REFRIGERATION SYSTEM AND CONTROL METHOD FOR REFRIGERATION SYSTEM

Description

BACKGROUND

Historically, refrigerants used within refrigeration and climate control systems have had the potential to contribute to global warming. More recently, there has been a desire to use alternative refrigerants having a lower potential to cause global warming. However, such alternative refrigerants often have the drawback of being flammable in the presence of air.

There is therefore a need for reducing the prospect of combustion and/or an explosion occurring due to the mixing of a refrigerant with air within or near to a refrigeration or climate control system.

SUMMARY

According to one embodiment, there is provided a control system for a refrigeration system, the control system comprising a plurality of processors that are collectively arranged to: receive system operation data indicative of a first temperature or pressure at a first location in the refrigeration system at a first time; compare the temperature or pressure to a threshold value, based on the comparison, output a control signal to alter an operating parameter of the refrigeration system; receive further system operation data indicative of a second temperature or pressure at the first location in the refrigeration system at a second time; compare the further temperature or pressure to the threshold value; and based on a determination that the second temperature or pressure is on the same side of the threshold value as the first temperature or pressure, output a warning signal indicative of a leak in the refrigeration system.

With such an arrangement, an ingress of air to the refrigeration system may be detected based on the operation data. In particular, the difference in the ratios of heat capacities (denoted by γ or κ) between air and the refrigerant may lead to different temperatures and pressures in the system. A typical refrigerant may have a value of κ around 1.15, whereas the value for air is about 1.4. This may lead to increased heating of the gas during compression, following the ideal gas laws for an adiabatic compression:

T out = T in ( P out P in ) γ - 1 γ

While temperatures and pressures in a refrigeration system may vary depending on the intended temperature of the refrigerated zone (known as a set point), a real temperature of the refrigerated zone (determined by measuring a return air temperature) and on ambient conditions, the alterations of the properties of the working fluid in the system, such as due to ingestion of air, may cause changes to the temperatures and pressures of the working system beyond the normal range. Further, the usual changes to operating parameters of the system may not have their desired effect as the control system is built on the assumption that the working fluid on the system has the properties of the refrigerant.

In other cases, where there is a leak in a system proximate a pressure sensor, the pressure in the system at that location may approach ambient pressure, i.e. the pressure of the environment outside the system. Alterations of the operation of the system may then fail to change the pressure in that location away from ambient pressure. It may therefore be determined that the system is leaking and the possibility of ingress of air may be determined.

In this way, the embodiments described herein may provide an accurate warning to an operator or may shut down automatically with greater reliability. This may provide improved safety.

The first temperature or pressure may be a compressor discharge temperature, the second temperature or pressure may be a compressor discharge temperature, and the threshold value may be a compressor discharge temperature threshold value. As is explained above, the alteration of the ratio of heat capacities of the working fluid may result in increased heating in the compressor. Where this increased heating results in a compressor discharge temperature above a compressor discharge temperature threshold value of, for example, 150° C. and where a change in operating parameter, such as a reduction in compressor speed or a change in opening of an expansion valve, does not reduce the temperature sufficiently, it may be determined that compression of air is occurring.

Further, the compressor discharge temperature may be a particularly important temperature to monitor for the prevention of combustion since a gas leaving the compressor has the highest temperature in the system. Therefore, if combustion is to occur, it is likely to occur at the compressor discharge. Therefore, a high compressor discharge temperature increases the likelihood of combustion as well as being an indication of air being present in the system.

The plurality of processors may be collectively arranged to determine the threshold value based on the operating conditions of the refrigeration system such as a temperature set point of the refrigeration system (which may also be referred to as a desired return air temperature), a measured return air temperature, an ambient environmental temperature, and/or an opening state of one or more expansion valves, and/or a compressor speed. Since the internal temperatures and pressures may change depending on the operating conditions of the refrigeration system, altering the threshold values based on the operating conditions may result in a reduced chance of a false indication of a leak being determined. Alternatively, tighter thresholds may be used when the thresholds can be adapted to changing operating conditions, resulting in earlier detection of leaks.

