Méthode de détermination du niveau de charge en fluide réfrigérant dans un circuit de refroidissement pour un système de climatisation

Abstract

A method for determining a level of refrigerant charge in a cooling circuit of an air-conditioning system and a module for leak detection are provided. The method includes determining a total quantity of refrigerant contained in the cooling circuit of the air-conditioning system solely based on data internal to the air-conditioning system.

Claims

1. A method for determining a level of refrigerant charge in a cooling circuit of an air-conditioning system, the method comprising: determining a total quantity of refrigerant contained in the cooling circuit of the air-conditioning system solely based on data internal to the air-conditioning system.

2. The method of claim 1, wherein the data internal to the air-conditioning system used to determine the total quantity of the refrigerant comprises: data corresponding to geometric and technical parameters of different components of the air-conditioning system; information on a type of the refrigerant; and physical data of the refrigerant measured in different parts of the cooling circuit corresponding to different enthalpy levels.

3. The method of claim 2, wherein the data corresponding to the geometric and technical parameters of the different components of the air-conditioning system includes one or more of thermodynamic characteristics of a compressor of the air-conditioning system; geometric characteristics of the compressor; internal geometric characteristics of an evaporator of the air-conditioning system; internal geometric characteristics of a condenser of the air-conditioning system; or internal geometric characteristics of a liquid line of the air-conditioning system.

4. The method of claim 2, wherein the physical data of the refrigerant measured in different parts of the cooling circuit corresponding to different enthalpy levels includes pressure measurements of the refrigerant and temperature measurements of the refrigerant.

5. The method of claim 4, wherein the pressure measurements of the refrigerant include a high pressure of an enthalpy cycle of the air-conditioning system and a low pressure of the enthalpy cycle, and the temperature measurements of the refrigerant include a superheating temperature of the enthalpy cycle and a subcooling temperature of the enthalpy cycle.

6. The method of claim 1, further comprising determining a mass flow of the refrigerant based in part on a measurement of a power supply voltage of a compressor of the air-conditioning system, wherein the total quantity of refrigerant in the cooling circuit is based in part on the mass flow of the refrigerant.

7. The method of claim 6, wherein the mass flow of the refrigerant is also determined based on a superheating temperature of an enthalpy cycle of the air-conditioning system, a subcooling temperature of the enthalpy cycle, a high ressimle enthalpy cycle, a low pressure of the enthalpy cycle, and thermodynamic characteristics of the compressor.

8. (canceled)

9. The method of claim 6, further comprising calculating a quantity of the refrigerant in gas phase based on geometric characteristics of the compressor; the mass flow of the refrigerant and an enthalpy cycle of the air-conditioning system.

10. The method of claim 9, further comprising calculating a quantity of the refrigerant in liquid phase based on internal geometric characteristics of a liquid line of the air-conditioning system, the mass flow of the refrigerant, and the enthalpy cycle of the air-conditioning system.

11. The method of claim 10, further comprising calculating a quantity of the refrigerant in an evaporator of the air-conditioning system based on internal geometric characteristics of the evaporator, the mass flow of the refrigerant, and the enthalpy cycle.

12. The method of claim 11, further comprising calculating a quantity of the refrigerant in a condenser of the air-conditioning system based on internal geometric characteristics of the condenser, the mass flow of the refrigerant, and the enthalpy cycle.

13. The method of claim 12, wherein the total quantity of the refrigerant contained in the cooling circuit is determined as a sum of the quantity of the refrigerant in the liquid phase, the quantity of the refrigerant in the gas phase, the quantity of the refrigerant in the condenser, and the quantity of the refrigerant in the evaporator.

14. The method of claim 13, further comprising defining a nominal level of refrigerant charge; analyzing the total quantity of the refrigerant contained in the cooling circuit relative to the nominal level of refrigerant charge; and deducing a loss of functionality prediction of the air-conditioning system.

15. The method of claim 14, further comprising: transmitting, by a communication device via radio or data transfer bus, the total quantity of the refrigerant contained in the cooling circuit to an analysis device on the ground, wherein the analysis device on the ground performs the analyzing step and the deducing step.

