Office buildings, school buildings and other commercial buildings use traditional fixed air volume ventilation, excessive fresh air during the vacancy period, ventilation energy loss of 20%-50%. On-demand ventilation DCV is the mainstream energy-saving program, and the CO₂ sensor is the core sensing hardware of the system.
In this paper, we will dismantle the core knowledge from the seven dimensions of sensor definition, indoor CO₂ hazards, on-demand ventilation principle, linked energy-saving mechanism, revenue data, equipment selection and optimization scheme, answer the frequently asked questions of operation and maintenance, and compare and contrast the unique advantages of the carbon dioxide sensors adapted to the energy-saving system of DCV.
What is a CO₂ Sensor?
Carbon dioxide sensor is a special air quality monitoring hardware for HVAC buildings, which uses ppm (parts per million) as the standard unit of measurement, and collects real-time CO₂ concentration value of indoor environment around the clock.
The device can be adapted to offices, classrooms, supermarkets, computer rooms and other types of confined commercial space, linkage of fresh air units, central air conditioning and building BMS self-control system, independently complete the indoor air quality monitoring, exceeding the safety alarms, ventilation air volume intelligent adjustment of the three core functions.
Relying on accurate concentration sampling data, it provides the basis for the regulation of on-demand ventilation DCV system, which is an indispensable core sensing component in the energy-saving renovation of intelligent buildings and ventilation compliance projects.
Why CO₂ Levels Matter in Buildings
CO₂ as a Ventilation Indicator
With a baseline outdoor CO₂ concentration of 400-420ppm and a human breath concentration of 35,000-50,000ppm, it is easy for CO₂ to build up in areas where people gather. The higher the indoor CO₂ concentration, the insufficient fresh air ventilation and the accumulation of various air pollutants.
ASHRAE 62.1 Official Grading Standards for Commercial Ventilation: 800ppm or less for good ventilation; 800-1000ppm for compliance; 1000-1500ppm for discomfort; 2000-5000ppm for excessive air quality and health risks.
Health and Cognitive Effects
High indoor carbon dioxide concentrations can directly cause drowsiness, headaches, dry throat, and loss of concentration. A joint experiment by Lawrence Berkeley National Laboratory and Harvard University confirms that people’s decision-making and logical processing abilities are significantly reduced when indoor concentrations exceed 1000ppm;
Excessive CO2 in school buildings reduces student concentration and increases absenteeism; excessive CO2 in office space directly reduces team productivity, exacerbates sick building syndrome, and raises the probability of respiratory germs spreading.
Impacts on Productivity and Learning
At this stage, all new buildings are sealed and insulated to minimize air conditioning heat and cold loss, but the airtight structure will block natural ventilation. If we rely on traditional constant fresh air ventilation, air quality will reach the standard but energy consumption will soar; if we reduce the amount of fresh air to save energy, carbon dioxide will exceed the standard and the indoor environment will deteriorate, and carbon dioxide sensing linkage on-demand ventilation is precisely the optimal solution to balance the contradictions between the two.
What is Demand Controlled Ventilation (DCV)
Demand-Controlled Ventilation (DCV) is an intelligent HVAC control technology for modern intelligent buildings, completely abandoning the traditional HVAC model of constant fresh air supply throughout the day. The system relies on real-time sensing data such as indoor CO₂ concentration, personnel presence load, etc., to dynamically and automatically adjust the amount of outdoor fresh air introduced;
After the personnel leave the scene and the CO₂ concentration falls back to the safe zone, the ventilation frequency and air volume are automatically reduced to minimize the energy consumption of fresh air cooling and heating treatment. This model accurately supplies fresh air on demand, balancing the three core needs of indoor air quality, personnel comfort and building HVAC energy consumption control, and is the mainstream technical solution for energy-saving transformation of commercial buildings.
Core Components
- Environmental sensing unit: the system data acquisition, high-precision carbon dioxide sensors as the main control monitoring equipment, with the human body occupancy sensors as a supplement, real-time collection of indoor CO₂ concentration, space personnel present in the state of the two major core data for ventilation control to provide a real environmental basis.
