HK1159234B - Methods and systems for compressor operation - Google Patents

Description

Method and system for compressor operation

Technical Field

The present invention relates to methods and systems for compressor operation before and during compressor start-up and/or shutdown, and in particular to methods and systems for reliable start-up of a compressor even at low ambient temperatures.

Background

Conventional refrigeration and air conditioning systems typically include a compressor, a heat rejecting heat exchanger or condenser, an expansion valve or device, and a heat accepting heat exchanger or evaporator. In operation, refrigerant circulates through these components in a closed circuit. The pressure and temperature of the refrigerant vapor is increased by the compressor before entering the heat rejection heat exchanger where it is cooled. The high pressure, lower temperature liquid is then expanded to a lower pressure by means of an expansion valve. In the heat accepting heat exchanger, the refrigerant boils and absorbs heat from its surroundings. The vapor at the outlet of the heat accepting heat exchanger is drawn into the compressor, completing the cycle.

However, at compressor shutdown and restart, components of the system, particularly the compressor, may be damaged or fail, especially at low ambient temperatures.

Disclosure of Invention

It is therefore an object of the present invention to provide a refrigeration system and a method of operating a refrigeration system, particularly but not exclusively for a transport refrigeration unit, the refrigeration system comprising a compressor and being operable to minimise system faults arising from or at start-up of the compressor, particularly when the compressor is started at low ambient temperatures.

According to the present invention, from a first broad aspect, there is provided a refrigeration system comprising a compressor, a heat rejecting heat exchanger, an expansion valve and a heat accepting heat exchanger. The system also includes a Pressure Equalization Valve (PEV) for equalizing a pressure differential between the compressor suction and the compressor discharge. Preferably, the pressure equalization valve includes a bypass passage connecting the compressor suction port to the compressor discharge port and bypassing the compressor. Preferably, the system further comprises a Liquid Valve (LV), preferably a Liquid Solenoid Valve (LSV), preferably arranged in the flow line between the heat rejecting heat exchanger and the expansion valve.

Accordingly, a refrigeration system is provided that includes a primary refrigerant flow path from a compressor to a heat rejecting heat exchanger, from the heat rejecting heat exchanger to a liquid valve, from the liquid valve to an expansion valve, and from the expansion valve to a heat accepting heat exchanger. A bypass refrigerant path or other pressure equalization valve is provided across the compressor (i.e., from the compressor suction to the compressor discharge) so that when it is opened, the bypass refrigerant flows around the compressor and so that the pressure differential between the compressor suction and compressor discharge can be minimized or, more preferably, the suction and discharge pressures can be equalized, particularly at compressor shutdown and most preferably at or shortly before compressor startup.

Preferably, the refrigeration system is operable according to at least one of a plurality of predetermined procedures, and the specific procedure(s) is preferably determined based on at least one parameter of the refrigeration system. Preferably, the parameter(s) comprise system parameters measured by at least one sensor.

In a preferred embodiment, a warm-up procedure to heat one or more components of the compressor is initiated when it has been determined that compressor startup is required. Preferably, the compressor body or housing, and/or the oil in the compressor, and/or the compressor motor, and/or any other suitable component, is heated. Preferably, the component(s) are heated for a predetermined period of time, which may be determined based on one or more system parameters. In a preferred embodiment, the period of time for which the component is heated is determined based on the temperature of the oil in the compressor, and/or the compressor shell temperature, and/or the compressor discharge temperature, and/or the temperature of the environment in which the compressor is located (i.e., the ambient temperature), and the like. Additionally or alternatively, the period of time for which the component is heated is determined based on the length of time the compressor has been shut down (e.g., if the compressor was only recently shut down, the component may only have to be heated for a relatively short time because the component may have retained some heat from its normal operating state and temperature).

Heating of the component(s) of the compressor is performed in any suitable manner. In a particularly preferred embodiment, the stator windings of a motor associated with the compressor, for example an internal ac motor (synchronous or asynchronous) of the compressor, are electrically connected to a power supply, for example a dc power supply, to thereby heat the windings and hence the compressor.

The pressure equalization valve may be opened before the compressor is started, but in a preferred embodiment the pressure equalization valve is opened at the start of the compressor (preferably substantially simultaneously with the start of the compressor). For example, in embodiments where the pressure equalization valve is a bypass passage, the passage is opened as the compressor is started to allow pressure equalization between the compressor suction and discharge ports by bypassing the compressor. Preferably, the pressure equalization valve is opened after the preheating step discussed above.

Preferably, the compressor is started slowly, for example at a frequency or speed significantly lower than the standard operating frequency. Starting the compressor and opening the pressure equalization valve allows the oil in the compressor to be mixed. This is advantageous because in a shutdown compressor, the temperature of the oil is not uniform in the compressor shell. When the compressor is started slowly with the pressure equalization valve open (and thus at very low refrigerant flow rates), hot oil from the motor is mixed with cold oil from the other parts and the oil warms up. In addition, the oil and other parts of the compressor are heated by the refrigerant bypassing the compressor via the pressure equalization valve, the vapor refrigerant from the discharge valve in the compressor is hotter than the actual suction port gas refrigerant, and the vapor heats the mechanical parts of the compressor and the oil as it passes through the bypass and compressor suction ports. That is, the bypass line typically emits heat to the compressor and heats oil circulating in the compressor. The pressure in the compressor body or shell is limited by the bypass.

