Operation and Energy Benefits of Computerized Control Systems
Computerized control systems provide benefits that can be categorized into four distinct groups:
- Information management
- Improved work conditions.
This paper will discuss these benefits in a very subjective manner based on experiences in the CA industry, since the application of computer based control systems began ten years ago. During this period, there has been an extensive progression of techniques designed to enhance the postharvest operation.
Initially, computers were primarily used for monitoring levels of oxygen and carbon dioxide in the CA rooms, and controlling vent fans when the oxygen levels dropped below desired setpoints. This new technology saved a lot of time in taking manual readings, and did a much better job of maintaining the oxygen at a constant level. Today, virtually every piece of equipment in a storage facility is monitored and controlled by a computerized system to minimize the time required to check for proper operation, take readings, and make adjustments. The automation of these routine tasks allows employees to focus on other non-routine duties, or to take on additional responsibilities. In fact, new storage facilities can be operated and maintained without hiring additional personnel.
In many cases, maintenance time is significantly less due to the reduced run-time of equipment, which extends the overhaul interval. For example, instead of continuously running the maximum number of compressors necessary to carry an anticipated peak load, a good control system will sequence units on or off as the refrigeration load varies. This can substantially cut the hours expended in rebuilding compressors by reducing operating time. Fan cycling and variable speed control of fans and compressors can also contribute to longer service of equipment.
Better monitoring of the plant operation, thus facilitating early detection of faulty equipment, can also minimize maintenance requirements. Computerized control systems provide information that would otherwise be unavailable, enabling personnel to quickly identify malfunctions before a complete failure occurs. In addition, time spent in troubleshooting problems is greatly decreased. A common example is the detection of leaking liquid refrigerant valves, or defective surge drum level control switches, by monitoring and recording the on/off cycles of these devices, which provides data that will quickly pinpoint the source of a flood-back problem.
Controlled atmosphere warehouses are generally unmanned, and as companies increase their storage capacity, storage rooms are often spread out geographically. It becomes harder to keep up with the vital need to make regular inspection of equipment to insure that proper conditions are maintained. Computerized control systems provide a means to easily stay in touch using dial-up modems. All of the control system functionality available at the storage facility can be utilized from anywhere in the world that a telephone is installed. This feature is especially useful for operations personnel at night, on weekends or holidays, and while on vacation.
Computerized control systems have a definite effect on the profitability of a CA storage operation. Although it is very difficult to quantify, the most important financial benefit is very likely the enhanced fruit quality that results from precisely maintaining the optimum temperature and oxygen level. The storage temperature is routinely kept within ±0.2 °F of the desired set point, and the oxygen level within ±0.1% of setpoint, when a computerized system is in control. This is not possible without a comprehensive control system. In addition, reduced fan operation through fan cycling or variable speed control, has proven to decrease fruit moisture loss through transpiration. The number of defrost cycles can be reduced by allowing the system to detect inefficient evaporator performance, thereby avoiding unnecessary heat gain which must be removed at the expense of additional moisture loss. The prevention of weight loss, which can be as much as 5%, and shrivel are very important factors in fruit quality, and thus revenue.
Some of the control system techniques mentioned above also have a great impact on the amount of energy required to operate a CA storage facility. Fan cycling and variable speed control of evaporator fans generally offer the greatest potential for cost reduction. Reduced fan operation can cut electrical energy use by 25 to 50% annually. Therefore, efficient control methods for compressors and condensers not only reduce maintenance costs; they have a very significant effect on power bills too. Unnecessary defrosting not only increases fruit moisture loss, but wastes energy as well.
The time-saving potential of computerized control systems was discussed previously. The reduction in operation and maintenance expenditures also has a very positive impact on business profitability.
The extensive monitoring features of a good control system can effectively be used to minimize the risk of casualty loss. If the storage parameters for temperature or oxygen exceed the adjustable limits, alarms are activated to quickly alert personnel. If no one is near the control computer, a telephone auto-dialer will call emergency numbers to insure that the problem is brought to the attention of responsible personnel. High suction pressure, ammonia leak, and computer failure are other conditions that will activate the alarm system. Insurance coverage may provide relief when damage to product or equipment occurs, but it is still financially advantageous to avoid or minimize such a mishap.
The computerized control system offers a significant advantage to the storage operation by performing many data management functions such as report generation and historical records needed for informational sales. This information is also useful for management decisions, quality analysis, and year to year comparison of operational data.
The computer is a very versatile tool for generating printed reports for CA logs or general plant operation. Historical records are automatically archived on the computer hard drive for subsequent retrieval and analysis. Data that is as much as several years old can be imported into a spreadsheet for tabular or graphical display. This feature has been vital for international fruit sales to Mexico and Japan. Historical records also provide a means to compare year-to-year operational parameters such as energy use, ambient temperature conditions, storage criterion for temperature, oxygen, and carbon dioxide, and equipment operation.
Plant operators find that the increased information provided by computerized control systems help them to understand more about their facility, and how better control and efficiency can be achieved. Alarm generation, as previously described in a financial context, is also pertinent to the discussion of information management since operations personnel are able to be notified any time that critical conditions exist. It is important that the people responsible have this information in a timely manner.
Improved Work Conditions
Rarely do CA facility operations personnel, once they have used a computerized control system, express a desire to go back to less sophisticated control methods. It is a great relief to eliminate the guesswork of inaccurate readings and the constant adjustments of control devices. A twice-daily walkthrough of the plant and quick scan of the information displayed on computer screens are usually all that is required. The rest of the day can be spent performing maintenance or other non-routine tasks, or a greater number of storages can be operated than would otherwise be possible.
The elimination of off-hour inspections is probably the most significant work conditions benefit of a computerized control system. Who would want to leave family and friends on Christmas, or other important holiday, or weekends for that matter, to go out in the cold to check a very lonely warehouse? A modem linl from wherever a notebook computer can be connected to a telephone line puts an operator in control of the CA facility. During the busy harvest season the modem feature is a real benefit in monitoring the pull-down of newly sealed rooms. It also is very convenient to check the plant from home, when an auto-dialer wakes an operator up in the middle of the night, to remotely fix the problem or determine if it is serious enough to leave a warm bed.
Another fringe benefit is the opportunity to work with state-of-the-art control equipment. Many plant operators have never used a computer before a computerized system was installed. Some have become quite proficient with the use of computers as a result of their exposure to the capabilities of new control systems. It is rewarding to learn new skills and keep up with technological advancements.
Computerized control systems have significantly improved postharvest operations over the last ten years. Plant operators have been relieved of the tedious tasks of keeping the facility at desired conditions by manual readings and adjustments, and have been able to focus on maintenance tasks or other responsibilities. Maintenance intervals are often extended and the same number of people can operate more facilities.
Business profitability is enhanced by improved control of the storage environment, which results in better fruit quality. Energy savings techniques can reduce electrical costs by 25 to 50% annually. Maintenance and labor expenses are also reduced.
Information available from the computerized system enables the compilation of historical reports, which are vital to international sales. Other reports, and alarm generation, keep operations and management personnel informed on the storage operation.
Working conditions of plant operators are improved by reducing the number of off-hour inspections, and providing the opportunity to work with state-of-the-art technology.
Computerized control systems are widely used in fruit storage facilities because they offer time savings, greater profitability, better information, and improved work conditions.
13th Annual Postharvest Conference