Most facility teams troubleshoot cooling problems by pulling the makeup-water report. For years, that’s been the acceptable starting point – hardness, silica, chlorides, alkalinity. These numbers matter. But they do not tell the whole story.
Heat exchanger failures don’t start with the makeup water. They start with the water after cycles of concentration get hold of it. By then, it’s been concentrated by evaporation and recirculation, and loaded with airborne contamination, corrosion products, and chemical treatment.
That’s the water that touches your heat-transfer surfaces, and it’s where heat exchanger scale, fouling, and related costs begin.
Understanding what’s on the heat-transfer surface – not just the makeup water – is the difference between cooling towers that run efficiently for years and ones that quietly bleed energy and money.
To save your facility time, money, and guesswork chasing heat exchanger failures, here’s what to look at instead.
The Windshield-Washer Problem
Imagine if your car’s windshield-washer fluid didn’t spray onto the glass and drain away. But if the fluid was collected, pumped back into the reservoir, and reused over and over again.
Each pass of the wipers would pick up a little more dirt, dust, pollen, and road grime. You could keep topping off the reservoir with fresh fluid, but that wouldn’t remove what’s already circulating. Before long, the fluid hitting your windshield would look nothing like the clean fluid you poured in.
A cooling tower works the same way.
The tower recirculates water to reject heat. Water leaves the system through evaporation, but minerals, salts, and most dissolved solids do not evaporate with it. They stay behind. Fresh makeup water is then added to replace what was lost – and that new water brings in another load of minerals. The cycle repeats, again and again.
The heat exchanger is not seeing fresh makeup water. It’s seeing the water that stayed behind.
Heat exchangers rarely fail overnight. Instead, insulating scale builds up day by day, quietly draining your energy budget long before the system shuts down. Here’s what that concentrated water is actually doing to your heat-transfer surfaces, and how to stop it.
What Are Cycles of Concentration?
Cycles of concentration, or CoC, describe how concentrated the recirculating water has become compared with the incoming makeup water.
In a cooling tower, water evaporates to reject heat and cool the remaining water. But minerals and contaminants do not evaporate with it – they stay behind. As the tower reuses the same water, concentration increases:
Note: These are simplified examples. Actual cooling-tower chemistry is heavily affected by pH, treatment strategy, blowdown volume, filtration, biological activity, and other operating conditions.
Your makeup water may look manageable on a laboratory report, but heat exchangers never see that fresh makeup water. Instead, heat-transfer surfaces are exposed to a highly concentrated recirculating cocktail – water cooling towers concentrate multiple times over.
High Cycles of Concentration Aren’t Bad (Uncontrolled Chemistry Is)
Emphasizing the risk of concentrated water doesn’t mean higher cycles are inherently bad. Increasing cooling tower cycles is a core water-conservation strategy. Higher CoC saves water, cuts utility bills, and reduces unnecessary blowdown waste. Increasing cycles is fundamentally good for sustainability.
But that efficiency requires balance. Every cycle gained to save water also concentrates the elements working against your heat exchanger equipment:
- Scale and fouling catalysts: calcium hardness, alkalinity, silica, sulfates and iron.
- Corrosive agents: chlorides.
- System load: suspended solids, biological growth, and the treatment chemistry added to control them.
Every cycle saves water, but every cycle also raises the stakes. There’s no real downside to running higher cycles if the chemistry stays controlled – the goal is to raise CoC without compromising heat-transfer surfaces, operating at the highest responsible concentration the system can handle.
The Real Cost of Chemical-Dependent Heat Exchanger Fouling
Heat exchangers rely on bare, clean metal surfaces to transfer heat efficiently. When dissolved mineral load exceeds what the water can hold, it forms scale. In addition to scale, suspended solids, organic material and biological buildup form layers on heat-transfer surfaces. Those layers do not have to be thick to degrade performance.
Think of it like wearing a windbreaker jacket on a hot day. The fabric doesn’t have to be thick to trap heat and make your body work harder to cool down. The same is true inside a heat exchanger.
Inside a heat exchanger, even a microscopic layer of scale acts as insulation. If heat is insulated, the heat exchanger works harder to move the same amount of heat, driving up energy use. That extra strain also means more frequent maintenance. Often, more scale inhibitor chemicals need to be fed, adding cost on top of lost efficiency accumulation.
The heat exchanger doesn’t have to fail to cost your facility money – it just has to operate slightly choked, day after day. Unless a fix is implemented.
What a Thin Layer Could Cost: A 1,000-Ton System
To put this into perspective, industry data for water-cooled condensers shows that a calcium-carbonate scale layer of just 0.012 inches can cause a 5% increase in required condenser power.
That is roughly the thickness of three sheets of standard printer paper. That is all.
For example, on a 1,000-ton cooling system, that thin layer carries a severe price tag:
- The Baseline: A modern water-cooled centrifugal chiller operating at full load draws approximately 501 kW.
- The Scale Penalty: A minor 5% efficiency loss due to scale adds 25 kW of continuous, unnecessary demand.
- The Annual Cost: At average industrial electricity rates, a continuously running system will waste approximately $19,000 more per year on electricity alone.
