The heat exchanger is the most crucial part of HVAC systems. Through a cooling system, heat is transferred from all around the surroundings. The heat exchanger of commercial HVAC is primarily located in the cooling towers. These towers are specialized heat exchangers. In this process, air and water work together to decrease or cool down the water’s temperature. When this happens, a small volume of water evaporates, creating a cooling effect. Cooling towers process water and transfer the heat, which goes back into the atmosphere.
Cooling towers are made of different parts. They tend to be complex machines that are big in size. Hence, they are often located in remote areas of industrial buildings. Cooling towers are prone to environmental, safety, and profitability impacts of failure. Thus, it is vital to monitor and keep these systems in optimal condition. Thus, installing automated and remote monitoring systems is of utmost importance.
Operation For Industrial Cooling Towers
Commercial and industrial buildings often used cooling towers. These towers help to cool down HVAC components. They also allow HVAC systems to function more easily and efficiently. Their primary function is to remove heat from the water coming from the condenser. Consequently, so that the water can be discharged to the environment. The water used in cooling towers can also be recirculated and reused.
According to Kubba, “Cooling towers are used in conjunction only with water-cooled chillers. They vary in size from small rooftop units to very large hyperboloid structures. Cooling towers are also characterized by the means by which air is moved.”
The most common type of cooling tower is the mechanical draft. Mechanical draft cooling towers use power-driven fans to function. They draw or force air through the tower. Mechanical draft towers are further classified into two types. These are the induced raft cooling towers and forced draft cooling towers.
As stated by Kubba, “Induced draft towers have a large propeller fan at the top of the tower. It draws the air upward through the tower while warm condenser water spills down. It requires much smaller fan motors for the same capacity as forced draft towers. Forced draft towers use a fan at the bottom or side of the structure. Air is forced through the water spill area and discharged out the top of the structure. It is pumped to a heat exchanger or condenser in the refrigeration after the water has been cooled in the cooling tower unit. This is where it picks up the heat again and is returned to the tower.”
Operational Failures of Industrial Cooling Towers
Cooling towers are prone to different operational failures. Mechanical draft cooling towers work through big fans. According to Skeirik, “These enormous fans are driven by motors via a right-angle gearbox. Despite their relatively slow rotational speed, the fans possess immense inertia. When allowed to run to failure, this inertia is transformed into a destructive force. It can bring down the tower. It can also compromise the structural integrity of the entire platform.” This kind of incident is a risk to the occupants’ health and safety. It can also prolong process shutdown or slowdown.
Aside from this, a cooling tower failure has a serious impact on production. Since cooling towers are not easily accessible, they require specialized manpower. They also need equipment to move and service. Skeirik wrote, “Crane machine is often necessary to perform service. This is due to the location and size of the equipment and the tower. Operation is further compromised when replacement components have long lead times. An unexpected failure could leave sections of the plant down for an extended period of time”.
Furthermore, the CDC warns about the potential risk of cooling towers in causing Legionnaires’ disease. According to the CDC, “Cooling towers contain large amounts of water. They are potential breeding grounds for Legionella bacteria. If they are not properly disinfected and maintained. Water within cooling towers is heated via heat exchange. It is an ideal environment for Legionella heat-loving bacteria to grow. Legionnaires’ disease can be acquired when an individual breathes in water droplets containing Legionella bacteria.”
Cooling towers can fail due to their components. The fans may fail due to an imbalance caused by the damage to one of the fan blades. Jackshaft can also cause failure. When the long shaft between the motor and gearbox becomes misaligned, it can lead to coupling wear. But gearbox itself is the most common cause of cooling towers failure. The gearbox can be broken, chipped, or worn gear teeth. It can also have defects in the bearings. These issues are usually caused by insufficient lubrication.
Cooling Towers Automated Monitoring Through Vibration Switches
The vibration sensor is the most preferred solution for cooling tower‘s operational failure. The components of cooling towers can be monitored by professionals. But the structure of cooling towers makes it difficult and dangerous for professionals to monitor them. Since cooling towers are always located in remote areas of buildings. It requires significant time and effort to reach the area. The vital components such as jackshaft, gearbox, and fans are also located inside the shrouds of cooling towers. Hence, it poses a great risk to access and monitor the components.
According to Skeirik, “Automated monitoring is the basic form of vibration switch. These basic systems utilize a simplistic operating mechanism. An embedded sensor detects excessive vibration and can shut off the unit.”
Vibration switches possess some disadvantages. They can only detect lower-frequency vibration. Vibration switches cannot detect most key failure modes. That is, under lubrication, gear defects, and bearing faults. These types of failures generate higher-frequency vibrations. The operator can only be notified after the cooling fan has already been tripped. Although a vibration switch can help keep away a disastrous failure, it offers not much. It does not give an advance alarm to help optimize maintenance. Also, reduce operational failure impacts.
One of the advantages of vibration switches is their maintenance-free operation. Skeirik added, “One of the biggest advantages to vibration switches can also be their biggest drawback. Continual exposure to water and chemical vapors can eventually lead to corrosion. This is despite their simplistic design. Vibration switches are usually unmonitored. The first indication that a switch is defective might occur when the fan runs to failure.”
Remote Monitoring To Prevent Operational Failures of Cooling Towers
The vibration sensor must provide two types of parameters. The low-frequency and the high-frequency. Like a vibration switch, low-frequency vibration provides an alert on fan imbalances. While the high-frequency vibration publishes the impacting signals. That is the under lubrication, gear defects, and bearing faults. The high-frequency vibration is often measured in peak acceleration. This is essential to the whole operation. It constitutes the level of impact happening in the gearbox and other components as well.
Skeirik noted the importance of the “Zero Principle“. According to them, “A piece of rotating equipment that is properly installed and well-lubricated should have little to no impacting. From this, we deduce the Zero Principle. The impact on a good machine should be at or close to zero. When the level of impacting reaches double digits, a defect is developing on the machine. Each time the amplitude of the impacting doubles, it represents an escalation in the criticality of the defect. This leads to the “Rule of 10s.’”
Remote monitoring is the most effective method to prevent failures of cooling towers. It helps address developing faults before they can lead to failure. According to Skeirik, “A vibration-monitoring system can detect all of the failure mechanisms. Distinctive alerts can be sent to the control room. An expert can review the vibration signal to identify the nature and severity of the defect. But the remote location of cooling towers can make the cost of running wires prohibitive”.
Recent advancements in wireless technology help remote vibration monitoring. It offers a cost-efficient method with no additional wiring costs to enhance remote vibration. A traditional cooling tower monitoring system has long communication cables. But the new technology now enables monitoring through wireless vibration sensors. It also has a wireless tunnel gateway that only needs one ethernet cable or cellular data network for remote sites with no wired network. AKCP wireless vibration monitoring system provides real-time updates thru its online user interface, AKCPro Server. All deployed AKCP gateways and attached sensors can be configured and monitored from AKCPro Server (APS). It relays information about the state of a cooling tower all while transmitting high-quality diagnostic data. AKCPro Server can be easily accessed on a smartphone, tablet, or PC.
According to Skeirik, “Wireless vibration sensors can publish many values to the control room. Here, the condition-monitoring system can compare the current values with predefined alert limits. The resulting alerts are only meaningful if they are conclusive. They translate into specific, immediate actions”.