Efficiency Factors to Consider in Cooling Tower Fan System Design

Hello, constant reader, and welcome to part three of our multi-part blog series on the factors that inhibit the efficiency of cooling tower fan systems. As this is part three of our series, we encourage you to read our previous two posts, part 1 & part 2. Each post builds upon the last and, as a result, you may find yourself quite lost if you are not familiar with the context of this series. In today’s post, we are going to pick up where we left off last time and delve deeper into the second main factor that can affect the efficiency of a fan system: The fan housing. Like most components in a large machine assembly, the fan housing plays a role that, if not properly optimized, can have a larger negative impact on the overall efficiency of the system than one would first suspect. Even a small decrease in efficiency can be enough to throw off an entire cooling tower system, which is why it is so important for engineers to make sure that their initial system is as optimal as possible before construction.

Don’t Take Your Fan Housing For Granted

In our previous post, we discussed the impact that system design can have on the overall efficiency of a cooling tower fan system. If inefficiencies are built into the system from the start, such as insufficient blade design and positioning, the system is never going to be able to perform at its peak. While these two factors account for a lot of the inefficiency found in fan systems, the housing of the fan assembly can also cause issues with overall efficiency. In the world of industrial cooling towers, one of the most important factors of system loss revolves around the air leakage around the tips of the fan blades. This loss is directly influenced by the tip clearance of the fan blades and the velocity pressure at the operating point and is caused by the tendency of high-pressure exit air to circulate around the fan blade tips into the low-pressure air in the inlet of the tower. For this reason, it is important to make sure that the inlet conditions of a cooling tower are as optimal as possible.

Pay Attention to the Inlet Conditions

In relation to wet cooling towers, a velocity recovery stack is a common means by which engineers can improve inlet conditions and conserve horsepower. To perform this function, velocity recovery stacks most often incorporate a slightly tapered exit cone in conjunction with a well-rounded inlet bell. This results in a significantly reduced velocity pressure at the exit of the inlet compared to the plane of the fan. Because the quantity of air on both planes is the same, however, the recovery of velocity pressure is converted into static regain, lowering the total pressure requirements of the fan. This results in less horsepower being needed to produce the required rotational velocity of the fan. Additionally, the entrance into the velocity recovery stack through the fan deck should not be neglected because, often, this entrance can create turbulence and losses in the fan system. Although most stack designs tend to incorporate a large inlet radius, heavy structural members beneath the stack or a sharp corner through the fan deck ca negate the smooth air flow condition in the stack itself. It is important to note that these issues are not under the control of the end user, meaning that the design of the cooling tower itself should try to limit these negative variables.

Thank you for taking the time to read our third entry into our blog series on cooling tower fan efficiency. Join us again next time as we conclude our series by discussing the recirculation of hot air how this factor can contribute to decreased efficiency in a cooling tower fan system. As always, if you would like to learn more about the cooling tower fan options that we offer here at Industrial Cooling Solutions, Inc., please contact us today.