🔄 Total Recovery Effectiveness
💰 Annual Heating Savings
Recovery Breakdown
Full Calculation Table
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How to Use the Energy Recovery Wheel Calculator
Choose a typical effectiveness tier, or select Custom to enter manufacturer-rated sensible and latent effectiveness values.
Enter the total outdoor airflow that will pass through the wheel, from the commercial ventilation calculator or your DOAS sizing.
Enter winter design outdoor temperature and typical building exhaust temperature and humidity to establish the recovery potential.
Click Calculate Energy Recovery to see preheat energy recovered, sensible and latent split, annual heating cost savings, and recommended purge sector angle.
Understanding Total Energy Recovery Wheels
An energy recovery wheel, also called a total enthalpy wheel, rotates a desiccant-coated matrix between the outdoor air and exhaust air streams inside an AHU or DOAS. As the wheel turns, it picks up heat and moisture from one airstream and releases it into the other, recovering energy that would otherwise be lost through the exhaust. In Canadian climates with significant heating degree days, this can substantially reduce the heating coil load on ventilation air, which is part of why ASHRAE Standard 90.1 now requires energy recovery on many outdoor-air-heavy systems.
Sensible and Latent Effectiveness Are Reported Separately
Manufacturers rate energy recovery wheels with separate sensible and latent effectiveness percentages, since the wheel's ability to transfer heat and its ability to transfer moisture depend on different physical mechanisms within the desiccant coating. Sensible effectiveness is often somewhat higher than latent effectiveness, though both matter for accurately estimating total energy recovered in a humid climate or a building with meaningful latent load from occupants and process moisture sources, a split the humidity ratio calculator can help quantify on the exhaust side.
Why Recovery Matters More in Cold Canadian Winters
The colder the outdoor design temperature, the larger the temperature difference between outdoor air and building exhaust air, and the more heating energy is available for recovery. A wheel serving a building in Winnipeg or Edmonton recovers substantially more heating energy per litre of outdoor airflow than the same wheel in Vancouver, simply because the winter design temperature difference is so much larger, a gap that shows up directly in each city's heating degree day totals. This calculator uses your specified winter design temperature to reflect that climate-specific recovery potential.
Purge Sector Prevents Cross-Contamination
As the wheel rotates from the exhaust airstream into the supply airstream, a small amount of exhaust air remains trapped in the wheel matrix and would otherwise carry directly into the supply air. A purge sector, a small angular section positioned between the two airstreams, allows a portion of outdoor air to sweep through this trapped air before it reaches the supply side, significantly reducing cross-contamination as measured by the Exhaust Air Transfer Ratio that AHRI's certification program verifies by test for rated wheels. Applications with sensitive exhaust air quality, such as laboratories or spaces with process exhaust, need a properly sized purge sector and may require additional care in wheel selection beyond a basic effectiveness rating.
Winter Frost Control
At very cold outdoor design temperatures common across much of Canada, the wheel surface on the exhaust air exit side can drop below freezing, where moisture from the exhaust air stream can form frost. Frost buildup reduces wheel effectiveness and can eventually block airflow if not controlled. Most Canadian installations include a defrost control strategy, commonly reducing wheel rotation speed at the coldest outdoor temperatures or adding a small preheat coil ahead of the wheel, to prevent this from becoming an operational problem.
Sensible-Only Alternative
Where latent recovery is not desired or where cross-contamination risk needs to be minimized further, a sensible-only heat recovery wheel or a plate heat exchanger avoids transferring any moisture between airstreams entirely. See the heat recovery wheel calculator for that alternative approach.
Frequently Asked Questions
An energy recovery wheel, often called a total enthalpy wheel, recovers both sensible heat and latent moisture between the exhaust and outdoor air streams. A heat recovery wheel typically recovers sensible heat only, without transferring moisture. Total enthalpy wheels are generally preferred where humidity control matters, while sensible-only wheels are simpler and avoid any risk of moisture cross-contamination between airstreams. See the heat recovery wheel calculator for the sensible-only version.
Total energy recovery wheels commonly achieve 60 to 80 percent combined sensible and latent effectiveness at design airflow, with higher effectiveness generally requiring a larger wheel diameter, slower rotation speed adjustment range, or additional wheel depth. Manufacturer-rated performance data should always be used for final selection rather than a general effectiveness assumption.
A purge sector is a small angular section of the wheel, positioned between the exhaust and supply airstreams, where outdoor air sweeps through the wheel matrix before it rotates into the supply airstream. This purges any exhaust air trapped in the wheel media, reducing cross-contamination of the supply air with exhaust air contaminants. A properly sized purge sector is essential in any application where exhaust air quality is a concern, such as laboratories or spaces with process exhaust.
Yes, at very cold outdoor temperatures the exhaust air side of the wheel can drop below freezing where it contacts extremely cold outdoor air, potentially forming frost that reduces performance and airflow. Most Canadian installations include a wheel defrost control strategy, such as slowing wheel rotation speed or a preheat coil ahead of the wheel, to prevent frost accumulation during the coldest design conditions.
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