Ventilation Rates & Fresh Air Lab
Work out outdoor air for every zone with the ASHRAE 62.1 ventilation rate procedure, roll it up to the air handler with the multi-zone system efficiency, compare against AS 1668.2 and CIBSE rates, add toilet and kitchen exhaust, and see the CO₂ each zone will settle at.
How to use: add your zones with their space type and area. Occupancy fills from the default density, and you can overwrite it. Tap i for explanations.
1. System settings
One air handler serving the zones below.
2. Zones
Bar length shows outdoor air per zone. Colour shows steady state CO₂.
3. Checks
4. Zone table
5. How the procedure works
Breathing zone outdoor air
ASHRAE 62.1 adds a people part and an area part: Vbz = Rp × Pz + Ra × Az. The people part dilutes what occupants emit, the area part dilutes what the building and furniture give off. Dividing by the zone air distribution effectiveness Ez gives the zone outdoor air Voz.
Multi-zone systems
When one air handler serves many zones, the zone needing the highest fraction of outdoor air in its supply (Zpz) sets the system ventilation efficiency Ev. The intake is the uncorrected outdoor air divided by Ev, so a single dense meeting room can drive up the fresh air for the whole floor. DOAS and FAHU systems avoid this.
CO₂ as a check
At steady state, indoor CO₂ rises above outdoor by the CO₂ each person exhales (about 0.0052 L/s for office work) divided by the outdoor air per person. 10 L/s per person gives roughly 520 ppm above outdoor.
Learning and checking tool. Use the edition of ASHRAE 62.1 or the local standard your authority has adopted. Healthcare spaces follow ASHRAE 170 or HTM 03-01 instead.