CO2 Demand-Controlled Ventilation: Ventilate Based on Real Occupancy
Traditional ventilation systems run at constant speed regardless of occupancy, or remain off entirely. Demand-Controlled Ventilation adjusts ERV fan speed in real time based on measured CO2, minimizing energy use in empty rooms while ensuring clean air when occupied.
Why CO2 Matters in the Bedroom
During sleep, the body exhales ~200 mL/min of CO2 per person. In a sealed 15m² bedroom, CO2 climbs to 1,500–2,500 ppm within 2–3 hours. At these levels: frequent waking, nightmares, morning headaches, and 15–50% reduction in next-day cognitive function (Fisk et al., 2022).
SCD41: The Right CO2 Sensor
Sensirion SCD41 uses true optical NDIR measurement (not MOX electrochemical proxy like SGP30): 0–5,000 ppm range, ±40 ppm + 5% accuracy, I2C interface, 1,200–1,500 THB. Auto Self-Calibration maintains accuracy long-term. The SCD41 (vs SCD40) adds single-shot low-power mode and on-chip pressure compensation.
ESPHome DCV Controller
The ESPHome configuration reads CO2 every 30 seconds and maps it to ERV fan speed: 0% below 600 ppm, 25% at 600–800 ppm, 50% at 800–1,000 ppm, 75% at 1,000–1,200 ppm, 100% above 1,200 ppm. For ERVs with 0–10V or PWM control, a PID controller (setpoint 800 ppm, Kp=0.05) provides smooth modulation that avoids audible fan speed changes during sleep.
Measured Sleep Quality Improvement
A crossover study (Fisk et al., 2022) found CO2 below 800 ppm yields 12% better sleep efficiency, 18% more slow-wave sleep, and 9% better next-day cognitive performance versus CO2 above 1,200 ppm. Installing CO2 DCV (SCD41 + ESPHome + ERV, 15,000–35,000 THB) while saving 30–50% ERV energy versus constant-speed operation.