Variable Differential Thermostat with Runtime-Based Fan Delay Control
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Solution Overview
Problem
Existing HVAC systems lack efficient control methods for heating and cooling ventilation fans, leading to suboptimal energy efficiency and thermal comfort due to fixed fan-off time delays and inadequate consideration of heating or cooling energy stored in heat exchangers or evaporator coils, resulting in wasted energy and reduced system performance.
Innovation Solution
A thermostat with advanced hysteresis control that provides variable fan-off time delays based on the duration of heating or cooling system operation, relative humidity, and energy stored in heat exchangers or evaporator coils, allowing for extended fan operation after the heating or cooling source has stopped to recover additional energy and improve efficiency.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If a fixed fan-off time delay is used, then the control method is simple, but energy efficiency is suboptimal due to wasted heating or cooling capacity
Solution Approach 1:
The patent implements a variable fan-off time delay that dynamically adjusts based on the runtime of the heating or cooling system. Instead of using a fixed delay, the system calculates the delay period based on how long the heat exchanger or evaporator coil has been operating, allowing the fan to run longer after extended system operation to fully recover stored thermal energy. This dynamic approach optimizes energy recovery while maintaining reasonable control complexity.
Solution Approach 2:
The patent changes the parameter of fan-off delay time from a fixed value to a variable value that depends on system runtime. By monitoring the operational duration of the heating or cooling system and adjusting the fan-off delay accordingly, the system recovers maximum thermal energy from the heat exchanger or evaporator coil, thereby reducing energy loss without requiring overly complex control mechanisms.
2Loss of energy
If fan operation is extended to recover energy, then energy efficiency improves, but thermal comfort may be compromised due to inadequate consideration of stored energy
Solution Approach 1:
The patent incorporates feedback mechanisms that monitor system runtime and thermal conditions to determine the optimal fan-off delay period. By continuously assessing how long the heating or cooling system has been operating and the resulting thermal energy stored in the heat exchanger or evaporator coil, the system adjusts fan operation to recover energy while maintaining thermal comfort. The feedback loop ensures the fan runs long enough to utilize stored energy without creating discomfort conditions.
Solution Approach 2:
The system performs preliminary assessment of the thermal energy stored in the heat exchanger or evaporator coil based on system runtime before determining the fan-off delay period. This preliminary action allows the system to plan fan operation that will effectively recover energy while avoiding conditions that would compromise thermal comfort, thereby balancing energy efficiency with reliability.
3Ease of operation
If fixed differential control is used, then the thermostat is easy to operate, but energy efficiency is reduced due to short cycling
Solution Approach 1:
The patent implements a variable differential control that dynamically adjusts the temperature differential based on system runtime and thermal conditions. Instead of using a fixed differential that causes short cycling, the system modifies the differential parameter in response to operational data, allowing the thermostat to maintain ease of operation while preventing energy-wasting short cycles. The differential expands or contracts based on how long the system has been running and the thermal energy available for recovery.
Applied Scientific Principles
This section explains which scientific principles are used to turn an abstract innovation direction into a practical engineering solution.
Function Achieved in This Case
The solution enhances energy efficiency by recovering additional heating or cooling capacity, reducing energy consumption, and improving thermal comfort by optimizing fan operation based on real-time system parameters, leading to improved performance compared to traditional fixed-time delay methods.
Implementation Method 1
heating or cooling energy stored in heat exchangers or evaporator coils
Implementation Method 2
energy stored in heat exchangers
Implementation Method 3
thermostat with advanced hysteresis control that provides variable fan-off time delays
Implementation Method 4
amount of latent cooling energy stored on the cooling evaporator (i.e., water condensed on the evaporator)
Data Source
AI summary
Apparatus and methods are disclosed for a variable differential variable delay thermostat. The variable differential is based on the duration of a thermostat call for cooling or the duration of a thermostat call for heating. The variable cooling fan-off delay is based on cooling system parameters including but not limited to the duration of the cooling cycle, duration of the thermostat call for cooling, conditioned space temperature, temperature split, thermostat temperature rate of change, or thermostat temperature reaching a minimum inflection point or crossing a fixed or variable thermostat differential or differential offset. The variable heating fan-off delay is based on heating system parameters including but not limited to the duration of the heating cycle, duration of the thermostat call for heating, conditioned space temperature, temperature rise, thermostat temperature rate of change, or thermostat temperature reaching a maximum inflection point or crossing a fixed or variable thermostat differential or differential offset.