In a particularly preferred embodiment, the oil temperature of the compressor is maintained above the saturated discharge temperature of the refrigerant in the compressor shell. At temperatures below the saturated discharge temperature, the vapor refrigerant condenses, and if the oil temperature is below the saturated discharge temperature, the refrigerant will condense into the oil. Preferably, the compressor shell temperature is also maintained above the saturated discharge temperature of the refrigerant. If the oil (and preferably also the mechanical parts and the shell of the compressor) is above the saturated discharge temperature, the refrigerant will not condense in the compressor.

Preferably, the compressor speed at start-up is lower than the normal operating speed of the compressor as described above. For example, in a preferred embodiment, the compressor at start-up operates at a frequency of 30 Hz. At start-up, a low compressor speed is desirable because the low flow rate through the compressor minimizes refrigerant condensation in the compressor.

Preferably, the liquid valve is closed before and during the start-up of the compressor. In a particularly preferred embodiment, the liquid valve is closed as the compressor stops and remains closed during compressor shutdown. Closing the liquid valve when the compressor is stopped restricts the flow of refrigerant into the compressor, thereby limiting condensation in the compressor oil.

Preferably, the liquid valve is opened at an appropriate time after the compressor is started. Thus, the system operates in some conditions where both the pressure equalization valve and the liquid valve are open and the compressor operates at a low frequency. This enables an increase in the refrigerant flow at the compressor suction, although this refrigerant flow is still lower than during normal system operation, because the pressure equalization valve is open (i.e., the compressor remains bypassed at this stage). Preferably, the liquid valve is opened when it is determined that the system parameter is at a desired level. For example, in a preferred embodiment, the system parameter is oil temperature, and when the oil temperature is determined (e.g., by measurement with a temperature sensor) to be sufficiently high (e.g., above a predetermined limit, and/or above a saturated discharge temperature of refrigerant in the compressor, etc.), then the liquid valve is opened. Of course other suitable parameters and limits may be used. For example, in a preferred embodiment, the parameter is alternatively or additionally the pressure in the compressor housing. Further, it is contemplated that the liquid valve may alternatively or additionally be opened in response to other events, such as after a predetermined period of time (e.g., from compressor startup, and/or from opening of the pressure equalization valve, or from any other action or event, etc.).

Preferably, the pressure equalization valve is closed after the liquid valve is opened. This occurs in response to any one or more of the following: after a predetermined period of time since the liquid valve was opened; after a period of time has elapsed after any other suitable event; after a period of time has elapsed after one or more system parameters are determined to reach a particular level; immediately after opening the liquid valve; and so on. In a preferred embodiment, the system parameter comprises compressor discharge temperature or oil temperature, and when the temperature is determined (e.g., by measurement with a temperature sensor) to be sufficiently high (e.g., above a predetermined limit, and/or above a saturated discharge temperature in the compressor, etc.), then the pressure equalization valve is closed. As a result, the pressures at the suction and discharge ports of the compressor are no longer balanced, and refrigerant passes through the compressor at a greater flow rate than when the pressure equalization valve is open (e.g., refrigerant no longer bypasses the compressor).

The compressor speed is then preferably increased immediately or preferably in response to the measured system parameter reaching a predetermined limit and/or after a period of time has elapsed, etc. Preferably, the compressor speed is slowly increased, preferably by a predetermined amount and/or at a predetermined rate, until a maximum or optimal speed is achieved and/or a predetermined period of time has elapsed. Alternatively or additionally, the compressor speed may be set to a maximum (i.e. standard) operating speed when the measured system parameter is determined to have reached a predetermined level (this is preferably after a slow increase in compressor speed for a period of time from an initial start-up speed). In a preferred embodiment, the compressor is controlled to operate at a normal operating speed when the compressor discharge temperature and/or the compressor oil temperature has reached a predetermined level.

The above preferred system and operating steps provide a compressor start-up procedure that enables the compressor to be started with minimal risk of failure that might otherwise occur due to condensation of refrigerant in the compressor after shutdown of the compressor, particularly at low ambient temperatures. The condensation of refrigerant in the compressor is detrimental because the condensed refrigerant may become mixed with oil in the compressor sump and the refrigerant may condense in the oil if the oil temperature in the compressor is below the saturated discharge outlet temperature of the refrigerant. When the compressor is started, the refrigerant in the oil is pumped by the oil pump and a malfunction may occur. Furthermore, the viscosity of the oil is affected by the presence of the refrigerant and may therefore be unsuitable for compressor operation, causing damage to the corresponding lubricated component. The preferred embodiments of the present invention and the preferred methods discussed below address these issues.

In another broad aspect of the invention, there is provided a method of optimizing compressor startup for a compressor of a refrigeration system comprising the steps of: will refrigeratePreheating at least one component of a compressor in the system; opening a pressure equalization valve connecting a suction port and a discharge port of the compressor to thereby reduce a pressure difference therebetween; preferably substantially simultaneously with opening the pressure equalization valve, preferably at a predetermined frequency f_lThe compressor is started. Preferably, the method further comprises the step of: the method includes opening a liquid valve located in a refrigerant flow path of the system in response to a first event, closing a pressure equalization valve in response to a second event, and increasing an operating frequency of the compressor.

