Valve assembly with low flow compensation for proportional variable deadband control
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Solution Overview
Problem
Proportional variable deadband control (PVDC) in HVAC systems faces challenges in achieving fast response times and fully closing valves during low or no flow conditions, as it may result in slow response times and inability to achieve a fully closed valve position.
Innovation Solution
A system and method that includes a valve and actuator with a flow rate sensor and controller, using a proportional variable deadband control technique to determine actuator positions, and implementing a low flow compensation setpoint with a negative flow rate value to bypass the deadband region and achieve a fully closed valve position when low flow criteria are met.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Stability of the object's composition
If proportional variable deadband control is used to maintain desired flow rates, then control stability is improved, but response time deteriorates during low or no flow conditions
Solution Approach 1:
The deadband parameter is made dynamic rather than fixed. The controller adjusts the deadband width based on operating conditions: a larger deadband is applied during normal flow conditions for stability, while the deadband is reduced or eliminated during low or no flow conditions to enable faster response and full valve closure.
2Stability of the object's composition
If proportional variable deadband control is used to prevent valve oscillation, then valve stability is improved, but the ability to achieve fully closed valve position deteriorates during low flow conditions
Solution Approach 1:
Different control strategies are applied to different operating conditions. During normal flow conditions, PVDC with a larger deadband maintains valve stability. During low or no flow conditions, the controller switches to a different strategy with reduced or zero deadband to achieve precise full closure, ensuring each operating regime receives the appropriate control quality.
3Use of energy by moving object
If a larger deadband is used in PVDC to reduce control activity, then energy consumption is reduced, but control precision deteriorates during low flow conditions
Solution Approach 1:
The deadband parameter is dynamically adjusted based on flow conditions. During normal operation, a larger deadband reduces unnecessary control activity and energy consumption. During low flow conditions, the deadband is reduced or eliminated to improve control precision and enable full valve closure, optimizing the trade-off between energy consumption and control precision for each operating regime.
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
Enables faster response times and ensures the valve can be fully closed, even during low or no flow conditions, improving control precision and energy efficiency in HVAC systems by shifting the deadband to increase error and drive the valve to a zero flow position.
Implementation Method 1
In some embodiments, the flow rate sensor is an ultrasonic flow rate sensor.
Data Source
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AI summary
A system for controlling a flow rate of a fluid through a valve is provided. The system includes a valve and an actuator. The actuator includes a motor and a drive device that is coupled to the valve for driving the valve between multiple positions. The system further includes a flow rate sensor and a controller that is communicably coupled with the flow rate sensor and the motor. The controller is configured to receive a first flow rate setpoint, determine a first actuator position setpoint using a proportional variable deadband control technique based on the first flow rate setpoint and a flow rate measurement, and receive a second flow rate setpoint. In response to a determination that certain low flow criteria are satisfied, the controller is configured to determine a second actuator position setpoint using the proportional variable deadband control technique based on a low flow compensation setpoint.