WO2005068919A1 - Control and security device for the compressor of a refrigerating machine - Google Patents

Abstract

The invention relates to a security device (5) for a compressor (1) of a refrigerating machine (1), comprising a programmable electronic control means (7) which can stop the compressor (1) from operating and/or prevent it from starting, a sensor capturing the pressure Pasp during the intake (6) of the compressor (1), said sensor being connected to the programmable electronic control means (7), and a sensor capturing the temperature Tasp during the intake of the compressor, said control means (7) being able to calculate the temperatureTsat of the refrigerating fluid at the point of the saturated vapour curve corresponding to the pressure during intake of the compressor Pasp, and being able to stop and/or prevent the compressor (1) from starting if said temperatureT asp differs by more than one threshold value from the calculated temperature Tsat.

Description

 Safety and control device for refrigeration machine compressor

Subject of the invention

The present invention relates to refrigeration machines, and more particularly to compressors present in refrigeration machines.

The present invention relates in particular to a safety, control and management device for a refrigerating machine compressor.

Technological background

In refrigeration machines, one or more compressors are used to compress a refrigerant. This type of installation is well known from the state of the art. These compressors are used individually or in groups of several compressors connected in parallel to form a refrigeration plant. Their function is to compress the refrigerant coming in gaseous form from an evaporator, and to restore it under high pressure to a condenser. They are used for long periods, without supervision, and must respond to variable load constraints, resulting from the conditions of use of the fridges or warehouses in which they are used, random weather conditions, and possible faults in the circuit to which they are connected. Many external causes can therefore be the source of operational problems that can lead to compressor failures. The causes and conditions under which a fault has arisen are not always easy to determine, which can cause liability issues, particularly during the warranty year of an installation. The lubrication of a compressor can be done by bubbling or using an oil pump. When the compressor stops, if the oil is too cold, the refrigerant dissolves in the oil, and can even condense. Since the refrigerant in liquid form has a density greater than that of oil, it then collects at the bottom of the compressor housing. When the compressor restarts, the oil pump circulates an oil loaded with refrigerant, or even pure condensed refrigerant. The refrigerant being a degreaser, the compressor deteriorates and seizes quickly. In addition, if the compressor starts when condensed refrigerant has collected in the bottom of the housing, the following phenomenon may occur: the action of the compressor decreases the pressure in the compressor housing. Under the effect of this decrease in pressure, the refrigerant evaporates, in the form of bubbles and crosses the layer of oil which covers it. This evaporation can occur suddenly, and cause an oil / vapor droplet emulsion of the refrigerant. This emulsion occupies the volume of the casing, and is finally driven by the compressor to the discharge, causing a large amount of oil in the refrigeration circuit. This phenomenon is known as the “mayonnaise effect”.

When the oil temperature is too high, its viscosity is reduced, thereby reducing its lubrication properties. Seizure or premature wear of the compressor may result. Sometimes it happens that the refrigerant does not evaporate properly in the evaporator, and returns to the compressor in the form of liquid. This phenomenon, called "liquid blow" is a major cause of compressor failure. It can occur when an expansion valve is incorrectly adjusted or blocked in the open position or during a malfunction of the evaporator. Sometimes, on the contrary, the refrigerant returns to the compressor in the form of superheated steam, which can cause the compressor oil to overheat and cause the problems mentioned above. above. This phenomenon is known as "significant overheating" by refrigeration engineers.

Other problems that can occur on this type of machine are: refrigerant leakage, poor cooling of the condenser, etc.

The problems mentioned above can generally be detected by a technician using measurements of temperature, pressure, oil level, etc.

State of the art

There are problems mentioned above that for the proper functioning of a refrigeration installation, it is necessary to control the operation of the compressor, according to measures such as temperatures, pressures, oil level, etc. These measurements determine whether the compressor can be started or must be stopped.

