Among heat exchange device types used in HVAC systems are energy recovery wheels and desiccant wheels. Each wheel type serves a different purpose and operates on different principles.
Purpose
An energy recovery wheel, also known as an enthalpy wheel or heat recovery wheel, is designed to recover energy from the exhaust air of a building and transfer it to the incoming fresh air. This process helps to reduce the heating and cooling loads on the HVAC system, thereby saving energy and improving efficiency.
Heat Exchange: The wheel rotates between the outgoing exhaust air stream and the incoming fresh air stream. It captures both sensible heat (temperature) and latent heat (moisture) from the exhaust air and transfers it to the incoming air.
Material: The wheel is typically made of materials with high thermal conductivity, such as aluminum or coated with a desiccant material to enhance moisture transfer.
Application: Energy recovery wheels are used in climates where there is a significant difference between indoor and outdoor temperatures, making them effective for both heating and cooling seasons.
Purpose: A desiccant wheel, also known as a dehumidification wheel, is designed primarily to remove moisture from the air. This process is useful in controlling humidity levels, which can be important for comfort, health, and certain industrial processes.
Moisture Absorption: The wheel is coated with a desiccant material, such as silica gel or lithium chloride, which has a high affinity for water vapor. As the wheel rotates, it passes through a regeneration zone where the desiccant is dried, allowing it to absorb moisture from the incoming air in the dehumidification zone.
Heat: The regeneration process typically involves heating the desiccant to release the absorbed moisture, which is then expelled from the system.
Application: Desiccant wheels are used in environments where humidity control is critical, such as in manufacturing processes, data centers, and places where mold or mildew must be prevented.
In summary, while both wheels involve the rotation of a material to transfer energy or moisture, energy recovery wheels focus on reclaiming energy from exhaust air to improve HVAC efficiency, whereas desiccant dehumidification wheels focus on dehumidifying the air for better humidity control.