Indoor air quality standards give the engineer measurable targets. They cover how much outdoor air to supply, how to filter it and what humidity to allow. This guide summarizes the main ones, and where to confirm the details for your project.
The main standards and what they set
| Standard | What it addresses |
|---|---|
| ASHRAE 62.1 | Ventilation rates, system design features such as filtration and humidity limits, and maintenance for acceptable IAQ in commercial buildings |
| ASHRAE 55 | Thermal comfort: temperature, humidity, air speed, clothing and activity |
| ASHRAE/ASHE 170 | Ventilation and pressure requirements in healthcare facilities |
| Adopted mechanical and building codes | Legal minimums, often by reference to standards |
| Owner or certification requirements | May add to or exceed the code, such as green building programs |
Editions differ, and so do local amendments. Confirm the edition your authority adopted before you finalize calculations.
Design features 62.1 asks for
- Ventilation rates by space type, calculated by the ventilation rate procedure.
- Particulate filtration of a minimum rating at points in the system, commonly MERV 8 or better upstream of coils. Check the edition for the exact requirement.
- Humidity control that limits space relative humidity at peak design latent load. The standard sets a limit, so check the figure in your edition.
- Intake location and separation from contaminant sources.
- Drain pans that drain freely, and access for inspection.
For a plain summary, see the commercial ventilation guide, and for design practice, the role of ventilation standards in building design.
Document and verify
- State the standard and edition in the basis of design.
- Show the ventilation calculations by zone and for the system.
- List the filter ratings and where they are.
- Specify TAB with outdoor air measurement at the intake.
- Review the TAB report against the calculations.
- Give the owner a short operations note on what to maintain.
Comfort and IAQ together
ASHRAE 55 describes comfort as a combination of air temperature, radiant temperature, humidity, air speed, clothing and activity. A room that meets the ventilation rate can still be uncomfortable, so design to both. See how to improve comfort without raising energy costs.
Common mistakes
- Designing to the last edition. The adopted edition governs.
- Treating filter ratings as an afterthought. The fan must handle the pressure drop.
- Not verifying outdoor air. Design numbers do not prove delivery.
Questions engineers ask about IAQ standards
Do the standards apply to existing buildings?
Many requirements apply to new work and major alterations. Existing buildings follow the standard in force when they were built, unless local rules say otherwise. Check with the authority.
How do I handle a change of use?
Recalculate the ventilation for the new use and occupancy, then check what the system can deliver.
What should I ask the balancer for?
Measured outdoor air at the minimum position, and total supply, return and exhaust airflow.
Related reading: How to Ensure Compliance with Air Quality Regulations in Design and How Facility Managers Can Stay Compliant with Air Quality Regulations.
To verify outdoor air against your calculations, call Ghazi Hussain at (908) 323-9780 for a quote.
