METHODS AND SYSTEMS FOR COMPRESSOR OPERATION
There is provided a refrigeration system (10) comprising a compressor (12) having a suction (11) and a discharge (13), a heat rejecting heat exchanger. (14), an expansion valve (16), and a heat accepting heat exchanger (18). Preferably the system (10) comprises any one or more of: a pressure equalisation valve (4O3 42) for equalising the pressure differential between the compressor suction (11) and compressor discharge (13); a liquid valve (44), preferably a liquid solenoid valve or an electronic expansion valve, the liquid. valve (44) arranged in a flow line (24) between the heat rejecting heat exchanger (14) and the expansion valve (16); and a check valve (46), preferably a solenoid valve or an electronic expansion valve, arranged in a flow line (22) between the heat rejecting heat exchanger (14) and the compressor (12). The valves (40, 42, 44, 46) are operated in a variety of manners upon compressor shutdown and startup to avoid damage to the components of the compressor (12). Preferably the system further comprises means for heating at least one component of the compressor (12) and preferably also control means for activating the heating means when appropriate, such as when compressor startup is required, and starting the compressor after heating.
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The present invention relates to methods and systems for compressor operation before and during compressor startup and/or shutdown and in particular to methods and systems for reliable startup of a compressor, even at low ambient temperatures.
Conventional refrigeration or airconditioning systems typically comprise 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 is circulated through these components in a closed circuit. The pressure and temperature of the refrigerant vapour is increased by the compressor before entering the heat rejecting heat exchanger where it is cooled. The high pressure, lower temperature liquid is then expanded to a lower pressure by means of the expansion valve. In the heat accepting heat exchanger, the refrigerant boils and absorbs heat from its surroundings. The vapour at the heat accepting heat exchanger outlet is drawn into the compressor, completing the cycle.
However on compressor shutdown and restart the components of the system, particularly the compressor, can be damaged or fail particularly in low ambient temperatures.
It is therefore an object of the present invention to provide a refrigeration system and a method of operating a refrigeration system, particularly although not exclusively for a transport refrigeration unit, the refrigeration system comprising a compressor and being operable such that failures of the system due to or on compressor start up are minimised, particularly when the compressor is started at low ambient temperatures.
In accordance with 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 further comprises a pressure equalisation valve (PEV) for equalising the pressure differential between the compressor suction and compressor discharge. Preferably the pressure equalisation valve comprises a bypass passage connecting the compressor suction to the compressor discharge and bypassing the compressor. Preferably the system further comprises a liquid valve (LV), preferably a liquid solenoid valve (LSV), the liquid valve preferably arranged in a flow line between the heat rejecting heat exchanger and the expansion valve.
Therefore there is provided a refrigeration system comprising a main refrigerant flow path from the compressor to the heat rejecting heat exchanger, from the heat rejecting heat exchanger to the liquid valve, from the liquid valve to the expansion valve and from the expansion valve to the heat accepting heat exchanger. A bypass refrigerant path or other pressure equalisation valve is provided across the compressor, i.e. from the compressor suction to the compressor discharge that, when opened, bypasses refrigerant flow around the compressor and enables the pressure differential between the compressor suction and the compressor discharge to be minimised, or more preferably the suction and discharge pressures to be balanced, particularly on compressor shutdown and most preferably at or shortly before compressor startup.
Preferably the refrigeration system is operable in at least one of a plurality of predetermined sequences, and the particular sequence (or sequences) used is preferably determined based on at least one parameter of the refrigeration system. Preferably the parameter (or parameters) comprises a system parameter measured by at least one sensor.
In preferred embodiments, when it is determined that compressor startup is required, a preheating sequence is initiated in which one or more components of the compressor is heated. Preferably the compressor body or shell, and/or the oil in the compressor, and/or the compressor motor, and/or any other suitable component, is heated. Preferably the component(s) is heated for a predetermined period of time, which may be determined based on one or more system parameters. In a preferred embodiment, the period 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), etc. The period for which the component is heated is additionally or alternatively determined based on the length of time for which the compressor has been shut down (for example if the compressor was only recently shut down, it may only be necessary to heat the component for a relatively short time, as the component may have retained some of the heat from its normal operating conditions and temperature).
