Demand-Controlled Ventilation
Optimize indoor air quality in modern HVAC
Adaptive ventilation strategies rely on sensor data to improve the indoor comfort and reduce HVAC energy consumption. Monitoring with BAS sensors enables an efficient and smarter environment.
Overview
In modern commercial buildings, creating comfortable and healthy indoor environments while minimizing energy consumption is a top priority. One of the most effective strategies for achieving this balance is Demand-Controlled Ventilation (DCV) – an HVAC control method that adjusts outdoor fresh air ventilation rates based on real-time occupancy and environmental conditions. While multiple components work together in a DCV system, carbon dioxide (CO2), relative humidity (RH), and temperature measurement are central for proper control. The Accuenergy AcuCO2, AcuTEMS, and AcuHUM sensors provide precise and accurate data for Building Automation Systems (BAS) to regulate airflow rates for the right amount of fresh air required to maintain indoor air quality (IAQ), thermal comfort and balanced humidity. This helps to dynamically control the ventilation of the system and reducing energy consumed while maintaining compliance with standards and code.
Figure 1: Overview of Accuenergy Sensors in Building Automation System
About Demand-Controlled Ventilation (DCV)
DCV is a HVAC control strategy that adjusts the volume of outdoor air introduced in a building based on actual occupancy and indoor environmental conditions. Traditional HVAC systems are designed for maximum occupancy and operate at full capacity, which can lead to significant energy waste during periods of low occupancy, as well as over-ventilation or under-ventilation that may lead to poor indoor air quality (IAQ). With DCV, improved energy efficiency and IAQ can be achieved as it aligns the ventilation with the actual demand of the space.
Historically, only CO2 sensors were used to estimate the building occupancy, but Temperature and RH are just as critical where occupancy rate is just not the primary factor. Prime examples for this application include commercial kitchens, testing laboratories, restrooms, fitness centres and similar places with fluctuating humidity. By integrating the crucial temperature and RH sensors data, accurate ventilation control can be achieved.
In the past century, DCV has significantly evolved from inefficient fixed ventilation practices to responsive, data-driven systems that integrate seamlessly with BAS for energy efficient and sustainable systems. With the advancement in sensor technology, increasing awareness of impact of IAQ on health, and stringent energy and ventilation standards by agencies such as ASHRAE and LEED, the need for DCV is reinforced accordingly.
DCV is widely implemented in new construction and integrated into existing buildings by using advanced BAS controls with high-efficiency motors, Variable Frequency Drives (VFDs), HVAC equipment, additional temperature, RH, CO2 and Volatile Organic Compound (VOC) sensors for effective zoned airflow management.
Importance of Temperature and Relative Humidity (RH)
Temperature and RH are the two fundamental indicators of indoor environmental quality. By monitoring these parameters, BAS can monitor beyond occupancy rate and control the system performance, comfort level and long-term physical durability of the building.
- Temperature control can influence the occupant comfort and thermal levels. It also can indicate potential HVAC system performance issues. Unexpected temperature deviations indicate inadequate ventilation, airflow imbalance and signals load shifts caused by occupancy or equipment use.
- Relative Humidity will impact both the human health and structural integrity of the building. High RH can lead to increased mould, microbial activity and respiratory discomfort, whereas low RH causes skin irritation, dryness, static buildup and irritation.
By continuously monitoring temperature and RH parameters, BAS controllers can make intelligent, data-driven ventilation decisions to adjust outdoor air intake, prevent moisture overload, optimize air temperatures.
Mounting Configurations and Accuenergy Sensors in DCV
Accuenergy sensors offer multiple mounting configurations to ensure environmental data is captured at the critical points in the ventilation system such as Duct Mount, Outside Air and Room (Space).
Duct Mount – AcuTEMS-DM and AcuHUM-DM
Duct-mounted sensor is installed directly within the HVAC ductwork, typically within the supply air duct, return air duct, or outside air intake plenum and continuously monitor the moving air streams.
Figure 2: Duct Mount Temperature and Humidity Sensor in AHU
Advantages
- Representative Measurements – Continuously measures the temperature and RH of the moving, well-mixed air within the ductwork, providing average system-level feedback to the BAS for precise ventilation control.
- Ventilation Verification – Confirms that the air being delivered to the space meets programmed set points.
- Fast Response – Detects atmospheric change which enables rapid control adjustments to the HVAC control loop.
Outside Air (OA) – AcuTEMS-OA and AcuHUM-OA
Outside Air sensors measure the temperature and RH of incoming outdoor ambient air before it mixes with the return air. They are typically located near the outdoor air intake of an Air Handling Unit (AHU).
Figure 3: Outside Air Humidity Sensor in AHU
Advantages
- Economizer Control – Enables cooling by comparing the ambient air with the return air which enables the BAS to control the air intake accordingly.
- Humidity Considerations – Prevents the intake of damp or dry air which helps protect the indoor environment.
- Ventilation Quality – Sets a baseline for the fresh air introduced in the building to maintain the IAQ.
Room (Space) Sensors – AcuTEMS-RM and AcuHUM-RM
Room sensors are installed within the occupied zones such as offices, conference rooms and classrooms. They provide the direct assessment of the environmental conditions experienced by its occupants.
Figure 4: Temperature and Humidity Room Sensors
Advantages
- Actual Space data – Allows monitoring the real environmental demand within the building so measurement is not solely dependent on duct-mount sensor.
- Localized control – Enables the BAS to adjust ventilation in a specific room if it requires different environmental conditions.
Benefits of Using Temperature and RH Sensor in DCV
Integrating Accuenergy sensors into a DCV strategy delivers measurable advantages across facility operations:
- Enhanced Indoor Air Quality – Maintains balanced ventilation levels that prevent stale air, and excessive humidity.
- Reduced Energy Costs – Prevents over-ventilation during low occupancy, which reduces the load on the heating and cooling system.
- Improved Comfort – Maintains stable thermal and humidity conditions across occupied spaces.
- Better System Performance – Reducing unnecessary ventilation cycles which extends the lifespan of HVAC systems.
Temperature and relative humidity sensors are indispensable components of advanced demand-controlled ventilation. By feeding accurate, timely environmental data into a BAS, building operators can achieve smarter ventilation control that enhances comf ort, supports health, and reduces energy use.
