DE102021211280B4 - Method and device for monitoring a refrigerant system - Google Patents

Abstract

The invention relates to a method and a device for monitoring a refrigerant system (2) with a circuit in which a refrigerant is circulated by means of a compressor (4), the compressor (4) having an instantaneous electrical power consumption (Pel) and a momentary mass flow (n) of the refrigerant, the refrigerant also having a low pressure (pein) and a suction gas temperature (Tein) on a suction side of the compressor (4) and a high pressure (poff) and a hot gas temperature (Toff) on a pressure side, and Power consumption (Pel), mass flow (m), low pressure (pein), suction gas temperature (Tein), high pressure (paus) and hot gas temperature (Toff) represent operating parameters and at least some of these operating parameters are recorded during operation. The momentary isentropic actual efficiency (ηis) of the compressor (4) is determined from the measured values of these operating parameters and a momentary actual state of the compressor (4) is concluded from this or from an actual variable derived therefrom. This makes it possible to determine the actual state of the compressor (4) with little effort.

Description

The invention relates to a method and a device for monitoring a refrigerant system with a circuit in which a refrigerant is conveyed by means of a compressor.

The compressor is one of the central components in a refrigeration system and largely determines the efficiency of the refrigeration system. Due to its moving components, it is also subject to wear and tear. There is therefore a fundamental need to check the compressor with regard to its efficiency and functionality.

From the WO 2004/099683 A describes a condition monitoring system for a refrigerant system. Among other things, the determination of an actual condition of the compressor based on the measurement of the suction-side and pressure-side pressure and temperature values can also be derived from this. Here, the fourth is calculated from three measured parameters and compared with a theoretical target value. In particular, the temperature on the pressure side, also known as the hot gas temperature, is determined from the other values and compared with a setpoint hot gas temperature. The mathematical determination of the hot gas temperature is sometimes difficult, among other things because the hot gas temperature can be subject to considerable fluctuations during operation.

From the EP 3450 880 B1 is the predictive maintenance of a compressor of an air conditioning system in a rail vehicle. For this purpose, a so-called health index is determined, which includes an isentropic efficiency.

From the JP 2012 - 172 957 A the monitoring of a compressor can be found in which pressure and temperature values are evaluated.

Proceeding from this, the invention is based on the object of enabling monitoring of a refrigeration system, specifically a compressor of such a refrigeration system, in a simple manner.

The object is achieved according to the invention by a method and by a device for monitoring a refrigerant system which has a circuit in which a refrigerant is conveyed by means of a compressor during operation. During operation, the compressor has an instantaneous electrical power consumption and an instantaneous speed and delivers an instantaneous mass flow. The refrigerant also has a low pressure and a suction gas temperature on an inlet or suction side of the compressor and a high pressure and a hot gas temperature on an outlet or pressure side. These parameters, namely power consumption, speed, mass flow, low pressure, high pressure, suction gas temperature and hot gas temperature form the operating parameters of the compressor. At least some of these operating parameters are recorded during operation. Either they are measured directly or they are derived from measured values. In particular, the pressures and the temperatures are directly measured by means of pressure sensors and temperature sensors. The electrical power consumption—insofar as it is used—is typically determined from a measured current value and optionally supplemented by a measured voltage value. Alternatively, it is determined from tables or curves stored - e.g. by the manufacturer of the compressor - depending on pressures, temperatures and / or the speed. A mass flow meter is typically used for the mass flow, if this is used. However, no mass flow is preferably measured. Rather, this is determined otherwise if necessary.

The isentropic actual efficiency of the compressor is determined from the values recorded during operation for the operating parameters. From this or from an actual variable derived therefrom, a current actual state of the compressor is inferred. In the simplest case, the actual efficiency of the compressor is used directly as a measure of the actual state.

The term "currently" refers to a current operating situation. The corresponding instantaneous parameters/parameter values/variables are also referred to as actual parameters/actual parameter values or actual variables.

The actual state is generally set in relation to a target state and compared with it. The target state, specifically the value of the isentropic target efficiency, is typically known as a function of the current operating conditions and is specified, for example, for the compressor used, specifically by the manufacturer of the compressor. Alternatively, the target state is determined from the values for mass flow and power consumption provided or calculated by the manufacturer, for example, as well as the pressure and temperature values. This comparison is used to draw conclusions about the general condition of the compressor. In the event of an impermissible deviation, a note is issued, for example a recommendation for action.