Heating of the component(s) of the compressor is carried out in any suitable manner. In a particularly preferred embodiment, the stator windings of a motor associated with the compressor, for example the internal electric alternating current motor (synchronous or asynchronous) of the compressor are electrically connected to an electrical source, e.g. a direct current source, to thereby heat the windings and thus heat the compressor.
The pressure equalisation valve can be opened prior to compressor start up, but in preferred embodiments the pressure equalisation valve is opened when the compressor is started (preferably at substantially the same time as the compressor is started). For example in the embodiment where the pressure equalisation valve is a bypass passage, the passage is opened as the compressor is started to allow pressure balancing between the compressor suction and discharge by bypassing the compressor. Preferably the pressure equalisation valve is opened after the preheating steps discussed above.
Preferably the compressor is started slowly, e.g. at a speed or frequency considerably lower than a standard operating frequency. Starting the compressor and opening the pressure equalisation valve allows oil in the compressor to be mixed. This is advantageous because in a shutdown compressor the temperature of the oil is not homogeneous in the compressor shell. When the compressor is started slowly with the pressure equalisation valve open (and therefore with very low refrigerant flow), the hot oil from the motor is mixed with the cold oil from the other parts and the oil is warmed. Furthermore the oil and other parts of the compressor are heated by the refrigerant that bypasses the compressor via the pressure equalisation valve, the vapour refrigerant from the discharge valve in the compressor being hotter than the actual suction gas refrigerant and when passing through the bypass and the compressor suction, the vapour heats the mechanical parts of the compressor and the oil. That is the bypass line generally emits heat to the compressor and heats the oil that is circulating in the compressor. Pressure in the compressor body or shell is limited by the bypass.
In particularly preferred embodiments 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 vapour refrigerant condenses and if the oil temperature is below the saturated discharge temperature, 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 components and the shell of the compressor, are above the saturated discharge temperature refrigerant will not condense in the compressor.
Preferably the speed of the compressor at startup is lower than the normal running speed of the compressor as previously mentioned. For example in preferred embodiments the compressor at startup operates at a frequency of 30 Hz. Low compressor speed is desirable at startup because a low flow rate through the compressor minimises refrigerant condensation in the compressor.
Preferably the liquid valve is closed prior to and during compressor startup. In particularly preferred embodiments the liquid valve closes as the compressor stops and remains closed during compressor shutdown. Closing the liquid valve on compressor shutdown limits the flow of refrigerant into the compressor limiting condensation in the compressor oil.
Preferably at an appropriate time after compressor startup the liquid valve is opened. Therefore the system is operating in some states with both the pressure equalisation valve and the liquid valve open and the compressor operating at low frequency. This enables increased flow of refrigerant at the compressor suction, although the refrigerant flow is still lower than during normal system operation because the pressure equalisation valve is open (i.e. the compressor remains bypassed at this stage). Preferably the liquid valve is opened when it is determined that a system parameter is at a desired level. For example in a preferred embodiment the system parameter is the oil temperature and when the oil temperature is determined (for example by measurement with a temperature sensor) to be sufficiently high (for example above a predetermined limit, and/or above the saturated discharge temperature of the refrigerant in the compressor, etc.), then the liquid valve is opened. Other suitable parameters and limits could of course be used. For example in a preferred embodiment the parameter is alternatively or additionally the pressure in the compressor shell. Furthermore it is envisaged that the liquid valve could instead or additionally be opened in response to other events, for example after a predetermined period of time (e.g. from compressor startup, and/or from opening of the pressure equalisation valve, or from any other action or event, etc.).
Preferably after the liquid valve is opened the pressure equalisation valve is closed. This occurs in response to any one or more of the following: after a predetermined period of time since opening the liquid valve; after a period of time has elapsed following any other suitable event; after a period of time has elapsed following one or more system parameters being determined to have reached a particular level; immediately after opening the liquid valve; etc. In a preferred embodiment the system parameter comprises either the compressor discharge temperature or the oil temperature and when the temperature is determined (for example by measurement with a temperature sensor) to be sufficiently high (for example above a predetermined limit, and/or above the saturated discharge temperature in the compressor, etc.), then the pressure equalisation valve is closed. The pressure of the suction and discharge of the compressor are therefore no longer balanced and refrigerant passes through the compressor at a greater flow rate than when the pressure equalisation valve was open (e.g. refrigerant no longer bypasses the compressor).
