An air-to-air heat exchanger (air-to-air heat exchanger) is a type of heat exchange device whose main function is to transfer heat from one airflow (usually exhaust air) to another airflow (usually fresh air) through thermal conduction, while physically isolating the two airflows to avoid direct mixing. Its working principle can be decomposed into the following steps:
Heat capture and transfer:
The exhaust (indoor air) carries heat (high temperature in winter and low temperature in summer) into one side of the heat exchanger.
Fresh air (air introduced from outside) flows through the other side of the heat exchanger.
Two types of airflow exchange heat inside the heat exchanger through conductive materials such as metal plates and heat pipes, transferring heat from the high temperature side to the low temperature side.
Airflow isolation:
The heat exchanger is designed with independent channels to ensure that exhaust and fresh air do not mix, preventing contamination or cross transfer of moisture.
Common channel forms include parallel plates, cross flow, or counter flow designs to optimize heat exchange efficiency.
Energy Recovery:
Winter: The heat from exhaust air preheats the fresh air, reducing the need for subsequent heating.
Summer: Pre cool fresh air with exhaust cooling capacity to reduce cooling load.
The heat exchange efficiency is usually between 50% and 90%, depending on the type of equipment and operating conditions.
Emissions and outputs:
After completing the heat exchange, the exhaust temperature decreases and is discharged outdoors.
After the fresh air is preheated or pre cooled, it enters the ventilation system or indoor use.
Main types and principles
Plate heat exchanger:
Composed of multiple layers of thin metal plates, the exhaust and fresh air flow in adjacent channels, usually using counter current or cross flow methods.
Advantages: Simple structure, high efficiency, and no moving parts.
Wheel heat exchanger (hot wheel):
Using a rotating heat storage wheel, the wheel body absorbs exhaust heat and rotates to the fresh air side to release heat.
Advantages: Suitable for high air volume, high heat recovery efficiency, but there may be a small amount of airflow mixing.
The heat pipe heat exchanger:
By utilizing the evaporation and condensation cycle of the working fluid inside the heat pipe to transfer heat, the heat on the exhaust side is absorbed and released on the fresh air side.
Advantages: No external power required, suitable for scenarios with large temperature differences.
Application of Air to Air Heat Exchanger
Air to air heat exchangers are widely used in scenarios that require ventilation and energy conservation, mainly including the following areas:
Building ventilation system:
Residential and commercial buildings: Recovering exhaust heat and preheating or pre cooling fresh air in HVAC systems. For example, in winter, northern regions transfer the heat from indoor exhaust at 20 ° C to fresh air at 0 ° C, reducing heating energy consumption.
Energy saving buildings: such as passive houses, maintain indoor air quality while reducing energy consumption through heat recovery ventilation systems (HRVs).
Industrial sector:
Factory exhaust gas treatment: Recovering heat from high-temperature exhaust gas for heating process air or water. For example, waste heat recovery from high-temperature exhaust in the metallurgical and chemical industries.
Drying system: recovers the heat from the discharged humid and hot air and preheats the fresh air to improve drying efficiency.
Data Center:
The data center servers generate a large amount of heat, which is transferred to the fresh air through an air-to-air heat exchanger to reduce the burden on the cooling system.
Agriculture and Greenhouse:
In greenhouse ventilation, heat exchangers are used to recover indoor heat, preheat winter cold air, and maintain the temperature required for plant growth.
Automobiles and Transportation:
In electric or internal combustion engine vehicles, recovering exhaust heat for cabin heating improves energy efficiency.
