Energy recovery wheels (also known as thermal wheels or rotary heat exchangers) are critical components in modern HVAC systems, designed to improve energy efficiency by reclaiming waste heat or coolness from exhaust air. Use the calculator below to estimate the sensible energy recovery and the resulting supply air temperature for your system.
Sensible Energy Recovery Calculator
Understanding Energy Recovery Wheels
An Energy Recovery Wheel (ERW) is a revolving cylinder filled with an air-permeable material (often aluminum or polymer) that offers a large surface area for heat transfer. As the wheel rotates between the outdoor air stream and the exhaust air stream, it picks up thermal energy from the warmer stream and releases it into the cooler stream.
How the Calculation Works
The efficiency of an energy recovery wheel is defined by its effectiveness. Effectiveness is the ratio of actual energy transferred to the maximum possible energy transfer. For sensible (temperature-only) calculations, the formula for the Leaving Supply Air Temperature ($T_{sa}$) is:
Tsa = Toa + ε × (Tra - Toa)
Where:
- Tsa: Leaving Supply Air Temperature
- Toa: Entering Outdoor Air Temperature
- Tra: Entering Return (Exhaust) Air Temperature
- ε: Sensible Effectiveness (as a decimal)
Why Use an Energy Recovery Wheel?
Implementing ERW technology in building ventilation systems offers several significant advantages:
- Reduced Utility Costs: By pre-heating or pre-cooling incoming fresh air, you significantly reduce the load on your primary boilers and chillers.
- Equipment Downsizing: Because the peak load is reduced, engineers can often specify smaller, less expensive HVAC units.
- Humidity Control: If the wheel is coated with a desiccant (total energy wheel), it can also transfer moisture, helping to maintain comfortable indoor humidity levels without over-cooling.
- Environmental Impact: Lower energy consumption leads to a smaller carbon footprint and contributes toward LEED certification.
Total vs. Sensible Recovery
While the calculator above focuses on sensible energy (temperature change), many modern wheels are "Enthalpy Wheels." These wheels transfer both sensible and latent energy (moisture). In humid climates, latent energy recovery is often more valuable than sensible recovery because dehumidifying air is an energy-intensive process.
Maintenance Considerations
To keep an energy recovery wheel operating at peak performance, regular maintenance is required. This includes checking the drive belt for tension, ensuring the seals are intact to prevent cross-contamination between air streams, and cleaning the wheel media to prevent pressure drop increases due to dust accumulation.