The plurality of processors may be collectively arranged to: receive further system operation data indicative of a compressor suction pressure in the refrigeration system at the first time; compare the compressor suction pressure at the first time to a compressor suction pressure threshold value, based on the comparison of the compressor suction pressure to the compressor suction pressure threshold value and the comparison of the compressor discharge temperature to the compressor discharge temperature threshold value, output the control signal to alter the operating parameter of the refrigeration system; receive further system operation data indicative of the compressor suction pressure in the refrigeration system at the second time; compare the further compressor suction pressure to the compressor suction pressure threshold value; and based on a determination that the compressor suction pressure at the second time is on the same side of the compressor suction pressure threshold value as the compressor suction pressure at the first time and/or that the compressor discharge temperature at the second time is on the same side of the compressor discharge temperature threshold value as the compressor discharge temperature at the first time, output the warning signal. In this way, the compressor suction pressure and the compressor discharge pressure may both be used to determine the presence of a leak. This may further reduce the prospect of false indications of leaks. The control system may also be more sensitive to leaks at different locations in the refrigeration system.

The first temperature or pressure may be a compressor suction pressure at the first time, the second temperature or pressure may be a compressor suction pressure at the second time, and the threshold value may be a compressor suction pressure threshold value. The intended or expected compressor suction pressure in a system may be greater than atmospheric pressure. The compressor suction pressure threshold value may be between atmospheric pressure and the intended or expected compressor suction pressure. If the compressor suction pressure in this case becomes below the compressor suction pressure threshold value, then it may be indicative of a leak in the system. Alternatively, the intended or expected compressor suction pressure may be less than atmospheric pressure. In this case, a compressor suction pressure being greater than the compressor suction pressure threshold value may be indicative of a leak. In both cases, the presence of a leak may be confirmed by the system being unable to change the compressor suction pressure to be further away from atmospheric pressure, i.e. the compressor suction pressure may not move across the compressor suction pressure threshold value in response to the alteration of an operating parameter.

The compressor suction pressure threshold may be equal to or less than atmospheric pressure. In this case, where the compressor suction pressure is less than atmospheric pressure, there is a greater risk of air ingress into the system.

The plurality of processors may be arranged to determine the compressor suction pressure threshold based on a temperature set point of the refrigeration system or a return air temperature of the refrigeration system, which may be a desired return air temperature or a measured return air temperature. The expected or intended compressor suction pressure of a system may vary based on the temperature set point or the return air temperature of the refrigeration system and so by varying the compressor suction pressure threshold value in this way, the prospect of false indications of leaks may be reduced. The compressor suction pressure threshold value may also be moved closer to the intended or expected compressor suction pressure, so that leaks may be detected earlier.

The plurality of processors may be collectively arranged to: receive a return air temperature value from a return air temperature sensor; compare the received return air temperature value or a temperature set point value for the refrigeration system, to a temperature set point threshold or to a return air temperature threshold, and output the warning signal based on the determination that second temperature or pressure at the second time is on the same side of the threshold as the first temperature or pressure at the first time and a determination that the temperature set point value is less than the temperature set point threshold or a determination that the return air temperature value is greater than the return air temperature threshold. In some cases, a temperature set point may be selected that requires a high compressor discharge temperature or a compressor suction pressure close to atmospheric pressure. This is usually due to a very low temperature set point. For example, the temperature set point threshold may be below −25° C. In this case, false indications of leaks may be reduced. The variation in measured return air temperature may also indicate a high cooling requirement, such as due to a high ambient temperature or poorly insulated refrigerated area. In this case, a high discharge pressure and a high discharge temperature (both being above a respective threshold value) may be expected and so comparisons showing these properties being above a threshold and remaining as such may not be indicative of a leak. However, in this case a suction pressure close to atmospheric pressure may be indicative of a leak.

The plurality of processors may be collectively arranged to: compare an ambient temperature value for the refrigeration system to an ambient temperature threshold, and output the warning signal based on the determination that the second temperature or pressure is on the same side of the threshold as the first temperature or pressure and a determination that the ambient temperature is less than the ambient temperature threshold. In some cases, a high ambient temperature may result in high compressor discharge temperatures, high compressor discharge pressures. Generally, the operation of the system at high ambient temperatures may result in usually undesirable system conditions. Therefore, one would not expect unusually high compressor discharge pressure or temperatures at low ambient temperature. By considering the ambient temperature, the system may reduce the prospect of a false determination of a leak.

