Sustainability and sensors: Environmental monitoring for a greener future

Sustainability and Sensors: Environmental Monitoring For a Greener Future

The role of sensors in environmental monitoring is crucial as we move towards a more sustainable future.

The climate crisis is driven by rising global energy consumption, energy-intensive manufacturing processes, greenhouse gases produced by domestic appliances, extensive farming practices like livestock production, and burning crop residues. All these increase environmental CO₂, affecting the quality of life. Various sensors, with their diverse range of functions, play a critical role in collecting accurate and reliable data on multiple aspects of the environment. Sensors are indispensable tools for assessing air and water quality, soil health, and even climate conditions. Advanced sensors enable precise and efficient real-time collection of this data. This article explains in detail the sensing solutions necessary for environmental monitoring by estimating the greenhouse gases in an indoor environment, agricultural land, and livestock farming for a greener environment.

Need for greenhouse gas detection in Domestic appliances

Greenhouse gases can be defined in terms of Global Warming Potential (GWP). The GWP measures the potential impact of greenhouse gases on the atmosphere, expressed as a factor relative to CO₂, the reference gas. Reducing greenhouse gas emissions in residential settings is essential for mitigating global climate change. Indoor domestic appliances like refrigerators and HVAC heating, ventilation, and air conditioning systems are significant sources of greenhouse gases. The commercial refrigeration industries and HVAC should prioritize efforts to minimize the emission of greenhouse gases and contribute to a sustainable environment.

Carbon dioxide (CO₂) sensors, which work on the principle of Photoacoustic Spectroscopy (PAS), can detect methane, propane, R-32, and R454B gases (additional gases possible), all of which are responsible for the greenhouse effect.

The Photoacoustic Spectroscopy (PAS) Principle

In Photoacoustic Spectroscopy (PAS), light in the form of pulses from an infrared source pass through an optical filter tuned to the absorption wavelength of the intended measured gas. The gas molecules inside the measurement chamber absorb the filtered light with each pulse, causing them to vibrate and produce a pressure wave. This phenomenon is termed the "photoacoustic effect." An acoustic detector, optimized for low-frequency operation, detects the pressure change generated, and the microcontroller converts the output into the gas concentration reading. The absorption chamber is acoustically insulated from outside noise to deliver precise gas-sensing data.

Figure 1: Photoacoustic spectroscopy technology(Source)

As depicted in Figure 1, different industries and applications use photoacoustic spectroscopy technology, particularly in detecting refrigerant leakage. Its high sensitivity and selectivity enable the detection of minute concentrations of the target gases of interest, helping to differentiate between various refrigerants. This specificity helps distinguish refrigerant leaks from other prevalent gases in the environment. Additionally, PAS technology provides the benefits of real-time monitoring and a wide detection range.

Infineon’s XENSIVTM PAS CO₂

The highly accurate and compact Infineon’s XENSIVTM CO₂ sensor has SMD capabilities, making it suitable for indoor air quality monitoring solutions, HVAC Home appliances, Smart home IoT devices, agriculture/ greenhouses, and In-cabin air quality monitoring units.

Figure 2: PASCO₂V019(Source)

figure Figure 3: Block diagram of PAS CO2 Sensor(Source)

Figure 3: Block diagram of PAS CO₂ Sensor(Source)

The sensor uses a MEMS microphone which is optimized for low-frequency operation, enabling it to detect the pressure change generated by CO₂ molecules within its cavity as shown in the Figure 3. XENSIVTM's direct ppm readings, tape and reel packing, SMD capability, and simple design allow it to be quickly and easily integrated into customers’ systems for low and high-volume applications.

Figure 4: Indoor HVAC example with CO2 sensor to monitor air quality in a room(Source)

Figure 4: Indoor HVAC example with CO₂ sensor to monitor air quality in a room(Source)

An indoor HVAC unit with a CO₂ sensor is shown in Figure 4. You can regulate the room’s ventilation by using the HVAC unit. Such regulation is made possible by a microcontroller that produces an I/O signal, which, in turn, activates an indoor fan to lower the room’s CO₂ level. The HVAC thus maintains an acceptable air quality in the monitored space.

Figure 5: Illustration of CO2 monitoring in a home setting, 26 ft x 21 ft space, with 1 occupant(Source)

Figure 5: Illustration of CO₂ monitoring in a home setting, 26 ft x 21 ft space, with 1 occupant(Source)

The monitoring of CO₂ in a poorly ventilated space is shown in Figure 5, with the AC system turned off. During the day, with only one occupant present and an open patio door (first dip in the curve), there was a significant drop in the CO₂ level. The occupant was always approximately 1 to 2 ft distant from the sensor, working on a laptop with a regular breathing pattern. The latter part of the curve indicates the person exiting the enclosed space, causing the curve to decrease from higher levels of CO₂ to a healthier (green) air quality in the room.

