Indoor Air Contaminant Monitoring with Return Air Fraction Analysis
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Solution Overview
Problem
Existing air quality monitoring systems struggle to accurately determine indoor air contaminant levels independent of outdoor air contaminants in spaces with return air handling units, leading to inaccurate dilution ventilation control and potential HVAC system overload.
Innovation Solution
A system comprising a first air contaminant sensor for a partially enclosed area, a second sensor for the supply air outlet of the return air handling unit, and a processor to determine the return air contaminant fraction, allowing for precise calculation of indoor air contaminant levels by accounting for the return air fraction and filtration porousness.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If outdoor air contaminants are pulled into the building through the air handling unit, then the indoor space receives fresh air supply, but the level of indoor air contaminants cannot be accurately determined independent of outdoor air contaminants
Solution Approach 1:
The patent segments the air contaminant monitoring into multiple measurement points: outdoor air contaminants, return air contaminants, and indoor space contaminants. By measuring at these separate locations and using the relationship between them, the system can determine indoor contaminant levels independent of outdoor sources without requiring a single complex sensor that directly isolates indoor contaminants.
Solution Approach 2:
The return air serves as an intermediary medium that carries information about both outdoor and indoor contaminants. By measuring contaminants in the return air and comparing them to outdoor air levels, the system uses the return air as a mediator to calculate the portion of contaminants that are truly indoor-generated, thereby achieving accurate indoor air quality assessment.
2Loss of energy
If return air is recirculated back into the indoor space instead of being exhausted, then energy efficiency is improved, but the accuracy of dilution ventilation control deteriorates
Solution Approach 1:
The system implements feedback by continuously measuring contaminant levels in the return air and using this information to calculate the actual indoor contaminant generation rate. This feedback loop allows the system to maintain accurate contaminant level determination even with high return air recirculation ratios, enabling precise control of dilution ventilation while preserving energy efficiency.
Solution Approach 2:
The patent changes the measurement parameter from direct indoor contaminant concentration to the rate of contaminant generation by analyzing the difference between return air and outdoor air contaminant levels. This parameter transformation allows accurate indoor air quality assessment independent of the return air recirculation ratio, maintaining measurement precision while allowing energy-efficient high recirculation operation.
3Reliability
If filters in the air handling unit reduce outdoor air contaminants, then the supply air quality is improved, but the ability to accurately measure indoor air contaminants independent of outdoor contaminants is reduced
Solution Approach 1:
The system extracts the outdoor air contaminant component from the total return air contaminant measurement by comparing return air levels to outdoor air levels. By taking out the outdoor contribution mathematically, the system can determine the indoor-generated contaminant portion independent of filter performance, maintaining measurement precision while allowing filters to improve supply air quality.
Data Source
AI summary
Methods and apparatus for determining indoor air contaminant levels independent of outdoor contaminant levels. In one embodiment, an infinite geometric series is used to compute a true indoor air contaminant level in a room.