That figure is only the baseline energy waste. It doesn’t include peak demand charges, additional chemical use, cleaning costs, lost capacity, or downtime.
A problem that starts quietly can be easily prevented – if you know where to look.
What the Heat Exchanger Sees Beyond Makeup Water
The dissolved load reaching the heat exchanger does not always come from the makeup water alone. Traditional chemical programs actively add to it, feeding in:
- Sulfuric acid: For pH control
- Bleach: For biological growth
- Phosphates and phosphonates: For scale inhibition
- Azoles or zinc-based inhibitors: For corrosion inhibition
Some of those chemicals react. Some leave the system through blowdown. But many add directly to the dissolved material circulating through the loop. Phosphates and phosphonates used to inhibit scale can themselves form scale under high pH or high calcium conditions.
The heat exchanger does not care where the load came from. It still has to operate in it.
You can’t solve a dissolved-load problem by adding more dissolved load. The good news: there’s a proven way to break that cycle entirely.
The Heat Exchanger Fouling Fix: Protection Beyond Traditional Chemicals
The goal of your water treatment program is not simply to run lower CoC or dump more chemicals into the tower. The ultimate goal is to keep your heat-transfer surfaces clean.
To achieve that, you must step outside the traditional chemical playbook and control the water at the surface, not just in the basin. That means shifting from reactive treatment to prevention.
A high-performance strategy protects the heat exchanger first by:
- Managing CoC based on actual water chemistry, not guesswork.
- Keeping the LSI in a stable range and adjusting treatment before fouling becomes a failure.
- Reducing organic load and biofilm, preventing mineral deposits from attaching to the tubes.
- Removing suspended solids and utilizing filtration when contamination risks increase.
- Watching actual exchanger performance, rather than just reading tower basin sensors.
Breaking the Cycle With NREL, GSA & DOE Findings
Predictable, uninterrupted heat exchanger performance requires addressing the root cause of surface fouling. By protecting the heat-transfer surface, facilities can save water without relying on harsh chemical dosing that feeds dissolved load.
Preventing fouling requires destroying biofilm in the water loop before it can trap scale. However, traditional chemicals don’t have the oxidation power to overcome this biological matrix. To deliver this, a non-chemical Advanced Oxidation Process (AOP) technology injects treated gas into the water loop to create hydroxyl radicals that rapidly destroy biofilm.
An independent U.S. federal study conducted by NREL for the GSA and Department of Energy found that Clear Comfort’s AOP cooling tower water treatment delivered:
- 26% Water Savings: By safely running at higher cycles of concentration, the system significantly reduced the volume of fresh makeup water needed.
- 50% Maintenance Reduction: Eliminating the biological layer prevented minerals from baking onto the tubes, cutting routine cleaning labor in half.
- Eliminated Most Chemical Use: The AOP technology met strict GSA water quality standards without requiring traditional scale inhibitors or biocides.
- 2.2-Year Payback: The combined water and maintenance savings delivered a 2.2-year simple payback – the highest savings-to-investment ratio (6.9) of any technology GSA evaluated.
Ultimately, protecting the surface directly minimizes wasteful blowdown without the heavy chemical loads that complicate the loop.
What to Measure Before Failure Shows Up
When a cooling system trips or loses efficiency, it is easy to point fingers at the hardware. Facilities often blame a wide range of operational or mechanical issues before looking at the recirculating water chemistry.
What Operators Usually Blame:
- The exchanger design or old metallurgy
- Bad process conditions
- Poor routine cleaning
- Insufficient chemical feed
- High ambient temperatures or tower capacity limits
Those factors can matter, but they are rarely the root cause. Before blaming the heat exchanger, you have to look at what the water has become.
The Warning Signs You Need to Track
The warning signs of heat exchanger fouling are almost always there before the failure happens. You just have to measure the right data.
To give your equipment real protection, track these critical indicators:
- System Performance Metrics
- Approach temperatures
- Heat exchanger pressure drops
- Blowdown rates
- Side-stream filtration performance
- Core Water Chemistry
- Cycles of concentration (CoC)
- Makeup vs. basin conductivity
- pH, Alkalinity, and Hardness
- LSI (Langelier Saturation Index) or other scaling indexes
- Contaminant & System Loads
- Silica, Chlorides, Sulfates, and Iron
- Bacteria or biofilm indicators
- Corrosion coupons
The Bottom Line: CoC is a Reliability Risk
Higher cycles of concentration are incredibly valuable. When managed correctly, raising your CoC saves massive amounts of water and drastically reduces blowdown discharge.
But unmanaged CoC turns completely normal makeup water into a highly concentrated threat that scales, fouls, corrodes, and slowly damages your heat exchangers.
Cycles of concentration are not just a water conservation metric. They are a core equipment reliability number.
The most profitable failure is the one that never starts.
Ready to See Your Facility’s Real Numbers?
You don’t have to wait for an audit finding to find out. Stop guessing what unmanaged cycles of concentration and traditional chemical contracts are costing your operation. Use our free, interactive calculator to map your system’s current water rates, tower tonnage and chemical spend to find your exact savings potential.
Doug White
VP of Business Development
