly appreciate the huge benefits of the “Mission Control” capabilities of their systems once they started using them. Since the control system monitors greenhouse conditions and equipment states continuously, you can use it to warn you about problems at the earliest possible instance. These early warning alarms can sometimes be a crop saver. You can also use the information generated by the system to keep track of wear and tear, duty cycles, and the total operating times for equipment. For growing, you can review the daily recorded records of climate conditions and equipment responses to make sure that all equipment systems are working properly to achieve your control objectives.Putting all the Pieces TogetherIt takes more than a computer to manage your greenhouse climate efficiently. You need all of the following:
The unfortunate thing about the above ingredients is that they are each a limiting factor - it’s the one that your operation is the most deficient in that will drag you down. So even if you have top quality heating equipment, you’ll never realize its potential if you are lacking in any of these other dependant areas. Only your experience and perspective can determine which of these areas, if any, are holding you back. The control system simply provides you with a more precise tool for accomplishing your objectives. |
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