Thermostat variable fan-off delay
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Solution Overview
Problem
Current HVAC systems face inefficiencies due to fixed fan speeds and delays, leading to increased energy consumption and thermal comfort issues, as they fail to accurately measure and adjust airflow according to changing conditions, resulting in wasted energy and reduced system capacity.
Innovation Solution
A Fault Detection Diagnostic (FDD) method that monitors HVAC parameters to detect faults, adjusts fan operation, and varies fan-off delays based on detected conditions, ensuring optimal energy efficiency and thermal comfort by comparing current and previous system parameters.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Use of energy by moving object
If the heater ventilation fan is operated at a lower speed during heating, then energy consumption is reduced, but heat soak increases and heating efficiency decreases
Solution Approach 1:
The fan controller dynamically adjusts fan speed based on real-time temperature differential measurements between the heat exchanger and conditioned space, transitioning from fixed low speed to variable speed operation that optimizes both energy consumption and heating delivery efficiency
2Productivity
If the central heating unit operates for longer periods, then heating capacity is maintained, but heat soak increases and unrecovered energy is lost to the environment
Solution Approach 1:
The system continuously monitors the temperature differential between the heat exchanger and conditioned space, using this feedback to determine when to extend fan operation beyond traditional shutdown conditions, thereby recovering heat that would otherwise be lost to the environment
3Use of energy by moving object
If the cooling ventilation fan is turned off immediately when the cooling source is de-energized, then energy consumption is reduced, but sensible cooling capacity is lost to the environment
Solution Approach 1:
The system performs preliminary cooling by extending fan operation after the cooling source is de-energized, utilizing the cold evaporator coil to deliver additional sensible cooling capacity to the conditioned space before the coil warms up and the cooling effect is lost
4Ease of operation
If fixed fan-on and fan-off delays are used in heat pump systems, then control simplicity is maintained, but thermal comfort issues occur and fan energy is wasted during start-up
Solution Approach 1:
The system replaces fixed delays with dynamic fan control that adjusts operation timing and duration based on real-time temperature differential measurements, eliminating thermal comfort issues and fan energy waste during start-up while maintaining control simplicity
Data Source
AI summary
A method for providing a variable fan-off delay after a thermostat call for cooling or after a heating on cycle for a Heating, Ventilation, Air Conditioning (HVAC) system. The variable fan-off delay may be ended based on comparing a measurement of a Conditioned Space Temperature (CST) to a CST threshold. The CST threshold may be based on a previous measurement of the CST monitored during the current variable fan-off delay. The CST threshold may be an inflection point where the rate of change of the CST with respect to time equals zero plus or minus a confidence interval tolerance. The CST threshold may also be a fan-off delay differential offset or a thermostat setpoint differential where the variable fan-off delay is ended when the measurement of the CST during the variable fan-off delay crosses the differential at least once after the cooling or heating on cycle.