Multiplexing Systems The Argus control system is designed to handle the monitoring and control of all types of irrigation and nutrient delivery systems.
Multi-Feed Systems… • Uses proven Argus Feed-Forward control intelligence for fast response and the highest dosing accuracy and safety. • Engineered to your specifications (single head, A/B, or multi-head options). • Ideal for pressurized in-line or dilute tank applications. • Low residual volumes for efficient feed switching. • Excellent mixing at all system flow rates. • High turndown models are available • Works with fresh supply and recirculating systems.
Argus Multi-Feed Systems… • Works with a wide range of stock concentration strengths. • No additional pumps required - works with your system pump • Works with system pressures from 15-75 psi. • Few moving parts - made from simple, high quality components. • Compact, easy-to-install, wall mountable design. • Easy to operate - controlled by your Argus system. • Uses standard monitoring, alarms, and nutrient control programs. • Positive isolation of stock solutions to prevent accidental siphoning.
Multiplexing Systems… • When designing a multiplexing irrigation system, the control system, injection equipment, and related switchgear is actually the easy part. • There are some fundamental plumbing and application issues that must be considered before you start. The type of delivery system you choose will ultimately depend on your needs and priorities.
Multiplexing Systems… Consider the following scenarios. They start from the simplest, to more complex systems. We’ll discuss their respective advantages and disadvantages as we go along.
Example 1 – A Single Zone System • One feed recipe • One distribution path (piping system) • One watering zone • No recirculation
Example 1 – Single Zone Systems… • With this system you always have the correct feed in the lines, and you can water whenever you likefor as long as you like. • This type of system easily lends itself to a dilute tank or a simple injection system. • Zone valves are seldom required and the pump can be operated either manually, or with a simple timer. • If the pump is operated by your Argus computer, you can use irrigation decision making programs for scheduling your waterings.
Example 1 – Single Zone Systems… Advantages: • Very simple design • Few parts • No waiting for other zones to finish watering • No cross-contamination of feeds or pathogens
Example 1 – Single Zone Systems… • Disadvantages: • Since everything is watered at the same time, all crops get the same amount of water and your pump and piping needs to be sized for 100% of the delivery capacity.
Example 2 – Multi-Zone Systems • One feed • One distribution path • Multiple watering zones • No recirculation More than one zone can be serviced by the same system.
Example 2…Multi-Zone Systems Irrigation systems are divided into zones for two reasons: • To enable different watering frequencies and applied volumes for different cropping sections or compartments. • To reduce the overall system capacity requirements by watering in sections at different times.
Example 2…Multi-Zone Systems It is seldom practical to construct an irrigation system with the capacity to service the entire facility at once. • For example, if you have a hectare of drippers to water, and the total capacity of the all the drippers requires 10,000 liters per minute, you will need to build a system capable of delivering 10,000 lpm. • However, if you can divide the hectare into 10 equal sized watering zones, each with its own solenoid valve, you can then water one zone at a time. This will reduce the watering requirement to 1000 liters per minute. • You can then construct a watering system that is 1/10 the size of a single zone system. This means you can use smaller, less expensive piping, and a much smaller pump.
Example 2…Multi-Zone Systems Advantages • Lower installation costs than a comparable one-zone system. • Lower installation costs than multiple independent systems (i.e. a separate irrigation system for each zone) • Design is relatively simple • Relatively few parts
Example 2…Multi-Zone Systems Disadvantages • If all of the zones cannot be watered simultaneously, then the system capacitymust be managed. Zones that require water may sometimes have to wait to be serviced. • There must be sufficient time for all zones to be watered sequentially, or as required. This is very important!If any of the zones need to be watered so frequently that the other zones will never get a chance to be watered, the system will fail.
Capacity Management Multi-zone watering systems that require capacity management can be managed in two ways: • Manually separate the watering times using a multi-zone irrigation time clock. • Use the features of the Argus System for automatic capacity management of independent zone watering schedules. (Unlike irrigation time clocks, Argus watering schedules do not need to manually separated in time. The system automatically handles irrigation requests whenever they occur, and processes them as system capacity becomes available.)
Example 3 – Multiple Feeds • Multiple feeds • One distribution path • Multiple watering zones • No recirculation
Multiple Feeds • This example further complicates matters by introducing multiple feed recipes that need to be delivered to multiple watering zones. • You now need a system that can either produce, or select between prepared fertilizer recipes. • At this point, irrigation time clocks are generally not an option - you are going to need a computer. • With the Argus control system and the Argus Multi-Feed nutrient injection system, you can easily specify the strength (EC) and pH of the fertilizers, as well as the selected fertilizer stock concentrates that are delivered to each zone.