The compressor speed is preferably then increased, either immediately or preferably in response to a 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 optimum speed is achieved and/or a predetermined time period has elapsed. Alternatively or additionally, when a measured system parameter is determined to have reached a predetermined level, the compressor speed may be set to the maximum (i.e. standard) operating speed (which is preferably after a period of slow increase in compressor speed from the initial startup speed). In a preferred embodiment, when the compressor discharge temperature and/or oil temperature of the compressor has reached a predetermined level, the compressor is controlled to operate at normal operating speeds.
The above preferred systems and operational steps provide compressor starting sequences that enable a compressor to be started with minimal risk of failure which otherwise might occur due to condensation of refrigerant in the compressor, particularly at low ambient temperatures, after compressor shutdown. Refrigerant condensation is detrimental in a compressor because condensed refrigerant can become mixed with oil in the compressor sump, and if the oil temperature in the compressor is below the saturated discharge temperature of the refrigerant then refrigerant can condense in the oil. When the compressor is started refrigerant in the oil is pumped by the oil pump and may fail. Furthermore the oil viscosity is affected by the presence of refrigerant and therefore may be inappropriate for compressor operation causing damage to components that should be lubricated. These problems are solved by the preferred embodiments of the present invention and by the preferred methods discussed below.
In a further broad aspect of the present invention, there is provided a method of optimising compressor startup for a compressor of a refrigeration system comprising the steps of: preheating at least one component of a compressor in a refrigeration system; opening a pressure equalisation valve that connects a suction and a discharge of the compressor to thereby reduce the pressure differential therebetween; starting the compressor, preferably with a predetermined frequency f1, preferably at substantially the same time as opening the pressure equalisation valve. Preferably the method further comprises the steps of opening a liquid valve that is located in a refrigerant flow path of the system in response to a first event, closing the pressure equalisation valve in response to a second event, and increasing the frequency of operation of the compressor.
Preferably the starting speed of the compressor f1 is less than the compressor standard operating speed fs. Preferably f1 is about 30 Hz. Preferably fs is about 60 Hz, preferably about 65 Hz or greater. Preferably the method comprises the further steps of: further increasing the frequency of operation of the compressor to a standard operating frequency, preferably in response to a third event.
Preferably the first event comprises at least one of a first predetermined period of time elapsing and a measured compressor oil temperature being determined to be above a predetermined threshold. Preferably the second event comprises at least one of a second predetermined period of time elapsing and a measured compressor oil temperature being determined to be above a predetermined threshold.
Preferably the method further comprises the steps 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 sequences 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 providing means for heating at least one component of the compressor, and activating the heating means to heat the component when it is determined that compressor startup 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, the oil in the compressor, and the compressor motor. In a particularly preferred embodiment the heating means comprises means for supplying DC electricity to the stator windings of an internal AC motor of the compressor. Preferably the method further comprises providing at least one sensor and measuring at least one parameter of the system with the sensor, and the heating means is activated for a predetermined period of time based on the at least one parameter. Preferably the predetermined period is based on at least one of the temperature of the oil in the compressor, the compressor shell temperature, the compressor discharge temperature, the ambient temperature and the length of time for which the compressor has been inactive.
Preferably the method further comprises the steps of measuring the temperature of oil in the compressor, determining the 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 discussed above, preheating a refrigeration system prior to compressor start up and controlling a liquid valve and a pressure equalisation valve before and during start up can advantageously reduce or eliminate refrigerant condensation problems, particularly in low ambient temperatures. However even the above system may experience failure or other problems on compressor startup for further reasons on or after compressor shutdown.
Therefore in accordance with a further 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), the liquid valve arranged in a flow line between the heat rejecting heat exchanger and the expansion valve, and a check valve arranged in a flow line between the heat rejecting heat exchanger and the compressor.
