Carbon Dioxide (CO₂) Sensors

People exhale carbon dioxide (CO₂) at predictable levels, making CO₂ a useful indicator of a room's ventilation needs based on the number of people in the room.

To meet fresh air requirements, buildings traditionally ventilate to meet peak occupant demand, regardless of actual occupant demand. During partial occupancy, energy is wasted to heat, cool, humidify and dehumidify more outside ventilation air than is required.

CO₂ sensors are a type of Demand-Controlled Ventilation (DCV) strategy that improves a building's energy efficiency and helps ensure proper indoor air quality. CO₂ sensors take frequent CO₂ measurements of a space and adjust ventilation supply accordingly to reach desired CO₂ levels. CO₂ sensors end up saving energy and money by supplying just the right of amount of ventilation air to satisfy occupant needs.

Incentive

• $200 per CO₂ sensor.

CO₂ sensor eligibility criteria

You must apply for pre-approval before beginning any work on the project and before purchasing any equipment.

• All CO₂ sensors must utilize infrared sensor technology.
• CO₂ sensors must control the ventilation system. Sensors used solely for data acquisition purposes are not eligible.
• CO₂ sensors must be permanently attached. Handheld CO₂ monitors are not eligible.
• Incentives are only available for spaces designed to hold at least 15 people at maximum design occupancy.
• Ventilation systems controlled by CO₂ sensors must operate a minimum of 1,000 hours between September 1 and May 31.
• Rebates are available for retrofit projects only.

Benefits

• Lower energy costs;
• Consistent indoor air quality and improved occupant comfort;
• Reduced greenhouse gas emissions;
• Less demand on your HVAC system; and
• Improved marketability of your building.

Typical Annual Savings
	Annual Savings	Payback with Incentive
Here are the typical savings for a school with 12 classrooms, a gymnasium, an auditorium, and a cafeteria (35,000 ft2 in size and seven CO2 sensors).	$1,800	2.5 to 3.0 years
Here are the typical savings for an office building (20,000 ft2 in size and four CO2 sensors).	$700	3.5 to 4.0 years
Saving examples assume that prior to CO2 sensor installation; ventilation was shut off or reduced to minimum levels during unoccupied hours. Energy savings may be significantly higher in situations where this is not the case.

Important facts about CO₂ sensor DCV systems

• Take frequent measurements of CO₂ and adjust ventilation supply to maintain proper indoor air quality:
  • When CO₂ readings are above target levels, more outside air is introduced to reduce CO₂ levels and improve indoor air quality.
  • When CO₂ readings are below target levels, ventilation is reduced to maintain appropriate indoor air quality.
• Have the greatest energy savings potential by eliminating over-ventilation during quiet periods. Fixed and time-controlled ventilation strategies cannot measure occupancy and therefore may over-ventilate at times (see Figure 2).
• Satisfy occupant ventilation needs at any given time. Ventilation air volume is adjusted to satisfy different occupancy levels (see Figure 3). These systems also have an advantage over occupancy sensors by detecting degrees of occupancy and varying fresh intake air accordingly.
• Suitable only for controlling occupant-related ventilation. A base ventilation rate may still be necessary to prevent poor indoor air quality due to other airborne contaminants, such as emissions from building materials.
• Only DCV strategy to adjust ventilation levels to account for the uncontrolled infiltration of outside air (e.g. through an open window or through cracks and holes). The ventilation system will make up only what is necessary.
• Can be the most costly DCV strategy to implement, but achieve the highest energy savings in buildings with variable occupancy, such as retail stores, offices, restaurants, movie theatres, gymnasiums, auditoriums, and conference rooms.

Unlike carbon monoxide (CO), which can be deadly when inhaled at relatively low levels, CO₂ is not considered harmful at levels normally found in buildings.

Time-controlled ventilation and occupancy sensors are other DCV options you can apply in your building.

For more information talk to your ventilation contractor.

Figure 2

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Figure 3

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