Patent Publication Number: US-2022234413-A1

Title: Vehicle air conditioning system

Description:
CROSS-REFERENCE TO RELATED APPLICATIONS 
     This application is a national phase entry of International Patent Application No. PCT/DE2020/100636 (filed 21 Jul. 2020), which claims priority to German Patent Application No. 10 2019 120 719.3 (filed 31 Jul. 2019). The entire disclosures of these applications are incorporated herein by reference. 
    
    
     BACKGROUND 
     Technical Field 
     The invention relates to an air-conditioning system for a rail vehicle with at least one chiller and one cold storage unit which is designed as a PCM storage system with one phase change material, wherein the refrigeration power required for air-conditioning the passenger compartment and the refrigeration power required for charging the PCM storage system are provided by means of the chiller and wherein 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 rail vehicle. Furthermore, the invention relates to a method for operating such an air conditioning system. 
     State of Art 
     Numerous technical solutions are known for the air conditioning of passenger conveyance rail vehicles, with which heating or cooling of the passenger compartments is achieved. 
     For example, DE 10 2009 056 968 B3 describes an air conditioning system for rail vehicles in which the assemblies required for air conditioning are arranged on the vehicle roof. These assemblies are placed in a device trough. The device trough is covered at the top by a separate component so that it forms part of the roof shape within the contour of the rail vehicle. 
     This and numerous similar designs are inherently suitable for air conditioning passenger compartments in rail vehicles. However, for some specific operating conditions, further aspects must be taken into account. For example, in addition to the technical specifications for the operation of the air-conditioning system (electrical current/voltage ratios, refrigeration/heating power, air volume, etc.), the requirements for longer journeys through tunnels are becoming increasingly relevant, because the tracks for high-speed trains in long-distance travel and for local trains in areas of high population density have, in recent years, frequently been outfitted with tunnels. Due to the release to the outside of heated air from the air conditioning system, the air temperature in tunnels increases sharply and can only cool minimally between the passage of successive vehicles. For this reason, it is inherently obvious to the person skilled in the art that the chiller assemblies of the air conditioning system, which are necessary for air cooling, are switched off while the vehicle is traveling in a tunnel. 
     A related technical solution is proposed in WO 2005/014 365 A1. In order to however ensure functional cooling, the rail vehicle is equipped with a plurality of refrigerant storage systems, wherein frozen water, in the form of ice or other low-temperature liquids, is kept in separate containers. During travel through tunnels, the ice or alternatively liquids are used to cool the air, so that the actual chiller can be switched off and virtually no additional heated air is released into the tunnel space. A disadvantage, however, is that the refrigerant storage system must be refilled on a regular basis. 
     Regular refilling of refrigerant storage systems is not necessary if so-called PCM (“Phase Change Material”) storage systems are used for the temporary storage of cold, these 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. PCM storage systems can store thermal energy with low losses and many repeat cycles. Preferably, solid-liquid phase transitions are used, which is to say solidification-melting. In addition to water or ice, special salts or paraffin waxes are used as storage media. PCM storage systems were initially used only for cold packs, heating pads and similar smaller objects, but they are now also being used for larger objects. 
     For example, DE 10 2009 058 842 A1 describes an air conditioning system for vehicles in which a phase change material can be brought into thermal contact with the passenger compartment and/or with drive components of the vehicle. This technical solution is designed for vehicles with an electric motor drive. Embodiments are described in which the passenger compartment is heated by conducting heat from a phase change material into the passenger compartment, or in which the passenger compartment is cooled by conducting heat from the passenger compartment into a phase change material, or by conducting cold from a phase change material into the passenger compartment. 
     For rail vehicles, a similar solution approach is known from EP 2 570 280 B1. The technical solution relates to cooling the air in the passenger compartment using a refrigeration circuit to perform cooling cycles. In the first cooling cycle, more cold is generated than is currently required to cool the passenger compartment. This excess cold is stored in a cold storage unit, which is designed as a PCM storage system. In the second cooling cycle, the stored cold is taken from the cold storage unit in specific operating states and also used to cool the air in the passenger compartment. The carrying out of a first or a second cooling cycle depends on whether the rail vehicle is in a braking phase or in a rolling phase. However, this reference does not provide any information relating to the operation of a PCM storage system depending on whether the vehicle is traveling outside or inside a tunnel. 
     EP 3 290 288 B1 describes an air-conditioning system for rail vehicles in which the cold required for driving through tunnels is supplied in advance to a storage system and once again taken from it during the journey in the tunnel. The system comprises a plurality of refrigeration units distributed in the vehicle, a chiller which supplies these refrigeration units with cold, and a storage unit which can also be charged with cold by the chiller. When outside a tunnel or a similar partially enclosed section of the track, the chiller supplies the refrigeration units of the air conditioning system with cold. If there is a surplus of refrigeration power, this surplus is charged into the storage unit. During longer tunnel passages, the stored cold is taken from the storage unit and fed to the assemblies for cooling the passenger compartment. During this process, the chiller is switched off and does not give off any additional heat in the tunnel space. A disadvantage, however, is that the cold storage unit is only charged if there is a surplus of cold. Thus, the amount of cold available from the cold storage unit is often insufficient for longer tunnel passages or for successive short travel sections through several tunnels. As a consequence, the chiller cannot be switched off or can only be switched off temporarily, such that, in sections, strongly heated air continues to be discharged into the tunnel. 
