Air conditioning system for rail vehicles

Abstract

The present invention relates to an air-conditioning system for rail vehicles, which is suitable for flammable refrigerants and is designed as a compact device to be installed on the roof. The object of the present invention is to produce a direct evaporation system, in which the electrical switch cabinet (electrical box) in the compact air-conditioning device for rail vehicles is isolated so that, in the event of a relevant leak in the component containing the refrigerant, this component will not come into contact with the flammable refrigerant either, and thus no combustible mixture will occur in these areas. This object is achieved in that the electrical box is designed as a fully enclosed component and is operatively connected to a component through which air is guided from an area outside the refrigerant-containing section of the air-conditioning system into the electrical box so that an overpressure is generated in the electrical box to prevent the flammable refrigerant from flowing into the electrical box.

Description

Field of the Invention

[0001] The present invention relates to an air conditioning system for a rail vehicle, wherein the air conditioning system is suitable for a flammable refrigerant and is designed as a compact device to be installed on the roof, and at least has a device part for air treatment, a compressor liquefier unit, and an electrical switch box (electrical cabinet), and optionally a device part for exhaust and / or a silencer. Background Art

[0002] Various refrigerants are known for use in air conditioning systems in vehicles. Among them, the use of synthetic refrigerants is particularly problematic from an ecological perspective. Therefore, refrigerant R134a has been very widely used in motor vehicles and also in rail vehicles. However, when this refrigerant escapes into the atmosphere, it acts as a greenhouse gas. Therefore, as of January 1, 2017, the use of refrigerant R134a has been discontinued in new passenger cars in the European Union.

[0003] As a substitute for R134a, refrigerant R1234yf is currently mainly used. Refrigerant R1234yf has a much lower greenhouse effect, but it is flammable and is classified as an A2L refrigerant. However, even the use of this refrigerant is now criticized by experts. For example, highly toxic hydrofluoric acid (HF) is formed when released at a temperature greater than 250 °C, and persistent trifluoroacetic acid (TFA) is formed as a degradation product in the atmosphere, especially accumulating in water. Due to the associated risks, the use of HFO refrigerants such as R1234yf is also generally abandoned in principle.

[0004] Another approach is to use carbon dioxide (R744) as a natural refrigerant. However, compared with other refrigerants, the use of R744 results in relatively complex equipment technology due to the need for a higher system pressure. In addition, at high ambient temperatures, the coefficient of performance (COP) drops significantly, so the energy demand for air conditioning increases significantly. Furthermore, as the ambient temperature rises, the cooling capacity drops sharply, which can be offset by appropriately increasing the component size.

[0005] Therefore, it is obvious that the refrigerants used so far ultimately represent a compromise between different functional, environmental, and safety requirements. Vehicle air conditioners, especially rail vehicles, need to use refrigerants that are not ecologically critical when discharged into the atmosphere, have high energy efficiency throughout the operating range, and can continue to utilize the knowledge and experience of the cold vapor technology used so far. For rail vehicles, these units are mainly designed as compact units on the roof.

[0006] Regardless of their specific design, such compact air conditioning units generally include an air treatment and a compressor liquefier unit part, and may optionally include an exhaust device, an electrical switch box, and / or a silencer part.

[0007] As a solution to the above requirements, flammable hydrocarbons such as propane (R290), propylene (R1270), or isobutane (R600a) have received attention as alternative refrigerants. These refrigerants are widely used in direct expansion systems with limited charge amounts (<150 g or <500 g), especially in stationary applications. If a larger charge amount is required to generate higher cooling capacity, an indirect system is preferred due to the flammability of these direct expansion systems.

[0008] For the air conditioning of rail vehicles, flammable refrigerants have hardly been used as direct evaporation systems or indirect evaporation systems so far due to the explosion and fire hazards associated with the refrigerants. In an indirect evaporation system, the above risks can be reduced by designing an air conditioning system with a secondary circuit system. In this case, a flammable refrigerant is used in a conventional compression refrigeration circuit, providing the required cooling (or heating) power in a primary circuit that is located outside the vehicle and thus has no direct connection to the vehicle interior. This cooling power is transferred to a secondary circuit, for example, designed as a brine circuit with a water - glycol mixture, via a heat exchanger (preferably, a plate heat exchanger).

[0009] Such a type of technical solution can be learned from WO 2018 / 137 908 A1. According to this document, a rail vehicle has a primary refrigerant circuit that is arranged outside the vehicle and is structurally completely separated from the passenger compartment. The secondary refrigerant circuit is at least partially arranged inside the rail vehicle. The heat exchange between the primary refrigerant circuit and the secondary refrigerant circuit is carried out via an intermediate heat exchanger arranged under the floor in the external area. Thus, the primary refrigerant circuit is completely arranged outside the rail vehicle interior. This design means that when using flammable substances, the safety factors to be considered mainly involve the external area, while the internal area can be assumed to be as safe as a conventional system. This means that, for safety - related reasons, refrigerants that have hardly been used for passenger compartment air conditioning so far can also be used. Therefore, WO 2018 / 137 908 A1 proposes to use flammable refrigerants such as propane, which is very suitable as a refrigerant from a functional point of view but has hardly been used so far due to the above - mentioned fire and explosion hazard problems.