The particular advantage of determining the isentropic actual efficiency, especially in comparison to that known from the prior art A comparison between the hot-gas temperature calculated from the operating parameters and a theoretical hot-gas temperature shows that the hot-gas temperature is subject to a wide range of fluctuation and is highly sensitive as a function of the measured pressure and temperature values, making it error-prone overall. In contrast, a derivation of the compressor status based on the determined isentropic efficiency is less sensitive and therefore offers a comparable value that can be used in the same way for different boundary conditions. Overall, the effort for the calculation and evaluation is simpler.

mit
η_is = isentroper Wirkungsgrad des Verdichters (des Verdichtungsprozesses)
h_is = spezifische Enthalpie des Kältemittels ausgangsseitig eines isentropen Verdichtungsprozesses,
h_ein = spezifische momentane Enthalpie des Kältemittels am Eingang des Verdichters im Betrieb,
h_aus = spezifische momentane Enthalpie des Kältemittels am Ausgang des Verdichters im Betrieb.The isentropic efficiency indicates the relationship between the real actual compressor work and a theoretical compressor work under isentropic conditions. The following relationship applies to the efficiency: $$n_{is}=\frac{H_{is}-H_{ein}}{H_{a\mathrm{and}s}-H_{ein}}$$

with
η _is = isentropic efficiency of the compressor (of the compression process)
h _is = specific enthalpy of the refrigerant on the outlet side of an isentropic compression process,
h _in = specific instantaneous enthalpy of the refrigerant at the compressor inlet during operation,
h _out = specific momentary enthalpy of the refrigerant at the outlet of the compressor during operation.

In a preferred embodiment, the actual efficiency is determined from the instantaneous values determined for the low pressure, the high pressure, the suction gas temperature and the hot gas temperature. From these determined values, the specific instantaneous enthalpy of the refrigerant at the inlet and outlet of the compressor and the specific enthalpy of the refrigerant used on the outlet side of an isentropic compression process are determined for determining the actual efficiency according to the above formula. For this purpose, the corresponding specific enthalpies are determined from the instantaneous (measured) values for the low pressure, high pressure as well as for the suction gas temperature and for the hot gas temperature with the help of tables or known functions. The specific enthalpy is a variable dependent on pressure and temperature. The specific enthalpy also depends in particular on the refrigerant used. For example, the specific enthalpy is determined using p, h diagrams/tables known for the refrigerant used. Look-up tables or a suitable calculation function are stored to determine the specific enthalpies.

Determining the actual efficiency on the basis of the temperature values and pressure values on the input and output side is the preferred variant, since these values are typically also regularly recorded in existing systems. In this respect, the method proposed here can also be easily retrofitted to existing systems, for example by means of a suitable software update.

In an expedient embodiment, the actual efficiency, as determined in particular according to equation (1) above, is compared with a target efficiency. If the actual efficiency deviates from the setpoint efficiency by a predetermined threshold value, an impermissible, defective condition of the compressor, hereinafter referred to as “bad condition”, is concluded and an error warning is issued. The threshold value is either fixed by the manufacturer or can be parameterized by the user. For example, an error warning is issued if there is a deviation of more than 5% or more than 10%.

According to a first variant, known values for the compressor used are used for the setpoint efficiency. The target efficiency is often specified by the compressor manufacturer, e.g. in the form of tables or diagrams.

In particular, if such values are not available, according to a preferred variant, the target efficiency is determined specifically by calculation. This is done in particular with the help of the following formulas and on the basis of a mass flow and an electrical power consumption. The mass flow and the power consumption are preferably not measured. The required data for the mass flow and the electrical power consumption are preferably calculated or taken from tables, e.g. from the manufacturer of the compressor, and are therefore compressor-specific. They are typically dependent, among other things, on the instantaneous pressure and temperature values of the refrigerant on the inlet side. An adiabatic compressor is used as a good approximation to determine (calculate) the target efficiency.