- Building automation BMS controller: the core of the system computing center, receive the data back from the sensing unit, the ASHRAE ventilation standard preset thresholds against the calculation and analysis, issued air volume adjustment instructions, coordinating the whole area of HVAC equipment to operate in tandem.
- HVAC Execution Unit: The execution end of the system on the ground contains three types of equipment: fresh air damper, variable air volume VAV fan, and air handling unit, which opens and closes the damper and adjusts the speed of the fan according to the instructions of the controller to accurately control the amount of fresh air introduced from the outdoor area, and to complete the dynamic adjustment of the ventilation air volume.
How CO₂ Sensors Enable DCV
Why CO₂ Sensors Are Ideal for DCV
- Strong correlation between supply and demand: the human body is the main source of indoor CO₂ emissions, CO₂ concentration can accurately reflect the number of people in real time, and directly determine the demand for fresh air ventilation, and regulate and match the real ventilation load of the building.
- Advantage of senseless monitoring in the whole area: the traditional infrared occupancy sensors can only detect the activities of people in local areas, there are detection blind spots, people sitting still and omission of judgment; CO₂ belongs to the whole area of diffusion-type gases, which can comprehensively reflect the degree of accumulation of pollutants of the human metabolism of the entire region, without the need to align the personnel, there is no detection of the dead zone, the monitoring dimension is more in line with the needs of the whole area of ventilation control.
How CO₂ Sensors Enable DCV: Step-by-Step
Real-time collection
The project commonly used wall-mounted, duct return type two types of DCV dedicated carbon dioxide sensors, strictly follow the HVAC industry installation standards, uniformly installed in the 0.9-1.8m human breathing height interval, while avoiding fresh air outlets, doors and windows convection area, direct sunlight heat source and other interference points, to avoid airflow, temperature interference caused by data deviation.
Equipped with a high-precision NDIR sensor chip, the device collects real-time ppm concentration of CO₂ around the clock, with stable sampling frequency and very low signal transmission delay, which can accurately capture the changes in air quality in the sub-area, and truly restore the indoor air conditions in the whole area, and provide an accurate source of data for the subsequent ventilation regulation.
Threshold Comparison
Building BMS built-in ASHRAE 62.1 commercial ventilation official standard thresholds, real-time access to the baseline concentration of outdoor natural CO₂ across the region to do the difference in accounting, abandoning the stereotypical pattern of a single indoor concentration determination.
The system combines multiple parameters such as space area, number of residents, and fresh air design air volume to intelligently classify three types of air working conditions, namely, safety standards, mild exceedance, and severe exceedance, and sends out differentiated damper opening and fan speed commands according to the classification standards to realize fine-graded ventilation regulation and control, taking into account both energy-saving effects and the safety bottom line of indoor ventilation.
Linkage Execution
Linkage execution: When the indoor CO₂ concentration is lower than the preset safety threshold and there are fewer people in the space, the BMS controller issues speed reduction commands, reduces the opening of the fresh air damper, lowers the operating speed of the fresh air blower, reduces the volume of the outdoor fresh air introduced, and reduces the ineffective energy consumption of the new air for heating, cooling, and dehumidification;
When the concentration of CO₂ exceeds the standard due to the gathering of people, the system automatically opens the fresh air valve and raises the fan airflow to quickly introduce clean fresh air from outdoors, efficiently diluting indoor human metabolic waste gas, suspended germs and odor pollutants, and quickly restoring a high-quality indoor air environment.
Closed-loop Fine-tuning
The carbon dioxide sensor returns real-time indoor CO₂ concentration data uninterruptedly in both directions, and builds a fully automatic closed-loop self-control circuit with the building BMS controller and the fresh air execution equipment, and the system relies on the real-time numerical value to dynamically fine-tune the opening of the air valves and the speed of the fans, and finely control the supply of fresh air.
This mode can avoid the two major problems of excessive energy consumption of fresh air and insufficient fresh air to exceed the air quality standards, balance the three major needs of building energy saving, human health and ventilation compliance, and guarantee the long-term stable operation of DCV system.
