DE2820209A1 - COOLING SYSTEM AND PROCEDURE FOR ITS IMPLEMENTATION - Google Patents

Description

-8- 2620209

Cooling system and method of implementation

The invention relates to a cooling system according to the preamble of claim 1.

Large capacity air conditioning systems have centrifugal compressors used with guide vanes located at the compressor inlet, which vanes are adjustable to both to regulate the direction (or "vortex") of the incoming gas as well as to create a pressure reduction, the is a function of the wing position. These wings, sometimes called the pre-rotation wings (PRV), are like this adjustable to vary the capacity of the compressor. In the condition the wide-open wing (WOV) has a small one Changing the wing position has no significant effect on the compressor head or capacity. When the PRV is close to are closed, a small change has a very significant effect on the compressor capacity, and can cause the Even a compressor into one. If no precautions have been taken, transfer the surge area to the guide vane position to adjust. Since a capacity control by changing the PRV position alone is an inefficient method of capacity control, attempts have been made to System capacity can only be increased by controlling the speed of the electric motor that drives the compressor regulate. If the speed control is used as the sole means of regulating capacity, the Compressor only work up to 70% of its full load - This is economically impractical for large facilities because for essential time periods the load is below 70% of the full load value.

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Accordingly, various attempts have been made to the Adjusting the PRV to combine with the regulation of the motor speed, which successfully lifts the load up to about 10% of the can reduce full load. A significant previous success in this direction is given in U.S. Patent 3,335,906, entitled "Refrigeration System Including Compressor Speed Variation Control". In In this arrangement, the engine speed as a function of the ratio between the compressor intake and The outlet pressure was adjusted and the PRV was adjusted in relation to a signal derived from the temperature of the heat exchange medium on the outflow side of the evaporator. The pressure ratio has been extremely simple experiments since then of the compressor is used to control the engine speed and the derivation of this pressure information has become turned out to be difficult and costly in practice. In addition, it has been found that the regulation of the PRV is a represents a complex function that has not been effectively controlled in order to avoid pumping and to operate most efficiently made possible by feeling just a single variable condition.

A first object of the present invention is therefore to provide a control system for regulating a cooling system, wherein The cooling system includes a centrifugal compressor in which not only is the motor speed controlled and the PRV position is set, but in which this speed control and wing adjustment along an optimal control path is accomplished with a minimal expenditure of energy.

A related important aspect of the present invention is the manufacture of such a control system, the one

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-ίο- 282020

enables such energy-efficient system operation and that at the same time 'Avoids pumping.

The creation of such a control system is of primary importance, which can be installed not only in connection with new facilities, but easily in connection with already existing systems can be installed in order to achieve the optimal control path in such systems and a Avoid pumping.

Another important object of the present invention is in the linearization of the PRV activity by a controller with a non-linear duty cycle in order to achieve a more uniform one Establish control panel.

Another important object of the present invention is it to achieve such precise system operation over a wide load range without the need for compressor pressures to sense the compressor pressure head value (compressor headvalue).

The control system of the present invention is useful to regulate a refrigeration system including a compressor, a Includes a condenser and an evaporator, all of which are interconnected in a closed refrigeration cycle. Inlet guide vanes are placed between the evaporator and the compressor to regulate the capacity of the compressor and some Means such as an electric motor are connected to the inlet guide vane position to adjust. Means / such as another electric motor drive the compressor. The tax system according to the invention is connected to both the means of setting the guide vane position and the means for driving the

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■ "II" ™

To regulate the compressor. A first temperature sensing means is placed near the condenser to generate a first signal, which is related to the condensation temperature of the coolant, to create. A second sensor is arranged in the evaporator to receive a second signal that corresponds to the evaporator temperature of the Coolant is related to generate. A summing means is connected to both the first and second signals and to produce a resultant signal including the pressure of the compressor. Use the tax system the resulting signal to control the cooling system. A third temperature sensing means is near the outflow of the cooling water of the evaporator arranged to generate a third signal. An adjustable means is in the control system intended to generate a tempera tor setpoint signal. Means are also provided to summarize the third Signal and the temperature setpoint signal to generate another control signal for use in controlling the refrigeration system.

In accordance with another aspect of the present invention, an additional means is attached to the inlet guide vanes coupled to produce an electrical signal indicative of the physical position of the inlet guide vanes. A means is provided to summarize the inlet vane position signal with the resulting signal to generate a regulation signal for system regulation.

In the attached figures shows:

Figure 1 is a block diagram showing the inventive

Control system associated with a refrigeration system using a centrifugal compressor contains.

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Figures 2, 3 and 4

The figure 5

graphical representations useful in understanding the operation of the invention.

a circuit diagram with the significant signal paths in the control system according to the invention.

Figures 6A, 6B, 6C

Echeaatic diagrams put together which represent details of the circuit of the control system according to the invention.

The figure 7

a graphic representation of the dependency of the compressor capacity on the PRV opening for different pressure altitude values.

Figures 8A to 8F

graphic representations useful in explaining an aspect of the invention;

Figure 9

a graphic representation of the dependency of the compressor speed on the PRV position for a fixed head value.

Figure 1 shows certain conventional components of a cooling system, such as a centrifugal compressor 20 for passing a refrigerant (such as R-11 or another suitable medium) through the line 21 to a condenser 22. In the condenser, the water runs from the Cooling tower from line 23 into the condenser and is returned via line 24 to the cooling tower or to the other ■ Bnx & head rejection means, warn vet—

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different systems can be used. The refrigerant on the outflow side of the condenser 22 is via the line 25 through a permanently installed outlet opening 26 (orifice) and the "line 27 to the Given refrigerant inlet connection of the evaporator. The coolant flows through the evaporator and out of the duct 30, which includes a plurality of inlet guide vanes 31 arranged as shown. In this description they are Intake wing with PRV (p_re-r_otation vanes) and the The position of the PRV is regulated by a small motor 32 which runs over a plurality of conductors, here as a single one Line 33 is shown receiving a control signal. The person skilled in the art will easily recognize in FIG. 1 that in each case a plurality is represented by ladders through a single line. The water with the higher temperature from the building (or a other cooling load) is cooled via line 34 in the evaporator. The cooled water is via line 35 to the Building returned.