16. A module for detecting leaks in a cooling circuit of an air-conditioning system, the module comprising: sensors configured to measure physical characteristics of a refrigerant in different parts of the cooling circuit, the different parts corresponding to different enthalpy levels; and a controller configured to determine a total quantity of refrigerant contained in the cooling circuit of the air-conditioning system based on data corresponding to geometric and technical parameters of different components of the air-conditioning system, a type of the refrigerant, and signals generated by the sensors, the signals representative of the physical characteristics of the refrigerant in the different parts of the cooling circuit measured by the sensors.

17. The module of claim 16, further comprising a communication device configured to communicate, via radio or a data transfer bus, the total quantity of the refrigerant contained in the cooling circuit, determined by the controller, to an analysis device on the ground.

18. The module of claim 16, further comprising a voltage sensor configured to measure a power supply voltage of a compressor of the air-conditioning system.

19. The module of claim 16, wherein the sensors comprise at least two temperature sensors and at least two pressure sensors.

20. The module of claim 19, wherein the at least two temperature sensors and the at least two pressure sensors comprise a first temperature sensor disposed on the cooling circuit between an expansion valve and a condenser of the air-conditioning system, the first temperature sensor configured to measure a subcooling temperature of the refrigerant in the cooling circuit, a second temperature sensor disposed on the cooling circuit between a compressor and an evaporator of the air-conditioning system, the second temperature sensor configured to measure a superheating temperature of the refrigerant in the cooling circuit, a first pressure sensor disposed between the compressor and the condenser, the first pressure sensor configured to generate a signal representative of a high pressure of the cooling circuit, and a second pressure sensor disposed between the compressor and the evaporator, the second pressure sensor configured to generate a signal representative of a low pressure of the cooling circuit.

21. (canceled)

22. (canceled)

23. A vehicle equipped with an air-conditioning system, the vehicle comprising: a module for detecting leaks in a cooling circuit of the air-conditioning system according to claim 16.

24. (canceled)

Description

DETAILED DESCRIPTION

[0036] The invention is described hereinafter in the context of a railway passenger carriage equipped with an on-board HVAC system. This configuration implementing the invention is described merely for better understanding of the invention, but cannot be regarded as limiting it. The same applies for all the other examples of implementation of the different features constituting the invention described hereinafter.

[0037] As shown in FIG. 1, a cooling circuit of an HVAC system 1 typically comprises a compressor 2, a condenser 4, a liquid line 5 comprising an expansion valve 10, and an evaporator 3. A refrigerant, for example R134a, flows in this circuit. This refrigerant in the circuit can sometimes be in liquid phase as in the liquid line 5, and sometimes in gas phase as in the compressor 2. In the condenser 4 and the evaporator 3, the refrigerant is in both gas phase and liquid phase. In order to detect a leak of refrigerant, the circuit of the HVAC system is equipped with a module for detecting leaks according to the invention. In one exemplary embodiment of the invention, the module for detecting leaks comprises a controller 8 and different sensors that transmit signals to the controller, exclusively representing internal parameters of the circuit 1 of the HVAC system. On the basis of these items of information supplied by the sensors, items of information relating to the thermodynamic and geometric characteristics of the components of the circuit, and the characteristics of the refrigerant used, for example R134a, the controller determines the quantity of refrigerant in the different components of the circuit and then deduces therefrom the total quantity of refrigerant contained in the circuit 1.

[0038] The module for detecting leaks also comprises a communication device 7 which transmits the total quantity of fluid determined by the controller 8 to an analysis station on the ground 6 that determines the fluid losses and the potential losses of functionality that arise therefrom. Data transmission between the communication device 7 of the module for detecting leaks and the analysis station on the ground can take place, for example, by radio transmission or via data transfer bus. The main controller of the carriage or of the HVAC system can be used in the module for detecting leaks to determine the quantity of refrigerant contained in the circuit. The same applies for all or some of the sensors transmitting the items of information that is required to the controller 8. Most of the sensors are already present in the HVAC systems of existing vehicles and can thus be re-used for the module for detecting leaks of refrigerant. For older vehicles, these sensors and the controller 8 can in most cases be installed, for example on the occasion of a maintenance operation.