Three Types of Mainstream Ventilation Control Mode
At present, the industry DCV on-demand ventilation system is divided into three types of mainstream control modes, adapting to different building industry, control standards and project budgets, with obvious adaptability differentiation:
- Basic proportional control: cost-effective control program, suitable for general commercial buildings with limited budgets and low indoor ventilation control standards, with simple operation and maintenance logic and low difficulty in transforming and landing.
- PID differential precision control: air volume speed regulation is gentle, airflow fluctuation is very small, excellent physical comfort, suitable for classrooms, open office areas and other high-frequency indoor ventilation requirements of the physical sense of the resident space.
- CO₂ + human occupancy dual-mode linkage control: combined with the presence of personnel, indoor CO₂ concentration of dual data linkage control, to eliminate ineffective fresh air supply, energy saving control with the highest precision, suitable for high-standard intelligent buildings.
Energy and Cost Savings
Typical Energy Savings
Special ventilation energy consumption of air handling units: against the traditional all-weather constant fresh air mode, equipped with CO₂ sensing linkage DCV system, the project field measurement of ventilation energy saving range of 14%-49%, excluding the interference of extreme working conditions, the industry’s overall median energy saving rate of up to 34%, the higher the frequency of movement of people in the space, the more prominent the effect of ventilation to reduce consumption.
Building-wide comprehensive HVAC energy consumption: covering cooling, heating, fresh air full-dimension HVAC load accounting, building overall comprehensive energy saving of 9%-33%; affected by the difference in energy consumption of fresh air cooling and heating, the winter fresh air heating gain in alpine heating areas is significantly better than the summer fresh air cooling energy-saving gain in southern high-temperature areas.
Cost Savings Metrics
Against the traditional fixed-air volume fresh air operation and maintenance mode, equipped with CO₂ linked DCV system transformation, commercial buildings save HVAC water and electricity, equipment loss and comprehensive operation and maintenance costs of about 0.09 U.S. dollars per square foot per year;
According to the fresh air volume accounting, each cubic foot of fresh air volume annual average savings in energy costs of 0.35-1.14 U.S. dollars. The higher the frequency of personnel movement, the longer the vacancy period of the office, education and training, assembly space, invalid fresh air reduction is greater, the energy consumption pressure drop is more significant, long-term operation and maintenance savings far more than the confined permanent space.
Payback Periods and Costs
Combined with the cost of the field project and annual energy saving data accounting, the whole set of carbon dioxide sensing + fresh air self-control retrofit project payback period range of 1-5 years; crowded, high proportion of vacant hours of the school building, office complex quality conditions, the shortest only 0.4 years to recover the transformation investment.
Cost level, single-area carbon dioxide sensing supporting self-control integration kit costs about $ 1500, the core NDIR carbon dioxide sensor single product market price of only $ 200-400, low hardware procurement costs, no large amount of reconstruction costs, superimposed on the 5-10 years of long service life of the equipment, depreciation costs are extremely low, the medium- and long-term energy-saving back to the cost of the advantage is very prominent.
Benefits of Using CO₂ Sensors in DCVs
Major Energy Savings
Relying on the dynamic on-demand fresh air logic, it can accurately reduce the energy consumption of ineffective fresh air cooling and heating, dehumidification and humidification processing, reduce the total power consumption of gas heating and electric power refrigeration from the source of HVAC and steadily reduce the annual carbon emissions of the building, which is in line with the low carbon control of the park.
The energy saving of governmental and enterprises, and the dual carbon assessment of a number of mandatory indicators, and help the building complete the annual low carbon accounts to meet the standard.
Improved Indoor Air Quality (IAQ)
The system is fully compliant with ASHRAE 62.1 International Fresh Air Ventilation Standard and California Title 24 Commercial Building Ventilation Control Regulations, relying on CO₂ concentration closed-loop self-control to dynamically equalize the amount of fresh air supply, avoiding the two major drawbacks of the traditional fixed-air-volume ventilation of excessive waste of fresh air and insufficient fresh air air quality exceeding the standard;
and comprehensively meeting the requirements for building fire verification, annual HVAC inspection, and the full process of residential construction and ventilation compliance audit, eliminating the need to manually review and rectify the air volume. Eliminate the need for manual air volume review and rectification work.