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 differential 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 further 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 would cause refrigerant to migrate to the compressor from the high side, e.g. from the condenser and also from the evaporator, particularly during long periods of compressor shutdown, for example 12 hours or more. Any refrigerant that migrates to the compressor during shutdown can condense in the compressor or otherwise migrate into the compressor oil, which can lead to compressor failure on start up, for example due to the low oil viscosity.
Therefore the system of the embodiments of this aspect of the present invention advantageously reduces the amount of, or even prevents, refrigerant reaching the compressor during shutdown and therefore little or no refrigerant can mix with the compressor oil. This is advantageous because the amount of refrigerant in the oil is minimised 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 differential between the valve inlet and the valve outlet is required to open the check valve, preferably a significant pressure differential. The system of this embodiment is further advantageous in that the check valve in combination with the liquid valve will maintain the refrigerant in the condenser (and in any other component that may be present between the check valve and the liquid valve, such as in preferred embodiments an accumulator and/or a dryer, etc.). Preferably the check valve is configured such that if the pressure at the inlet and the outlet of the check valve is balanced, which may occur over time after the compressor is shut down, the valve remains closed. That is in preferred embodiments the check valve is configured such that refrigerant can pass through the valve only when the valve inlet pressure is higher than the valve outlet pressure, for example when the compressor is started. Preferably the check valve comprises a resilient means such as a spring or the like that biases the valve into a closed position when the pressure at the inlet and the outlet of the check valve is balanced. This is advantageous because prior art valves leak refrigerant when the pressure at the inlet and the outlet is balanced, whereas in the embodiment of the present invention having the inventive check valve, a greater inlet pressure is required to open the valve and the amount of refrigerant leak under other conditions is minimised.
The above preferred refrigeration system prevents or substantially 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 the compressor to be started, even after a long shutdown period, with minimised risk of failure from refrigerant having mixed with the compressor oil.
From a further broad aspect of the present invention, there is provided a method of controlling a refrigeration system comprising the step of: initiating shutdown of a compressor of the system, closing a check valve provided in a flow line between the compressor and a heat rejecting heat exchanger of the system, and closing a liquid valve of the system that is located in a flow path between the heat rejecting heat exchanger and an expansion device of the system. In preferred embodiments a pressure differential between the condenser and the compressor that occurs on 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 flow of refrigerant 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 at substantially the same time as each other to prevent refrigerant migration.
Preferably the method further comprises the steps of: starting the compressor thereby causing a pressure differential between the condenser and the compressor and opening the check valve provided in the flow line therebetween, and opening the liquid valve. The pressure differential between the condenser and the compressor is such that the pressure on the condenser side of the check valve (e.g. the outlet) is lower than the pressure on the compressor side of the check valve (e.g. the inlet) after the compressor is restarted. This opens the check valve to enable flow of refrigerant therethrough. Preferably the method further comprises the step of biasing the check valve into a closed position, wherein the biasing force must be overcome in order to open the valve.
As discussed above, providing a liquid valve and a 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. The compressor can therefore be restarted and the risk of compressor failure due to the presence of refrigerant in the oil after refrigerant migration is minimised. However even the above system may experience failure or other problems on compressor start up due to a further effect that also arises from compressor shut down.
Therefore in accordance with a further 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 pressure equalisation valve (PEV) for equalising the pressure differential between the compressor suction and compressor discharge. The pressure equalisation valve is operable to open after or at the same time as the compressor is shutdown, preferably substantially immediately after compressor shutdown is effected. Preferably the pressure equalisation valve comprises a bypass passage connecting the compressor suction to the compressor discharge and bypassing the compressor.
