Ventilation Systems and Airflow Calculations

Ventilation Basics

• A room is considered positive (+ve) if more air enters than leaves, and negative (-ve) if more air leaves than enters.
• In +ve rooms, calculate fresh air in CFM (cubic feet per minute) first, then exhaust air is 0.85-0.95 of fresh air.
• In -ve rooms, calculate exhaust air in CFM first, then fresh air is 0.85-0.95 of exhaust air.

Ventilation Examples

• Examples of -ve rooms: kitchens, garages, bathrooms, engines room

Calculating CFM

• CFM = (ACH × V) / 1.7, where V is volume in m^3 and ACH is air change per hour
• ACH values for different spaces:
  • Stores: 4-6
  • Garages (normal case): 4-6
  • Garages (fire case): 10
  • Bathroom: 10-12
  • Private Kitchen: 15-20
  • Central Kitchen: 20-30

Garage Ventilation

• Two design options: ventilation by duct and ventilation by jet fans
• Ventilation by duct:
  • Draw air in two levels: 33.333% from low level (above car, 30-40 cm from floor) and 66.66% from high level (at top of garage)
• Ventilation by jet fans: no additional information provided

Bathroom Ventilation

• Typically uses only an exhaust fan, with no fresh air fan
• Withdraws 50-100 CFM

Ventilation with Hoods

• Hoods are used for ventilation in central kitchens where temperature and humidity are high
• Types of stainless steel used for hoods:
  • 201 SS: very low quality
  • 304 SS: industrial
  • 316 SS: medical

Central Kitchen Hood Types

• Wall Mounted Hood: space-saving, easy installation, limited coverage for island cooking
• Single Island Canopy Hood: 360-degree coverage, sleek design, requires ceiling mounting
• Double Island Canopy Hood: dual extraction zones, balanced extraction, higher cost due to dual units
• Eyebrow Hood: discreet and minimalist, limited extraction capacity
• Back Shelf Hood: storage space, efficient use of space, bulkier appearance
• Condensate Hood: high-capacity extraction, ideal for high-volume cooking areas, typically larger and industrial-looking

Home Hood Types

• Flat hood:
  • Requires exhaust fan
  • No direct expulsion of air, only filters air before sending to exhaust fan
  • Better appearance, bad performance
• Pyramidic hood:
  • No exhaust fan needed
  • Directly expels air out of kitchen, uses sand trap to prevent insects
  • Good appearance, good performance

Hood Design Parameters

• Hood height
• Hood dimensions
• CFM exhaust
• CFM fresh