Types Of Piping Systems

Understanding of the three basic types of piping systems: closed-loop, open-loop, and once-thru

Closed-Loop (Evaporator)

In a closed-loop piping system, the water is contained within a closed piping system, or loop, through which it circulates. While there may be some nominal contact with the air depending on the type of tank used, the system is considered closed to the environment. Typically, closed-loop systems are chemically treated to control corrosion, scale, slime, and algae within the piping but their chemical treatment requirements typically are not as extensive as an open-loop.

Example of a Closed-Loop Piping System

Open-Loop (Condenser)

In an open-loop piping system, the water is in constant contact with the air and the system is therefore open to the atmosphere. A typical example of an open-loop system is a recirculating condenser water system with a cooling tower where the water is circulated through the cooling tower, sprayed over the tower media surface, collected into the tower basin, circulated through the condenser, and then sent back through the cooling tower.

Example of an Open-Loop Recirculating System


In this type of system, water passes through the system once and is then discharged. An example of a once-thru system would be a chiller with river water piped into its water-cooled condenser. The rejected heat from the condenser is introduced back into the river, which is not always acceptable from an environmental perspective. In general, once-thru systems that use “city” water are not allowed because they use excessive amounts of water.

Example of a Once-Thru System


What are the key differences between closed-loop and open-loop piping systems?
The primary difference between closed-loop and open-loop piping systems lies in their interaction with the environment. Closed-loop systems are self-contained, with water circulating within a closed piping system or loop, whereas open-loop systems draw water from an external source, such as a river or lake, and discharge it back into the environment after use. This fundamental difference affects the chemical treatment requirements, corrosion control, and overall system design. Closed-loop systems require less extensive chemical treatment, whereas open-loop systems need more rigorous treatment to address the variability of the external water source.
How does the type of tank used affect a closed-loop piping system?

The type of tank used in a closed-loop piping system can influence the level of contact between the system and the environment. For example, an open-top tank may allow for some air contact, whereas a sealed tank would minimize air exposure. However, even with some air contact, closed-loop systems are still considered closed to the environment due to the limited interaction. The tank design and materials used can also impact the system’s overall performance, corrosion resistance, and maintenance requirements.

What are the typical applications for once-thru piping systems?

Once-thru piping systems are commonly used in applications where a large volume of water is required for a short duration, such as in industrial processes, power generation, or desalination plants. These systems are often used in situations where the water source is abundant and the water can be discarded after a single pass through the system. Once-thru systems are typically less complex and less expensive than closed-loop or open-loop systems, but they may require more extensive water treatment and have higher environmental impacts.

How does chemical treatment differ between closed-loop and open-loop piping systems?

Chemical treatment requirements vary significantly between closed-loop and open-loop piping systems. Closed-loop systems require less extensive chemical treatment, primarily focusing on controlling corrosion, scale, slime, and algae within the piping. In contrast, open-loop systems need more rigorous treatment to address the variability of the external water source, including pH adjustment, disinfection, and removal of suspended solids. The chemical treatment regimen for open-loop systems must also consider the potential environmental impacts of the discharged water.

What are the advantages of using a closed-loop piping system in HVAC applications?

Closed-loop piping systems offer several advantages in HVAC applications, including reduced water consumption, lower chemical treatment requirements, and decreased environmental impact. Closed-loop systems also provide better control over water quality, which can improve the overall efficiency and reliability of the HVAC system. Additionally, closed-loop systems are less prone to scaling and fouling, reducing the need for frequent cleaning and maintenance. These benefits make closed-loop systems a popular choice for many HVAC applications.

Can a piping system be designed to combine elements of closed-loop and open-loop systems?

Yes, it is possible to design a piping system that combines elements of closed-loop and open-loop systems. For example, a system might use a closed-loop configuration for the majority of the piping, but incorporate an open-loop section for a specific process or application. These hybrid systems can offer the benefits of both closed-loop and open-loop designs, but require careful consideration of the system’s overall performance, water quality, and environmental impacts. A thorough understanding of the system’s requirements and constraints is essential to design a successful hybrid piping system.