English version machine-translated from the Vietnamese original — under review.
1. Introduction to ASHRAE 62.1
- Purpose: Sets minimum outdoor air supply rates for each type of space in commercial buildings, to ensure that indoor air quality meets human health and perception requirements
- Scope: Not intended for residential dwellings (covered by Standard 62.2), and not applicable to smoking areas or healthcare facilities (which have moved to ASHRAE 170)
2. Evolution of the Editions
- The standard is continuously maintained and updated. The 2019 edition (and the latest, 2022) focuses on expansion: covering both the IAQ procedure and natural ventilation, and removing sections that are no longer relevant (for example: smoking areas)
3. The Three Main Design Procedures in the Standard
- Ventilation Rate Procedure (VRP): A method that determines the outdoor air flow rate based on the occupant density and floor area of each space. This is the most commonly used method
- Indoor Air Quality Procedure (IAQP): A method based on actual air performance (including filtration systems and contaminant control), allowing more flexibility than VRP if supported by data.
- Natural Ventilation Procedure: Design based on natural ventilation, which must take into account climatic conditions, window area and the ability to measure air circulation
4. Other Important Factors
- Air classification (Air Class): Determines the level of outdoor pollution so that design inputs are appropriate (for example, near industrial zones or busy roads…).
- Building envelope and HVAC system construction issues: Floor plan density, envelope tightness and the HVAC systems all affect the ability to supply/exhaust and circulate air.
- Operation and maintenance: Ensures the system maintains its design air supply performance throughout its service life.
5. A Practical Example: Saving Energy While Still Ensuring IAQ
- According to recent updates (for example the article "Optimizing ventilation…"):
- Apply VRP and suitable exhaust systems for each type of space (such as bathrooms and toilets, with two flow rate levels: continuous vs intermittent).
- Calculate the design density based on the highest number of people that may be present to ensure the system operates effectively.
Conclusion
- ASHRAE 62.1: The primary standard for commercial/high-occupancy buildings, specifying the minimum outdoor air flow rate for each space, with the aim of ensuring air quality, health and energy efficiency.
- The latest edition (2022) expands with a more flexible IAQ approach and removes sections that are no longer relevant, while retaining the 3 core design procedures.
- Practical application needs to balance system design (air quality), operation (maintenance, dimming) and energy-saving goals.
6. How to Calculate VRP for Each Type of Space
VRP (Ventilation Rate Procedure) is the most common design method in ASHRAE 62.1, requiring:
Outdoor air supply flow rate = (Rp × Pz) + (Ra × Az) Where:
- Rp = Flow rate per person (L/s.person)
- Pz = Design number of people in the zone
- Ra = Flow rate per unit area (L/s.m²)
- Az = Zone floor area
Calculation example:
Space: Office
- Rp = 5 L/s.person
- Ra = 0.6 L/s.m²
- Area Az = 100 m²
- Design number of people Pz = 10
Calculation:
- Per person: 5 × 10 = 50 L/s
- Per area: 0.6 × 100 = 60 L/s → Total flow rate: 110 L/s
Notes:
- The Rp and Ra values for each type of space are given in detail in Table 6-1 (ASHRAE 62.1).
- Spaces with high occupant density (e.g. classrooms, conference rooms) have a high Rp. Spaces that are not regularly occupied (e.g. storage rooms) have almost only Ra.
7. How to Apply the IAQP (Indoor Air Quality Procedure)
IAQP is a design method based on actual contaminant concentrations instead of applying a fixed formula as in VRP.
How to carry out the IAQP:
Identify the main contaminants: CO₂, VOCs, formaldehyde, PM2.5…
Determine the target concentrations: Based on international guidelines (EPA, WHO or ASHRAE Appendix B).
