Power Setting versus Temperature Setting in Hot Air Heaters

Air heaters come in many shapes and sizes but the fundamentals of how they work is consistent across most tools. A resistance wire element heats up when a current flows through it and an air source provides air flow across the heated wires. Passing air across the hot element heats the air which can then be used to perform any desired task.

Heaters are specified according to power rating (related to the current flowing through the element and the source voltage), this article will use the SI unit for power: kilowatts or kW. Power is a quantification of how much energy per unit time the heater is able to transfer. It’s this energy transfer that causes heating or a rise in temperature of the object subjected to the flow of hot air.

Setting Power – What does it mean?

Some air heaters can be controlled using a Percentage Power setting. This means the user sets the power output of the heater between 0 and 100% of the maximum kW rating. This should not be confused with setting the temperature of the heater, although power and temperature are related. As the power is increased, the air flowing over the element can be heated to a higher temperature.

The power of a heater can be set to achieve a desired temperature however the temperature will not be held constant; any changes in the process or environment (i.e. changes in input air flow, ambient temperature, etc.) will cause the output temperature to fluctuate.

Setting Temperature – What does it mean?

Some air heaters can be controlled by setting the target output temperature. To keep the output temperature constant the heater must be able to continuously adjust the power up or down to compensate for external influences or designed process parameter changes. In order to accomplish this two things are required:

• There must be a feedback/measurement loop which measures the actual output temperature from the heater (this is typically a thermocouple or RTD).
  
• There must be control electronics which will compare the set target temperature to the actual measured output and adjust the power accordingly
  

The measurement device and control electronics can be built into the heater or can be external components.

When to use Which

While setting the power output of a heater is much more straightforward than setting and controlling the output temperature it is also less precise. In many applications the added sophistication of temperature control is not necessary. In cases where there is little change in the processing environment or where the process isn’t sensitive to moderate temperature variation a heater with simple power adjustment will likely suffice. In cases where the temperature is a critical parameter of the process or when there may be large fluctuations in the environment conditions, it likely that temperature control will be required.

For more information on related topics please see the following articles:

• Temperature Control of Air Heaters
• ​Thermocouples in Hot Air Systems

If you still have questions about choosing the right heater for you, please call STANMECH and talk to one of our Technical Sales Representatives.