18th May 2025
1. Why Proper Exhaust Fan Calculation Matters
- 1. Worker Health: Prevents heatstroke and fumes inhalation (OSHA-compliant).
- 2. Machine Longevity: Reduces overheating in CNC/generator rooms.
- 3. Energy Savings: Avoids overloading fans (cuts power bills by 15-30%).
- 4. Regulations: Meets Indian Factory Act ventilation standards.
2. 5 Factors That Decide Your Fan Count
- 1. Shed Volume: (L × W × H in feet) -
Example: 150ft × 100ft × 30ft = 450,000 cu.ft - 2. Air Changes Per Hour (ACH): Higher ACH for chemical/textile units (see table below).
- 3. CFM Rating: Check fan specs (e.g., Aruth's AEF-1250 = 44,000 CFM)
- 4. Heat/Fume Load: Welding needs 2X more ACH than warehousing.
- 5. Placement: Roof fans move 20% more air than wall-mounted
3. Step-by-Step Calculation (With Example)
Scenario:
- 1. Shed Size: 150ft (L) × 100ft (W) × 30ft (H)
- 2. Industry: Textile Dyeing (needs 25 ACH)
Formula:
- 1. Required CFM : (Volume × ACH) ÷ 60
- = (450,000 × 25) ÷ 60
- = 187,500 CFM
Fan Requirement:
- If using Aruth's 44,000 CFM fans
- = 187,500 ÷ 44,000
- = 4.26 → Round up to 5 fans
3. ACH Recommendations for Indian Industries
Warehouses
ACH Needed: 6-10
Special Notes: Add HVLS fans for cost savings
Welding Shops
ACH Needed: 10-15
Special Notes: Use spark-proof fans
Pharmaceutical
ACH Needed: 15-20
Special Notes: FRP fans for chemical resistance
Textile Dyeing
ACH Needed: 20-30
Special Notes: Pair with fume extractors
4. Common Mistakes to Avoid
Traditional Fans
- 1. Ignoring Intake Air: Exhaust fans need fresh air inlets (place opposite to fans).
- 2. Wrong Fan Type: Chemical fumes need FRP fans, not metal.
- 3. Poor Placement: Install fans near heat/fume sources (e.g., above dyeing vats).
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