The plurality of processors may be collectively arranged to: compare an expansion valve opening state for the refrigeration system to an expansion valve opening state threshold, and output the warning signal based on the determination that the second temperature or pressure is on the same side of the threshold as the first temperature or pressure and a determination that the expansion valve opening state is greater than the expansion valve opening state threshold. In cases where an expansion valve is opened to a significant degree, the system may falsely determine that there is a leak. By considering the opening state of an expansion valve, the prospect of a false determination of a leak is reduced.

The plurality of processors may be collectively arranged to: compare the first and/or second temperature or pressure to a second threshold, the second threshold being different from the first threshold, and shut down the refrigeration system based on the comparison. In some cases, a temperature, such as a compressor discharge temperature may be so high that it is immediately known that a leak has occurred, and the temperature may be sufficiently high to approach a combusting temperature. For example, the second compressor discharge temperature threshold value may be 200° C. Alternatively, a pressure may deviate from an intended or expected pressure to such a degree that a leak is certain, such as a drop in pressure from an intended or expected high pressure to atmospheric pressure. In this case, the system may be automatically shut down without an attempt to alter an operating parameter. This may reduce the prospect of catastrophic failure of the system.

The operating parameter may be a compressor speed, a throttle valve opening or a hot-gas by-pass duty cycle, and the control signal may be arranged to: reduce a compressor speed, open a throttle valve, and/or increase a hot-gas by-pass duty cycle. By carrying out these measures, the system may reduce a compressor discharge temperature or may move a compressor suction pressure away from atmospheric pressure. This may allow the system to run continuously and to avoid a false indication of a leak. Generally, the term “operating parameter” will be understood to mean an aspect of the refrigeration system that is controllable by a user or by a control system of the refrigeration system, as opposed to a condition of the working fluid that results from the function of the refrigeration system or an external environmental condition.

The first temperature or pressure may be a compressor suction temperature at the first time, the second temperature or pressure may be a compressor suction temperature at the second time and the threshold value may be a compressor suction temperature threshold value.

The compressor suction temperature threshold value may be determined based on a received ambient temperature value.

The intended or expected compressor suction temperature may be different from ambient temperature, but a leak in the system may bring the compressor suction temperature towards ambient temperature by the ingress of air at ambient temperature. Consequently, a compressor suction temperature that is on the same side of the compressor suction temperature threshold value as the ambient temperature may be indicative of a leak.

The first temperature or pressure may be a compressor discharge pressure at the first time, the second temperature or pressure may be a compressor discharge pressure at the second time, and the threshold value may be a compressor discharge pressure threshold value.

As air is not condensable at the temperatures and pressures found in a normal refrigeration system, the pressure increase in a compressor may be higher when the working fluid includes air. A compressor discharge pressure above a threshold value may therefore be indicative of air being within the system.

The processors may be collectively arranged to: compare the compressor discharge pressure, compressor discharge temperature, compressor suction pressure, and/or compressor suction temperature to respective thresholds, output the control signal to alter an operating parameter of the refrigeration system based on the comparisons and/or determine whether a leak has occurred based on the comparisons.

The determination of whether an operating parameter of the refrigeration system should be altered and/or whether a leak has occurred may comprise a democratic voting scheme based on the comparisons of the temperatures and pressures. For example, the processors may be collectively arranged to output the control signal to alter an operating parameter of the refrigeration system based on a majority of the temperatures or pressures being outside an allowable range as determined by a comparison to a respective thresholds. Further, the processors may be collectively arranged to determine that a leak has occurred based on a majority of the temperatures or pressures remaining on the same side of their respective thresholds after the operational parameters of the system have been altered.

According to another embodiment, there is provided a refrigeration system comprising: a compressor arranged to increase the pressure of a working fluid; a condenser arranged to allow heat transfer from the working fluid; an expansion valve arranged to decrease the pressure of the working fluid; an evaporator arranged to allow heat transfer to the working fluid; and a control system according to the first aspect.

The refrigeration system may further comprise a working fluid in the system. The working fluid may be an A2L refrigerant.

