Temperature management system and related methods

Abstract

A system (1) for temperature management of a lubricating fluid in a lubricant reservoir (3) in a compressor (4), the system comprising: a temperature sensor (5) configured to measure the temperature of the lubricating fluid (2); a pressure sensor (6) configured to measure the pressure in the lubricant reservoir (3); a heating element (7) configured to be switchable between an off state wherein no heat is provided to the lubricating fluid (2) and an on state wherein heat is provided to the lubricating fluid (2); and a control unit (8) in signal communication with the temperature sensor (5), pressure sensor (6) and heating element (7); wherein the control unit (8) is configured to: receive a pressure measurement of the lubricant reservoir (3) from the pressure sensor (6) and based on the pressure measurement calculate a condensation temperature of the working fluid; determine a lower temperature limit as the condensation temperature plus a temperature offset; receive a temperature measurement from the temperature sensor (5) and compare the temperature measurement with the lower temperature limit; and switch the heating element (7) to the on state to provide heat to the lubricating fluid (2) when the temperature measurement from the temperature sensor (5) is below the lower temperature limit.

Description

[0001] TEMPERATURE MANAGEMENT SYSTEM AND RELATED METHODS

[0002] FIELD

[0003] The present invention relates to a temperature management system for a lubricating fluid in a lubricant reservoir. The temperature management system finds particular utility in use with a lubricant reservoir in a compressor, and particularly when the compressor is provided in a heat pump utilising a condensable working medium.

[0004] BACKGROUND

[0005] Thermal machines such as heat pumps are known devices. Heat pumps are generally used to heat indoor spaces or supply hot water to a user. Use of heat pumps is desirable as they provide for more sustainable heat than heating devices which use fossil fuels. Heat pumps transfer thermal energy from a low-temperature heat source to a high-temperature heat sink.

[0006] A working fluid known as a refrigerant is used in the heat pump system. The refrigerant is a specially selected fluid which absorbs or rejects heat as it circulates through the heat pump system. A compressor in the form of a displacement device is used to pressurise the refrigerant and move the refrigerant through the system.

[0007] An expansion valve is used as a controlling device which controls the balance between the operating pressures / temperatures and refrigerant / working fluid flow in combination with the compressor. The expansion valve provides a simple means for reducing the pressure, and hence the temperature, between the condenser section and the evaporator section of the heat pump, therebycompleting the thermodynamic cycle, as will be easily understood by a person skilled in the art.

[0008] Many industrial processes require heat at high temperatures in the form of, for example, steam or hot water, which is extremely energy-intensive to produce, especially when primary energy sources are used. Examples of industries utilising heat at high temperatures include paper, food and beverages, chemicals, automotive, metal, plastic, engineering, textiles and wood. For example, in the food and beverage industry, heat at high temperatures is used in processes such as drying, evaporation, pasteurisation, sterilisation, boiling, distillation, blanching, scalding, concentrating, tempering and smoking, to name merely a handful of examples.

[0009] Industrial waste heat is usually not utilised due to the low temperature of such waste heat, which is lower than the temperature required in many industrial processes. This waste heat can be upgraded using a high-temperature thermal machine such as a high-temperature heat pump, and thus reused, which has clear economic and environmental benefits.

[0010] Current high-temperature heat pumps face challenges with regard to the working fluid and with regard to maintaining the desired properties of the lubricant in the compressor.

[0011] Using a reciprocating compressor results in small amounts of working fluid blowby (working fluid leaking past the pistons) entering the internal volume filled with lubricant. Some of the working fluid condenses and mixes with the lubricant, reducing the viscosity of the lubricant. Some arrangements provide a passivebreather to allow the refrigerant to leave the crank case. A way to reduce the interference of working fluid in the lubricant is to heat the lubricant to a higher temperature to evaporate the working fluid therefrom. However, heating the lubricant also results in reduced viscosity and shorter service life.

[0012] Viscosity of a lubricating fluid in a compressor depends on temperature and dilution. Where given a specific pressure the dilution strives for a state of equilibrium depending on the temperature of the lubricating fluid. More refrigerant will accumulate in the lubricating fluid the closer the lubricating fluid temperature is to the saturation temperature of the working fluid.

[0013] To keep the viscosity in an allowable range the lubricating fluid temperature has to stay in a certain temperature range above the saturation temperature.

[0014] One method, described in US patent document US2023151744, relates to measuring the temperature and pressure of the lubricant in the compressor of a heat pump. From the pressure reading the condensation temperature of the working fluid is determined, and this is used as the lower limit of a temperature range within which the temperature of the lubricant should be maintained. The upper limit of the temperature range within which the temperature of the lubricant should be maintained is between 2K and 15K greater than the condensation temperature. When the temperature of the lubricant falls below the condensation temperature, the control system heats the lubricant with a tempering element. When the temperature of the lubricant goes above the upper limit of the temperature range the control system cools the lubricant with the temperingelement. In this way, the lubricant is maintained within a temperature range above the condensation temperature of the working fluid.

