With weather patterns more unpredictable than ever and climate concerns leading to more uncertainty, precipitation seems more unreliable than ever. Enter irrigation systems. Once seen as a backup to Mother Nature, these have become critical infrastructure for farmers, assuring precipitation even during dry periods.
What goes into engineering an irrigation water system that benefits the agriculture industry? What components are needed and what considerations factor into getting the most out of the system? To answer these questions, let’s take a closer look at how certain system components such as variable frequency drives and permanent magnet motors can deliver water consistently across any given area.
Accessing water is one thing. Optimizing and controlling its delivery is something else entirely. Too much water, and you can flood fields. Too little and the effort is wasted. In both cases, money is also wasted with excess water usage or spoiled crops.
This is where a VFD system comes in. VFDs put technology to work for owners, allowing them to control water with constant pressure and precision. They are available in an array of submersible and aboveground applications with varying horsepower options. When selecting a VFD, users should consider the features that offer the biggest benefits to the agriculture industry, such as constant pressure, soft-start protection, input and output adjustments, and reporting capabilities.
Another top consideration is the motor. While the VFD can help control the motor for maximum efficiency, some motors offer lower operating costs than others. For example, the energy used by induction motors can equate to up to 97% of the motor’s total lifetime cost. In contrast, a pumping system powered by a permanent magnet motor and optimized with a drive runs much more efficiently (up to 94% efficiency rate) and delivers up to 21% energy savings when compared with its counterpart. This is especially true in a demanding agriculture and irrigation setting where the pump runs constantly to maximize production results. These savings can add up and will multiply over the years. Running these in specific applications can mitigate operational costs and quickly offset additional initial investment expenses.
To understand the benefit of the constant pressure supplied by a VFD system, consider what likely happens without one. Many conventional irrigation systems utilize a pumping system running at a single speed to distribute water across a field. The result is often inconsistent surface-level watering, coverage gaps, increased watering time, runoff and wasted water. That’s where constant pressure systems can offer better performance, as they are designed to maintain a set pressure across the entire system. Whether driving a center pivot, multiple sprinklers, a drip system or misters, the system is designed to perform efficiently across a field. Constant pressure allows operators to dial in the ideal pressure required to operate their nozzles and emitters to what’s best for their application and crops.
Wasting water isn’t the only concern for irrigation systems. Systems need to be built for resiliency, to adapt and overcome unforeseen environmental conditions. For example, with the effects of climate change and warmer temperatures, a pivot irrigation sprinkler system in Texas that used to be supplied by three wells needs to expand to more than 10 wells. A situation like this equates to additional energy requirements that could be partially or completely offset with PM motors.
In contrast with the demand during the peak irrigation season, it’s also important to slow the system down when irrigation demand is more limited. The installation of a constant pressure system allows irrigation professionals to set the pressure to one setpoint at varying flow rates to match a pump’s performance for irrigation demand that changes with the season, vegetation type or drought conditions. Most VFD systems use a pressure sensor to measure water pressure. The sensor sends a signal to the VFD which automatically regulates the speed of the pump to meet the demand for water, all while keeping pressure constant throughout the system.
Dry seasons can also lead to low water levels in a well. VFDs can account for this and are customizable for underload sensitivity and off time. This helps to protect a pump from dry run while it also reduces the risk of the well running dry entirely.
Agricultural irrigation operations put a unique type of strain on pumping systems, especially during seasonal or daily startup. The average number of starts per day over a period of months or years influences the life of a submersible pumping system. Too much stress can lead to water hammer, hard starts and premature pump failure. With a VFD, this stress can be alleviated.
VFDs improve system life with a soft-start feature that controls the electrical current and therefore the voltage applied to a motor to reduce stress. This “easing-in” to running at full speed minimizes pressure on elbows, underground pipe joints and pivot nozzles. It also helps reduce the heat input to the motor, which can be a big help in prolonging motor life.
VFDs also provide benefits and flexibility with respect to the power quality that is applied to the motor. Most importantly, a VFD can provide three-phase power to the motor even when the power supplied by the utility may be unstable or unbalanced. This is common in rural applications where the site is located at the end of a power run, resulting in voltage fluctuations in response to large changes in load. Applying unbalanced voltage to a motor results in additional heat, which in turn reduces the life of the motor. The balanced power output from a VFD is important for extending the life of the motor.
At the beginning of the growing season, VFDs help to reduce water hammer with a pipe-fill mode. Water hammer occurs when empty pipes in an irrigation system are rushed full of water. Pressure can’t be controlled, and this causes a flood of water to overwhelm the pipes and check valves, creating mini shock waves across the system. It’s like slamming a hammer on your pipes, and this force can damage piping, fittings, emitters and valves. If severe enough, it can also damage the thrust bearing in a submersible motor. With a VFD’s pipe-fill mode, operators can automatically reduce the flow and velocity of water to mitigate this effect.
In addition to regulating water pressure during start-up, VFDs can protect against over-pressure or underload, stabilizing the entire system. Whether your water levels are high or low, a VFD paired with a properly sized pump will offer consistent operation in various conditions.
Today’s VFDs are engineered to deliver ease of use and can be seamlessly paired to perform with PM motors driving increased efficiency. As technology progresses, manufacturers continue to develop cost-effective solutions that are built around designs engineered to operate with both induction and PM technology. This means that even if you don’t choose to pair your VFD with a PM motor initially, you can upgrade it in the future.
VFDs can also come with advanced features like dual demand or dual setpoints. This is important in irrigation systems that vary in distance, elevation, zone size or water coverage needs. For example, if a farm is near a mountainous area and experiences elevation changes across its property, this may affect water distribution. Dual setpoints can manually be established to ensure consistent water across the fields, from valleys to hills. If a system uses different irrigation emitters, such as drip tape in one area and overhead sprinklers in another, dual setpoints can optimize coverage for various types of distribution.
Farmers and irrigation operators also have more customizable control over their system with a VFD. With that system, run commands can be tied into sprinkler timers or other irrigation controls so that the pump and motor will only run when the system is ready to irrigate. Users can also take advantage of built-in relays and other input and outputs on the VFD to communicate with propulsion motors and start-stop commands. These advanced communication options also provide the potential to be utilized with remote monitoring of multiple systems to enable status tracking and added control. This information is stored and readily available for run reports or to allow service professionals to access needed details about the system.
A water pumping system paired with a VFD can help agriculture professionals prioritize what’s most important for their system. Constant pressure is essential, as is reporting capabilities, soft-start protection and energy savings. It’s also important to understand the long-term performance capabilities of the system. Can it prevent a dry-well scenario, protect against pipe leaks and electrical surges and reduce stress on plumbing? The biggest benefits come from selecting the best system from the start, one that’s maximized for energy efficiency and designed to easily upgrade or retrofit down the road.