The compressor may be an open-drive compressor. An open-drive compressor is a compressor having a motor that is fluidly coupled to the environment, as opposed to an hermetic compressor where the motor is sealed within the compressor housing. In an open-drive compressor, a shaft-seal of the compressor therefore provides a barrier between the atmosphere and the working fluid. For this reason, open-drive compressors may be more susceptible to air ingress than hermetic compressors.

The refrigeration system may further comprise one or more sensors, the sensors may be temperature and/or pressure sensors and may be arranged adjacent to a compressor suction port and/or a compressor discharge port. The sensors may be communicatively coupled to the control system to transfer system operational data to the control system.

According to yet another embodiment, there is provided a method of controlling a refrigeration system, the method comprising: receiving system operation data indicative of a first temperature or pressure at a first location in the refrigeration system at a first time; comparing the temperature or pressure to a threshold value, based on the comparison, outputting a control signal to alter an operating parameter of the refrigeration system; receiving further system operation data indicative of a second temperature or pressure at the first location in the refrigeration system at a second time; comparing the further temperature or pressure to the threshold value; and based on a determination that the second temperature or pressure is on the same side of the threshold as the first temperature or pressure, output a warning signal indicative of a leak in the refrigeration system.

The detected leak may be a leak in a compressor of the refrigeration system.

The method of the third aspect may be carried out on the refrigeration system of the second aspect.

BRIEF DESCRIPTION OF THE DRAWINGS

In the detailed description that follows, embodiments are described as illustrations only because various changes and modifications will become apparent to those skilled in the art from the following detailed description. The use of the same reference numbers in different figures indicates similar or identical items.

FIG. 1 is a schematic drawing of a vehicle including a refrigeration system according to one embodiment;

FIG. 2 is a schematic drawing of a refrigeration system according to one embodiment;

FIG. 3 is a flow chart illustrating a method of controlling a refrigeration system according to one embodiment; and

FIGS. 4a and 4b are schematic drawings of compressor bays.

DETAILED DESCRIPTION

FIG. 1 shows a vehicle 10 having a climate control system 14. The vehicle 10 is formed of a prime mover 12a and a refrigerated box 12b. It will be understood that the climate control system 14 may be incorporated in any vehicle, such as a straight truck, a lorry, a van, a train or any marine or intermodal application. The climate control system 14 may be alternatively used outside a vehicle, such as in a warehouse or retail building.

Within the refrigerated box 12b, the climate control system 14 is arranged to control a temperature of a plurality of different temperature-controlled zones 20a, 20b, 20c. While the climate control system 14 shown is arranged to control a temperature of three zones, it will be understood that there may be any number of temperature-controlled zones, such as 1, 2, 4, 5 or more. The temperature-controlled zones are separated by partition walls 18, 18. The partition walls 18 may be thermally insulative in order to allow the zones 20a, 20b, 20c to be more easily controlled at different temperatures. The partition walls 18 may be of any form.

On the front of the refrigerated box 12b is a compressor bay 13. The compressor bay 13 houses several components of the climate control system 14. In particular, the compressor bay houses a compressor 34 and optionally the compressor bay 13 may house a condenser 32 and/or a controller 50. A compressor bay 13 is also shown in FIGS. 4a and 4b.

The climate control system 14 is now described with reference to FIG. 2, which shows a schematic diagram of the climate control system 14, which may also be referred to as a refrigeration system. The climate control system 14 circulates a working fluid, that may be a refrigerant such as an A2L refrigerant, about a circuit.

At a compressor 34, the pressure and temperature of the working fluid are increased. This may result in the working fluid becoming a hot, high pressure gas. The compressor 34 may comprise a prime mover or rotor arranged in a housing. The prime mover may be a rotatable component positioned within the housing and rotatable such that gas within the compressor is moved from an entry port to an exit port and the pressure and temperature of the gas may be increased during this process. The rotational speed of the rotor within the compressor, or reciprocating frequency of a piston in the case of a reciprocating compressor, may be referred to as a compressor speed and may be controlled by a controller of the refrigeration system. As a higher compressor speed may result in a greater increase in pressure across the compressor, the pressure in the system may be controlled at least partially by adjustment of a speed of the compressor.