$${\eta }_{is,soll}=\frac{h_{is}-h_{ein}}{h_{aus,soll}-h_{ein}}$$

The target efficiency is determined in particular according to the following formulas: $$H_{a\mathrm{and}s,sOll}=H_{ein}+\frac{P_{el,be\mathrm{right}}}{m_{be\mathrm{right}}}$$

$$n_{is,sOll}=\frac{H_{is}-H_{ein}}{H_{a\mathrm{and}s,sOll}-H_{ein}}$$

• h_{aus, soll} = die ermittelte / berechnete spezifische momentane Soll-Enthalpie am Ausgang des Verdichters,
• h_ein = die spezifische momentane Enthalpie des Kältemittels am Eingang des Verdichters im Betrieb,
• h_is = die spezifische Enthalpie des Kältemittels ausgangsseitig eines isentropen Verdichtungsprozesses,
• η_is,soll = der isentrope Soll-Wirkungsgrad des Verdichters (des Verdichtungsprozesses)
• P_{el. ber} = der aus den (Hersteller-) Angaben ermittelte / berechnete elektrische Wirkungsgrad,
• m_ber = der aus den (Hersteller-) Angaben ermittelte / berechnete Massenstrom.

Here are:

• h _{out, target} = the determined / calculated specific instantaneous target enthalpy at the outlet of the compressor,
• h _on = the specific instantaneous enthalpy of the refrigerant at the inlet of the compressor during operation,
• h _is = the specific enthalpy of the refrigerant on the outlet side of an isentropic compression process,
• η _is,soll = the isentropic desired efficiency of the compressor (of the compression process)
• P _{el. ber} = the electrical efficiency determined / calculated from the (manufacturer) information,
• m _ber = the mass flow determined / calculated from the (manufacturer) information.

Alternatively, the values for the electrical power consumption and for the mass flow can also be measured. However, this is laborious. Therefore, the values - as explained above - are preferably not measured, but determined in particular using information from the manufacturer of the compressor - depending on the current pressures / temperatures / compressor speed - taken, for example, using tables / diagrams / functions and/or e.g. by interpolation or extrapolation calculated.

As an alternative to determining a compressor-specific setpoint efficiency, the setpoint efficiency can be defined independently of the compressor actually used in the refrigerant system. In particular, the target efficiency is therefore independent of specific target data of the compressor actually used. In this embodiment, a fixed target efficiency of at least 55%, for example, is assumed. A calculation and/or recourse to e.g. manufacturer information is therefore not necessary.

This is based on the consideration that the compressors used today regularly have a sufficiently high quality and, at least in the initial state, have an isentropic efficiency which, independent of the compressor, lies within a narrow efficiency window. Furthermore, this approach assumes that if the value for the efficiency of the compressor falls below the value specified independently of the compressor, this is unacceptable and generally leads to excessive energy consumption.

In this way, for example, defective compressors that already show insufficient efficiency in the initial state - possibly after a run-in period after commissioning - can be identified and replaced. It is generally possible to identify a compressor that is already defective in the initial state and is not limited to this variant with the fixed value for the efficiency.

According to the invention, the instantaneous actual electrical power requirement is inferred from the determined actual efficiency. The actual state is then deduced from a comparison with a target electrical power consumption. The actual power requirement is therefore a derived actual variable. This measure can therefore directly identify an increased energy requirement. An increased energy requirement indicates wear and/or a lack of functionality or other errors. In particular, a prognosis for a remaining service life is also derived from the actual power requirement, in particular from a change over time, and is output or stored as information. Alternatively, a recommendation for action is made directly on the basis of the determined actual power requirement, without a remaining service life being determined.

The determination of the actual power requirement is carried out in particular according to the following formula: $$P_{el}=\frac{m_{be\mathrm{right}}\cdot \left(H_{is}-H_{ein}\right)}{n_{is}}$$

und Einsetzen in Gleichung (3) erhält man $${\eta }_{is,soll}=\frac{m_{ber}\cdot \left(h_{is}-h_{ein}\right)}{P_{el,ber}}$$

analog zu Gleichung (4). P_el ist die momentane elektrische Leistungsaufnahme. Dabei wird insbesondere angenommen, dass der Massenstrom auch bei Verschleiß konstant bleibt.By rearranging equation (2) above $$H_{a\mathrm{and}s,sOll}-H_{ein}=\frac{P_{ei,be\mathrm{right}}}{m_{be\mathrm{right}}}$$

and substituting into equation (3) one obtains $$n_{is,sOll}=\frac{m_{be\mathrm{right}}\cdot \left(H_{is}-H_{ein}\right)}{P_{el,be\mathrm{right}}}$$

analogous to equation (4). P _el is the instantaneous electrical power consumption. In particular, it is assumed that the mass flow remains constant even with wear.

