Introduction to Thermal Actuator

Posted on September 28, 2022

Thermo-electric Actuators are very common in underfloor heating system, radiators, fan coils, and other applications where the remote ON/OFF control of hot and cold fluids is required.

Indicating which one is thermal actuator and which one is thermo-electric actuator.

The Thermal Actuator is the most crucial component of thermo-electric actuators. It decides how efficient, durable, and reliable a thermo-electric actuator will be.

What is a Thermal Actuator?

The thermal actuator is a compact actuator that converts electric/thermal energy to linear mechanical motion by taking advantage of the outstanding expansion characteristic of the wax as it transforms from the solid phase to the liquid phase.

iSwell thermal actuator consists of a brass housing, a PTC thermistor connected at the bottom as the heat source, and a piston inserted in the "elastomer bag" to deliver linear displacement. Check this post to learn more about this squeeze-push type structure.

Exploded view for Thermal Actuator

Working Principle of a Thermal Actuator

The wax volume responds to temperature changes much more significantly than other common substances. The temperature-sensitive wax is the basis of a thermal actuator. It must be precisely proportioned and evenly mixed. iSwell is capable of developing different wax recipes to achieve different melting temperature ranges for specific demands.

Here is the working principle of iSwell thermal actuator, step by step.
• The temperature starts rising when the PTC powers on
• The solid wax inside the brass housing starts to melt and expand as the temperature gets closer to the melting point
• As the space inside the brass housing is unchanged, the volume expansion of wax keeps squeezing the "elastomer bag"
• The "elastomer bag" pushes the piston out as there is less and less space left in the "bag"

Working principle of a thermal actuator

The temperature starts going down when the PTC powers off. The wax transforms from the liquid phase to the solid phase, and its volume contracts. The occupied space inside the "elastomer bag" is restored. But the piston will not return to its initial position by itself due to the existing frictional resistance between components. An external return spring is required to help the piston go back. That's why every thermo-electric actuator has a spring inside.

How Does a Thermo-electric Actuator Work in Underfloor Heating Systems?

The thermo-electric actuator is installed on the underfloor heating manifolds and controlled remotely by room thermostats to open or close valve for individual circuits/loops.

iSwell Thermal actuator working animation inside a thermo-electric actuator
Menred Underfloor Heating Manifolds with Thermo-electric Actuators using iSwell Thermal Actuators

For a normally closed (NC) thermo-electric actuator, the valve being controlled stays closed when the actuator is powered off. When there is a demand to increase the room temperature from the thermostat, the thermo-electric actuator powers on. The thermal actuator inside the thermo-electric actuator starts heating up, and its piston pushes out as the wax expands. Then the valve is opened, and the hot water starts to flow in the corresponding circuit/loop for this room. As the result, the room temperature increases gradually to reach the set value on the thermostat.

The thermo-electric actuator powers off when the room temperature reaches the set value. The thermal actuator inside the thermo-electric actuator cools down. Then the piston returns to its initial position with the assistance of the return spring to close the valve. The hot water stops flowing in the circuit/loop as the valve is closed.

What Are The Benefits of a Thermal Actuator?

There are many benefits from a thermal actuator when compared to solenoid.
• Compact size and few components
• High output force throughout the entire working stroke
• No maintenance is required
• Complete silent
• Long service life
• Reliable and excellent for applications in extreme conditions

Bottom Line

Thermal actuators are the ideal solution for temperature regulation and valve control systems based on the benefits above. iSwell is capable of customizing, designing and manufacturing thermal actuators to meet various demands.

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