Preferably, the starting speed f of the compressor_lLess than the standard operating speed f of the compressor_s. Preferably, f_lAbout 30 Hz. Preferably, f_sAbout 60 Hz, preferably about 65 Hz or greater. Preferably, the method comprises the further steps of: the operating frequency of the compressor is preferably further increased to the standard operating frequency in response to a third event.

Preferably, the first event comprises at least one of a first predetermined period of time elapsing and the measured compressor oil temperature is determined to be above a predetermined threshold. Preferably, the second event comprises at least one of a second predetermined period of time elapsing and the measured compressor oil temperature is determined to be above a predetermined threshold.

Preferably, the method further comprises the step of: at least one system sensor is provided and at least one parameter of the system is measured with the sensor and the system is caused to operate according to at least one of a plurality of predetermined procedures based on the at least one parameter measured by the sensor.

Preferably, the step of preheating at least one component of the compressor comprises the steps of: means are provided for heating at least one component of the compressor, and the heating means are activated to heat the component when it has been determined that start-up of the compressor is required. Preferably, the means for heating at least one component of the compressor comprises means for heating at least one of the compressor body or shell, oil in the compressor, and the compressor motor. In a particularly preferred embodiment, the heating means comprises means for providing DC power to the stator windings of the internal AC motor of the compressor. Preferably, the method further comprises providing at least one sensor and using the sensor to measure at least one parameter of the system, and activating the heating means for a predetermined period of time based on the at least one parameter. Preferably, the predetermined period of time is based on at least one of a temperature of oil in the compressor, a compressor shell temperature, a compressor discharge temperature, an ambient temperature, and a length of time that the compressor has been inactive.

Preferably, the method further comprises the step of: the method includes measuring a temperature of oil in the compressor, determining a saturated discharge temperature of refrigerant in the compressor, and heating at least one component of the compressor such that the oil is maintained at a temperature above the saturated discharge temperature.

As described above, preheating the refrigeration system prior to compressor startup and controlling the liquid valve and the pressure equalization valve prior to and during startup may advantageously reduce or eliminate refrigerant condensation problems, particularly at low ambient temperatures. However, even the above-described systems may experience a malfunction or other problem at compressor start-up due to other reasons at or after compressor shutdown.

Thus, according to another broad aspect of the present invention, there is provided a refrigeration system comprising a compressor, a heat rejecting heat exchanger, an expansion valve, and a heat accepting heat exchanger. The system further comprises a Liquid Valve (LV), preferably a Liquid Solenoid Valve (LSV) or an electronic expansion valve (EXV), arranged in the flow line between the heat rejecting heat exchanger and the compressor, and a check valve arranged in the flow line between the heat rejecting heat exchanger and the expansion valve.

The refrigeration system is advantageous in that when the compressor is shut down, the liquid valve is actuated to close and the check valve is also closed. Preferably, the check valve is closed by the pressure difference between the high pressure side of the system and the compressor. In other preferred embodiments, the check valve is a solenoid valve and is actuated to close. In other embodiments, the check valve comprises a combination of a solenoid valve and a pressure actuated valve. In a standard circuit without this valve arrangement, the pressure differential will cause the migration of refrigeration from the high side (e.g., from the condenser and from the evaporator) to the compressor, particularly during long periods of compressor shutdown, such as 12 hours or more. Any refrigerant migrating to the compressor during shutdown may condense in the compressor, or migrate into the compressor oil, which may lead to compressor failure at start-up, for example, due to low oil viscosity.

Thus, the system of embodiments of this aspect of the invention advantageously reduces the amount of refrigerant reaching the compressor during shutdown, or even prevents refrigerant from reaching the compressor during shutdown, so little or no refrigerant can mix with the compressor oil. This is advantageous because the amount of refrigerant in the oil is minimized and therefore the oil viscosity will remain sufficiently high, whereas low viscosity oil is dangerous for the compressor.

Preferably, the check valve is configured such that a pressure difference between the valve inlet and the valve outlet is required to cause the check valve to open, in particular a significant pressure difference. The system of this embodiment is also advantageous in that the combination of the check valve and the liquid valve will retain the refrigerant in the condenser (and in any other components that may exist between the check valve and the liquid valve, such as in the accumulator and/or dryer, etc. in the preferred embodiment). Preferably, the check valve is configured such that if the pressures at the inlet and outlet of the check valve are balanced, the valve remains closed, which balancing may occur over time after the compressor is shut down. That is, in a preferred embodiment, the check valve is configured such that refrigerant can only pass through the valve when the valve inlet pressure is higher than the valve outlet pressure, such as when the compressor is started. Preferably, the check valve includes a resilient device, such as a spring, that biases the valve to the closed position when the pressures at the inlet and outlet of the check valve are balanced. This is advantageous because prior art valves leak refrigerant when the pressures at the inlet and outlet are balanced, whereas in embodiments of the present invention having the inventive check valve, a greater inlet pressure is required to open the valve and minimize the amount of refrigerant leakage under other conditions.

The above-described preferred refrigerant system prevents or significantly reduces refrigerant migration from the condenser and other high-side components of the system, and/or from the low side of the system, to the compressor after compressor shutdown, and thus enables starting of the compressor even after long shutdown periods with minimal risk of failure of the refrigerant being mixed with compressor oil.