Readings were taken every minute, with the graph quickly updating to mirror changes in the CO₂ concentration. This monitoring is essential in smaller settings with higher occupancy, clearly showing the need for improved airflow.

Total volatile organic compounds (TVOC) detection for better air quality in indoor infrastructures

Volatile organic compounds (VOCs) are the primary contributors to poor indoor air quality. They monitor pollutants like detergents, perfumes, cooking ingredients, etc., in critical places, such as schools, public buildings, and homes.

Figure 6: Sources of the TVOC inside a Home (Source)

The sources of volatile organic compounds are shown in Figure 6. Depending on the interior decoration and use patterns, different organic compounds can simultaneously contaminate a room. The health risks associated with VOC exposure depend on the concentration levels of these compounds. Hence, it is vital to use reliable and sensitive instrumentation to detect their concentrations.

Renasas’s gas sensor ZMOD4410 is compact and easy to implement, making it uniquely capable of monitoring the TVOC in various locations over an extended product lifespan.

Indoor Air Quality (IAQ) Sensor for assessing TVOC concentration in an Indoor environment

Figure 7: ZMOD4410(Source)

The Renesas ZMOD4410 Gas Sensor Module monitors indoor air quality (IAQ) by detecting the TVOC. It can estimate CO₂ levels, taking advantage of the fact that the gas is easier to detect than TVOC. The sensor module can reliably estimate the correlation between TVOC and CO₂ concentration in indoor environments. The module can work effectively in various conditions, including humid and dusty applications where water spray, condensation, or immersion can occur. The sensing element is a Si-based microhotplate with a robust and highly sensitive metal oxide (MOx) chemiresistor.

MOX-based TVOC sensors measure TVOC concentration and use this data to estimate the human-generated CO₂ concentration (eCO₂) base. Equation 1 shows the proportionality constant.

eCO₂=a*b+TVOC -------- Equation 1

where b is the ratio between the humanly generated CO₂ and TVOC, and a is a constant offset.

Specific boundaries are established to increase the accuracy of the estimated CO₂ concentration, with the minimum concentration being the earth's atmosphere CO₂ concentration, about 400 ppm. Users can expect indoor concentrations to stay within this value. Maximum concentrations are unlikely to exceed 5000 ppm in-home or indoor environments.

Figure 8: Example of a TVOC Measurement and corresponding eCO2 in a Kitchen(Source)

Figure 8: Example of a TVOC Measurement and corresponding eCO₂ in a Kitchen(Source)

A measurement series taken in a kitchen over one hour is shown in Figure 8. At the beginning of data acquisition, as people enter and exit the kitchen, both TVOC (ordinate y-axis in mg/m3) and eCO₂ (ordinate y-axis in ppm) level rises because of human respiration activity or release of CO₂. However, during cooking, only the TVOC level rises from kitchen odors while the eCO₂ level remains constant.

Sensors for sustainable agricultural practices

Due to adverse environmental impacts, farmers face pressure to abandon traditional farming techniques like burning crop residues and intensive tillage. Additionally, cattle rearing produces methane (CH4) through enteric fermentation (digestive processes) and manure management, further increasing environmental concerns. Sensors designed for sustainable farming offer technological solutions to increase productivity and a more cost-effective operation, reducing the agricultural byproducts with GWP. For example, these sensors prevent disease and improve herd health by closely monitoring individual animal health and adjusting their nutrition correspondingly. They also help scrutinize soil conditions, allowing a targeted application of pesticides and fertilizers.

Figure 8: NTAG smart sensor(Source)

NXP’s NTAG SmartSensors provide insight into animal wellness, soil conditions, and optimized growing conditions, among many others. The IC of NHS3152, an NTAG SmartSensor product family member, is optimized explicitly for therapy adherence monitoring and logging. It has an embedded NFC interface, an internal temperature sensor, and a direct battery connection. These features support an effective system solution with minimal external components and a single-layer foil implementation for pill usage monitoring. It works either battery-powered or NFC-powered. It contains multiple features, including power-down modes and a selectable CPU frequency of 8 MHz and down for ultra-low power consumption.

Farnell has partnered with suppliers catering to various environment sensors and related accessories such as Gas detection sensors, humidity sensors, PH sensors, Air quality sensors, Temperature sensors, TVOC sensors

Conclusion

Sensing technologies hold immense potential for tackling environmental issues and fostering a sustainable future. Sensors such as CO₂ sensors and TVOC sensors help to maintain Indoor air quality by monitoring the release of greenhouse gases from household appliances. These are essential for a habitable environment. Similarly, using sensors to determine the adequate quantity of fertilizers required in farming and livestock management can reduce the hazardous byproducts from the agricultural sector. By adopting and promoting green technologies, we can curb CO₂ emissions and improve the overall quality of our environment.