Supply Airflow Sequence Control With Dual-Sensor Temperature Loops
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Solution Overview
Problem
HVAC systems with multiple temperature affecting devices face challenges in simultaneous control, leading to undesired oscillating control signals, energy inefficiency, and mechanical wear, particularly when using a single sensor and traditional PI or PID controller tuning methods.
Innovation Solution
A system with a common controller receiving values from multiple sensors positioned along the airflow line to control each temperature-affecting device independently, allowing for precise control of supply airflow temperature by adjusting control signals for heating and cooling coils, heat exchangers, and other devices, thereby mitigating oscillations and reducing wear on mechanical components.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Device complexity
If multiple temperature-affecting devices are controlled simultaneously using a single sensor and traditional PI or PID controller, then the system structure remains simple, but undesired oscillating control signals occur with large envelope and high frequency
Solution Approach 1:
The control system is segmented into multiple independent control loops, each with its own sensor and controller. The first control loop controls the first temperature-affecting device using the first sensor, while the second control loop controls the second temperature-affecting device using the second sensor. This segmentation eliminates the oscillation problems associated with single-sensor control of multiple devices.
Solution Approach 2:
Each temperature-affecting device is equipped with its own sensor providing local feedback to its dedicated controller. This localized feedback mechanism allows each controller to independently adjust its device based on actual temperature conditions at its specific position, preventing the oscillating control signals that occur when a single sensor serves multiple devices.
2Ease of operation
If traditional PI or PID controller tuning methods are used with multiple temperature-affecting devices, then the control approach remains conventional and simple, but energy efficiency deteriorates and mechanical wear increases
Solution Approach 1:
The system divides the control functionality into separate segments, with each temperature-affecting device having its own dedicated controller and sensor. This allows each control loop to be optimized independently for energy efficiency, avoiding the energy waste that occurs when multiple devices share a single control loop with conventional tuning methods.
3Device complexity
If a single sensor controls multiple temperature-affecting devices, then the number of components remains low, but wear and tear on actuators, valve bodies, gears, dampers and other mechanical components increases
Solution Approach 1:
The control system is divided into separate segments where each temperature-affecting device has its own dedicated controller and sensor. This segmentation reduces the mechanical wear on actuators, valve bodies, gears, and dampers by eliminating the oscillating control signals that occur when a single sensor controls multiple devices, thereby improving the reliability and durability of mechanical components.
4Temperature
If multiple temperature-affecting devices are controlled in sequence along an airflow line, then the temperature control coverage is improved, but the control stability deteriorates due to oscillating signals
Solution Approach 1:
The sequential control of multiple temperature-affecting devices along the airflow line is achieved through segmentation, with each device having its own dedicated sensor and controller. The first sensor and controller manage the first temperature-affecting device, while the second sensor and controller manage the second temperature-affecting device. This segmented approach maintains temperature control coverage while eliminating the oscillating signals that would otherwise destabilize the control system.
Data Source
Figure 1(a)
Figure 1(b)~1(c)
Figure 1(d)~1(e)
AI summary
There is provided a system (101) for controlling supply airflow temperature along a supply airflow line (102), wherein the supply airflow line comprises a first temperature-affecting device (104), a second temperature-affecting device (106), a first sensor (110) and a second sensor (112). The system further comprises a controller (116), wherein the controller (116) is configured to receive a first actual value from the first sensor (110), a second actual value from the second sensor (112), and a set-point value from a receiver (142), and to control the first temperature-affecting device (104) based on the first actual value and the set-point value, and to control the second temperature-affecting device (106) based on the second actual value and the set-point value.