A Ahsaug-Motor 36 is via a shaft 37 with the Centrifugal compressor 20 is connected and is itself operated by an inverter 37. The inverter receives at the input a DC voltage via a line 38 and in this way determines the amplitude of the output voltage of the inverter. A Krdis for voltage regulation 40 is between a voltage supply line 41 and a line 38, which the voltage to the inverter is provided. This can be a conventional circuit, for example a phase-controlled rectifier circuit, which receives an input AC voltage on line 41 and produces a DC voltage on line 38, and in accordance with the signal received over line 41 is regulated. If no regulation is required is, a DC voltage from batteries,

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from a transformer and rectifiers or any other suitable source to the inverter. the The frequency of the inverter output voltage is regulated by the periodicity of the time or gate signals sent by a logic circuit 44 can be applied via line 43. It is a well-known circuit that sends a control signal to the line 45 receives and uses this control signal to control the frequency of the pulses applied to line 43. One known arrangement receives a DC voltage as a control signal on line 45 and a voltage controlled oscillator in logic circuit 44 generates pulses at a frequency which is controlled by the amplitude of the signal on line 45. The logic circuit generally includes a ring counter type circuit to feed the pulses to as many thyristors or others to distribute switches used in the inverter circuit.

In accordance with the present invention, the control system 50 is used not only to determine the speed of the intake motor 36 but also to determine the physical position of the prv ^ re-rotation vanes) 31 by a signal to control the speed, which is applied via line 51 and a guide vane position signal (open or closed) on line 33, to control. The circuit arrangement according to the invention ensures that a sudden surge is avoided and that the compressor ii is the most energy efficient Way is controlled. In this embodiment the signal is to control the voltage, a DC voltage signal originating from an integrating circuit 52 and the guide vane control signal can either send an "open guide vane" signal the line 53 or a "guide vane close" signal on the Line 54 or no signal ("guide vane stop"). These

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Output control signals come from different input signals here that a first signal on the line 55 originating from a thermistor or other temperature sensing unit 56, which is positioned to communicate with the coolant in the Konäensorausflußleitung ^ ii To be in contact. A second signal is present on line 57 and is received by a second sensor or Thermistor 58 is obtained which is exposed to the saturated refrigerant vapor leaving the evaporator. The first and that second signals are combined in a summing means 59, which may be a differential amplifier circuit, to produce a resultant To generate a signal on line 60 which is related to the head of the compressor. the Circuit means in the control system using this signal and the other input signals will be discussed later in connection with FIGS. 6A and 6C. At the moment it is important to emphasize that the generation of information is about the pressure head at the compressor from this simple temperature difference determination is an essential point of the present invention is. Without knowing that the pressure head of the compressor is a virtual linear function of this temperature difference is, expensive pressure transducers would have to be positioned in or adjacent to the compressor in order to generate a signal to produce which is related to the pressure head of the compressor. Accordingly, the realization in which the pressure head of the compressor can be derived in this way, represents an important part of the inventive contribution.

It is shown a potentiometer 61, which moves with his Arm or grinder mechanically coupled to the PRV or to the output shaft of the motor 32 which drives the PRV is. In this way, the electrical signal on line 62 shows the physical position (janz open, three-

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quarter open, etc.) the inlet guide vanes in a continuous manner. The following describes the circle which combines the inlet vane position signal with the indication signal of the pressure head of the compressor to at to help control the operation of the compressor.

A third temperature sensing means which is another thermistor can be, is arranged to control the temperature of the chilled water, flowing out of the evaporator 28 to feel. The thermistor in this way produces a third signal which is applied via line 64 to a further differential amplifier stage which is also a temperature set point signal from a potentiometer 66 or other suitable unit, such as a thermostat / in the building room. In this way the output signal on line 67 represents the difference between the condition to be established (indicated by the from signal derived from component 66) and the current load condition (represented by the signal on line 64) represent.

An unload control stage 68 is with the movable ann of the potentiometer 66 coupled. Level B8 represents the means to limit the Consumption of electrical energy by changing the temperature setpoint or ¥ fSs effecting a different circuit setting to change the load on the compressor and to reduce the rate of energy consumption. The average specialist will recognize that this is similar to physically changing the thermostat setting. In large However, installations can do this automatically through a control system that increments the rate of energy consumption.

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28202Q9

have time periods (such as in half-hour intervals) indicates and prevents the device from using more than a predetermined amount of energy in any given Time period ± u consume.

Of the additional signal paths shown in FIG. 1, line 70 provides a means for setting a shutdown signal for logic circuit 44 when an overload condition is indicated by the control system. To this and To determine other operating signals, a signal is used to determine the amplitude of the current flowing through the windings of the motor flows, is related, via line 71 to the control system and another signal related to engine speed is provided over line 72 given to the tax system. The motor current signal is derived from a current transformer in a known manner and is not shown. The motor current signal can be derived from a conventional tachometer (not shown) to produce a DC voltage signal on line 72 indicative of engine speed. It is not required as by that Line 72 shown to have an external set of conductors to return a signal related to engine speed. Instead, the tax system may use a Use the internal line connected to the output of stage 52, which carry the control signals for regulating the engine speed and use a portion of this DC speed signal to determine the motor speed to display. After this general perspective of the complete cooling arrangement and control system, one will now be made detailed explanation given.

