Filtration Guide for Closed-Loop Heating and Cooling Systems

Have you considered how filtration in closed loop systems can drastically improve water quality and system longevity? 

While closed loop systems offer protection against many external contaminants, they aren’t immune to internal challenges like rust, scaling, and debris from new construction. How can you ensure the water in these systems remains pristine? 

The answer lies in effective filtration. By integrating the right filtration methods into your closed-loop system, you can combat internal contaminants, reduce maintenance costs, and extend equipment life. 

Dive into this guide to understand the importance of filtration in closed-loop systems, best practices, and the benefits you can reap. 

Types of Contaminants in Closed-Loop Systems

Closed-loop systems, while protected from many external contaminants, are still susceptible to a variety of internal contaminants. These include: 

Organic Contaminants: These can be introduced from sources like microbial growth or decaying plant matter that might have entered the system during maintenance or construction. 

Minerals: Hard water can introduce minerals like calcium and magnesium, which can lead to scaling. 

Chemical Contaminants: These can arise from the breakdown of glycols, some inhibitors or from external sources if there are leaks in the system. 

Understanding the Need for Closed-Loop System Filtration

Filtration isn’t just an add-on; it’s a necessity for the longevity and efficiency of closed loop systems. Even in a theoretically “closed” environment, suspended solids find their way into the system. These might be introduced during the new construction process, through corrosion, additions to older systems, leaks, or even poor commissioning practices. 

One clear sign of suspended solids is the turbidity or discoloration of the water. 

Unfiltered, these suspended solids lead to: 

  • Erosion of metals, increasing the need for closed-loop system corrosion prevention. 
  • Deposit formation, which can hinder the closed-loop water treatment process. 
  • Increased wear on seals, control valves, piping, and instrumentation. 
  • Microbiological growth, which can compromise the system’s health. 
  • Decreased performance of water treatment chemicals. 

Benefits of Closed-Loop Filtration

The advantages of incorporating filtration into your closed-loop system maintenance plan is clear: 

  • Enhanced equipment efficiency, allowing the chemical treatment to work optimally  
  • Prevention of unexpected system shutdowns  
  • Decreased labor and maintenance costs 
  • Reduced system component damage 
  • Reduced energy and water usage 

Filtration Methods for Closed Systems

Incorporating a closed-loop filtration system into your water treatment program effectively removes suspended solids. Typically, side-stream or by-pass filtration is the go-to choice, ensuring the main water stream remains uninterrupted even if the filter requires maintenance or replacement. 

When considering filtration methods for closed systems, several factors come into play: 

  • Operational costs, including filter or filter bag replacement 
  • Manual vs. automatic operation 
  • Solids loading on the filter 
  • Particle size removal 
  • Labor required 
  • Temperature 
  • Water losses 

Maintenance Schedule for Closed-Loop Filtration

A regular maintenance schedule is crucial for the longevity and efficiency of your closed-loop system. Here’s a recommended checklist: 

Weekly: Check for visible signs of turbidity or discoloration in the water. Monitor system pressure and flow rates. Check filters and filter solids load. Change if necessary. 

Monthly: Inspect filters for good flow. Change if flow rates through the filter are significantly less than when freshly installed. Check seals, control valves, piping, and instrumentation for signs of wear or damage. 

Quarterly: Replace or clean filters if they have not been changed recently. Conduct a thorough inspection of the entire system. 

Filming Amine Treatments and Filtration in Closed-Loop Systems

When introducing filming amine treatments, especially products like AQUAGUARD 810 or 819 into closed-loop systems, the importance of filtration cannot be overstated. Here’s why: 

Initial Filming Amine Treatment and Filtration

Filtration is especially important during the initial stages of filming amine treatment. When introducing filming amines into closed-loop systems, there’s an initial period where pre-existing system contaminants are removed. 

Whether you are treating a new system or one switching from an inorganic treatment, filming amines will clean the system and lay-down a protective film. Even new systems can be fouled with flash rust, oils, and new construction debris. 

Depending on the degree of system fouling, the cleaning process may take a few weeks or even a few months. Progress is often gauged by monitoring the total iron concentration in the system. As system surfaces are cleaned, suspended solids and iron will initially increase. It’s crucial to have an efficient filtration system in place to remove these contaminants from the system. During this phase of treatment, filters should be monitored daily and changed as needed. 

Filming amines are exceptional cleaners for closed-loops—and they do a great job of protecting surfaces from further corrosion damage. In fact, filming amines are so good at cleaning, that we recommend initially treating with ½ the long-term treatment dosage. This is to avoid blinding the filters as they remove high levels of suspended solids. 

Proper filtration and monitoring during initial filming amine treatment ensures any released contaminants are properly filtered out, ensuring optimal system health and longevity. 