According to another broad aspect of the present invention, there is provided a method of controlling a refrigeration system, comprising the steps of: the method includes initiating a shutdown of a compressor of the system, closing a check valve provided in a flow line between the compressor and a heat rejection heat exchanger of the system, and closing a liquid valve of the system located in a flow path between the heat rejection heat exchanger and an expansion device of the system. In a preferred embodiment, the pressure differential between the condenser and the compressor that occurs at shutdown is such that the pressure on the condenser side of the check valve is higher than the pressure on the compressor side of the check valve after shutdown, and this closes the check valve to prevent refrigerant flow therethrough. In other preferred embodiments, the check valve comprises a solenoid valve, and preferably both valves are closed as soon as possible after compressor shutdown and preferably substantially simultaneously with each other to prevent refrigerant migration.

Preferably, the method further comprises the step of: the compressor is started, causing a pressure difference between the condenser and the compressor and opening a check valve provided in a flow line therebetween, and the liquid valve is opened. The pressure differential between the condenser and the compressor is such that the pressure on the condenser side (e.g., outlet) of the check valve is lower than the pressure on the compressor side (e.g., inlet) of the check valve after the compressor is restarted. This opens the check valve to enable refrigerant to flow therethrough. Preferably, the method further comprises the step of biasing the check valve to a closed position, wherein the biasing force must be overcome in order to open the valve.

As discussed above, the provision of the liquid valve and check valve of the present invention enables the system to be operated to prevent or substantially reduce refrigerant migration from the condenser and other high-side and/or low-side components of the system to the compressor after compressor shutdown. Thus, it is possible to restart the compressor and minimize the risk of compressor failure due to the refrigerant present in the oil after refrigerant migration. However, even the above-described systems may experience a malfunction or other problem at compressor start-up due to other effects that also result from compressor shutdown.

Thus, according to another broad aspect of the present invention, there is provided a refrigeration system comprising a compressor, a heat rejecting heat exchanger, an expansion valve, and a heat accepting heat exchanger. The system also includes a Pressure Equalization Valve (PEV) for equalizing a pressure differential between the compressor suction and the compressor discharge. The pressure equalization valve is operable to open after or simultaneously with compressor shutdown, preferably substantially immediately after compressor shutdown is achieved. Preferably, the pressure equalization valve includes a bypass passage connecting the compressor suction port to the compressor discharge port and bypassing the compressor.

By opening the pressure equalization valve simultaneously with or just after the compressor is shut down or stopped, the pressure differential between the compressor suction and discharge ports is equalized as quickly as possible. This is advantageous because the high pressure differential between the compressor suction and discharge at compressor shutdown causes oil to migrate from the compressor toward the suction side of the compressor, out of the compressor and into the suction line, whereas in the present invention, equalization or balancing of discharge and suction pressures prevents such migration. It is undesirable for oil to leave the compressor when restarting the compressor, with little or no oil available for compressor lubrication. Furthermore, at restart, the compressor has a mixture of oil and refrigerant in the suction line, which may lead to compressor failure when this mixture is sucked into the compressor. Still further, oil leaving the compressor and entering the suction line may migrate to the evaporator, which may cause further failure, and if the expansion valve is controlled with respect to the evaporator temperature (e.g., evaporator outlet temperature), the presence of oil at the sensor may cause the expansion valve to open even if the system is shut down.

However, embodiments of the present invention provide an improved refrigeration system in which migration of oil from the compressor to the low side of the system after compressor shutdown is minimized or prevented by equalizing the pressure differential between the compressor discharge and suction ports just after compressor shutdown. It is also contemplated to carry out the method of the present invention, and therefore according to another broad aspect of the present invention there is provided a method of controlling a refrigeration system comprising the steps of: triggering a compressor shutdown of the system; and opening a Pressure Equalization Valve (PEV) to equalize a pressure differential between the compressor suction and the compressor discharge. The pressure equalization valve is preferably opened at or just after the compressor is shutdown, preferably substantially immediately after the compressor shutdown is achieved, to substantially equalize the high side discharge pressure and the low side suction pressure of the compressor. Preferably, the pressure equalization valve includes a bypass passage connecting the compressor suction port to the compressor discharge port and bypassing the compressor.

Drawings

The above and other features of various embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

FIG. 1 shows a schematic diagram of a refrigeration system according to an embodiment of the invention;

FIG. 2 shows a flow chart illustrating the operational modes of a refrigeration system according to an embodiment of the present invention;

FIG. 3 illustrates a first, standard operating procedure for starting a compressor of a refrigeration system in accordance with an embodiment of the present invention;

FIG. 4 illustrates a second, long operating sequence for starting a compressor of a refrigeration system in accordance with an embodiment of the present invention;

FIG. 5 illustrates a third, short operating sequence for starting the compressor of the refrigeration system in accordance with an embodiment of the present invention;

FIG. 6 shows a schematic diagram of another refrigeration system according to an embodiment of the present invention;

FIG. 7A shows a schematic diagram of another refrigeration system according to an embodiment of the present invention after compressor shutdown;

FIG. 7B shows the system without the pressure equalization valve of the embodiment of FIG. 7A in two states, the first being shortly after compressor shutdown and the second being some time after compressor shutdown; and

FIG. 8 shows a schematic diagram of a refrigeration system according to another embodiment of the present invention.

Detailed Description

The principles of the present invention may be incorporated into any suitable system. Examples of such suitable systems include refrigeration and air conditioning systems, and particularly, but not exclusively, transport or truck refrigeration systems. For ease of reference, the particular embodiments discussed herein are described with reference to a refrigeration system suitable for a transport refrigeration unit or the like.