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Figure 2 shows a graph of operating characteristics of a conventional compressor extracted from the data of a text block. The compressor head is plotted versus flow (or capacity). These characteristics are described in detail in connection with FIG. The three surfaces represented by the graph of Figure 2 represent areas of system operation at a constant Mach number or compressor speed. For example, the top surface represents the possible pressure head changes and capacity during operation at a Mach number of 1.5. If the operating parameters change beyond the longer of the upper limit lines for the 1.5 surface, the surge area will be exceeded, indicating that the system is becoming unstable and that the compressor will surge. The upper boundary line of this 1.5 surface represents the operation with wide open guide vanes and the three dash-dotted lines are used to represent the areas of operation with three-quarters open guide vanes, half-open guide vanes and one-quarter open wings. These areas are shown as discrete lines, but the system can be continuously adjusted over the entire vane opening range, allowing operation at any vane opening. For operation at a lower speed or Mach number of 1.4, the system falls on the intermediate surface shown in FIG. In a similar manner, the system falls in a further reduction of the operation to a Mach number of 1.3 to the lowest of the three surfaces illustrated. It is also understood that in a system in which the compressor speed is continuously adjustable, the

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Mach number changes do not, as shown, in large increases can be made, but the setting is in the space between the surfaces, which are shown in Figure 2, continuously when the compressor speed is reduced. With this representation of the compressor head flow for the constant speed regions, a description of the compressor characteristics will now be given in another Form listed.

FIG. 3 shows a graph with the minimum Mach number M _Q along the left ordinate, the extent of the PRV opening along the abscissa and the compressor capacity r specified at selected points, all of which are based on the compressor pressure head represented by the Curve series is shown, are related. The minimum Mach number M _Q can be viewed as representing the engine speed. More precisely, it is the ratio of the impeller tip speed to the suction stagnation acoustic velocity (this speed is referred to below as A). Since the induction motor is coupled to the compressor, the motor speed can be viewed as directly related to the top speed of the drive wheel. For this analysis, it is assumed that A for a given refrigerant does not vary significantly over the typical operating range of the evaporator and therefore that M _Q can be viewed solely as a function of engine speed. The PRV opening is shown in increments from a condition in which the vane is fully closed to a condition in which the vane is wide open (WOV). The capacitance denoted by θ is

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technically the ratio of suction (in cfm) * 2.4 and this term is divided by the product of A * the square of the impeller diameter. The compressor head, represented by the curves in FIG. 3, is technically the dimension of the head (in feet) times the constant 32.2 and this product is divided by A. Since Aals is considered essentially unchanged, as was stated above, the consideration of the capacity Θ and the pressure head value Si— of the compressor is simplified.

Each of the various curves in FIG. 3 represents a constant pressure altitude value SL and the minimum speed and PRV which are necessary to adjust a given capacity without entering a surge region. For example, the curve in the upper right part with a head value of 1.2 indicates the speed changes of the motor and the PRV opening changes that must be made to reduce the capacity at that head value. The arrow 75 shows the direction of the reduction in capacities and if only the motor speed (and thus the compressor speed) is reduced, the capacity is reduced as shown by the decreasing value of £) on the right-hand side of the graph. However, if the speed is decreased to the point indicated by a and it is still desired to decrease the capacity without decreasing the compressor head below J.2, at this point the motor speed must be kept constant and the PRV must be gradually increased shoot. In this way, the capacity is

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shows, reduced to point b, at which Θ has the value O _f 58 and the guide vanes are approximately three quarters open. The system will "pump" if the speed is further reduced at point b. It is important to note that if there is a further reduction in capacity at the same pressure level, the vanes will continue to close, but the motor speed must now be increased to the point indicated by c.

Similarly, the vanes can be kept wide open when the head value is 1JO while the speed up to the value at dem 0 x 0.0385 is decreased will. This point is denoted by b. From this point the speed is kept constant and the guide vanes are gradually closed until they are about three quarters open, as shown in point e. Then the Hotor speed is increased again gradually while closing the guide vanes up to the point marked f is continued. Points a to f are also shown in FIG. It can be seen that a complex control function is required around the Regulation of both the compressor speed (by regulating the motor speed) and the opening to coordinate the PRV. For a given system, if the load line were drawn in Figure 3, it would be different Cross pressure height curves. It is therefore necessary to change both the pressure height and view the current position of the PRV and the current engine speed when making a change in the "m Syst ·" is made to be sure that a

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Pumping is avoided and that the most efficient operation is achieved.

The control path for connecting the control of the motor speed and the control of the opening of the PRV, which has been found to be effective in the implementation of such a control without entering the pumping area, is shown in FIG. The curves of constant pressure height are shown for the ideal control path 80 in the background. It is assumed that the system is initially operating at full capacity and with wings wide open. This is at the point labeled g _; If it is desired to reduce the load, the capacity is reduced by reducing the motor speed along the curve which goes through point h and finally goes straight down to point j. At that time, the control algorithm must be changed to include adjusting the PRV position to maintain the optimum control path. The guide vanes are then gradually closed, up to an 80% open position, while the engine speed is increased from the level indicated at j to the level indicated at point k. From this point, the closing of the guide vanes foxkjeset, but the motor speed is reduced again until the control path 80 reaches the base point at point m. In this part of the curve the guide vanes are approximately 35% open and since the closure of the guide vanes continues, the speed is then increased up to point η.

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If it is desired to increase the load, assume that If the system is now operating under the conditions as shown in point η, the PRV opening will be gradual increased, while the engine speed is reduced until the point m is reached. After that, if the opening of the guide vanes is made further, the motor speed is increased up to the point k. In accordance with a significant aspect of this invention the increase in engine speed continues, since the guide vanes are opened further, along the segment kh of the control cam; the other two Ästenkj and jh is not followed when restoring the load. Instead, the control path leads directly from k to h and then up to g after the guide vanes are fully open.

Since it has been found that this approach avoids pumping and provides very high operating efficiency It is important that the tax system "knows" not only the amount of changes required, but also the direction in which the change is to be made. As will be described, this requires both combination logic as well as stored information regarding the compressor design in the control system to determine the optimum, in the To achieve control path 80 shown in FIG.

FIG. 5 shows a diagram with general signal flows of the circles shown in Figures 6A, 6B and 6C in more detail are shown. In general, the cooling water output from the thermistor 63 (Figure 5) and the Temperature setpoint signal either from the potentiometer

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or may be derived from any other means for establishing the desired temperature control level, combined to produce a temperature error signal on line 67. A response threshold network 81 is provided to produce separate output signals on line 82 (representing a plurality of conductors) to avoid switching commands to the PRV control logic 96 and to the inverter speed logic 83 when in the PRV working control portion until the temperature error signal to the door determined by the amount the response threshold has been exceeded. The output of the logic arrangement 83 is given via an integrating stage 52 to produce the motor speed control signal on line 51 in order to regulate the inverter operating frequency and thus the speeds of the motor and the compressor.

