Method for determining an optimal condensing temperature of a refrigerant

Abstract

A method for determining an optimal condensing temperature of a refrigerant being used in a compressor-condenser-arrangement is presented, comprising the following steps: determining an actual operating condition of the compressor-condenser-arrangement; determining base-values of compressor-operation; determining base-values of condenser-fan-operation; determining an actual value of compressor-operation and calibrating the base-values of compressor-operation, and / or determining an actual value of condenser-operation and calibrating the base-values of condenser-fan-operation; determining a total power and determining the operating condition of the compressor-condenser-arrangement for which the total power is minimized and determining the condensing temperature for this operating condition as the optimal condensing temperature. Furthermore, an apparatus adapted to carry out the method and an according computer program are described.

Description

[0001] The present invention relates to a method for determining an optimal condensing temperature of a refrigerant according to claim 1, an apparatus adapted to carry out the method according to claim 13 and a computer program according to claim 14.

[0002] Refrigeration plants generally comprise a compressor for compressing a refrigerant, a condenser for condensing the compressed refrigerant transferring the condensation heat of the refrigerant to an ambient medium of the condenser, an expansion valve for expanding the compressed refrigerant and an evaporator for evaporating the expanded refrigerant absorbing the energy needed for evaporation of the refrigerant from an ambient medium of the evaporator.

[0003] In order to save expenses for energy and also for environmental protection the energy input for a cycle of the refrigerant as described above and therefore, the energy input for a refrigeration plant shall be kept as low as possible, i.e. the efficiency of such a refrigerant-cycle is desired to be as high as possible.

[0004] The energy input for a cycle of the refrigerant is influenced by many factors. Improvements can be reached, for example, by improving the insulation of pipes, in particular pipes carrying the expanded refrigerant. In the field of compressor development large efforts are taken to improve the degree of efficiency of the compressors leading to less energy consumption for compressing the refrigerant.

[0005] However, the afore-mentioned measures for decreasing the energy consumption of a refrigeration plant are by far not the only measures for saving energy.

[0006] In a refrigeration plant the compressor realizes the temperature lift from an evaporating temperature of the refrigerant to a condensing temperature of same. The condenser is, as already mentioned above, used to transfer the condensation heat to ambient. Most condensers are using fans, that help transfer the condensation heat to ambient. When the speed of the fan is doubled, the fan power will roughly become 8 times higher.

[0007] The condensing temperature of a refrigeration plant is generally controlled by changing the speed of the condenser fan. A higher fan speed will lead to a better heat transfer, and this will improve the performance of the condenser, leading to a lower condensing temperature. This lower condensing temperature will lead to a smaller temperature lift from the evaporating temperature of the refrigerant to the condensing temperature of same and will, therefore, lead to a lower power consumption of the compressor.

[0008] Although an increasing condenser fan speed will lower the power consumption of the compressor, at some point, the additional fan power needed due to an increase in the speed of the fan can become larger than the reduction in compressor driving power which may be achieved by reducing the temperature lift from the evaporating temperature of the refrigerant to the condensing temperature of same.

[0009] Therefore, the energy consumption of a refrigeration plant is also affected by an operating condition of the compressor-condenser-arrangement which should be balanced in a way that the total energy consumption of the compressor-condenser-arrangement being a sum of the energy consumption of the compressor and the energy consumption of the condenser is minimized.

[0010] A methodology for a control system of a refrigeration plant to calculate the optimum machine speeds, whilst taking account of fan, heat exchanger and compressor characteristics is proposed in Ciaran Dowling: "Determining the Optimum Condenser Fan Speed for Refrigeration Systems", IIR Rankine Conference 2020, DOI: http: / / dx.doi.org / 10.18462 / iir.rankine.2020.1112. However, this method is based on a theoretical performance of the condenser and compressor and therefore, deviations due to, for example, runtime-dependent changes in the refrigeration plant like fouling of the condenser which influence the power consumption of the plant may occur.

[0011] It is, therefore an object of the present invention to provide a method for determining an optimal condensing temperature of a refrigerant being used in a compressor-condenser-arrangement to make sure that the compressor-condenser-arrangement will be operating at the optimal condensing temperature even when the performance of the compressor and condenser is different than specified by predetermined values, for example values given by the supplier of the compressor-condenser-arrangement. It is, furthermore, an object of the present invention to provide an according apparatus adapted to carry out the method and a computer program comprising instructions which when executed by a processing system cause the processing system to perform the method.

[0012] The aspect of the object referring to a method is solved by a method according to independent claim 1. The aspect referring to a method is, therefore, solved by a method for determining an optimal condensing temperature of a refrigerant being used in a compressor-condenser-arrangement, said refrigerant being provided to be compressed by the compressor and being provided to be condensed in the condenser, the condenser comprising one or more than one fan, the method comprising the following steps: a) determining an actual operating condition of the compressor-condenser-arrangement; b) determining base-values of compressor-operation comprising a base-value of compressor-operation for the actual operating condition of the compressor-condenser-arrangement, the base-value of compressor-operation for the actual operating condition of the compressor-condenser-arrangement being associated with a compressor driving power for the actual operating condition of the compressor-condenser-arrangement, and additional base-values of compressor-operation for operating conditions of the compressor-condenser-arrangement other than the actual operating condition of the compressor-condenser-arrangement, the additional base-values of compressor-operation for the operating conditions of the compressor-condenser-arrangement other than the actual operating condition of the compressor-condenser-arrangement being associated with compressor driving powers for the operating conditions of the compressor-condenser-arrangement other than the actual operating condition of the compressor-condenser-arrangement; c) determining base-values of condenser-fan-operation comprising a base-value of condenser-fan-operation for the actual operating condition of the compressor-condenser-arrangement, the base-value of condenser-fan-operation for the actual operating condition of the compressor-condenser-arrangement being associated with a condenser-fan driving power for the actual operating condition of the compressor-condenser-arrangement, and additional base-values of condenser-fan-operation for the operating conditions of the compressor-condenser-arrangement other than the actual operating condition of the compressor-condenser-arrangement, the additional base-values of condenser-fan-operation for the operating conditions of the compressor-condenser-arrangement other than the actual operating condition of the compressor-condenser-arrangement being associated with condenser-fan driving powers for the operating conditions of the compressor-condenser-arrangement other than the actual operating condition of the compressor-condenser-arrangement; d) determining an actual value of compressor-operation for the actual operating condition of the compressor and calibrating the base-values of compressor-operation using the actual value of compressor-operation, receiving as a result calibrated values of compressor-operation, and / or determining an actual value of condenser-operation for the actual operating condition of the condenser and calibrating the base-values of condenser-fan-operation using the actual value of condenser-operation, receiving as a result calibrated values of condenser-operation; e) determining a total power for the actual operating condition of the compressor-condenser-arrangement and for the operating conditions of the compressor-condenser-arrangement other than the actual operating condition of the compressor-condenser-arrangement being a sum of the compressor driving power and the condenser-fan driving power for the actual operating condition of the compressor-condenser-arrangement and the operating conditions of the compressor-condenser-arrangement other than the actual operating condition of the compressor-condenser-arrangement using the base-values of compressor-operation and the calibrated values of condenser-operation, or using the calibrated values of compressor-operation and the base-values of condenser-fan-operation, or using the calibrated values of compressor-operation and the calibrated values of condenser-operation; f) determining the operating condition of the compressor-condenser-arrangement for which the total power is minimized and determining the condensing temperature for this operating condition as the optimal condensing temperature.

[0013] According to the method an actual operating condition of the compressor-condenser-arrangement is determined. Furthermore, values (called base-values of compressor-operation) associated with the compressor driving power for several operating conditions, namely for the actual operating condition and for operating conditions deviating from the actual operating condition are determined. Moreover, values (called base-values of condenser-fan-operation) associated with the condenser-fan driving power for several operating conditions, namely for the actual operating condition and for operating conditions deviating from the actual operating condition are determined. The afore-mentioned values associated with the compressor driving power and the afore-mentioned values associated with the condenser-fan driving power may be, for example, determined by a calculation using information (specification) given by the supplier of the compressor-condenser-arrangement or may be determined using look-up tables etc.

