Performance evaluation of CO2-based ventilation control to reduce CO2 concentration and condensation risk in residential buildings

As the airtightness of a building envelope gets higher to achieve energy efficiency, the necessity of appropriate ventilation for residential buildings is continually increasing. Many residential buildings are equipped with energy recovery ventilators (ERV) for energy-efficient ventilation; however, the ERVs are usually operated by occupants' manual control, which often leads to insufficient or unnecessary ventilation. Because it is difficult to operate an ERV during nighttime, when occupants cannot control the system, a residential building can suffer from poor indoor air quality and increasing condensation risks. Herein, a CO2-based ventilation control strategy was implemented in an existing ERV system for residential buildings. Considering that most ERV systems operate with a central control, the appropriate CO2 sensor location (or representative room) was investigated in a mock-up residential building. Comparative experiments were conducted to evaluate the control performances in terms of indoor air quality (CO2 control performance) and fan energy consumption. Experimental results showed that a living-room-based control can maintain an overall CO2 concentration in the entire space at acceptable levels. It was also shown that a living-room-based control resulted in reduced ventilation energy if the CO2 dispersed through open bedroom doors. The CO2-based ventilation control was modified to mitigate the condensation risk while minimizing the possibility of fan noise or cold draught. Through mock-up experiments on a modified CO2-based ventilation control, it was shown that CO2 concentrations can be maintained at acceptable levels and condensation risks can be mitigated even when the outdoor temperature decreases to −15 °C.