Industrial plants utilize process cooling systems such as chillers to regulate equipment and environmental temperatures. For example, chillers run cold water through machinery that runs hot to keep temperatures down. If equipment overheats, a system can default, causing production to stop until that device cools. Also, if a machine or device is working harder than necessary, it can consume more power. Maintaining an optimal operating temperature ensures that the machine operates efficiently, avoiding production halts while minimizing costs.

Fluids are a component of many process cooling systems. Water might run through chillers while HVAC systems could use oils or a water-glycol solution. Typically, a pump keeps the fluids circulating through these systems.

Monitoring fluid flow is important for accurate operations. Flow meters offer the ability to monitor fluids going through the pump to ensure that a process cooling system has an appropriate volume for proper operations.

Paddle-wheel flow meters

Paddle-wheel flow meters monitor various fluids in applications such as chillers/cooling circuits and industrial process control applications. | Image provided by AW-Lake

Choosing a Flow Meter

While various flow meters are available, choosing one that operates properly in specific environments and fluids is important for optimized and ongoing operations. Keep in mind that some applications focus more on economical operation while others focus on high accuracy. Here are some qualifying questions to ask when choosing a flow meter for a process cooling application.

1. What Fluid Will Run through the Meter?

Some meters are built to operate in water applications. As a result, they can better tolerate certain fluids found in chiller or cooling circuits, medical equipment and industrial process control applications. For example, while paddle-wheel and turbine flow meters both can operate in water or water/glycol fluids, the turbine flow meter can handle higher viscosity fluids such as antifreeze and fuels. Technologies such as positive-displacement flow meters are not suited for use in running water or water-glycol solutions. While the equipment might seem fine, water deposits can build up on the meters, causing premature failure.

2. What Is the Expected Flow Rate?

Flow rate is the movement of liquid through a pipe or other channel, and it determines a sufficient flow of fluids in industrial process cooling systems. Too much or too little flow can make a process cooling system inefficient, resulting in expensive equipment outages and production downtime.

The process cooling system design determines the flow of water that keeps a device at a certain temperature. For example, flow requirements to cool a CNC machine could be 5 gal/min or 0.5 gal/min. Flow meters determine if the flow rate deviates from the designed parameters (too high or low) and relays that information to a control system via pulse frequency or 4 to 20mA output. A programmable logic controller (PLC) in the control room then send a signal to the pump, or an operator receives information to adjust the pump. In most cases, the flow meter automatically signals the pump that it needs to increase or decrease its speed (rotations per minute, or rpm).

If no flow is occurring due to a break in a pump line, the flow meter will stop sending a reading. A zero signal to the control room indicates no flow. In most cases, the flow meter sends a signal to the pump to turn off. A pump working without fluid could become damaged, disrupting the rest of the system because it is unable to maintain the process cooling.

Monitoring fluid flow is important for accurate operations.

Typically, a pump keeps fluids circulating through systems. Monitoring fluid flow is important for accurate operations. | Image provided by AW-Lake

3. What Accuracy Is Needed from the Flow Meter?

Flow meter accuracy ensures that the correct quantities of fluid are moving from point A to point B. Accuracy is proportional to the number of measurements collected for flow calculation (e.g., 1 percent accuracy requires the capture of at least 100 readings). Accurate flow measurements are essential to properly monitor the process, diagnose system problems and ensure quality performance.

Flow rate transmitter

The weathertight and rugged construction of the flow rate transmitter makes it suitable for environments requiring a waterproof seal. Designed without delicate internal components, the meter will not break, abrade or corrode. The flow transmitters provide visual indication of flow rate that matches the transmitter output. | Image provided by AW-Lake

Some processes require different levels of accuracy when monitoring flow. Most process cooling applications do not require great accuracy because they do not need to verify the dispensed amount. While many turbine meters offer a ±1 percent or better reading for accuracy, a more economical paddle-wheel meter that offers ±2 percent or better accuracy can do the job.

For example, an MRI machine using a cooling system to control heat could use a paddle-wheel flow meter to ensure the correct amount of fluid. MRI systems require that the correct amount of flow to the machine is verified, but they do not require precise measurement readings.

4. What Is the Budget?

Your budget will guide you in selecting the flow meter that will best fit your application needs. Remember, customized options such as construction materials, ports and mounting options can add to costs.

Using Flow Meters in Real-World Process Cooling Applications

A few brief examples can illustrate how a flow meter is applied in process cooling applications.

Flow Meters Replace Switches to Control Tankless Water Heaters. Tankless water heaters serve multiple industrial purposes such as supplying warm water for emergency showers and eyewash stations. To gain better control of the heaters in large and small systems, a paddle-wheel flow meter can be used in place of a switch to turn the heaters on and off. A switch only monitors flow or no flow at one specific rate while the flow meter can monitor flow rate. In effect, the heaters can be turned on and off based on water consumption and not a fixed switch point. Larger systems using multiple heaters run more efficiently when turned off instead of running constantly.

For these reasons, a flow meter was installed in one a tankless water heater application. While chosen for its low pressure drop and cost, the paddle-wheel flow meter was customized to double its resolution. Changing to a curved-vane impeller design also improved the meter’s low flow performance and increased the rotational speed of the impeller. These customizations quadrupled the output signal. Fitting the flow meter with a three-pin connector and changing the signal cable location to the back of the unit simplified installation. Changing out flow switches with the flow meter makes the tankless water heaters more efficient, saving money and making water temperature control more precise.

Flow Meters Ensure Correct Water Flow in Power Plant Cooling Systems. In the generation of electricity, power plants produce a lot of heat. As in industrial plants, water cools different components to ensure that the plant operates at a stable temperature.

Many plants recycle water using a recirculating water system that cools warmed water for reuse. As the water becomes dirty, a scrubber filters water through a vaporization process to remove debris. Flow meters located outside the scrubber monitor the flow of the cleaned water as it travels back into the different lines of the plant to cool different components. In one installation, three flow rate transmitters serve as a redundant system to monitor water flow based on specifications. A specific flow of water (gallons per minute) is needed to ensure enough movement of water to cool equipment. The flow meters provide both a visual indication of flow rate that match a 4 to 20 mA transmitted output to a programmable logic controller. PC