[0014] At least either the afore-mentioned values associated with the compressor driving power for the actual operating condition of the compressor-condenser-arrangement and for the operating conditions of the compressor-condenser-arrangement other than the actual operating condition of the compressor-condenser-arrangement or the afore-mentioned values associated with the condenser-fan driving power for the afore-mentioned operating conditions are calibrated using a corresponding actual value for the actual operating condition (which might, for example be a measured value or a value calculated using another actual value of the system, etc.). By calibrating the respective values, deviations of the values caused by deviations of the compressor-condenser-arrangement from the specification, for example, caused by changes of properties / deterioration of components of the compressor and / or the condenser or caused by tolerances in the manufacturing process, are considered. Calibrating only the values associated with the compressor driving power or the values associated with the condenser-fan driving power is favorable if the deviations of the values caused by deviations of the compressor-condenser-arrangement from the specification are quite large for only the compressor-related values or only the condenser-related values and small for the other values. If both kinds of values show large deviations, both kinds of values might be calibrated.

[0015] By using calibrated values for determining the total energy consumption of the compressor and the condenser deviations a reliable and precise determination of the operating point having a minimal total energy consumption is possible. Therefore, the optimal condensing temperature can be determined using the found operating point.

[0016] It should be noted that in step f) the operating condition of the compressor-condenser-arrangement is determined for which the total power to deliver the required cooling capacity of the arrangement to a recipient, for example, a refrigeration plant, is minimized.

[0017] Below the compressor driving power may be called shortly compressor power and the fan driving power may be called shortly fan power.

[0018] In an embodiment of the method, step a) comprises: measuring, by direct or indirect measurement, actual measured operating conditions of the compressor-condenser-arrangement, in particular an actual measured condensing temperature (Tcond_act_meas) of the refrigerant and an actual measured compressor driving power (P_act_meas) and an actual measured condenser fan speed (V_act_meas) and step b) comprises: b-1) determining an actual calculated compressor cooling capacity (C_act_calc) for the actual operating conditions and an actual calculated compressor driving power (P_act_calc) for the actual operating conditions; b-2) determining calculated deviating compressor driving powers (P_deviate_calc) for condensing temperatures (Tcond_deviate) higher and lower than the actual condensing temperature of the referigerant (Tcond_act_meas) said calculated deviating compressor driving powers (P deviate_calc) delivering the actual calculated compressor cooling capacity (C_act_calc) for the condensing temperatures (Tcond_deviate) higher and lower than the actual condensing temperature (Tcond_act_meas) of the refrigerant; and step c) comprises determining an actual calculated condenser fan speed (V_act_calc) for the actual measured condensing temperature of the refrigerant (Tcond_act_meas) and determining calculated deviating condenser fan speeds (V_deviate_calc) for the condensing temperatures (Tcond_deviate) higher and lower than the actual condensing temperature of the refrigerant (Tcond_act_meas); and step d) comprises d-1) determining a compressor driving power relationship (Cal_value_for_P) between the actual measured compressor driving power (P_act_meas) and the actual calculated compressor driving power (P_act_calc); d-2) Calibrating the actual calculated compressor driving power (P_act calc) and all calculated deviating compressor driving powers (P deviate_calc) based on the compressor driving power relationship (Cal_value_for_P) receiving calibrated calculated compressor driving powers (P_calibrated_calc) for the actual measured condensing temperature (Tcond_act_meas) and for the condensing temperatures (Tcond_deviate) higher and lower than the actual condensing temperature (Tcond_act_meas); d-3) Determining a fan speed relationship (Cal_value_for_V) between the actual measured condenser fan speed (V_act_meas) and the actual calculated condenser fan speed (V_act_calc); d-4) Calibrating the actual calculated condenser fan speed (V_act calc) and all calculated deviating condenser fan speeds (V_deviate_calc) based on the fan speed relationship (Cal_value_for_V) receiving calibrated calculated condenser fan speeds (V_calibrated_calc) for the actual measured condensing temperature (Tcond_act_meas) and for the condensing temperatures (Tcond_deviate) higher and lower than the actual condensing temperature (Tcond_act_meas); and step e) comprises e-1) determining calculated calibrated fan powers (Pfan_calibrated_calc) based on the calibrated calculated condenser fan speeds (V_calibrated_calc) for the actual measured condensing temperature (Tcond_act_meas) and for the condensing temperatures (Tcond_deviate) higher and lower than the actual condensing temperature (Tcond_act_meas); e-2) adding each of the calibrated calculated compressor driving powers (P_calibrated_calc) for the actual measured condensing temperature (Tcond_act_meas) and for the condensing temperatures (Tcond_deviate) higher and lower than the actual condensing temperature (Tcond_act_meas) to the corresponding calculated calibrated fan powers (Pfan_calibrated_calc) for the actual measured condensing temperature (Tcond_act_meas) and for the condensing temperatures (Tcond_deviate) higher and lower than the actual condensing temperature (Tcond_act_meas) receiving a total power (P_total) for each of the actual measured condensing temperature (Tcond_act_meas) and of the condensing temperatures (Tcond_deviate) higher and lower than the actual condensing temperature (Tcond_act_meas); and step f) comprises determining the temperature of the actual measured condensing temperature (Tcond_act_meas) and of the condensing temperatures (Tcond_deviate) higher and lower than the actual condensing temperature (Tcond_act_meas) as the optimal condensing temperature (T_cond_determined) for which the total power (P_total) is minimized.

[0019] In this embodiment variables / values are used which are generally easily accessible since the respective sensors detecting said values are mounted generally in most refrigeration plants. Therefore, no additional sensors etc. have to be added to the refrigeration plant.

[0020] The step of measuring of the actual operating conditions can comprise direct or indirect measuring of an ambient temperature and / or a wet bulb temperature, direct or indirect measuring of an evaporating temperature and direct or indirect measuring of a compressor speed and / or the compressor driving power and / or the condenser fan speed and / or the condenser fan power.

[0021] It should be noted that in a direct measurement the measured value / variable is compared directly with a scale or a standard. In an indirect measurement another value / variable is measured and used to determine the value / variable to be measured using a known, clear relationship between the other value / variable and the value / variable to be measured.

[0022] Step b) of the method may be performed using predetermined values, in particular values delivered by the manufacturer of the compressor, which are dependent on the respective compressor. Alternatively, or in addition thereto step c) might be performed using predetermined values, in particular values delivered by the manufacturer of the condenser, which are dependent on the respective condenser. In this case easily accessible values may be used leading to low expenses for the usage of the data given by the manufacturer.

[0023] In another embodiment step b) and / or step c) can be performed using an artificial intelligence engine. Once trained, the artificial intelligence machine may reduce the needed calculating power in comparison to, for example, complex calculations needed for determining the values.

[0024] The compressor driving power relationship (Cal_value_for_P) between the actual measured compressor driving power (P_act_meas) and the actual calculated compressor driving power (P_act_calc) may be the quotient (P_act_meas / P_act_calc) of the actual measured compressor driving power (P_act_meas) and the actual calculated compressor driving power (P_act_calc). This helps to lower the needed calculating power since the calibration of the compressor driving power is a nearly linear operation, i.e. the compressor power is almost linear to the condensing temperature.

[0025] The fan speed relationship (Cal_value_for_V) between the actual measured condenser fan speed (V_act_meas) and the actual calculated condenser fan speed (V_act_calc) is determined by calculating the reduction in a condenser capacity at the actual measured conditions that leads to a calculated fan speed that is equal to the measured fan speed. Here, an easily accessible value is used for the calibration related to the condenser.

[0026] Step b) and / or step c) may be performed using polynomial calculations. These calculations deliver precise results while the efforts in calculating power remain acceptable.

[0027] It should be noted that step b) and / or step c) may be performed for a certain period of time using polynomial calculations or any other type of calculation not making use of an artificial intelligence machine and may then be performed for another period of time using an artificial intelligence machine. In particular, the polynomial calculations or any other type of calculation not making use of an artificial intelligence machine may be used while a training of the artificial intelligence machine is performed, replacing after finishing said training of the artificial intelligence machine the use of polynomial calculations or any other type of calculation not making use of an artificial intelligence machine by using the artificial intelligence machine

[0028] If an artificial intelligence engine is used, the artificial intelligence engine may use, in particular in step b), a sklearn non-linear regression and a motor speed, a saturated suction temperature and a saturated discharge temperature of the compressor. Alternatively, or additionally, the artificial intelligence engine may, in particular in step c), use regression tree, Random forest, Gradient Boosting Machines (GBM), Artificial Neural Networks, and support Vector Machine (SVM).

