Test of 5-Step Method in DOE Facilities

Estimate Outdoor Ventilation Rate (Step 3 in the 5-Step Method)

1. Demonstration in Controlled Room Environment:

Use the carbon dioxide (CO₂) decay method to determine outside air ventilation rate.

• Scenario 1: Assess the effect on ventilation rate by combining 1) an exhaust fan in an open door and 2) a room circulation fan.

• Scenario 2: Assess the effect on ventilation rate by combining 1) an exhaust fan in an open door, 2) opening a window, and 3) a room circulation fan.

These examples demonstrate the effectiveness of using box fans to enhance outside air ventilation.

2. Real-Life Classroom Demonstration:

Use the steady state CO₂ level to estimate ventilation rate.

This is the model that schools will use to assess ventilation in naturally ventilated classrooms.

Why Carbon Dioxide (CO₂)?

All animals and humans inhale oxygen and exhale CO₂. The CO₂ level in exhaled air is about 3.8%, or 38,000 ppm (parts per million). When CO₂ is exhaled it is quickly mixed with the surrounding air and, if the ventilation is good, the concentration is quickly reduced to harmless levels. If ventilation is not optimal, CO₂ levels in occupied rooms can increase.

Indoor CO₂ levels usually vary between 400 and 2,000 ppm. Outdoor CO₂ levels are usually 400 - 450 ppm. In Honolulu, a value of 415 ppm was measured for this experiment.

CO₂ is often used as an indirect measure of ventilation. When a building is occupied, the CO₂ concentrations indoors are elevated by CO₂ exhaled by occupants. This project will test the level of CO₂ and showcase how fast air outside air can replace the indoor air with assistance from a fan.

Dry ice (the solid form of CO₂) was used to increase the concentration of CO₂ in indoor air, as shown in the Controlled Room Environment example.

International recommendations for the maximum concentration of CO₂ in occupied buildings:

• 5,000 ppm - Maximum concentration during an 8-hour working-day according to OSHA³ and ASHRAE⁴.

• 2,000 ppm - May produce a significant increase in drowsiness, tiredness, headache and a common discomfort.

• 1,000 ppm - Maximum concentration in a closed room recommended as the maximum comfort level in many countries.

• 800 ppm - Target maximum carbon dioxide level by commercial HVAC companies.

• 400–800 ppm - Risk for over-ventilation (too much fresh air = energy wasted).

• 400-450 ppm - Common outdoor concentration.

³ United States Occupational Safety and Health Administration

⁴ American Society of Heating, Refrigerating and Air-Conditioning Engineers