[0015] There are several disadvantages with the solution described in US2023151744. Firstly, the tempering element provides heating at the condensation temperature. It is known that at the condensation temperature of the working fluid, a reasonable proportion of working fluid will already be condensed into the lubricant, and thereby affecting the viscosity of the lubricant, and thereby affecting the lubricant performance. Secondly, there is a lack of redundancy in the solution, in that the temperature at which the tempering element should turn on to heat the lubricant at is determined based on the measured pressure, thereby leading to a vulnerability in the system if the measured pressure is not accurate. Thirdly, the tempering element is set to turn on to heat the lubricant when the lubricant temperature equals the condensation temperature. In such an arrangement, the tempering element will, so called, short cycle, i.e. turn on and off repeatedly. Short cycling typically causes energy inefficiencies and associated increased running costs and increased wear on the system components.

[0016] US5318151A relates to an apparatus for regulating a compressor lubrication system. The apparatus includes an oil-flooded rotary gas compressor, a reservoir flow connected to the compressor, a heat exchanger for cooling a lubricant, and a controller. A thermal mixing valve regulates the temperature of the lubricant flowing to the compressor. A first temperature sensor measures a discharge temperature at a compressor outlet, and provides a signalcorresponding to the discharge temperature to the controller. A second temperature sensor measures a lubricant temperature at a lubricant inlet to the compressor, and provides a signal corresponding to the lubricant temperature to the controller. A pressure sensor measures the pressure at the outlet of the compressor, and provides a corresponding pressure signal to the controller. A valve means continuously regulates the supply of lubricant to the compressor, the valve means being controlled by the controller in response to the temperature signal of the first temperature sensor and the pressure signal. Operation of the thermal mixing valve is controlled by the controller, in response to the temperature signal of the second temperature sensor, to continuously regulate the temperature of the lubricant supplied to the compressor to minimize preheating of the low pressure gas.

[0017] US2020240415A1 relates to an oil feed type air compressor including a compressor body; a separator; a compressed air-feeding system feeding the compressed air separated by the separator to a use destination of the compressed air; an oil-feeding system feeding the oil separated by the separator to the compression chamber of the compressor body; an oil cooler and a temperature sensor disposed in the oil-feeding system; and a controller enabling execution of a temperature control. The temperature control by the controller is performed by variably controlling a rotation speed of a cooling fan such that, during the load operation, a temperature detected by the temperature sensor is a target value T1, and during the unload operation, the temperature detected by the temperature sensor is a target value T2 (with the proviso of T 1 >T2).At least one aim of the invention is to obviate or at least mitigate one or more drawbacks of prior art.

[0018] SUMMARY

[0019] According to a first aspect of the invention, there is provided a system for temperature management of a lubricating fluid in a lubricant reservoir in a compressor, the system comprising: a temperature sensor configured to measure the temperature of the lubricating fluid; a pressure sensor configured to measure the pressure in the lubricant reservoir; a heating element configured to be switchable between an off state wherein no heat is provided to the lubricating fluid and an on state wherein heat is provided to the lubricating fluid; and a control unit in signal communication with the temperature sensor, pressure sensor and heating element; wherein the control unit is configured to: receive a pressure measurement of the lubricant reservoir from the pressure sensor and based on the pressure measurement calculate a condensation temperature of the working fluid; determine a lower temperature limit as the condensation temperature plus a temperature offset; receive a temperature measurement from the temperature sensor and compare the temperature measurement with the lower temperature limit; and switch the heating element to the on state to provide heat to the lubricating fluid when the temperature measurement from the temperature sensor is below the lower temperature limit.The pressure sensor may be configured to measure the pressure in the lubricant reservoir or in a gas-filled space in direct fluid communication with the lubricant reservoir, the gas-filled space primarily being filled with working fluid in a gaseous state.

[0020] The temperature offset may be between 1 K and 15K or between 1 K and 10K or between 2K and 10K or between 3K and 7K or around 5K. The temperature offset may be 5K.

[0021] The control unit may be configured with a hysteresis temperature range applicable to the lower temperature limit such that in use: when the heating element is switched to the on state, the control unit maintains the heating element in the on state until the temperature measurement from the temperature sensor reads a temperature above the lower temperature limit plus the hysteresis temperature range; and when the temperature measurement from the temperature sensor reads a temperature above the lower temperature limit plus the hysteresis temperature range, the control unit switches the heater element to the off state.

[0022] The control unit may be configured with a hysteresis time delay applicable to the lower temperature limit such that in use: when the heating element is switched to the on state, the control unit maintains the heating element in the on state until the time delay has elapsed; and when the time delay has elapsed, the control unit switches the heater element to the off state.The hysteresis temperature range may be between 1 K and 12K or between 2K and 10K or between 4K and 8K or around 6K. The hysteresis temperature range may be 6K.