[0029] In order to even enhance the precision of the determined optimal condensing temperature, when the condenser is an evaporative condenser the method may comprise furthermore a step of determining the expenses for a coolant, in particular for water, needed to cool the condenser for each of the actual measured condensing temperature (Tcond_act_meas) and of the condensing temperatures (Tcond_deviate) higher and lower than the actual condensing temperature (Tcond_act_meas), wherein the expenses for the coolant are considered when determining the optimal condensing temperature (T_cond_determined).

[0030] The method can be implemented on a computer.

[0031] The aspect of the object of the present invention referring to an apparatus is solved by an apparatus according to claim 13, i.e. an apparatus adapted to carry out the afore-described method.

[0032] The aspect of the object of the present invention referring to a computer program is solved by a computer program according to claim 14, i.e. a computer program comprising instructions which when executed by a processing system cause the processing system to perform the afore-described method.

[0033] Further optional features of the invention are given in the following description of the figures. The respective features described can be realized individually or in any combination. Accordingly, the invention is described below with reference to the accompanying drawings and with reference to exemplary embodiments shown there. The drawings show in: Fig. 1 a diagram of a refrigeration plant in which the method according to the invention can be realized; Fig. 2 a flow diagram of a first embodiment of the method according to the present invention; Fig. 3 a flow diagram of a second embodiment of the method according to the present invention; Fig. 4 a flow diagram of a third embodiment of the method according to the present invention; Fig. 5 a table showing the results of a second step of an example of a method according to the present invention; Fig. 6 a table showing the results of a third step of an example of a method according to the present invention; Fig. 7 a table showing the results of a first sub-step of a fourth step of an example of a method according to the present invention; Fig. 8 a table showing the results of a second sub-step of the fourth step of an example of a method according to the present invention; Fig. 9 a table showing the results of a fifth step of an example of a method according to the present invention; Fig. 10 results of a machine learning prediction for the compressor power are shown compared to measured values and values as calculated in the first embodiment; and Fig. 11 a diagram of a fourth embodiment of the method according to the present invention using machine learning prediction.

[0034] A refrigeration plant 10 in which the method for determining an optimal condensing temperature of a refrigerant being used in a compressor-condenser-arrangement may be implemented is shown in Fig. 1. The refrigeration plant 10 comprises a compressor 12, a condenser 14, an expansion valve 16 and an evaporator 18. The compressor 12 and the condenser 14 are connected by a first pipe 20, the condenser 14 and the expansion valve 16 are connected by a second pipe 22, the expansion valve 16 and the evaporator 18 are connected by a third pipe 24 and the evaporator 18 and the compressor 12 are connected by a fourth pipe 26. The afore-mentioned components establish a closed refrigeration circuit 28 (or refrigeration plant 10) in which the refrigerant circulates.

[0035] The refrigerant is, in a gaseous state, sucked in by the compressor 12. There it is compressed to a high pressure and a high temperature (generally higher than the outside temperature). After compression the refrigerant flows via the first pipe 20 at high pressure and in the gaseous state to the condenser 14. In the condenser 14, the refrigerant is liquefied by cooling. The condenser 14 transfers heat from the refrigerant to the environment. In order to enhance the cooling power of the condenser 14 the condenser 14 comprises a first fan 30 and a second fan 32. Instead of two fans 30 and 32 only one fan or more than two fans may be installed in the condenser 14.

[0036] The refrigerant is then channeled via the second pipe 22 through the expansion valve 16 in liquid form and at high pressure. It loses its high pressure in the process, but remains liquid. In the liquid state being under low pressure, the refrigerant is led, via the third pipe 24 to the evaporator 18 where the refrigerant can then evaporate while extracting the necessary evaporation-heat (energy needed to vaporize) from the environment. In the evaporated (i.e. gaseous) state and being under low pressure, the refrigerant is led via the fourth pipe 26 back to the compressor 12.

[0037] In order to find an optimal condensing temperature for the refrigerant, according to a first embodiment of the method according to the present invention, a flow diagram of which is shown in Fig.2, in a first step (step a)) an actual operating condition of the compressor-condenser-arrangement is determined by measuring actual measured operating conditions of the compressor-condenser-arrangement, namely an actual measured condensing temperature (Tcond_act_meas) of the refrigerant and an actual measured compressor driving power (P_act_meas) and an actual measured condenser fan speed (V_act_meas).

[0038] While the afore-mentioned operating conditions are, in the first embodiment, all measured directly, the measurement may be performed in alternative embodiments for one or more of the values in an indirect way. The actual measured condensing temperature (Tcond_act_meas), for example, may be measured based on the pressure of the refrigerant in the condensing stage.

[0039] In further embodiments additional values defining the actual operating conditions might be measured (again the measurements may be direct measurements or indirect measurements). These values are, for example, an ambient temperature and / or a wet bulb temperature, an evaporating temperature and a compressor speed.

[0040] In a second step (step b)) an actual calculated compressor cooling capacity (C_act_calc) for the actual operating conditions and an actual calculated compressor driving power (P_act_calc) for the actual operating conditions are determined. Furthermore, calculated deviating compressor driving powers (P_deviate_calc) for condensing temperatures (Tcond_deviate) higher and lower than the actual condensing temperature of the refrigerant (Tcond_act_meas) are determined, said calculated deviating compressor driving powers (P deviate_calc) delivering the actual calculated compressor cooling capacity (C_act_calc) for the condensing temperatures (Tcond_deviate) higher and lower than the actual condensing temperature (Tcond_act_meas) of the refrigerant.

[0041] In other words, in this step the compressor cooling capacity is determined for the actual operating conditions and based on this value, compressor driving powers for condensing temperatures (Tcond_deviate) higher and lower than the actual condensing temperature (Tcond_act_meas) of the refrigerant are determined assuming that the actual calculated compressor cooling capacity for all condensing temperatures (Tcond_deviate) higher and lower than the actual condensing temperature (Tcond_act_meas) shall be constant.

[0042] In the first embodiment the calculations are performed using polynomial functions. However, in other embodiments also other functions or a calculation based on several values of the system, for example an evaporation temperature (given in °C), a suction loss (given in bar or pa), a superheat (useful and non-useful, given in Kelvin) the condensing temperature (given in °C), a discharge line loss (given in bar or pa) and a subcooling at condensing (given in Kelvin) may be used. Also, a calculation based on a specification of the compressor 12 given, for example by the manufacturer, may be used.

[0043] An actual calculated condenser fan speed (V_act_calc) for the actual measured condensing temperature of the refrigerant (Tcond_act_meas) and calculated deviating condenser fan speeds (V_deviate_calc) for the condensing temperatures (Tcond_deviate) higher and lower than the actual condensing temperature of the refrigerant (Tcond_act_meas) are determined in a third step (step c)). In the first embodiment a procedure to calculate the performance of the condenser is based on the specification of the condenser given by the supplier. This step is, in the first embodiment, based on a simple formula, keeping the needed calculating power low, may, however, in alternative embodiments be also based on polynomial calculations. Performing the calculation, it is taken into account that the amount of heat to be removed by the condenser (condenser capacity (kW)) is equal to the compressor cooling capacity plus the compressor driving power.

[0044] The afore-described third step is followed by a calibration step being the fourth step (step d)) of the method according to the first embodiment.

[0045] The fourth step comprises a first sub-step of determining a compressor driving power relationship (Cal_value_for_P) between the actual measured compressor driving power (P_act_meas) and the actual calculated compressor driving power (P_act_calc). The compressor driving power relationship (Cal_value_for_P) is, in the first embodiment, the quotient (P_act_meas / P_act_calc) of the actual measured compressor driving power (P_act_meas) and the actual calculated compressor driving power (P_act_calc).