Information on the position of the PRV is taken from potentiometer 61 over line 84 and a portion of this signal is applied to inverter speed logic circuit 83. Another part of the PRV position signal is given via line 85 to a duty cycle control circuit 86. In addition, the PRV position signal is given over a network 87 and combined with the minimum Mach number M signal on line 88. As previously described, this minimum Mach number signal is UNOE derived for wide-open vane of the condensing temperature, as measured by the thermistor from the evaporator it tempera door, as measured by the thermistor 58th These two signals are combined to form a minimum Mach number M signal (for wide open vanes) on line 89. he-

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2B20209

witness. When this signal is passed on line 88 and combined with the output of network 87, it constitutes a composite signal on line 90 which is then combined with the current engine speed signal received on line 72 to display on the Line 91 to generate an error signal. This error signal is the error in the speed set point when the system is controlling the PRV position in addition to controlling engine speed. The engine speed signal is also compared to the M _Q signal on line 89 to produce a logic signal on line 82 indicating whether the current engine speed is above or below M _Q. This signal is then applied to PRV control logic 96 and to inverter speed logic 83 via line 99.

The duty cycle control circuit receives both the PRV position control signal Another signal from an overload circuit 94 via line 85 and also via line 93. The output of circuit 86 is provided on line 95 to PRV control logic circuit 96 which determines whether the Guide vane position should be changed, in which direction the guide vane should be moved and the amount of movement, to be made. The overload circuit 94 receives a signal on line 71 that is proportional to the motor current, and in addition to producing a signal on line 93 for the duty cycle control circuit 96 another signal on line 97 for the PRV control logic circuit 96 and another signal on the line 98 for the inverter speed logic control circuit 83. With this general representation of the system, the specialist

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the representations of FIGS. 6A to 6C are easier to use with the entire device represented in FIG Connect.

In the illustration of Figures 6A to 6C, the Kühlwasserausgangsteraperatur has been derived from the thermistor 63 and via line 64 and optionally one of the 24 k Sl resistors to a Eingnngsanschluß of the differential amplifier 100th The signal from the setpoint potentiometer 66 is passed through the other 24 kJL resistor to the other input connection of stage 100, which generates the temperature door error signal on its output 1 line 67. To help those skilled in the art, the IC components are designated later and the operating voltages of the various stages are shown in a circle. The + sign in a circle means that the B + voltage of 12 volts is applied to this point. The cooling water temperature and setpoint signals are also combined in another comparator stage 101 to produce a signal on line 102 for the inverter logic when a deep water temperature condition is measured. The use of this signal and other overload signals are not shown in the logic circuit, but those skilled in the art will easily understand the use of these signals to switch off the inverter operation when the cooling water temperature is too low.

The stages 103 and 104 are in a duo compensation circuit (lead-lap compensation circuit) for the system. This network creates a phase lead at 0.007 Hz and a phase post-healing at 0.02 Hz. In this way, the error signal on line 67 passes over the line

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to this network so that the output of the network on line 105 is a compensated temperature signal for application to the inverter speed logic.

The signal on line 67 is via another comparison ^ circle 106 to produce a logic signal on line 107 that is a logic 1 * (or high voltage) is when the cooling water outlet temperature is greater than the setpoint temperature and is a logical 0 (low Voltage) if the cooling water temperature is lower than the setpoint temperature. This signal is sent to a Input connection of NOR gate 108 applied. The steps 110 and 111 are connected to each other by logic signals on lines 112, 113 when the difference between the setpoint temperature and the cooling water temperature exceeds the amount of the response threshold or the dead zone. In the embodiment shown, the dead zone was set up, to include a temperature difference of _ + 0.15 * F, seen electrically by the difference between 5.12 and 5.86 volts, which is applied to the two stages 110 and 111 are applied, is shown. A reference or mid-band voltage of 5.5 volts is used as a reference. The NOR stage 114 and an inverter stage 115 are as shown connected to a logic signal for use in the inverter speed logic control circuit to manufacture. These levels and the additional levels 116, 117, 118, 120 and 121 become designated at the end of the description in order to enable the person skilled in the art to implement the invention with a minimum of effort apply to experiments. Also, another inverter 122 and gates 123, 124 and 125 are responsible for the application of signals to regulate the integrating stage 52, also designated.

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The signal from the PRV position potentiometer 61 is derived and applied to line 62 as shown. A portion of the signal is applied via line 64 to a connection of a comparator stage 130, which is also receives a DC reference signal on its other input connection. The wiper of the potentiometer 61 is in the zero resistance (tip) position in the condition of the wide open guide vanes. This attitude and the others Circle components and voltages, which are shown in the drawing, act together around a logic "1" signal the conductor 131 on the exit side of the step 130 when the inlet guide vanes are in the wide open position. The signal becomes a logic "0" when the guide vane is open is reduced starting from the wide open guide vane condition. The signal is sent to an input connection of the NAND gate 120 is applied and is also inverted in the inverter stage 132. The inverted signal comes through the Line 133 to NAND gate 117 and NAND gate 134, the output of which provides an input to NAND gate 135 in PRV control logic circuit 96.

The vane position signal on line 62 is also applied to the negative input connection of each of the comparator stages 136 to 140 created. As shown, the outputs of these comparators are coupled to gate circuits 141 to 145, respectively. These output signals from the gates are summed in stage 146 to produce a signal indicative of the speed deviation from the minimum Mach number based on the current vane position. the Condensing temperature of the coolant determined by the thermistor 56 is measured, generates a signal on line 55 and the refrigerant vapor temperature, which is determined by the thermistor 58 "

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is measured, generates another signal on line 57. These two signals are in a differential amplifier combined to generate a signal on lines 88 and 89 that corresponds to the minimum Mach number M for wide open Guide vane is related. At this point on the circle the signal is only related to the compressor head and does not include any factor related to the vane position. Part of the vaporizer signal on the Line 57 is sent to another comparator 148 to provide a shut-down signal on line 150 for the inverter logic to generate when the evaporator temperature falls below a predetermined value, which Value is generated by the reference voltage applied to the other input connection of this stage.

