Asymmetrical Building Zone Control for Lower HVAC Energy Use
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Solution Overview
Problem
Building automation systems face inefficiencies in energy expenditure when controlling variables like temperature, as more energy is required to correct deviations in one direction (e.g., cooling) compared to the other (e.g., heating), leading to discomfort and increased energy costs.
Innovation Solution
Implementing an asymmetrical control strategy where the processing circuit responds to errors at different rates based on the sign of the error, delaying responses for high energy expenditure errors to minimize energy usage while maintaining comfort levels.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If a conventional symmetrical control strategy is used to minimize error between controlled variable and setpoint, then comfort conditions are maintained, but energy expenditure increases due to equal response rates for both error directions
Solution Approach 1:
The control system implements asymmetrical response rates based on the sign of the error. When the error indicates a direction requiring high energy expenditure (e.g., cooling), the controller responds at a first, slower rate. When the error indicates a direction requiring lower energy expenditure (e.g., heating), the controller responds at a second, faster rate. This asymmetry in control response resolves the contradiction by reducing energy consumption while maintaining acceptable comfort levels.
Solution Approach 2:
The controller dynamically adjusts its response rate based on the current error sign and the associated energy expenditure characteristics. The control strategy switches between two different response rates (first rate and second rate) depending on the operational conditions, making the system adaptive rather than static. This dynamic adjustment allows the system to optimize energy usage while responding appropriately to comfort requirements.
2Reliability
If the controller responds quickly to all errors to maintain setpoint accuracy, then comfort conditions are improved, but energy costs increase due to aggressive correction in high energy expenditure scenarios
Solution Approach 1:
The system applies different control aggressiveness levels based on the error direction. For errors that would trigger high energy expenditure (such as extensive cooling), the controller uses a more conservative, slower response rate. For errors requiring lower energy (such as heating), the controller responds more aggressively and quickly. This asymmetrical approach balances setpoint accuracy with energy cost considerations.
Solution Approach 2:
The control system changes the response rate parameter based on the error sign and associated energy characteristics. By switching between a first response rate (slower) and a second response rate (faster), the system adapts its control aggressiveness to the specific operational context, thereby reducing energy costs while maintaining acceptable setpoint accuracy.
3Speed
If the controller uses aggressive correction strategies to minimize error rapidly, then transient response is improved, but energy expenditure increases significantly
Solution Approach 1:
The controller dynamically selects between two response rates based on the error sign. When rapid correction is energy-efficient, the faster second rate is used, providing quick transient response. When rapid correction would be energy-intensive, the slower first rate is used, accepting a more gradual transient response to save energy. This dynamic selection resolves the contradiction between response speed and energy expenditure.
Solution Approach 2:
The system implements asymmetrical transient response characteristics depending on the error direction. Corrections in the low energy expenditure direction are performed rapidly with the second response rate, while corrections in the high energy expenditure direction are performed more gradually with the first response rate. This creates asymmetrical transient behavior that optimizes the trade-off between response speed and energy use.
Data Source
AI summary
A method for controlling a controlled variable of a building zone to minimize an error between the controlled variable and a setpoint includes receiving an input at a first interface regarding the controlled variable from a sensor provided in the building. The method further includes using a processing circuit to determine a sign of the error based on the input and the setpoint. The method yet further includes using the processing circuit to cause a controller configured to affect the controlled variable to respond to the error at a first rate when a first sign of the error is present. The method further includes using the processing circuit to cause the controller to respond to the error at a second rate when a second sign of the error is present, the first rate being slower than the second rate. The first sign of the error can be associated with a high energy expenditure required to minimize the error relative to an energy expenditure required to minimize the error relative to the second sign.