Air-Flow Thermal Conditioning Control to Prevent Window Fogging
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Solution Overview
Problem
In electric vehicles, transitioning from cooling to heating modes in thermal conditioning systems can lead to fogging on vehicle windows due to condensation of water on heat exchangers, which poses a driving hazard.
Innovation Solution
A method for controlling the thermal conditioning circuit that evaluates humidity levels on the heat exchanger surfaces, delaying the transition to heating mode if humidity is high, and using additional heating devices to prevent fogging by evaporating moisture.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Temperature
If the heat exchanger operates in cooling mode and then switches to heating mode, then the heating function is activated, but water vapor condenses on the heat exchanger surface and creates fog on vehicle windows
Solution Approach 1:
The control unit delays the switch to heating mode until the heat exchanger surface temperature reaches the dew point temperature or higher. This preliminary temperature check prevents water vapor condensation before it can occur, thereby avoiding fogging on vehicle windows while maintaining the heating function.
2Productivity
If the heat exchanger surface temperature is lowered to enable cooling mode operation, then cooling performance is improved, but water condensation occurs on the surface
Solution Approach 1:
The control unit continuously monitors the heat exchanger surface temperature and compares it with the dew point temperature. Based on this feedback, the control unit determines the appropriate timing for mode switching, ensuring that the heat exchanger operates efficiently in cooling mode while preventing excessive water condensation that would occur at lower temperatures.
3Object-generated harmful factors
If the switch from cooling to heating mode is delayed to prevent fogging, then visibility is maintained, but the heating response time is increased
Solution Approach 1:
The control unit dynamically adjusts the heat exchanger operating parameters, specifically the surface temperature, to reach the dew point temperature threshold before switching to heating mode. This parameter-based approach prevents fogging while minimizing the delay, as the temperature threshold is the minimum required to prevent condensation rather than an arbitrary time-based delay.
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
Prevents fogging on vehicle windows by ensuring safe transitions between cooling and heating modes, maintaining visibility, and optimizing energy use in electric vehicles.
Implementation Method 1
a heat exchanger configured to be traversed by a refrigerant fluid and to exchange heat with the air flow
Implementation Method 2
The high-pressure fluid undergoes condensation, releasing a quantity of heat to ensure the heating of, for example, the passenger compartment of the vehicle
Implementation Method 3
The fluid vaporizes by taking the heat necessary for vaporization from the outside air flow
Implementation Method 4
The water vapor present in the air can thus condense on contact with the exchanger, the surface of which may be at a temperature lower than the dew point temperature of the air
Implementation Method 5
If a heating phase is subsequently triggered while water in liquid form is present on the heat exchanger, it tends to vaporize and be carried away by the air flow intended for the passenger compartment
Data Source
Figure 1~2
Figure 3~4
Figure 5~6
AI summary
The invention relates to a method for controlling a thermal conditioning circuit (100) for thermally conditioning an air flow (1), notably intended for a motor vehicle interior (2), the circuit comprising a heat exchanger (4) configured to have a refrigerant pass through it and exchange heat with the air flow (1), the heat exchanger (4) being configured to operate selectively in at least: - a mode known as cooling mode, - a mode known as heating mode, the method comprising the steps of: - evaluating a level of humidity in a region in contact with an exterior surface (5) of the heat exchanger (4), - detecting an instruction to switch from cooling mode to heating mode, - if the evaluated level of humidity is below a predetermined first threshold (s1), allowing refrigerant to circulate through the exchanger (4) in response to the instruction to switch to heating mode, - if the level of humidity is above a predetermined second threshold (s2), preventing the refrigerant from circulating through the exchanger (4) for a first predetermined length of time (D1), so as to delay the switch to heating mode.