[0023] The system may further comprise: a cooling element configured to be switchable between an off state wherein no cooling is provided to the lubricating fluid and an on state wherein cooling is provided to the lubricating fluid; wherein the control unit is in signal communication with the cooling element and is configured to: determine an upper temperature limit as the lower temperature limit plus the hysteresis temperature range plus a dead band; receive a temperature measurement from the temperature sensor and compare the temperature measurement with the upper temperature limit; and switch the cooling element to the on state to provide cooling to the lubricating fluid when the temperature measurement from the temperature sensor is equal to or above the upper temperature limit.

[0024] The dead band may be a non-constant dead band. The dead band may be variable. The control unit may be configured to adjust the dead band.

[0025] The temperature offset may be between 1 K and 15K or between 1 K and 10K or between 2K and 10K or between 3K and 7K or around 5K. The temperature offset may be 5K.

[0026] The hysteresis temperature range may be between 1 K and 12K or between 2K and 10K or between 4K and 8K or around 6K. The hysteresis temperature range may be 6K.According to a second aspect of the invention, there is provided a method of temperature management of a lubricating fluid in a lubricant reservoir in a compressor, the method comprising the steps of: providing a temperature management system according to the first aspect of the invention; arranging the temperature management system in operative connection with a lubricant reservoir comprising lubricating fluid in a compressor; measuring the temperature of the lubricating fluid with the temperature sensor and sending the measured temperature to the control unit; measuring the pressure in the lubricant reservoir with the pressure sensor and sending the measured pressure to the control unit; calculating the condensation temperature of the working fluid based on the measured pressure; determining a lower temperature limit as the condensation temperature plus a temperature offset; comparing the temperature measurement with the lower temperature limit; and switching the heating element to the on state to provide heat to the lubricating fluid when the temperature measurement from the temperature sensor is below the lower temperature limit.

[0027] The temperature offset may be between 1 K and 15K or between 1 K and 10K or between 2K and 10K or between 3K and 7K or around 5K. The temperature offset may be 5K.

[0028] The method may further comprise the steps of: configuring the control unit with a hysteresis temperature range applicable to the lower temperature limit; when the heating element is switched on, maintaining the heating element in the on state until the temperature measurement from the temperature sensor reads a temperature above the lower temperature limit plus the hysteresis temperaturerange; and when the temperature measurement from the temperature sensor reads a temperature above the lower temperature limit plus the hysteresis temperature range, switching the heater element to the off state.

[0029] The hysteresis temperature range may be between 1 K and 12K or between 2K and 10K or between 4K and 8K or around 6K. The hysteresis temperature range may be 6K.

[0030] The method may further comprise the steps of: configuring the control unit with a hysteresis time delay applicable to the lower temperature limit; when the heating element is switched on, maintaining the heating element in the on state until the time delay has elapsed; and when the time delay has elapsed, switching the heater element to the off state.

[0031] The method may further comprise the steps of: providing a cooling element configured to be switchable between an off state wherein no cooling is provided to the lubricating fluid and an on state wherein cooling is provided to the lubricating fluid; arranging the control unit in signal communication with the cooling element; determining an upper temperature limit as the lower temperature limit plus the hysteresis temperature range plus a dead band; receiving a temperature measurement from the temperature sensor and comparing the temperature measurement with the upper temperature limit; switching the cooling element to the on state to provide cooling to the lubricating fluid when the temperature measurement from the temperature sensor is above the upper temperature limit.The dead band may be a non-constant dead band. The dead band may be variable. The control unit may be configured to adjust the dead band.

[0032] The temperature offset may be between 1 K and 15K or between 1 K and 10K or between 2K and 10K or between 3K and 7K or around 5K. The temperature offset may be 5K.

[0033] The hysteresis temperature range may be between 1 K and 12K or between 2K and 10K or between 4K and 8K or around 6K. The hysteresis temperature range may be 6K.

[0034] Given a specific pressure, the viscosity of the lubricating fluid in a compressor changes due to temperature variations. For each pressure, there is a window that the lubricating fluid viscosity should be held within. This is done by applying an upper limit of the temperature to which the lubricating fluid is heated - that is the above-described condensation temperature plus the temperature offset plus the hysteresis range plus the dead band.

[0035] A lubricating fluid conditioning function, which includes both heating and cooling, can optimise or maintain the lubricating fluid within a band around this optimal viscosity. This band can be adjusted to be wider or narrower depending on the specific needs of the compressor and the required lubricating fluid viscosity. By allowing the heat pump to operate with a wide range of crankcase pressures, the system can automatically adapt its band of acceptable lubricating fluid temperature, ensuring optimal performance and protection of the compressor components.BRIEF DESCRIPTION OF THE DRAWINGS

[0036] The embodiments of the invention will now be described, by way of example only, with reference to the accompanying drawing, in which:

[0037] Fig. 1 shows a schematic of a compressor comprising a lubricant reservoir and a first temperature management system;

[0038] Fig. 2 shows a schematic of a compressor comprising a lubricant reservoir and a second temperature management system; and

[0039] Fig. 3 shows a schematic of a compressor comprising a lubricant reservoir and a third temperature management system.

