Zonal demand control ventilation for a building
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Solution Overview
Problem
Conventional Demand Control Ventilation (DCV) methods fail to adjust CO2 levels in individual zones based on the number of occupants, leading to under-ventilation in densely occupied areas and over-ventilation in less occupied zones, resulting in inefficient energy use and inadequate fresh air distribution.
Innovation Solution
A Pulse Width Modulation (PWM) control sequence is employed to decouple breathing air and conditioning air, using 'high outdoor air' and 'low outdoor air' time periods to provide sufficient fresh air to individual zones, allowing for virtual dual ventilation channels in a single duct system, ensuring appropriate ventilation based on occupancy levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Ease of operation
If conventional DCV methods use a single CO2 sensor in the return duct to control outdoor air damper, then the system is simple and energy cost is reduced, but the CO2 level of individual zones cannot be adjusted according to the number of occupants, leading to under-ventilation in densely occupied areas and over-ventilation in less occupied zones
Solution Approach 1:
The patent segments the ventilation control by introducing individual zone CO2 sensors and separate outdoor air dampers for each thermal zone, allowing independent control of fresh air distribution to each zone based on its specific occupancy levels, thereby resolving the inability of conventional single-sensor systems to address zonal ventilation needs
Solution Approach 2:
The patent implements feedback control by using CO2 sensors in each thermal zone to monitor local CO2 levels and automatically adjust the corresponding outdoor air damper positions, creating a closed-loop system that responds to actual zonal ventilation demands rather than relying on building-wide averaged measurements
2Device complexity
If standard single duct systems mix breathing air and conditioning air, then the duct system is simple, but zones with more occupants do not receive enough fresh air while zones with fewer occupants are over-ventilated, wasting energy
Solution Approach 1:
The patent segments the air streams by providing separate outdoor air dampers for breathing air control and separate VAV box dampers for conditioning air control, allowing independent optimization of fresh air delivery and energy conditioning for each thermal zone, thereby eliminating the energy waste associated with over-ventilation
Solution Approach 2:
The patent applies local quality by allowing each thermal zone to have customized outdoor air intake levels based on its specific occupancy and ventilation requirements, rather than applying a uniform fresh air ratio across all zones, thus preventing energy waste in lightly occupied zones while ensuring adequate ventilation in densely occupied zones
3Device complexity
If the AHU outdoor air damper and VAV box dampers are not coordinated, then the control system is simpler, but sufficient outdoor air cannot be ensured for individual zones
Solution Approach 1:
The patent implements coordinated feedback control where the AHU outdoor air damper position is automatically adjusted in response to signals from individual zone VAV box dampers and CO2 sensors, ensuring that the total outdoor air intake is properly distributed to meet the specific requirements of each thermal zone
Solution Approach 2:
The patent applies preliminary action by pre-coordinating the control sequences between the AHU outdoor air damper and VAV box dampers to ensure proper outdoor air distribution before ventilation demands arise, allowing the system to proactively maintain adequate outdoor air supply to all zones
Data Source
AI summary
A method for operating an air handling unit of an HVAC system. The method includes opening an outside air flow control device to enable breathing air flow during a high outdoor air time period to a first zone having a first number of occupants and a second zone having a second number of occupants that is less than the first number of occupants. The outside air flow control device is then closed to enable conditioning air flow during a low outdoor air time period to the first and second zones. Further, a variable air volume (VAV) air flow control device provides desired amounts of breathing air to the first and second zones suitable for the first and second number of occupants, respectively. A VAV air temperature control device then provides conditioning air to the first and second zones having a suitable temperature for the first and second number of occupants.