[0046] In a second sub-step of the fourth step the actual calculated compressor driving power (P_act calc) and all calculated deviating compressor driving powers (P_deviate_calc) are calibrated based on the compressor driving power relationship (Cal_value_for_P). The results of the calibration are calibrated calculated compressor driving powers (P calibrated_calc) for the actual measured condensing temperature (Tcond_act_meas) and for the condensing temperatures (Tcond_deviate) higher and lower than the actual condensing temperature (Tcond_act_meas).

[0047] A fan speed relationship (Cal_value_for_V) between the actual measured condenser fan speed (V_act_meas) and the actual calculated condenser fan speed (V_act_calc) is determined in a third sub-step of the fourth step.

[0048] Calibrating of the actual calculated condenser fan speed (V_act_calc) and all calculated deviating condenser fan speeds (V_deviate_calc) based on the fan speed relationship (Cal_value_for_V) receiving calibrated calculated condenser fan speeds (V_calibrated_calc) for the actual measured condensing temperature (Tcond_act_meas) and for the condensing temperatures (Tcond_deviate) higher and lower than the actual condensing temperature (Tcond_act_meas) is performed in a fourth sub-step of the fourth step of the first embodiment of the method according to the present invention. The calibration is done by calculating the reduction in condenser capacity (at the measure conditions) that leads to a calculated fan speed that is equal to the measured fan speed.

[0049] In a fifth step (step e)) of the method according to the first embodiment calculated calibrated fan powers (Pfan_calibrated_calc) are (in a first sub-step of the fifth step) determined based on the calibrated calculated condenser fan speeds (V_calibrated_calc) for the actual measured condensing temperature (Tcond_act_meas) and for the condensing temperatures (Tcond_deviate) higher and lower than the actual condensing temperature (Tcond_act_meas).

[0050] Each of the calibrated calculated compressor driving powers (P_calibrated_calc) for the actual measured condensing temperature (Tcond_act_meas) and for the condensing temperatures (Tcond_deviate) higher and lower than the actual condensing temperature (Tcond_act_meas) is (in a second sub-step of the fifth step) added to the corresponding calculated calibrated fan powers (Pfan_calibrated_calc) for the actual measured condensing temperature (Tcond_act_meas) and for the condensing temperatures (Tcond_deviate) higher and lower than the actual condensing temperature (Tcond_act_meas). As a result, a total power (P_total) for each of the actual measured condensing temperature (Tcond_act_meas) and of the condensing temperatures (Tcond_deviate) higher and lower than the actual condensing temperature (Tcond_act_meas) are received.

[0051] In the results of the fifth step, in a sixth step (step f)), the temperature of the actual measured condensing temperature (Tcond_act_meas) and of the condensing temperatures (Tcond_deviate) higher and lower than the actual condensing temperature (Tcond_act_meas) is determined as the optimal condensing temperature (T_cond_determined) for which the total power (P_total) is minimized. This result may be used for controlling the refrigeration plant 10 reducing the energy consumption of the refrigeration plant 10, more precisely, reducing the energy consumption of the compressor 12 and the condenser 14 of the refrigeration plant 10.

[0052] In alternative embodiments in which the condenser is an evaporative condenser the expenses for a coolant are in an additional step (seventh step) determined, in particular the expenses for water, needed to cool the condenser for each of the actual measured condensing temperature (Tcond_act_meas) and of the condensing temperatures (Tcond_deviate) higher and lower than the actual condensing temperature (Tcond_act_meas), wherein the expenses for the coolant are considered when determining the optimal condensing temperature (T_cond_determined).

[0053] The first embodiment may be summarized as follows: Method for determining an optimal condensing temperature of a refrigerant being used in a compressor-condenser-arrangement, said refrigerant being provided to be compressed by the compressor 12 and being provided to be condensed in the condenser 14, the condenser 14 comprising one or more than one fan 30, 32, the method comprising the following steps: a) measuring, by direct or indirect measurement, actual measured operating conditions of the compressor-condenser-arrangement, in particular an actual measured condensing temperature of the refrigerant and an actual measured compressor driving power and an actual measured condenser fan speed and b-1) determining an actual calculated compressor cooling capacity for the actual operating conditions and an actual calculated compressor driving power for the actual operating conditions; b-2) determining calculated deviating compressor driving powers for condensing temperatures higher and lower than the actual condensing temperature of the refrigerant said calculated deviating compressor driving powers delivering the actual calculated compressor cooling capacity for the condensing temperatures higher and lower than the actual condensing temperature of the refrigerant; and c) determining an actual calculated condenser fan speed for the actual measured condensing temperature of the refrigerant and determining calculated deviating condenser fan speeds for the condensing temperatures higher and lower than the actual condensing temperature of the refrigerant; d-1) determining a compressor driving power relationship between the actual measured compressor driving power and the actual calculated compressor driving power. d-2) Calibrating the actual calculated compressor driving power and all calculated deviating compressor driving powers based on the compressor driving power relationship receiving calibrated calculated compressor driving powers for the actual measured condensing temperature and for the condensing temperatures higher and lower than the actual condensing temperature; d-3) Determining a fan speed relationship between the actual measured condenser fan speed and the actual calculated condenser fan speed; d-4) Calibrating the actual calculated condenser fan speed and all calculated deviating condenser fan speeds based on the fan speed relationship receiving calibrated calculated condenser fan speeds for the actual measured condensing temperature and for the condensing temperatures higher and lower than the actual condensing temperature; and e-1) determining calculated calibrated fan powers based on the calibrated calculated condenser fan speeds for the actual measured condensing temperature and for the condensing temperatures higher and lower than the actual condensing temperature; e-2) adding each of the calibrated calculated compressor driving powers for the actual measured condensing temperature and for the condensing temperatures higher and lower than the actual condensing temperature to the corresponding calculated calibrated fan powers for the actual measured condensing temperature and for the condensing temperatures higher and lower than the actual condensing temperature receiving a total power for each of the actual measured condensing temperature and of the condensing temperatures higher and lower than the actual condensing temperature; and f) determining the temperature of the actual measured condensing temperature and of the condensing temperatures higher and lower than the actual condensing temperature as the optimal condensing temperature for which the total power is minimized.

[0054] A second embodiment of the method according to the present invention is similar to the first embodiment. A flow diagram of the second embodiment is shown in Fig. 3.

[0055] The first, the second and the third step are identical to the first embodiment.

[0056] In the fourth step, however, the first sub-step of determining a compressor driving power relationship (Cal_value_for_P) between the actual measured compressor driving power (P_act_meas) and the actual calculated compressor driving power (P_act_calc) and the second sub-step, i.e. the sub-step of calibrating the actual calculated compressor driving power (P_act_calc) and all calculated deviating compressor driving powers (P_deviate_calc) based on the compressor driving power relationship (Cal_value_for_P) are omitted.

[0057] The third and the fourth sub-step of the fourth step are identical to the ones of the first embodiment.

[0058] In the fifth step (step e)) like in the first embodiment calculated calibrated fan powers (Pfan_calibrated_calc) are determined based on the calibrated calculated condenser fan speeds (V_calibrated_calc) for the actual measured condensing temperature (Tcond_act_meas) and for the condensing temperatures (Tcond_deviate) higher and lower than the actual condensing temperature (Tcond_act_meas).

[0059] In contrast to the first embodiment, in the second embodiment not each of the calibrated calculated compressor driving powers (P_calibrated_calc) for the actual measured condensing temperature (Tcond_act_meas) and for the condensing temperatures (Tcond_deviate) higher and lower than the actual condensing temperature (Tcond_act_meas) is added to the corresponding calculated calibrated fan powers (Pfan_calibrated_calc) for the actual measured condensing temperature (Tcond_act_meas) and for the condensing temperatures (Tcond_deviate) higher and lower than the actual condensing temperature (Tcond_act_meas).