[0039] In addition to the controller 8 and the communication device 7, the module for detecting leaks of refrigerant comprises two pressure sensors mounted on the cooling circuit 1. A high pressure sensor 13 is situated between the compressor 2 and the condenser 4 of the on-board air-conditioning system, and a low pressure sensor 14 is situated between the compressor 2 and an evaporator 3 of the on-board air-conditioning system. These pressure sensors 13 and 14 transmit signals to the controller 8 that are representative of the pressure of the refrigerant downstream and upstream of the compressor 2. The module for detecting leaks also comprises two temperature sensors also installed on the cooling circuit 1. A first temperature sensor 11 is situated between the expansion valve 10 and the condenser 4 of the on-board air-conditioning system. This temperature sensor 11 measures the subcooling temperature of the refrigerant in the circuit. A second temperature sensor 12 is situated between the compressor 2 and the evaporator 3 of the on-board air-conditioning system. This temperature sensor 12 measures the superheating temperature of the refrigerant in the circuit. Optionally, a voltage sensor 9 can be mounted on the power supply to the compressor 2 so that the signal representative of the power supply voltage of the compressor is transmitted to the controller 8.

[0040] FIG. 2 shows the logic on which the method for detecting leaks of refrigerant is based, implemented by the controller 8 for determining the total quantity of refrigerant contained in the cooling circuit. Transmitting the total quantity of fluid contained in the circuit makes it possible to monitor fluid quantity change as a function of time. Before being transmitted by the communication device 7 to the analysis device on the ground 6, the signal is filtered in order to identify and eliminate unwanted effects resulting from any surcharges of refrigerant with respect to the critical charge. The method for determining the level of refrigerant charge in the circuit of an HVAC system solely uses data internal to the cooling circuit as described below. This data corresponds to the geometric and technical parameters of the different components of the cooling circuit, information about the type of refrigerant used, and the high and low pressures as well as the superheating and subcooling temperatures of the refrigerant measured in different parts of the circuit by sensors positioned as described above and corresponding to different enthalpy levels.

[0041] The data corresponding to the geometric and technical parameters of the different components of the air-conditioning system are the thermodynamic and geometric characteristics of the compressor 2, the internal geometric characteristics of the evaporator 3 and of the condenser 4, and the internal geometric characteristics of the liquid line 5.

[0042] Thus, as shown in FIG. 2, the mass flow of the refrigerant in the cooling circuit is determined on the basis of the measured high and low pressures as well as the superheating temperature, the power supply voltage of the compressor, and the thermodynamic characteristics of the compressor. The pressure/temperature enthalpy cycle of the refrigerant is obtained on the basis of the measured high and low pressures, of the superheating and subcooling temperature, and of the thermodynamic characteristics of the compressor.

[0043] In turn, the pressure/temperature enthalpy cycle and the mass flow make it possible to determine the quantity of gas in the gas line and the compressor with the geometric characteristics of the compressor, the quantity of gas and liquid in the evaporator with the geometric characteristics of the evaporator, the quantity of gas and liquid in the condenser with the geometric characteristics of the condenser, and the quantity of liquid in the liquid line with the geometric characteristics of the liquid line. Once determined, these four quantities of refrigerant make it possible to obtain the total quantity of refrigerant contained in the circuit as a whole.

[0044] The mass flow of refrigerant drawn in and discharged by the compressor is calculated by using the polynomial formulas given by the manufacturer. Such as for example: M=C0+C1*S+C2*D+C3*S.sup.2+C4*S*D+C5*D.sup.2+C6*S.sup.3+C7*D*S.sup.2+C8*S*D.sup.2+C9*D.sup.3. In this formula, C1 to C9 are coefficients, S is the evaporation temperature in ° C., D is the condensation temperature in ° C., and the resultant M is the sought mass flow in kg/s. The mass flow is calculated for a nominal superheating value. It must therefore be recalculated for the actual superheating value on the cooling circuit in view of the impact of temperature on the density of the gas that is drawn in by the compressor 2. The coefficients, for their part, are calculated for a certain frequency. It is therefore necessary to recalculate the mass flow for the actual frequency by multiplying the result by the ratio: actual frequency/nominal frequency.

