A Constructive Intro to Increasing Cooling Tower Efficiency

Increasing Cooling Tower Efficiency

Increasing cooling tower efficiency plays quite a significant role in improving the overall efficiency of commercial and industrial cooling systems. The cooling tower is an indispensable component of these systems, be it a commercial system intended for an office building or an industrial one for a refinery, and therefore, maintaining and further increasing its efficiency would be quite beneficial if not crucial.

We at Linquip, as one of the best suppliers of cooling tower parts and products, will provide you with a good insight into what to be considered for increasing cooling tower efficiency.

Increasing cooling tower efficiency
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Efficiency Enhancements

There are some factors to look for when we seek ways to increase cooling tower efficiency. Nonetheless, how could someone quantify the effect of applied changes to the system and track them once the areas for improvement have been identified?

(Please read this article to find out about the factors contributing to a cooling tower’s efficiency and learn about the terminology used here.)

The truth is that this improvement measuring can only be done through some other measurements! Water flow meters and conductivity meters, for example, should be installed to monitor and track makeup water and blowdown conductivity to see how COC is changing. Therefore, it is essential to consider some reference values to evaluate the extent to which  changes have contributed to the system’s performance.

Mitigation of Blowdown

Blowdown limits the performance of the cooling system and mitigating its adverse effects is something that we need to address when increasing cooling tower efficiency is desired. The question here then would be how?

As was discussed in our other article on cooling tower efficiency, to which you can find the link in the beginning of this article, the goal is to minimize blowdown in order to have higher values of COC, which would result in increasing cooling tower efficiency.

Of course by lowering blowdown, the amount of discharged chemical waste would be reduced that is good news for both the environment and the economical status of the operator. Some stream filtration could also be arranged to control the amount of solid debris discharged to the environment.

Water Savings for Increasing Cooling Tower Efficiency

One of the most important economical and environmental considerations of the cooling towers is to minimize water consumption for the system. Therefore, water saving strategies could be considered as essential steps towards increasing cooling tower efficiency.

An optimum operation is when the cycles of concentration is at its highest possible value, and any COC lower than that maximum indicates that there is room for increasing the cooling tower efficiency through raising COC and hence resulting in more water savings.

Re-using Wastewater Streams

Some wastewater steams of the facility could be used as the cooling water makeup in order to minimize the amount of freshwater use. Such water streams could be pre-treated and employed as a source of makeup water without inflicting any damage to the equipment or deterioration of the performance.

Such reusable wastewater sources vary from one facility to another, but treated waste water from water treatment plants, boiler blowdown, facility equipment and floor washdowns, filter backwash, etc. could be considered as such.

Cooling Tower Water Treatment

Other than reusing treated water from other waste streams to increase water savings, there is also the possibility and necessity to treat the cooling tower’s own water for increasing cooling tower efficiency. What needs to be considered here is the concentration of minerals in the cooling process water.

The water for the cooling tower could be taken from surface water resources, such as lakes or rivers, or groundwater. Apart from that, as water moves throughout the passages to carry out its cooling duties, it takes with itself some impurities from the contact surfaces along the way. It is clear that such impurities will result in corrosion and scale formation that reduce the service life of the equipment.

Cooling tower water treatment will help eliminate the chance of scaling, fouling, and deterioration of the equipment as well as preventing malfunctioning of heat transfer surfaces. Increasing cooling tower efficiency can therefore be achieved through enhancing the quality of treated cooling tower water through more advanced water treatment technologies.

Static vs. Dynamic Driver Speeds

In case of using a mechanical draft cooling tower, there is the need for using a motor to drive the fan for heat removal. Moreover, every water pump in the cooling tower that pushes the cool water through the system has a motor as its driver. It can be understood that the motor speed plays a significant role while increasing cooling tower efficiency is intended.

Old cooling tower motors could only operate at a specified speed, i.e. its full load rating, which does not seems to be an efficient way of operation, due to the fact that there are situations in which there is no need for full power operation of the motors. This kind of motors are called static drivers.

In order to solve the issue of static driver speed, cooling towers are not equipped with dynamic drivers that use enhanced technologies that would not only assist with increasing cooling tower efficiency, but also contribute to lower noise emissions and higher reliability and safety.

New cooling tower equipment utilizing improved motor drive technology can increase overall efficiency, while also improving noise reduction, reliability and safety. Such dynamic drivers commonly come in the form of VFD or RVSS that will be discussed shortly in the following. This comes in two forms of cooling tower frequency drives — Variable Frequency Drive (VFD) and the Reduced Voltage Soft Starter (RVSS).

Reduced Voltage Soft Starter (RVSS)

Soft starters reduce motor speed during the start up in order to eliminate the danger of high initial torque. They share many benefits with VFDs, but they are cheaper and require less space. Nonetheless, motor voltage modulation cannot be done with soft starters; they are only solving the issue of motor startup as can also be inferred from the name. Therefore, the control over these drivers is lower compared to VFDs.

Variable Frequency Drive (VFD)

VFDs start stably at lower speeds that help minimize the oscillation and noise during motor startup. This means that the chance for component malfunction or failure due to full power startup of static drivers is almost zero and as a result a high level of torque exerted on stationary components is eliminated. Their speed is then adjusted based on load demand, and all this results in a much more efficient motor operation and power consumption as well as more service life of the equipment.

Despite the fact that these drivers are much more expensive than the static ones, the amount of money saved in the long term completely balances out this initial cost and results in even higher savings due to reduced water and electricity use, and low maintenance costs.

You may read here to have a better understanding of the difference between these two dynamic driver types and where to use which one in order to make a better decision for increasing cooling tower efficiency.

Additional Benefits of Increasing Cooling Tower Efficiency

Now that we have seen how some actions could result in higher efficiency of the cooling tower, we might also see how they could benefit the facility in general.

As already mentioned, better water treatment lowers the amount of scale buildup in the corresponding tower sections that guarantees higher heat transfer rates lowers the workload on the compressor.

Considering this as an example, increasing cooling tower efficiency not only yields better a performing component performance, but also leads to better performance of all the other components of the system that work together interactively, resulting in lower operation costs, maintenance costs, and watching over the environment.

More on cooling tower efficiency enhancement

To find out more about the calculations regarding tower efficiency read our post here. You may also refer to here to know some other efficiency considerations of the cooling tower.

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Ramzy
Ramzy
Linquip Content Managment Team

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