Ventilation Rates: ASHRAE 62.1 vs EN 16798 vs GB 50736 — Three-Standard Comparison
ASHRAE 62.1 (United States), EN 16798-1 (Europe), and GB 50736 (China) each specify minimum outdoor air rates for commercial buildings — but use different calculation methods, units, and underlying philosophies. This guide gives engineers and designers a direct side-by-side comparison for the most common space types.
1. Calculation Method Comparison
| Feature | ASHRAE 62.1-2022 | EN 16798-1:2019 | GB 50736-2012 |
|---|---|---|---|
| Method name | Ventilation Rate Procedure (VRP) | Category-based (I–IV) | Per-person fresh air rate |
| Two-component formula | Yes: Rp (per person) + Ra (per area) | Yes: per person + per area | No: per person only (+ ACH minimums) |
| IAQ categories | No category system (one minimum) | 4 categories (I = best, IV = minimum) | No category system |
| Occupant density basis | Default occupant densities in Table 6.2.2 | Design occupancy (actual or default) | Fixed per-person values |
| System efficiency factor | Ev (multi-zone systems, Section 6.2.5) | Not required (single-zone default) | Not specified |
| Primary units | cfm/person, cfm/ft² | L/s·person, L/s·m² | m³/h·person |
2. Outdoor Air Rates by Space Type: Side-by-Side
| Space Type | ASHRAE 62.1 (L/s·person + L/s·m²) | EN 16798 Cat II (L/s·person + L/s·m²) | GB 50736 (m³/h·person) |
|---|---|---|---|
| Office (open plan) | 2.5 + 0.30 | 10 + 1.0 | 30 (8.3 L/s) |
| Office (enclosed, private) | 2.5 + 0.30 | 10 + 1.0 | 30 (8.3 L/s) |
| Conference room | 2.5 + 0.30 | 10 + 1.0 | 30 (8.3 L/s) |
| Classroom (K-12) | 3.8 + 0.55 | 7.0 + 0.7 | 20–25 (5.6–6.9 L/s) |
| Retail store | 1.5 + 0.90 | 7.0 + 1.0 | 20 (5.6 L/s) |
| Hotel guest room | 2.5 + 0.30 | 8.0 + 0.5 | 30 (8.3 L/s) |
| Hospital patient room | 4.0 + 0.30 | 10 + 1.0 | 50 (13.9 L/s) |
| Restaurant dining | 3.8 + 0.90 | 10 + 1.0 | 20 (5.6 L/s) |
| Gym / fitness | 10.0 + 0.90 | 14 + 1.4 | 40 (11.1 L/s) |
Sources: ASHRAE 62.1-2022 Table 6.2.2.1; EN 16798-1:2019 Annex B Table B.3 (Category II); GB 50736-2012 Table 6.3.1. L/s values derived from GB m³/h per-person rates. EN values are minimum outdoor air at Category II (normal new buildings).
3. EN 16798 Category System Explained
EN 16798-1 defines four IAQ categories based on the percentage of occupants expected to be dissatisfied (PPD):
| Category | PPD Criterion | Typical Application | Office: Per Person | Office: Per Area |
|---|---|---|---|---|
| Cat I | <6% dissatisfied | Sensitive occupants, hospitals, luxury | 14 L/s·person | 1.4 L/s·m² |
| Cat II | <20% dissatisfied | New buildings (typical design target) | 10 L/s·person | 1.0 L/s·m² |
| Cat III | <30% dissatisfied | Existing buildings, renovations | 7 L/s·person | 0.7 L/s·m² |
| Cat IV | <40% dissatisfied | Minimum acceptable (rarely used) | 4 L/s·person | 0.4 L/s·m² |
4. ASHRAE 62.1 VRP Method: Step-by-Step
For a single-zone system (the common case):
- Determine design occupancy — use actual count or default density from Table 6.2.2
- Calculate people component: Vbz_people = Pz × Rp (L/s)
- Calculate area component: Vbz_area = Az × Ra (L/s)
- Zone outdoor airflow: Vbz = Vbz_people + Vbz_area
- Zone outdoor air fraction: Zp = Vbz / Vpz (design supply airflow)
- For multi-zone systems, apply system ventilation efficiency Ev per Section 6.2.5
Worked Example: 200 m² Open-Plan Office, 20 Occupants
| Standard | Calculation | Total OA (L/s) | Per Person |
|---|---|---|---|
| ASHRAE 62.1 | (20 × 2.5) + (200 × 0.3) = 50 + 60 | 110 L/s | 5.5 L/s/person |
| EN 16798 Cat II | (20 × 10) + (200 × 1.0) = 200 + 200 | 400 L/s | 20 L/s/person |
| GB 50736 | 20 × 30 m³/h = 600 m³/h = 167 L/s | 167 L/s | 8.3 L/s/person |
This example shows EN 16798 Category II requiring 3.6× more outdoor air than ASHRAE 62.1 for the same office. The gap narrows at lower occupant densities; at very low density (1 person/100 m²), the area component dominates and the standards converge more closely.
