The Fresh Air Auxiliary Duct Electric Heater is a series-connected auxiliary heating device specifically designed for fresh air system ducts. It is directly embedded within the fresh air supply duct, providing continuous online heating to low-temperature fresh air, effectively addressing issues such as insufficient winter fresh air temperature, uneven indoor thermal distribution, and excessive heating load on the main unit. It serves as a core supporting device for enhancing winter air supply comfort and system stability in fresh air systems of commercial buildings, industrial workshops, and cleanrooms.
1. Working Principle
The equipment operates based on the principles of resistive heating and forced convection heat transfer. After being connected in series to the air supply duct, low-temperature fresh air passes uniformly through the heat exchange core of the heater under the pressure of the duct airflow. Stainless steel finned electric heating tubes or PTC heating elements convert electrical energy into thermal energy upon power-on, achieving thorough heat exchange with the flowing air through densely arranged finned surfaces. During the duct transportation process, the fresh air is heated. By coordinating with a temperature control system to detect the outlet air temperature in real time and dynamically adjusting the heating power, precise constant-temperature air supply can be achieved.
II. Core Structure and Design Features
1. Air duct compatible shell structure
The casing is made of galvanized steel plate or 304 stainless steel, with standard flange interfaces as the default configuration. It can directly connect to various duct sections such as circular and rectangular types, ensuring seamless integration with existing duct systems. The interior is filled with insulation cotton to effectively reduce heat dissipation from the duct and prevent condensation on the outer wall. The entire design adopts a modular frame structure, allowing the heating core to be extracted for maintenance without the need to dismantle the entire duct.
2. High-Efficiency Heat Exchange Heating Core
The mainstream design employs an array of stainless steel finned electric heating tubes, with tightly wound and uniformly spaced fins to maximize heat exchange area within the limited duct cross-section, resulting in low air resistance and high heat transfer efficiency, achieving a thermal conversion efficiency of over 96%. For low airflow clean air scenarios, PTC ceramic heating elements can also be selected, featuring self-limiting temperature properties that eliminate overheating risks at the component level.
3. Low Aerodynamic Resistance Flow Path Design
The internal flow channel has undergone fluid optimization, with the heating tube arrangement aligned with the airflow direction of the duct to prevent vortices and pressure loss. The frontal wind speed is compatible with the conventional duct velocity range of 2~3 m/s, causing minimal impact on the original fresh air system's supply air pressure. No additional fan replacement is required for adaptation.
4. Multi-layer Security and Intelligent Control
• Equipped with dual thermal overheat protection, it automatically cuts off power when temperature exceeds limits to prevent dry burning damage in case of no airflow or airflow blockage;
• Supports fan interlock control, allowing the heater to power on only after the fan starts, and cutting off heating in advance before shutdown to logically prevent dry burning without airflow;
• Supports multi-stage power adjustment and PID precise temperature control, automatically matching heating output based on outdoor fresh air temperature to reduce operational energy consumption.
III. Main Application Scenarios
1. Commercial building fresh air main duct: The main air supply duct for centralized fresh air systems in office buildings, hotels, shopping malls, hospitals, etc., which preheats the fresh air for the entire space in winter to prevent direct cold air flow from terminals and maintain uniform indoor temperatures.
2. Industrial Plant Ventilation Ducts: Air supply and exhaust pipelines for production workshops and warehousing logistics, designed to raise the temperature of air delivered during winter, improve working conditions, and meet the basic temperature requirements for process environments.
3. Cleanroom air purification duct: A duct for delivering purified air in dust-free workshops, laboratories, and pharmaceutical production facilities, achieving constant temperature air supply without compromising air cleanliness, compliant with duct standards for purification systems.
4. Fresh air system for cold regions: In low-temperature environments in northern areas, the fresh air is preheated in the inlet duct section to prevent freezing and cracking of the subsequent air conditioning surface cooler and heat exchange coils, while also compensating for the heat deficit during the main unit's defrosting period.
5. Supporting fresh air equipment: It can be built-in or externally connected to the air supply section of fresh air ventilators or modular air conditioning units, and used as a standard auxiliary heating module.
IV. Key Points of Selection, Installation, and Maintenance
1. Core Parameters for Model Selection
The power and specifications must be determined based on the duct cross-sectional dimensions, fresh air volume, and designed temperature difference between inlet and outlet air. The core calculation formula is:
Heating power (kW) = Airflow (m³/h) × Temperature rise (℃) × Specific heat capacity of air at constant pressure × Air density / 3600 / Thermal efficiency
For actual selection, it is recommended to reserve a power margin of 20%~30% to cope with extreme low-temperature weather conditions. Additionally, the air velocity in the ducts should be matched, ensuring the frontal wind speed remains below 2.5 m/s to balance heat exchange efficiency and low-noise operation.
2. Installation Specifications
• Prioritize installation in the fresh air delivery section or downstream of the air handling unit's surface cooler to prevent low-temperature, high-humidity air from directly contacting the heating element and causing condensation;
• Maintain a straight pipe section of ≥1.5 times the duct diameter before and after the equipment to ensure uniform airflow over the heating surface and enhance heat exchange efficiency;
The entire air duct must be properly insulated and sealed to minimize heat loss during transportation;
• Must be electrically interlocked with the fresh air fan, and heating is strictly prohibited without airflow.
3. Routine Maintenance
• Regularly clean dust and debris from the heating fin surface to maintain clean heat exchange surfaces, preventing increased wind resistance and reduced heat transfer efficiency;
• Regularly inspect the thermal protector and terminal block conditions to ensure the safety protection devices are sensitive and reliable;
Before restarting after long-term shutdown, it is necessary to check the insulation resistance and ensure proper line connections before powering on.
V. Product Value Summary
The auxiliary air duct electric heater for fresh air adopts the "direct duct installation and online heating" approach, efficiently addressing the winter temperature compensation needs of the fresh air system without occupying additional building space. With its flexible installation, strong adaptability, and stable heating performance, it not only enhances indoor air supply comfort but also alleviates the heating burden on the main air conditioning system, reducing operational load and energy loss. It serves as a cost-effective supporting solution for ensuring stable winter operation of various fresh air and ventilation systems.
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Post time: Jul-07-2026
