Does Frosting in Rotary Heat Recovery Occur on the Exhaust or Fresh-Air Side?

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Frost formation in rotary heat recovery (also called a rotary heat exchanger) usually occurs on the fresh-air side, especially under the following conditions:

❄️ Reasons frost forms on the fresh-air side:
Under winter operating conditions:
When the outdoor temperature is very low (usually below 0°C) while the indoor exhaust-air temperature is relatively high (around 20°C), the wheel continuously rotates between the exhaust and fresh-air sides, transferring heat from the exhaust side to the fresh-air side.

During the heat-exchange process:
The wheel carries heat away from the exhaust side and releases it to the fresh air when it rotates to the fresh-air side. However, because the outdoor fresh air is too cold, the water vapor in the air condenses upon contacting the wheel and forms frost on the fresh-air side.

🌬️ Why doesn't frost form on the exhaust side?
The air on the exhaust side comes from indoors and is relatively warm and humid.

The exhaust side mainly "loads" heat onto the wheel and is unlikely to cool down to the frosting point.

In contrast, the fresh-air side is the "receiving end" of heat; the temperature difference can lower the wheel surface temperature below 0°C, causing frost to form.

✅ Engineering countermeasures
Install a bypass or preheating device: to avoid frosting.

Add defrost control logic: such as timed reverse rotation or wheel stoppage.

Use a heater to preheat the fresh air: to avoid excessively low fresh-air temperature.

结霜发生在哪一侧

在冬季新风温度很低时，转轮回收排风热量后，新风侧（冷侧）表面温度可能低于 0℃ 而结霜，排风侧通常温度较高不易结霜。结霜会堵塞通道、降低效率。应对办法包括新风预热、转轮旁通与间歇反转除霜。更多要点见选型完全指南。

冬季运行建议

寒冷地区建议新风入口设预热盘管或转轮旁通，将新风侧最低温度控在 0℃ 以上；可间歇反转转轮除霜，保障连续稳定运行。

冬季运行建议

寒冷地区建议新风入口设预热盘管或转轮旁通，将新风侧最低温度控在 0℃ 以上；可间歇反转转轮除霜，保障连续稳定运行与换热效率，避免结霜堵塞通道导致风量骤降。

结霜风险高的地区，建议在控制逻辑中预留除霜策略与报警，保障连续运行；也可考虑新风侧预处理以从源头降低结霜概率。

高寒地区项目应将防霜与除霜纳入自动控制系统设计，并设置温度与效率的连锁保护，既保障连续运行，也防止结霜堵塞导致的风量骤降与能耗激增，提升系统鲁棒性。