Cooling tower problems that affect chiller performance
A cooling tower rejects heat from the condenser water to the atmosphere before returning the water to the chiller to absorb heat in the next cycle. If water quality is not properly managed, scale, algae, microorganisms and biofilm can accumulate along the pipework and heat exchange surfaces.
These deposits act like thermal insulation, forcing the chiller to consume more energy to maintain the required chilled water temperature. The problems that typically follow include:
- Higher Condenser Approach Temperature
- Reduced heat exchange efficiency
- Chiller consuming more energy than normal
- Frequent condenser tube brushing or cleaning
- Continuous chemical and maintenance costs
- Risk of tube erosion from chemicals or mechanical cleaning
For this reason, cooling tower water treatment is not only about controlling algae or keeping the water clear. It must also preserve heat transfer efficiency and reduce the chiller’s workload.
What is ozone water treatment, and how does it manage a cooling tower?
Ozone water treatment is a technology that generates ozone gas from oxygen and dissolves it into water, in order to control microorganisms, algae and biofilm in a recirculating water system.
Ozone is a highly effective oxidant. Once it has reacted, it reverts to oxygen, so it does not leave behind residuals in the way that some water treatment chemicals do. Using ozone in a cooling water system therefore reduces reliance on chemicals, along with the burden of chemical storage, dosing and wastewater management.
In a cooling tower, ozone is important in controlling biological factors such as bacteria, algae and biofilm. As pipe and equipment surfaces become cleaner, condenser water heat exchange becomes more efficient, allowing the chiller to operate closer to its intended performance.
Results at a leading hospital in Bangkok
After this leading hospital installed the ECONOWATT Ozone Water System, model OZG209N5Y, comparative data was collected from October 2025 to May 2026, using Condenser Approach Temperature as one of the system’s performance indicators.
An important point about this project: the condenser tubes were not brushed or cleaned before installation, because the existing tubes were at risk of erosion after a long history of brush and chemical cleaning. The change in Approach Temperature therefore reflects the effect of operating the ozone system under real site conditions.
Before and after comparison
| Item | Before ozone | After ozone | Change |
| Chiller 1 – Load | 85% | 93% | Increased by 8 percentage points |
| Chiller 1 – Condenser Approach Temperature | 3.3°F | 1.4°F | Reduced by approximately 58% |
| Chiller 2 – Load | 76.4% | 83% | Increased by 6.6 percentage points |
| Chiller 2 – Condenser Approach Temperature | 4.9°F | 2.8°F | Reduced by approximately 43% |
The data shows that although both chillers were carrying a higher load but the Condenser Approach Temperature fell. Ordinarily, when load increases the system needs to reject more heat and Approach Temperature would be expected to rise. The result therefore indicates that heat transfer inside the condenser improved.
What is Condenser Approach Temperature?
Condenser Approach Temperature is the difference between the condensing refrigerant temperature and the leaving condenser water temperature. It is used as one of the indicators of heat exchange efficiency inside the condenser.
In general, the lower the value, the better heat is transferred from the refrigerant to the water. If the condenser tubes accumulate scale, biofilm or fouling, heat transfer capability declines and Approach Temperature typically rises.
This project used a reference criterion that Condenser Approach Temperature should not exceed 4°F. After installation:
- Chiller 1 recorded 1.4°F within the good range
- Chiller 2 fell from 4.9°F, which was above the criterion, to 2.8°F, returning it to a good level
Why Approach Temperature fell without tube cleaning
The project’s key finding is that Approach Temperature fell even though the hospital did not brush or clean the condenser tubes, and the chillers were operating at a higher load than before.
This indicates that ozone water treatment contributed to controlling the accumulation of microorganisms, biofilm and biological deposits in the cooling water system, leaving the heat exchange surfaces cleaner and better able to transfer heat.
However, results will differ from project to project depending on the original water quality, system size, cooling load, tube condition, ozone dosing control method, and overall cooling tower maintenance. Systems should therefore be designed and monitored to suit the conditions at each individual site.
How much energy can ozone water treatment save?
Based on the project report, the energy saved from the reduction in Condenser Approach Temperature was estimated using the assumption that chiller efficiency improves by approximately 1.5% for every 1°F reduction in Approach Temperature.
Estimated annual energy saving
| Item | Chiller 1 | Chiller 2 | Total |
| Approach Temperature reduction | 1.9°F | 2.1°F | – |
| Efficiency improvement (per assumption) | 2.85% | 3.15% | – |
| Load used for calculation | 89% | 80% | – |
| Power draw at load | 119.3 kW | 107.2 kW | – |
| Operating hours | 6,570 h/year | 6,570 h/year | – |
| Annual energy consumption | 783,500 kWh | 704,300 kWh | 1,487,800 kWh |
| Energy saved | 22,330 kWh/year | 22,190 kWh/year | 44,520 kWh/year |
The calculation shows the system saving approximately 44,520 kWh per year, worth approximately 187,000 THB per year at an electricity tariff of 4.2 THB per unit.