The M signal on line 88 is combined with the rate change signal at point 90 and applied to the negative input connection of operational amplifier 151. In this way, this link receives a composite input signal that is a function of both the speed change signal and the minimum Mach number M _Q. The other input connection of stage 151 receives an indication signal of the current engine speed on line 72 as described above. In this manner, the output signal of stage 151, which is provided on the line 91 to the inverter speed logic array, the error in the velocity command signal is, when the refrigeration system in the PRV control section operates by both the engine speed must be regulated as well as the Leitflügelposition to the optimal control path 80, which is shown in FIG. 3, to follow.

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In FIG. 6B, the speed signal on line 91 is also applied to the positive input connector of another Comparator 153 applied, which receives a reference voltage at its other input connection. The output signal from the stage 153 is therefore a logic signal that is given via the line 154 to the NAND circuit 120, whether the current engine speed is above or below the desired engine speed for the given Operating conditions. In short, this logic signal is used to allow temperature error information modify the engine speed control command and get faster system response when such modifications do not involve the risk of transferring the system into the pumping area.

The duty cycle control circuit 86 operates to limit the time of contact closure in the "drive open" and "close" parts of the PRV control as a function of the current PRV position. This is an important aspect of the present invention because when the vanes are closed to leave only a small opening, a "do not drive" signal is prevented from being applied at a rate faster than the system response rate. The duty cycle control circuit 86 can also be viewed as a drive control circuit because it determines the percentage of time in a given time interval at which a drive signal is instantaneously applied . the PRV motor or any other suitable capacity control means which is adjustable to vary the capacity of the compressor. Therefore, the PRV motor 32 provides a means

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to regulate the adjustable capacity control means, the PRV itself.

The problem posed by prior PRV control systems can be better understood in connection with FIG. Various curves shown therein show changes in compressor capacity as a function of PRV opening, for various constant values of pressure head (-Q- /. For example, curve 300 shows the relationship between capacity and vane opening for a value of Compressor head of 1.2 The following curves 301, 302, 303 and 304 show decreased values of the compressor head, down to an SL of 0.8 for curve 304. As the compressor head up to 1.0 and values below this level decreases, the inclination of the right curve parts of a PRV opening becomes increasingly smaller by about 1/2. For low values of the PRV opening, however, the inclinations of the curves are very large regardless of the pressure altitude values therefore, when the guide vanes are closed or almost closed, a very large change in system capacity e curves shown in the figure would be more linear and the duty cycle control circuit 86 is directed to linearizing the system operation.

The duty cycle control circuit or drive control circuit 86 (FIG. 6B) essentially contains an integrator stage 156, a NOR gate 157, and a comparator stage 160. This drive control circuit receives two different input signals. as

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The first input from the drive control circuit can be conductor 200 receiving a timing signal from the oscillator 155. This time signal, which in the illustrated embodiment 0.033 Hz, a 1.3 M J ^ resistor to the upper input terminal of the integrator stage 156 and also applied to the upper input terminal of NOR gate 157. This signal is generally generated by the Waveform 201 of Figure 8A is shown. The NOR gate 157 generates an output signal which corresponds to a logic "1", when both inputs are at a low potential or zero. When the oscillator signal generated by waveform 201 assumes a low potential, the 5.5 volt reference voltage at the other input terminal of the Integrator 156 that this stage begins to charge at time t and an output voltage corresponding to the reference numeral 202 (Figure 8B) on line 161 for the top input port of the comparator 160 is generated. This comparator also receives a position signal on line 85; this Position signal varies as a function of the setting of the adjustable capacity control means used in this embodiment are the PRV of the compressor. When the PRV is virtually completely closed, the DC voltage level is on line 85, represented by line 203 in Figure 8B, is nearly 2 volts. When the signal is rising from the integrator 156 over the line 161 at point A die 2 volt line, the comparator 160 switches to Time t-j, as indicated by waveform 204 in Figure 8C is shown. This is how the signal was from the comparator 160 in the period between t and t "low" and the signal represented by curve 201 (FIG. 8A) from the

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Integrator 156 was also "deep". Therefore, the output of NOR gate 157 was "high" at this time, as indicated by the pulse near the beginning of curve 205 in Figure 8D. As long as the comparator output remains "high", as shown by curve 204, there is no further output signal from NOR gate 157. Signal 204 goes "low" again when the decreasing slope of curve 202 exceeds the 2 volt voltage. Line at time t exceeds _5. At this time, however, the oscillator output will be "high" and consequently no further output will appear from NOR gate 157 until the rising slope portion of integrator curve 202 again crosses the 2 volt line 203. In this way, the drive signal for the PRV, or for the means for controlling the adjustable capacitance control means, clearly a function of the guide vane position, which is represented by the level of the signal on the input line 85.

Assuming that the PRV are virtually wide open, a 10 volt signal is generated on line 85; this signal is represented by line 206 in FIG. 8B. It is apparent, therefore, that the upward sloping portion of curve 202 will cross the 10 volt line at point B or at time t ₃ , as illustrated by curve 207 in Figure 8E. At this time, the output of comparator 160 goes "high" as shown by curve 207, preventing an output from gate 157. However, prior to this switching between times t _Q and t 1, the output of the NOR gate was Ί37 "high", as shown by curve 208 in FIG. 8F, because both input signals of this gate were "low". This creates a

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much longer pulse duration in curve 208 to drive the PRV or any other adjustable capacity means. In of the illustrated embodiment generated the circle components a pulse of nearly 1 second in waveform 205 and nearly 5 seconds in waveform 208. Intermediate positions of the PRV generate corresponding pulses with lengths in between. Of course, others can too Driving control loops can be used to produce a variation of some other signal characteristics, such as for example the amplitude to the change in the adjustable capacity control means in accordance with the to regulate the instantaneous position of the adjustable capacity control means.

