Demand controlled ventilation, or DCV, adjusts outdoor airflow in response to measured occupancy or indoor air quality signals. It is not the same as VAV or economizer control, which respond to different variables. As one code-screening example, specific editions of the International Energy Conservation Code (IECC) include thresholds above 500 ft² and at least 25 people per 1,000 ft², but applicability also depends on the adopted edition, qualifying system, exceptions, and local amendments.[1]
This guide is for HVAC designers, controls contractors, commissioning providers, facility engineers, and equipment buyers; it covers system concepts, code context, control signals, and fan-selection information, not a project-specific ventilation calculation, sensor layout, wiring diagram, or sequence of operation.
Key Takeaway
DCV resets outdoor ventilation in response to occupancy-related demand. It is not simply fan-speed control: sensors, control logic, dampers or fans, minimum-air requirements, and airflow verification must work as one system.
DCV vs. Fixed Ventilation and VAV: What’s Actually Being Controlled
Demand controlled ventilation changes the amount of outdoor air delivered to a space as occupancy-related demand changes. Fixed ventilation holds outdoor airflow near a scheduled or design value, even when the room is lightly occupied. Variable air volume, or VAV, usually changes total supply airflow to meet a thermal load. An economizer decides when outdoor air can help provide cooling. These functions may operate in the same air-handling unit, but they are not different names for one control strategy.
| System function | What it controls | Typical trigger | Common misunderstanding |
|---|---|---|---|
| DCV | Outdoor ventilation airflow | CO2, occupancy count, schedule, or another IAQ signal | Often mistaken for general fan-speed control |
| VAV | Total supply airflow to a zone | Temperature or cooling and heating demand | Often assumed to control outdoor-air quantity by itself |
| Economizer | Use of outdoor air for cooling | Outdoor and return-air conditions | Often confused with occupancy-based ventilation |
Temperature-driven fan speed in a fan coil unit is also different from DCV because the control objective is room temperature, not outdoor-air demand. If your project involves both systems, treat them as separate control problems rather than assuming one covers the other; that distinction is discussed further in our guide to EC motors for fan coil units.
How a DCV System Works: Sensors, Controllers, and Airflow Response
A demand controlled ventilation system works through three linked layers: sensing, control logic, and airflow response. At the sensing layer, a CO2 sensor, people counter, occupancy signal, or building schedule indicates whether the space is lightly or heavily occupied. CO2 is the gas most often associated with occupancy-based DCV because people generate it during normal respiration, so indoor CO2 concentration can indicate ventilation relative to occupancy, tending to rise when occupancy increases and ventilation is insufficient for that load.
The controller then converts the sensor input into an outdoor-air request. Some systems use a proportional reset between minimum and maximum ventilation levels. Others use staged control, zone-level calculations, or a building automation sequence that combines several signals. The exact sequence varies, but the controller’s job is the same: translate current demand into a target airflow or equipment command.
The execution layer acts on that request. A motorized outdoor-air damper may open or close, an EC fan may change speed, or both devices may respond together. During occupied operation, a low occupancy signal does not automatically mean outdoor air can fall to zero: the sequence may need to retain airflow for the area-related ventilation component, exhaust makeup air, pressure control, or other project requirements. In an established unoccupied mode, however, the system may close the outdoor-air damper if the adopted code and the building’s pressure, purge, and process requirements allow it.
In our experience, one common misunderstanding appears when a high CO2 reading is treated as a sensor problem before you check the ventilation response. A rising reading may be the correct signal. The real question is whether the controller and airflow devices respond as the sequence intended.
Why Facilities Install DCV: Energy, Air Quality, and Compliance
Facilities install DCV to reduce unnecessary outdoor-air conditioning, match ventilation more closely to occupancy, and meet project or code requirements where DCV applies. Outdoor air often needs heating, cooling, dehumidification, or humidification before it enters the occupied space. Reducing excess outdoor airflow during low-occupancy periods can therefore lower the load on the heating and cooling system.
Fan-energy savings need a more careful explanation. Under the fan laws, fan power falls quickly as rotational speed falls, often described by the approximate cube relationship between speed and power for similar operating conditions. But a DCV system only reduces fan electricity when the fan or total supply airflow really slows down. If the system changes only an outdoor-air damper while the main supply fan continues at the same airflow, most of the savings come from reduced outdoor-air heating or cooling rather than from the fan motor.
