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

This quiz covers the principles of ventilation systems, including positive and negative rooms, and calculations for air flow rates, such as cfm and ACH. Examples of negative rooms are also provided.