Among the safety devices traditionally used are low pressure switches, connected to the compressor housing. These pressure switches are adjusted once and for all during installation, and do not allow intelligent control of an installation. Traditionally, sensors are installed on a refrigeration installation, and they are connected to a control panel. This control panel includes many electrical and electronic components. It is generally assembled on site, which represents a workload and a source of errors. In addition, this control panel being installed at a certain distance from the compressor (s), it requires numerous electrical and hydraulic connections. These numerous disjointed elements are not designed to collaborate with each other and to optimize the operation of the compressor. EP 0 907 058 A2 discloses a control device for a refrigerating machine compressor. This device includes an electronic circuit in a box that can be installed on the compressor. In this device, high and low oil pressure alarms are used to stop the compressor. According to this invention, the electronic circuit includes a timer which has the function of delaying the restart of the compressor after the oil pressure has returned to normal. During this period, the oil stabilizes, and any refrigerant present in the oil separates. A user can communicate with the device using a portable device. However, this device does not include any pressure measurement means, which makes it incapable of detecting the faults mentioned above.

There is also known a control device for a compressor of a refrigerating machine from document US 5,901,559. This device describes an oil level controller, capable of admitting the oil collected in a tank into the casing of a compressor. . According to this document, a first delay is provided when the low oil level is detected, before the oil intake. A second time delay is also provided to maintain the oil intake for a delay after the oil level has returned above the low threshold. This document also discusses the possibility of measuring other parameters (See "input device 98" in Figures 2 and 5, as well as in the text, column 2, line 54 to 62, and column 5, lines 38 to 59). However, only the problem of controlling the oil level in the compressor crankcase is dealt with in this document, the use of other parameters being mentioned only very generally. Finally, a distributed intelligence control device for commercial refrigeration is known from document US 6,332,327. This device describes the use of a master controller 70, and of security and control modules 48, installed on each of the compressors, and in communication with the master controller. This document does not, however, address the safety issues specific to each individual compressor.

These known devices therefore do not solve all the above problems, which affects the life of the compressor. In particular, the principle of control of these devices is based on the assumption that the compressor is in a correct operating state after a certain period of time has elapsed, without there actually being a measurement of this state.

Aims of the invention The present invention aims to provide a safety device for a compressor of a refrigerating machine, making it possible to extend the life of the compressor.

In particular, the present invention aims to provide a device and a method which detects problems which may deteriorate the compressor, and which takes the measures necessary for its safeguarding. The present invention also aims to provide a device for carrying out the regulation of a refrigeration plant.

Summary of the invention

The present invention relates to a safety and control device for a refrigerating machine compressor, placed on the compressor casing, comprising a programmable electronic control means capable of stopping operation and / or prohibiting starting of the compressor, a pressure sensor at the suction of the compressor p _as , this sensor being connected to the programmable electronic control means, further comprising a sensor of the temperature at the suction of the compressor T _aS p, the control means being able to calculate the temperature T _sa t that the refrigerant would have at the point of the saturated vapor curve corresponding to the suction pressure of the compressor p _asp , and to stop and / or prohibit starting the compressor if this temperature T _asp differs more than one threshold value of the calculated temperature T _sa t.

In this device, the programmable electronic control means may include means capable of receiving parameters A1 and B1, and making it possible to calculate the temperature T _sat as a function of the pressure p _aSp by means of the relation

T _sat = (B1 / (A1-Ln (p _asp +1)) - 273

said parameters being chosen as a function of the refrigerant used in the refrigerating machine.

The device can advantageously include a sensor of the oil temperature in the compressor T _h a, and the control means programmable electronics include means capable of receiving the characteristics of the oil and of the refrigerant used, and of determining the concentration of refrigerant in the oil and the kinematic viscosity of the oil, as a function of the temperature of the oil in the compressor, T _h uiie, and of the suction pressure of the compressor, p _aS p, and to stop and / or prohibit the start of the compressor if this viscosity is less than a predetermined threshold.

