Monitoring the levels of CO2 in buildings is increasingly being recognised as important for the health of the people living and working in them. Only a small increase in CO2 levels can cause yawning and drowsiness. Following the awareness of the harmful effects of high levels on CO2 on health, HVAC or Indoor Air Quality (IAQ) systems are increasingly incorporating CO2 monitors, so that the air change is controlled by the need to reduce the CO2 levels. There are several driving forces behind this. Firstly, the need to meet legislation designed to ensure a healthy working environment. The US Occupational Safety and Health Administration (OSHA) has set a Permissible Exposure Limit (PEL) for CO2 of 5,000 parts per million (ppm) (or 0.5 %) over an 8-hour workday. Secondly, the need to save money, as changing the air in a building has an energy cost – especially if incoming air also has to be heated or cooled. This is particularly relevant at night time and weekends, when buildings may not be fully occupied. Fewer people means less CO2 being produced, so that the rate of air change can be reduced accordingly to save money.
‘Smart building’ can result in an energy reduction of between 30% and 40%. This helps achieve zero carbon consumption targets, and also saves money. This is supported by a report by the Minnesota Department of Commerce on Demand Control Ventilation (DCV) that can have a payback of between four to eight years. This is because DCV uses CO2 or occupancy sensors to estimate the number of people in an area, and only supplies as much ventilation air as is needed at a given time. This is particularly appropriate for areas of widely varying occupancy, such as meeting rooms, auditoriums, etc.
However, installing CO2 monitors throughout a building can be expensive because of the amount of cabling required to provide them with the mains power that they need. Installation costs are even greater in existing buildings due to the costs of redecorating after cable installation. Schneider Electric and Gas Sensing Solutions (GSS) have been collaborating to cut out the need for mains power and the associated installation costs. The solution is a CO2 monitor that can be powered by batteries for up to 10 years.
Gilles Chabanis, IoT Sensors Excellence Center Manager at Schneider Electric, explained, “We really understand the requirements of the smart building control market. The CO2monitor has to be fit and forget. So we needed a CO2 sensor with such a low power requirement that the self-contained monitor could work for at least ten years. GSS’ use of proprietary LEDs at the heart of its infrared monitoring technology means that its sensors use very little power and so can be powered by batteries for years.”
Schneider’s new Smart Building Control monitor not only measures CO2 but also temperature and humidity. Data is reported on over a wireless link so there is no need for any cabling at all. This also makes it quick and easy to change the position of monitors so that there are no rewiring and redecorating costs should the office layout ever need changing.
Calum MacGregor, GSS’s CEO, added, “We’ve worked closely with Schneider to create a custom sensor to meet their requirements of high accuracy and very low power. A version of the resulting, ultra low power, CO2 sensor is now available in our standard product line up for other customers with similar low power and long product lifetime requirements.”
To find out more about our low power, ambient air CO2 sensors for monitoring air quality, for building control and HVAC applications, click here
CO2 sensors work by measuring how much light is absorbed by CO2 molecules in the 4.2 and 4.4 microns range as it passes through the sample gases, which is called Non-Dispersive Infra Red (NDIR) absorption. The amount of absorption indicates how much CO2 is present. GSS developed proprietary LEDs that are specifically tuned to emit at these wavelengths. The LEDs use very little power and turn on almost instantly, enabling sensor readings to be made in less than a second. As a result, GSS has pioneered the development of CO2 sensors that can be powered by batteries for long periods of up to ten years. Competitor sensors use IR sources that require significantly more power per measurement and also take much longer to reach a stable condition for a measurement, resulting in the need for mains power.