Where the compressor is an hermetic compressor, the prime mover may receive torque from a motor that is sealed within the housing, such that the chance of a leak in the compressor is reduced. Alternatively, the compressor may be an open drive compressor. In an open drive compressor, a motor arranged to rotate the prime mover may be arranged outside the housing, with a shaft coupling the motor to the prime mover. The housing may be sealed by a shaft seal arranged around the shaft, intended to prevent fluid communication between the inside of the housing and the environment. Such a shaft seal may be more liable to leak, and to allow ingress of air to the refrigeration system or exit of working fluid from the refrigeration system.

After exiting the compressor. the working fluid enters a heat exchanger 32, which may be a condenser 32, which is arranged to allow heat transfer to the environment from the working fluid. The working fluid may at least partially condense in the heat exchanger 32 to become a low temperature, high pressure liquid or liquid-gas mixture.

After leaving the condenser 32, the working fluid then passes through an expansion valve 30. The expansion valve 30 is arranged to cause a pressure drop in the working fluid at substantially constant enthalpy. The working fluid may then become a low-temperature, low-pressure liquid-gas mixture. The expansion valve 30 may be an electronic expansion valve.

An evaporator 28 is arranged downstream of the expansion valves 30. The evaporator 28 is arranged to allow heat transfer between the working fluid inside the evaporator 28 and air outside the evaporator 28. The working fluid in the evaporator 28 may therefore receive heat from air in a respective temperature-controlled zone, for example one of the temperature-controlled zones 20a, 20b, 20c of FIG. 1. In this way, the working fluid may undergo evaporation to become a low-temperature gas and in doing so may cool the air within the temperature-controlled zone 20a, 20b, 20c.

To improve heat transfer to the evaporator, the climate control system 14 may further comprise one or more blowers 28. The evaporators 28 may each be adjacent to a respective blower 28, which may blow air onto and through the respective evaporator, to improve the amount of heat energy transferred to the working fluid.

In at least one of the temperature-controlled zones 20a, 20b, 20c, there is a temperature sensor 22 arranged to determine a temperature in the respective zone 20a, 20b, 20c. The temperature sensor 22 may be arranged behind the blowers relative to an airflow direction through the blowers and may be arranged to sense a return air temperature in the zones. The return air temperature is a temperature of air that has circulated through the zone and is returning to the evaporator. This may provide a more accurate indication of a temperature experienced by goods in the temperature-controlled zone.

The climate control system 14 may be controlled by a controller 50, which may also be referred to as a control system 50. The controller 50 may contain one or more processors arranged to carry out a control method to control the climate control system 14. The controller may comprise a memory storing instructions to carry out the control method. The controller 50 may also have one or more input ports arranged to receive data and one or more output ports arranged to output control signals. The controller 50 is arranged to receive temperature data and/or pressure data from temperature sensors and/or pressure sensors in the refrigeration system and to output control signals to control operating parameters of the refrigeration system, such as electronic expansion valve openings and a rotational speed of the compressor.

The refrigeration system 14 includes a compressor discharge pressure sensor 52. The pressure compressor discharge pressure sensor 52 may be arranged to detect a pressure of the working fluid as it leaves the compressor 34. The working fluid at discharge from the compressor 34 may have the highest pressure of any point within refrigeration system 14. The compressor discharge pressure sensor 52 is arranged to transfer compressor pressure discharge pressure data to the controller 50. The compressor discharge pressure data may include an indication of the compressor discharge pressure.

The refrigeration circuit 14 may also include a compressor discharge temperature sensor 54, which may be arranged to detect a compressor discharge temperature. The compressor discharge temperature is the temperature of the working fluid as it is discharged from the compressor 34. As the temperature of the working fluid will rise as it is compressed by the compressor 34, the temperature of the working fluid as it leaves the compressor 34 may be the highest temperature in the refrigeration circuit 14. The compressor discharge temperature sensor 54 may transfer compressor discharge temperature data to the controller 50, the compressor discharge temperature data including information of the compressor discharge temperature.

