Vehicle air conditioning system
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Solution Overview
Problem
Existing air conditioning systems for rail vehicles face challenges in maintaining effective cooling during longer tunnel passages, as the cold storage unit often lacks sufficient cold when the chiller is switched off, leading to heat discharge into tunnels.
Innovation Solution
A divided refrigeration circuit with a primary refrigerant circuit and a secondary water-glycol circuit, utilizing a PCM storage system and a water heat exchanger, where the chiller charges the cold storage unit and provides cooling to the passenger compartment, with adjustable ratios and bypass lines controlled by three-way valves to optimize energy use.
Engineering Contradictions & Design Principles
Engineering Contradiction Analysis
1Loss of energy
If the chiller is switched off during tunnel passages to avoid heat discharge, then energy efficiency is improved, but the cold storage unit lacks sufficient cooling capacity
Solution Approach 1:
The system pre-charges the PCM storage system before tunnel passages using the chiller when the vehicle is outside the tunnel. This preliminary action ensures that sufficient cold energy is stored in advance to maintain cooling capacity during the subsequent tunnel passage when the chiller must be switched off.
Solution Approach 2:
The invention utilizes a phase change material (PCM) in the storage system that absorbs and releases thermal energy through phase transitions (solid-liquid). During charging, the PCM absorbs heat during melting; during discharge in tunnels, it releases heat during solidification, providing reliable cooling capacity without requiring the chiller to operate.
2Reliability
If the chiller operates continuously to maintain cooling capacity, then cooling reliability is improved, but heat discharge into tunnels increases
Solution Approach 1:
The system performs preliminary charging of the PCM storage system during periods when the vehicle is outside tunnels. This allows the chiller to operate intermittently rather than continuously, storing cooling capacity in advance and avoiding heat discharge during tunnel passages.
Solution Approach 2:
The PCM storage system acts as an intermediary between the chiller and the air conditioning assemblies. It decouples the chiller operation from the immediate cooling demand, allowing the chiller to operate only when necessary for charging, while the storage system provides cooling during tunnel passages.
3Loss of energy
If a divided refrigeration circuit with PCM storage is implemented, then energy efficiency is improved, but device complexity increases
Solution Approach 1:
The refrigeration circuit is segmented into a primary circuit (chiller with refrigerant) and a secondary circuit (water-glycol mixture with PCM storage and air conditioning assemblies). This segmentation allows independent optimization of each circuit and enables the PCM storage system to be charged and discharged flexibly based on operational conditions.
Solution Approach 2:
The PCM storage system serves multiple functions: it acts as a thermal buffer during tunnel passages, provides cooling capacity during high-demand periods, and enables the chiller to operate more efficiently by decoupling its operation from immediate cooling demands. This multi-functionality justifies the added complexity.
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 ensures sufficient cooling of the passenger compartment without significant heat discharge into tunnels, improving the coefficient of performance and reducing refrigerant usage, making it suitable for high-speed trains and urban trains with frequent tunnel sections.
Implementation Method 1
PCM storage systems are also referred to as phase change storage systems or latent heat storage systems. This is functionally a heat storage system that stores an incoming thermal energy and releases it through a change in phase.
Implementation Method 2
The refrigeration power is transferred to the secondary circuit via a plate heat exchanger
Implementation Method 3
the chiller assemblies of the air conditioning system, which are necessary for air cooling
Data Source
AI summary
A vehicle air-conditioning system includes at least one chiller and one cold storage unit which is designed as a PCM storage system with phase change material. The refrigeration power required for air-conditioning and for charging the PCM storage system are provided by the chiller where the cold stored in the PCM storage system is supplied to the assemblies for air-conditioning the passenger compartment in selected operating states of the vehicle. A sufficiently large amount of cold can be conducted from a phase change material of the PCM storage system into the passenger compartment such that the chiller of the air conditioning system designed for cold generation is largely put out of operation and the discharge of larger amounts of heat from the rail vehicle into the tunnel is thereby avoided.