Understanding Closed-Loop Water Systems: Benefits, Challenges, and Applications

From heating and cooling to process control, closed-loop water systems are used in contained environments where water is isolated from the atmosphere. If water is recirculated via a piping system without using much makeup water, it’s considered a closed loop.

While this type of system can effectively heat and cool homes, it’s often applied to industrial applications to reduce waste and conserve water. When water is placed in a closed system, it will recirculate in a loop to undergo a cooling or heating process. Once the water is set to the desired temperature or conditions, it can be reused.

While a closed loop water system can be highly effective depending on the application, there are also some challenges to consider, such as the potential for corrosion. To better understand how closed-loop water systems work, it’s important to compare them to open-loop circulation.

An open-loop system will pump water directly into an open tank, after which the liquid will be returned to the bath. This type of circulation pushes water out with pressure before pulling it back with suction.

The main difference between an open-loop system and a closed-loop one is that it’s cost-efficient and less labor-intensive. However, the piping system and water will be exposed to contaminants at a higher rate than a closed-loop system. The purpose of this guide is to help you understand the benefits and challenges associated with closed-loop water systems.

Key Components of Closed-Loop Water Systems

Closed-loop water systems consist of pipes and circulation mechanisms, heat exchangers, pumps, and control systems. The heat load in a closed-loop water system is made with equipment that limits heat as one of the byproducts. Most closed-loop water units are comprised of sophisticated piping systems that connect all the components. With this system in place, the fluid can circulate between the pump, heat load, and heat exchanger.

The heat exchanger is a type of device that transfers heat to a cooler medium, which can be a radiator or fluid cooler. The pump system is necessary to transfer fluid from the heat load to the heat exchanger. Keep in mind that the heat can be dissipated with cooling methods like refrigeration, ambient air cooling, or evaporative cooling.

Advantages of Closed-Loop Water Systems

From better water conservation to a lower environmental impact, there are many reasons why your facility should opt for closed-loop water systems. For example, these systems provide you with more precise control over the temperature in your heat-producing equipment and machinery. They also have low makeup water requirements, which should make it easier for you to control the water quality and conserve resources. Your facility shouldn’t consume as much water every day. You’ll only need to use makeup water when a leak has occurred or when the system needs to be repaired. Keep in mind that closed-loop systems don’t produce much evaporation.

Having access to high-quality water also ensures that scale deposits won’t be an issue when used for makeup situations. This water should also limit the potential for fouled exchangers, cracked cylinders, and broken heads. Biological fouling rarely occurs in closed-loop systems.

Closed systems also have a lower environmental impact. Open systems generate a considerable amount of geothermal energy, which isn’t a problem with closed ones. The closed-loop setup doesn’t corrode easily. The only areas where oxygen can enter include the hot well and the bottom of the surge tank. If you properly treat the makeup water you need to use, you should be able to eliminate corrosion.

Common Applications of Closed-Loop Water Systems

Closed-loop water systems are used across many different applications, which include the following:

• Industrial processes
• Data centers
• Heating, ventilation, and air conditioning (HVAC) systems
• Renewable energy systems

Challenges and Considerations

Even though closed-loop water systems are often preferable over open ones, they have their own challenges and considerations. For example, closed-loop systems are designed to be sealed. However, they can still lose up to 25% of their water volume per month because of overflow from nearby tanks and leaks in the mechanical seals. If you need to add makeup water to mitigate these losses, you’ll likely introduce impurities to the closed-loop system. The types of impurities that can get into the water include the following:

• Suspended solids
• Microorganisms
• Dissolved gases
• Entrained air
• Organic matter
• Minerals

There’s also the potential for microbiological growth and corrosion that can’t be ignored. In closed-loop systems, sulfate-reducing and denitrifying bacteria can thrive. When these bacteria grow, they can reduce the heat transfer and cause corrosion and fouling. Stagnant areas within the closed-loop system are more susceptible to microbiological growth.