[0040] DETAILED DESCRIPTION

[0041] Fig. 1 shows a schematic of a compressor comprising a lubricant reservoir and a first temperature management system configured to provide heating of the lubricant in the lubricant reservoir when the temperature of the lubricant falls below a lower temperature limit. Fig. 2 shows a schematic of a compressor comprising a lubricant reservoir and a second temperature management system configured to provide heating of the lubricant in the lubricant reservoir when the temperature of the lubricant falls below a lower temperature limit and cooling of the lubricant in lubricant reservoir by means of an externally located cooling jacket when the temperature measured is above an upper temperature limit. Fig.

[0042] 3 shows a schematic of an alternative arrangement of the cooling element, wherein the cooling element is provided within the lubricant reservoir and is submerged within the lubricant.Fig. 1 shows a system 1 for temperature management of a lubricating fluid 2 in a lubricant reservoir 3 in a compressor 4. The lubricating fluid 2 in the presently described example is oil although it will be understood that alternative lubricating fluids may be used in other examples. Although not shown in Fig. 1 , the compressor 4 may be installed within a heat pump, for example within a high-temperature heat pump. The system 1 comprises a temperature sensor 5 configured to measure the temperature of the lubricating fluid 2 and a pressure sensor 6 configured to measure the pressure in the lubricant reservoir 3. The system further comprises a heating element 7 configured to be switchable between an off state wherein no heat is provided to the lubricating fluid 2 and an on state wherein heat is provided to the lubricating fluid 2.

[0043] Still referring to Fig. 1 the system 1 further comprises a control unit 8. The control unit 8 is connected in signal communication with the temperature sensor 5 via a communication cable 5a. The control unit 8 is connected in signal communication with the pressure sensor 6 via a communication cable 6a. The control unit 8 is connected in signal communication with the heating element 7 via a communication cable 7a. In the presently described examples in Figs. 1 to 3, the components of the system 1 are connected by cables to provide signal communication, however it will be understood by a person skilled in the art that communication between components of the system 1 may be provided by alternative means, such as but not limited to wired or wireless communication means, such as but not limited to bus wireless connections, Bluetoothcommunication and WiFi communication. Components of the system may be 4G or 5G enabled, for example.

[0044] Still referring to Fig. 1 the control unit 8 is configured to receive a pressure measurement of the pressure in the lubricant reservoir 3 from the pressure sensor 6 and based on the pressure measurement calculate a condensation temperature of the working fluid.

[0045] Although not shown in the Figures, the compressor 4 is for compressing a working fluid. As is known in the art, in such compressors, it is undesirable to allow the working fluid to condense and mix with the lubricating fluid. The lubricating fluid 2 is selected to have a particular viscosity and other specific properties to provide optimal lubrication to the compressor components. Mixing of condensed working fluid into the lubricating fluid 2 results in an undesirable change in the viscosity of the lubricating fluid 2 which may greatly affect the lubricating properties of the lubricating fluid 2.

[0046] It is therefore highly desirable to calculate the condensation temperature at which the working fluid will condensate, and therefore mix with the lubricating fluid 2 in the lubricate reservoir 3. The calculation required to calculate the condensation temperature of the working fluid at a particular pressure is well known to the skilled person. The control unit 8 may be provided with the parameters needed to perform this calculation when the control unit 8 receives the pressure measured in the lubricant reservoir 3 from the pressure sensor 6. The parameters of the working fluid may be stored in the memory of the control unit 8 or may be obtained from a remote server such as a database stored in thecloud. The control unit 8 may have a user input device (not shown) wherein the user may select a working fluid from a stored database of working fluids and associated properties, or enter properties of the working fluid used such that the control unit 8 can calculate the condensation temperature of the working fluid when the pressure in the lubricant reservoir 3 is measured and sent to the control unit 8.

[0047] After the control unit 8 has calculated the condensation temperature of the working fluid, the control unit 8 determines a lower temperature limit as the condensation temperature plus a temperature offset. For example, if the condensation temperature is determined to be x-degrees Celsius, the lower temperature limit is determined to be x + temperature offset. In prior art solutions the lower temperature limit is set as the condensation temperature, however at the condensation temperature a relatively large amount of working fluid will have already mixed into the lubricating fluid 2, thereby detrimentally affecting the viscosity and therefore lubricating properties of the lubricating fluid 2. The setting of the lower temperature limit as higher than the condensation temperature, ensures that the working fluid does not condensate to a degree that it greatly affects the viscosity and / or other lubricating properties of the lubricating fluid 2.

