Improved indoor air quality creates a healthier, more comfortable, and productive workplace. Ventilation systems improve air quality by exhausting stale or polluted indoor air from a building and replacing it with fresh outdoor air. Proper ventilation reduces CO2 levels along with other airborne contaminants such as dust, odours, and moulds.
The most basic ventilation system consists of an air-handling unit with a supply air fan and control dampers. The system mixes outside air with recirculated building air and redistributes the mixed air supply within the building.
Ventilation rates are traditionally based on a maximum assumed occupancy level. For example, 15 cubic feet per minute (cfm) of fresh outside air per person multiplied by the maximum design occupancy. Ventilation air is fixed at this rate to ensure fresh air needs are met at any occupancy level.
Fixed ventilation may be adequate in buildings with no significant changes in occupancy. Over-ventilation can still occur when actual occupancy falls below design levels.
The cost to heat, cool, humidify, and dehumidify excess ventilation air can be significant. For example, it costs roughly $3,500 per year in natural gas to heat 1,000 cfm of fresh outside air, 24 hours a day, 7 days a week. Energy costs are incurred unnecessarily if your building is over-ventilated.
Example of a CO2 sensor, actual monitor may differ from photo.
Click for larger image.
People exhale carbon dioxide (CO2) at predictable levels, making CO2 a useful indicator of a room's current ventilation needs.
To maintain fresh air requirements, buildings are often designed to provide a constant volume of outside ventilation air based on their maximum design occupancy. 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 DCV strategy that improves a building's energy efficiency and helps ensure proper indoor air quality. CO2 sensors take frequent measurements and match the supply of ventilation air to actual occupant needs at any given time. CO2 sensors save energy and money by eliminating over-ventilation.
The maximum eligible incentives are $250,000 for all electrical measures and $100,000 for all natural gas measures included in the project.
You must apply for pre-approval before beginning any work on the project or purchasing any equipment. Rebates are available for retrofit projects only.
|Typical Annual Savings|
|Building Examples||Annual Savings||Payback with Incentive|
|The savings examples above assume:
|School with 12 classrooms, library, and multi-purpose room (16,000 ft2 with 14 CO2 sensors)||$1,680||0 to 1.3 years|
|Retail space (4,000 ft2 with 1 CO2 sensor)||$420||0 to 0.5 years|
A time-controlled ventilation (TCV) system is a low-cost way to achieve ongoing energy savings. Facilities with highly predictable occupancy that is limited to a set number of hours per day, such as some offices and classrooms, can significantly reduce energy consumption with TCV.
Ventilation systems in an office building, for example, can be set to operate during regular occupant hours only. At the end of the workday, offices shut off or reduce ventilation to minimum levels.
Time clocks control ventilation to occur only during regular business hours. During this time, outside ventilation air is often set at full design occupancy, regardless of actual occupancy. When occupancy falls below the maximum design level during regular occupant hours, unnecessary ventilation may occur. TCV systems save energy during unoccupied hours only. To maximize energy savings, consider a DCV system.
Occupancy sensors can be an inexpensive DCV option for spaces with a fixed number of occupants for limited hours per day, such as warehouses and other storage spaces.
Occupancy sensors typically use infrared technology to detect when people are present. When sensors detect occupants, they trigger ventilation fans to turn on at maximum design levels. When sensors do not detect occupants, they shut off outside air delivery or reduce ventilation to minimum design levels.
Buildings with long and variable occupancy achieve less energy savings as sensors typically cannot detect varying levels of occupancy. Over-ventilation may still occur during slow periods, as the system provides enough ventilation for a fully occupied room, even if only 1 occupant is present.