[0010] Taking into account the state of the art according to WO 2018 / 137 908 A1 and similar proposed solutions, it can be expected that the acceptance of using flammable refrigerants in air-conditioning systems for rail vehicles will increase significantly in the medium term. However, it should be noted that indirect circuits still result in disadvantages in terms of energy use due to heat losses in the intermediate heat exchanger, as well as additional weight and the need for additional installation space. Therefore, for the widespread use of flammable refrigerants, a direct evaporation system, a system that avoids these disadvantages, is desired. In order to be able to ensure a high level of safety against fire and explosion, including in the event of possible operating failures, further structural measures for the air-conditioning system of rail vehicles may thus ultimately be required, thus enabling the specific design of the various components.

[0011] A sensitive component in this regard is the electrical switch cabinet (electrical box) in a compact air-conditioning unit. Such electrical boxes are typically designed as a separate area within the air-conditioning unit, which has interfaces and houses all the components required to control or monitor the air-conditioning unit. To avoid danger, especially when using flammable refrigerants, it is necessary that no flammable mixture is allowed to enter the electrical box. This can basically be avoided by creating an overpressure inside. DE 10 2014 101 184 A1 relates to an electrical switch cabinet in which a fan is used to generate an overpressure inside to prevent the inflow of harmful particles, etc. However, this design is not suitable for flammable refrigerants. Similarly, if flammable refrigerants are used, it is not allowed to draw the air required for overpressure from the direct external environment of the air-conditioning system, as the pollution risk here is very high. Alternatively, a very high volume flow rate can be provided to achieve the corresponding dilution of the possibly contaminated air. However, the disadvantage of this is that higher fan power is required, and a very high volume flow rate will result in additional contamination, which in turn requires additional filtration. Summary of the Invention

[0012] Accordingly, the task of the present invention is to implement a direct evaporation system in which the electrical switch cabinet (electrical box) within a compact air-conditioning unit for rail vehicles is closed such that in the event of a relevant leak in the refrigerant delivery component, the component does not come into contact with the flammable refrigerant, and thus no flammable mixture will occur in these areas. Specifically, the aim is to prevent the flammable refrigerant from flowing into the electrical box after a leak.

[0013] This is achieved in that the electrical switch cabinet / electrical box is operatively connected to a component through which air is directed from an area outside the refrigerant delivery section or from an external area of the air-conditioning system to the electrical box, such that an overpressure can be generated in the electrical box, which is sufficiently closed for this purpose to prevent the accumulation of flammable refrigerant. This component for feeding air into the electrical box is designed as a separate fan through which air is drawn in from the surroundings of the air-conditioning system, thereby generating an overpressure in the electrical box. Alternatively, this component for air supply is designed as a duct structure that starts from an overpressure area of the air supply section of the air handling unit of the air-conditioning system and introduces a partial volume of the supply air stream into the electrical box. In another alternative, this component for air supply is designed as a duct structure that starts from an overpressure connection of the exhaust pipe of the air-conditioning system equipped with an exhaust fan and introduces a partial volume of the exhaust air stream into the electrical box.

[0014] Independently of the specific design, the component for supplying air to the electrical box from an area outside the refrigerant delivery section or from an external area of the air-conditioning system is designed such that an overpressure can be generated in the electrical box. To achieve this, the electrical box is designed as a sufficiently enclosed component. Alternatively, the electrical box can be designed with a free or duct-type exhaust duct leading to an exhaust outlet for directional ventilation and / or heat dissipation of the electrical components installed in the electrical box.

[0015] Thus, the novelty compared to the known prior art lies in that the electrical box is designed as a closed box. Thus, no contamination of the combustible mixture occurs during the stop period. The fan (which is present in any case) in the air-conditioning unit or vehicle has an additional function as an air supply fan or an exhaust fan. In addition, a separate fan can also be integrated into the design as required. Air is drawn from an area in the air-conditioning unit or from a vehicle with a non-flammable atmosphere, which is achieved by drawing air from an area without refrigerant delivery components. The air duct leading to the electrical box is provided by a separate duct or duct section, and the ventilation of the electrical box ensures at least a slight overpressure for the environment.

[0016] The technical solution according to the present invention improves the acceptance of using flammable refrigerants in air-conditioning systems for rail vehicles. This is because now the fire and explosion protection performance of the electrical switch cabinet (electrical box), which is a sensitive component in this regard, can be significantly improved, even in the case of the escape of flammable refrigerant in the vicinity of a compact air-conditioning system. Since an overpressure is permanently generated in the electrical box, the inflow of flammable refrigerant can be effectively prevented. Description of the Drawings

[0017] Hereinafter, embodiments of the present invention will be explained in more detail with reference to the accompanying drawings.

[0018] Figure 1Shows a stylized representation of a compact air - conditioning unit for a rail vehicle in a top view, with different arrangements of its parts and variants of their allocation to an electrical box.

[0019] Figure 2 Shows a stylized representation of an electrical box with internal over - pressure and different flow variants.

