How People Affect Cooling Requirements
Every person in a room is essentially a 75-100 watt heater. The human body continuously generates heat through metabolism, and this heat must be removed by your air conditioning system. In rooms with many occupants—conference rooms, family gatherings, parties, or shared living spaces—this occupant heat load can significantly exceed the heat from the building itself.
Heat Generation Per Person
The heat each person generates depends on activity level:
- Seated, quiet (office work): 400 BTU/hour (115 watts)
- Light activity (walking, standing): 500 BTU/hour (145 watts)
- Moderate activity (light exercise): 600-700 BTU/hour (175-200 watts)
- Heavy activity (dancing, sports): 800-1,000 BTU/hour (235-290 watts)
For standard calculations, 400-600 BTU per person is the common assumption depending on activity level.
When Occupancy Becomes the Dominant Factor
High-Density Rooms
In rooms with high occupancy relative to floor area, people become the primary heat source:
Example: 200 sq ft conference room with 10 people
- Base calculation (room only): 200 × 25 = 5,000 BTU
- Occupant heat (10 × 500 BTU): +5,000 BTU
- Total: 10,000 BTU (doubled by occupancy)
Without accounting for occupancy, you'd install a 0.4-ton AC that's completely inadequate. With proper calculation, you need 0.8-1 ton.
Types of High-Occupancy Spaces
- Conference rooms: 10-20 people in 200-400 sq ft
- Living rooms during parties: 15-30 people
- Home theaters: 6-10 people in enclosed space
- Gaming rooms: Multiple people plus electronics heat
- Home gyms: High activity = high heat per person
- Classrooms: 20-30 students in educational settings
Calculating for Variable Occupancy
The Peak vs. Average Dilemma
Many rooms have variable occupancy—a living room might host 2 people normally but 20 during a party. How do you size for this?
Guidelines:
- Frequent high occupancy (daily/weekly): Size for maximum expected occupancy
- Occasional high occupancy (monthly/rarely): Size for average use, supplement for events
- Consistent high occupancy (conference rooms): Always size for full capacity
Supplemental Cooling for Events
If you only host large gatherings occasionally, rather than oversizing your permanent AC:
- Use portable AC units for events
- Run ceiling fans to distribute cool air better
- Open windows for cross-ventilation if weather permits
- Pre-cool the space before guests arrive
- Reduce other heat sources (dim lights, no oven use)
Room-by-Room Analysis
Conference Rooms
Characteristics:
- Consistent high occupancy during meetings
- Electronics (projector, laptops) add heat
- Often interior rooms with no windows
- Glass walls may have heat gain from adjacent spaces
Sizing approach:
- Calculate for full seating capacity
- Add 200-400 BTU for projector/electronics
- Add 20% buffer for extended meetings
Living Rooms
Characteristics:
- Variable occupancy (2-15+ people)
- TV and electronics add some heat
- Connected to other spaces (kitchen heat)
Sizing approach:
- Size for typical evening use (4-6 people)
- Have supplemental fans or portable cooling for parties
- Consider open floor plan heat flow
Home Theaters
Characteristics:
- Enclosed space for sound isolation
- 6-10 people seated for 2-3 hours
- Electronics (projector, audio equipment) generate heat
- Dark room = less window heat gain
Sizing approach:
- Calculate for full seating
- Add 500-1,000 BTU for electronics
- Quiet AC essential—look for low dB rating
Home Gyms
Characteristics:
- High activity = 800-1,000 BTU per person
- Equipment adds minimal heat
- Users prefer cooler temperatures (18-22°C)
Sizing approach:
- Use high activity heat values (800 BTU/person minimum)
- Size for simultaneous users
- Consider dehumidification for sweat/humidity
Practical Sizing Examples
Small Conference Room (10 people)
- Room: 200 sq ft × 25 = 5,000 BTU
- People: 10 × 500 = 5,000 BTU
- Electronics: 400 BTU
- Total: 10,400 BTU = 0.87 ton → Install 1 ton
Living Room Party (20 people)
- Room: 400 sq ft × 25 = 10,000 BTU
- People: 20 × 500 = 10,000 BTU
- Lighting/TV: 300 BTU
- Total: 20,300 BTU = 1.7 ton → Install 1.5-2 ton
Home Theater (8 people)
- Room: 250 sq ft × 25 = 6,250 BTU
- People: 8 × 400 = 3,200 BTU (seated, quiet)
- Electronics: 800 BTU
- Total: 10,250 BTU = 0.85 ton → Install 1 ton (quiet model)
Home Gym (4 people exercising)
- Room: 200 sq ft × 25 = 5,000 BTU
- People: 4 × 900 = 3,600 BTU (high activity)
- Equipment/lights: 200 BTU
- Total: 8,800 BTU = 0.73 ton → Install 0.75-1 ton
Ventilation and Air Quality Considerations
Fresh Air Requirements
High-occupancy rooms need adequate fresh air, not just cooling. Many building codes require 15-20 CFM of fresh air per person. This fresh air adds to the cooling load as outdoor air must be cooled.
CO2 Levels
Crowded rooms with inadequate ventilation see CO2 levels rise, causing drowsiness and discomfort even if temperature is controlled. Consider:
- ERV (Energy Recovery Ventilator) to bring in fresh air efficiently
- Periodic window opening between meetings/events
- CO2 monitor to track air quality
Humidity Control
People generate moisture through breathing and perspiration. High-occupancy rooms may have humidity issues even with adequate cooling. Ensure AC runs long enough to dehumidify, or consider supplemental dehumidification.