Thermal Load Dead Time Coordination for Grid-Responsive Refrigeration
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Solution Overview
Problem
Refrigeration loads, such as compressors, experience 'dead times' during which they are unresponsive, limiting their ability to adjust to peak or troughs in electric power supply, leading to inefficiencies in energy usage and increased costs due to synchronized ON/OFF cycles with other compressors.
Innovation Solution
A method and system where a central server overrides local control loops to advance or delay the dead times of thermal loads, ensuring they do not coincide with other loads, and optionally uses battery power to maintain responsiveness during these times, thereby reducing or eliminating overlapping dead times.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If compressors operate in synchronized ON/OFF cycles to maintain temperature within allowable ranges, then temperature control reliability is improved, but responsiveness to peak or troughs in energy supply deteriorates due to overlapping dead times
Solution Approach 1:
The system performs preliminary action by driving the temperature down ahead of a predicted trough in energy supply or predicted peak in energy demand. The server receives information about predicted energy supply/demand patterns and proactively adjusts compressor operation schedules before the predicted event occurs, ensuring compressors are ready to respond when needed while avoiding overlapping dead times.
Solution Approach 2:
The system makes the compressor operation dynamic by allowing the server to override local control loops and adjust ON/OFF schedules in real-time based on actual energy supply/demand conditions. This dynamic adjustment enables the system to adapt its temperature control strategy to match fluctuating energy availability, resolving the contradiction between maintaining reliable temperature control and responding flexibly to energy supply changes.
2Loss of energy
If compressors are turned on during peak energy supply to drive temperature down, then energy cost is reduced, but the compressors may not be able to respond quickly when needed due to dead time constraints
Solution Approach 1:
The system performs preliminary cooling action during periods of high energy supply by turning on compressors in advance, driving the temperature down below the minimum operating temperature threshold. This creates a temperature buffer that allows compressors to be turned off during subsequent periods without immediately risking temperature violation, thereby enabling faster response to energy supply changes while still achieving energy cost reduction.
Solution Approach 2:
The system uses the thermal mass of the refrigerated space as a self-service energy buffer. By allowing the temperature to go below the minimum threshold during high supply periods, the cold thermal mass itself serves as temporary cooling capacity, reducing the need for immediate compressor operation during subsequent periods and improving overall response speed.
3Loss of energy
If the temperature is allowed to rise ahead of predicted peak supply or trough demand, then energy cost is reduced, but temperature control reliability may be compromised
Solution Approach 1:
The system performs preliminary heating action by turning off compressors in advance of predicted peak supply or trough demand periods, allowing the temperature to rise below the maximum operating temperature threshold. This creates a temperature buffer that ensures the compressors can be turned on quickly when needed without immediately violating the maximum temperature constraint, thereby maintaining reliability while reducing energy costs.
Solution Approach 2:
The system uses the thermal mass of the refrigerated space as a self-service energy buffer in reverse. By allowing the temperature to rise above the minimum threshold during low supply periods, the warm thermal mass serves as temporary heating capacity, reducing the immediate need for compressor operation and enabling faster response when energy supply increases, while the maximum temperature threshold provides a safety buffer for reliability.
Data Source
Figure 1
Figure 2a~2b
Figure 2c
AI summary
A responsive load system with improved responsiveness through reducing or eliminating the impact of dead times of thermal loads is disclosed. The responsive load system comprises at least a first and a second thermal load controlled by means of local control loops in response to at least one local thermostat. A server stores information relating to the dead times of the thermal loads and may intervene in the operation of the responsive load; this may comprise overriding the local control loop of the first thermal load so as to advance or delay its dead time so that it does not entirely coincide with the dead time of the second thermal load.