5. ACH (Air Change Rate) Minimums for Specific Spaces
| Space Type | ASHRAE 62.1 (ACH) | EN 16798 Cat II (ACH) | GB 50736 (ACH) |
|---|---|---|---|
| Toilet/WC | — (exhaust rate: 25–50 cfm) | — | ≥10 ACH |
| Commercial kitchen | — (exhaust-based sizing) | — | ≥40 ACH (range hood area) |
| Hospital operating room | 15 ACH (ASHRAE 170) | 15–25 ACH (ISO 14644) | 12–15 ACH (GB 51039) |
| Car park / garage | ≥1.5 cfm/ft² or CO monitor | 6 ACH or CO/NO₂ control | 6 ACH |
| Hotel room (no OA ducted) | N/A — OA required | 0.35 ACH natural min | — |
6. Unit Conversion Reference
| cfm/person | L/s·person | m³/h·person |
|---|---|---|
| 5 cfm | 2.36 L/s | 8.5 m³/h |
| 7.5 cfm | 3.54 L/s | 12.7 m³/h |
| 10 cfm | 4.72 L/s | 17.0 m³/h |
| 15 cfm | 7.08 L/s | 25.5 m³/h |
| 20 cfm | 9.44 L/s | 34.0 m³/h |
Quick conversion: cfm × 0.472 = L/s; L/s × 3.6 = m³/h; m³/h × 0.278 = L/s.
7. Standards Reference
- ASHRAE 62.1-2022 — Ventilation and Acceptable Indoor Air Quality in Residential Buildings (commercial portions)
- EN 16798-1:2019 — Energy performance of buildings — Ventilation for buildings — Indoor environmental input parameters for design and assessment of energy performance
- EN 16798-3:2017 — For residential buildings
- GB 50736-2012 — Design Code for Heating Ventilation and Air Conditioning of Civil Buildings (民用建筑供暖通风与空气调节设计规范)
- ASHRAE 170-2021 — Ventilation of Health Care Facilities
8. Frequently Asked Questions
What outdoor air rate does ASHRAE 62.1 require for offices?
ASHRAE 62.1-2022 uses the VRP: Rp = 2.5 L/s·person (5 cfm/person), Ra = 0.3 L/s·m² (0.06 cfm/ft²). A 100 m² office with 10 people: OA = (10 × 2.5) + (100 × 0.3) = 55 L/s total.
How does EN 16798-1 differ from ASHRAE 62.1?
EN 16798-1 is category-based (Cat I–IV), while ASHRAE 62.1 specifies a single minimum. EN Category II requires 10 L/s·person + 1.0 L/s·m² for offices — roughly 3–4× higher than ASHRAE's minimum for the same space. EN 16798 is the primary ventilation standard referenced by the EU Energy Performance of Buildings Directive (EPBD).
What ventilation rates does GB 50736 require?
GB 50736-2012 specifies minimum fresh air: offices 30 m³/h·person (8.3 L/s), hotel rooms 30 m³/h·person, hospital wards 50 m³/h·person, classrooms 20–25 m³/h·person. Toilets require ≥10 ACH, commercial kitchen range hood areas ≥40 ACH.
How do I convert cfm/person to L/s·person?
1 cfm = 0.472 L/s. So 5 cfm/person = 2.36 L/s·person; 10 cfm/person = 4.72 L/s·person. Multiply L/s by 3.6 to get m³/h.
Which ventilation standard is most stringent?
EN 16798-1 Category I is most demanding (14 L/s·person for offices). For typical new commercial buildings: EN Cat II (10 L/s) > GB 50736 (8.3 L/s) > ASHRAE 62.1 (2.5 L/s people component only). The comparison reverses at very low occupant densities where ASHRAE's area component becomes dominant.