[0060] Instead of the calibrated calculated compressor driving powers (P_calibrated_calc) for the actual measured condensing temperature (Tcond_act_meas) and for the condensing temperatures (Tcond_deviate) higher and lower than the actual condensing temperature (Tcond_act_meas), the (uncalibrated) calculated compressor driving powers (P_act_calc and P_deviate_calc) for the actual measured condensing temperature (Tcond_act_meas) and for the condensing temperatures (Tcond_deviate) higher and lower than the actual condensing temperature (Tcond_act_meas) are added to the corresponding calculated calibrated fan powers (Pfan_calibrated_calc) for the actual measured condensing temperature (Tcond_act_meas) and for the condensing temperatures (Tcond_deviate) higher and lower than the actual condensing temperature (Tcond_act_meas). As a result, a total power (P_total) for each of the actual measured condensing temperature (Tcond_act_meas) and of the condensing temperatures (Tcond_deviate) higher and lower than the actual condensing temperature (Tcond_act_meas) are received using uncalibrated values for the compressor driving powers and calibrated values for the condenser fan powers.

[0061] The sixth step is again identical to the one known from the first embodiment.

[0062] In particular, in plants showing large deviations of the calculated condenser power and the calibrated condenser power and showing small deviations in the compressor driving power between the calculated values and the calibrated values good results can be achieved while less calculating power is needed since no calibration step of the compressor power is necessary.

[0063] The second embodiment may be summarized as follows: Method for determining an optimal condensing temperature of a refrigerant being used in a compressor-condenser-arrangement, said refrigerant being provided to be compressed by the compressor 12 and being provided to be condensed in the condenser 14, the condenser 14 comprising one or more than one fan 30, 32, the method comprising the following steps: a) measuring, by direct or indirect measurement, actual measured operating conditions of the compressor-condenser-arrangement, in particular an actual measured condensing temperature of the refrigerant and an actual measured compressor driving power and an actual measured condenser fan speed and b-1) determining an actual calculated compressor cooling capacity for the actual operating conditions and an actual calculated compressor driving power for the actual operating conditions (actual condensing temperature of the refrigerant); b-2) determining calculated deviating compressor driving powers for condensing temperatures higher and lower than the actual condensing temperature of the refrigerant said calculated deviating compressor driving powers delivering the actual calculated compressor cooling capacity for the condensing temperatures higher and lower than the actual condensing temperature of the refrigerant; and c) determining an actual calculated condenser fan speed for the actual measured condensing temperature of the refrigerant and determining calculated deviating condenser fan speeds for the condensing temperatures higher and lower than the actual condensing temperature of the refrigerant; d-1') Determining a fan speed relationship between the actual measured condenser fan speed and the actual calculated condenser fan speed; d-2') Calibrating the actual calculated condenser fan speed and all calculated deviating condenser fan speeds based on the fan speed relationship receiving calibrated calculated condenser fan speeds for the actual measured condensing temperature and for the condensing temperatures higher and lower than the actual condensing temperature; and e-1) determining calculated calibrated fan powers based on the calibrated calculated condenser fan speeds for the actual measured condensing temperature and for the condensing temperatures higher and lower than the actual condensing temperature; e-2') adding each of the calculated compressor driving powers for the actual measured condensing temperature and for the condensing temperatures higher and lower than the actual condensing temperature to the corresponding calculated calibrated fan powers for the actual measured condensing temperature and for the condensing temperatures higher and lower than the actual condensing temperature receiving a total power for each of the actual measured condensing temperature and of the condensing temperatures higher and lower than the actual condensing temperature; and f) determining the temperature of the actual measured condensing temperature and of the condensing temperatures higher and lower than the actual condensing temperature as the optimal condensing temperature for which the total power is minimized.

[0064] In particular, in refrigeration plants showing small deviations of the calculated condenser power and the calibrated condenser power and showing large deviations in the compressor driving power between the calculated values and the calibrated values good results can be achieved using a third embodiment of the method according to the present invention, a flow diagram of which is shown in Fig. 4. Also, the third embodiment is below described being based on the first embodiment.

[0065] Again, the first, the second and the third step are identical to the first embodiment.

[0066] In the fourth step, the first sub-step and the second sub-step are identical to the first embodiment. The third sub-step and the fourth sub-step of the fourth step, however, are omitted.

[0067] In contrast to the first embodiment the fifth step (step e)) no calculated calibrated fan powers (Pfan_calibrated_calc) are determined for the actual measured condensing temperature (Tcond_act_meas) and for the condensing temperatures (Tcond_deviate) higher and lower than the actual condensing temperature (Tcond_act_meas), i.e. the first sub-step of the fifth step is also omitted.

[0068] In the second sub-step of the fifth step of the third embodiment, in contrast to the second sub-step of the fifth step of the first embodiment, each of the calibrated calculated compressor driving powers (P_calibrated_calc) for the actual measured condensing temperature (Tcond_act_meas) and for the condensing temperatures (Tcond_deviate) higher and lower than the actual condensing temperature (Tcond_act_meas) is added to corresponding calculated fan powers (Pfan_act_calc and Pfan_deviate_calc) for the actual measured condensing temperature (Tcond_act_meas) and for the condensing temperatures (Tcond_deviate) higher and lower than the actual condensing temperature (Tcond_act_meas) which are calculated based on the actual calculated condenser fan speed (V_act_calc) for the actual measured condensing temperature of the refrigerant (Tcond_act_meas) and based on the calculated deviating condenser fan speeds (V_deviate_calc) for the condensing temperatures (Tcond_deviate) higher and lower than the actual condensing temperature of the referigerant (Tcond_act_meas). As the result of the addition a total power (P_total) for each of the actual measured condensing temperature (Tcond_act_meas) and of the condensing temperatures (Tcond_deviate) higher and lower than the actual condensing temperature (Tcond_act_meas) will be received which is determined based on uncalibrated values for the condenser power and based on calibrated values for the compressor driving power.

[0069] The sixth step of the third embodiment is again identical to the one known from the first embodiment.

[0070] The third embodiment may be summarized as follows: Method for determining an optimal condensing temperature of a refrigerant being used in a compressor-condenser-arrangement, said refrigerant being provided to be compressed by the compressor 12 and being provided to be condensed in the condenser 14, the condenser 14 comprising one or more than one fan 30, 32, the method comprising the following steps: a) measuring, by direct or indirect measurement, actual measured operating conditions of the compressor-condenser-arrangement, in particular an actual measured condensing temperature of the refrigerant and an actual measured compressor driving power and an actual measured condenser fan speed and b-1) determining an actual calculated compressor cooling capacity for the actual operating conditions and an actual calculated compressor driving power for the actual operating conditions; b-2) determining calculated deviating compressor driving powers for condensing temperatures higher and lower than the actual condensing temperature of the refrigerant said calculated deviating compressor driving powers delivering the actual calculated compressor cooling capacity for the condensing temperatures higher and lower than the actual condensing temperature of the refrigerant; and c) determining an actual calculated condenser fan speed for the actual measured condensing temperature of the refrigerant and determining calculated deviating condenser fan speeds for the condensing temperatures higher and lower than the actual condensing temperature of the refrigerant; d-1) determining a compressor driving power relationship between the actual measured compressor driving power and the actual calculated compressor driving power. d-2) Calibrating the actual calculated compressor driving power and all calculated deviating compressor driving powers based on the compressor driving power relationship receiving calibrated calculated compressor driving powers for the actual measured condensing temperature and for the condensing temperatures higher and lower than the actual condensing temperature; and e-1') determining calculated fan powers based on the calculated condenser fan speeds for the actual measured condensing temperature and for the condensing temperatures higher and lower than the actual condensing temperature; e-2') adding each of the calibrated calculated compressor driving powers for the actual measured condensing temperature and for the condensing temperatures higher and lower than the actual condensing temperature to the corresponding calculated fan powers for the actual measured condensing temperature and for the condensing temperatures higher and lower than the actual condensing temperature receiving a total power for each of the actual measured condensing temperature and of the condensing temperatures higher and lower than the actual condensing temperature; and f) determining the temperature of the actual measured condensing temperature and of the condensing temperatures higher and lower than the actual condensing temperature as the optimal condensing temperature for which the total power is minimized.

[0071] Below an example for the use of a method according to the present invention will be described.

[0072] In the first step (step a)), a wet bulb temperature of 14.2 °C, an evaporating temperature of the refrigerant of 2.6 °C, a condensing temperature of 23.1 °C (Tcond_act_meas), a compressor speed of 2393 rpm, a compressor power of 71.8 kW and a condenser fan speed of 100% are measured as the actual measured operating conditions of the compressor-condenser-arrangement.

