See how Willow can help you cut costs, save energy, and operate your buildings more efficiently and sustainably.
Indoor Air Quality (IAQ) is critical when thousands of people gather in environments like airports, hospitals, university campuses, and stadiums. These spaces experience rapid fluctuations in occupancy, which can lead to spikes in CO₂ levels and other pollutants. Traditional HVAC systems often operate on fixed schedules or assumptions, making it difficult to respond dynamically to changing conditions. This can result in compromised comfort, energy inefficiency, and potential health risks.
Demand-Controlled Ventilation (DCV), as touched upon in a previous IAQ blog, changes the game by using real-time data to optimize airflow. By integrating occupancy signals and CO₂ sensors with HVAC controls, DCV ensures ventilation adapts instantly to actual conditions. When IAQ begins to deteriorate during peak gatherings, DCV can increase fresh air intake and maintain healthy environments.
At the same time, energy is conserved during low-occupancy periods. As a result, DCV represents one of the highest-impact, lowest-friction opportunities to reduce energy waste. Ventilation alone is responsible for a significant share of fan, heating, and cooling loads in HVAC systems. Every cubic foot of fresh air brought into a building has to be conditioned, moved, and often reheated at the Terminal Unit. Optimizing ventilation cuts down on energy consumption as well as equipment wear and tear. For facility teams, this can mean healthier spaces, lower operational costs, and a smarter approach to managing IAQ in complex, high-traffic environments.
With Willow, this is realized with seamless integration of sensor data, predictive insights, and automated HVAC adjustments via Active Control. This creates a responsive system that balances air quality, energy costs and sustainability goals. Let’s dig into the details.
In the industry, a key challenge with implementing DCV at scale has been that each of the systems operate in silos. Traditional building automation systems have context of each HVAC Terminal Unit, but they’re rarely aware of the spaces they serve or what the current room occupancy or air quality is.
Willow solves this by creating a unified context in the Knowledge Graph. This connects Terminal Units in the BMS, e.g. VAV boxes, FPBs, FCUs, etc., with spaces they serve like hallways and offices. Space information in Willow includes the exact type and square footage. This is combined with occupancy signals of real-time headcount or presence. To build a digital twin of the building, metadata is pulled directly from design and construction documentation. This means that the system has ground truth about whether a space is a hallway or a classroom. Building documents provide the actual square footage that determines ventilation requirements. Further, a real-time occupancy signal is captured from people counting or monitoring CO2 levels, as opposed to an assumption based on previously determined classroom or meeting schedules.
Willow can ingest telemetry from CO₂ sensors as an additional real-time signal on occupancy and adjust ventilation accordingly. If CO₂ is low, indicating limited occupancy, the system can further reduce airflow. Conversely, when CO₂ rises, indicating high occupancy, Willow automatically increases outdoor air. Airflow is continuously recalculated based on real-time concentration levels.
A Willow Skill that addresses DCV is Setback Terminal Unit Airflow Setpoint Low Limit When Unoccupied.
This ensures that ventilation meets the true needs of the space and is not dictated by a static minimum based on calendar events and schedules. The system is then allowed to reduce HVAC energy consumption while maintaining or even improving indoor environmental quality.
With all of this data linked together, Willow enables ventilation decisions based on space usage.
After hydrating the Knowledge Graph with space types and sizes, Willow’s Activate Technology dynamically calculates building code-required minimum ventilation rates. Referencing an industry standard like ASHRAE 62.1, Willow determines ventilation based on two components: Area Component (Ra × Area), which leverages the space type from ASHRAE tables and scales with the square footage of the room, with the People Component (Rp × People), which depends on the number of occupants. In Willow, this is informed by real-time signals from occupancy sensors.
For many indoor space like offices, classrooms, conference rooms, and training rooms, ASHRAE allows ventilation to drop as low as zero when the space is unoccupied. This is where the energy savings potential becomes transformative.
When Willow is deployed with telemetry streams from room-level occupancy sensors, facility teams can confidently reduce minimum ventilation to 0 CFM whenever a space is unoccupied and ASHRAE allows it. This is especially impactful for intermittent-use rooms. As an example, stadiums are at highest occupancy on game day. Classrooms are often empty for parts of the school day and on weekends. Airport terminals have highest occupancy during the holidays. Conference rooms, meeting rooms and training spaces may have sporadic usage patterns. Historically, buildings ventilate these rooms at fixed minimums of 8 to12 hours per day, wasting energy in the process. Willow eliminates that waste with dynamic calculations and automated control.
Willow’s Active Control brings all the pieces together to automatically adjust HVAC damper positions as occupancy changes over time. Willow’s Skills run continuously in the background. As a result, every few minutes, the system reads occupancy sensors, CO₂ levels, references the space type and square footage, calculates the ASHRAE minimum ventilation requirement and commands updated airflow setpoints to Terminal Units via the BMS. This is DCV running exactly as it was intended: real-time, responsive, and evidence based.
DCV powered by Willow delivers an ideal balance between occupant comfort and operational efficiency. In high-occupancy environments such as bustling terminals, crowded lecture halls, or packed stadiums, air quality can deteriorate quickly as CO₂ levels rise. Willow integrates real-time occupancy and air quality data with HVAC controls, ensuring ventilation ramps up when needed. This proactive approach maintains healthy indoor environments, supporting comfort and well-being without manual intervention.
Conversely, when spaces are empty or lightly used, DCV automatically reduces ventilation to match actual demand. This prevents unnecessary energy consumption, lowers utility costs, and minimizes wear and tear on equipment. Early estimates with customer deployments indicate that buildings can realize significant savings with this approach, and these numbers add up with multi-building portfolios. By dynamically adjusting airflow based on live conditions, Willow enables peak performance during busy periods and energy conservation during downtime. As a result, organizations no longer have to choose between comfort and efficiency, and DCV becomes an operational strategy with Willow.