Maintaining indoor air quality is essential in many buildings including offices, workplaces, schools and public buildings to ensure the wellbeing of occupants.
data loggers, in conjunction with temperature
and humidity loggers, can play an important role in helping to
verify that indoor heating, ventilation and air conditioning
systems are performing correctly: areas with inadequate ventilation
can lead to a build-up in CO2 levels and poor air
quality, which in turn can cause reduced concentration and
productivity in occupants and in some cases can lead to health
temperature and humidity will help ensure appropriate comfort
levels, preventing conditions becoming too hot or too cold. Both
can result in discomfort and reduced performance in occupants:
overheating can lead to tiredness and even headaches, while cold
conditions can cause unpleasant sensation in extremities and
CO2 Levels: Contributory Factors
Oxygen is breathed in, and carbon dioxide exhaled. Outdoors,
CO2 levels usually range from 350-450ppm (but are higher
in areas with very heavy traffic). Indoor CO2 levels are
therefore generally higher than outdoors, and typically vary
between 400 and 1200 ppm. Levels are affected by the number of
occupants in the room, the activity levels of occupants, the amount
of time occupants spend in the room and the ventilation rate.
measuring indoor CO2 levels, air quality can be
maintained by finding the balance between the carbon dioxide that
humans produce and a 'dilution effect' as ventilation systems
operate. The CO2 content is used to identify and control
the amount of fresh air per person in a room. By using the known
difference between indoor and outdoor CO2
concentrations, and by monitoring indoor concentrations of carbon
dioxide, ventilation performance can be determined.
In the UK, HM Government Building Regulations covering the
control of ventilation state that "It is important that ventilation
is controllable so it can maintain reasonable indoor air quality
and avoid waste of energy", and go on to mention that using
CO2 detectors can be one means of achieving this.
Specific regulations exist for school buildings. Building
Bulletin 101 (BB101): The Ventilation of School Buildings -
specifies that ventilation should be provided to limit the
concentration of carbon dioxide in all teaching and learning
spaces. In the absence of any major pollutants, carbon dioxide is
taken to be the key indicator of ventilation performance for the
control of indoor air quality. During the continuous period between
the start and finish of teaching on any day, the average
concentration of carbon dioxide should not exceed 1500 parts per
In addition, based on the recommendations of the Health and
Safety Executive, it suggests that the maximum concentration of
carbon dioxide should not exceed 5000 ppm during the teaching day,
and that at any occupied time, including teaching, the occupants
should be able to lower the concentration of carbon dioxide to 1000
ppm, although these levels may not be suitable for areas such as
science laboratories and food technology rooms etc.
The guidelines suggest using CO2 sensing
as a means of assessing ventilation performance, possibly in
conjunction with temperature
monitoring control to provide night-cooling control, and to
limit excessive heat loss in winter.
This approach has been used in schools in England and Wales, and
also in Europe, where more specific guidelines often exist for
monitoring carbon dioxide levels in buildings other than schools.
For example, in Denmark, carbon dioxide is measured to check
whether the ventilation is sufficient for the room compared to the
number of people that are going to use it. The Labour Inspectorate
in Denmark recommends an upper limit of 1000ppm with the
recommended value for school classrooms is 1200ppm.
In Sweden and many other countries, 1000ppm is the recommended
maximum level, with several Swedish companies recommending a
maximum level of 800ppm for peak staff performance.
Tinytag CO2 Data Loggers
There are two Tinytag CO2 data
loggers, which have been designed to monitor in different areas
with varying concentration levels, reflecting the guidance and
recommendations above. The
TGE-0010 monitors up to 2000ppm, while for more specialist
areas or applications, the
TGE-0011 monitors up to 5000ppm. Both units have a user-defined
upper ppm limit, and if this limit is reached a flashing red LED
will be activated.
loggers, in conjunction with temp/RH
loggers, can be used for many applications to monitor air
quality, and has included university research into air quality and
energy system performance in a wide range of buildings.
Building Bulletin 101
HM Government Building Regulations 2010, F1 Means