[0073] In the second step (step b)) the actual calculated compressor cooling capacity (C_act_calc) for the actual operating conditions and the actual calculated compressor driving power (P_act_calc) for the actual operating conditions are determined, using polynomial calculations. The results are an actual calculated compressor cooling capacity (C_act_calc) of 632 kW and an actual calculated compressor driving power (P_act_calc) of 71,8 kW. An EER-ratio, being the ratio of the actual calculated compressor cooling capacity (C_act_calc) for the actual operating conditions and the actual calculated compressor driving power (P_act_calc) for the actual operating conditions, is 8.80.

[0074] Alternatively, the actual calculated compressor cooling capacity (C_act_calc) for the actual operating conditions and the actual calculated compressor driving power (P_act calc) for the actual operating conditions could be calculated (as already mentioned above) using the evaporation temperature (given in °C), the suction loss (given in bar or pa), the superheat (useful and non-useful, given in Kelvin) the condensing temperature (given in °C), the discharge line loss (given in bar or pa) and the subcooling at condensing (given in Kelvin).

[0075] Furthermore, the calculated deviating compressor driving powers (P deviate_calc) for condensing temperatures (Tcond_deviate) higher and lower than the actual condensing temperature of the referigerant (Tcond_act_meas) are calculated with said calculated deviating compressor driving powers (P_deviate_calc) delivering the actual calculated compressor cooling capacity (C_act_calc). The result of the calculation is shown in the table of Fig. 5 (titled Pe line).

[0076] It should be noted that when the condensing temperature of a refrigeration system changes while keeping all other conditions (and compressor speed) the same, this will lead to a change in the compressor cooling capacity. For the performed calculations a constant compressor cooling capacity is assumed and it is, furthermore assumed that a compressor cooling capacity control will adapt the compressor speed accordingly. In the table of Fig. 5 polynomial functions to calculate the EER for different condensing temperatures were used and this value was used to calculate the compressor driving power (Pe Line = compressor cooling capacity / EER). The values for the actual measured operating conditions can be found in the second line (condensing temperature = 23.1 °C).

[0077] The actual calculated condenser fan speed (V_act_calc) for the actual measured condensing temperature of the refrigerant (Tcond_act_meas) and the calculated deviating condenser fan speeds (V_deviate_calc) for the condensing temperatures (Tcond_deviate) higher and lower than the actual condensing temperature of the referigerant (Tcond_act_meas) are calculated in the third step (step c)), resulting in the values shown in the table depicted in Fig. 6. Next to the variables known already from Fig. 5, in the table in Fig. 6, the condenser capacity can be found in the fourth column and the values for V_act_calc and V_deviate_calc can be found in the fifth column (titled: Theoretical Fanspeed (%)).

[0078] It should be noted that specifications being the basis for calculating the values for V_act_calc and V deviate_calc have been provided by the manufacturer of the condenser and are used to calculate the respective values for the different condensing temperatures. The calculation takes into account that the amount of heat to be removed by the condenser (condenser capacity (kW)) is equal to the compressor cooling capacity plus the compressor driving power.

[0079] In the fourth step (step d)) calibration of the values for the compressor driving power (P_act_calc, P_deviate_calc) is performed. It can be seen in the table shown in Fig. 5 that at the measured condition (condensing temperature 23,1°C) the calculated compressor driving power P_act_calc is 72,3 kW. The measured value P_act_meas, however, is 71,8 kW. The values of the Pe line which were calculated in the step summarized in Fig.5, are now calibrate to calculate a calibrated Pe line by performing a linear correction to all calculated compressor driving powers (Pe line Calibrated = Pe line * 71,8 / 72,3). The results for the calibrated Pe line are shown in the table being depicted in Fig. 7.

[0080] Moreover, in the fourth step also the calibration of the actual calculated condenser fan speed (V_act_calc) and all calculated deviating condenser fan speeds (V_deviate_calc) is performed. The results for the calibrated fan speed is shown in Fig. 8.

[0081] The calibration is done by calculating the reduction in condenser capacity (at the measured conditions, here Tcond_act_meas) that leads to a calculated fan speed that is equal to the measured fan speed. For this example, the theoretical condenser capacity was changed from 1302 to 1056 kW).

[0082] A significant difference between the calculated and the measured fan speed (66 % versus 100 %) can be seen. For most of the condenser systems a significant difference between the theoretical and practical performance of the condenser can be seen. Reasons for this underperformance can be fouling, air recirculating, mistakes in measuring ambient temperature and others.

[0083] It should still be mentioned that the calibrated fan speed at 23°C condensing temperature is larger than 100 %, so that this condition cannot be realized and needs to be ignored.

[0084] In the fifth step (step e)), the results of which are shown in Fig. 9, the calculated calibrated fan powers (Pfan_calibrated_calc, shown in the column titled "Fan Power (kW)") and the total energy consumption P_total (shown in the column titled "Ptot (kW)" are calculated.

[0085] The condenser 12 is equipped with two fans each requiring 5.26 kW at full speed. As the condenser 12 of the present example is not equipped with a power meter we calculate the fan power at lower speeds (fan power = fan speed^2.9 * 2 x 5.26).

[0086] The total power consumption is calculated by adding compressor power and fan power ("Pe line calibrated" and "Fan Power"). For total power consumption it is meant the total power necessary for delivering the required compressor cooling capacity to the refrigeration plant.

[0087] The optimal condensing temperature which is then determined in the sixth step (step f)) has the lowest total power consumption ("Ptot") being 80.4 kW for condensing temperatures of 24.2 °C, 24.4 °C and 24.7 °C.

[0088] A fourth embodiment of a method according to the present invention is based on the first embodiment. Modifications of the fourth embodiment can, for example be based on the second embodiment and the third embodiment.

[0089] In the fourth embodiment the second step (step b)) and the third step (step c)) are performed using an artificial intelligence engine. In alternative embodiments only one step, namely either the second step (step b)) or the third step (step c)), is performed using an artificial intelligence engine.

[0090] In particular, in the fourth embodiment, the artificial intelligence engine is based on a machine learning (ML) algorithm for prediction of t the compressor performance and / or the condenser performance.

[0091] For predicting the performance of the compressor, the compressor power and compressor cooling capacity needs to be predicted.

[0092] For the ML prediction of the compressor power training data are used for training the ML machine, which when fully trained will then be able to correctly output the compressor power.

[0093] As an example, the training data may comprise: 1. a saturated discharge temperature of the refrigerant when being discharged from the compressor (saturated_Discharge_Temperature), 2. a suction pressure of the refrigerant when entering the compressor (suction_Pressure), 3. a run time / operation hours of the compressor (compressor_RunTime_Hours), 4. the operation capacity of the compressor (capacity), 5. a motor speed of the compressor (motor_Speed), 6. a motor current of the compressor (motor_Current), 7. a compressor annunciation status whether there is a "warning", "shutown" or "notification" has been issued for the compressor (compressor_Annunciation_Status), 8. a discharge pressure of the refrigerant when being discharged from the compressor (discharge_Pressure), 9. a discharge temperature of the refrigerant when being discharged from the compressor (discharge_Temperature), 10. a difference between the actual measured temperature at the suction of the compressor and the saturated suction temperature (suction_Superheat), 11. a motor running status indication representing whether the motor is on or off (motor_Running), 12. a power demand of the compressor (kWh_Demand), 13. an ambient air temperature (ambient Air Temperature_1 / wet_Bulb Temperature_1) and 14. a temperature for the measured saturation pressure at which the refrigerant boils into its vapor phase (saturated_Suction_Temperature).

[0094] Preferably, the ML model is a supervised ML model. Examples of supervised ML models are linear regression, Gradient Boosting Machines (GBM), XGBoost, Random forest, Gaussian Process Regression (GPR) and sklearn non-linear regression.

[0095] More preferably, the ML model is a sklearn non-linear regression.

[0096] Among the training data the following ones have been found to be of enhanced relevance: the motor speed of the compressor (motor_Speed), the saturated suction temperature of the compressor (saturated_Suction_Temperature), and the saturated discharge temperature of the refrigerant when being discharged from the compressor (saturated_Discharge_Temperature).