The characteristics of the oil and of the refrigerant used can be determined by parametric curves giving firstly, for each temperature of the oil in the compressor T _h a _e and each pressure at the suction of the compressor p _asp , the concentration of refrigerant in the oil, and then giving, for each temperature of the oil in the compressor T _nU ii _e and each concentration of refrigerant in the oil, the kinematic viscosity of the oil. In a preferred variant of the invention, the programmable electronic control means comprises means capable of stopping operation and / or prohibiting the start of the compressor when the pressure at the suction of the compressor p _asp is less than a threshold predetermined. In another preferred variant of the invention, the device comprises a sensor for the discharge pressure of the PHP compressor and this sensor is connected to the programmable electronic control means so as to stop the operation and / or prohibit the starting of the compressor when the discharge pressure of the PHP compressor is above a predetermined threshold.

The pressure sensors are preferably ceramic sensors with thick layers, or piezoresistive sensors. The programmable electronic control means preferably comprises a microprocessor. The programmable electronic control means can also include storage means and / or communication means. The programmable electronic control means may favorably be able to activate local and / or remote signaling means.

In a preferred embodiment of the invention, the device is designed for use in a refrigeration plant, in which each compressor comprises a device according to the invention, these devices being interconnected. The programmable electronic control means of one of the compressors determines, as a function of a set value, of a measured or calculated parameter, whether they should start the compressor which they control, taking into account the measurements of the sensors, stored information and that communicated by at least one other similar device installed on another compressor.

The present invention also relates to a refrigeration plant comprising a plurality of compressors, in which at least one compressor comprises a safety and control device according to any one of the preceding claims. The present invention finally relates to a method of using a compressor for a refrigeration machine, comprising the following steps: - measuring the pressure at the suction of the compressor p _asp; - the temperature at the suction of the compressor T _asp is measured _; - the temperature T _sa t that the refrigerant would have at the point of the saturated vapor curve corresponding to the pressure at the suction of the compressor p _asp is calculated; - the compressor is stopped and / or prohibited from starting if the suction temperature of the compressor T _asp differs by more than a threshold value from the calculated temperature T _sat .

Brief description of the figures [0033] Figure 1 represents a refrigeration installation of the state of the art comprising a compressor fitted with a device according to the invention. FIG. 2 represents the pressure-enthalpy diagram representative of the thermodynamic cycle traversed by a refrigerant in the installation of FIG. 1.

Figure 3 shows the curves of the characteristics of a lubricating oil and a refrigerant.

4 shows a group of compressors for operation in a refrigeration plant, each compressor being provided with a device according to the invention, these devices being interconnected by means of a network.

Detailed description of a preferred embodiment of the invention As illustrated in a simplified manner in FIG. 1, a refrigeration installation comprises: - a compressor 1 which compresses a refrigerant in the gas phase, by increasing its temperature; - a condenser 2 which, cooled by a cold source such as outside air or water, drops the temperature and condenses the refrigerant; - a tank in which the liquid refrigerant is stored (not shown); - a regulator 3; - And an evaporator 4 in which the refrigerant passes from the liquid phase to the vapor phase by taking calories from its environment. The evaporator 4 therefore allows the production of cold in a cold room, a refrigerated cabinet or can also cool a liquid in a heat exchanger.

The security device according to the invention comprises a housing

5 which is fixed on the compressor casing 1, preferably at the location provided for the oil level sight glass. A piezoresistive pressure sensor 6 inside the housing 5 is in contact with the pressure prevailing in the compressor casing and transmits an analog signal to the microcontroller or a microprocessor 7. A temperature probe 8, by example a thermoresistor, immerses in the oil 9 contained in the bottom of the compressor casing 1, and also transmits a value to the microcontroller 7. A second pressure sensor 10, also piezoresistive, is installed in the housing 5 and is connected by a tube 11 at the compressor discharge 1. Finally, a temperature sensor measures the temperature T _asp at the compressor intake. All these sensors are either integrated into the housing 5, or connected directly to the latter by a short cable or tube 11. Compressor 1 fitted with its safety device forms a compact unit, easy to assemble and test in the factory. In the use of the device according to the invention, the joint use of an analog pressure transmitter and a microcontroller makes it possible to vary the thresholds and the triggering and switching on times of the compressor. If this pressure becomes too low, for example in the event of a refrigerant leak, incorrect setting or the closing of a valve, the compressor is stopped, and an alarm is signaled. There is therefore a flexibility of use which it was not possible to obtain with conventional pressure switches. The use of a pressure sensor has, compared to the use of a pressure switch, the advantage of giving a real measurement of the pressure, not presenting the inaccuracies that one can have with a mechanical pressure switch. The microcontroller 7 has a logic output making it possible to control the contactor of the compressor 1 motor, thus making it possible to stop the compressor or to prohibit starting it if it is stopped. The microcontroller 7 also includes a logic output making it possible to control one or more signals located on the box 5 itself, or nearby, or on a remote control panel.

