CO2 sensor, air quality sensor CO2

Our AERASGARD® air quality sensors offer CO2 measuring ranges of up to 5000 ppm for reliable and sustainable CO2 monitoring and control of work and living spaces, break rooms, cinemas, schools, etc. The sensors are available as desktop, room, outdoor, duct, flush-mounted and pendant devices.

Guide and useful information about CO2 sensors and air quality sensors

CO2 sensor for building automation & ventilation

For demand-based control, energy efficiency and standard-compliant room air monitoring

Author: S. Becker | Status: 03.02.2026

A CO2 sensor does not measure "air quality" in the general sense - but provides a very specific, reliable parameter: the CO2 content of the room air in ppm. This is extremely valuable in building automation because CO2 is a reliable indicator of occupancy and ventilation.
In practice, rooms are rarely "evenly used": meeting rooms, classrooms, waiting areas or open-plan offices have dynamic loads. This is precisely where a CO2 air quality sensor creates the basis for a control strategy that does not run according to a time program, but according to real demand.

Typical targets in building automation:

Demand-controlled ventilation (DCV)
Reduced energy consumption due to less outside air when it is not needed
Greater comfort thanks to stable air quality (fewer "tired rooms")
Monitoring and trend recording via BMS / BMS

Why is a CO2 sensor so relevant in building automation? CO2 in indoor air: what is actually measured? Typical control strategies with CO2 sensors Places of use: Where a CO2 air quality sensor is particularly useful Which signals & interfaces are relevant in practice? Selection guide: What should you really look out for? Select CO2 sensor for BMS & field device integration now

Why is a CO2 sensor so relevant in building automation?

When looking at modern HVAC systems, CO2 measurement is one of the most important control variables because it answers several typical questions during operation:

Is the room currently occupied?
CO2 rises indoors mainly due to people. A CO2 sensor can indirectly map occupancy - even if there is no presence detector or it only has limited informative value.

Is the air exchange rate sufficient or is the ventilation "missing the mark"?
Many systems are set to run "on the safe side". This works, but costs energy in the long term. With CO2 control, ventilation can be planned - and above all measured.

How stable is the indoor air in real use?
In theory, volume flows fit, but in practice, usage profiles, door openings and boundary conditions change. A CO2 sensor shows whether the system delivers the result for which it was planned.

From an operational management perspective, CO2 is so interesting because it is not just a measured value, but operating status information that can be directly translated into control, alarms and optimization.

CO2 sensor vs. "air quality sensor": What's the difference?

In projects, CO2 is often equated with "air quality". This is partly true - but not completely. CO2 maps occupancy and ventilation requirements very well. Odors / VOC / other air parameters are not automatically recorded.

For many typical applications in building automation, however, CO2 is exactly the right choice because it:

suitable for regulation,
stably interpretable,
and is directly linked to outdoor air demand

If other air quality aspects are also relevant (e.g. VOC), these are often combined in extended concepts - but CO2 often remains the "basic parameter".

CO2 in indoor air: what is actually measured?

A CO2 sensor records the concentration of carbon dioxide (CO2) in ppm (parts per million).
Typical orientation values from practice:

~400 ppm: typical outdoor air (depending on environment)
800-1,000 ppm: often target range for good indoor air
>1,200 ppm: Air quality is often perceived as "heavy"
>1,500 ppm: significant ventilation requirement / poor indoor air quality

Source: Federal Environment Agency, Health assessment of carbon dioxide in indoor air

Important in building automation: A CO2 sensor does not measure "how fresh" the air is, but how high the CO2 load is - and thus very well whether enough outside air is being supplied.
Especially in tightly constructed buildings (modern windows, high airtightness), CO2 values reliably show how much a room is actually "breathing through".

Typical control strategies

In practice, there are several ways in which CO2 sensors can be used:

1) CO2-controlled volumetric flow control (VAV / CAV with actuating variable)
The CO2 measured value is used to create control variables, e.g:

Control of VAV controllers
Setpoint specification for volume flow controller
Adaptation of fan speed / pressure control by a higher-level control system

Advantage: Air volume follows the usage, not the schedule.

2) CO2 as release / stage signal for ventilation units
Especially in simpler systems, CO2 is used as:

Level signal (e.g. low/medium/high fan speed)
Release for ventilation operation with actual occupancy
Combination with time profiles ("only really start up when necessary")

This is technically less complex, but often highly effective.

3) CO2 monitoring & alarming in the BMS (without direct control)
In some projects, CO2 is not the control variable, but a monitoring variable:

Trend recording (verification, optimization, complaint clarification)
Alarm if limit values are exceeded (e.g. comfort or hygiene limits)
Analysis of ventilation times vs. indoor air quality

This is particularly relevant in existing buildings if you want to create transparency without major interventions.

