What is an energy recovery wheel?
An energy recovery wheel, also known as a heat recovery wheel or enthalpy wheel, is a component used in HVAC systems to recover energy from exhaust air and transfer it to incoming fresh air. An energy recovery wheel can be made to recover sensible-only heat (temperature) or include latent heat (moisture). It is comprised of a rotating wheel made of a long coil of porous thermal conductive material--typically aluminum or a polymer. The coil provides in total a large surface area.
Here's how an energy recovery wheel works
- Airflow: The HVAC system pulls in fresh outdoor air and extracts stale exhaust air from the building. These air streams are directed through the energy recovery wheel.
- Rotation: The energy recovery wheel rotates continuously, with one half exposed to the incoming fresh air and the other half exposed to the outgoing exhaust air. The wheel rotates at a slow speed, usually about 20 RPM. The rotation is generally driven by a fractional HP electric gear motor.
- Heat and Moisture Transfer: As the wheel rotates, the mass material (a layered coil of aluminum or polymer) exchanges heat and moisture between the two airstreams.
Heat transfer types
Sensible Heat Transfer
Sensible heat refers to the heat associated with temperature change without moisture transfer. The energy recovery wheel allows sensible heat transfer between the exhaust and supply air streams. This helps to pre-cool or pre-heat the incoming air. The mass media of the wheel absorbs the heat from one air stream and transfers it to the other as it rotates.
Latent Heat Transfer
Latent heat refers to the heat associated with moisture transfer. The wheel can also transfer moisture between the air streams, allowing for humidity control and preventing excessive moisture buildup or dryness in the conditioned space. AIRotor utilizes a 3A molecular sieve to transfer the moisture between air streams.
Efficiency and Effectiveness: The efficiency of an energy recovery wheel is measured in sensible effectiveness, latent effectiveness, and total effectiveness. These metrics determine how much heat and moisture can be transferred between the air streams.
Pressure drop: Pressure is added to the air streams due to the resistance created as the air is forced through the gaps between the coil layers.
Contamination: The wheel design minimizes the transfer of contamination from the return air stream to the supply air stream by utilizing seals. The 3A desiccant applied to the rotor media traps water molecules but not volatile organic compounds.
By using an energy recovery wheel, an HVAC system can recover a significant portion of energy from the exhaust air, reducing the load on heating and cooling systems, and improving energy efficiency. The energy recovery wheel helps maintain indoor air quality, control humidity levels, and contribute to a comfortable and healthy indoor environment.
