Monitoring ventilation with CO₂ sensors


02 November 2022

Hong Cheng of LG explores the importance of constantly monitoring indoor CO₂ levels in real-time for improved indoor air quality in line with the new new Part F of Building Regulations in England.

The updated Building Regulations came into effect in England on June 15. The new revision of the Regulations has highlighted the importance of indoor air quality and its impact on the health and wellbeing of building occupants.
Recognising the significance of adequate building ventilation in reducing the spread of airborne infection during the current pandemic, the new approved document Part F Volume 2 for buildings other than dwellings, has included several new guidelines for the purposes of good indoor air quality including:

  • Air quality standard for outdoor air to minimise ingress of external pollutants into buildings.
  • Measures to reduce risk of transmission of airborne infection for recirculation of air in shared offices.
  • Indoor air pollutant levels and exposure time.
  • Indoor CO₂ monitoring as an indicator of overall indoor air quality to guide building ventilation. It is further recommended that a CO₂ level of 800 ppm is acceptable in suitably ventilated building and a level of 1500 ppm is a starting point at which action needs to be taken to improve ventilation.

The new revision has shown that energy efficiency and adequate ventilation should go hand in hand with design, construction and building operation. These new changes will help to reduce carbon emissions associated with commercial buildings in order for the UK to achieve its target of carbon Net Zero by 2050. 

It has been reported that, for healthy fresh outdoor air, the CO2 level is typically found to be below or around 400 ppm. For occupied indoor spaces, CO₂ concentration usually varies in the range of around 400 to 1000 ppm depending on the building location and the specific air exchange rate of the building. In closely packed meeting rooms, it is not surprising to find the CO₂ level is in the region of 1500-3000 ppm. It has been known that exposure to excessive levels of indoor carbon dioxide over a prolonged period can have negative health impacts on the building occupants. Although the precise relationship between indoor CO₂ level and its effect on human health is not fully understood yet, it is only logical and sensible to keep indoor CO₂ levels below a certain limit if possible.

Potential risk to health

In densely populated indoor spaces such as lecture theatres, conference rooms where many people congregate, indoor CO₂ levels generated by audiences’ breathing could be excessive and potentially become a risk factor to health without adequate ventilation. If the indoor space is unventilated or poorly ventilated, the indoor CO₂ concentration will continue to accumulate and can rise to a much higher level over time. Inversely, elevated CO₂ levels in buildings indicate poor ventilation.

In the indoor environment, CO₂ levels has long been used as a surrogate indicator for the quality of indoor air where the need for ventilation is linked to the presence of people. This has now become a requirement in Part F of the Building Regulations in England. CO₂ monitoring is recommended to be used as an approach to assess whether ventilation to an occupied indoor space is adequate, and can be integrated into the building ventilation management system. 

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Some Energy Recovery Ventilator (ERV) products in the current market have embedded CO₂ sensing in the unit, such as those manufactured by LG which are suitable for commercial and residential buildings respectively. These systems constantly monitor the indoor CO₂ level in real-time, which is used to control the ventilation rate automatically according to the measured values. The measured CO₂ level can also be displayed on the wired remote controller. The original design intention of this feature was for energy saving to ensure that the fan is off when the indoor CO₂ level is low. Even if the new Part F for dwellings in England does not require CO₂ monitoring, LG’s residential ERVs have this capability built within the unit.  

Obviously, the outdoor air intake and the indoor air exhaust of the ERV unit need to be properly managed in the design and installation stage to prevent exhausted air from re-circulation returning back into the building again. These devices can also be integrated into the Building Management System (BMS) to control ventilation for large commercial buildings.

If the ERV is set in Auto mode, the CO₂ level is used to control the fan speeds (i.e. link to building ventilation rate) automatically. For example, the typical operation control logic used in LG’s product is as follows:

CO2 Sensor Reading

ERV Fan Operation

Less than 500 ppm


500~700 ppm

Low speed

700~900 ppm

High speed

More than 900 ppm

Super high speed


When the measured indoor CO₂ level is above 500 ppm, the sensor will activate the fan at a low speed to start to ventilate the building. If the measured value is above 700 ppm, the fan will run at a high speed to increase the ventilation rate. During this process, the sensor will continue monitoring the indoor carbon dioxide level, until the CO₂ level is reduced to under 500 ppm, when the fan will switch off automatically. The threshold values used in the control logic will ensure a healthy CO₂ level indoors.

In addition, all LG’s ERV units are able to clean the incoming outdoor air by removing fine particles with high efficiency filters and supply fresh air indoors. These high-performance filters are rated according to ISO EN BS 16890 standard (optional ISO ePM1 75% for the commercial unit and built-in ISO ePM1 95% for the residential unit respectively). Furthermore, the recently launched residential ERV also has UVnano (i.e. UV-C germicial irradiation technology), a bacteria/mould-resistant heat exchanger and air pathways built within the unit to reduce the risks of transmission of airborne infection in the indoor environment. 


In conclusion, these ERV products, suitable for new-build and retrofit, can meet the requirements of the new building regulation in several aspects to achieve the improved indoor air quality for the occupants, including constant CO₂ monitoring, automatic ventilation control, and preventing ingress of external pollutants with the high efficiency filters.