Refrigeration plant.

p0001The invention relates to a method of regulating the superheating of the refrigerant at the exit of a driven in at least one more compressor and an expansion valve containing refrigerant circulation evaporator of a refrigeration system in which the superheat temperature is continuously measured at the evaporator outlet and from the superheat temperature measured value and other monitored parameters of the refrigerant circuit by comparison with a set value, a control signal for the expansion valve is derived. Moreover, the invention relates to a refrigeration system having a refrigerant circuit which includes at least one compressor, one constructed as a control valve expansion valve and an evaporator, with a arranged at the output of the evaporator temperature measuring device for measuring the superheat temperature of the refrigerant and with a control device consisting of a by the temperature emitted, characteristic of the superheat temperature signal and indicative of other parameters of the refrigerant circuit signals derives a control signal for the expansion valve. Finally, the invention relates to a pressure-balanced expansion valve for such a refrigeration system with an electric motor drive for a valve housing adjustably mounted valve member.

p0002Under "chillers" in this sense are understood quite generally working with a cyclic process of the refrigerant thermodynamic systems in which sucked vapor refrigerant at the outlet of an evaporator and compressed, then condensed under heat, then expanded via an expansion valve and evaporated in an evaporator, thereby absorbing heat is , Such facilities include air conditioning, heat pumps, heat recovery systems, freezing systems, Eiserzeugungsanlagen, refrigeration systems, to name just a few examples.

p0003In these systems, provision must generally be taken to ensure that on the one hand, the available heat exchange surface of the evaporator is optimally utilized, but on the other hand ensures that the refrigerant is transferred entirely in the vapor state when entering the compressor. In leaving the evaporator sucked from the compressor vapor refrigerant liquid droplets still present in fact lead to a significant mechanical stress on the compressor (slugging); they must therefore be avoided in view of the proper operation and the life of the compressor. Practically this is achieved by making the refrigerant to the evaporator with a certain overheating leaves, so that the compressor from drawing in non-vaporized liquid shares. * Journal "air conditioning, refrigeration, heating" October 1985 pages ...

p0004This overheating is controlled via the expansion valve, which always supplies the evaporator with a mass flow of liquid refrigerant such size that, under the respective operating conditions under which the refrigerant evaporates, a balance between supply of the liquid and aspirated superheated vapor refrigerant is maintained. It is known, by means of two temperature sensors to measure the temperature of the refrigerant at the evaporator inlet and the evaporator outlet and to generate the difference between these two temperature values ​​an overheat signal is derived from the in a controller by means of a setpoint / actual value comparison, a control signal for the expansion valve whose drive has a temperature-controlled, diaphragm drive motor or an electrically driven stepping motor. *

p0005Because of the inevitable refrigerant-side pressure drop in the evaporator which deviates from the temperature measurement at the evaporator inlet and evaporator outlet derived overheating signal from the actual overheating greater or lesser extent from, with the result that operated in consideration of the compressor for safety reasons the evaporator with a relatively large overheating must be, which is typically in the order of 12-13 ° K. The consequent deterioration of the utilization of the evaporator must be taken into account. In evaporators with high pressure loss can be achieved at all only with additional measures optimum utilization of the evaporator surface, which are complicated and expensive.

p0006The object of the invention is, therefore, a way to show which allows to work without endangering the compressor by aspirated, non-evaporated liquid particles with a lower superheat of the refrigerant at the evaporator outlet and hence to ensure optimum use of the heat exchanger surface of the evaporator.

p0007To achieve this object is achieved according to the method mentioned initially proceeded in a manner that in addition measured to the superheat temperature of the pressure of the vaporized refrigerant at the evaporator outlet and running the corresponding saturation temperature value is determined this saturation pressure value in the state diagram of the refrigerant that the difference between the measured superheat value and the saturation temperature value determined in this way and this determines the actual overheating corresponding actual temperature difference value compared with a predetermined desired temperature difference value and from the comparison the control signal for the expansion valve is derived.

p0008The direct measurement of the saturation vapor pressure at the evaporator outlet and the consequent taking place calculating the associated saturation temperature ensures that detected regardless of the design of the respective evaporator and the size of the occurring in pressure loss of the refrigerant that actually existing refrigerant superheat at the evaporator outlet exact measurement technology becomes. This allows to limit the superheat to a small value which is sufficient to prevent the compressor from damage, while on the other hand, the utilization of the heat exchange surface of the evaporator is optimized accordingly. Also practical experience has shown that a wide variety of refrigeration systems can be operated with reliable overheat of only 3 ° K in this way.