In a preferred embodiment, the method presented here is used as part of a condition monitoring system and is also used in particular to estimate or determine a remaining service life of the compressor. For this purpose, in particular the time profile of the determined actual efficiencies or the time profile of the actual variable derived therefrom, such as the actual power requirement, is generally evaluated.

As an alternative to this, in a preferred embodiment, the remaining service life is not determined and instructions for action are issued immediately.

In a preferred embodiment, the actual efficiency and the actual state of the compressor are determined by means of a decentralized evaluation unit that is part of the refrigerant system. The evaluation therefore takes place directly within the refrigeration system itself. The evaluation unit is integrated, for example, in a control unit that controls the operation and in particular the circuit of the refrigeration system.

As an alternative to this, the actual state of the compressor is determined and, if necessary, the actual efficiency is also determined in a central evaluation unit that is remote from the refrigerant system. This central evaluation unit is, for example, at a different location than the refrigerant system and is, for example, part of a cloud solution and/or part of a central server of the refrigeration system manufacturer. Alternatively, the central evaluation unit is responsible for several systems/refrigerant systems within a building. For example, it is part of a smart home system.

An embodiment of the invention is explained in more detail below with reference to the single figure. This shows a section of a refrigerant system in a greatly simplified representation.

The refrigerant system 2 shown in detail has a compressor 4, which is arranged in a refrigerant circuit 6 and is used in this for compressing and circulating a refrigerant. Such a refrigerant circuit 6 is known in principle and, in addition to the compressor 4, comprises a condenser, a throttling element and an evaporator, which are arranged downstream of the compressor in the flow direction of the refrigerant, as further main components which are not shown here.

The refrigerant system 2 also includes pressure sensors 8 and temperature sensors 10, which are each arranged on the suction side and pressure side at the inlet and at the outlet of the compressor 4. These sensors 8, 10 are used to determine a current intake gas temperature T _in and a low pressure p _in on the inlet side and a current hot gas temperature T _out and a high pressure p _out on the outlet side, preferably by measuring. The measured instantaneous values (=actual values) of these operating parameters are transmitted to an evaluation unit 12, which is part of the refrigerant system 2, for example, and is integrated into it as a decentralized evaluation unit. Alternatively, it is embodied outside of the refrigerant system 2 and is only in communication with it and is embodied as a central evaluation unit.

The evaluation unit 12 contains a computing unit 14 which determines the isentropic actual efficiency η _is from the instantaneous values of the operating parameters. Furthermore, a comparison unit 16 is integrated, within which the actual efficiency η _{is is} compared with a setpoint efficiency η setpoint. Depending on the comparison, further actions are preferably initiated, such as issuing a report on the current state of the compressor 4 or a recommendation for action, such as maintenance or replacement of the compressor 4.

Furthermore, in a preferred embodiment, the evaluation unit 12 is also designed to predict a remaining service life of the compressor 4 on the basis of the determined actual state. For this purpose, in particular, the actual degrees of efficiency η _is determined over time and any actual variables derived therefrom are stored and evaluated with their progression over time.

The compressor 4 is checked by calculating or determining the actual efficiency η _{is ,} for example, at predetermined time intervals and thus more or less continuously during operation. In particular, the check is carried out at least whenever the compressor 4 is activated and, in particular, is in an approximately stationary operating state.

As an alternative to evaluating the specified temperatures T and pressures p, there is also the possibility of determining a mass flow m of the refrigerant and an instantaneous electrical power consumption P _el and of determining the actual efficiency η _is from this. The instantaneous electrical power consumption P _el also defines the instantaneous electrical power requirement. The mass flow is measured at a suitable point in the cycle, for example after the condenser, since there are good conditions for measuring the mass flow m. Alternatively, the mass flow m is measured in the area of the compressor, specifically at the compressor inlet.

