What Is Infrared Heating Efficiency? How Can We Know The Heating Efficiency?

When a customer asks about the efficiency of quartz infrared heating, an inexperienced salesperson might simply cite the lamp's reflector efficiency—such as 70% for quartz tubes with ceramic reflectors or over 90% for those with gold-coated reflectors. This easily leads to conceptual confusion, as "lamp reflector efficiency" is not the same as the "electro-thermal efficiency" of the entire heating system or the workpiece itself. Industrial infrared heating efficiency must be determined by considering actual operating conditions and experimental data.

For a heating system comprising a quartz IR lamp, a reflector, and a workpiece, it is crucial to understand the following parameters:

• Radiation efficiency of the lamp itself
• Reflector efficiency
• Distance between the lamp and the workpiece
• Infrared absorption/emissivity of the workpiece
• View factor between the lamp and the workpiece
• Surface temperature of the workpiece
• Airflow around the workpiece
• Radiation absorption by oven or chamber walls
• Radiation loss from the lamp away from the workpiece
• Heat loss from the workpiece to the environment via radiation and convection

Consequently, the performance of an infrared system is influenced by a combination of factors; the system's overall efficiency cannot be adequately described by the lamp's reflector efficiency alone.

So, how can the actual electro-thermal efficiency of the entire IR heating system be determined? 

Without specific information about the workpiece, heating conditions, equipment configuration, and experimental data, it is not possible to determine an exact heating efficiency.

The actual efficiency of an infrared heating system depends on many factors, including the infrared radiation efficiency of the heating element, reflector efficiency, distance and geometry between the infrared lamps and the workpiece, the infrared absorption characteristics of the workpiece, view factor, thermal insulation, air convection, and heat losses from the heater and furnace structure.

For a practical efficiency evaluation, the most reliable method is to use actual test data. The electrical energy consumed by the system should be measured with an energy meter, while the mass, specific heat capacity, initial temperature, and final temperature of the workpiece are recorded.

The useful thermal energy absorbed by the workpiece can then be estimated from:

Q = m × Cp × (T₂ − T₁)

and the overall electrical-to-thermal efficiency of the heating system can be estimated as:

η = Q / Electrical

where Electrical is the actual electrical energy consumed during the heating process.

If required, additional measurements of the workpiece's cooling curve after the heating process can be used to estimate convective and radiative heat losses. However, these losses should be treated as part of the overall heat-balance analysis and should not simply be added to the useful heat absorbed by the workpiece without clearly defining the measurement boundary and time period.

Therefore, the most reliable way to determine the actual efficiency of an infrared heating system is to conduct a controlled heating test under the intended operating conditions and calculate the efficiency from the measured electrical energy input and the measured temperature rise of the workpiece.