p0009In order to enable an adaptation to the specific requirements of the refrigeration system, it is advantageous if the reference value is continuously adjustable. Also, in response to the measured pressure by engaging on the actuating signal of the expansion valve the maximum evaporation temperature can be continuously limited in order to protect the driving of the compressor from overload.

p0010A new superheat control containing refrigeration system is characterized according to another invention in that it has a pressure of vaporized refrigerant at the evaporator outlet continuously measured and a signal indicative of the measured saturation pressure signal releasing pressure measuring device which is connected downstream of the signal-processing programmed computer, which generates a for the saturation temperature value of the respective measured superheat temperature value corresponding to the state diagram of the refrigerant signal indicative that a signal indicative of the difference between the two temperature values ​​actual-value signal is produced in a subtraction means of the characterizing for the superheat temperature and the saturation temperature signals and that this feedback signal with a predetermined temperature difference setpoint comparative controller is present which produces a function of this setpoint value / actual value comparison, the control signal for driving the expansion valve.

p0011This refrigeration system is characterized in that it always works without great additional expense with an exactly predetermined and kept constant superheat of the refrigerant at the evaporator outlet, which is substantially smaller without compromising the compressor than is the case with known similar systems.

p0012The temperature measuring device and the pressure measuring device advantageously have each a sensor and a signal whose output downstream analog-digital converter, which supplies at its output digital signals for the downstream, as appropriately programmed microprocessor trained computer. Also, it contributes to a further simplification, if the controller itself emits a digital electrical control signal and the pressure balanced expansion valve comprises an electric stepper motor drive.

p0013The computer or controller may be associated with a device for limiting the maximum evaporation temperature to a freely selectable within a predetermined range maximum value, the one that you supplied saturation pressure signal with the predetermined maximum value comparative and the maximum value is exceeded, the control signal in the closing sense of the expansion valve influencing electrical having circuit. Characterized the drive motor of the compressor is protected against overloading. It is also advantageous if the stepper motor drive is associated with an external energy independent electrical energy storage, through which the expansion valve can be moved into the closed position. This ensures that both, ie the expansion valve completely closes momentarily during automatic operation of the refrigeration system at compressor shutdown, as even after a complete waste of energy supply. By this measure the use of a conventional solenoid valve which is installed upstream of the expansion valve becomes unnecessary.

p0014In addition, the refrigeration system can expediently comprise means for continuous adjustment of the desired temperature difference value in order to allow an adaptation to different operating conditions.

p0015For the refrigeration system described is advantageously an expansion valve of the type mentioned use, which is according to the invention characterized in that the valve housing is closed by a coupled on its one side with the valve member first membrane to which on the other hand an actuating member of the the valve housing mounted electric motor drive acts, that the actuating member is coupled with a second membrane, which is on one side subjected to the pressure prevailing in the valve housing refrigerant pressure in a direction which is opposite to the direction of the originating from the refrigerant pressurization of said first diaphragm and in that the electric motor drive is sealed by the diaphragms hermetically against the refrigerant.

p0016The typically a stepping motor having electric motor drive is not with its winding consequently in the refrigerant circuit, but only in the atmosphere, so that no special cold-resistant enameled wire insulation are required. Moreover, the actuator is fully pressure compensated, with the result that the electric motor drive need only be designed for a minimum driving performance, which may be at the usual valve sizes from about 3 to 10 watts to give an idea of ​​the magnitude.

p0017A particularly simple and space-saving construction is obtained when the electric motor drive has a coaxial spindle drive driving electric motor whose hollow shaft is a spindle nut or connected to a rotationally fixed such and surrounds a forming the actuator screw. This eliminates a separate gear, resulting in minimal dimensions.

p0018It is also advantageous if the electric motor is connected on its one end side via a coaxial, the first membrane containing the first membrane housing with the valve housing and on its other end face carries a second membrane containing the second membrane housing in via a pressure compensating line to the valve housing connection , where the threaded spindle is coupled with both sides of the two membranes on their free sides refrigerant. The membrane housing can be releasably connected to the electric motor, so that the whole assembly can be easily disassembled. In case of failure of the electric motor that can be easily exchanged together with the spindle drive without the refrigerant circuit must be opened.

