Information for Using CO2 monitors
Information for Using CO2 monitors
CO2 monitoring measures the ingress of outdoor air to dilute indoor sources of CO2. This gives a good indication of ventilation in spaces with high occupancy for long periods of time. It is particularly well suited to venues above 50m2 where customers stay for periods of 1 hour or more. Once spaces become very large (>320m2) then you are likely to need multiple monitors as the outdoor air may enter the space but not mix well across the whole area.
Smaller venues or venues where customers only stay for short time periods are not well suited to CO2 monitoring. In these cases high readings can still highlight a need for improvement but low readings do not indicate adequate ventilation.
Where there are significant sources of CO2 in the space the interpretation below cannot be used. Short duration releases of CO2 such as in confetti cannons are not an issue provided you account for them when viewing the results. Where there is significant combustion e.g. in kitchens, then CO2 monitoring will not be reliable. If you use theatrical smoke that is generated using CO2 over long time periods then CO2 monitoring is not recommended.
The monitor should be a non-dispersive infrared (NDIR) monitor.
Some monitors provide alarms, lights and easy to read displays which may be helpful (or not).
Some monitors log data and allow you to look back at recent trends, others will only provide an instantaneous reading. Think about how you would like to use access the information
Most monitors require mains power, some are battery operated.
There are many different brands on the market. Below provides a few examples
Place at, or a little above head height. Mounting at arms reach above head height is often most practical in busy spaces.
Away from drafts and air supplies
Place CO2 monitor 50cm away from peoples heads to avoid inaccurate readings.
Avoid cookers, gas fires, or any other form of combustion as they are a source of CO2. If your venues uses propellants for confetti cannons or similar avoid placing close to the release. If you use a lot of candles do a test to check results when candles are not in use.
If your venue uses theatrical smoke that is based on CO2 then a CO2 monitor is not recommended. Water based smoke machines are unlikey to affect readings from NDIR monitors. If you purchase a cheap, non-NDIR monitor then this may result in inaccurate readings. Where using theatrical smoke it is worth carrying out a check that this does not affect the sensor e.g. by observing results when held in smoke stream during low occupancy.
Avoid placing too close to beer pumps / drink taps.
Where there are concerns about damage/theft then monitors can be placed within cages, or hidden from sight e.g. located behind speakers / behind the bar.
At first it may be useful to move the CO2 monitors around to ensure outdoor air is reaching all parts of your venue and to identify any areas with inaccurate readings.
Firstly check your monitor is working correctly. Following a long period of zero occupancy, or when taken outside you would expect a reading of ~400PPM. CO2 monitors are known to drift over time so you should regularly check this.
Initially, attempt to measure your CO2 levels with your existing ventilation practices for a good period of time (a week at least). This will allow you to capture periods of low and high occupancy so that you can tailor any ventilation strategies to these times. It is particularly important to capture high occupancy periods to ensure your ventilation is adequate when your venue is full.
Readings below 800 PPM indicate good air flow for the number of people in the space. Be aware of low CO2 readings that rise rapidly. These could indicate poor ventilation. If you observe readings over 1500 PPM then ventilation should be prioritised for improvement. There are some helpful tips below.
Other factors to check include:
CO2 values should rise when people enter the space.
If occupancy or ventilation changes a lot then CO2 values will bounce around
If values continue to rise over a long period (~40minutes) of constant occupancy then this indicates the space is poorly ventilated even if the CO2 values remains low. This may occur in low occupancy spaces.
If you get a few high spikes in CO2 which quickly reduce it is usually not a significant concern. It is sustained CO2 values that indicate a risky environment. The occasional high spike may be someone breathing near the monitor.
Air cleaners do not remove CO2 from the air so where these are used the monitors provide no information on their efficacy.
If your readings are surprisingly high it is worth checking the results. Did you place the monitor where it catches someone's breath? Can you recheck the calibration by measuring outdoor concentrations. Perhaps do a trial with the monitor in a different location.
Where possible increase ventilation via opening windows, increasing fan speed if you have any mechanical ventilation available.
Where conditions do not allow constant ventilation consider purging the space by opening an external door for short periods regularly.
Ensure you have a clear plan for when you will purge the air, and who is responsible.
Where noise is an issue preventing openings consider purchasing an Air Cleaner. These just plug into the wall
Air cleaners will not adjust your CO2 readings but will remove particulates, including viruses in exhaled breath, from the air.
Install mechanical systems. Wall mounted fans are easier to retrofit. Heat recovery options are available and are recommended to help reduce energy bills.
Typical cost: £1500 for 100 people. For fans only, building works and running costs not included.
~£15000 for heat recovery (incl installation)