Fig. 1 schematically illustrates a refrigeration system 10 having a refrigerant cycle or circuit 20 that enables refrigerant flow throughout the system. The system comprises a compressor 12, which compressor 12 is connected from its outlet or discharge 13 via a flow path 22 to a heat rejecting heat exchanger, in this embodiment a condenser 14. The condenser 14 is connected to an expansion device 16 via a flow path 24, and the expansion device 16 is connected to a heat accepting heat exchanger, in this embodiment an evaporator 18, via a flow path 26. The evaporator 18 is connected to the compressor 12 at an inlet or suction port 11 of the compressor 12 via a flow path 28. The expansion device 16 is preferably a thermostatic expansion valve and is controlled in this embodiment via a control line 36 in response to conditions of the system 10. The system condition controlling the opening of the expansion valve 16 may be, for example, the temperature of the evaporator 18, or a related temperature such as the bulb temperature at the evaporator outlet, or the like. In the present embodiment, additional optional components, an accumulator 32 and a dryer 34, are also provided on the flow path 24 between the condenser 14 and the valve 16.

The system 10 also includes a Pressure Equalization Valve (PEV) across the compressor 12 (i.e., connecting the compressor suction port 11 to the discharge port 13). The PEV includes a bypass passage 40 and a device 42, such as a valve, for opening and closing the passage 40.

The system 10 also includes a Liquid Valve (LV), which in the preferred embodiment is a liquid solenoid valve 44, in the flow path 24 between the condenser 14 and the expansion valve 16. It is contemplated that LV 44 may be energized to open or close as desired, thereby opening or closing flow path 24 to enable or disable refrigerant flow throughout circuit 20.

In operation, high pressure and high temperature refrigerant vapor exits compressor 12 and enters condenser 14 where it is cooled to a lower temperature, high pressure liquid refrigerant. This liquid is then expanded by expansion valve 16 to a lower pressure and passed to evaporator 18 where the refrigerant boils and absorbs heat from its surroundings. The vapor at the outlet of the evaporator 18 is drawn into the compressor 12, completing the cycle.

When the compressor 12 is shutdown, refrigerant may be present in the compressor 12, and in particular, if the compressor 12 is shutdown for a significant period of time, additional refrigerant may migrate from the condenser 14 to the compressor 12, as will be discussed in more detail below.

The refrigerant in the compressor 12 may condense on the compressor shell, particularly at low ambient temperatures, and the condensed refrigerant will mix with compressor oil having an affinity for the refrigerant. If the compressor oil temperature is below the saturated discharge temperature of the refrigerant, the refrigerant may condense in the oil. The refrigerant dilutes the oil and when the compressor 12 is restarted, the diluted oil becomes less effective in lubricating the components of the compressor 12, which can cause damage. In addition, the compressor oil pump will draw in refrigerant, which may also cause damage.

Thus, in accordance with an embodiment of the present invention, one or more compressor start-up procedures are employed to minimize or eliminate refrigerant condensation in the compressor 12. FIG. 2 is a flow chart of an embodiment of the present invention wherein a control device or the like determines the status of the system 10 (e.g., the system 10 of any of FIGS. 1, 6, 7A or 8), and in particular the length of time T that the compressor has been shut down_stopAnd discharge temperature T of compressor 12_ref. If the compressor 12 is shut down for a significant period of time, the discharge temperature T_refSubstantially equal to ambient temperature. In other embodiments, the ambient temperature may be measured. The control determines from these parameters what steps should be taken to minimize or eliminate the problem of refrigerant condensation in the compressor 12 before and during compressor start-up. Of course, other parameters may alternatively or additionally be used in this determination, such as the temperature of the oil in the compressor 12, the temperature of the refrigerant in the compressor 12, and/or the pressure within the compressor shell, among others. The parameters used may depend on the sensors present in the system 10, and thus on what may be measured in order to make this determination.

In the embodiment of fig. 2, the routine begins at step 1.1 and determines the time T since the compressor 12 stopped in step 1.2_stop. If it is less than 1 hour, the time is further determined in step 2.1, and if T is_stopLess than 1/2 hours, the time is determined further in step 3.2. For a shutdown period of less than 1/2 hours, it is determined that the compressor 12 need not be warmed up, and a normal start-up sequence is initiated in step 4.3 (e.g., as shown in fig. 3). For the shut-down period between 1/2 hours and 1 hour, the discharge outlet temperature T is determined in step 3.1_refAnd if the discharge outlet temperature T is_refIs low (below 20 c), a short (3 minutes) warm-up of the compressor 12 is initiated in step 4.2 and the normal start-up sequence is then started in step 5.2 as discussed below. However, if T_refAlready high enough, no preheating is required and a short start-up sequence is started in step 4.1 (e.g. as shown in fig. 5)。

When the compressor 12 has been shut down for longer than 1 hour, the discharge temperature T is determined in step 1.3_refAnd is also determined in steps 1.4, 1.5, 1.6, 1.7 and 1.8 depending on the temperature. Furthermore, according to T_refThe compressor 12 is warmed up for 12, 9, 6 or 3 minutes (steps 2.2, 2.3, 2.4 and 2.5 respectively) and then a long start-up sequence is started in step 3.3 (e.g. as shown in fig. 4). However, if T is determined as in step 1.7_refHigh enough (between 0 ℃ and 20 ℃), a 3 minute warm-up is initiated in step 2.6, and then the normal start-up procedure is started in step 3.4. If T is as determined in steps 1.8 and 1.9_refAlready even above 20 ℃, no preheating is required and a normal start-up procedure is initiated in step 2.7, or for very high temperatures (above 40 ℃) a short start-up procedure is initiated in step 2.8.