     DE 198 60 057 A1 describes a vehicle air conditioning system comprising a primary refrigerant refrigeration circuit, a secondary water-glycol circuit and a plate heat exchanger connecting these one after the other. In the secondary circuit, a cold storage system and a heat exchanger are arranged one after the other. This allows air conditioning when the primary circuit is not in operation. 
     BRIEF SUMMARY 
     The task of the invention is to provide an air conditioning system for rail vehicles with a cold storage unit designed as a PCM storage system, wherein 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, during longer tunnel passages, the chiller of the air conditioning system designed for cold generation is largely switched off and the discharge of larger amounts of heat from the rail vehicle into the tunnel is thereby avoided. 
     This task is solved by dividing the refrigeration circuit into a primary circuit with a refrigerant and a secondary circuit with a water-glycol mixture, with the primary circuit providing the refrigeration power for air conditioning the passenger compartment and for charging the PCM storage system, and wherein the refrigeration power is transferred to the secondary circuit via a plate heat exchanger. 
     The PCM storage system and a water heat exchanger for cooling the air in the passenger compartment are arranged one behind the other in the direction of flow in the secondary circuit. In this manner, a lower temperature level can be achieved for the cold storage unit. The resulting slightly higher temperature level of the refrigerant on leaving the cold storage unit is still sufficient for the heat exchanger to the passenger compartment. The cold storage unit is thereby at a lower temperature level than the heat exchanger to the passenger compartment. When operating from the cold storage unit, there is no significant change in temperature level compared to operation with the chiller running. 
     The phase change material is designed in the form of small plate-shaped segments, arranged in a container of the PCM storage system and the water-glycol mixture of the secondary circuit flows around the phase change material in this container. 
     One bypass line is arranged at the PCM storage system and one at the water heat exchanger in the secondary circuit, which bypass lines are opened or shut off by a three-way valve as a function of the current operating mode of the air-conditioning system. 
     In terms of process technology, this air-conditioning system is operated in such a way that during operation of a rail vehicle while traveling outside a tunnel, the chiller primarily charges the cold storage unit with cold and that when the chiller is not in operation, the cold energy stored in the PCM storage system is fed to the water heat exchanger. Various alternatives are possible: 
     For example, during operation while the rail vehicle is traveling outside a tunnel, the chiller can initially only charge the cold storage unit with cold and provide cold for cooling the passenger compartment only after the cold storage unit has been fully charged. 
     Preferably, however, the air conditioning system is used in parallel operation, such that the chiller charges the cold storage unit with cold while in operation during travel outside a tunnel and at the same time also provides cold for cooling the passenger compartment. In this variant, it is preferable that the percentage ratio of the charging or provision of cold for the cold storage unit and for the passenger compartment is adjustable. In this, route topography, interior and exterior temperatures, number of passengers, frequency and duration of door openings at stations and similar parameters can, for example, be taken into account as the basis of a regulation or control. 
     Regardless of the specific variant selected, the cooling of the passenger compartment can be further optimized as soon as the cold storage unit is charged. Changing priorities in the allocation of the available refrigeration power between the passenger compartment and the cold storage unit are possible, of which three possible alternatives are named below: 
     (a) Renunciation of charging of the cold storage unit when there is a very high demand for refrigeration power in the passenger compartment, for example, typical of rush-hour commuter traffic. 
     b) Charging of the cold storage unit exclusively when the demand for refrigeration power is low, making use of the upper temperature limit for the passenger compartment 
     c) Targeted proactive lowering of the passenger compartment temperature within the permissible temperature control range and thereby use of the passenger compartment as storage system. 
     The technical solution according to the invention results in several advantages over the conventional designs used to date. For example, a cold energy storage system has to store less energy than a warm energy storage system, since the compressor energy does not have to be stored. A better coefficient of performance (COP) is achieved in the ratio of refrigeration power generated to the energy used for this purpose in storage mode. A further advantage consists in that by combination with a secondary refrigeration circuit, the amount of refrigerant used is reduced. Likewise, fewer assemblies are required because the same heat exchanger is used to cool the supply air in hybrid mode and in conventional cooling mode. There is no need to modify the supply air flow by adding another heat exchanger. 
     The technical solution according to the invention is preferentially suitable for high-speed trains in long-distance traffic and for local trains in urban centers where the track has longer tunnel sections or similar enclosed track sections. Furthermore, operating times without power supply can be bridged, for example, for pre-cooling of parked rail vehicles before the start of operation at high outside temperatures or for emergency cooling in the event of sudden failures. Independent of the specific application, a large enough quantity of cold is fed from the phase change material of a PCM storage system into the passenger compartment that sufficient cooling of the passenger compartment is ensured even when the chiller of the air conditioning system designed for cold generation is not in operation, without discharging large amounts of heat from the rail vehicle. 
    
