Air-conditioning system for a rail vehicle
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Solution Overview
Problem
The air conditioning systems in rail vehicles face significant temperature fluctuations in the passenger compartment due to interruptions in the heat pump function, particularly in the transition range between -5°C and +5°C, leading to inefficiencies and safety concerns when electrical heating devices are activated, making it difficult to comply with relevant standards.
Innovation Solution
The system is enhanced by dividing the refrigeration circuit into a primary and a secondary circuit connected via a third heat exchanger, with a switchable electric heating device for the coolant inflow, and a thermal accumulator function in the secondary circuit to stabilize supply air temperatures, incorporating a reservoir to maintain heat storage capacity and prevent icing.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Reliability
If the heat pump function is interrupted to prevent icing on the evaporator at temperatures below -5°C, then icing is prevented, but temperature fluctuations occur in the passenger compartment
Solution Approach 1:
The refrigeration circuit is divided into a primary refrigeration circuit (including compressor, condenser, expansion valve) and a secondary refrigeration circuit (including electrical heating device, evaporator), connected via a heat exchanger. This segmentation allows independent control of heating and cooling functions, enabling the secondary circuit to maintain supply air temperature while the primary circuit manages heat pump operation and defrosting cycles
Solution Approach 2:
A heat exchanger serves as an intermediary between the primary and secondary refrigeration circuits. The primary circuit cools a coolant in the heat exchanger, which then cools the supply air in the secondary circuit. This intermediary allows thermal energy transfer while decoupling the two circuits, enabling temperature stabilization during heat pump interruptions
2Temperature
If an electrical heating device is switched on to compensate for heat pump interruption, then supply air temperature can be maintained, but safety risks arise from high surface temperatures exceeding 300°C
Solution Approach 1:
The heat exchanger acts as a thermal intermediary between the primary refrigeration circuit and the secondary circuit containing the electrical heating device. It transfers heat from the cooled coolant to the supply air, enabling temperature maintenance while keeping the electrical heating device isolated from direct contact with the air supply, thus reducing safety risks
Solution Approach 2:
The refrigeration system is segmented into primary and secondary circuits, with the electrical heating device confined to the secondary circuit. This segmentation allows the heating device to operate independently without directly affecting the air supply temperature control, enabling safer operation by decoupling the high-temperature heating element from the air handling path
3Reliability
If the refrigeration circuit is interrupted for defrosting in the transition range between -5°C and +5°C, then ice accumulation is removed, but compliance with climate standards becomes difficult
Solution Approach 1:
The refrigeration circuit is divided into primary and secondary circuits, allowing the primary circuit to be interrupted for defrosting while the secondary circuit continues to maintain supply air temperature. This segmentation enables independent operation of each circuit, permitting defrosting cycles without compromising climate standard compliance in the passenger compartment
Solution Approach 2:
The secondary refrigeration circuit is prepared in advance with an electrical heating device and heat exchanger configuration that can immediately compensate for any temperature drops caused by primary circuit interruptions. This preliminary setup ensures continuous temperature control capability during defrosting operations
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 configuration reduces temperature fluctuations in the passenger compartment, allows efficient operation of the heat pump without icing, and ensures consistent supply air temperatures, enhancing compliance with standards and safety by decoupling the electrical heating from the air supply.
Implementation Method 1
a primary refrigeration circuit (1), which includes the first heat exchanger (3), the expansion valve (11), the compressor (10), the valve arrangement (5) for switching between cooling mode and heating mode, and a primary side of a third heat exchanger (16)... and a secondary refrigeration circuit (2), which comprises a secondary side of the third heat exchanger (16)
Implementation Method 2
a switchable electric heating device (14) for heating a coolant inflow for the second heat exchanger (12) between a cold fluid outlet on the secondary side of the third heat exchanger (16) and a cold fluid inlet of the second heat exchanger (12)
Implementation Method 3
Water condenses when the ambient air falls below the dew point. At lower temperatures below 0°C, icing occurs on a heat transfer surface of the evaporator
Data Source
Figure 1
Figure 2
Figure 3
AI summary
The invention relates to an air-conditioning system for a rail vehicle, comprising a coolant circuit which can be switched between a cooling operation and a heating operation and which has - a first heat exchanger (3) that interacts with surrounding air (A) and operates as a condenser during the cooling operation and as an evaporator during the heating operation, - a second heat exchanger (12) which conditions supply air (Z) for a passenger compartment, - an expansion valve (11), - a compressor (10), and - a valve assembly for switching between the cooling operation and the heating operation. The invention is characterized in that the coolant circuit has - a primary coolant circuit (1), which comprises the first heat exchanger (3), the expansion valve (11), the compressor (10), the valve assembly for switching between the cooling operation and the heating operation, and a primary side of a third heat exchanger (16) that operates as an evaporator during the cooling operation and as a condenser during the heating operation, and - a secondary coolant circuit (2), which comprises the secondary side of the third heat exchanger (16) and the second heat exchanger (12). A switchable electric heating device for heating a coolant supply flow for the second heat exchanger (12) is arranged between the coolant fluid outlet on the secondary side of the third heat exchanger (16) and a coolant fluid inlet of the second heat exchanger (12).