Choosing the Best Filters for Closed-Loops

Cartridge filters are often ideal for smaller closed recirculating loops (less than 2,000 gallons), these manually operated filters require regular monitoring. They come in various filtration sizes, typically ranging from 0.35 to 50 microns. These filters trap particles, ensuring water clarity by removing suspended solids. 

Larger systems will often benefit from longer cartridge filters, moving from the standard 10” filter to a 20” or 30” filter. Also, bag filters or multiple cartridge filter housings allow for greater flow for much larger systems. For example, a 10” cartridge filter is ridiculously undersized for a 20 storey building. 

Combined with your water treatment program, filtration aids in the effective control of microbial contaminants. For closed-loops with microbial concerns, start with 50-micron filters and gradually transition to 1-micron filters to prevent filter blinding and optimize biomass removal. As microbes are trapped and removed, any soluble organics they’ve absorbed are also eliminated. 

For challenging filtration scenarios, polyquats such as Aquaguard 630 and Aquaguard M2 enhance results by coagulating suspended solids, increasing microbial clump size, and clearing biofilm from system surfaces. 

Filter Efficiency Over Time

As filters trap more and more contaminants, their efficiency can decrease. This means: 

Decreased Flow Rate: As filters clog, water flow can be restricted, leading to decreased system efficiency. 

Increased Energy Use: The system may need to work harder to pump water through a clogged filter, leading to increased energy costs. 

Reduced Contaminant Removal: A clogged filter may not remove contaminants as effectively, leading to decreased water quality. 

Regular monitoring and timely replacement or cleaning of filters can ensure they operate at peak efficiency.

Cost-Benefit Analysis of Filtration in Closed-Loop Systems

Investing in a robust filtration system for your closed-loop can lead to: 

Long-Term Savings: Reduced maintenance costs including chemical treatment costs, extended equipment lifespan, and decreased energy use can lead to significant savings over the life of the system. 

Improved System Efficiency: A well-maintained system with effective filtration can operate more efficiently, leading to further energy savings. 

Reduced Downtime: Effective filtration can reduce the risk of system failures, leading to decreased downtime and associated costs. 


Closed-loop systems are the arteries of a facility. They play a critical role in ensuring the comfort for building occupants and seamless operation of equipment. While these systems are designed to shield against a myriad of external contaminants, they are not impervious to internal challenges. Corrosion, suspended solids, and microbial contamination can compromise their efficiency and longevity. 

Filtration, combined with effective chemical water treatment addresses these challenges. By ensuring the water circulating within these closed systems is free from contaminants, you enhance the system lifespan and optimize its performance. Investing in robust filtration is not just about maintaining water clarity; it’s about safeguarding the very heart of your facility’s heating and cooling operations. 

To learn more about the intricacies of closed-loop systems, check out our comprehensive HVAC Closed-Loop Water Treatment Guide. And if you’re curious about the financial aspects, our article on Closed-Loop Water Treatment Costs provides insights into the economics of chemical treatment. 

So, what’s next? When you’re ready, contact Guardian Chemicals to learn how you can Create a Better Future with closed-loop treatment Chemistry Done Better! 

FAQs on Closed-Loop Systems: Filtration

Why is filtration important in a closed-loop system?

Filtration helps remove suspended solids from corrosion, scale, microbial contamination, and construction debris. These solids can cause erosion, deposit formation, microbiological growth, and decreased efficiency of water treatment chemicals.

How do I choose the right filter size for my closed-loop system?

The choice of filter size depends on the system’s specific needs, especially the type and size of contaminants present. Start with a broader filter and gradually transition to finer ones to optimize contaminant removal without causing filter blinding.

How does filter efficiency change over time?

As filters trap contaminants, flow rates decrease, resulting in increased energy use, and reduced contaminant removal. Regular monitoring, maintenance, and filter changes ensure filtration systems operate efficiently.

How often should I change the filters in my closed-loop system?

The frequency of filter changes depends on the filter type, the system size, and amount of suspended solids. For instance, bag and cartridge filters require monitoring and are changed when they approach their filtration capacity.

How do I know if my closed-loop system has suspended solids?

Turbidity or discoloration in the water is a clear sign of suspended solids. Regular system checks, monitoring, and employing filtration solutions help manage and reduce these solids.

Can closed-loop systems operate without filtration?

While they can operate without filtration, it’s not recommended. Without proper filtration, the system is more susceptible to issues like corrosion, deposit formation, and microbiological growth, which reduce system life and efficiency.

What are the long-term benefits of investing in a closed-loop filtration system?

Investing in a good filtration system improves equipment efficiency, reduces maintenance costs, and extends equipment life. Good closed-loop filtration leads to improved system health and significant long-term savings.

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