By opening the pressure equalisation valve at the same time as or just after the compressor is shutdown or stopped, the pressure differential between the compressor suction and discharge is balanced as quickly as possible. This is advantageous because a high pressure differential between the compressor suction and discharge on compressor shutdown causes oil from the compressor to migrate towards the suction side of the compressor, leaving the compressor and entering the suction line, whereas in the present invention, equalisation or balancing of the discharge and suction pressures prevents such migration. It is undesirable for oil to leave the compressor as upon restarting the compressor, little or no oil is available for compressor lubrication. Furthermore upon restart the compressor has a mixture of oil and refrigerant in the suction line, which can lead to compressor failure as the mixture is sucked into the compressor. Still further the oil that leaves the compressor and enters the suction line can migrate to the evaporator which can cause further failure and also if the expansion valve is controlled in relation to the evaporator temperature (e.g. the evaporator outlet temperature) then the presence of oil at the sensor can lead to opening of the expansion valve even though the system is shut down.
However the 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 is minimised or prevented after compressor shutdown by equalising the pressure differential between the compressor discharge and suction just after compressor shutdown. A method of carrying out the invention is also envisaged and therefore from a further broad aspect of the present invention, there is provided a method of controlling a refrigeration system comprising the steps of: initiating shutdown of a compressor of the system; and opening a pressure equalisation valve (PEV) for equalising the pressure differential between a compressor suction and a compressor discharge. The pressure equalisation valve is opened preferably as or just after the compressor is shutdown, preferably substantially immediately after compressor shutdown is effected, thereby substantially equalising the high side discharge pressure and the low side suction pressure of the compressor. Preferably the pressure equalisation valve comprises a bypass passage connecting the compressor suction to the compressor discharge and bypassing the compressor.
The above-mentioned and other features of the various embodiments of the present invention will now be described, by way of example only and with reference to the accompanying drawings, in which:
The principles of the present invention can be incorporated within any suitable system. Examples of such suitable systems include refrigeration and airconditioning systems and particularly, although not exclusively, transport or truck refrigeration systems. For ease of reference, the specific embodiments discussed herein are described with reference to a refrigeration system suitable for a transport refrigeration unit or the like.
The system 10 further comprises a pressure equalisation valve (PEV) across the compressor 12, i.e. connecting the compressor suction 11 to the discharge 13. The PEV comprises a bypass passage 40 and means 42, such as a valve, for opening and closing the passage 40.
The system 10 further comprises a liquid valve (LV), which in preferred embodiments is a liquid solenoid valve 44, in the flow path 24 between the condenser 14 and the expansion valve 16. The LV 44 can be energised to open or close as required, thereby opening or closing the flow path 24 to enable or disable refrigerant flow around the circuit 20.
In operation, high pressure and high temperature refrigerant vapour exits the compressor 12 and enters the condenser 14 where it is cooled to a lower temperature, high pressure liquid refrigerant. This liquid is then expanded to a lower pressure by the expansion valve 16 and passes to the evaporator 18 where the refrigerant boils and absorbs heat from its surroundings. The vapour at the evaporator 18 outlet is drawn into the compressor 12, completing the cycle.
When the compressor 12 is shut down, refrigerant may be present in the compressor 12 and, particularly if the compressor 12 is shut down for prolonged periods, additional refrigerant can migrate from the condenser 14 to the compressor 12 as 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 the compressor oil which has an affinity for refrigerant. If the compressor oil temperature is below the saturated discharge temperature of the refrigerant, the refrigerant can condense in the oil. The refrigerant dilutes the oil and, when the compressor 12 is restarted, the diluted oil is less effective at lubricating the components of the compressor 12, which may lead to damage. Furthermore the compressor oil pump will draw in refrigerant which may also lead to damage.
Therefore in accordance with embodiments of the present invention, one or more compressor startup sequences are employed to minimise or eliminate refrigerant condensation in the compressor 12.
In the
When the compressor 12 has been shut down for longer than 1 hour, the discharge temperature Tref is determined in step 1.3 and dependent on the temperature, also in steps 1.4, 1.5, 1.6, 1.7 and 1.8. Furthermore, dependent on Tref, the compressor 12 is preheated for 12, 9, 6 or 3 minutes (steps 2.2, 2.3, 2.4 and 2.5 respectively) before a long starting sequence (for example as shown in
The above sequences ensure that if the discharge temperature of the compressor 12 is low, the compressor 12 is heated, preferably prior to compressor startup, to raise 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 the compressor components on startup, but also because a sufficiently high oil temperature (greater than the saturation discharge temperature of the refrigerant) reduces or eliminates refrigerant condensation in the compressor 12 that occurs when the compressor shell and oil are cool.