[0097] The trained artificial intelligence engine outputs compressor power when inputted with the motor speed of the compressor (motor_Speed), the saturated suction temperature of the compressor (saturated Suction Temperature) and the saturated discharge temperature of the refrigerant when being discharged from the compressor (saturated_Discharge_Temperature).

[0098] In Fig. 10 the results of the ML prediction for the compressor power are shown together with the measured values and the calculated values of compressor driving power (being uncalibrated base-values of compressor-operation) calculated as described in the first embodiment (using a polynomial method), said calculated values being denoted as "digital twin" in Fig. 10.

[0099] Likewise, the ML prediction of the compressor cooling capacity requires first a training step. Initially the ML algorithm for the prediction of the compressor cooling capacity has been trained with a model (digital twin) of the compressor cooling capacity, due to unavailability of actual measurements of the compressor cooling capacity, used for checking whether the correctness of the predicted compressor cooling capacity during the training process.

[0100] For the ML prediction of the compressor cooling capacity, training data are used for training of the ML machine.

[0101] As an example, the training data may comprise: 1. the saturated discharge temperature of the refrigerant when being discharged from the compressor (saturated_Discharge_Temperature), 2. the suction pressure of the refrigerant when entering the compressor (suction_Pressure), 3. the run time / operation hours of the compressor (compressor_RunTime_Hours), 4. the operation capacity of the compressor (capacity), 5. the motor speed of the compressor (motor_Speed), 6. the motor current of the compressor (motor_Current), 7. the compressor annunciation status whether there is a "warning", "shutown" or whether a "notification" has been issued for the compressor (compressor Annunciation_Status), 8. the discharge pressure of the refrigerant when being discharged from the compressor (discharge_Pressure), 9. the discharge temperature of the refrigerant when being discharged from the compressor (discharge_Temperature), 10. the difference between the actual measured temperature at the suction of the compressor and the saturated suction temperature (suction_Superheat), 11. the motor running status indication representing is the motor is on or off (motor_Running), 12. the digital twin compressor cooling capacity which has been determined from the polynomial method (DT_Compressor_Capacity), 13. the ambient air temperature (ambient Air Temperature_1 / wet_Bulb_Temperature_1) and 14. the temperature for the measured saturation pressure at which the refrigerant boils into its vapor phase (saturated_Suction_Temperature).

[0102] Preferably, the ML model is a supervised ML model. Examples of supervised ML models are linear regression, Gradient Boosting Machines (GBM), XGBoost, Random forest, Gaussian Process Regression (GPR) and sklearn non-linear regression.

[0103] More preferably, the ML model is a sklearn non-linear regression.

[0104] Among the training data the following ones have been found to be of enhanced relevance: the motor speed of the compressor (motor_Speed), the saturated suction temperature of the compressor (saturated_Suction_Temperature), and the saturated discharge temperature of the refrigerant when being discharged from the compressor (saturated_Discharge_Temperature).

[0105] The trained artificial intelligence engine outputs compressor cooling capacity power when inputted with the motor speed of the compressor (motor_Speed), the saturated suction temperature of the compressor (saturated_Suction_Temperature), and the saturated discharge temperature of the refrigerant when being discharged from the compressor (saturated_Discharge_Temperature).

[0106] Condenser power may also be determined through ML prediction.

[0107] For the ML prediction of the condenser power, training data are used for training of the ML machine.

[0108] As an example, the training data may comprise: 1. the digital twin compressor cooling capacity which has been determined from the polynomial method (DT_Compressor_Capacity) (DT_Compressor_Capacity), 2. a temperature read by a thermometer covered in cloth which has been soaked in water at ambient temperature (a wet-bulb thermometer) and over which air is passed (wet_bulb temperature), 3. the saturated discharge temperature of the refrigerant when being discharged from the compressor (saturated_Discharge_Temperature), 4. the motor speed of the compressor (motor_Speed), 5. an outlet temperature of water to the condenser (outlet_Temperature), 6. an inlet temperature of water to the condenser (inlet_Temperature), 7. the temperature for the measured saturation pressure at which the refrigerant boils into its vapor phase (saturated_Suction_Temperature), 8. a total active power which is the sum of all measured power values (total_Active_Power), 9. a motor speed in percent of condenser fan 2 (condenser_Device_2_Motor_Speed_Percentage), 10. a motor speed in percent of condenser fan 3 (condenser_Device_3_Motor_Speed_Percentage),

[0109] Preferably, the ML model is a supervised ML model. Examples of supervised ML models are regression trees, Random forest, Gradient Boosting Machines (GBM), Artificial Neural Networks, and support Vector Machine (SVM).

[0110] The condenser power is related to the calculated condenser fan speed through the formula:

[0111] The prediction of compressor power, compressor cooling capacity and condenser power, are the inputs for simulating the compressor and condenser energy consumption for a range of condensing temperatures from a minimum to a maximum condenser operating temperature. With this for every row of operating data it is possible to determine the optimal condensing temperature for which the total power is minimized.

[0112] As shown in Fig. 11, the following steps are performed: 1. predicting compressor power, compressor cooling capacity, and condenser power through ML. 2. simulating energy consumption for various condensing temperatures. 3. calculating through ML the temperature that minimizes power consumption.

[0113] Prediction of compressor power, compressor cooling capacity and condenser power may be calculated though ML, as discussed above.

[0114] The calculation of optimal condensing temperature may also be outputted by a trained ML model.

[0115] As an example, the training data input to such ML model may be: 1. compressor power (resulting from ML model), 2. compressor compressor cooling capacity (resulting from ML model), 3. condenser power (resulting from ML model), 4. condensing temperature arrays (range from minimum to maximum of condensing temperature in which the condenser can operate), 5. the temperature for the measured saturation pressure at which the refrigerant boils into its vapor phase (saturated_Suction_Temperature), 6. the saturated discharge temperature of the refrigerant when being discharged from the compressor (saturated_Discharge_Temperature), 7. the ambient air temperature (ambient Air Temperature_1 / wet_Bulb Temperature_1), 8. a condenser inlet temperature (condenser_Inlet Temperature_1), and 9. a condenser outlet temperature (condenser_Outlet Temperature_1).

[0116] The training data set 1-9 is directly or indirectly measured though sensors. The data originating from sensors may be logged for at least 1 year, in order to take into consideration variations of measurement values which are dependent on the season of the year in which the measurements are collected. The data are collected with a resolution between 1 second to 1 minute, preferably between 10 seconds to 30 seconds, more preferably every approximately 20 seconds.

[0117] Preferably, the ML model for the calculation of the optimal condensing temperature is a supervised ML model. Example of suitable supervised ML model are Random Forest, Artificial Neural Network, Gradient Boosting Machines (GBM), and Support Vector Machines (SVM)

[0118] The trained artificial intelligence engine is able to output the optimal condensing temperature when inputted with the compressor power, compressor cooling capacity condenser power, condensing temperature arrays (range from minimum to maximum of condensing temperature in which the condenser can operate), the saturated suction temperature (saturated_Suction_Temperature), the saturated discharge temperature (saturated_Discharge_Temperature), the ambient air temperature (ambient Air Temperature_1 / wet_Bulb Temperature_1), a condenser inlet temperature (condenser_Inlet Temperature_1), and a condenser outlet temperature (condenser_Outlet Temperature_1).

[0119] Advantages of using a full machine learning approach for the prediction of compressor power, compressor cooling capacity, condenser power and prediction of the optimal condensing temperature would allow to leverage historical data of compressor and condenser performance without relying on a digital twins and without the need of correcting such digital twin, due to fluctuations of the digital twin depending on the season in which the refrigeration plant is operating.

[0120] Although specific embodiments have been described above, these embodiments are not intended to limit the scope of the present disclosure, even where only a single embodiment is described with respect to a particular feature. Examples of features provided in the disclosure are intended to be illustrative rather than restrictive unless stated otherwise. The above description is intended to cover such alternatives, modifications, and equivalents as would be apparent to a person skilled in the art having the benefit of this disclosure.