p0019The drawing shows an embodiment of the object of the invention is shown. Show it:<ul><li>FIG. 1 shows a refrigeration system according to the invention, in a schematic block diagram,</li><li>Fig. 2 is a LGP ​​/ h diagram to illustrate the cycle of the refrigeration system of FIG. 1, and</li><li>Fig. 3, the expansion valve of the refrigeration system of FIG. 1, in axial section, in a side view.</li></ul>

p0020The refrigeration system shown in FIG. 1 has a compressor or compressor 1, a condenser 2, an expansion valve designed as control valve 3 with an associated motorized actuator 4 and an evaporator 5. These elements are placed in the stated order in a direction indicated at 6, with a suitable refrigerant (ammonia, freon, freon, etc.). The compressor 1, the condenser 2 and the evaporator 5 are of known type and therefore not further described. The refrigeration system operates basically after in the Mollier h, lgp-state diagram illustrated cycle. In the state diagram, the pressure p of the refrigerant is logarithmically plotted against enthalpy h of the refrigerant. With x = 0 and x = 1, the two limit curves of Naßdampfgebietes are designated, where x is the specific vapor content;

p0021At the outlet of the evaporator 5 is sucked from the compressor 1, superheated refrigerant vapor ( "a") and (approximately adiabatically) to the condenser pressure p brought ( "b"), which is so high that then when in the capacitor 2 condensation heat of the pressure P corresponding saturation temperature t to the surroundings (air, coolant water) can be discharged, as indicated by an arrow 7 in FIG. 1. The at "c" liquefied refrigerant is in the expansion valve 3 along a throttle curve to the evaporator pressure p_O relaxed ( "d"); then it is evaporated at the associated evaporator temperature T in the evaporator 5_O thereby absorbing heat from the medium to be cooled (air, brine, water, etc.), as indicated by an arrow 8 in FIG. 1.

p0022Due to the occurring pressure drop in the evaporator 5, the evaporator of the refrigerant pressure p_O in the described work diagram actually not constant; it lies at the evaporator outlet ( "a '") deeper than the evaporator inlet ( "d), so that the compressor 1 actually sucks at the evaporator outlet superheated refrigerant vapor from the lower pressure (" a' ").

p0023Directly at the outlet of the evaporator 5, a temperature sensor 9 and a pressure sensor 10 are arranged in the circuit. 6 The temperature sensor 9 thus measures the evaporator outlet immediately overheating temperature t_ü the vaporized refrigerant (when "a '" in Fig.2), while by the pressure sensor 10 at the same point ( "a'"), the saturation pressure p_s the vaporized refrigerant is measured. The temperature sensor 9 and the pressure sensor 10 provide respective measurement values ​​for the characteristic analog signals to the input of a common analog / digital converter 11, which is part of a case 12 schematically indicated electronic regulator. From the output of the analog / digital converter 11, the corresponding digitized superheat temperature signals are directly supplied to a subtraction circuit 13 of the controller 12, while the digitized saturation pressure signals are fed to a trained as a microprocessor control unit 14 of the controller 12, the signal output in turn with the subtraction 13 is connected. The microprocessor of the computer 14 is programmed with the data of the state diagram (Fig. 2) of the refrigerant used in each case. It is calculated from the supplied thereto, for the respective saturation pressure p_s characterizing signals from the stored limit curve x = 1.0 continuously the measured saturation pressures p_s corresponding values ​​of the associated saturation temperature t_s and emits at its output corresponding saturation temperature signals to the subtraction circuit. 13

p0024The subtraction circuit 13 calculates for the overheating temperature and the saturation temperature t from the_ü or t_s characterizing signals the temperature difference .DELTA.t_eff= t_ü - t_sIe the actual value of the overheating actually occurring at the evaporator outlet. For this overheating .DELTA.t_eff characterizing signals are compared in the controller 12 with the votes of a setpoint generator 15 setpoint signals; depending on the comparison, the controller 12 outputs electrical control signals via a line 16 to the actuator 4 of the expansion valve. 3 The expansion valve is controlled in this way so that it remains exactly the mass flow of liquid refrigerant fed into the evaporator 5, which during the evaporation under the respective operating conditions, the theoretical value of the overheating Δ t_should appropriate balance between supplied and aspirated refrigerant results.

p0025The controller 12 works proportional-integral; he can in principle be designed but also for any other purpose appropriate control method. Since in the described manner via the direct measurement of the saturation pressure p_s at the evaporator outlet and the measurement of the superheat temperature t_ü at the same location, the actual superheat .DELTA.t_effis metrologically very accurately detected, and the overheating range is very precisely controlled, which means that only the required for the protection of the compressor 1 low superheat must be maintained and no safety tolerances are so far required.

p0026With the reference value generator 15, an actuator 17 is connected, which allows the target value .DELTA.t_should continuously changing in order to allow optimal adaptation to the respective requirements of the refrigeration system.

