Industrial facilities rely on power-distribution systems to maintain stable and efficient operation. Plant systems have greater power demands than ever before. In most cases, when electric installations and devices shut down or malfunction, the problem is thermal.
This article describes how ultrasonic flow measurement can be used to optimize closed-loop (hydronic) cooling of integrated power-distribution systems. Ultrasonic meters monitor flow conditions throughout the system and provide data to help determine if fluid volumes are consistent and meet the necessary coolant demand.
Increasing awareness of limited energy resources coupled with the drive to minimize operating costs has focused attention on energy management. For industrial organizations, enhanced power-distribution systems are necessary to keep pace with technology improvements and support a fully integrated solution maximizing the efficient use of installed power generation.
The Need for Effective Cooling for Plant Operations
Electrical power is used in every aspect of plant operations, including processing units, control rooms, alarms, pollution controls, wastewater treatment facilities and cooling towers, instrument air supplies, lighting and personnel quarters.
A constant power supply is crucial for plants to operate safely and economically. The reliability of major equipment and facilities is essential to maintaining electricity supply and quality. Even the slightest shutdown or malfunction of the electrical installation can have major — even catastrophic — financial repercussions for a company, regardless of its business sector (figure 1).
Plants utilize distributed-power technologies to ensure a robust energy supply and increase productivity. Heat generated by electronic devices and circuitry however, must be dissipated to improve reliability and prevent premature failure. Traditional techniques for heat dissipation include heat sinks and fans for air-cooling as well as liquid cooling and other forms of automated cooling.
Hydronic cooling (i.e., the use of water as a heat-transfer medium) is commonly employed to keep the plant power systems within the proper operating temperature range. Water has a high thermal conductivity, meaning it absorbs heat easily — even more so than air. As such, it is effective for cooling power-supply equipment. Water cooling works by transferring heat from each part to a radiator that dissipates the heat and keeps the liquid cool. (In fact, it works almost exactly like a car’s radiator does.)
In any industrial hydronic cooling application, the liquid medium must flow within the system at the designed flow rates. It also is important to assess load variations. Load is calculated using the flow rate and the associated supply- and return-fluid temperatures. Hydronic cooling systems can be difficult to balance due to the presence of multiple system branches, changes in cooling demand and pressure differences among the various supply and return lines. Including balancing valves and flowmeters at each terminal or branch circuit facilitates balancing. To help reduce cooling system energy requirements, system designers also seek to minimize the cooling system pressure drop.
It is critically important to measure the bidirectional flow of liquid circulating in the hydronic system in order to monitor proper cooling performance. Flow measurement instruments are used to detect reduced flow rates, possible leakage and other abnormal conditions affecting the robustness of the cooling equipment.
Selecting the Right Flowmeter for Industrial Power Distribution Systems
Companies designing power-distribution systems for industrial facilities count on precise flow-measurement instrumentation to monitor flow through hydronic system piping to ensure coolant volumes remain consistent. Flow readings are needed at strategic locations to give a general overview of coolant supply and demand. In many cases, this necessitates a non-invasive metering solution. The flowmeter can easily be attached to piping to gather flow data without disrupting the system’s configuration and normal operation.
Certain flow-metering techniques lack the accuracy or responsiveness to optimize hydronic cooling operation. Poor meter performance can lead to large fluctuations in the coolant flow rate. This, in turn, results in excessive energy consumption at pumps due to continuous loading and unloading.
Where mechanical meters are used in liquid flow-measurement applications, there is an increased likelihood of deteriorating accuracy caused by wear and tear on the device. Additionally, the need for mechanical meters to be periodically tested, recalibrated and repaired means they have to be removed from service, forcing the user to replace the meter with a temporary device until the original unit is refitted back into the line.
Many power-system designers focus on transit-time ultrasonic flow measurement as an alternative to inline metering. Externally mounted, clamp-on ultrasonic meters are well suited for use with coolant-distribution lines. They are quick and easier to install than inline flowmeters because there is no need to cut the line, interrupt service or drain the pipe. The meters do not require the installation of bypass piping and valves for removal, and there is no pressure drop as with some other technologies.
Unlike Doppler-type ultrasonic flowmeters that depend on large particles or bubbles in the flow path to read a flow rate, ultrasonic devices employing a transit-time measurement method provide an accurate and reliable output without modifying the coolant flow.
Putting the Flow-Metering Solution to Work
For many power-distribution applications, the use of clamp-on, solid-state ultrasonic flowmeters meet key accuracy and bidirectional measurement criteria with an installation approach that satisfies cost, reliability and uninterrupted operation needs (figure 2).
A transit-time ultrasonic meter utilizes two transducers functioning as both ultrasonic transmitters and receivers. It operates by alternately transmitting and receiving a frequency-modulated burst of sound energy between the two transducers. The burst is first transmitted in the direction of fluid flow and then against fluid flow. Because sound energy in a moving liquid is carried faster when it travels in the direction of fluid flow (downstream) than it does when it travels against fluid flow (upstream), a differential in the times of flight will occur. The sound’s time of flight is accurately measured in both directions, and the difference in time of flight is calculated. The liquid velocity (V) inside the pipe can be related to the difference in time of flight (ΔT) through the following equation
V = K x D x (ΔT)
where K is a constant and D is the distance between the transducers (figure 3).
Transit-time ultrasonic flowmeters do not have moving parts to maintain or replace, making fluid compatibility and pressure head loss a non-issue. An aluminum enclosure also allows for a long service life. Most meters have a large measuring range that enables reliable readings at all designed AC IFTP system flow rates.
When integrated in the cooling apparatus for an industrial power-distribution system, the ultrasonic meters provide an analog 4 to 20 mA output to a data-acquisition system that corresponds to the instantaneous volumetric flow rate of the coolant. The meters offer low energy consumption, and the flow measurement data can be used to help reduce cooling system variability and maximize operational efficiency.
The ability to accurately measure both the quantity and rate of coolant passing through an industrial facility’s power system is crucial to gaining an informed understanding of overall power-distribution and management performance. With to ultrasonic flow-measurement technology, plants can be better equipped to meet the operational objectives while ensuring greater power-system reliability.