http://www.digitaljournal.com/tech-and-science/technology/low-power-co2-sensor-detects-building-occupants/article/514283

Low power CO2 sensor detects building occupants

Posted Feb 7, 2018 by Tim Sandle
A new type of sensor to detect carbon dioxide has the ability to indicate whether people are inside buildings to enable smart building management. The sensor is also capable of running off a low level of power.
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File photo: An employee on her computer at Google's head office.
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The new sensors have been devised by technologists working at Purdue University (West Lafayette, U.S.) as part of a U.S. Department of Energy project to introduce a sensor targeted at reducing environmental impact of operating a building's HVAC (heating, air-conditioning, and ventilation) system. A secondary aim was to lower costs.
The key innovative feature with the new sensor is in assessing human risk. The senor can determine how many people are in a room or building (depending on the number of sensors in place). This is through calculating variations in carbon dioxide concentration, given that the gas is exhaled by people. This functionality enables energy savings to be made through restricting air conditioning and heating to low occupied areas.
The sensor uses two technologies for this: carbon dioxide detection and a sensor that can perform accurate measurements to assess how many people are in a particular room. The second sensor is deactivated unless the carbon dioxide sensor is triggered; thereby saving the energy costs that would ordinarily be required for running two sensors.
The carbon dioxide sensor uses microelectromechanical technology, which involves the use of vibrating plates that are coated with a film. The film absorbs carbon dioxide, which triggers a change in the vibration frequency in the presence of the exhaled gas.
Speaking with Smart2Zero, the researcher behind the new sensor, Professor Jeffrey Rhoads, explains: "The big picture is that being able to turn off the heating and air conditioning in a sensible way would allow you to save a substantial part of U.S. energy consumption.”
He adds: “To do that you need to be able to tell when a room is occupied and how many people there are."
In related sensor news, the company Teracom has introduced the TCW210-TH type of data loggers. These devices are for remote temperature and humidity monitoring applications. The instruments can monitor up to 8 temperature-humidity sensors from almost any brand; this is via 1-Wire interface or MODBUS RTU over RS485. These types of sensors are used with shipping and other forms of global transport, to provide important data for supply chains and for incorporation into blockchains.