[0048] In use, the control unit 8 receives a temperature measurement from the temperature sensor 5 and compares the temperature measurement with the lower temperature limit (which is above the condensation temperature). If the temperature measurement is below the lower temperature limit, the control unit 8 switches the heating element 7 to the on state to provide heat to the lubricatingfluid 2. In this way, the lubricating fluid 2 is maintained at a temperature wherein no working fluid is condensed and mixed into the lubricating fluid 2 or nondetrimental amounts of working fluid are condensed and mixed into the lubricating fluid 2. By “non-detrimental” it is meant that although small amounts of working fluid are condensed and mixed into the lubricating fluid 2, the small amount is such that the viscosity of the lubricating fluid 2 is affected only by a small and acceptable amount. For example, in some cases a “non-detrimental” amount of working fluid may be up to 30% by volume.

[0049] Still referring to Fig. 1 the control unit 8 is configured with a hysteresis temperature range applicable to the lower temperature limit in use such that short cycling of the heating element 7 is avoided. It is well understood that turning on and off repeatedly, i.e. short cycling typically causes energy inefficiencies and associated increased running costs and increased wear on the system components. The hysteresis range ensures that when the heating element 7 switched to the on state, the heating element 7 stays on for a period of time until the temperature recorded reaches the upper limit of the hysteresis range, at which point the control unit 8 turns off the heating element 7.

[0050] Said another way, the control unit 8 is configured to maintain the heating element 7 in the on state when the heating element 7 is switched to the on state, until the temperature measurement from the temperature sensor 5 reads a temperature above the lower temperature limit plus the hysteresis temperature range.Referring now to Fig. 2, there is provided a second example of a temperature management system. The second temperature management system T has many of the same features as the temperature management system 1 described with reference to Fig. 1 , therefore the same reference numerals as used to indicate the same or similar features with the addition of prime ('). Notably, the second temperature management system T additionally comprises a cooling element 9’ configured to be switchable between an off state wherein no cooling is provided to the lubricating fluid 2’ and an on state wherein cooling is provided to the lubricating fluid 2’. In the example described in Fig. 2, the cooling element 9’ is provided as a cooling jacket located at least partially around the lubricant reservoir 3’. In some examples the cooling jacket may be provided in the form of cooling pipes or tanks or channels or ribs through which a cooled fluid is circulated.

[0051] The control unit 8’ is in signal communication with the cooling element 9’. The exact means of signal communication, i.e. wired or wireless communication is not important. In the presently described example, the cooling element 9’ is connected by means of a communication cable 9a’.

[0052] The control unit 8’ is configured to determine an upper temperature limit as the lower temperature limit plus the hysteresis temperature range plus a dead band. A person skilled in the art will understand that a dead band refers to a temperature range in which neither heating nor cooling is provided. The control unit 8’ receives a temperature measurement from the temperature sensor 5’ and compares the temperature measurement with the upper temperature limit in use.The control unit 8’ switches the cooling element 9’ to the on state to provide cooling to the lubricating fluid 2’ when the temperature measurement from the temperature sensor 5’ is equal to or above the upper temperature limit.

[0053] As previously mentioned, the other components of the second temperature management system T shown in Fig. 2 are as shown and described with reference to Fig. 1, including the second temperature management system T comprising a heating element 7’, a pressure sensor 6’ and associated communications cables 7a’ and 6a’ connected to the control unit 8’. Further, the temperature sensor 5’ is provided with an associated communication cable 5’ connected to the control unit 8’. Finally, the temperature management system T in use with a compressor 4’. Although not shown in Fig. 2, the compressor 4’ may be installed within a heat pump, for example within a high-temperature heat pump.

[0054] The methods of operation of the first 1 and second T example temperature management systems can now be summarised. In operation of the first temperature management system 1 to provide heating of the lubrication fluid 2 in the lubricant reservoir 3, the method starts by providing the temperature management system 1 shown in Fig. 1 arranged in operative connection with a lubricant reservoir 3 comprising lubricating fluid 2 in a compressor 4 as shown in Fig. 1. The temperature of the lubrication fluid 2 is measured with the temperature sensor 5 and sent as the measured temperature to the control unit 8. The pressure in the lubricant reservoir 3 is measured with the pressure sensor 6 and is sent as the measured pressure to the control unit 8. The control unit 8then calculates the condensation temperature of the working fluid based on the measured pressure and determines a lower temperature limit as the condensation temperature plus a temperature offset. The control unit 8 then compares the temperature measurement with the lower temperature limit and switches the heating element 7 to the on state to provide heat to the lubricating fluid 2 when the temperature measurement from the temperature sensor 5 is below the lower temperature limit.

[0055] Optionally, the method may include configuring the control unit 8 with a hysteresis temperature range applicable to the lower temperature limit. When heating element 7 is switched on, maintaining the heating element 7 in the on state until the temperature measurement from the temperature sensor 5 reads a temperature above the lower temperature limit plus the hysteresis temperature range; and when the temperature measurement from the temperature sensor 5 reads a temperature above the lower temperature limit plus the hysteresis temperature range, switching the heater element 5 to the off state.