This figure reflects the estimated savings from improved Chiller efficiency based on Approach Temperature. The additional savings of at least THB 100,000 per month during the summer come from avoiding operation of the 200-ton standby Chiller during peak building load. This is separate from the annual savings above and should not be directly combined.
Reducing carbon emissions by approximately 21.1 tonnes CO₂e per year
Applying the electricity Emission Factor of 0.4750 kgCO₂e/kWh stated in the project report, the 44,520 kWh saved per year reduces greenhouse gas emissions by approximately:
44,520 × 0.4750 = 21,147 kgCO₂e per year
That is approximately 21.1 tonnes CO₂e per year, comparable to the carbon absorbed by around 2,350 trees in a year, assuming one tree absorbs approximately 9 kilograms of carbon annually.
Figures like these allow an organisation to connect the effect of improving cooling system efficiency to its energy reduction, ESG and greenhouse gas reduction targets far more clearly.
Benefits the hospital gained from ozone cooling tower water treatment
Introducing ozone into the cooling tower delivered a clear improvement in cooling system performance, in both energy and maintenance terms, particularly when viewed through the reduction in Condenser Approach Temperature and the improvement in chiller heat exchange efficiency.
1. Reduced chemical use
Switching to ozone reduced reliance on water treatment chemicals, lowered chemical costs, and simplified the processes of storing, dosing and controlling chemicals within the hospital premises.
2. Reduced risk to the condenser tubes
Reducing the frequency of brushing or chemical tube cleaning lowers the risk of tubes eroding or being damaged by repeated cleaning, particularly in systems where the tubes have been in service for a long time.
3. Improved heat exchange efficiency
The lower Condenser Approach Temperature indicates that the system is rejecting heat more effectively, allowing the chiller to operate closer to full capability even while carrying a higher load than before.
4. Lower electricity cost
Better chiller efficiency reduces electricity consumption. At the same time, during peak load periods the hospital no longer needed to bring an additional standby chiller online, which significantly reduced electricity costs during the hot season.
5. Support for environmental targets
Reducing chemicals, energy consumption and greenhouse gas emissions supports a sustainable approach to building management and lowers long-term environmental impact.
Recommendations for maintaining the system after ozone installation
Although ozone in a cooling water system helps control microorganisms and keep the system clean, overall cooling tower maintenance remains important. We recommend cleaning the cooling tower as appropriate, and adding covering material over basin areas exposed to direct sunlight, to reduce algae growth.
In addition, water quality, ozone level, Approach Temperature, chiller operating load and equipment condition should all be monitored regularly, so that the system continues to operate effectively and any abnormality is detected early.
Ozone water treatment: a sustainable route to better chiller efficiency
This case study from a leading hospital demonstrates that the ECONOWATT ozone water treatment system can help keep condenser tubes clean and improve heat exchange efficiency under real operating conditions. Condenser Approach Temperature fell by approximately 58% on Chiller 1 and approximately 43% on Chiller 2, with no tube cleaning and with both machines operating at a higher load.
Beyond reducing chemical use, the system saved approximately 44,520 kWh per year, reduced greenhouse gas emissions by approximately 21.1 tonnes CO₂e per year, and allowed the hospital to avoid running its standby chiller during the hot season, generating additional savings.
For buildings, hospitals, hotels or factories looking to improve cooling system efficiency, reduce maintenance burden and lower environmental impact, ozone water treatment should be designed around the site’s water quality and operating profile. ECONOWATT provides end-to-end solutions from system analysis through design and installation, so your organisation can reduce its carbon footprint and use energy more efficiently.
Get in touch
- Line: @econowatt
- Facebook: Thai Energy Conservation — Econowatt Water Treatment & Energy Conservation Systems
- Tel: +66 2 809 1601
- Email: sales@econowatt.co.th
FAQs about Ozone Water Treatment
Q: What types of buildings is ozone water treatment suitable for?
A: It can be used in a wide range of buildings, hospitals, hotels, office buildings, shopping centres and industrial plants. However, the system must be designed and the site assessed by specialists before installation, so that it suits the actual operating conditions.
Q: How does an ozone system reduce carbon emissions?
A: When chiller efficiency improves, less electricity is consumed, which in turn reduces the indirect greenhouse gas emissions associated with that electricity use. In this case study, emissions were reduced by approximately 21.1 tonnes CO₂e per year.
Q: After installing an ozone system, does the cooling tower still need maintenance?
A: Yes, ongoing care and maintenance is still required, including checking water quality, cleaning the cooling tower, controlling sunlight exposure at the basin, and monitoring chiller performance, so that the system continues to operate efficiently over the long term.