What Is a Circulation Pump and What Does It Do?

The circulation pump moves fluids through closed systems. It’s typically a centrifugal pump that uses an impeller to impart pressure to the fluid, forcing it through the circuit. Let’s see what it does, how it works, and its applications in more detail.

Key Takeaway

• Primary Function: Circulation pumps do not lift fluids; they simply overcome pipe friction in a closed-loop system (heating, cooling, or solar thermal).
• Wet Rotor vs Dry Rotor: Wet rotor designs (canned motor) are silent and maintenance-free, ideal for residential and light commercial use. Dry rotor inline pumps handle much larger GPM flows.
• Energy Saving: Modern circulators utilize Electronically Commutated Motors (ECM) to adjust speed based on building demand, cutting power use by up to 50%.

Understanding What a Circulation Pump Is

A circulation pump is a type of pump designed to move fluids in a closed system. It ensures the pressure is sufficient to overcome the system’s friction and that it meets head requirements. That way, the system operates efficiently.

The pump is usually smaller than conventional types and is built to generate comparatively lower pressure levels. That’s because it focuses more on recirculating the fluid than offering improved head pressure.

Other features that distinguish it from conventional types, such as the booster pump, are control options. The features include activation technologies to enable them to respond to demand and achieve energy savings.

Primary Functions of a Circulating Pump 

It keeps a fluid moving in a loop for heating or cooling purposes. That way, circulation systems maintain the required fluid pressure and flow rates, ensuring they perform as desired.

For instance, it can circulate hot water in a heating system or recycle coolant in a cooling/air conditioning system. In addition to efficiency, it ensures the flow is consistent with system requirements.

Core Components of a Closed Loop Circulation Pump

The device uses various components to push a fluid through a recirculation system. Let’s understand its construction by examining the parts that make it up, starting with the drive.

Motor/Drive

The motor converts electrical energy to kinetic energy, providing the motion needed to operate the impeller. Most units have the motor sealed into them. However, larger types have the motor mounted externally.  

The Impeller

The impeller is the heart of this device. It rotates to suck fluid through the inlet, increases its pressure, and sends it out via the discharge to the pipes. It comes in various designs, sizes, and materials.

Case/Housing

The housing or casing protects internal components against damage. It also directs the flow and helps keep the pressures inside. The housing can be of various materials, such as cast iron, stainless steel, and bronze.

Inlet/Outlet Ports

The ports control the entry and exit of the fluid under circulation. The inlet allows fluid to enter, while the outlet is where the fluid exits at a higher pressure. Most ports are aligned for easy, inline installation.

Other Parts

It also contains smaller parts which are necessary for its proper operation. They include seals, bearings, and controls. Seals prevent leaks, while bearings smooth the rotation and reduce friction.

The control buttons and switches allow users to operate the device and adjust functions. Advanced control functions improve a user’s experience and include digital electronics for programmed operation.

Wet Rotor vs. Dry Rotor Circulators

When specifying a circulator for HVAC or heating networks, engineers must choose between two motor designs:

• Wet Rotor (Canned Motor) Pumps: The rotor is submerged in the pumped fluid, which cools the motor and lubricates the bearings. This design has no mechanical seals, meaning it is 100% leak-free, silent, and virtually maintenance-free. It is the standard for domestic boilers and residential heating.
• Dry Rotor (Inline) Pumps: The motor is separated from the liquid by a mechanical seal. These pumps are louder and require scheduled seal maintenance, but they can handle much higher flow rates and temperatures, making them ideal for district cooling and heavy industrial loops.

How Does a Circulation Pump Work?

The pump works by creating a pressure difference between the supply line and the return line. It’s typically a centrifugal pump that utilizes an impeller to push the fluid and maintain a stable, constant flow. Here’s its operation explained:

• Fluid from the supply enters via the inlet, where it meets a rotating impeller.
• The impeller blades push the fluid, increasing its velocity.
• The accelerated fluid enters a volute where it slows down while the pressure increases.
• The fluid exits via the outlet port and into the pipeline.
• The fluid goes to the point of use, which can be a heating or cooling system.
• The fluid returns to the reservoir via the return lines for recirculation.

Modern circulating pumps are typically built to conserve energy. They only turn on when needed, such as when the system requires a flow. Some are timer-controlled, while some rely on sensors.

What is a Circulation Pump Used For?

Its applications fall under these main categories: heating and cooling, hot water recirculation, and lubrication systems. Let’s dive into how the device helps move fluids and specific use cases.

Heating and Cooling Systems

It recirculates heated liquids or coolants. The moving fluid elevates temperature levels or reduces heat. That, in turn, serves the required function in a home, commercial building, or industrial facility.

Example uses include air conditioning (HVAC), hydronic heating systems, and chillers. The pump ensures the proper performance of these systems by maintaining flow.

Hot Water Recirculation

One of the device’s most common applications is maintaining hot water circuits. It sits between the water heater and various points of application, such as showers and faucets, ensuring a constant supply of warm water.

The pump has uses in homes, residential apartments, commercial buildings, and various other places where warm potable water is needed.

Lubrication Systems

It pushes a lubricant, such as oil, through moving parts to lubricate and cool them. It works by taking the oil from a reservoir, circulating it through lubrication channels and then returning it to the reservoir.

The pump in this application handles a viscous fluid, requiring more power and a robust construction. It helps protect engine components, gearboxes, industrial machinery, etc.

Industrial Processes

Many industrial processes require a constant flow of a fluid. They include chemical transfer and delivery systems, food processing, water treatment, and product manufacturing.

The device usually circulates the fluid to maintain a desired temperature, prevent clogging, or ensure a fluid’s availability. It may also circulate slurries in a water treatment system.  

Circulation Pump Sizing

Anyone installing the pump must understand how to size it correctly. It helps avoid a mismatch that can lead to increased energy use, inadequate utilization, and an overworked system.

Determine the required head and flow rate. The device must overcome the resistance of the pipes, manifolds, valves, and other fittings. It must also deliver the necessary amounts of the fluid.

Use the system’s height and friction loss to calculate head pressure. Study the specific pump curves to understand its flow characteristics, which usually vary at different pressure levels.

Calculate the required flow rate in gallons per minute, GPM. The values you get will depend on your system’s size, pipe length and diameter, and the number and types of fittings.

Conclusion

A circulation pump is the heart of any modern closed-loop heating or cooling system. By maintaining continuous flow with minimal pressure, it ensures even temperature distribution across the entire facility. Selecting between wet-rotor and dry-rotor models depends entirely on your system’s GPM flow and maintenance tolerance.