Office CO2 Buildup & Cognitive Performance

Office Setup

Occupancy 10 people

Fresh-air rate 8 L/s · person

Room volume 120 m³

Live Readouts

CO₂ now

420 ppm

Steady-state target

420 ppm

Cognitive performance index

100%

4001000200035005000+ ppm

How it works

The room is modelled as one well-mixed air volume. Each occupant exhales CO₂ at a steady metabolic rate G; the HVAC system replaces air at a fresh-air rate Q proportional to occupancy. The concentration C obeys a first-order mass balance:

V · dC/dt = N · G · 10⁶ − Q · (C − C_out)
   V = room volume (L)      N = occupants
   G ≈ 0.0052 L/s/person    Q = N · q  (q = fresh-air rate, L/s/person)
   C_out ≈ 420 ppm (outdoor ambient)

Solved forward with a clamped Euler step, C relaxes exponentially toward the steady state C_out + N·G·10⁶ / Q — note Q cancels occupancy in the ratio, so raising the *per-person* fresh-air rate is what actually caps the ceiling, not just adding vents. The simulation runs at 30× real time so the multi-minute approach to equilibrium is visible in seconds.

The cognitive-performance index is a piecewise curve reflecting the broad pattern reported in indoor-air-quality decision-making studies (e.g. Satish et al. 2012, Harvard "CogFx" 2015/2016): performance is essentially flat below ~600 ppm, drifts down through 1,000–2,500 ppm, and drops sharply above ~3,500 ppm as CO₂ itself (not just a proxy for other pollutants) measurably impairs strategic thinking and information usage.

Occupancy — more people, more CO₂ generated per second.
Fresh-air rate — ASHRAE 62.1 recommends roughly 2.5–10 L/s per person for offices; below ~5 the steady state usually exceeds 1,000 ppm.
Room volume — a bigger air buffer slows how fast concentration changes, but doesn't change the eventual steady state.
Open a window — temporarily multiplies the fresh-air rate for 30 simulated seconds, showing how fast a burst of ventilation pulls CO₂ back down.

420

PPM CO₂

Fresh air / desk Exhaled CO₂ plume

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