The capacitance control signal is passed from NOR gate 157 into NAND gate 162 and also into the other above NAND gate 135 given. The mode of operation of the logical arrangement for opening or closing the leading flights1 is shown with the additional stages 163 to 168 and 170 connected as shown.

Ztjm example produces a logic "0" signal from the NOR stage 165 (Figure 6C) no gate drive for the npn transistor which is the light emitting diode of B + and the 1 KΛ resistor supplied with energy and the one Establishes gate control for the thyristor that is energized and generates a signal on line 54 to close the guide vanes. The connection below the 0.22ytfF capacitor, the labeled X corresponds to the other similarly labeled terminal in the vane open circuit and represents is a common electrical connection for the PRV engine.

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Of course, the system can also be moved manually by rotating the mode selector switch 171 from the automatic position in which it is shown to any of the other three positions. When the movable contact is moved to come into contact with the "hold" contact, the guide vane motor cannot be opened or closed, but remains in the current position. When the contact is rotated to the "open" position, an excitation circuit is closed _{/ to} switch the thyristor through and to generate a signal on line 53 to open the guide vanes. Similarly, operation of the logic circuit produces the required gate energize signal to energize the thyristor and produce a "close vanes" signal on line 54 when the switch is moved further to the "close" position.

The motor current level signal is received via the conductor 71 and divided via the 3 K-β potentiometer shown, a portion of this signal being branched via the line 172 to the first current limiter stage 173. When the level of the motor current reaches a predetermined value representing 100% of the current rating, stage 173 switches and produces an output signal which is provided to both the PRV logic control circuit and the inverter speed logic control circuit as shown. In the inverter speed control part, this means that the inverter motor cannot be driven faster _/ as long as this 100% current level is maintained, and the speed is actually reduced. Also, under these conditions, the operation of the PRV logic control circuit is such that the guide vanes do not

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can be opened. But when a signal is a decreasing one Load is generated, the guide vanes can be closed to reduce the load on the system. If the current level continues to rise to a level indicating that 103% of the rated current is in the motor windings flows, the stage 174 is switched to a signal for the PRV control circuit that begins to generate the guide vanes drive towards the closed position to reduce the load. If the current continues to rise At a level of 106% of the measured current, this signal is sampled via line 175 and stage 176 switches, am to generate a signal on line 70, which the inverter logic switches off and thus adjusts the power supply to the motor in a corresponding manner.

Figure 9 shows a pair of curves showing the change in compressor speed represents the functin of opening the PRV for a fixed compressor pressure altitude value. The curve 307 shows a surge curve developed from actual data so that the operation is in the lower left part of this Curve would cause a compressor surge. In order to avoid pumping, an actual function 308 was derived, which represents a mathematical function / to the operation of the To regulate control system according to the invention. By regulating the speed of the electric drive machine 36 and the extent to which the PRV is opened by function 308 follow, not only is pumping avoided, but the system is essentially operated in the most efficient manner possible. That the control system can control operation along the curve is due in part to the effective. Derivation.

ORIGINAL INSPECTED

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the minimum Mach number M _o on line 89 (Figure 5) returned from the condenser and evaporator temperatures. Thereafter, this minimum Mach number or pressure altitude indication signal is given to the output side of the network 87. The signal derived from the PRV position potentiometer 61 is modified / to produce a modified or functional signal on line 90 for combination with the minimum Machaahl signal by network 87. This combination of signals on line 90 produces a signal which is then combined with the actual motor speed signal on line 72 to produce a speed boost signal for the inverter speed control portion of the control system. The term speed addition refers to the speed correction desired for the suction motor driving the compressor by looking at the minimum Mach number M, the function signal on the output side of network 97, and the actual motor speed signal. The resulting additional speed signal represents an effective correction value for optimal regulation of the speed of the intake motor.

Technical advantages.

The present invention enables effective control for a refrigeration system using compressors, which is adjustable Have inlet guide vanes in which the compressor is driven by a variable speed electric motor will. The system and method of the invention have been made successfully tested and it turns out that the automatic setting of the compressor speed and the inlet

ORIGINAL INSPECTED

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vane position can adjust the compressor pressure and flow requirements for a given evaporator load while maintaining the cooling water at a constant temperature. The control path as shown in Figure 4 aims to minimize the energy requirements of the system while at the same time avoiding compressor surge. In addition, the control system and method of the present invention have demonstrated an ability to maintain the temperature of the cooling water within 0.15 ^° F of its set point throughout the possible load range. In particular, the maximum possible use of the engine speed control is effected before beginning to adjust the PRV position to change the compressor load. This is the most energy efficient method of operating an arrangement with adjustable inlet guide vanes and has been found to be much more efficient than systems that use a combination of PRV control and hot gas bypass to avoid pumping. The present arrangement has eliminated the need for a gearbox and permits operation with smaller, more efficient, higher speed motors. In addition, the compressor is quieter in a partial load range, it is driven more slowly at a guide vane angle which is more adapted to a noise reduction.

In part, the present invention is based on an understanding of the compressor characteristics and the derivation of the minimura Macheähl M _o , which is limited by the head in the compressor. This ¹ use of the Mach number for wide open vanes becomes persistent in the control system

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displayed to meet the load requirements for the capacity of the Adjust compressor at the time. It is very important that the maximum range of speed control is used is turned over to the area of the PRV control ^ is switched, as has been described in connection with FIG. The derivation of the pressure information from the at both temperatures is an important aspect of the present invention. This enables precise control with minimal converter costs because thermistors can be used in place of the more expensive pressure sensors that are often used be used in such arrangements.

The system and method of the present invention controls the cooling system in both the speed control area as well as in the PRV tax area. In the speed control area, the control concept is simple therein, the compressor speed by regulating the frequency of the inverter output voltage either upwards or down depending on whether the system capacity is to be increased or decreased. The mistake in the cooling water temperature with regard to the target value is used for the earth-related system capacity changes to determine. The technique is easy to understand and can be used after determining the response, stability and the Line merging requirements can be easily accomplished with low cost electronic circuit means. In the PRV tax area Cooling water error changes require more complex control change and persistent change Display of the system variable. It is not only necessary to adjust the PRV position, but rather to avoid pumping the

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Compressor speed according to the pressure altitude measurements and the pre-stored PRV position (network 87) can be regulated. In addition to these two areas of the control characteristics and their dependent limit definition problem, there is a requirement that the for compressor speed and PRV position adjustment The chosen control path must be energy-conserving.