The refrigeration system 14 may also have a compressor suction pressure sensor 56, which may detect a compressor suction pressure. The compressor suction pressure is the pressure of the working fluid as it is drawn into the compressor 34. The compressor suction pressure 56 may be the lowest pressure in the working fluid system and may be above or below atmospheric pressure. The compressor suction pressure sensor 56 may be arranged to transfer compressor suction pressure data to the controller 50. In some cases, such as underwater applications, the compressor suction pressure may be around 1 bar, while the ambient external pressure may be greater than 1 bar. In this case, a leak in a low pressure portion of the refrigeration system may result in ingress of air to a greater extent than an exit of refrigerant.

The refrigeration system 14 may also include a compressor suction temperature sensor 58, which may detect the temperature of the working fluid as it is drawn into the compressor 34. The compressor suction temperature sensor 58 may transfer compressor suction temperature data to the controller 50.

The refrigeration system 14 may include further pressure and temperature sensors elsewhere in the refrigeration system, which may provide temperature and pressure values to the controller 50 indicative of the operation of the system.

Generally, the data transferred to the controller 50 from the sensors may be referred to as system operation data.

The refrigeration system 14 may also comprise a user interface 60. The user interface 60 may include a screen/or an audible warning system that may alert a user as to the functioning of the refrigeration system 14. The user interface 60 may also include a user input device that may allow the user to input operational information to the refrigeration system 14, such as setpoint temperature for controlling a refrigerated zone.

It will be understood that further pressure and temperature sensors may be arranged in different locations around the refrigeration system and that such sensors may provide indications of the properties of the working fluid at different locations.

The refrigeration system 14 may also comprise further components that are not shown, such as a hot-gas bypass valve, a receiver tank, an accumulator tank or further throttle valves and evaporators. A hot-gas bypass valve may provide a fluid path allowing direct communication between high and low pressure portions of the refrigeration cycle, such as by allowing hot gas output from the compressor to bypass the condenser and expansion valve and optionally the evaporator and to rejoin the refrigeration circuit before entering the compressor and optionally before the evaporator. A receiver may store working fluid to account for a varying mass of working fluid in the refrigeration circuit. An accumulator may also store liquid working fluid to prevent liquid working fluid from entering the compressor.

In the refrigeration system 14, a leak may develop. The leak may be in the compressor, such as at a shaft seal. A leak may allow ingress of air into the refrigeration system, such that the air may mix with the original working fluid, resulting in the true working fluid of the refrigeration system being a mixture of air and the original working fluid. For example, where the original working fluid is a refrigerant, the working fluid may become a mixture of air and refrigerant.

Since air may have significantly different properties from refrigerants, the properties of the working fluid may alter due to the ingress of air. For example, due to the different ratios of specific heat capacities between air and refrigerant, the increase in the temperature of the working fluid from the compressor suction port to the compressor discharge port may increase. This may result in the compressor discharge temperature being higher than would be expected for a refrigeration system with a working fluid that does not contain air.

Further, since air is unlikely to condense at the temperatures and pressures found in a refrigeration system, the pressure increase from a compressor suction port to a compressor discharge port may increase due to the presence of air in the working fluid. This may result in the compressor discharge pressure being higher than would be expected for a refrigeration system with a working fluid that does not contain air.

Other properties of the refrigeration system may also alter as the result of a leak. For example, if the leak occurs in a high pressure portion of the system, working fluid may leave the working fluid via the leak. This may reduce the mass of working fluid in the refrigeration system, resulting in low pressures being found in the working system.

Alternatively, if a leak occurs in a low pressure portion of the refrigeration system, air may enter the refrigeration system, resulting in local pressures close to ambient pressure and temperature. This may be an increase or a decrease in temperature or pressure.

In either case, there may be an exchange of air and working fluid between the refrigeration system and the environment as a result of a leak.

It will also be understood that pressures and/or temperatures in a refrigeration system may vary over time due to system loading, changing set points, and changing ambient temperatures. The measured return air temperature sensor and/or ambient air temperature sensor may provide an indication of such environmental conditions and may transmit such information to the control system.

Generally, where pressures and/or temperatures outside the normal range for a refrigeration system occur, there are changes in operating parameters that may be made in order to bring the pressures and/or temperatures back within the normal range. This may be changes in compressor speed or expansion valve opening for example. However, where the working fluid includes air, the changes in operating parameters may fail to return the pressures and temperatures back within the normal range.