The above procedure ensures that if the discharge temperature of the compressor 12 is low, the compressor 12 is preferably heated prior to compressor startup to increase the compressor temperature, including the oil temperature. This is advantageous not only because the viscosity of the oil is improved, making the oil more suitable for lubricating compressor components at start-up, but also because the oil temperature (above the saturated discharge temperature of the refrigerant) is sufficiently high to reduce or eliminate refrigerant condensation in the compressor 12 that occurs when the compressor shell and oil are cooled.

Fig. 3, 4 and 5 schematically illustrate a preferred embodiment of a start-up procedure for starting the compressor 12 after shutdown. Fig. 3 shows a "normal" or default start-up sequence, fig. 4 shows a long start-up sequence and fig. 5 shows a short start-up sequence. In the preferred embodiment, the start-up procedure disclosed in fig. 2 corresponds to the procedures of fig. 3, 4 and 5, but it is also envisaged that this could be different or modified by the skilled person. Furthermore, the preheating procedures disclosed in fig. 3, 4 and 5 may correspond to the preheating procedure of fig. 2, or may be different or modified.

Fig. 3 shows a normal start-up sequence for the compressor 12. In a preferred embodiment, some or all of the steps of the routine of FIG. 2 are performed as the first step of a normal start-up routine. Accordingly, the discharge temperature of the compressor 12 is preferably at least 20 ℃, or the compressor off time period is less than 1/2 hours. Referring to the system 10 shown in fig. 1, the Pressure Equalization Valves (PEVs) 40, 42 are initially closed, and the Liquid Valve (LV) 44 is also closed. When the compressor 12 is to be started, the PEV is opened, thereby opening a bypass of the compressor 12. The compressor 12 starts, but at a relatively low frequency of about 30 Hz, which is significantly less than the full operating speed of the compressor 12. At compressor 12 start-up, heat from the bypass refrigerant gas passing through the PEV is transferred to compressor 12 and to the compressor oil. Thus, the oil in the compressor 12 is (further) heated and the risk of condensation is further minimized, in particular since the refrigerant bypassing the compressor 12 cannot condense in the compressor 12. Furthermore, the LV is closed to restrict the flow of refrigerant into the compressor 12, thereby further reducing the risk of condensation.

When the oil temperature in the compressor 12 is sufficiently high, such as when it is measured, determined or otherwise expected to be above the saturated discharge temperature of the refrigerant, and/or after the oil has been heated for a sufficient period of time (which in a normal start-up procedure is 20 seconds) in the present embodiment, the liquid valve is opened and the PEV remains open. The refrigerant flow at the compressor suction 11 is slightly increased, but it is still relatively low because the compressor 12 is still bypassed by the open PEV. When the oil temperature in the compressor 12 is sufficiently high, such as when it is again measured, determined and/or expected to be above the saturated discharge temperature of the refrigerant, and/or in this embodiment after it has been heated for a sufficient period of time (which is another 20 seconds in a normal start-up procedure), the PEV is closed while the liquid valve remains open. Thus, refrigerant flows throughout the circuit 20 of the system 10 under the influence of the compressor 12 no longer being bypassed.

When the oil temperature in the compressor 12 is sufficiently high, for example when it is again measured, determined or otherwise expected to be above the saturated discharge temperature of the refrigerant, and/or after it has been heated for a sufficient period of time in this embodiment (which is yet another 20 seconds in this embodiment), the speed of the compressor 12 is gradually increased, preferably at 5 Hz per second, until the optimum or normal operating frequency is reached, after which standard compressor speed control is applied as is known in the art. In other embodiments, the standard operating speed control may be initiated after it is again determined or otherwise expected that the oil temperature is still above the saturated discharge temperature.

However, a normal start-up procedure may not be appropriate under certain circumstances, such as when the temperature at which the compressor 12 is shut down is low (e.g., less than about 5℃.) and/or when the compressor 12 has been shut down for an extended period of time (over about an hour). Alternatively, a long start-up procedure as shown in fig. 4 may be more appropriate. The long start-up sequence differs from the normal start-up sequence in that the time period between events is typically significantly longer. For example, the LV is kept closed for 5 minutes instead of 20 seconds after the compressor is started, allowing additional time for the oil to warm up. The delay before closing the PEV is also longer and is about 2 minutes, thereby allowing the system 10 to operate at a reduced flow rate for a longer period of time. The time period before increasing the compressor frequency is also longer and about 21/2 minutes, after which the frequency is increased more slowly than in a normal start-up procedure, to increase at about 1 Hz every 5 seconds. The long start-up sequence differs from the normal start-up sequence at this stage in that an additional step is included before the standard compressor speed control is initiated, during which the compressor is operated at a maximum frequency of 60 Hz for 1 minute. The long start-up sequence is significantly slower than the normal start-up sequence, allowing the system temperature to gradually increase before the compressor 12 is fully loaded, which is appropriate in colder conditions, particularly if the compressor 12 has been inactive for a long period of time. Furthermore, as discussed with respect to fig. 2, it may be appropriate to heat the oil for a longer period of time before initiating the long start-up procedure.

