Emission rate of carbon dioxide while sleeping

Area of Science:

• Environmental Health
• Human Physiology
• Building Science

Background:

• Carbon dioxide (CO2) concentration indicates ventilation rate (VR) and indoor air quality (IAQ).
• Carbon dioxide emission rate (CER) can estimate VR, but data for sleeping subjects is limited.
• Understanding sleeping CERs is crucial for optimizing bedroom ventilation and IAQ.

Purpose of the Study:

• To measure CERs in sleeping adults and reduce the knowledge gap.
• To investigate the impact of temperature and IAQ on sleeping CERs.
• To validate CERs against existing calculation methods and standards.

Main Methods:

• Eleven healthy adults (7 females, 4 males) slept in a controlled capsule for four nights.
• Experiments were conducted at two temperatures (24°C, 28°C) and two VRs (maintaining ~800 ppm and ~1700 ppm CO2).
• Physiological responses (heart rate, temperature) and sleep quality were monitored; CERs were calculated using a mass-balance equation.

Main Results:

• The average CER was 11.0 ± 1.4 L/h per person, with males emitting 8% more than females (P < 0.05).
• Neither increased temperature nor decreased IAQ (lower VR) affected measured CERs.
• No observable differences in physiological responses were noted across conditions.

Conclusions:

• Measured sleeping CERs align with calculations based on sleep energy expenditure and respiratory quotient.
• Findings confirm CERs predicted by ASHRAE Standard 62.1, ASHRAE Handbook, and ASTM D6245-18.
• Results offer a reference for bedroom ventilation design but require further validation across diverse populations and age groups.