Places of use: Where a CO2 air quality sensor is particularly useful

CO2 sensor technology is useful wherever occupancy fluctuates or where comfort/quality must be verifiable:

Meeting rooms / conference areas
Classrooms / training rooms
Offices (individual and open space)
Waiting areas (e.g. public authorities, healthcare)
Canteens / social rooms
Hotels, lounges, event areas

In building automation, it is usually most economically effective to place CO2 sensors where load peaks occur - i.e. rooms that are heavily occupied for short periods but otherwise have low demand.

Which signals & interfaces are relevant in practice?

Many people look first at the measuring range or accuracy of a CO2 sensor - that is correct. In automation projects, however, something else is often decisive:

How well can the sensor be integrated into the BMS - and how usable is the measured value during operation?

Typical connections are:

Analog signals

0-10 V (often standard in building automation)
4-20 mA (robust, good for longer distances and interference immunity)

Advantage: uncomplicated, compatible, quick to integrate.

Example: What does a 0 - 10 V output in ppm mean?

In building automation, CO₂ is often output as a standardized analogue signal - usually 0 - 10 V.
Example: Measuring range is set to

0 V = 0 ppm CO₂
10 V = 2000 ppm CO₂

This results in a linear characteristic curve:

5 V corresponds to approx. 1000 ppm
7.5 V corresponds to approx. 1500 ppm

In practice, this means

The controller can work directly with a voltage value
Setpoints (e.g. 1000 ppm) can easily be defined as a threshold

Important: In many devices, the characteristic curve can be set on the sensor (e.g. via measuring range switching or parameterization).
Depending on the configuration, a 0 - 10 V output can map 0 - 2000 ppm or 0 - 5000 ppm, for example.

Digital communication / bus systems

In larger systems or with standardized BMS structures, the digital connection is often the technically clean solution - especially if diagnostic information, status data or several measured variables are to be transmitted together in addition to the pure CO2 value.

In practice, bus systems such as Modbus play an important role, as they also enable simple and reliable wired integration in existing systems without requiring a great deal of effort.

Selection guide: What should you really look out for?

To ensure that a CO2 sensor works reliably in the field over the long term, the selection is not just a question of "data sheet values". In real systems, these points are often decisive:

Measuring principle & long-term stability

CO2 sensors in HVAC applications typically work with established measuring principles that are designed for stability in continuous operation. The most important factors here are: drift behavior, reproducibility and behavior under changing ambient conditions.

Suitable measuring range (ppm)

For classic indoor spaces, it makes sense to select the range so that typical operating values are "in the middle" and not at the edge. This provides more stable control and better resolution in the relevant range.

Mounting & measuring location

A CO2 sensor can be technically perfect - but if it is installed incorrectly, the values are still unusable. Typical errors in practice:

Installation directly in draughts (near windows, door flow)
Installation above heat sources
Placement in areas with "incorrect room air" (e.g. in niches, behind fixtures)

A clean installation means that the measured value represents the real occupied zone.

Dynamics: reaction time vs. control behavior

If the sensors are too slow, the systems "lag behind".
Control that is too aggressive, on the other hand, can become unstable. In practice, it is important that the sensor and controller match: Change in measured value → plausible control response.

Output signal matching the automation structure

That sounds banal, but it is crucial:

Which input cards are available?
Is 0-10 V preferred or 4-20 mA?
Should CO2 be connected directly to a controller or first to the BMS?

The more clearly the project defines this, the fewer coordination loops arise.

Select CO2 sensor for BMS & field device integration now

In many projects, CO2 measurement only becomes an issue when users complain about poor air quality - or when energy consumption is conspicuous. However, clean CO2 measurement can prevent systems from breaking down at an early stage:

Too little ventilation (comfort/hygiene suffer)
or
Ventilate too much (unnecessarily high energy consumption)

A suitable CO2 air quality sensor provides the basis for clear measured values, stable trends and control that remains traceable during operation - exactly what counts in building automation: Measured value → Logic → Effect.

Select CO2 sensor

FAQ

What does a CO2 sensor do in a ventilation system?

It measures the CO2 concentration in the room and thus enables needs-based ventilation control. The ventilation can thus be automatically adapted to usage and occupancy.

Is a CO2 sensor the same as an air quality sensor?

A CO2 sensor is often a sub-area of air quality measurement. It provides a very clear, technical parameter (ppm) that is particularly suitable for control and BMS evaluation.

Why is CO2 used as a control variable at all?

In indoor spaces, CO2 is mainly released by people. The CO2 value is therefore a reliable indicator of how heavily a room is used and how much fresh air is required to maintain good air quality.

Which output signals are common in BMS projects?

Depending on the system environment, 0-10 V and 4-20 mA are the most common in practice. This allows CO2 sensors to be connected directly to DDC/PLC/GLT.

Where should a CO2 sensor be installed in the room?

A CO2 sensor should be positioned in the occupied zone in such a way that it realistically measures the room air that is actually used. Draughts, peripheral areas and "dead corners" should be avoided, as the measuring location is decisive for the quality of the CO2 values recorded.

We also manufacture individually

Do you have special requirements? As a manufacturer with our own production facilities in Germany, we are also able to produce products outside of the standard range at any time.

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