[0056] In operation of the second temperature management system T to provide heating and cooling of the lubrication fluid 2’ in the lubricant reservoir 3’, the method starts by providing the temperature management system T shown in Fig.

[0057] 2 arranged in operative connection with a lubricant reservoir comprising lubricating fluid 2’ in a compressor 4’ as shown in Fig. 2. The temperature of the lubrication fluid 2’ is measured with the temperature sensor 5’ and sent as the measured temperature to the control unit 8’. The pressure in the lubricant reservoir 3’ is measured with the pressure sensor 6’ and is sent as the measuredpressure to the control unit 8’. The control unit 8’ then calculates the condensation temperature of the working fluid based on the measured pressure and determines a lower temperature limit as the condensation temperature plus a temperature offset. The control unit 8’ then compares the temperature measurement with the lower temperature limit and switches the heating element 7’ to the on state to provide heat to the lubricating fluid 2’ when the temperature measurement from the temperature sensor 5’ is below the lower temperature limit.

[0058] The method operation of the second temperature management system T comprises configuring the control unit 8’ with a hysteresis temperature range applicable to the lower temperature limit. When heating element 7’ is switched on, maintaining the heating element 7’ in the on state until the temperature measurement from the temperature sensor 5’ reads a temperature above the lower temperature limit plus the hysteresis temperature range and when the temperature measurement from the temperature sensor 5’ reads a temperature above the lower temperature limit plus the hysteresis temperature range, switching the heater element 7’ to the off state.

[0059] The method of operation of the second example temperature management system T further comprises, as shown in Fig. 2, providing a cooling element 9’ configured to be switchable between an off state wherein no cooling is provided to the lubricating fluid 2’ and an on state wherein cooling is provided to the lubricating fluid 2’. The control unit 8’ is arranged in signal communication with the cooling element 9’. The control unit 8’ determines an upper temperaturelimit as the lower temperature limit plus the hysteresis temperature range plus a dead band. The control unit 8’ receives a temperature measurement from the temperature sensor 5’ and compares the temperature measurement with the upper temperature limit. The control unit 8’ switches the cooling element 9’ to the on state to provide cooling to the lubricating fluid 2’ when the temperature measurement from the temperature sensor 5’ is equal to or above the upper temperature limit.

[0060] Referring now to Fig. 3 there is shown a third alternative arrangement of a temperature management system 1”. The third temperature management system 1” has many of the same features as the temperature management system T described with reference to Fig. 2, therefore the same reference numerals as used to indicate the same or similar features with the addition of prime ('). In this regard, the third temperature management system 1” is for managing the temperature of a lubricating fluid 2” in a lubricant reservoir 3” in a compressor 4”. Although not shown in Fig. 3, the compressor 4” may be installed within a heat pump, for example within a high-temperature heat pump. The system 1” comprises a temperature sensor 5” configured to measure the temperature of the lubricating fluid 2” and a pressure sensor 6” configured to measure the pressure in the lubricant reservoir 3”. The system further comprises a heating element 7” configured to be switchable between an off state wherein no heat is provided to the lubricating fluid 2” and an on state wherein heat is provided to the lubricating fluid 2”, and a cooling element 9” configured to beswitchable between an off state wherein no cooling is provided to the lubricating fluid 2” and an on state wherein cooling is provided to the lubricating fluid 2”.

[0061] Still referring to Fig. 3 the system 1” further comprises a control unit 8”. The control unit 8” is connected in signal communication with the temperature sensor 5” via a communication cable 5a”. The control unit 8” is connected in signal communication with the pressure sensor 6” via a communication cable 6a”. The control unit 8” is connected in signal communication with the heating element 7” via a communication cable 7a”. The control unit 8” is connected in signal communication with the cooling element 9” via a communication cable 9a”. Still referring to Fig. 3 the control unit 8” is configured to receive a pressure measurement of the pressure in the lubricant reservoir 3” from the pressure sensor 6” and based on the pressure measurement calculate a condensation temperature of the working fluid.

[0062] The compressor 4” is for compressing a working fluid. The control unit 8” may be provided with the parameters needed to perform this calculation when the control unit 8” receives the pressure measured in the lubricant reservoir 3” from the pressure sensor 6”. The parameters of the working fluid may be stored in the memory of the control unit or may be obtained from a remote server such as a database stored in the cloud. The control unit 8” may have a user input device (not shown) wherein the user may select a working fluid from a stored database of working fluids and associated properties, or enter properties of the working fluid used such that the control unit 8” can calculate the condensationtemperature of the working fluid when the pressure in the lubricant reservoir 3” is measured and sent to the control unit 8”.

