Flow Sensor Output Compensation for Below-Range HVAC Valve Control
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Solution Overview
Problem
HVAC systems face challenges in accurately measuring and controlling fluid flow rates outside the working range of flow rate sensors, leading to unreliable measurements and difficulty in reaching desired flow setpoints.
Innovation Solution
A system that includes a flow rate sensor and a controller capable of calculating a corrected flow rate by determining a minimum valve position threshold and a minimum flow rate threshold, using interpolation functions such as polynomial or exponential functions, to compensate for measurements outside the sensor's working range.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Measurement precision
If a flow rate sensor is used to measure flow rate, then flow rate measurement is enabled, but measurements become unreliable when flow rate is outside the sensor's working range
Solution Approach 1:
The patent introduces an intermediary calculation process that uses the relationship between valve position and flow rate to estimate actual flow rates when sensor readings are unreliable. The controller acts as a mediator between the valve control system and the flow rate sensor, using mathematical models to compensate for measurement errors outside the working range.
Solution Approach 2:
The patent replaces direct mechanical sensor measurement with a computational approach. Instead of relying solely on the physical sensor to accurately measure all flow rates, the system uses mathematical calculations based on valve position and differential pressure to substitute for direct measurement when the sensor is outside its reliable range.
2Reliability
If the flow rate sensor working range is limited, then the sensor can provide reliable measurements within that range, but the system cannot accurately control flow rates outside that range
Solution Approach 1:
The patent makes the flow control system universal by enabling it to handle both within-range and out-of-range flow conditions using a single integrated approach. The controller combines direct sensor measurement for reliable readings with calculated estimates for out-of-range conditions, allowing the system to function effectively across the entire possible flow range rather than being limited to the sensor's narrow working range.
Solution Approach 2:
The patent changes the approach from relying on a fixed sensor parameter (working range) to using variable parameters including valve position and differential pressure. By monitoring how these parameters change together, the system can determine actual flow rates even when the sensor reading parameter becomes unreliable outside its specified range.
3Ease of operation
If no compensation is made for out-of-range measurements, then the system is simple, but the system cannot reach desired flow setpoints when actual flow is below minimum readable flow
Solution Approach 1:
The patent applies preliminary action by pre-establishing the relationship between valve position and flow rate characteristics before actual control is needed. The system proactively monitors whether the sensor is within its working range and preemptively switches to calculated estimation mode when out-of-range conditions are detected, preventing control failures before they occur.
Data Source
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AI summary
A system for monitoring and controlling flow rate of a fluid through a valve, the system including a flow rate sensor configured to measure the flow rate of the fluid through the valve, and a controller in communication with the flow rate sensor. The controller is configured to receive the measured flow rate from the flow rate sensor and determine if the measured flow rate is equal to a predetermined flow rate value. In response to determining equality, the controller is configured to determine a minimum valve position threshold (xmin), and determine a minimum flow rate threshold (ymin) corresponding to xmin. The controller is further configured to calculate a corrected flow rate (ŷf) using xmin, ymin, and an indication of valve position (v). Additionally, the controller is configured to control a valve operation using the corrected flow rate (ŷf).