However, in other cases, neither a normal or long start-up procedure may be appropriate, such as when the temperature at which the compressor 12 is shut down is relatively high (e.g., above about 40℃.) and/or when the compressor 12 is only shut down for a short period of time (less than one hour). In this case, a short start-up procedure as shown in fig. 5 may be more appropriate. This short start-up procedure differs from the normal start-up procedure in that the time period between events is typically much shorter, and in some embodiments, only minimal or little delay between events is required. For example, the LV does not remain closed after the compressor is started, but is opened quickly, as the oil may not need any additional time to warm up at lower operating speeds. The delay before closing the PEV is also short, or may not even be needed, and the PEV can be closed quickly after the compressor is started. The time period before the compressor frequency is increased is also short and is about 5 seconds, after which the frequency is increased at a slower rate than the normal start-up procedure, at about 1 Hz per second. The short start-up sequence is significantly faster than the normal start-up sequence because the system temperature does not need to be gradually increased and the compressor 12 can be operated at full load relatively quickly. Furthermore, as shown in fig. 2, it may not even be necessary to heat the oil before initiating the short start-up sequence.

Fig. 6 schematically illustrates an alternative embodiment of the present invention, however, this system 10 may be, and preferably is, combined with the system 10 shown in fig. 1 or indeed with fig. 7A by simply adding the PEV of fig. 1 (e.g., as shown in fig. 8). In the fig. 6 embodiment, the components are largely identical to those of the fig. 1 embodiment and have the same reference numerals. However, the embodiment of fig. 6 also includes a check valve 46, the check valve 46 being a one-way valve that prevents fluid flow or migration in one direction (from the condenser 14 toward the compressor 12) but allows fluid flow in the other direction (from the compressor 12 toward the condenser 14).

The system 10 of fig. 6 operates normally when the compressor 12 is running. However, in prior art systems, when the compressor is shut down, refrigerant migrates from the condenser and/or evaporator to the compressor due to pressure and temperature differences, and the refrigerant may condense and mix with oil in the compressor, as discussed above, which is undesirable. However, in the fig. 6 embodiment, refrigerant is effectively trapped between the check valve 46 and the Liquid Valve (LV) 44, and thus does not reach the compressor 12. The present embodiment operates as follows. When the compressor 12 is stopped, the LV is closed (preferably, the LV is a liquid solenoid valve and the valve is closed by energizing the solenoid), and the check valve 46 is closed (preferably, the check valve is also a solenoid valve and the valve is closed by energizing the solenoid, or the check valve may be closed by a pressure difference between the condenser 14 and the compressor 12). The refrigerant that would otherwise migrate into the compressor 12 is thus held in the refrigerant circuit 20 between the two valves 44, 46. Even if the pressures at the inlet and outlet of the check valve 46 are balanced, the check valve 46 will not open because, in this embodiment, the check valve 46 includes a spring (not shown) inside so that if the pressures are balanced, no leakage occurs. The inlet pressure of the check valve 46 must be higher than the outlet pressure to allow circulation of the fluid. Any additional components in the circuit 20, such as the accumulator 32 and the dryer 34, help store refrigerant during compressor shutdown. When the compressor 12 is restarted, the LV is energized to open and the check valve 46 is energized or opened due to the changing pressure differential.

Fig. 7A illustrates another embodiment of the present invention, which, although shown as a separate embodiment, is also within the scope of the present invention, as the system 10 will be combined with any one or more of the systems 10 shown in the other figures. The system 10 includes similar components to the other embodiments, including the pressure equalization valves 40, 42 discussed with respect to fig. 1, and the fig. 1 embodiment may also operate in accordance with the following disclosure.

The conventional refrigeration system 110 is shown in fig. 7B and shows a first state shortly after compressor shutdown and a second state longer after shutdown. When the compressor 112 is shut down, there is a large pressure differential between the compressor suction 111 and the compressor discharge 113, which effectively pushes the compressor oil 100 out of the compressor 112 on the suction side of the circuit 120, into line 128 and toward the evaporator 118. Thus, at compressor start-up, there is less oil than should be present, and in some cases there is little or no oil in the compressor 112, so that compressor components are likely to be damaged. Further, as shown in the second diagram of fig. 7B, after a period of time, the oil 100 may migrate and begin to fill the evaporator 118, and the relatively hot oil may also fill a bulb (bulb) of an expansion valve 116 control 136 located at the outlet of the evaporator 118 (i.e., in line 128). This may cause the expansion valve 116 to open (if not desired), further affecting system performance at compressor start-up and liquid in the compressor suction line may damage the compressor.

The refrigeration system 10 of the embodiment of fig. 7A overcomes this problem by providing a PEV that is opened during or preferably just after compressor shutdown. This equalizes the pressure differential between the compressor suction port 11 and discharge port 13 and thus prevents oil migration from the compressor to the low side of the system 10.

Fig. 8 schematically shows another embodiment of the invention. In the present embodiment, the system 10 includes a check valve 46, a liquid valve 44, and pressure equalization valves 40, 42. Thus, this system with the combination of all valves provides all the advantages disclosed with respect to the other embodiments and discussed above.