Since a mixture of air and refrigerant may be combustible, and the risk of combustion may be exacerbated by high temperatures and pressures, it may be necessary to stop the functioning of the system when air is detected in the system.

The detection of air may be performed by the controller 50 by carrying out a control method 100 illustrated in FIG. 3.

At step 102, the controller may receive system operation data including at least one temperature or pressure value for the refrigeration system. The system operation data may be data from one or more temperature sensors and/or one or more pressure sensors that are arranged to detect a pressure or temperature in the refrigeration system. For example, the controller may receive a compressor discharge temperature from a compressor discharge temperature sensor. Alternatively, at step 102 the controller may receive a compressor suction pressure value.

At step 103, the system may determine one or more threshold values for allowable temperatures and/or pressures in the refrigeration system. The controller may receive data regarding ambient conditions such as ambient temperature and load on the system (which may be determined based on a measured return air temperature). The controller may also receive or retrieve a temperature set point value. The controller may then determine, for example, a compressor discharge temperature threshold based on one or more of the received or retrieved values. Alternatively, the thresholds may be predetermined and step 103 may be omitted.

At step 104, the controller may compare the received temperature or pressure value to a threshold value for that temperature or pressure. For example, there may be a known maximum compressor discharge temperature and the received compressor discharge temperature value may be compared to the maximum compressor discharge temperature value. Alternatively, at step 104 the controller may compare a received compressor suction pressure value to a minimum compressor suction pressure value. If the received value is determined to be allowable based on the comparison, the method may return to step 102 and may continue to monitor the system.

Alternatively, if it is determined the received value is outside the allowable range, the method may move to step 106.

The comparison at step 104 may also comprise a comparison of the received value to a further threshold. The further threshold may indicate that air is present in the system and that a system shut down should occur in order to avoid a possible combustion event. For example, where the received value is a compressor discharge temperature, the further threshold may be a further maximum compressor discharge temperature. If the comparison indicates that the compressor discharge temperature is above the further threshold, the method may move to step 108.

Further, at step 104, ambient conditions and operating requirements may be considered and may be compared to thresholds. For example, an ambient temperature value may be received from an ambient temperature sensor, a return air temperature value may be received from a return air temperature sensor, and/or a temperature set point value may be retrieved. In some cases, such as where there is a high ambient temperature, a high return air temperature, or a high difference between a return air temperature and a temperature set point, one or more of the temperatures or pressures received at step 102 may be removed from consideration.

At step 106, an operating parameter of the refrigeration system may be altered. The operating parameter is a controllable aspect of the refrigeration system that may be controlled by the controller. For example, the operating parameter may be a rotational speed of the compressor. The pressure change and the temperature change across the compressor may be reduced by a reduction in compressor speed and therefore, in response to determining that the compressor discharge pressure is greater than a threshold value, the controller may output a signal to cause a reduction in the rotational speed of the compressor.

The controller may alternatively alter other operating parameters of the system, such as a throttle valve opening or a hot-gas by-pass duty cycle.

At step 108, the system may be automatically shut down. In this case, the compressor may be automatically turned off and stopped from rotating. This may reduce the prospect of a catastrophic failure of the system, such as due to a combustion event.

After step 106, the method moves to step 110. At step 110, further temperature and pressure data is received from the temperature and pressure sensors. The further temperature or pressure data may comprise a further compressor discharge temperature value. The further temperature or pressure data may be received after a time delay after the change in operating parameter(s) at step 106, in order to allow the change in operating parameter(s) to affect the temperatures and pressures in the system.

At Step 112, the further temperature or pressure data is compared to a further threshold value. The further threshold value may be the same as either of the threshold values used for the comparison at step 104. Generally, the further threshold value will be the same as the threshold value requiring a change in operating parameter(s). A determination that the pressure or temperature data is on the same side of the threshold as at step 104 indicates that the change in operating parameter(s) has not had the expected effect on the system and that therefore it is likely that air is present in the system.