DCV can also help a system avoid two opposite operating errors: overventilating an almost empty room and failing to increase ventilation when occupancy rises. It does not prove that every indoor pollutant is controlled, but it gives the ventilation system a way to follow a defined demand signal. Compliance is the third reason, because energy codes may require DCV in certain high-density spaces and ventilation standards shape how minimum outdoor airflow is calculated.
The energy result still depends on climate, occupancy pattern, operating hours, control sequence, and the baseline system. So a promised percentage should not be copied from another building. The useful question is which load actually changes in your design: outdoor-air treatment, fan speed, or both.
The Compliance Basis: ASHRAE 62.1 and IECC Requirements
ASHRAE 62.1 and the International Energy Conservation Code address different parts of the DCV question. ANSI/ASHRAE Standard 62.1-2025 is titled Ventilation and Acceptable Indoor Air Quality. Its Ventilation Rate Procedure expresses breathing-zone outdoor airflow as the sum of a people component and an area component:
In this simplified teaching form, Rp × Pz represents ventilation associated with occupants, while Ra × Az represents ventilation associated with the floor area. DCV commonly resets the people-related component as occupancy changes. During occupied operation, reducing Pz does not erase the area-related component; that is one reason the occupied DCV sequence commonly preserves a minimum outdoor-air level. This formula alone does not determine what happens in an approved unoccupied mode, which must be established separately by the project requirements and control sequence.
The IECC addresses when DCV may be required. In editions using the earlier numbering, Section C403.2.6.1 covers demand controlled ventilation. Newer editions may place the requirement under C403.7.1. The cited criteria include spaces larger than 500 square feet, a design occupant density of at least 25 people per 1,000 square feet, and qualifying system conditions such as an economizer, automatic outdoor-air damper control, or design outdoor airflow above 3,000 cfm. Exceptions and wording depend on the adopted edition, system type, and local amendments.
The practical distinction is straightforward. ASHRAE 62.1 helps establish ventilation rates and control logic. The IECC tells you when an energy code requires DCV under defined conditions. You should not treat one as a substitute for the other.
CO2 setpoints also need project-specific interpretation. A value of 1,000 ppm is not a universal health threshold or a universal DCV design value. California requirements provide one example of jurisdiction-specific rules, including control approaches based on outdoor concentration plus 600 ppm in some cases and 1,000 ppm in others. Those figures should not be copied into a project in another jurisdiction without checking the locally adopted code and sequence.
Setpoint debates often appear late, during testing, because someone reused the value from a previous project. That shortcut can create trouble when the occupancy assumptions, sensor basis, or code edition has changed. As ASHRAE’s own position document on indoor carbon dioxide cautions, CO2 also does not represent volatile organic compounds, particles, humidity, or every other indoor contaminant. Meeting a CO2 target does not by itself prove acceptable indoor air quality.
The Execution Layer: How EC Fans Respond to DCV Control Signals
After the DCV controller calculates the required ventilation level, the request must become a physical airflow change. Depending on the system, that change may come from an outdoor-air damper, a variable-speed fan, or coordinated control of both. An EC fan is well suited to this execution layer because its electronic motor controller is built into the motor assembly and can accept a speed command without a separate variable frequency drive.
Current Proventofan product guidance lists 0-10 V DC and PWM speed control across its EC fan families, with optional Modbus RS485 on models other than the 133 mm analog-control model. These interfaces can let a DCV controller or building automation gateway send a speed request to an EC axial fan, centrifugal fan, or plug fan. Because interfaces can vary by model revision and configuration, confirm 0-10 V, PWM, and optional Modbus availability against the current datasheet for the exact model before specifying it.
The interface is only one half of the job. A 6 V analog signal, a 60 percent PWM command, or a Modbus speed value does not prove that the required outdoor airflow reached the room. The actual result depends on the fan curve, duct resistance, damper position, filter condition, pressure changes, and the control mapping. During commissioning, the project team may verify airflow through direct measurement, pressure-based methods, calibrated feedback, or checks at the minimum and maximum operating points.