    
     
       DESCRIPTION OF THE DRAWINGS 
       In the following, an embodiment example of the invention is explained in more detail. Herein, 
         FIG. 1  shows the basic structure of an air-conditioning system for a rail vehicle designed according to the invention with a PCM storage system as the cold storage unit. 
     
    
    
     DETAILED DESCRIPTION 
     The air conditioning system shown in stylized form in  FIG. 1  is designed for a rail vehicle and comprises a chiller  1  and a cold storage unit  12 . The cold storage unit  12  is designed as a PCM storage system with phase change material. The chiller  1  provides the refrigeration power required for air conditioning the passenger compartment (not shown) and the refrigeration power required for charging the PCM storage system  12 . The cold stored in the PCM storage system  12  is supplied to the assemblies for air conditioning the passenger compartment in selected operating states of the rail vehicle—preferentially during travel in a tunnel. 
     It can be seen from the drawing that the cooling circuit is divided into a primary circuit (TOP) with a refrigerant and a secondary circuit (BELOW) with a water-glycol mixture. All available refrigerants are suitable as refrigerants for the primary circuit, which is to say both synthetic (for example, R134a) and natural (for example, CO 2  or propane) refrigerants. 
     The primary circuit with the chiller  1 , a condenser  2  and an expansion valve  9  provides the refrigeration power for air conditioning the passenger compartment and for charging the PCM storage system  12 . 
     For this purpose, the refrigeration power is transferred from the primary circuit to the secondary circuit via a plate heat exchanger  10 . In this secondary circuit, the PCM storage system  12  and a water heat exchanger  3  for cooling the air in the passenger compartment are arranged one after the other in the direction of flow from the plate heat exchanger  10 . A water pump  11  is arranged downstream of the water heat exchanger  3 , in the flow path, which in turn is in operative connection with the plate heat exchanger  10 . 
     The phase change material, which is not shown in more detail, is in the form of small plate-shaped segments and is arranged in a container of the PCM storage system  12 , which is also not shown in more detail. The water-glycol mixture of the secondary circuit flows around the phase change material in this container. The phase change material can largely be any material available on the market for this purpose, preferably paraffin waxes with a melting point of between 0° C. and 15° C. or water. 
     Furthermore, the PCM storage system  12  and the water heat exchanger  3  in the secondary circuit are each operatively connected to a separate three-way valve  14 . The two three-way valves  14  can be switched in such a way that the PCM storage system  12  and the water heat exchanger  3  can be bypassed using an associated bypass line, this dependent on the current operating mode of the air-conditioning system. 
     An air-conditioning system set up in this way is operated in such a way that, during operation of a rail vehicle while traveling outside a tunnel, the chiller  1  primarily charges the cold storage unit/PCM storage system  12  with cold. At the same time, the cold storage unit  12  can thereby be charged with cold and cold can be provided for cooling the passenger compartment. In this operating state, the percentage ratio of the charging or provision of cold for the cold storage unit  12  and for the passenger compartment can be set. Alternatively, it is also possible that initially only the cold storage unit  12  is charged with cold and cold is provided for cooling the passenger compartment only once the cold storage unit  12  has been fully charged. If the chiller  1  is not being operated, which is to say, preferentially while driving in a tunnel, the cold energy stored in the PCM storage system  12  is fed to the water heat exchanger  3 .