[0121] The scope of the present disclosure includes any feature or combination of features disclosed herein (either explicitly or implicitly), or any generalization thereof, whether or not it mitigates any or all of the problems addressed herein. In particular, with reference to the appended claims, features from dependent claims maybe combined with those of the independent claims and features from respective independent claims may be combined in any appropriate manner and not merely in the specific combinations enumerated in the appended claims.

Claims

1. Method for determining an optimal condensing temperature of a refrigerant being used in a compressor-condenser-arrangement, said refrigerant being provided to be compressed by the compressor (12) and being provided to be condensed in the condenser (14), the condenser (14) comprising one or more than one fan (30, 32), the method comprising the following steps: a) determining an actual operating condition of the compressor-condenser-arrangement; b) determining base-values of compressor-operation comprising - a base-value of compressor-operation for the actual operating condition of the compressor-condenser-arrangement, the base-value of compressor-operation for the actual operating condition of the compressor-condenser-arrangement being associated with a compressor driving power for the actual operating condition of the compressor-condenser-arrangement, and - additional base-values of compressor-operation for operating conditions of the compressor-condenser-arrangement other than the actual operating condition of the compressor-condenser-arrangement, the additional base-values of compressor-operation for the operating conditions of the compressor-condenser-arrangement other than the actual operating condition of the compressor-condenser-arrangement being associated with compressor driving powers for the operating conditions of the compressor-condenser-arrangement other than the actual operating condition of the compressor-condenser-arrangement; c) determining base-values of condenser-fan-operation comprising - a base-value of condenser-fan-operation for the actual operating condition of the compressor-condenser-arrangement, the base-value of condenser-fan-operation for the actual operating condition of the compressor-condenser-arrangement being associated with a condenser-fan driving power for the actual operating condition of the compressor-condenser-arrangement, and - additional base-values of condenser-fan-operation for the operating conditions of the compressor-condenser-arrangement other than the actual operating condition of the compressor-condenser-arrangement, the additional base-values of condenser-fan-operation for the operating conditions of the compressor-condenser-arrangement other than the actual operating condition of the compressor-condenser-arrangement being associated with condenser-fan driving powers for the operating conditions of the compressor-condenser-arrangement other than the actual operating condition of the compressor-condenser-arrangement; d) determining an actual value of compressor-operation for the actual operating condition of the compressor and calibrating the base-values of compressor-operation using the actual value of compressor-operation, receiving as a result calibrated values of compressor-operation, and / or determining an actual value of condenser-operation for the actual operating condition of the condenser and calibrating the base-values of condenser-fan-operation using the actual value of condenser-operation, receiving as a result calibrated values of condenser-operation; e) determining a total power for the actual operating condition of the compressor-condenser-arrangement and for the operating conditions of the compressor-condenser-arrangement other than the actual operating condition of the compressor-condenser-arrangement being a sum of the compressor driving power and the condenser-fan driving power for the actual operating condition of the compressor-condenser-arrangement and the operating conditions of the compressor-condenser-arrangement other than the actual operating condition of the compressor-condenser-arrangement - using the base-values of compressor-operation and the calibrated values of condenser-operation, or - using the calibrated values of compressor-operation and the base-values of condenser-fan-operation, or - using the calibrated values of compressor-operation and the calibrated values of condenser-operation; f) determining the operating condition of the compressor-condenser-arrangement for which the total power is minimized and determining the condensing temperature for this operating condition as the optimal condensing temperature.

2. Method according to claim 1, wherein step a) comprises: measuring, by direct or indirect measurement, actual measured operating conditions of the compressor-condenser-arrangement, in particular an actual measured condensing temperature of the refrigerant and an actual measured compressor driving power and an actual measured condenser fan speed and step b) comprises: b-1) determining an actual calculated compressor cooling capacity for the actual operating conditions and an actual calculated compressor driving power for the actual operating conditions; b-2) determining calculated deviating compressor driving powers for condensing temperatures higher and lower than the actual condensing-temperature of the refrigerant said calculated deviating compressor driving powers delivering the actual calculated compressor cooling capacity for the condensing temperatures higher and lower than the actual condensing temperature of the refrigerant; and step c) comprises determining an actual calculated condenser fan speed for the actual measured condensing temperature of the refrigerant and determining calculated deviating condenser fan speeds for the condensing temperatures higher and lower than the actual condensing temperature of the refrigerant; step d) comprises d-1) determining a compressor driving power relationship between the actual measured compressor driving power and the actual calculated compressor driving power. d-2) Calibrating the actual calculated compressor driving power and all calculated deviating compressor driving powers based on the compressor driving power relationship receiving calibrated calculated compressor driving powers for the actual measured condensing temperature and for the condensing temperatures higher and lower than the actual condensing temperature; d-3) Determining a fan speed relationship between the actual measured condenser fan speed and the actual calculated condenser fan speed; d-4) Calibrating the actual calculated condenser fan speed and all calculated deviating condenser fan speeds based on the fan speed relationship receiving calibrated calculated condenser fan speeds for the actual measured condensing temperature and for the condensing temperatures higher and lower than the actual condensing temperature; and step e) comprises e-1) determining calculated calibrated fan powers based on the calibrated calculated condenser fan speeds for the actual measured condensing temperature and for the condensing temperatures higher and lower than the actual condensing temperature; e-2) adding each of the calibrated calculated compressor driving powers for the actual measured condensing temperature and for the condensing temperatures higher and lower than the actual condensing temperature to the corresponding calculated calibrated fan powers for the actual measured condensing temperature and for the condensing temperatures higher and lower than the actual condensing temperature receiving a total power for each of the actual measured condensing temperature and of the condensing temperatures higher and lower than the actual condensing temperature; and step f) comprises determining the temperature of the actual measured condensing temperature and of the condensing temperatures higher and lower than the actual condensing temperature as the optimal condensing temperature for which the total power is minimized.

3. Method according to claim 2, wherein the step of measuring of the actual operating conditions comprises direct or indirect measuring of an ambient temperature and / or a wet bulb temperature, direct or indirect measuring of an evaporating temperature and direct or indirect measuring of a compressor speed and / or the compressor driving power and / or the condenser fan speed and / or the condenser fan power.

4. Method according to one of the preceding claims, wherein step b) is performed using predetermined values, in particular values delivered by the manufacturer of the compressor, which are dependent on the respective compressor, and / or step c) is performed using predetermined values, in particular values delivered by the manufacturer of the condenser, which are dependent on the respective condenser.

5. Method according to one of claims 1 to 3, wherein step b) and / or step c) is / are performed using an artificial intelligence engine.

6. Method according to one of claims 2 to 4, wherein the compressor driving power relationship between the actual measured compressor driving power and the actual calculated compressor driving power is the quotient of the actual measured compressor driving power and the actual calculated compressor driving power.

7. Method according to one of claims 2 to 4 or 6, wherein the fan speed relationship between the actual measured condenser fan speed and the actual calculated condenser fan speed is determined by calculating the reduction in a condenser capacity at the actual measured conditions that leads to a calculated fan speed that is equal to the measured fan speed.

8. Method according to one of the preceding claims wherein step b) and / or step c) is performed using polynomial calculations.

9. Method according to claim 5, wherein the artificial intelligence engine uses, in particular in step b), a sklearn non-linear regression and a motor speed, a saturated suction temperature and a saturated discharge temperature of the compressor.

10. Method according to claims 5, wherein the artificial intelligence engine uses, in particular in step c) regression trees, Random forest, Gradient Boosting Machines (GBM), Artificial Neural Networks, and support Vector Machine (SVM).

11. Method according to one of the preceding claims, wherein the condenser is an evaporative condenser and the method comprises furthermore step of determining the expenses for a coolant, in particular for water, needed to cool the condenser for each of the actual measured condensing temperature and of the condensing temperatures higher and lower than the actual condensing temperature, wherein the expenses for the coolant are considered when determining the optimal condensing temperature.

12. Method according to one of the preceding claims, wherein the method is implemented on a computer.

13. An apparatus adapted to carry out the method according to one of the preceding claims.

14. A computer program comprising instructions which when executed by a processing system cause the processing system to perform a method according to one of claims 1 - 12.

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