For example, at step 104 it may be determined that the compressor discharge temperature is greater than a compressor discharge temperature threshold value and at step 112 it may be determined that, following a change in operating parameter(s), the compressor discharge temperature remains greater than the compressor discharge temperature threshold value. In this case, it can be determined that the change in operating parameter(s) is not having the desired effect and that the system may have a leak.

Alternatively, at step 104 it may be determined that the compressor suction pressure is below the compressor suction pressure threshold value and at step 112 it may be determined that, following a change in operating parameter(s), the compressor suction pressure remains below the compressor suction pressure threshold value. In this case, it may be determined that the system has a leak.

Generally, the temperature or pressure value being on the same side of the relevant threshold before and after the change in operating parameter may mean that the temperature or pressure is lower than the threshold before and after the operating parameter is changed or is greater than the threshold before and after the operating parameter is changed.

If, at step 112, it is determined that the temperature or pressure value is on the same side of the threshold after the change in operating parameter(s) as before, the method may move to step 114. At step 114, the system may be shut down or a warning signal may be output. The warning signal may be output as an indication on a user interface or may be a signal to a further part of the program registering one indicium of the presence of a leak.

Alternatively, if the temperature or pressure value has crossed the threshold and has moved to within an allowable range, the method may return to step 102 and the controller may continue to monitor and to control the system. In this case, it may be determined that the system does not have a leak.

Further, at each of steps 102, 104, 106, 110 and 112, data regarding multiple temperatures and/or pressures may be received and each temperature or pressure value received may be compared to a respective threshold. The controller may determine the requirement to change an operating parameter based on at least one value being outside the allowable range or based on a majority of the values being outside the allowable range. Similarly, the presence of a leak may be determined based on at least one value being outside the allowable range or based on a majority of the values being outside the allowable range.

While the above disclosure relates to detection of leaks and the possibility of ingress of air into a refrigeration system, a further hazard exists which is the possibility of exit of a refrigerant, such that the refrigerant may mix with air in a compressor bay or housing surrounding one or more components of the refrigeration system. This may result in a combustible mixture being present in the compressor bay.

In order to address this issue, there may be provided a refrigeration apparatus comprising: a compressor, the compressor comprising: a compressor housing; a moveable component disposed within the compressor housing, a shaft extending through the compressor housing at a first point and arranged to impart a torque to the moveable component to rotate the moveable component, an apparatus housing containing the compressor, and a vent in the apparatus housing arranged to allow fluid communication between the interior of the apparatus housing and the external environment, wherein the vent is arranged beneath the first point.

Generally, a shaft may extend through a housing of a compressor where a hole is provided in the housing. In order to reduce or prevent the exit of refrigerant from the housing and to reduce or prevent the ingress of air into the housing a shaft seal may be arranged around the shaft. However, the shaft seal may provide a point of weakness in the housing, such that the most likely location for a leak to develop in the housing is at the shaft seal. Therefore, in order to allow any refrigerant that leaks out of the compressor to leave the compressor bay, there may be a vent provided underneath the shaft seal. This may allow the refrigerant to leave the compressor bay under gravity, as opposed to accumulating in the compressor bay. In this way, a risk of combustion in the compressor bay may be reduced.

FIG. 4a shows a profile view of a schematic drawing of a compressor bay and FIG. 4b shows a front view of a schematic drawing of a compressor bay. In FIGS. 4a and 4b, it can be seen that a compressor bay is provided that contains a compressor 34. The compressor 34 comprises a housing 34a, a motor 34 and a shaft seal 34c arranged on the housing. The shaft seal is arranged to seal around a shaft (not shown) extending from the motor 34b into the housing 34a.

A vent 38 is arranged in an outer housing of the compressor bay 13. The vent 38 allows fluid communication between the inside of the compressor bay 13 and the surrounding environment. The vent 38 is arranged below the shaft seal 34c so that any refrigerant leaving the refrigeration system via the shaft seal 34c may leave the compressor bay 13 via the vent 38. In this way, the concentration of refrigerant within the compressor bay 13 may be maintained at a lower level in the event of a leak.

The vent 38 may be a louvred vent and/or may comprise a cover in order to reduce the ingress of dirt and other undesirable matter into the compressor bay 13 from the environment.