Figure 2 illustrates the pressure-enthalpy diagram of a refrigerant. In this diagram, the fluid is in liquid form in zone A, in gaseous form in zone C. The liquid and gas phases coexist in zone B. The portion 20 of the phase change curve is the "vapor curve saturated ”. Point 1 is representative of the compressor suction. Segment 1-2 represents compression, segment 2-3 represents condensation. Segment 3-4 represents expansion in the regulator, and segment 4-1 evaporation. In the optimal conditions of operation, all the fluid is vaporized at the end of the journey in the evaporator. The problems mentioned above, namely "liquid blow" and "significant overheating" result in a point representative of the fluid at the inlet of the compressor not at point 1 of the diagram, but in a point on the left for the liquid blow (all the fluid is not evaporated), or to the right of it for significant overheating (the gas has been heated in the evaporator beyond normal). These two problems are solved by the device of the invention in the following way: The microcontroller calculates the temperature that the fluid should have at point 1 of the saturated vapor curve corresponding to the pressure measured at suction. The portion 20 of the curve can be approached by the pressure-temperature relationship, of the shape

T _sat = (B1 / (A1-Ln (p _asp +1)) - 273

The parameters A1 and B1 are determined for the refrigerant used, and recorded in the microcontroller 6, either by insertion of an EEPROM memory previously programmed, or by a wired infrared link. 'Ln' denotes the "natural logarithm" function. The temperature T _asp , measured by the sensor 12, is compared with the value it should have if the operating point was indeed point 1, that is to say T _sat . If T _asp is less than or equal to T _sat , there is a risk of liquid blow. If this difference is greater than a threshold, the compressor is stopped. The threshold can be between 5 and 20 °, for example 10 °. If, on the contrary, T _asp is greater than T _sat , there is a significant overheating, which risks overheating the oil. The compressor is therefore stopped if this difference is greater than a threshold. This second threshold can also be between 5 and 20 °, for example 10 °. By using this device and this method, an effective protection of the compressor is therefore obtained, both against significant overheating and against liquid blow, by performing a simple calculation, based on two parameters, and on a pressure measurement, and a temperature measurement. The device according to the invention may also include a high pressure sensor 10 PHP, connected by a hose 11 to the high pressure part of the cylinder head of the compressor. If the pressure is too high, whose main cause is poor cooling of the condenser (fan out of service, dirty battery or lack of water for water condensers), the microcontroller signals a high pressure alarm. An intensity sensor measures the intensity of the compressor motor. If this intensity deviates too much from a nominal value, the microcontroller signals an intensity alarm. This is to prevent the compressor from operating under abnormal and harmful intensity conditions. Oil contained in the compressor housing ensures good lubrication of moving parts. Lubrication can be ensured by bubbling for small powers and by an oil pump for larger compressors. The type of oil used depends on the type of refrigerant used in the installation and operating temperatures as well as the recommendations of the compressor manufacturer. We also see in Figure 1 an oil temperature sensor, which measures the oil temperature. If the oil is too cold, it is impossible to avoid the migration of refrigerant into the oil. When the compressor starts, the refrigerant mixed with the oil is injected by the oil pump into the bearings of the compressor. As the refrigerant is a degreaser, the compressor quickly seizes up. To avoid this problem, a crankcase heater is energized to keep the temperature high enough. If the temperature is sufficient, this voltage can be cut to save energy. The control means put the crankcase heater on or off, depending on the oil temperature and the desired temperature that the microcontroller determines from the type of gas, the type of oil and the low pressure. As long as the concentration of refrigerant in the oil is not acceptable, the microcontroller prevents the compressor from starting and continues to heat the oil. Figure 3 shows the curves of the characteristics of a lubricating oil and a refrigerant. These curves are recorded in the microcontroller, in the form of tables, or parametric curves, either by insertion of an EEPROM memory previously programmed, or by a wired infrared link. The microcontroller can then determine, on based on the oil temperature and the suction pressure p _as , the content of refrigerant which has dissolved in the oil. For example, for a temperature of 30 ° C, is under a pressure of 5 bar, it is noted that the refrigerant R22 dissolves in SUNISO 4GS oil, up to a content of 10%. The microcontroller can then determine, for this same temperature of 30 ° C, on the curve "10% of refrigerant in oil", that the kinematic viscosity of this oil is 30 cSt. To avoid lubrication faults, the microcontroller signals an alarm and prohibits starting the compressor when the viscosity is less than a determined value, generally specified by the manufacturer of the compressor. To extend the life of a compressor, it must be avoided that it starts more than six times an hour. In the device according to the invention, the microcontroller detects the start of the compressor thanks to the intensity sensor, and are connected to a clock, which makes it possible to perform this function.

