Air Quality and CO2 measurement and control for classrooms

There is an increasing requirement from the education sector to monitor air quality for the benefit of student outcomes as well as to improve energy efficiency of schools in order for the country to meet its climate obligations. Implementation of a system that allows for the minimum requirement as well as to meet and exceed the overall objective of the school plan is considered below.

Scope:  The initial design scope calls for measurement, display and visual indication of a CO₂ over-threshold state in classrooms.

The design objectives below deal with the initial (minimum) requirement as well as two improved options that advantage the building, reduce operational complexity and duplication, and improve energy efficiency.

Option 1(initial): minimum requirement to measure and display CO₂, indoor temperature and outdoor temperature.  To have a visual indication when CO₂ goes over a threshold level.

Option 2: includes Option 1 and adds automatic control of passive or forced ventilation in order to reduce the CO₂level in the room. 

Option 3: includes options 1&2 an adds control of lighting level based on room lux level to save energy, and motorised window using pushbuttons

Option 4: includes options 1,2,&3 and adds central building control for timing of ventilation and changing of CO₂thresholds

The solutions below are designed to deliver the initial scope as well as the improved scopes based around a screen and sensor from ABB and additional KNX components.

Solutions:

Option 1: Using ABB Room temperature controller with CO2/ moisture sensor KNX with an external PT1000 sensor installed on an outside wall of the room.  The screen is configured to show CO2, indoor temp and outdoor temp.  If the CO2 exceeds a set level then the screen changes from black/white to red/ black until the level reduces below the threshold.

Option 2: Passive ventilation (window) is opened automatically to compensate for rise in CO₂ level. Means the window will actually be opened when the air quality reduces and shut when it improves.

Option 3: Manual control of window opening from switch.  Energy saving by control of light level from switch in room to a chosen lux level, saving energy.

Light level is altered from the switch to turn on/off lighting in the room and to vary the absolute light level in the room to compensate for natural light from windows by adding artificial light.  So, if there is low daylight in the room the intensity of the ceiling lights will modulate accordingly to maintain the desired lux level.

The ceiling sensor responds to absence of presence in the room after a preset time (say 30 minutes) and turns off lighting automatically.

The windows may be ‘manually’ controlled from the switch to allow for classroom intervention to, for instance, allow additional cooling to the room, or provide ventilation on demand. This overrides the automated CO₂ control operation.

All aspects are combined in one simple to use control station on the wall. Simple, effective and easy to install.

Option 4: Central control screen added to the KNX system allowing the school to monitor classroom temperatures, change CO₂ threshold levels and, timed events (such as scheduled window opening, or lighting level changes) and see any alarm states centrally.