Air exchange rate is a critical factor in maintaining Indoor Air Quality (IAQ) by ensuring adequate ventilation. It refers to how often indoor air is replaced with fresh outdoor air within a given time period.
In this article:
1. What is Air Exchange Rate (ACH)?
📌 Air Changes per Hour (ACH) = The number of times air is completely replaced in a room within one hour.
Formula:
Where:
- CFM = Cubic feet per minute (airflow rate).
- Room Volume = Length × Width × Height (in cubic feet).
Example Calculation:
- Room size: 20 ft × 20 ft × 10 ft → 4,000 cu. ft.
- Ventilation rate: 200 CFM
ACH=200×60/4000=3 air changes per hour.
2. Recommended Air Exchange Rates by Application
| Building Type | Recommended ACH |
|---|---|
| Homes | 0.35 – 1.0 ACH |
| Offices | 4 – 10 ACH |
| Classrooms | 5 – 8 ACH |
| Hospitals | 6 – 12 ACH |
| Surgical Rooms | 15 – 25 ACH |
| Laboratories | 6 – 12 ACH |
| Restaurants/Kitchens | 15 – 30 ACH |
| Gyms/Fitness Centers | 6 – 8 ACH |
3. What is IAQ( Indoor Air Quality) in HVAC?
IAQ (Indoor Air Quality) in HVAC refers to the air quality within buildings and how it affects the health, comfort, and well-being of occupants.
4. How Air Exchange Affects IAQ
🔹 Too Low ACH (<0.35 in Homes, <4 in Offices)
❌ Stale air, increased CO₂ buildup.
❌ Accumulation of pollutants, allergens, VOCs, and mold.
❌ Poor health outcomes (headaches, respiratory issues).
🔹 Too High ACH (>12 in Offices, >30 in Kitchens)
❌ Higher energy costs (excessive heating/cooling loss).
❌ Uncomfortable drafts.
❌ Over-ventilation can dry indoor air excessively.
✅ Balanced ACH Improves IAQ:
✔ Removes pollutants, CO₂, and excess moisture.
✔ Maintains oxygen levels and prevents stale air.
✔ Enhances occupant comfort and **productivity
5. Why IAQ Important?
✅ Improves health by reducing respiratory issues and allergies.
✅ Enhances comfort by maintaining proper temperature & humidity.
✅ Increases productivity in workplaces and schools.
HVAC systems play a crucial role in maintaining IAQ through ventilation, filtration, and air purification.
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