Optimize Indoor Temperature and Humidity
During the rainy season and coastal high humidity climate, the system actively controls the volume of high humidity outdoor fresh air introduced into the room, eliminating the uncontrolled influx of humidity into the room, stabilizing the indoor temperature and humidity in the comfort zone of the human body for a long time, reducing the corners of the walls, the inner walls of the air ducts;
and the condensation of air-conditioning unit mold and mildew, reducing the HVAC disinfection, air duct cleaning, and mold control maintenance frequency, and reducing the cost of manpower and consumables for the logistics and maintenance of the building.
Sustainability and Compliance Benefits
Compliance landing CO₂ sensing linkage DCV on-demand ventilation renovation project, complete information can be declared LEED green building, the national standard green building special scoring points, the transformation of the construction volume is small.
The input cost is low, no need to large-scale transformation of the HVAC mainframe, you can pull up the green rating of the building, the valuation of the assets, to enhance the core competitiveness of the commercial leasing, property investment and empowering the building long-lasting asset value added.
Better Humidity and Comfort Control
The system follows the indoor personnel load to dynamically fine-tune the fresh air temperature and air volume, avoiding the stuffy feeling of carbon dioxide buildup in confined spaces, and eliminating the physical drawbacks of the harsh cold air brought by the direct supplemental fresh air in winter;
The hot air brought by the fresh air in summer, so as to optimize indoor air comfort across the board, significantly reduce the discomfort of the personnel and air conditioning complaints, and optimize the spatial experience of the whole scenario of office, teaching and commercial consumption.
Choosing the Right CO₂ Sensor for Your Building
Key Performance Specifications
Accuracy Compliance Requirements: Comply with ASHRAE Industry Ventilation Accuracy Specification, with measurement error ≤±75ppm, and preferably equipped with ABC automatic baseline calibration function to avoid numerical drift in the long run;
Working Conditions and Range Selection: Suitable for 0-50℃, 0-85%RH building wide temperature and humidity operating environment; 0-2000ppm range is preferred for regular office commercial space; 0-10000ppm large range special model is selected for chemical industry, confined warehouse and other high-risk industrial scenarios.
Integration and Compatibility
- Single-channel NDIR sensor: suitable for office buildings, classrooms, street stores and other intermittent operation of the building, relying on the night unoccupied time to complete the baseline calibration, the overall cost-effective and outstanding, suitable for conventional energy-saving renovation projects.
- Dual-channel NDIR sensor: Suitable for hospitals, scientific research laboratories and other 24-hour all-weather operation buildings, no vacancy calibration window period, stronger anti-interference ability, long-term stability of baseline values, suitable for high-standard wind control and ventilation scenarios.
Placement and Coverage
Communication and installation selection rules: the wired sensor is natively adapted to BACnet, Modbus two mainstream industrial communication protocols, strong compatibility, can be seamlessly connected to the Corestar full range of mainstream building automation systems, stable data transmission, anti-electromagnetic interference ability, suitable for new standardized intelligent buildings;
Inventory of old building renovation, subject to pipeline construction, ceiling modification restrictions, preferred Bluetooth, LoRa wireless wiring-free models, convenient construction, lower transformation costs. On-site installation height uniform control 0.9-1.8m human respiratory sampling area, the whole process away from doors and windows convection position, fresh air outlets direct light points, heat source light area, from the source of installation to ensure that the CO₂ sampling data is accurate and reliable.
Cost and Lifecycle
The standard service life of regular NDIR carbon dioxide sensor can be up to 5-10 years, the industry preferred Senl, Siemens, Corestar, Belimo, Infineon and other first-tier brand products; before the project scale landing, it is recommended to carry out a small-area pilot test, avoiding the interference of on-site temperature and humidity airflow in advance, preventing the sensor from numerical drift, and safeguarding the precision of the system linkage control.
Advanced Optimization Strategies
Control Strategy Hierarchy
Combining the building’s historical pedestrian flow data, quarterly weather forecasts, and campus commuting and teaching scheduling data, and relying on the building automation back-end algorithm modeling, the system predicts the trend of CO₂ concentration during the time period in advance.
