Standard 163: Vibration Limits in Water Cooling Towers
Interested in learning more about vibration limits in water cooling towers? If so, CTI has the perfect resource paper to take advantage of!
What are Water Cooling Towers?
Water cooling towers are heat exchanging devices that cause air and water to come in contact directly with each other. When these elements meet, this causes a small amount of water to evaporate into a vapor. The vapor is then recirculated throughout the unit and causes the temperature of the water to cool. These types of towers are primarily used for ventilation, industrial, heating, and air conditioning (HVAC) purposes. Additionally, one of the important things about cooling towers is that they provide both an energy-efficient and cost-effective way to remove heat and revitalize it to heat or cool buildings.
There are multiple types of water cooling towers but the most common types include crossflow and counterflow towers. Each type of water cooling tower is categorized by how either air or water pushes through them. In a crossflow cooling tower, water enters on each end of the tower. The air is then drawn in from the side of the tower, which is perpendicular to the flow of water. Then, the air continues into the middle of the tower where the fan pushes the air out of the top of the tower. In a counterflow cooling tower, the air is drawn into the tower from the bottom and moves in the opposite direction of the water. The water is then moved through the fill and is pushed out of the top of the tower by the fan.
What are Vibration Limits and What are the Necessary Tools to Use to Measure These Standards?
Vibration limits are specific standards set forth by organizations to follow in order to avoid damages to the machines that have any rotating parts, specifically in water cooling towers. The primary rotational frequencies that produce vibrations in cooling towers are as follows:
Fan rotational speed
70-400 revolutions per minute (rpm)
Drive motor speed
Fan blade passing
Fan speed X number of blades (400-3,000 CPM)
Gear mesh (6,000-60,000 cycles per minute)
Also, note that variable speed drive motors are commonly used to control cooling tower fan speeds. With this being said, the drive motor speeds from 600 RPM to synchronous speed of the motor are encountered during situ measurements.
When testing vibration standards and limits in water cooling towers, it is important that the broadband velocity measurements are taken and should be made with a standard industrial accelerometer. This device should also be used to complete both velocity and displacement measurements. Additionally, the results of the tests should be contrasted with the requirements of an FFT analyzer.
When using an accelerometer, it is important to mount the device to the machine so the measurements can be taken accurately and efficiently. Also, vibration measurements should be taken of each of these items: motor vibration, gear reducer vibration, belt drive fans, and fan stacks. Furthermore, the criteria for measuring cooling tower mechanical vibration levels should be taken in broadband total vibration levels.
The overall vibration level of a cooling tower is always in a combination of vibration levels at different rotational frequencies and system harmonics related to the fundamental rotational frequencies of the machine. With this being said, vibration analyzers may be used to measure the various required units such as displacement, velocity, and acceleration.
CTI Resource About Vibration Limits
CTI’s resource paper is catered to providing cooling tower owners and manufacturers specific specifications for acceptable mechanical vibration levels, specifically focusing on new cooling towers. Detailed inside this standard paper is an overview of vibration limits in water cooling towers. It also includes standards and guidelines for vibration standards/limits based on the various materials of construction classification. Additionally, CTI’s paper includes multiple diagrams of the typical fiberglass or wood cooling towers and their mechanical equipment arrangement. Lastly, the diagrams included in this standard state the specific frequency vibration guidelines on these types of measurements: measurement location, frequency range (CPM), zone classification [velocity inches/sec (mm/sec) peak], and fan balance qualities.
Are you interested in learning more about vibration limits in water cooling towers? If so, purchase the full standard here!
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Cooling Technology Institute provides independent, third-party thermal performance testing to help participating manufacturers and owners/operators achieve the best performance from their cooling towers. CTI is also an advocate in promoting the use of environmentally responsible Evaporative Heat Transfer Systems (EHTS), cooling towers, and cooling technology for the benefit of the public. CTI has published many papers about various cooling technology topics. For more information, contact us today!