[0063] After the control unit 8” has calculated the condensation temperature of the working fluid, the control unit 8” determines a lower temperature limit as the condensation temperature plus a temperature offset. For example, if the condensation temperature is determined to be x-degrees Celsius, the lower temperature limit is determined to be x + temperature offset. In prior art solutions the lower temperature limit is set as the condensation temperature, however at the condensation temperature a relatively large amount of working fluid will have already mixed into the lubricating fluid 2”, thereby detrimentally affecting the viscosity and therefor lubricating properties of the lubricating fluid 2”. The setting of the lower temperature limit as higher than the condensation temperature, ensures that the working fluid does not condensate to a degree that it greatly affects the viscosity and / or other lubricating properties of the lubricating fluid 2”.

[0064] In use, the control unit 8” receives a temperature measurement from the temperature sensor 5” and compares the temperature measurement with the lower temperature limit (which is above the condensation temperature). If the temperature measurement is below the lower temperature limit, the control unit 8” switches the heating element 7” to the on state to provide heat to the lubricating fluid 2”. In this way, the lubricating fluid 2” is maintained at a temperature wherein no working fluid is condensed and mixed into the lubricating fluid 2” or non-detrimental amounts of working fluid are condensed and mixed into the lubricating fluid 2”. By “non-detrimental” it is meant that although smallamounts of working fluid are condensed and mixed into the lubricating fluid 2”, the small amount is such that the viscosity of the lubricating fluid 2” is affected only by a small and acceptable amount. By “mixed” into the lubricating fluid, it will be understood by a person skilled in the art that the working fluid goes into the lubricating fluid and builds a new mixture and acts as a new fluid.

[0065] The control unit 8” is configured with a hysteresis temperature range applicable to the lower temperature limit in use such that short cycling of the heating element 7” is avoided. It is well understood that turning on and off repeatedly, i.e. short cycling typically causes energy inefficiencies and associated increased running costs and increased wear on the system components. The hysteresis range ensures that when the heating element 7” switched to the on state, the heating element 7” stays on for a period of time until the temperature recorded reaches the upper limit of the hysteresis range, at which point the control unit 8” turns off the heating element 7”.

[0066] Said another way, the control unit 8” is configured to maintain the heating element 7” in the on state when the heating element 7” is switched to the on state, until the temperature measurement from the temperature sensor 5” reads a temperature above the lower temperature limit plus the hysteresis temperature range.

[0067] The control unit 8” determines an upper temperature limit as the lower temperature limit plus the hysteresis temperature range plus a dead band. The control unit 8” receives a temperature measurement from the temperature sensor 5” and compares the temperature measurement with the uppertemperature limit. The control unit 8” switches the cooling element 9” to the on state to provide cooling to the lubricating fluid 2” when the temperature measurement from the temperature sensor 5” is equal to or above the upper temperature limit.

[0068] Notably, in the third temperature management system 1” the cooling element 9” is provided as a cooling element 9” located within the lubricating fluid 2” in the lubricant reservoir 3”. The cooling element 9” may be for example water cooling pipes provided through the lubricant reservoir 3” and configured to circulate cold water through the lubricant reservoir 3” when the cooling element is in the on state.

[0069] Referring to all three example temperature management systems described herein, the lower temperature limit is determined as the condensation temperature plus a temperature offset. This temperature offset may in some examples be between 1 K and 15K, more preferably between 1 K and 10K , more preferably between 2K and 10K, more preferably between 3K and 7K, more preferably around 5K, more preferably 5K.

[0070] Where a hysteresis temperature range is provided, the hysteresis temperature range may in some examples be between 1 K and 12K, more preferably between 2K and 10K, more preferably between 4K and 8K, more preferable around 6K, more preferably 6K.

[0071] Fig. 2 shows cooling of the lubricant in lubricant reservoir by means of an externally located cooling jacket. In some arrangements the cooling element may be partially or entirely attachable to and detachable from the lubricant reservoir.In Fig. 3 the cooling element is provided within the lubricant reservoir and is submerged within the lubricant. In some examples the cooling element may be integrated within the lubricant reservoir during manufacture of the lubricant reservoir.

[0072] It will be understood that when a pressure sensor is provided and configured to measure the pressure in the lubricant reservoir in some examples the pressure sensor will be located in the pocket above the lubricating fluid whereas in other examples the pressure sensor may even be located in the lubricating fluid. Alternatively, in some other examples the pressure sensor may be provided in a different location and be configured to measure the pressure in the lubricant reservoir.

[0073] Although in the described embodiments only the cooling element is shown as being possibly located outside of the lubricant reservoir, it will be understood that it is also possible to locate the heating element outside of the lubricant reservoir. In this regard, direct and indirect cooling of the lubricating fluid in the lubricant reservoir is possible as well as direct and indirect heating of the lubricating fluid in the lubricant reservoir.

[0074] It will be understood that in in the presently described examples a single temperature sensor is provided for simplicity of explanation, however in alternative examples multiple temperature sensors may be provided. The readings from multiple temperature sensors may be averaged or the temperature measurement may be the lowest or highest of all of the temperature sensors. It will be understood that in some examples the readings from the temperaturesensors may be computed by the control unit to determine the temperature measurement to be used.