If dissolved oxygen gets into the closed-loop system, corrosion can develop. The metallic surfaces might also begin to corrode if the water’s pH level drops. In a low-pH environment, the metal oxide passivation layers will start to degrade, which means that the rate of corrosion will increase. If you don’t quickly resolve this issue, you may experience high maintenance costs, equipment damage, and lower operational efficiency.

When using closed-loop water systems in your warehouse, you must regularly maintain and monitor them to look for signs of corrosion and microbiological growth. It’s also a good idea to inspect the system regularly to ensure it isn’t leaking.

Make sure you select the appropriate materials and inhibitors for your closed-loop water system. Inhibitors are special chemicals that can limit scale formation and corrosion. If you don’t treat your makeup water, issues like corrosion and pitting are more likely.

Best Practices for Design and Maintenance

When designing and maintaining a closed-loop water system, it’s highly recommended that you implement the following best practices for design and maintenance.

System Design Considerations

As mentioned previously, you should consider using specially formulated inhibitors that can keep scale buildup and corrosion from developing in the system. It’s also a good idea to use closed-loop biocides, which are designed to prevent microbiological growth and fouling.

Biocides can help you prevent the accumulation of biofilms on the surfaces of your pipes. They can also mitigate the type of corrosion that occurs because of high microbial concentration. Once you introduce biocides to the closed-loop system, they will eliminate sulfate-reducing, iron-reducing, and denitrifying bacteria.

Consider using freeze protection as well. When a closed-loop water system is in freezing conditions for an extended period, the commercial and industrial applications it’s being used for won’t be as effective. Your best option is to obtain and administer inhibited glycol to vulnerable systems. Ethylene and propylene glycol are two solutions that might reduce the effects of freezing conditions.

When designing a closed-loop water system, make sure it’s paired with a filtration unit if you wish to effectively remove particulate and suspended solids. These substances can cause extensive damage to the process equipment and piping. You can filter a closed-loop water system with side-stream filtration. Filtering the water should reduce equipment damage and enhance efficiency.

Recommended Maintenance Protocols

There are several options that can help you maintain closed-loop water systems. For example, it’s recommended that you regularly use chemical treatments. These treatments allow you to pump or inject certain chemicals into the water to control its chemistry. You should be able to prevent microbiological issues and corrosion with this approach. The types of chemical treatments available to you include scale inhibitors, biocides, pH boosters, and corrosion inhibitors.

You might also want to consider using sulfite and other oxygen scavengers to get rid of dissolved oxygen. With corrosion inhibitors like azole and nitrites, you can provide the piping system with a protective layer that reduces the potential for corrosion on copper and steel surfaces.

Keep in mind that you can eliminate microbial growth with biocides. To improve the efficacy of your maintenance techniques, use automated control systems to obtain real-time sensor data that will allow you to set the proper chemical dosing rates.

If you manage or own an older building that doesn’t use a comprehensive water treatment system, you might experience corrosion in your closed-loop system. Use chemical cleaners to restore efficiency and remove partial blockages.

Monitoring and Treatment Strategies

When you use a closed-loop water system in your facility, it’s important that you monitor and treat the water regularly. Water testing allows you to capture real-time readings and perform periodic analyses of water samples. The results of these tests will allow you to identify the quality of the water that you’re using in the system. The key performance indicators (KPIs) that you should monitor include the following:

• Conductivity
• Bacterial count
• Dissolved oxygen
• Temperature
• Total hardness
• pH

Consider performing microbiological testing to identify the concentration of bacteria in your closed-loop system. To conduct this test, you must collect multiple water samples from areas in your system that are prone to stagnation. These samples will be analyzed with total bacterial count, ATP, and similar tests. The data allows you to track any changes that occur to microbial populations.

Conclusion

A closed-loop water system uses an intricate system of pipes to increase or decrease the temperature of water without consuming an ample amount of makeup water. These systems are often employed in data centers, industrial processes, and HVAC systems.

The potential for corrosion and microbiological growth is much lower in a closed-loop system than in an open one, which should make it easier for you to prevent damage and efficiency losses. Closed-loop water systems have been widely adopted in industrial facilities. Because of the advantages they provide over open systems, they should retain their popularity in the coming years.