Why a Wheel
A rotary wheel is a slowly spinning matrix that can reach 80-85 percent sensible effectiveness and 70-80 percent latent (enthalpy) effectiveness - the highest of any air-to-air device. It also recovers moisture, which matters in humid climates.
Key Selection Parameters
- Wheel diameter and depth - deeper media holds more energy per rotation
- Media type - aluminium (sensible) or molecular-sieve coated (enthalpy)
- Rotation speed - set so the wheel spends enough time in each stream
- Seal quality - better seals mean less stream carryover
Sizing Approach
Define the required sensible and latent recovery, then select wheel size and speed to meet both at your design airflow. Because a wheel is compact for its capacity, it suits large air-handling units.
Watch-outs
- Slight carryover between airstreams - avoid in strict containment zones
- Motor, seals, and bearings need a maintenance plan
- Summer bypass is needed when no recovery is wanted
Verify
Check the certified effectiveness (Eurovent or AHRI 1060) at your operating point, not the headline number.
Before You Start
A successful Rotary (Enthalpy Wheel) Heat Exchanger Selection Guide project begins with measurement. Record the supply and exhaust airflow rates, the temperatures on each side, and the hours the system runs per year. Note any contaminants in the exhaust and the available space for the core and ductwork. These figures decide both the type of exchanger and whether the payback makes sense.
Step-by-Step
First, choose the exchanger type from the air cleanliness and recovery target. Second, size the core using the measured airflow and the log-mean temperature difference, leaving margin for fouling. Third, lay out the duct path so the exhaust is filtered before the core and the supply side has drainage if it may condense. Fourth, add a bypass for free cooling and wire the fans to a simple control. Finally, commission the unit and record baseline temperatures.
Verification
After startup, compare the pre- and post-installation supply temperatures at the same outdoor condition. A steady recovery of 50 percent or more confirms correct sizing. Re-check each season and clean the exhaust side when the recovered temperature begins to fall, because fouling quietly erodes performance over time.
Frequently Asked Questions
Do I need a bypass? In most climates yes, so the system can free-cool when outdoor air is mild. How is sizing done? From measured airflow and the log-mean temperature difference, not from estimates.