When the oil temperature in the compressor 12 is sufficiently high, e.g. when it is measured, determined or otherwise expected to be greater than the saturated discharge temperature of the refrigerant, and/or in this embodiment after the oil has been heated for a sufficient period of time which in the normal starting sequence is 20 seconds, the liquid valve is opened and the PEV remains open. The refrigerant flow at the compressor suction 11 increases slightly, but is still relatively low as the compressor 12 is still bypassed by the open PEV. When the oil temperature in the compressor 12 is sufficiently high, e.g. when it is again measured, determined and/or expected to be greater than the saturated discharge temperature of the refrigerant, and/or in this embodiment after it has been heated for a sufficient period of time which in the normal starting sequence is a further 20 seconds, the PEV is closed whilst the liquid valve remains open. Refrigerant therefore flows around the circuit 20 of system 10 under the influence of the compressor 12, which is no longer bypassed.
When the oil temperature in the compressor 12 is sufficiently high, e.g. when it is yet again measured, determined or otherwise expected to be greater than the saturated discharge temperature of the refrigerant, and/or in this embodiment after it has been heated for a sufficient period of time which in the normal starting sequence is a still further 20 seconds, the speed of the compressor 12 is gradually increased, preferably by 5 Hz per second until an 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 can be started after it is again determined or otherwise expected that the oil temperature is still higher than the saturated discharge temperature.
However a normal starting sequence may not be appropriate under certain circumstances, for example when the temperature of the shutdown compressor 12 is low (e.g. less than about 5° C.) and/or when the compressor 12 has been shutdown for a long period (more than about one hour). Instead a long starting sequence as shown in
However under other circumstances neither a normal nor a long starting sequence may be appropriate, for example when the temperature of the shutdown compressor 12 is relatively high (e.g. more than about 40° C.) and/or when the compressor 12 has been shutdown for only a brief period (less than an hour). In such circumstances a short starting sequence as shown in
The system 10 of
A conventional refrigeration system 110 is shown in
Furthermore as shown in the second diagram of
The refrigeration system 10 of the embodiment of
Claims
1. A refrigeration system comprising:
- a compressor having a suction and a discharge;
- a heat rejecting heat exchanger;
- an expansion valve;
- a heat accepting heat exchanger; and
- a pressure equalisation valve for equalising the pressure differential between the compressor suction and compressor discharge.
2. A refrigeration system as recited in claim 1, wherein the pressure equalization valve comprises a bypass passage connecting the compressor, suction to the compressor discharge to enable the compressor to be bypassed and a valve to control flow of refrigerant therethrough.
3. A refrigeration system as recited in claim 1, further comprising: a liquid valve, preferably a liquid solenoid valve, arranged in a flow line between the heat rejecting heat exchanger and the expansion valve.
4. A refrigeration system as recited in claim 1, further comprising:
- control for operating the system in at least one of a plurality of predetermined sequences; and
- at least one sensor, wherein the control operates the system in a particular one of the plurality of predetermined sequences based on at least one parameter of the system measured by the sensor.
5. (canceled)
6. (canceled)
7. (canceled)
8. (canceled)
9. (canceled)
10. (canceled)
11. (canceled)
12. (canceled)
13. A method of optimizing startup of a compressor of a refrigeration system comprising the steps of:
- providing a refrigeration system comprising a compressor, a heat rejecting heat exchanger, an expansion valve, a heat accepting heat exchanger, and a pressure equalisation valve that connects a suction and a discharge of the compressor for equalising the pressure differential between the compressor suction and compressor discharge;
- preheating at least one component of the compressor;
- opening the pressure equalisation valve to thereby reduce the pressure differential between the compressor suction and discharge; and
- starting the compressor, preferably at substantially the same time as opening the pressure equalisation valve.
14. A method as recited in claim 13, wherein the step of starting the compressor comprises operating the compressor at a predetermined frequency f1 that is less than the operating frequency fn of the compressor during normal operating conditions of the system.