By adjusting the opening of the fresh air damper and the air volume of the unit in advance, the traditional concentration-triggered passive ventilation is upgraded to the big data prediction active ventilation, which avoids the peak energy consumption caused by temporary air exchange and improves the comprehensive HVAC energy-saving rate of more than 15% on top of the original energy-saving basis.
Sensor Fusion and Multi-Sensor Approaches
Adopting multi-Sensor Fusion and linkage technology, NDIR carbon dioxide sensors with human occupancy, VOC odor, indoor particulate matter, outdoor temperature and humidity multi-category sensing equipment network linkage, access to the Corestar central control platform for unified joint computing.
The system comprehensively determines the number of people present, the degree of air pollution, the outdoor fresh air temperature and humidity quality of multiple parameters, eliminating the ineffective ventilation action during unoccupied hours and poor-quality fresh air hours, taking into account the multiple needs of ventilation and energy saving, air purification, odor control, adapted to shopping malls, hospitals, complexes and other composite air quality control scenarios.
System-Level and Operational Optimizations
Relying on the backstage of building self-control in the whole region, it optimizes the logic of linkage regulation of air supply temperature, fan static pressure and zone dampers of variable air volume units in buildings, integrates the balanced distribution of the total amount of fresh air in the whole building;
fine tunes the proportion of fresh air in the public areas and independent functional areas, breaks the barrier of single-region independent regulation and control, avoids excessive energy saving in local areas and energy consumption of overloading of fresh air in the rest of the regions, and solves the operation and maintenance pains of imbalance in HVAC energy consumption in the whole region of the building, and uneven heating and cooling. Pain Points.
Emerging and Research-Driven Techniques
Equipped with a new generation of intelligent self-checking operation and maintenance algorithms, it can automatically identify hidden equipment failures such as sensor value drift, new air damper jamming, fan frequency failure, communication disconnection, etc.,
and push maintenance warning in the background pop-up window and mobile terminal at the first time, and the operation and maintenance personnel can just overhaul it at fixed points to guarantee the closed-loop and stable operation of DCV on-demand ventilation throughout the year, and to prevent the system from failing as a result of hardware failures, and to return to the mode of high-energy-consuming fixed-air-volume ventilation.
Hybrid Zonal Demand-driven Ventilation Strategy
The implementation of zoned differentiated on-demand ventilation control strategy is suitable for complex buildings with complex functional zoning: meeting rooms, lecture halls and other high-density resident areas, relying on Corestar linkage CO₂ sensors for dynamic frequency conversion ventilation;
Corridors, lobbies, equipment aisles and other public access areas, set up a fixed low air volume duty ventilation, taking into account the public basic ventilation compliance and zoning precision consumption reduction, suitable for commercial and residential integration, office support commercial, campus complexes of multiple industry buildings.
Implementation Tips and Considerations
- Installation error: the sensor is installed close to the air outlet, heat source, and direct area, the airflow and temperature interference will cause CO₂ sampling distortion, resulting in the Corestar automatic control system air volume regulation and control error, ventilation compliance, energy saving effect is all invalid.
- Low-cost hardware pit: the project compression costs, abandon the regular NDIR sensor, choose poor quality electrochemical sensors, the equipment is easy to numerical drift, signal failure, resulting in the failure of the DCV linkage, the system returns to the high-energy fixed-air-volume mode of operation.
- Omit commissioning and acceptance: the completion of the Corestar center control, air valve, unit linkage debugging is not completed, the equipment communication is not sufficient, the response of the new air linkage is lagging behind, and it is not possible to form a closed-loop self-control system.
- Unreasonable threshold setting: The operation and maintenance personnel privately adjusted the CO₂ control threshold downward, and the fresh air supply exceeded the standard, which violated the ASHRAE industry standard and significantly increased the HVAC energy consumption, offsetting all the energy-saving benefits of the DCV system.
Conclusion
The carbon dioxide sensor is the core sensing hardware of the DCV on-demand ventilation system, controlling the precision of ventilation regulation. Compared with traditional ventilation models, the CO₂-linked DCV system can take into account the three values of building energy efficiency, ventilation compliance, and human health. Commercial buildings use compliant NDIR sensors, with Corestar building automation debugging, is a mature, cost-effective intelligent HVAC energy-saving program.
