A closed 4 × 4 × 2.5 m bedroom, two people, eight hours. Watch the CO₂ climb, then add things and see what each one does — and doesn't — fix.
It filters the air that is already in the room. Nothing new comes in, so CO₂ is untouched.
Carbon removes odours and VOCs. It does not remove CO₂. Only the airflow does.
A round exhaust grille in the ceiling, ducted through the roof void to a cowl outside. The duct's friction makes it pass less air than its 123 cm² bore suggests. Wind and stack effects at the roof are not modelled.
Only needed if the door gap can't pass the inlet flow without the fan losing pressure.
Together: — of CO₂ and — of O₂ used.
CO₂ generation: Persily A., de Jonge L. (2017) “Carbon dioxide generation rates for building occupants”, Indoor Air 27(5):868–879 — NIST. BMR from Schofield (1985). Rates at the paper's 0 °C reference; at room temperature the true rate is ~9 % higher.
Bands: ASHRAE 62.1 (≈700 ppm above outdoor → ~1000–1100 ppm comfort/odour guideline); cognitive/sleep effects reported at 1400–2000+ ppm; OSHA PEL 5000 ppm (8-h TWA); OSHA oxygen-deficient < 19.5 %.
PM2.5: WHO Global Air Quality Guidelines 2021 (24-h 15 µg/m³, annual 5 µg/m³); US EPA 24-h 35 µg/m³. Bedding source, deposition 0.2 h⁻¹, penetration 0.8 and filter grades are illustrative.
Door gap: orifice, Cd 0.65 (sharp edge 0.61; 0.65 for door cracks in multizone models, e.g. LBNL Modelica Buildings), ρ 1.2 kg/m³, linear fan curve.
OSHA calls < 19.5 % oxygen-deficient. You will never get there in a bedroom; CO₂ is the problem.
CO₂ rate per Persily & de Jonge 2017 (0.95 met). Rates at 0 °C reference; at room temperature the true rate is ~9 % higher. Fog shows room average. Illustrative tool, not a safety instrument.
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