Multipoint Exhaust Sampling for Dynamic Fan Setback Control
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Solution Overview
Problem
High plume exhaust fan systems are energy-inefficient and unreliable due to the high energy consumption of bypass airflow, which is not significantly reduced by existing energy conservation measures, and contaminant sensing methods are prone to fouling and inaccuracies, leading to unstable operation and potential health risks.
Innovation Solution
Implement a multipoint air sampling system with sensor protection mechanisms, such as dilution sampling and adaptive sequence delays, to ensure accurate contaminant detection and stabilize exhaust fan operation, and incorporate IoT connectivity for remote monitoring and override features to maintain safe and efficient fan operation.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If exhaust fans operate at high speed continuously to ensure contaminant dispersion, then safety and contaminant removal are improved, but energy consumption increases
Solution Approach 1:
The exhaust fan speed is made dynamic rather than continuous. The system adjusts fan speed based on real-time contaminant detection: high speed when contaminants are present, low or idle speed when air is clean, optimizing both safety and energy consumption
Solution Approach 2:
A feedback control system uses contaminant sensor readings to automatically adjust exhaust fan operation. The sensor continuously monitors air quality and feeds this information back to the control system, which then modulates fan speed accordingly, resolving the contradiction between safety and energy use
2Measurement precision
If sensors are exposed directly to exhaust air for contaminant detection, then detection accuracy is improved, but sensor fouling increases
Solution Approach 1:
An intermediary sampling system is introduced between the exhaust air and the sensor. Air samples are drawn through tubing to the sensor location, allowing the sensor to detect contaminants without direct exposure to the harsh exhaust environment, thus maintaining both detection accuracy and sensor reliability
Solution Approach 2:
The detection system is segmented into separate functions: sampling (drawing air through tubing), detection (sensor in protected location), and control. This segmentation allows the sensor to perform detection without being exposed to conditions that would cause fouling
3Reliability
If bypass airflow is used to dilute exhaust plume, then contaminant dispersion is improved, but energy consumption increases
Solution Approach 1:
The bypass airflow rate is made dynamic rather than constant. The system adjusts bypass flow based on contaminant levels: higher bypass flow when contaminants are detected, reduced or eliminated bypass flow when air is clean, reducing energy loss while maintaining dispersion effectiveness
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The system enables reliable and energy-efficient operation of exhaust fans by reducing sensor fouling and improving contaminant detection accuracy, ensuring stable fan performance and enhanced safety through adaptive control logic and remote monitoring capabilities.
Implementation Method 1
a multipoint air sampling system to sense for the presence of contaminates in the exhaust air
Implementation Method 2
methods of sample dilution
Implementation Method 3
exhaust fan systems which are used to convey exhaust air from a building
Data Source
AI summary
Methods and apparatus for an exhaust demand control system for measuring one or more contaminants at one or more exhaust locations within one or a plurality of exhaust ducts or plenums served by an exhaust fan system. Example systems and methods can include sensing the one or more contaminants within the one or more exhaust duct locations using a multipoint air sampling system having one or more sensors and flow control elements, comparing contaminant concentration measurements from the one or more of said exhaust duct or plenum locations against an action level to create a fan setback signal, and ensuring sensor accuracy and reliability by implementing a sensor protective mode when the contaminant concentration measurements from the one or more exhaust locations exceeds an action level.