A 2025 inquiry from a Thailand air-purifier manufacturer shows an analogous sensor-controller-fan signal chain at a smaller equipment scale. It was demand-controlled air cleaning, not a code-compliance DCV installation, because the purifier recirculated room air rather than metering outdoor ventilation air. The customer’s monitoring module measured PM1.0, PM2.5, PM10, CO2, humidity, and temperature; PM2.5 and CO2 were intended to drive an existing 0-10 V DC control box that adjusted centrifugal-fan speed. Proventofan proposed DC centrifugal fan options with 0-10 V or PWM variable-speed control in 96 mm and 148 mm sizes for quotation quantities of 100 and 500 units.
The project had not reached a confirmed order, so the useful lesson is the integration requirement rather than a claimed sales result. The customer had already solved the sensor-output side. If you’re in a similar position, the remaining questions are whether the fan can accept the signal cleanly, run continuously through the required command range, and meet airflow and pressure needs at both ends of that range.
We’ve seen the same pattern in other CO2-driven control discussions. You’ll often start by asking whether a fan has a 0-10 V wire, but the stronger request includes minimum airflow, maximum airflow, static pressure at both points, supply voltage, feedback needs, and the intended control signal. Detailed wiring, PWM ranges, and Modbus register work belong in the model documentation and commissioning plan. Our separate guide explains how to control an EC fan; the EC fan solutions hub provides the wider product and application context.
Where DCV Works Best and Where It Falls Short
DCV works best where the design occupancy is high but the actual headcount changes substantially through the day. In those spaces, fixed outdoor airflow is often sized for a peak that occurs only part of the time. Meeting rooms, classrooms, auditoriums, restaurants, theaters, and shared training rooms are common examples.
Strong-fit situations include:
- Spaces with large and predictable swings in occupancy
- Systems that can reset outdoor airflow while preserving required minimum ventilation
- AHU or dedicated outdoor-air systems with controllable dampers, variable-speed fans, and a defined control sequence
- Projects where the adopted energy code calls for DCV based on space size, occupant density, and system configuration
DCV needs extra caution when:
- Laboratories depend on contaminant control, hood exhaust, or pressure relationships
- Commercial kitchens need exhaust makeup and process-driven ventilation
- Manufacturing spaces release volatile organic compounds, particles, moisture, or process gases
- Occupancy-related CO2 is not the main pollutant or safety driver
We see the strongest DCV interest in rooms where occupancy can move from nearly empty to full within a short period. That fits the engineering logic: the larger the gap between design occupancy and actual occupancy, the more useful demand reset can become. But if your space falls into the second list above, treat CO2-only DCV as a starting point for discussion rather than a default design choice, since a single-contaminant strategy should not be stretched into applications where another contaminant or pressure requirement governs ventilation.
AHUs and dedicated outdoor-air systems are common platforms for DCV because they already contain dampers, controls, filters, and fans. Retrofit questions involving fan arrays and system architecture are covered in our EC plug fan AHU retrofit guide. Fan duty-point selection and AHU application details belong in the AHU fan guide.
That covers the full loop this guide set out to explain: what DCV actually controls, how the sensing-to-airflow chain works, what ASHRAE 62.1 and the IECC require, and where an EC fan fits as the execution device. If your open question is now about a specific fan for a specific duty point, the FAQ and the selection checklist below are the next step.
Frequently Asked Questions
What is demand controlled ventilation?
Demand controlled ventilation is an HVAC control strategy that adjusts outdoor-air delivery according to measured occupancy or an indoor-air signal such as CO2. Instead of supplying the same design airflow at every hour, the system resets ventilation between a required minimum and a higher level as demand changes. The controller may command dampers, variable-speed fans, or both.
What gas is monitored in a demand control ventilation system?
Carbon dioxide is the gas most often monitored in occupancy-based DCV. People generate CO2 during respiration, so indoor concentration can serve as an indirect indicator of occupancy-related ventilation demand. CO2 is not a complete measure of indoor air quality, and it does not represent particles, volatile organic compounds, humidity, or process contaminants.
Does DCV turn off outdoor air when a room is empty?