Calculate the minimum outdoor air needed to keep these contaminants at acceptable levels, which may be combined with:
- Air filters (HEPA, carbon…)
- In-room air treatment devices (e.g. ionization, UV-C)
- CO₂ concentration control systems or automatic VOC sensors
Advantages:
- Reduced outdoor air flow rate → energy savings
- Better optimized for smart buildings, large offices or flexible spaces
Limitations:
- Requires a specific air quality analysis
- Requires simulation reports & field measurements
8. Notable Changes in ASHRAE 62.1-2022
| Topic | What's new (2022) |
|---|---|
| Removal of smoking areas | Air supply for "smoking areas" is no longer calculated |
| IAQ zoning | Clearer definition of each "air class" and the rules for air transfer |
| Ventilation Zone Distribution Effectiveness (Ez) | Additional explanation of how to select Ez in zoned systems (zone-level supply) |
| Natural Ventilation | Updated requirements for verifying weather conditions, with clearer aerodynamic measurement |
| Building Envelope Impact | Requires checking and simulating the effect of air leakage (envelope leakage) on the ventilation system |
| Energy analysis | Refers to combining with ASHRAE 90.1 (Energy Standard) when using IAQP to save energy |
Conclusion
| Situation | Recommended method |
|---|---|
| Conventional, simple projects | VRP (easy to use, standard values readily available) |
| Energy-saving, high-end projects with IAQ control | IAQP (flexible, technically demanding) |
| Open spaces, natural ventilation, or special designs | Natural Ventilation Procedure |
9. Rp / Ra REFERENCE TABLE – ASHRAE 62.1-2022 (Table 6-1)
| Space type | Default occupant density (people/m²) | Rp (L/s.person) | Ra (L/s.m²) |
|---|---|---|---|
| Office (Office space) | 0.06 | 5.0 | 0.6 |
| Meeting room (Conference room) | 0.12 | 3.8 | 0.3 |
| Classroom (Classroom: ages 5–8) | 0.25 | 5.0 | 0.9 |
| Classroom (Classroom: > 9 years) | 0.25 | 2.5 | 0.9 |
| Auditorium (Lecture hall) | 0.5 | 3.8 | 0.3 |
| Restaurant / dining (Dining) | 0.7 | 5.0 | 0.6 |
| Fitness room (Gym) | 0.4 | 10.8 | 0.8 |
| Cinema / Theater | 0.15 | 3.8 | 0.3 |
| Hospital – patient room | 0.125 | 2.4 | 0.6 |
| Hotel – bedroom | 0.06 | 5.0 | 0.3 |
| Corridor area (Corridor) | Rp not applied | — | 0.3 |
| Public restroom (Public toilet) | Rp not applied | — | 0.5 |
| Storage room | Rp not applied | — | 0.3 |
| Reception / Waiting lobby (Lobby) | 0.1 | 3.8 | 0.3 |
| Laboratory (Dry lab) | 0.06 | 5.0 | 1.8 |
Notes:
- Rp: Required outdoor air flow rate per person (liters/second/person).
- Ra: Required outdoor air flow rate per square meter of floor area (liters/second/m²).
- The total outdoor air supply flow rate for each zone is calculated using the formula:
- Pz: Design number of people
- Az: Zone floor area (m²)
Voz = Rp × Pz + Ra × Az
Where:
Pz: Design number of peopleAz: Zone floor area (m²)
Below is a summary table of indoor air quality (IAQ) indicators related to CO₂, humidity, VOCs, PM2.5 and PM10 according to ASHRAE 62.1-2022 and the reference documents used by ASHRAE.
Important note: ASHRAE 62.1-2022 does not directly specify a particular "maximum limit" for every contaminant; rather, it requires them to be controlled at levels that do not affect health or perception, and refers to other documents such as WHO, EPA, OSHA, etc. – especially where the IAQP (Indoor Air Quality Procedure) is applied.
1. CO₂ – Carbon Dioxide
| Control level | Recommended value | Reference source |
|---|---|---|
| Acceptable IAQ limit | ≤ 1,000 ppm (relative to outdoors) | ASHRAE 62.1 Appendix C |
| Default outdoor concentration | ≈ 400–420 ppm | Design note |
| Alarm concentration for unacceptable IAQ | ≥ 1,200 ppm | Common practice, school regulations |
IAQP target: keep indoor CO₂ ≤ 700 ppm above outdoors (~1,100–1,200 ppm in total)
2. Relative Humidity (RH)
| IAQ condition | Proposed value | Notes |
|---|---|---|
| Optimal RH for IAQ | 40% – 60% | Recommended by ASHRAE |
| Recommended maximum limit | ≤ 65% | Prevents mold and bacteria |
| Minimum limit | ≥ 30% | Prevents dry nose and dry skin |
ASHRAE 62.1 recommends maintaining reasonable humidity; it does not specify a hard figure, but requires humidity to be controlled to prevent mold and adverse health effects.
3. VOCs – Volatile Organic Compounds
| Total VOC index (TVOC) | Limit (µg/m³) | Reference |
|---|---|---|
| Acceptable (IAQP) | ≤ 500 µg/m³ | WHO, LEED |
| Good (ideal level) | ≤ 200 µg/m³ | WELL v2, RESET |
| IAQ alarm threshold | ≥ 1,000 µg/m³ | May affect health |
ASHRAE does not specify a particular VOC threshold, but if IAQP is used, common VOCs (formaldehyde, benzene, toluene...) must be kept at levels that do not affect health or perception.
4. PM2.5 and PM10 – Fine Particulate Matter
| Particle type | Recommended maximum (24h average) | Source |
|---|---|---|
| PM2.5 | ≤ 15 µg/m³ | WHO 2021; referenced by ASHRAE |
| PM10 | ≤ 45 µg/m³ | WHO 2021 |
With IAQP, if PM sensors and filtration are installed, fine particulate matter must be kept below the WHO thresholds for IAQ to be acceptable.
Summary – Minimum IAQ Control Levels for IAQP (suggested for practical use)
| Parameter | Safe design threshold |
|---|---|
| CO₂ | ≤ 1,000 ppm |
| RH | 40 – 60% RH |
| TVOC | ≤ 500 µg/m³ |
| PM2.5 | ≤ 15 µg/m³ |
| PM10 | ≤ 45 µg/m³ |
Conclusion
- ASHRAE 62.1-2022 requires air quality to be controlled so that it does not affect health or perception, especially when IAQP is used.
- Further details of the reference documents, such as WHO, EPA and OSHA, can be found in Appendices B, C and E of ASHRAE 62.1-2022.
- The above criteria are usually combined with IAQ sensors, air filtration and smart CO₂ control systems in modern buildings.
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