Load control system and method for regulating power supply to a thermostat
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Solution Overview
Problem
Thermostat delays in HVAC systems lead to extended periods of load shedding, reducing the effectiveness of demand response systems and causing discomfort to property owners, as the system does not account for the time it takes for thermostats to resume power distribution after a load control relay is restored.
Innovation Solution
A controller is programmed to measure the thermostat delay time and adjust the cycle shed and restore times to compensate for this delay, ensuring that the HVAC system receives power for the maximum intended duration by modifying the commanded cycle percentages based on the measured delay.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If a protection timer is used to delay power supply to HVAC loads after LCR restoration, then utility grid stability is improved, but load control effectiveness and property owner comfort deteriorate
Solution Approach 1:
The controller performs preliminary action by measuring the thermostat delay time in advance and using this measurement to pre-calculate adjusted cycle shed and restore times. This allows the system to compensate for the protection timer delay before the next control cycle begins, ensuring that the HVAC load is restored at the optimal moment rather than waiting passively for the delay to expire.
Solution Approach 2:
The system implements feedback by measuring the actual thermostat delay time and using this measured value to adjust subsequent control decisions. The controller continuously monitors the delay between LCR restoration and thermostat power receipt, then uses this feedback information to optimize cycle timing parameters, creating a closed-loop control system that adapts to actual system behavior.
2Device complexity
If cycle shed and restore times are calculated without compensating for thermostat delay, then control system simplicity is maintained, but active power reception time is reduced
Solution Approach 1:
The controller performs preliminary action by measuring the thermostat delay time in advance and using this measurement to pre-calculate adjusted cycle shed and restore times. This allows the system to compensate for the protection timer delay before the next control cycle begins, ensuring that the HVAC load is restored at the optimal moment rather than waiting passively for the delay to expire.
Solution Approach 2:
The system implements feedback by measuring the actual thermostat delay time and using this measured value to adjust subsequent control decisions. The controller continuously monitors the delay between LCR restoration and thermostat power receipt, then uses this feedback information to optimize cycle timing parameters, creating a closed-loop control system that adapts to actual system behavior.
3Measurement precision
If LCR is restored immediately according to cycle percentages, then demand response control accuracy is improved, but thermostat protection requirements are violated
Solution Approach 1:
The controller performs preliminary action by measuring the thermostat delay time in advance and using this measurement to pre-calculate adjusted cycle shed and restore times. This allows the system to compensate for the protection timer delay before the next control cycle begins, ensuring that the HVAC load is restored at the optimal moment rather than waiting passively for the delay to expire.
Solution Approach 2:
The system implements feedback by measuring the actual thermostat delay time and using this measured value to adjust subsequent control decisions. The controller continuously monitors the delay between LCR restoration and thermostat power receipt, then uses this feedback information to optimize cycle timing parameters, creating a closed-loop control system that adapts to actual system behavior.
Data Source
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AI summary
A system for controlling a load control relay (LCR) supplying power to a thermostat of a heating, ventilating, and air conditioning (HVAC) system includes a controller programmed to maximize the amount of time that a load of the HVAC system may receive power. The controller operates by measuring a thermostat delay time of the thermostat and modifying cycle shed and restore times for controlling the LCR based on the measured thermostat delay time. By controlling the LCR according to the modified cycle shed and restore times, the controller compensates for the thermostat delay time, and the load is able to be active for a longer period of time than it otherwise would be when operating under demand-response controls.