Claims (18)

1. A refrigeration system (10) comprising

A compressor (12) having a suction port and a discharge port;

a heat rejecting heat exchanger (14);

an expansion valve (16);

a heat receiving heat exchanger (18); and

a pressure equalization valve (40, 42) for equalizing a pressure differential between the compressor suction port and a compressor discharge port, the pressure equalization valve including a bypass passage (40) connecting the compressor suction port to the compressor discharge port to enable bypassing of the compressor and a valve (42) controlling a flow of refrigerant through the bypass passage; it is characterized by also comprising:

a liquid valve (44) arranged in a flow line between the heat rejecting heat exchanger (14) and the expansion valve (16);

means for heating at least one component of the compressor (12);

control means for activating the heating means when it has been determined that compressor start-up is required, the control means starting the compressor after heating the at least one component;

a sensor for sensing a temperature of oil in the compressor; and

means for determining a saturated discharge outlet temperature of refrigerant in said compressor;

wherein the means for heating at least one component of the compressor comprises means for heating at least oil in the compressor, and wherein the control means controls the heating means such that the oil is maintained at a temperature above the saturated discharge temperature.

2. The refrigerant system as set forth in claim 1, wherein said liquid valve is a liquid solenoid valve.

3. The refrigeration system of claim 1, further comprising:

control means for operating the system in at least one of a plurality of predetermined programs; and

at least one sensor, wherein the control device operates the system at a particular one of the plurality of predetermined procedures based on at least one parameter of the system measured by the sensor.

4. The refrigeration system of claim 1, wherein said means for heating at least one component of said compressor comprises means for heating at least one of a compressor body or shell, oil in the compressor, and a compressor motor.

5. The refrigeration system of claim 1 or 4, further comprising:

at least one sensor, wherein the control means activates the heating means for a predetermined period of time based on at least one parameter of the system measured by the sensor.

6. The refrigeration system of claim 5, wherein the predetermined period of time is determined based on at least one of a temperature of oil in the compressor, a compressor shell temperature, a compressor discharge temperature, an ambient temperature, and a length of time that the compressor has been inactive.

7. The refrigeration system of claim 1, wherein the heating device comprises:

means for supplying current to windings of a motor of the compressor to heat the windings.

8. The refrigeration system of claim 7, further comprising:

control means for controlling heating of the windings, wherein the current provided to the motor windings comprises Direct Current (DC) and is provided for at least one predetermined period of time.

9. The refrigerant system as set forth in claim 1, wherein said control opens said pressure equalization valve substantially simultaneously with starting said compressor.

10. A method of optimizing the start-up of a compressor of a refrigeration system comprising the steps of:

providing a refrigeration system comprising a compressor (12), a heat rejecting heat exchanger (14), an expansion valve (16), a heat accepting heat exchanger (18), and a pressure equalization valve (40, 42), the pressure equalization valve (40, 42) connecting a suction port and a discharge port of the compressor (12) so as to equalize a pressure difference between the compressor suction port and compressor discharge port;

heating at least one component of the compressor (12);

opening the pressure equalization valve (40, 42) to reduce a pressure differential between the compressor suction and discharge ports; and

starting the compressor (12) after heating the at least one component; and is

Wherein starting the compressor (12) comprises:

at a predetermined frequency f₁Operating the compressor (12), the predetermined frequency f₁Less than the operating frequency f of the compressor (12) during normal operating conditions of the system_n；

Opening a liquid valve (44) provided in a refrigerant flow path between the heat rejecting heat exchanger (14) and the expansion valve (16) in response to a first event;

closing the pressure equalization valve (40, 42) in response to a second event; and

increasing the operating frequency of the compressor (12); and is

Wherein the method further comprises the steps of:

measuring a temperature of oil in the compressor;

determining a saturated discharge port temperature of refrigerant in the compressor; and

heating at least one component of the compressor such that the oil is maintained at a temperature above the saturated discharge temperature.

11. The method of claim 10, wherein the step of starting the compressor (12) is performed substantially simultaneously with opening the pressure equalization valve.

12. The method of claim 10, further comprising the step of:

further increasing the operating frequency of the compressor to the operating frequency f of the compressor during normal operating conditions of the system_n。

13. The method of claim 10 or 12, wherein:

the first event comprises at least one of a first predetermined period of time elapsing and the measured compressor oil temperature is determined to be above a predetermined threshold; and

the second event includes at least one of a second predetermined period of time elapsing and the measured compressor oil temperature is determined to be above a predetermined threshold.

14. The method of claim 10, further comprising the step of:

providing at least one system sensor and measuring at least one parameter of the system with the sensor; and

operating the system in at least one of a plurality of predetermined procedures based on at least one parameter measured by the sensor.

15. The method of claim 10, wherein the step of preheating at least one component of the compressor comprises the steps of:

providing means for heating at least one component of the compressor; and

activating the heating device to heat the component when it has been determined that compressor start-up is required.

16. The method of claim 15, wherein the means for heating at least one component of the compressor comprises means for heating at least one of a compressor body or shell, oil in the compressor, and a compressor motor.

17. The method of claim 15 or 16, further comprising the step of:

providing at least one sensor and measuring at least one parameter of the system with the sensor; and wherein the heating device is activated for a predetermined period of time based on the at least one parameter.

18. The method of claim 17, wherein the predetermined period of time is determined based on at least one of a temperature of oil in the compressor, a compressor shell temperature, a compressor discharge temperature, an ambient temperature, and a length of time that the compressor has been inactive.