Multiple Feeds… A major drawback of this type of design is not the control of the system, but a physical design problem: • Since there is only one distribution path (piping system), whenever the feed is switched, there will always be a residual volume of the wrong feed in the distribution lines. • Depending on the amount of residual volume in relation to the amount to be delivered, this may be a minor nuisance, or a significant problem. • In the worst cases, it could mean that little or none of the intended feed may reach the target crop, since it will first receive the (wrong) residual feed that is in the lines. This will happen every time the feed is switched!
Multiple Feeds… • As a compromise, some irrigation systems are designed with purge valves to dump the residual volumes in the distribution lines whenever there is a feed switchover. • This dumped feed can be either wasted or delivered to a holding tank for some sort of reuse. • This situation is often less than ideal. Purging can take up time from an already busy system, and the purged volumes are wasteful, particularly if the feeds are being switched often (some growers have found a use for captured purge water on low value outdoor crops). • It is possible, but seldom practical to return the purged feeds to separate holding tanks
Multiple Feeds… There are other instances where centrally mixed, multiple-feed systems may be impractical, particularly in research facilities: • The diverse and changing needs of research projects can make it impractical to rely on a central system to deliver multiple fertilizer recipes. • The negative effects of variable fertilizer content on controlled studies is obvious. Therefore, line purging is almost always necessary. This may create a waste disposal issue. • With changing needs, there may be times when more recipes are required than your system is designed to accommodate. • As the central mixing requirements become more complex, maintenance and management requirements will also increase.
Multiple Feeds… Many customers opt for a compromise: • Use a central fertilizer mixing system to deliver one or two ‘house’ feeds in dedicated distribution piping lines. For example, each compartment can be supplied with manual and automated valves for each house feed that is provided, as well as plain water. • Prepare and deliver project-specific feeds in the zones. When a project needs specialized feed recipes, users can resort to the standard ‘garbage-can-and-Little-Giant-pump’ systems or other in-zone fertilizer delivery methods.
Multiple Feeds… We have seen this compromise approach work very well in many institutional settings. • If your compartments are provided with computer controlled outlets and a few spare inputs for monitoring, you can still have fully automated control. • You can use your Argus system to manage these one-bench irrigation systems with as much sophistication as your central system.
Example 4 • Multiple feeds • Multiple Distribution Lines • Multiple watering zones • No recirculation
Multiple Distribution… It is possible to provide an independent distribution line for each centrally mixed feed. • This avoids the problems of residual volumes of the wrong fertilizer in the lines. • The practicality of this design depends on the number of feeds you intend to supply and the distribution distances that are involved. • Though more expensive to install, it solves the problem of residual feeds. In practice however, due to the expense and complexity of the equipment required, this design is seldom used for more than two or three feeds.
Recirculation… • Many facilities recirculate some or all of their drain water from irrigation activities. • While reducing waste, recirculation adds further complexity and risk.
Recirculation… The physical, chemical, and biological qualities of the recirculated water must be considered before it is added back into the irrigation system.
Recirculation… Physical Depending on the design of your delivery system (drippers, sprinklers, flood tables etc.), you may need to remove particulates before the recirculated water is suitable for reuse.
Recirculation… Chemical • The EC and pH of the recirculated nutrients must also be compensated for before it is returned to the crop. • In the longer term, complete comical analysis is often required to monitor the balance of nutrients and other chemicals that may accumulate in the water as a consequence of recirculation.
Recirculation… Biological • Since it is possible for water-borne pathogens to spread through recirculated irrigation systems, you may need to take measures to disinfect the recirculated water. • This could require pasteurization, UV sterilizations, slow sand filtration, or other methods.
Recirculation… Drain Water Collection • The Argus control system can be used to manage drain water collection for one or more feeds. • Though useful for waste control, a single drain reservoir for multiple feeds is generally impractical for recirculation, since it defeats the purpose of individual feeds. • It is possible to install a number of drainage reservoirs, one for each feed, and to use the control system to manage the required isolating switchgear. • If any common return piping is shared, cross- contamination with pathogens and other chemicals can still occur. • In situations that demand strict isolation, the only practical solution is to use single-zone or single-bench recirculating systems. The Argus system can be used to operate these as well as central mixing systems.
Conclusions Multiplexing irrigation and nutrient delivery feed systems almost always sound like a great idea until you study the details.
Conclusions… The notion of having almost any feed recipe ‘on tap’ is an attractive one. Computerized control systems such as the Argus system have helped to make this goal attainable.
Conclusions… You need to consider: • the complexity of the equipment and piping systems involved • the isolation requirements • the day-to-day management issues • the compromises that must be made when you employ a multiplexing system.
Conclusions… • Argus has many years experience in designing and providing multiplexing irrigation and nutrient control systems. • We can provide systems as simple, or as complex as you require. • Generally, the simplest approaches are the most successful in the long run.