[0075] It will be understood that in in the presently described examples a single pressure sensor is provided for simplicity of explanation, however in alternative examples multiple pressure sensors may be provided. The readings from multiple pressure sensors may be averaged or the pressure measurement may be the lowest or highest of all of the pressure sensors. It will be understood that in some examples the readings from the pressure sensors may be computed by the control unit to determine the pressure measurement to be used in the determination of the lower temperature limit and upper temperature limit.

[0076] It will be further understood that the control unit may be a dedicated control unit only for receiving the pressure and temperature measurements, determining the lower and upper temperature limits and controlling the heating and cooling elements where required, or the control unit may be a part of a larger control unit for controlling other systems, such as other systems of a high-temperature heat pump.

Claims

CLAIMS1. A system (1 ) for temperature management of a lubricating fluid (2) in a lubricant reservoir (3) in a compressor (4), the system comprising:a temperature sensor (5) configured to measure the temperature of the lubricating fluid (2);a pressure sensor (6) configured to measure the pressure in the lubricant reservoir (3);a heating element (7) configured to be switchable between an off state wherein no heat is provided to the lubricating fluid (2) and an on state wherein heat is provided to the lubricating fluid (2); anda control unit (8) in signal communication with the temperature sensor (5), pressure sensor (6) and heating element (7);wherein the control unit (8) is configured to:receive a pressure measurement of the lubricant reservoir (3) from the pressure sensor (6) and based on the pressure measurement calculate a condensation temperature of the working fluid;determine a lower temperature limit as the condensation temperature plus a temperature offset;receive a temperature measurement from the temperature sensor (5) and compare the temperature measurement with the lower temperature limit; andswitch the heating element (7) to the on state to provide heat to the lubricating fluid when the temperature measurement from the temperature sensor (5) is below the lower temperature limit.

2. The system (1 ) according to claim 1 , wherein the control unit (8) is configured with a hysteresis temperature range applicable to the lower temperature limit such that in use:when the heating element (7) is switched to the on state, the control unit (8) maintains the heating element (7) in the on state until the temperature measurement from the temperature sensor (5) reads a temperature above the lower temperature limit plus the hysteresis temperature range; andwhen the temperature measurement from the temperature sensor (5) reads a temperature above the lower temperature limit plus the hysteresis temperature range, the control unit (8) switches the heater element to the off state.

3. The system (1 ) according to claim 2, further comprising:a cooling element (9) configured to be switchable between an off state wherein no cooling is provided to the lubricating fluid (2) and an on state wherein cooling is provided to the lubricating fluid (2);wherein the control unit (8) is in signal communication with the cooling element (9) and is configured to:determine an upper temperature limit as the lower temperature limit plus the hysteresis temperature range plus a dead band;receive a temperature measurement from the temperature sensor (5) and compare the temperature measurement with the upper temperature limit; andswitch the cooling element (9) to the on state to provide cooling to the lubricating fluid when the temperature measurement from the temperature sensor (5) is equal to or above the upper temperature limit.

4. A method of temperature management of a lubricating fluid (2) in a lubricant reservoir (3) in a compressor (4), the method comprising the steps of:providing a temperature management system according to claim 1; arranging the temperature management system in operative connection with a lubricant reservoir (3) comprising lubricating fluid (2) in a compressor (4);measuring the temperature of the lubricating fluid (2) with the temperature sensor (5) and sending the measured temperature to the control unit (8);measuring the pressure in the lubricant reservoir (3) with the pressure sensor (6) and sending the measured pressure to the control unit (8);calculating the condensation temperature of the working fluid based on the measured pressure;determining a lower temperature limit as the condensation temperature plus a temperature offset;comparing the temperature measurement with the lower temperature limit; andswitching the heating element (7) to the on state to provide heat to the lubricating fluid when the temperature measurement from the temperature sensor (5) is below the lower temperature limit.

5. The method according to claim 4, further comprising the steps of:configuring the control unit (8) with a hysteresis temperature range applicable to the lower temperature limit;when the heating element (7) is switched on, maintaining the heating element (7) in the on state until the temperature measurement from the temperature sensor (5) reads a temperature above the lower temperature limit plus the hysteresis temperature range; andwhen the temperature measurement from the temperature sensor (5) reads a temperature above the lower temperature limit plus the hysteresis temperature range, switching the heater element to the off state.

6. The method according to claim 5, further comprising the steps of:providing a cooling element (9) configured to be switchable between an off state wherein no cooling is provided to the lubricating fluid and an on state wherein cooling is provided to the lubricating fluid;arranging the control unit (8) in signal communication with the cooling element (9);determining an upper temperature limit as the lower temperature limit plus the hysteresis temperature range plus a dead band;receiving a temperature measurement from the temperature sensor (5) and comparing the temperature measurement with the upper temperature limit;switching the cooling element (9) to the on state to provide cooling to the lubricating fluid when the temperature measurement from the temperature sensor (5) is equal to or above the upper temperature limit.

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