In the method and system of the present invention, the observation is that the compressor head an almost linear function of the difference between the condensation temperature of the coolant and the evaporation temperature is of scientific importance. In addition, experimental data on the compressor used have shown that the minimum permissible Mach number to avoid pumping is linearly related to the compressor pressure head. It was then determined that the compression head in conjunction with the PRV position could be used to pump out the compressor to determine both with partially open guide wings and with wide open guide wings and thereby the desired System operation path shown in Figure 4 to be established. In this way, signals from relatively low-host converters that reduce the condensation and evaporating temperature, compressor speed and PRV position along with cooling water temperature indicate the basis of the effective control system and method of the present invention.

The method of the system control can easily be understood in connection with FIG. In dear ^ proceedings -will

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the compressor head signal continuously as a function the temperature of the condensing refrigerant and the evaporation temperature of the refrigerant; this pressure altitude signal appears on line 89. A function signal, that is related to the current position of the inlet guide vanes is derived on the output side of the network 87. The pressure altitude indication signal and the function signal are then combined to form an intermediate signal on the line 90 to generate. A signal related to the current engine speed is generated on line 72; this can be from the motor itself or from the line or from some other source. The current engine speed signal and the intermediate signal are combined, to provide a first signal on line 92 to indicate the speed of the compressor drive motor to regulate. A temperature error signal that is related to the temperature difference between the cooling medium the evaporator outlet and the desired target temperature is generated on line 67 and the temperature error signal is used as a second signal to regulate both the speed of the compressor drive motor and the Position of inlet guide vanes used.

Another way of understanding the method after the present The invention is shown in connection with FIG. As shown there, it is assumed that the system originally works in a first operating condition, which is denoted by g. Then the speed of the Compressor drive motor from the first operating condition g via a second operating condition h to a third operating condition j decreased while the inlet guide vanes

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be kept wide open. Then a gradual one begins Close the inlet guide vanes and at the same time increase the speed of the compressor drive motor enlarged by one to achieve fourth operating condition k. The closing of the inlet guide vanes continues while the speed of the drive motor is reduced at the same time in order to achieve a fifth operating condition m. Closing the Inlet guide vane continues while at the same time the speed of the drive motor is increased to one sixth operating condition η is reached.

It is important to note that the control sequence for Restoring the capacity of the system differs significantly from the one just described (g, h, j, k, m, n), if the most energy efficient way is followed. First, the inlet guide vanes are gradually opened while the speed of the corapressor drive motor is decreased when the system changes from the sixth operating condition η moves to the fifth operating condition m. Then the inlet guide vanes are opened wider while simultaneously the speed of the motor is increased as the system moves away from the fifth operating condition m. Then the inlet guide vanes are more open while simultaneously the speed of the motor is increased while the system moves away from the. fifth operating condition m to the fourth operating condition k moves. The opening of the inlet guide vanes is increased and at the same time the speed of the compressor drive motor is increased when the system moves from the fourth operating condition k directly to the second operating condition h without going through the third operating condition j to go. The inlet guide vanes are

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completely open in the second operating condition h. In the end the speed of the compressor drive motor is increased to increase the system capacity until the first Operating condition g is reached again. In short, the method according to the invention regulates the position of the Inlet wing and the speed of the compressor drive motor essentially, in accordance with the functional changes shown in FIG. 4 and described above, to pumping Avoid during operation in an energy efficient manner.

Those skilled in the art will recognize that the control system of the invention is readily applicable to a heat pump arrangement in which both the speed of the compressor and the amount of gas transferred to the compressor vary be to follow an »optimal control path.

The following is one. Specified parts list in which the components not specified in FIGS. 6A to 6C and Components are designated.

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IC type MLM2902P MLM2902P MC14016BCP MLM2902P MLM2902P MLM2902P MC14016BCP CA3.160S MLM2902P MC14572BCP MC14023BCP MC14001BCP MC 14011BCP MC14001BCP MC14541BCP T231OA NSL5057

IN914

Steps (Figs. 6A-6C)

59, 140, 148, 149 136, 137, 138, 139 141, 142, 143, 144 65, 101, 103, 104 106, 110, 111, 156 130, 146, 151, 153 123, 124, 125, 145

160, 173, 174, 176 114, 115, 116, 117, 122, 120, 135, 162 108, 121, 165, 167 134, 164, 166, 170 118, 157, 163, 168

All triacs

All light emitting diodes All transistors All diodes

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282Q209

A system according to the invention can be used both within existing facilities, by means of a back adaptation as well as can be used in conjunction with newly installed systems.

In the appended claims the term "connected" means a direct current connection between two components with one virtual zero DC resistance between these components. The term "coupled" indicates that there is a functional There is a relationship between two components, with the possible interposition of other elements between the two than components referred to as "coupled" or "inter-coupled".

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Empty soap

Claims (13)