15. A method as recited in claim 14, further comprising the steps of:
- providing a liquid valve in a refrigerant flow path between the heat rejecting heat exchanger and the expansion valve;
- opening the liquid valve in response to a first event;
- closing the pressure equalization valve in response to a second event; and increasing the operating frequency of the compressor.
16. (canceled)
17. (canceled)
18. A method as recited in claim 13 further comprising the steps 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 sequences based on the at least one parameter measured by the sensor.
19. A method as recited in claim 13, wherein the compressor has a compressor body, a compressor motor and oil in the compressor and the step of preheating at least one component of the compressor comprises the step of:
- heating at least one of the compressor body, the oil in the compressor, and the compressor motor when it is determined that compressor startup is required.
20. (canceled)
21. A method as recited in claim 19, further comprising the steps of:
- providing at least one sensor;
- measuring at least one parameter of the system with the sensor; and
- heating the at least one component of the compressor for a predetermined period of time based on the at least one parameter.
22. A method as recited in claim 21, wherein the predetermined period is based on at least one of a temperature of the oil in the compressor, a compressor shell temperature, a compressor discharge temperature, an ambient temperature and a length of time for which the compressor has been inactive.
23. A method as recited in claim 13, further comprising the step of:
- measuring the temperature of oil in the compressor;
- determining the 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.
24. A refrigeration system comprising:
- a compressor;
- a heat rejecting heat exchanger;
- an expansion valve;
- a heat accepting heat exchanger;
- a liquid valve, preferably a liquid solenoid valve or an electronic expansion valve, the liquid valve arranged in a flow line between the heat rejecting heat exchanger and the expansion valve; and
- a check valve, preferably a solenoid valve or an electronic expansion valve, arranged in a flow line between the heat rejecting heat exchanger and the compressor.
25. A system as recited in claim 24, wherein the check valve is configured such that a pressure differential between an inlet of the valve and an outlet of the valve opens the check valve.
26. (canceled)
27. A system as recited in claim 25, wherein the check valve comprises resilient means, preferably a spring or the like, that biases the valve into a closed position when the pressure at the inlet and the outlet of the check valve is balanced.
28. (canceled)
29. A method of controlling a refrigeration system comprising the steps of: providing a refrigeration system comprising a compressor, a heat rejecting heat exchanger, an expansion valve, a heat accepting heat exchanger, a liquid valve between the heat rejecting heat exchanger and the expansion valve, and a check valve between the heat rejecting heat exchanger and the compressor;
- initiating shutdown of the compressor;
- closing the check valve and the liquid valve, preferably substantially simultaneously with shutdown of the compressor.
30. (canceled)
31. A method as recited in claim 29, wherein the liquid valve and the check valve comprise solenoid valves and the step of closing the check valve and the liquid valve comprises activating the solenoid valve(s).
32. A method as recited in claim 29 31, further comprising the steps of:
- starting the compressor thereby causing a pressure differential between the condenser and the compressor and opening the check valve provided in the flow line therebetween; and
- opening the liquid valve.
33. (canceled)
34. (canceled)
35. A method of controlling a refrigeration system comprising the steps of:
- providing a refrigeration system comprising a compressor, a heat rejecting heat exchanger, an expansion valve, a heat accepting heat exchanger, and a pressure equalization valve that connects a suction and a discharge of the compressor for equalizing the pressure differential between the compressor suction and compressor discharge;
- initiating shutdown of the compressor; and
- opening the pressure equalization valve for equalizing the pressure differential between the compressor suction and discharge.
36. A method as recited in claim 35, wherein the step of opening the pressure equalization valve comprises opening the valve as or substantially immediately after compressor shutdown is effected.
Type: Application
Filed: Jul 23, 2008
Publication Date: May 19, 2011
Applicant: Carrier Corporation (Farmington, CT)
Inventors: Fabienne Peyaud (Saint Pierre De Chandieu), JeanPhilippe Goux (Toussieu), David Veillon (Amberieu En Bugey), Frederic Brisset (Druillat)
Application Number: 13/003,942
International Classification: F25B 1/00 (20060101); F25B 43/02 (20060101);