Closed loop water treatment is the process of maintaining water quality in closed-loop HVAC, heating, and cooling systems. These systems circulate water continuously, making proper treatment essential to prevent corrosion, scaling, and microbial growth.
Without proper treatment, closed-loop systems can develop issues that reduce efficiency, increase maintenance costs, and shorten equipment life. Problems like scale buildup, corrosion, and biological fouling can impact heat exchangers, pumps, and piping, leading to system failures and costly repairs.
Key Parameters in Closed Loop Water Treatment
1. Water Hardness
Hardness refers to the concentration of calcium (Ca) and magnesium (Mg) ions in water. These solids precipitate out of water when it heated and build a scale on heat exchangers and tubes. Excess hardness can lead to scaling, which reduces heat transfer efficiency and clogs pipes. TEST, TEST ,TEST your water using a water test kit! If you don’t test, you don’t know.
- Ideal range: 85-250 ppm
- Solution: Water softening via ion exchange to remove hardness ions.
IMPORTANT NOTE: If you have excessively soft water, the PH will begin to drop and can cause corrosion in the system.
2. Total Dissolved Solids (TDS)
TDS includes all the remaining dissolved minerals and impurities in the water (other than Ca and Mg). High TDS levels can increase corrosion rates and promote scale formation. You can use a TDS meter to measure the TDS in the water.
- Ideal range: <2000 ppm
- Solution: Deionization is the preferred method for TDS removal. It strips the source water of dissolved minerals. Reverse osmosis and distillation can also be used but are not preferred.
3. pH Balance
Maintaining the correct pH level is also important. You can test water with PH strips. Water that is too acidic or too alkaline can damage system components.
- Ideal range: 7.5 – 10.0
- Solution: pH adjustments using chemical additives.
IMPORTANT NOTE: Many systems have glycol additives for freeze protection. Overtime glycol breaks down and as it does the PH of the water will drop with it. You can use additives to temporarily get by but you will need to drain and reconstitute the system at some point.
4. Chlorides
Chlorides feature negatively charged ions. High chloride levels can lead to pitting corrosion, which weakens metal surfaces over time. This is not a common issue anymore because the Safe Drinking Water Act of 1974 regulated it down to 4ppm in municipal water.
- Ideal range: <250 ppm
- Solution: Removal through citric acid treatment, carbon filtration, or commercial water treatment solutions.
5. Filtration
Filtration is crucial to remove suspended solids, iron oxide, and magnetite, which can accumulate and cause blockages. These solids can plug heat exchangers and cause them to not receive proper water flow.
Common filtration methods:
- Y-strainers (#20 mesh standard)
- Dirt and magnetic separators
- Side-arm inline filters
Best Practices for Closed Loop Systems
1. Regular Water Testing
- Monitor hardness, TDS, pH, and chlorides monthly to ensure water remains within ideal ranges.
- Use test strips, TDS meters, and pH test kits for accurate readings.
2. Chemical Treatment Programs
- Corrosion inhibitors protect metal surfaces from oxidation.
- Biocides prevent bacterial growth that can cause biofouling
- Scale inhibitors reduce mineral deposition inside piping and heat exchangers.
3. Air Management
- Use air separators to remove dissolved oxygen and entrained air, which can accelerate corrosion.
4. Minimize Make-up Water
- Adding fresh water introduces new contaminants. Make-up water should not exceed 5% of total system volume annually.
5. System Cleaning and Flushing
- Before filling a closed-loop system, clean and flush it to remove debris, old treatment chemicals, and residual contaminants.
Make Up Water In Closed Loop Systems
Make up water in closed looped systems is a touchy subject. Many manufacturers will say that make up water should not be more than 5% of system volume annually. This prevents continually feeding a leaking system with raw make up water (which ultimately will destroy a heat exchanger). Some mechanical contractors have decided to turn off make up entirely and lets systems that develop leaks error out on low pressure. While this will take a system down, it can prevent a leak from going unnoticed.
Future Trends in Closed Loop Water Treatment
Advancements in closed loop water treatment are shaping the industry. Automation and remote monitoring are becoming more prevalent, as smart sensors and IoT technology allow for real-time water quality monitoring. This reduces the need for manual testing and improving system efficiency. Eco-friendly treatment solutions are also gaining traction. Non-toxic, biodegradable treatment chemicals becoming the preferred choice as industries prioritize sustainability. Additionally, enhanced filtration methods are making a significant impact. With magnetic and high-efficiency particulate filters improving system performance by capturing even finer contaminants, further preventing buildup and operational issues.
Conclusion
Closed loop water treatment is essential for maintaining efficient and reliable HVAC, boiler, and cooling systems. By monitoring key water quality parameters, using proper filtration, and applying chemical treatments, facility managers can prevent costly issues. Implementing best practices and staying up to date with emerging technologies will ensure long-term success in closed-loop system maintenance.
