Experimental and numerical investigation of the thermal impact of defrost cycle of residential heat and energy recovery ventilators

• The thermal impacts of the defrost cycle of the HRV/ERV were studied experimentally.
• Efficiency patterns were developed for performance prediction using TRNSYS.
• The savings of the defrost cycle depended on its threshold temperature.
• The HRV ran the defrost cycle 3.5 times longer than the ERV.

In this study, the thermal impact of defrost cycle of both residential heat and energy recovery ventilators (HRV and ERV) was investigated using TRNSYS. The thermal efficiency patterns of the units were obtained from winter experiments, and then implemented into the existing HRV and ERV models for simulations in the context of airtight environment. Throughout the heating season, the minimum humidity of the airtight house was increased due to the reintroduction of humid indoor air/melted frost. For the HRV, simulation results indicated that its yearly demand of defrost cycle was 3.5 times higher the ERV. In other words, the HRV used in cold days could significantly deteriorate indoor air quality, which contradicted the main purpose of mechanical ventilation.