In general, the user of a refrigerating machine is not permanently close to his installation. It is therefore interesting to know the current state of compressor 1 and any corresponding alarms, but also the past state. This is why the device according to the invention comprises a memory, in which the microcontroller 7 can record information relating to the state and the alarms of the compressor.

The stored information includes the temperatures and pressures measured, the temperatures and viscosity calculated, the alarms reported. In this example, the information is recorded every 30 seconds, and the memory is sufficient to store the information corresponding to a duration of one month.

The device according to the invention also comprises means of communication, allowing the microcontrollers 7 to exchange with a user information on the state and the current and past alarms of the compressor. These means of communication also allow the user to give instructions and parameters to the microcontrollers, for example the type of refrigerant, the type of oil, the limit values corresponding to each alarm, etc. These means of communication can include a wired or wireless local area network.

Each of the alarms can give rise to the display of a message, to a recording, a starting ban on the compressor or a stopping of the latter if it is running, possibly after the expiration of a certain deadline or the fulfillment of other conditions. Alarms can be signaled to maintenance operators by the lighting of light-emitting diodes on one face of the housing 5, or, when the device is connected to a network, to a central display panel or screen. Figure 4 shows a machine equipped with several compressors. Such a machine is called a refrigeration plant. The purpose of a refrigeration plant is to maintain a low pressure or a constant high pressure, depending on the load variation of the installation. This variation in load is due to the cold shutdown on a station when it is stopped or when it has reached the desired temperature. In the refrigeration plant, each compressor is equipped with a device according to the invention 5, therefore comprising a low and / or high pressure sensor. The microcontroller of a compressor decides whether the compressor it controls should be started or stopped according to the low or high pressure measured, a set pressure and the state of the other compressors with which it can communicate thanks to means of communication 30 wired or wireless (by radio wave). They obviously also take into account the generated alarms. Each device makes its decision independently of the others, which has the advantage of a statistical balancing of the operating times of each compressor, and the absence of a central unit, a fault of which would be harmful to all of the compressors. The device according to the invention therefore provides a simple and easy to implement safety device to avoid the conditions that can cause compressor failures. It also makes it possible to regulate a refrigeration plant, without having to resort to a centralized control body.

