As energy and water costs continue to rise, improving the efficiency of cooling tower operations has become a significant priority across industries. More efficient cooling towers reduce energy consumption through optimized heat transfer and can also conserve water through effective cycles of concentration and blowdown control. Even minor improvements in cooling tower performance can yield substantial cost savings and environmental benefits.

This article covers the fundamentals of cooling tower efficiency.

What Constitutes Cooling Tower Efficiency?

At its core, an efficient cooling tower maximizes heat rejection while minimizing water consumption. The key metrics used to gauge cooling tower efficiency focus on these areas:

Heat Transfer Rate

This measures how much heat is dissipated by the cooling tower over a given timeframe, usually expressed in BTUs/hr or kW. Effective heat transfer depends on factors like airflow rate and the temperature differential between inlet and outlet water.

Cycles of Concentration

This refers to the accumulation of dissolved solids in the circulating water. Higher cycles translate to less bleed-off and make-up water required. Most cooling towers operate between two and four cycles of concentration.

Water Usage Rate

By directly measuring makeup water consumption, operators can calculate cooling tower water usage on a gallons per minute (gpm) or gallons per hour (gph) basis. Lower water usage indicates higher efficiency.

Blowdown Percentage

This metric looks at the percentage of circulating water bled off to control cycles of concentration. Minimizing blowdown saves water and the energy needed to condition replacement water.

Tracking metrics like these over time is crucial for evaluating equipment upgrades, operational changes, and water treatment improvements that aim to enhance efficiency. Even small optimizations add up substantially for heavy-duty cooling tower applications across industries.

Monitoring Inputs and Outputs

Properly monitoring and controlling what goes into and comes out of a cooling tower is central to efficient operation. The key inputs and outputs include:

Inputs:

• Makeup Water: The fresh water added to replace water lost through evaporation, drift, and blowdown. Tracking makeup water consumption provides insight on real-world efficiency.
• Electricity: Energy used to power fans, pumps, and auxiliary equipment. Optimizing and rightsizing motors and components saves power.
• Chemicals: Water treatment chemicals for corrosion, scale, and microbiological control.
• Dirt and Debris: Cooling towers are oftentimes located in areas that can suck in dirt and debris from nearby locations, which can clog basins and impact overall efficiency

Outputs:

• Heat Rejection: The waste heat transferred out of the circulating water, measured in BTUs/hr or kW. Key indicator of the cooling tower’s primary job.
• Evaporation Loss: Water evaporated out of the cooling tower to discharge heat. Too much indicates excessive airflow or high heat load.
• Blowdown Water: The bleed-off water discharged to control mineral concentration. Minimizing blowdown conserves water.

Online instrumentation and data logging equipment make it easier than ever to monitor these parameters in real-time. Tracking output changes in response to input adjustments provides visibility on overall efficiency and opportunities for improvement.

Understanding Cycles of Concentration

Cycles of concentration is a critical metric for evaluating and optimizing cooling tower efficiency. This term refers to the accumulation of dissolved minerals and total dissolved solids (TDS) in the recirculating water.

As pure water evaporates out of a cooling tower, it leaves behind any contaminants that entered through the makeup water source. Over time this increases the concentration of TDS as compared to the new makeup water entering the system.

To help understand this concept, EAI’s Ryan Vargas shares a simple analogy: “As the water evaporates inside of a cooling tower, dissolved solids suspended inside the water get more and more concentrated. To oversimplify, it’s like making a bowl of ramen instant noodles. Have you ever put the spice packet into the water and when it starts to boil, forget about it? You come back when you smell something funny, all of your water is boiled off and the salt and spices are concentrated at the bottom.”

Cycles measure this increase—if the cooling water has a TDS level three times higher than the incoming makeup water, it is operating at three cycles of concentration. The higher the cycles, the less blowdown is required to purge contaminants. This conserves water and the energy needed to condition it.

In addition, elevated mineral concentration also raises the risk of scale formation on heat transfer surfaces. There is a practical limit around seven cycles for most towers, especially in the West and Southwest, after which scaling and deposition rapidly reduce efficiency.

Optimizing cycles of concentration requires balancing water savings against heat transfer impacts:

• Adjusting bleed and feed rates to stay in the sweet spot that manages operational risk and energy/water consumption
• Exploring makeup water pretreatment to increase cycles of concentration
• Using scale inhibitors to target more aggressive cycles safely

The cycles value that maximizes water conservation without excessive scaling varies. But understanding and controlling concentration is pivotal for getting the most out of a cooling tower system.

