Scientists have long been aware of the effect of CO2 gas (carbon dioxide, carbon dioxide) on the human body. According to the information specified in the classifier of harmful substances GOST 12.1.007-76, carbon dioxide is considered a low-hazard substance (4th class), has a low concentration in atmospheric air. By itself, CO2 has a low degree of harmful effects on the environment, however, an increase in gas concentration in the air up to 7% can harm the human body: breathing is difficult, suffocation occurs. A feature of carbon dioxide is that it does not have the ability to glow with the body, with a decrease in the concentration of CO2 in the air, breathing is completely restored.
ASHRAE: standardization of HVAC equipment
High levels of CO2 concentration in atmospheric air (from 0.1 to 0.7%) have a negative effect on humans, dramatically reducing their performance. Unlike carbon dioxide, oxygen is able to change the concentration in broad values, without causing harm to health. The ASHRAE standardization committee for HVAC equipment has set the acceptable carbon footprint in rooms with people at 0.1% of the total air volume. It is the allowable CO2 value indicated by ASHRAE that is considered the baseline in calculating air exchange.
CO2 measurement goal
In a general sense, the level of carbon dioxide in the air determines its stuffiness, which, in turn, depends on the number of people in the room. The amount of carbon dioxide is the main criterion for indoor air quality, therefore, focusing only on the concentration of carbon dioxide, and if there is a ventilation system containing CO2 sensors, it is possible to effectively regulate indoor air quality.
When breathing, the average person, breathing oxygen, is able to exhale from 0.35 to 0.5% carbon dioxide. In other words, a gas mixture exhaled by a person is 100 times higher than the concentration of CO2 compared to outside air. If a person is indoors, for several hours the concentration of carbon dioxide in the air increases many times, and air quality decreases sharply.
Respiratory CO2 Limits
Despite the fact that carbon dioxide has neither color nor odor, its increased concentration is easily felt by a person. When inhaling air with a high CO2 content, fatigue is felt, distraction occurs, a person becomes inattentive. The problem of air with excessive carbon dioxide content is especially acute in closed public and educational institutions, medical institutions.
Experts in laboratory conditions have established that a gas concentration of more than 0.1% is already capable of exerting a negative effect on humans. The concentration of carbon dioxide in the range from 0.04 to 0.07% is optimal for human life. Carbon dioxide in a concentration of 0.07 to 0.1% is found in crowded rooms and public transport, a similar proportion of gas in the air is not capable of causing great harm and is considered permissible for breathing.
An increased concentration of carbon dioxide (from 0.05 or more) contributes to a low activity of the human body, drowsiness, a slowdown in reactions and a low rate of thought, a sensation of suffocation appears.
Room air quality control: wall-mounted CO2 sensor
Wall mounted carbon dioxide sensors continuously measure CO2 and provide a control signal to the ventilation unit to remove excess carbon dioxide. Complex climate systems may have built-in sensors, but it is possible to use an external carbon dioxide sensor CO2 with subsequent connection via separate outputs to the fan.
Various options for wall mounted sensors are available on the market, there are devices with relay or analog outputs, as well as outputs for the monitor screen. Since manufacturers can supply control sensors with only one output, some owners modify the devices themselves. Improved CO2 sensor with its own hands and containing all of the above options for transmitting the output signal, it is most effective because it is compatible with any ventilation system. In modern CO2 sensors, a self-calibration system should be implemented to increase the reliability and durability of the device.
Wall-mounted sensors have two of the most common modifications: a CO2 sensor with a relay output, containing a CO2 LED indicator and buttons for controlling the ventilation system modes; a sensor that does not contain LED indicators and individual control buttons.
Sensors are powered by low- current AC networks . Some manufacturers provide an additional option to connect a power supply to the CO2 sensor.
CO2 sensor functionality
Almost all sensors are capable of measuring the concentration of carbon dioxide in the air stream, controlling the boundary indicators. CO2 sensors are capable of measuring gas concentrations in the following ranges:
- from 0 to 2000 ppm (0.02%);
- from 0 to 3000 ppm (0.03%);
- from 0 to 5000 ppm (0.05%);
- from 0 to 10,000 ppm (0.1%).
The data received by the device are converted into 0-10V active output signals. Sensors for calculating CO2 concentration absorb non-scattered infrared radiation (NDIR). Devices are equipped with a protective shell of maximum protection classes IP65-IP68.
In the absence of integrated devices for visual display of measurement results, a CO2 sensor with an analog output is used. Instruments for determining the concentration of carbon dioxide have the function of automatic and manual calibration of zero value. Before starting calibration, ensure uninterruptible power supply to the device for 10 minutes. The room in which the sensor is installed must be ventilated. The carbon dioxide level corresponding to the zero point is 300 ppm (0.003%). Most models of sensors that monitor the carbon dioxide content are calibrated once, and further periodic calibration is performed automatically.
After the CO2 sensors are connected to the power supply for the first time and started up, the device conducts its own testing and performs installation procedures. During the first five minutes after starting, the output data may not correspond to the actual values.
Residential Adaptive Ventilation
Adaptive ventilation differs from the traditional one only in the control of operating modes. Traditional fans work in one mode, energy consumption does not depend on the number of people in the room and the quality indicators of air in it.
The adaptive ventilation operating mode is automatically controlled, which is why a CO2 sensor is used for ventilation, which controls the carbon dioxide content in the air. Thanks to the intelligent control system, the fan will supply the volume of air that is necessary and sufficient.
The need for ventilation control by CO2 sensor
The permissible level of CO2 concentration is regulated by state standards, one of which is GOST 2.1.005-88 (sanitary and hygienic requirements for air in the working area). According to GOST, when considering the acceptable values of carbon dioxide in the air, the minimum performance indicators of ventilation equipment (30 m 3 / h per person) are also taken into account. Based on the requirements of GOST, each person present in the room, for 1 hour should receive 30 m 3 of flowing air.
CO2-controlled ventilation systems
Specialists in ventilation equipment often use the concept of air distribution efficiency. Under the air distribution efficiency is meant the speed with which the fresh air stream reaches the resting area or workplace (breathing zone). The quality of the supply air entering the breathing zone should not decrease as you move around the room, in other words, the fresh air flow should not come into contact with that which contains a high concentration of CO2.
Modern climate systems and technologies quite effectively and economically perform the functions of airing the premises. Built-in sensors and carbon dioxide meters are able to control the ventilation system, ensuring proper air quality in the room, while minimizing energy consumption.
Climatic systems in the work are guided by indicators of CO2 concentration in air, electronics compares the obtained value with the set value. CO2 sensors control the ventilation system while maintaining optimal air quality. Similar systems are successfully used in rooms with a variable number of people. A high class of energy saving is achieved by optimizing the ventilation power.
Where to install a sensor or CO2 level meter
The choice of the location of the carbon dioxide sensor must be carried out based on the restrictions:
- the device must be at least 1 m from the place of permanent residence of people;
- household CO2 sensor does not fit closer than 1 meter to fresh air;
- the organization of optimal power for the device implies its close proximity to an energy source.