Not automatically. During occupied operation, a zero or low people count does not by itself eliminate the area-related ventilation component, and the system may also need outdoor air for pressurization, exhaust makeup, or process requirements. A verified unoccupied mode is a different operating state: its outdoor-air damper may be allowed to close when the adopted code and project sequence permit it. Do not use a low CO2 reading alone as proof that zero outdoor airflow is acceptable.
Is demand controlled ventilation the same as VAV?
No. DCV resets outdoor ventilation airflow according to occupancy-related demand. VAV usually changes total supply airflow according to heating or cooling load. A VAV system can include DCV, but one does not automatically provide the other. Economizer control is another separate function because it decides when outdoor air can help meet cooling demand.
Does DCV always reduce fan energy?
No. Fan-energy savings occur when the fan or total system airflow actually decreases. If DCV only adjusts an outdoor-air damper while the supply fan continues at the same speed and airflow, the main savings come from reducing the heating, cooling, or moisture load associated with outdoor air. The result depends on the system arrangement and control sequence.
Is 1,000 ppm the correct CO2 setpoint for DCV?
Not for every project. A 1,000 ppm value appears in some guidance and jurisdiction-specific requirements, but it is not a universal health threshold or a universal design setpoint. California provides one example where control rules may use outdoor CO2 plus 600 ppm in some cases and 1,000 ppm in others. The project team should follow the locally adopted code, ventilation standard, sensor basis, and approved control sequence.
What are the benefits of using DCV?
DCV can reduce unnecessary outdoor-air heating and cooling, keep ventilation closer to current occupancy, and help meet energy-code requirements where the strategy applies. It can also reduce overventilation during lightly occupied periods. Savings and indoor-air outcomes depend on climate, occupancy variation, minimum-air settings, fan control, sensor performance, and commissioning quality.
Can EC fans be used in a DCV system?
Yes. EC fans can act as variable-speed airflow devices in a DCV system when their control interface matches the controller or building automation architecture. Current Proventofan product guidance lists 0-10 V and PWM across its EC fan families, with optional Modbus RS485 on models other than the 133 mm analog-control model; verify the exact interface against the current model datasheet. Model selection still needs the minimum and maximum airflow, static pressure, voltage, signal type, and any feedback or alarm requirements.
Planning a DCV Fan Application?
Prepare the following information before requesting a fan selection.
A useful fan request should describe the system at both ends of the operating range. Include:
- System type, such as DOAS, AHU, or standalone ventilation equipment
- Minimum and maximum outdoor airflow
- Static pressure at the minimum and maximum operating points
- Control signal: 0-10 V, PWM, or Modbus RS485
- Supply voltage and phase
- Required airflow feedback, speed feedback, fault alarm, or communication output
- Space and mounting limits
- Filter, damper, and duct conditions that affect system resistance
This information lets a supplier check the control interface and the actual fan duty together. It also reduces the risk of selecting a fan that accepts the command signal but cannot cover the required airflow and pressure range.
References
- ASHRAE, American Society of Heating, Refrigerating and Air-Conditioning Engineers. ANSI/ASHRAE Standard 62.1-2025: Ventilation and Acceptable Indoor Air Quality. ASHRAE Standards 62.1 and 62.2
- International Code Council. International Energy Conservation Code, Section C403: Demand Controlled Ventilation. Accessed through UpCodes
- ASHRAE. Position Document on Indoor Carbon Dioxide. ASHRAE position documents
- California Energy Commission. 2025 Nonresidential Compliance Manual and Demand Control Ventilation Acceptance Test resources. 2025 Building Energy Efficiency Standards
- U.S. Environmental Protection Agency. Can I Measure Carbon Dioxide Indoors to Get Information on Ventilation? EPA indoor CO2 guidance
Disclaimer
This article gives a simplified explanation of ASHRAE 62.1, IECC provisions, and demand controlled ventilation practice. It does not replace the full standard text, the code edition adopted for a project, approved construction documents, or professional engineering judgment. The California example is included only to show that CO2 setpoints can vary by jurisdiction. DCV design, sensor selection, control programming, testing, and acceptance should be handled by qualified HVAC and commissioning professionals. EC fan control specifications should be confirmed against current Proventofan product documentation for the selected model.