[0045] In the modelling of the enthalpy cycle of the refrigerant, the polynomials of the fluid used are: the pressure with respect to the temperature, the density of the liquid with respect to the pressure, the density of the gas with respect to the density, the molar specific heat of the liquid with respect to the pressure, the molar specific heat of the gas with respect to the pressure, the enthalpy of the liquid with respect to the pressure and the enthalpy of the gas with respect to the pressure. The graph of pressure against temperature, shown in FIG. 3, is obtained. With this data it is possible to draw the pressure/temperature enthalpy graph shown in FIG. 4.

[0046] The dimensions of the tubes constituting the condenser, the evaporator and the liquid line are used to estimate the volume, the velocity and the density of the fluid in the tubes. For example:

TABLE-US-00001 Number of tubes Length Rows Diameter Thickness Volume Condenser 19 1.10 mm 8 9.52 mm 0.28 mm 10.5 l  Evapo- 10 1.05 mm 6 9.52 mm 0.28 mm 4.0 l rator Liquid 4.13 mm 16.0 mm  1.0 mm 0.6 l line

[0047] As the liquid line 5 is full of liquid, it is possible to determine the volume of fluid therein by considering the density of the fluid at the pressure of the condenser (given by the high pressure sensor 13) and the subcooling temperature (given by the subcooling temperature sensor 11).

[0048] It is also possible to determine the density in the evaporator 3 and the condenser 4, knowing the number of circuits in the heat exchanger and the mass flow, which is fixed throughout the whole length of the circuit. The equivalent density is calculated by integrating superheating/desuperheating in the percentage of liquid according to the enthalpy diagram.

[0049] Because the density of the gas is 1000 times lower than that of the liquid, it is possible to disregard the volume contribution of the gas line and of the compressor 2.

[0050] FIG. 5 shows the results of tests conducted in the laboratory with a cooling circuit in a climate chamber at different exterior and interior conditions. The x-axis shows the condensation pressures. The y-axis shows the calculated refrigerant level. The curves in different colours show the results of the calculation for the different tested levels of charge of fluid. The deformation of the curves for the low condensation pressures is due to the effect of the excess of liquid in the condenser.

[0051] The method described above is transcribed into a computer program the instructions of which, when they are executed by a controller, make it possible to determine the quantity of refrigerant contained in a cooling circuit for an HVAC system. The program can equally well be installed in a specific controller of the module for detecting leaks of refrigerant as in a main controller, such as the one that manages the operation of the HVAC system.

[0052] The combination of the advantages obtained by the different aspects of the method and the module described above make it possible to determine the total quantity of fluid in a cooling circuit for an HVAC system solely on the basis of parameters internal to the circuit. It is thus possible to eliminate the impact of clogging of the heat exchangers and of the volume of air surrounding them on all the other variables affecting the heat transfer coefficient. The theoretical approach described above thus makes it possible to apply the solution of the invention to all the vehicles of a fleet without a costly programme of tests, since only one adjustment test is necessary.

[0053] As the module for detecting leaks of refrigerant is a stand-alone product, it can be installed in all the vehicles equipped with on-board HVAC systems, whether they are new or due to be updated.

[0054] Communication by data transfer bus or by radio between the controller 2 of the module for detecting leaks and the analysis station on the ground 6 makes it possible to monitor the state of the HVAC systems of a fleet of passenger transport vehicles and to assess the interval for an operation to repair and/or refill the circuit as a function of monthly temperature forecasts. In terms of ecological impact, the ability to intervene on the HVAC system before the cooling circuit is completely discharged significantly reduces emission into the atmosphere of refrigerant responsible for global warming.

[0055] Although in the above description the specific aspects of the invention, in particular the implementation of the method for determining the quantity of refrigerant in a cooling circuit, and the method for detecting leaks for on-board HVAC systems, have been described in the context of a passenger carriage, they could be implemented in other configurations, in particular with other types of passenger transport vehicle.