Operational Best Practices

While advanced technology upgrades can improve efficiency, most towers benefit greatly from simpler operational measures first. Consistent cooling tower water treatment, monitoring, maintenance, and training helps optimize existing performance with little or no capital expenditure.

Key best practices include:

• Regular inspection and preventative maintenance of fans, pumps, fill media, water distribution system, and all rotating components according to manufacturer guidelines. This prevents fouling and mechanical issues that erode efficiency over time.
• Online monitoring and active adjustment of cooling tower bleed rates and cycles of concentration. This directly minimizes water consumption while keeping heat exchange surfaces clear of scale buildup.
• Investing in training for in-house operators on critical measurements and chemistry adjustments. With staff turnover, don’t assume knowledge will persist. Well-informed teams enhance day-to-day efficiency.
• Routine cleaning and disinfection of cooling towers, in line with ASHRAE standards

“I recommend checking the system once per week for facilities that have some type of a controller that is either wired into the system or is able to report out. The latter will alert your vendor if a measurement is abnormal,” says Vargas.

Many facilities find that consistency with basic operational diligence not only optimizes efficiency, it also reduces the risk of unplanned downtime events that can severely disrupt production. The fundamentals may not be glamorous, but excellent tower performance depends on their reliable execution.

Advanced Efficiency Strategies

Once sound operational practices are established, facilities seeking to stretch their cooling tower performance may consider advanced technologies and upgrades including:

• High-Efficiency Fill Retrofits: Replacing old splash-type fill with modern film-type fill media improves heat transfer via a thinner water film for air contact. This allows either increased capacity or fan power reduction.
• Variable Frequency Drives: Adding VFDs to modulate fan and pump speeds based on demand saves substantial electricity compared to continually running these components at full speed.
• Water Conservation Retrofits: Technologies like wastewater recycling, rainwater harvesting, and condenser water recovery reduce reliance on potable makeup water. This further curbs expenses and some equipment loads.
• Data Analytics: Leveraging data analytics uncovers efficiency optimization opportunities that may not be intuitive otherwise. The added visibility pays dividends.

The feasibility and return on investment of advanced upgrades will vary for each facility. But where cost-effective, these measures can compound operational gains to reduce cooling tower overhead costs. Performance incentives and local regulations may also subsidize certain upgrades. For most operators, efficiency is a long game with no finish line.

Cooling Tower Variations Between Industries

While the core function of cooling towers remains the same across applications, factors like load size, environment, and downtime risk create differences in cooling tower design between industrial facilities and commercial buildings.

Industrial sites like oil refineries, petrochemical plants, and power plants often utilize very large, field-erected cooling towers. Their high heat loads and continuous uptime requirements call for robust construction with redundant fans and pumps. Materials also vary per the process environment—a refinery cooling tower handles hydrocarbons, while a nuclear plant contends with radioactive water.

Commercial cooling towers for offices, hospitals, and district energy systems tend to be smaller prefabricated units mounted on rooftops or along HVAC equipment. Their intermittent operation allows for simpler systems, often with a single fan. Cost and footprint are bigger considerations. Additionally, commercial towers must account for winter shutdowns and legionella control given their integration with human-occupied buildings.

While tower specifics differ across sites, employing efficiency best practices and advanced technologies can benefit both industrial and commercial operators. The potential savings make optimization worth pursuing, even for smaller commercial towers. Efficiency gains at scale translate to even more dramatic reductions for high-capacity industrial towers.

Working Towards Efficiencies

The reality is that most facilities leave substantial efficiency improvements on the table with their existing cooling tower assets. By monitoring key parameters and proactively adjusting operations and upkeep, operators can extend the life of cooling equipment, curb overhead costs, and reduce environmental impacts. The incentives are stacked for those who prioritize efficiency across their thermal management systems.

With this foundation on maximizing cooling tower performance, commercial buildings and industrial sites alike have actionable best practices to start driving efficiency gains today. Consistent incremental improvements over months and years ultimately accumulate to optimize these critical assets for the long run. If you need help improving the efficiency of your cooling towers, contact us today for a free on-site analysis.