Heat Pump De-icing Using PCM Accumulator and Recirculation
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Solution Overview
Problem
The de-icing of heat exchangers in motor vehicle air-conditioning systems, particularly in electric or hybrid vehicles, poses a challenge due to the high battery load and reduced range, as conventional methods require significant electrical energy and result in impaired heat exchange efficiency due to ice formation, which is exacerbated by using refrigerant R744.
Innovation Solution
A method that utilizes a heat accumulator, such as a latent heat accumulator with PCM material, to supply heating energy during de-icing, combined with reducing air circulation speed and increasing air temperature by closing radiator grille shutters and operating fans downstream, to accelerate defrosting while minimizing battery load, and using recirculation mode to reduce heating energy requirements.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Power
If the heat exchanger on the outside air side is used for heating operation with a heat pump, then heating efficiency is improved, but ice formation on the heat exchanger surfaces occurs due to temperatures below freezing point
Solution Approach 1:
The system performs preliminary heating of the outside air-side heat exchanger using the inside air-side heat exchanger before the ice formation becomes critical. By detecting early signs of ice formation through temperature and humidity sensors, the system activates the de-icing mode in advance, reversing the refrigerant flow to heat the outside heat exchanger and prevent further ice accumulation that would block air flow channels.
Solution Approach 2:
The system converts the harmful effect of ice formation into a beneficial de-icing process by reversing the refrigerant flow direction. The inside air-side heat exchanger, which normally releases heat, is used to heat the outside air-side heat exchanger and melt the ice. This transforms the problem of ice blocking heat exchange into an opportunity to use the heat pump system itself to remove the ice.
2Reliability
If conventional de-icing methods are used by reversing refrigerant flow, then ice can melt, but the de-icing process takes about 3 minutes causing heating interruption
Solution Approach 1:
The system performs preliminary heating of the outside air-side heat exchanger using the inside air-side heat exchanger before the ice formation becomes critical. By detecting early signs of ice formation through temperature and humidity sensors, the system activates the de-icing mode in advance, reversing the refrigerant flow to heat the outside heat exchanger and prevent further ice accumulation that would block air flow channels.
Solution Approach 2:
The system maintains continuous heating operation by implementing a controlled de-icing process that minimizes interruption. During de-icing mode, the system continues to supply heated air to the vehicle interior using the inside air-side heat exchanger while simultaneously removing ice from the outside heat exchanger. The gradual reduction of ice formation allows the system to switch back to heating mode without complete interruption, ensuring continuous thermal comfort.
3Reliability
If electrical resistance heater is used during de-icing to maintain interior heating, then heating comfort is maintained, but battery power consumption increases significantly
Solution Approach 1:
The system uses its own heat pump components to provide heating during de-icing operations. The inside air-side heat exchanger continues to release heat into the vehicle interior through the air circulation system, maintaining heating comfort without requiring additional electrical resistance heating. The heat pump system serves itself by using the inside heat exchanger as a heat source during the de-icing process, eliminating the need for separate heating elements.
Solution Approach 2:
The heat pump system performs multiple functions simultaneously: the inside air-side heat exchanger serves both as a heat release component for interior heating and as a heat source for de-icing the outside heat exchanger. The refrigerant circuit reverses flow to enable the inside heat exchanger to provide thermal energy to the outside heat exchanger, demonstrating multi-functionality that eliminates the need for separate heating devices during de-icing operations.
4Reliability
If refrigerant R744 is used in the heat pump system, then environmental impact is reduced and non-flammability is achieved, but very low temperatures on the cold side increase ice formation risk
Solution Approach 1:
The system implements continuous monitoring of temperature and humidity conditions at the outside air-side heat exchanger using sensors. When the system detects conditions favorable for ice formation (low temperature combined with high humidity), it automatically activates the de-icing mode by reversing the refrigerant flow. This feedback mechanism allows the system to respond proactively to changing environmental conditions, maintaining the environmental benefits of R744 while preventing ice formation through timely intervention.
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
This approach effectively reduces the battery current requirement during de-icing, accelerates the defrosting process, and maintains vehicle interior heating without significant power consumption, ensuring efficient heating operation and reduced ice formation risks.
Implementation Method 1
supplying heat from a heat accumulator to the vehicle interior, in particular from a latent heat accumulator with a PCM heat accumulator material
Implementation Method 2
extract the required thermal heat from the ambient air by means of a heat pump, for which purpose a conventional and already existing air conditioning refrigeration circuit can be used by reversing the flow direction of the refrigerant
Implementation Method 3
the compressor of the refrigerant circuit generally requires significantly less electrical energy
Implementation Method 4
a conventional and already existing air conditioning refrigeration circuit can be used by reversing the flow direction of the refrigerant
Data Source
Figure 1
Figure 2
AI summary
According to a method for de-icing an external-air heat exchanger (14) of a motor vehicle air-conditioning system with a heat pump, wherein, when a predefined degree of icing of the external-air heat exchanger (14) is detected or estimated during a heating operation, it is temporarily switched over to a cooling operation in order to bring about entire or partial thawing of the ice on the external-air-side heat exchanger (14), one or more of the following measures are provided in order to maintain the heating of the vehicle passenger compartment during the de-icing process: a) heat is supplied from a PCM latent heat accumulator (24) to the vehicle passenger compartment and/or b) the ventilation system is switched over into a recirculation mode and/or the recirculation of passenger compartment air is reduced and/or c) the air flowing against the external-air-side heat exchanger (14) is reduced, and/or d) the temperature of the air flowing against the external-air-side heat exchanger (14) is increased, for example by closing a radiator grille shutter (18). Therefore, a loss of range in an electric vehicle owing to heating is counteracted by minimizing the required electrical heating power.