Claims

1. Safety and control device (5) for compressor (1) of refrigerating machine, comprising a programmable electronic control means (7) capable of stopping the operation and / or prohibiting starting of the compressor, a pressure sensor to the suction of the compressor (6) p _asp , this sensor (6) being connected to the programmable electronic control means (7), characterized in that it comprises a temperature sensor at the suction of the compressor (12) T _asp , said control means (7) being capable of calculating the temperature T _sa t that the refrigerant would have at the point of the saturated steam curve corresponding to the suction pressure of the compressor p _asp , and to stop and / or prohibit starting the compressor (1) if this temperature T _asp differs by more than one threshold value from the calculated temperature T _sa t. 2. Device (5) according to claim 1, characterized in that the programmable electronic control means (7) comprises means capable of receiving parameters A1 and B1, and making it possible to calculate the temperature T _sat as a function of the pressure p _asp by means of the relation T _sat = (B1 / (A1-Ln (p _asp +1)) - 273, said parameters being chosen as a function of the refrigerant used in the refrigerating machine. 3. Device (5) according to any one of the preceding claims, characterized in that it comprises a temperature sensor (8) of the oil (9) in the Thuiie compressor, and that the programmable electronic control means (7) comprises means capable of receiving the characteristics of the oil (9) and of the refrigerant used, and of determining the concentration of refrigerant in the oil and / or the kinematic viscosity of the oil, as a function of the temperature of the oil (9) in the compressor T _h uii _e , and of the suction pressure of the compressor p _asp , and to stop and / or prohibit the starting of the compressor (1) if this viscosity is less than a predetermined threshold, or if the concentration of refrigerant in the oil (9) is greater than a threshold. 4. Device (5) according to claim 3, characterized in that the characteristics of the oil (9) and of the refrigerant used are determined by parametric curves giving, firstly, for each temperature of the oil in the compressor T _e ^ n and each suction pressure p _asp compressor, the refrigerant concentration in the oil, and then giving, for each oil temperature in the compressor and each T _h uiie refrigerant concentration in oil, the kinematic viscosity of the oil (9). 5. Device (5) according to any one of the preceding claims, characterized in that the programmable electronic control means (7) comprises means capable of stopping the operation and / or prohibiting the starting of the compressor when the pressure at compressor suction _asp is less than a predetermined threshold. 6. Device (5) according to any one of the preceding claims, characterized in that it comprises a sensor of the discharge pressure of the compressor (10) PHP, this sensor (10) being connected to the programmable electronic control means ( 7) so as to stop the operation and / or prohibit the starting of the compressor (1) when said discharge pressure of the PHP compressor is greater than a predetermined threshold. 7. Device (5) according to any one of the preceding claims, characterized in that the pressure sensor (s) (6, 10) are selected from ceramic sensors with thick layers and piezoresistive sensors. 8. Device (5) according to any one of the preceding claims, characterized in that the programmable electronic control means (7) comprises a microprocessor. 9. Device (5) according to any one of the preceding claims, characterized in that the programmable electronic control means (7) comprises storage means and / or communication means (30) wired or wireless. 10. Device (5) according to any one of the preceding claims, characterized in that the electronic control means programmable (7) is able to activate local and / or remote signaling means. 11. Device (5) according to any one of the preceding claims, for use in a refrigeration plant, in which each compressor (1) comprises a device (5) according to the invention, these devices (5) being interconnected, characterized in that the programmable electronic control means (7) determines, as a function of a set value, of a measured or calculated parameter, whether they should start the compressor (1) which they control, by taking takes into account the measurements of the sensors (6, 8, 10, 12), the stored information and that communicated by at least one other similar device (5) installed on another compressor. 12. Refrigeration plant comprising a plurality of compressors (1), in which at least one compressor (1) comprises a safety and control device (5) according to any one of the preceding claims. 13. Method of using a compressor (1) for a refrigerating machine, comprising the following steps: - measuring the pressure at the suction of the compressor p _asp; - the temperature at the suction of the compressor T _asp is measured _; - the temperature T _sat that the refrigerant would have at the point of the saturated vapor curve corresponding to the pressure at the suction of the compressor p _asp is calculated; - the compressor start (1) is stopped and / or prohibited if the suction temperature of the compressor T _asp differs by more than a threshold value from the calculated temperature T _sat .