Dlpl.-Phy «. U. M. Hall ^ Mütchen 22, den Maximilianstrasse 15 Tel. 294818 Claims (i). Control system for a refrigeration system with a compressor, a Condenser and an evaporator, all of which are connected to one another in a closed cooling circuit, the Compressor an adjustable capacity control means (inlet guide vane) , Means (motor) for regulating the adjustable capacity control means and an electric prime mover for driving the compressor, characterized in that a control circuit for the Drive machine (36) first circuit means (56, 58, 59) for deriving a signal which is related to the Compressor pressure level changes, and means (44, 37) for using the pressure level indicator signal to regulate the Speed of the electric drive machine (36), so that the combined control of _Speed the prime mover (36) and the adjustable capacity control means (31) in an energy-conserving manner and without transferring the compressor (20) into its pumping area is effected. 2. Control system according to claim 1, characterized in that means (155) are provided for producing a time signal are that means (61) are provided for generating a position signal which emerges as a function of the setting of the 809846/0905 adjustable capacity control means changed, and that a drive control circuit (156, 157, 160) has a first input, the is coupled to the means (155) for generating the time signal, a second input which (via 85) to means (61) is coupled to generate the Positbnssignals, and a Having output coupled (via PRV logic 96) to means for controlling the adjustable capacity control means (31) is that the drive control circuit generates an output signal having at least one characteristic known as a function of the position signal varies so as to adjust the adjustable capacity control means (31) as a function of the To regulate the position of the adjustable capacity control means (31). 3. Control system according to claim 1, characterized in that a second circuit (83) is provided, the a signal (via 51) for the means (44) for regulating the speed of the electric drive machine (36) as a function of the pressure height including Signal generated, and that a third circuit (96) is provided _{/ to} generate a signal (via 53, 54) for the means (32) for regulating the adjustable capacity control means (31), so that the combined control of the speed of the prime mover ( 36) and the adjustable capacity control means (31) is effected in an energy sustaining manner and that thereby compressor pumping is avoided. 4. Control system according to claim 3, characterized in that the first circuit has a first sensing means (56) positioned to generate a first signal (via 55) related to stands for the coolant condensation temperature and a second 809846/0905 Cooling means (58) which is positioned _/ to generate a second signal which is related to the coolant evaporation temperature, and means (59) comprises first to Zusammenfassunjdes and second signals to produce the pressure altitude containing signal. 5. Control system according to claim 3, characterized in that Means (61) to the adjustable capacity control means (31) are coupled to generate an electrical signal indicative of the physical location of the capacity control means (31), and in that means are provided for applying the position indicating signal to the third circuit (96) in order to provide a drive signal (via 53, 54) for the means for regulating the adjustable Generate capacity control means (31) as a function of capacity control means position. 6. Control system according to claim 3, characterized in that a Temperaturftihlmittel (63) is arranged to generate a signal (via 64) which is related to the cooling water outflow temperature of the evaporator, that adjustable means (66) for generating a temperature setpoint signal s are provided and that means (65) for combining the cooling water temperature signal and the temperature setpoint signal are provided / to generate a temperature error signal (at 67) which is sent to the second circuit (83) and the third circuit (86) for use in the control of the operation of the cooling system is applied to aid in regulating the speed of the prime mover (36) as well as the adjustable capacity controls. 7. Control system according to claim 5, characterized in that a Network (87) is provided to the position indicator signal 809846/0905 to modify and to use a modified signal to regulate the electric drive machine. 8. Control system according to claim 7, characterized in that resistance means are provided for combining the modified signal and the signal containing the pressure level _{/ to} generate a combined signal (at 90), that means are provided for generating a signal (at 72) related to the instantaneous speed of the electric prime mover (36) and that means (151) are provided for combining the combined signal and the speed signal to produce a signal (at 91) for regulating the speed of the electric prime mover (36). 9. Control system according to claim 6, characterized in that a Uhlastkreis (68) is provided which is coupled to the adjustable means (66) to generate the Tempera gate target value signal , and which is operable to change the temperature _{setpoint signal (} ub so changing the load on the compressor and decreasing the rate at which energy is consumed. 10. Method for controlling a cooling system with a compressor, a condenser and an evaporator, all of which are connected to one another in a closed cooling circuit, the Compressor -adjustable inlet blades for changing the Includes compressor capacity and an electrically adjustable speed motor that drives the Compressor is connected so that the setting of the motor speed also changes the capacity, whereby the 809846/0908 -5-driving has the following steps: a) the continuous production of a compressor pressure height signal as a function of the condensing temperature the refrigerant and the evaporation temperature of the refrigerant; b) the derivative of a function signal that is related the current position of the inlet guide vanes; c) the combination of the signal indicating the pressure altitude and the function signal to generate an intermediate signal; d) the production of a signal related to the current present engine speed; e) summarizing the current engine speed signal and the intermediate signal for generating a first signal for controlling the speed of the compressor drive motor and f) the derivative of a temperature error signal related to the temperature difference between the temperature of the Refrigerant at the outlet of the evaporator and the desired setpoint temperature, and the use of the Temperature error signal as a second signal to regulate both the speed of the compressor drive rotor ala also the position of the inlet guide vanes. 11. The method according to claim 10, characterized in that the Compressor drive motor speed and position 809846/090 & 2S20209 the inlet guide vanes can be regulated to increase the system capacity in accordance with the following steps, which are carried out successively to reduce: a) reducing the speed of the compressor drive motor, while the inlet guide vanes remain wide open, from a first working condition to a second Working condition to a third working condition; b) gradually closing the inlet guide vanes and at the same time increasing the speed of the compressor . drive motor to achieve a fourth operating condition; c) continuing the closure of the inlet guide vanes during at the same time the speed of the drive motor is reduced in order to achieve a fifth working condition and d) thereafter continuing the closing of the inlet guide vanes ₇ while at the same time increasing the speed of the drive motor until a sixth operating condition is reached. 12. The method according to claim 11, characterized in that the following steps are also provided in succession are / To restore the capacity of the system: a) the gradual opening of the inlet guide vanes during the The speed of the compressor drive motor is reduced, 809846/0905 - when the system changes from the sixth operating condition moved to the fifth operating condition; b) continuing the opening of the inlet guide vanes while at the same time the speed of the motor is increased while the system changes from the fifth operating condition moved to the fourth operating condition; c) continuing the enlargement of the opening of the inlet guide vanes and the simultaneous increase in the speed of the compressor drive motor when the - System from the fourth operating condition directly to the second operating condition moves without durd the third To go operating condition, wherein the inlet guide vanes are fully open in the second operating condition and d) continuing to increase the speed of the compressor drive motor to increase the system capacity St until the first operating condition is reached. 13. Method of regulating a cooling system, with a compressor with adjustable guide vane, which is driven by a variable speed motor is driven, with the position of the inlet vanes and the speed of the Compressor drive motor together essentially in accordance with the functional changes shown in FIG and those described in the description can be regulated to operate a / pumping in an energy efficient Way to avoid. 809846/0905