HVAC Filter Clog Sensing Under Variable Blower Speeds
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Solution Overview
Problem
Existing methods for determining when a gas filter in HVAC systems needs to be changed are affected by changes in blower speed, which can either mimic or hide filter clogging, leading to inaccurate readings.
Innovation Solution
A sensing system that compares measurements taken during monitoring events to earlier calibration measurements to account for changes in blower speed, recalculating the clog threshold as needed, without requiring additional sensors for air flow or blower fan speed.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If blower speed changes are monitored to detect filter clogging, then filter condition detection is enabled, but false readings occur due to blower speed variations mimicking or hiding clogging
Solution Approach 1:
The system performs calibration measurements when the blower is operating at a known stable speed to establish baseline values. This preliminary action creates reference data that can be used to detect subsequent changes in filter condition, allowing the system to distinguish between readings caused by filter clogging versus those caused by normal blower speed variations.
Solution Approach 2:
The system continuously compares current measurements against stored calibration values and uses this feedback to determine whether filter clogging has occurred. By monitoring changes in the relationship between current and baseline measurements, the system can reliably detect filter condition while compensating for blower speed variations.
2Measurement precision
If additional sensors for air flow or blower fan speed are added to compensate for speed changes, then measurement accuracy improves, but device complexity increases
Solution Approach 1:
The system uses the existing blower motor's electrical characteristics to infer blower speed information without requiring separate speed sensors. By monitoring voltage, current, or power consumption of the motor, the system self-generates the compensation data needed to correct filter clogging measurements, eliminating the need for additional air flow or speed sensors.
Solution Approach 2:
The existing motor sensors serve multiple functions: they control blower operation and simultaneously provide speed compensation data for accurate filter clogging detection. This multi-functionality allows the system to achieve high measurement precision without adding dedicated sensors for each function.
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
This approach ensures accurate detection of filter clogging by distinguishing between valid and invalid readings due to blower speed changes, allowing for timely filter replacement without unnecessary changes.
Implementation Method 1
If air flow velocity is greater, then more energy is dissipated away from the heated sensor.
Implementation Method 2
a first temperature sensor, which is coupled to a heater, and a second temperature sensor, which is unheated, are positioned in a duct
Data Source
AI summary
A sensing system and method for use with a gas filter in a gas conduit attached to a gas blower, having a motor for producing a first gas flow blower speed, discards readings taken when the blower is off or during blower startup and shutdown, and recalculates a clog threshold in response to changes in the fan speed of a multi-speed blower.