p0027The expansion valve 3 is seen in its construction from Fig.3:

p0028In a valve housing 18 having a refrigerant inlet socket 19 and a refrigerant outlet port 20, a cone-shaped valve closure member 21 is mounted axially displaceably by means of a coaxial valve spindle 22, which cooperates with a valve seat 23 which controls a passage channel 24th With the valve stem 22, a diaphragm plate 25 is connected at the end, the 26 is under the action of a compression spring and is supported against a diaphragm 27 which is clamped peripherally sealed in a first membrane housing 28, which in turn is screwed by means of a threaded connector 29 on the valve housing 3 , The membrane 27 is on the valve spindle 22 side facing acted upon with pressurized refrigerant, which fills a space 30 of the valve housing 18, which communicates with passage 24 via an equalizing duct 30a into connection. About a screw 31 the bias of the compression spring 26 is adjustable. The compression spring 26 applies to the required closing force, 44 is required to overcome all frictional forces in the mechanical valve and the hysteresis of both membranes 27th

p0029The expansion valve 3 is so far known in its construction; it is used as a thermostatic expansion valve used with its diaphragm housing 28 is in communication with one of the capillary filled with a Ausdehungsflüssigkeit temperature sensor.

p0030Notwithstanding these known construction, is a stepping motor 32 mounted in the present case on the diaphragm housing 28, the bearing plate 33 is connected to a flange 34, which is releasably screwed onto a threaded connector 35 of the open top membrane housing 28th At its opposite end, the stepping motor 32 carries also a mounted on the bearing plate 33 connecting flange 34, which in turn is screwed to the threaded socket 35 of a second diaphragm housing 36th The indicated at 37 rotor of the stepping motor 32 is rotatably mounted on a hollow shaft 38 in the two end shields 33rd The hollow shaft 38 encloses a cylindrical member forming an actuating spindle 39 which carries an external thread 40 at its lower end which cooperates with an internal thread 41 of the hollow shaft 38 to form a spindle drive.

p0031On both sides, the spindle 39 is supported against two diaphragm plate 42 that are 36 out in the two membrane housings 28, axially movable, while the spindle 39 rotatably even at 43, but is axially displaceably held. The upper diaphragm plate 42 rests against a housing 36 in the membrane edge sealed clamped second membrane 44, which is connected via a pressure compensating line 45 with the space 30 of the valve housing 18 and thus acted upon by the refrigerant pressure. Both membranes 27, 44 are thus loaded on opposite sides with the same pressure, with the result that the forming the actuator spindle 39 is axially fully relieved from the pressure of the refrigerant.

p0032Under the action of the stator winding 46 of the stepping motor 32 via the line 16 (Fig. 1) supplied to the pulse-shaped control signals rotates the rotor 37 of the stepping motor 32 its hollow shaft 38, whereby the spindle 39 is displaced by a corresponding amount in the axial direction. They adjusted for example via the diaphragm plate 25th 26 the valve member 21, wherein deflects against the action of the pressure spring out of the space 30 through the diaphragm 27 displaced refrigerant through the pressure compensation pipe 45 in the second diaphragm housing 36 so that always a pressure compensation of the spindle maintained 39 remains and the stepping motor 32 has only to invest sufficient to overcome the predetermined by the compression spring 26 biasing force.

p0033The stepper motor 32 can be seen through the two membranes 27, 36 hermetically sealed to the refrigerant. He is in the case of a defect easily replaceable, since it needs to be unscrewed only by the two membrane housings 27, 36 without the refrigerant circuit must be opened.

p0034To achieve that in the automatic operation of the refrigeration system, ie completely closed when switching off of the compressor 1, and even after a complete loss of power supply, the expansion valve 3 in a short time (eg. about 4 seconds), an alien energy independent energy storage is provided. This is formed by a direction indicated in Fig. 1 at 47 capacitor whose discharge energy is sufficient to only a small drive energy-requiring step motor 32 while driving until the valve member 21 is driven safely in the closed position. The corresponding one of the output from the capacitor 47 discharge current step pulses for the stepping motor 32 generating electronic circuit is indicated at 48th

p0035Since in the described refrigeration system by the pressure sensor 10, the pressure of the refrigerant on the outlet side of the evaporator 5 is measured in any case, the thus obtained saturation pressure signal can be directly used to limit the maximum evaporation temperature to a freely selectable within a predetermined range maximum value. Since with increasing evaporation temperatures, the driving power of the compressor is rapidly increased in a refrigeration system, it is expedient, especially in deep-freeze and brine systems etc. to limit the suction pressure of the compressor.

p0036For this purpose, a computer 14 the associated maximum value limiting circuit 49 is provided in the controller 12, which makes it possible to choose within a predetermined range the respective desired maximum value free. The circuit 49 compares the supplied thereto from the output of the analog / digital converter 11 digitized saturation pressure signal with the maximum value; if the maximum value is exceeded, the computer 14 at its output to the subtraction circuit 13, such a signal from that of the controller 12 via the line 16 to the valve drive 4 supplied control signal is influenced in the closing sense of the expansion valve. 3