The Frost Problem

When cold outside air meets warm, moist exhaust, the exhaust surface can drop below 0 C and ice forms. Left unchecked, frost blocks channels and collapses effectiveness.

Selection Choices That Help

• Wider channels - slow frost buildup and ease defrost
• Preheat coil - warm intake air above the frost point
• Defrost bypass or recirculation - periodic warm-air purge
• Frost-resistant media - hydrophobic surfaces

Technology Note

Rotary wheels handle frost well via purge sectors and modulation, but need controls. Plate cores need an explicit defrost strategy set from the coldest expected temperature, not the annual average.

Climate Thresholds

Below about -2 C exhaust dewpoint, plan active frost protection. The colder the design temperature, the more robust the strategy must be.

Verify

Model the worst week of the year, not the average, and confirm the controls actually trigger defrost at the set point.