[0020] Figure 3 Shows a stylized representation of the basic arrangement of an electrical box as part of a compact air - conditioning unit.

[0021] Figure 4 Shows a stylized representation of a supplementary view according to Figure 3 a variant.

[0022] Figure 5 Shows a stylized representation of another supplementary view according to Figure 3 a variant. Detailed description

[0023] The air - conditioning system of the rail vehicle shown in the drawings is designed as a compact device to be installed on the roof and preferably operates with flammable refrigerants of classes A2, A2L, and A3 (e.g., R290). A plurality of components are provided through which over - pressure can be generated in an electrical switch box / electrical box to prevent the inflow of flammable refrigerants into the electrical box. The corresponding air required to establish a predetermined over - pressure enters from an area outside the refrigerant delivery section or from an external area, ensuring that there is no accumulation of flammable refrigerant inside the electrical box before a combustible mixture is reached.

[0024] Figure 1 Shows a top view of such a compact air - conditioning unit, with different variants for arranging the parts of the air - conditioning unit and their allocation to the electrical box.

[0025] Figure 1 a) Shows the over - pressure generated by sucking in ambient air with the help of a separate fan, which is specifically used to generate over - pressure in the electrical box.

[0026] Figure 1 b) Shows the over - pressure generated by a duct from the air - handling unit to the electrical box. In this case, conditioned air or mixed air is taken from an over - pressure area upstream of the electric heater in the air - handling unit and conveyed to the electrical box via a duct.

[0027] Figure 1 c) Shows the over - pressure generated by a duct from the exhaust duct to the electrical box. Here, an exhaust fan generates over - pressure in the electrical box.

[0028] Figure 1g) to 1j) show other variants in which overpressure is generated, where the various parts of the air-conditioning system are arranged alternately.

[0029] Figure 2 Different variants of an electrical box with internal overpressure and air outflow are shown.

[0030] Figure 2 d) shows a compact electrical box without a centralized outflow. This means that the heat source does not flow out, so the electrical components do not dissipate heat. The overpressure is generated by one of the above variants until a constant overpressure is achieved within the pressure tightness range reached.

[0031] Figure 2 e) shows a moderate rate of air leakage in the electrical box but no centralized outflow. The establishment and maintenance of the overpressure are achieved by the inflow of air by one of the above variants. In the non-pressure-sealed section of the air handling unit, outflow and leakage through gaps are possible. However, among other things, there is no significant outflow from the air handling unit to prevent the supply air from being ozone-polluted. The air exchange inside the electrical box results in non-directional heat dissipation.

[0032] Figure 2 f) shows the outflow from the electrical box via a conduit and the centralized heat dissipation of the electrical components. The establishment and maintenance of the overpressure are also carried out by the air injection process of one of the above variants. Therefore, the air exchange in the electrical box also results in the heat dissipation of the electrical components. Here, for example, directional heat dissipation is achieved by discharging along the electrical components to be cooled through a pipe to the discharge port.

[0033] Figure 3 The arrangement of an electrical box as part of a compact air-conditioning unit is shown. Here, the generation of overpressure is achieved, for example, by a fan whose intake grille is designed by several lines parallel to each other and having a rectangular profile.

[0034] In Figure 4 this basic design can be seen in more detail again, where the process of the air flow is also shown. Here, overpressure is generated for the interior of the electrical box by sucking in ambient air with a separate fan. This ambient air is sucked in by the fan via a specially designed weatherproof panel. Alternatively, there is an air filter in front of the fan to clean the ambient air.

[0035] Figure 5 Further details are shown, especially the fan in the electrical box with an interface to the environment.

Claims

1. An air conditioning system for a rail vehicle, the air conditioning system being configured to use a flammable refrigerant and being designed as a compact device to be installed on the roof, the air conditioning system comprising: an air handling unit; a compressor unit; and an electrical switch box, designed as a fully enclosed assembly and operably connected to an air supply assembly through which air is directed from an area outside the refrigerant delivery section of the air conditioning system into the electrical switch box such that overpressure can be generated within the electrical switch box to prevent the flammable refrigerant from entering the electrical switch box.

2. The air conditioning system according to claim 1, wherein: the air supply assembly for directing air from an area outside the refrigerant delivery section of the air conditioning system into the electrical switch box includes a separate fan configured to be able to generate overpressure within the electrical switch box.

3. The air conditioning system according to claim 1, wherein: the air supply assembly for directing air from an area outside the refrigerant delivery section of the air conditioning system into the electrical switch box includes a duct structure for starting from an overpressure area of the air supply part of the air handling unit and feeding a partial volume flow of the supply gas into the electrical switch box.

4. The air conditioning system according to claim 1, further comprising: an exhaust fan, wherein the air supply assembly for directing air from an area outside the refrigerant delivery section of the air conditioning system into the electrical switch box includes a duct structure that directs a partial volume flow of the discharge air from the exhaust fan from an exhaust duct into the electrical switch box.

5. The air conditioning system according to claim 1, wherein: the electrical switch box has openings for discharging and / or cooling electrical components installed inside the electrical switch box.

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