How efficient is the heat exchanger of your home’s air conditioner? Is the fan motor working harder than it has to for the amount of cooling you’re using? Since many of the people reading this are probably engineers, you may be able to provide a specific answer, but most people don’t probably know. The cost of potential inefficiency is simply too small to justify any effort to measure or fix it.
For industrial users with huge air-cooled heat exchangers, the answer could be far more important. Major amounts of money could be at stake, but many users are not making any effort to measure or fix the situation. The cost of getting the needed information and putting it to use is too high, or so they think. In an article in the January 2019 issue of Process Heating, Measure and Improve Air-Cooled Heat Exchanger Performance, Brian Joe challenges that notion and offers practical alternatives.
In the past, monitoring air-cooled heat exchanger performance was often too expensive. Wireless instruments and pre-built analytics have greatly simplified the required effort. The size of the installation and the potential for energy savings will determine the return on investment possible compared against the cost necessary to realize such savings.
Understanding what a user needs to be concerned about depends on understanding how a heat exchanger works, so Brian spends some time explaining the processes. Once understood, tools are needed to quantify the critical attributes.
The ability to determine how efficiently a heat exchanger is operating depends on measuring what it is doing. Ideally, any installation should be equipped with a full complement of instrumentation to monitor process fluid inlet and outlet temperatures along with process fluid flows. With the data from these instruments, it is possible to determine the heat exchanger’s efficiency.
Brian makes the point that the instrumentation needed is basic stuff, a few temperature transmitters and rotating equipment monitors to evaluate the operation of fan motors and the like. They can be installed using WirelessHART to avoid the costs of wiring them to a conventional automation system. It’s probably those costs that keep many facilities from making the effort, so eliminating them is the most important step to implementation in most cases.
A sophisticated installation will likely have these instruments — or at least some of them — in place. The actual instruments may not be attached directly to the heat exchanger, but the same temperatures may be measured at other points upstream or downstream. By contrast, a more sparse installation may have none of these measurements, leaving the heat exchanger to operate at one speed and the process to deteriorate without warning.
The article goes into more detail about what problems tend to persist, such as fouling, which is able to rob efficiency and decrease performance. It also discusses ways in which those problems can be detected using the instrumentation and analysis software to turn the data into useful information.
Analysis apps designed to perform specific asset monitoring and evaluation functions augment and complement the wireless sensor network. These apps are purpose-built to capture data from instruments attached to plant assets. They include algorithms to look for fault conditions such as fouling by calculating changes in differential pressure across the process fluid line and temperature implications.
The apps, in this case, are from the Plantweb Insight family, specifically one designed just for air-cooled heat exchangers. There are many other apps available in this product family to cover the bulk of critical assets in a typical process plant, and each is easy to use and inexpensive to deploy.
You can find more information like this and meet with other people looking at the same kinds of situations in the Emerson Exchange365 community. It’s a place where you can communicate and exchange information with experts and peers in all sorts of industries around the world. Look for the Condition Monitoring and IIoT Groups, and other specialty areas for suggestions and answers.
Posted by Deanna Johnson, Rosemount Measurement & Analytical Global Marcom Manager, Emerson Automation Solutions
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