A data unit 18 additionally provides data for the comparison unit 16, which are either directly the desired data, such as, for example, desired data for a compressor type used, specifically a type-specific desired efficiency η _is,soll . It can be provided that such setpoint efficiencies η _is, setpoint are stored in a table or by polynomials, namely for different temperatures and pressures on the inlet and outlet side and/or in tables or polynomials for different speeds of the compressor.

Alternatively or additionally, the data unit 18 also contains data about the compressor 4 actually used, for example performance data such as an isentropic efficiency specified by the manufacturer.

The setpoint efficiency η _{is, soll} can additionally or alternatively also be determined from the instantaneous mass flow m and a theoretical compressor output, as specified, for example, by the manufacturer of the compressor 4 .

If the comparison between the determined actual efficiency η _is and the theoretical target efficiency η _{is shows} a deviation that is, for example, above a specified limit value g (η _{is, target} - η _is > g), then a lack of functionality is considered to be Actual state of the compressor 4 closed and there is a risk that the compressor 4 can fail in the future. A preventive replacement of the compressor 4 can then be proposed via a corresponding error message in order to avoid a failure of the refrigerant system 2 .

A particular advantage of the method described here and the system described here can be seen in the fact that only a small number of sensors are required, which are typically already available anyway (pressure and temperature sensors 8, 10). A low computing capacity is also sufficient, since essentially only the instantaneous values or also only a few values are considered, with the few values preferably not being recorded continuously, but rather only at regular time intervals. It is not necessary to take (further) environmental parameters into account, and it is preferably not provided either.

In comparison to the concept in which an actual state of the compressor 4 is deduced based on a hot gas temperature comparison between a calculated and a theoretical hot gas temperature, there are several significant advantages. On the one hand, in the variant described here, an assessment and determination of the actual state of the compressor is possible without special knowledge of the performance parameters of the compressor used and is therefore possible in particular without specific manufacturer information. Rather, the ascertained actual efficiency η _is directly indicates the actual state of the compressor 4 .

The evaluation based on the hot gas temperature is also fundamentally much more difficult, as this is subject to significant fluctuations during operation depending on the current operating situation. For example, the hot gas temperature in a system can vary between 65 °C and 120 °C, depending on the design of the compressor, the speed and the refrigerant used. In contrast, a variance in the range of, for example, 60%-74% can be expected for the efficiency η _is at most. It is generally assumed that the actual efficiency η _is should generally be over 65%.

Finally, a further advantage of determining the actual efficiency η _is is that it gives a direct indication of the electrical power requirement of the compressor 4 , in particular in relation to an optimal state of the compressor 4 . The instantaneous electrical power requirement of the compressor 4 _is therefore preferably also determined directly from the actual efficiency η is . No special, complex calculations are required for this. There is a predetermined correlation between the actual efficiency η _is and the instantaneous electrical power consumption, so that a drop in the actual efficiency η _is can simultaneously indicate a higher power requirement.

In particular, no direct measurement of the power consumption of the compressor is provided. Appropriate measuring devices would be required for this purpose, for example for measuring the current of the compressor current on the input side. In some systems, especially in systems with a lower capacity, e.g. up to 6 kW or up to 9 kW heating capacity of the refrigerant system, such measuring devices are not provided and would lead to additional costs.

Determining the instantaneous power requirement allows an immediate statement as to whether the compressor 4 should be replaced. A knowledge or a correlation to a remaining service life, which would first have to be determined, is not required and is preferably not carried out. Rather, based on the electrical power requirement determined, it is directly estimated whether the compressor 4 used is insufficient and would, for example, lead to an unreasonably high consumption.

Overall, the method described here achieves a simple determination of the actual state of the compressor 4 and a recommendation for action is derived from this if it is found that the compressor 4 has a poor performance.

Reference List

2

refrigerant system

4

compressor

6

cycle

8th

pressure sensor

10

temperature sensor

12

evaluation unit

14

unit of account

16

comparison unit

18

data unit

thein

suction gas temperature

dew

hot gas temperature

pain

low pressure

pause

high pressure

m

mass flow

Pel

electric power consumption

ηis

isentropic actual efficiency

ηis,should

isentropic target efficiency

G

threshold

Claims (10)

Method for monitoring a refrigerant system (2) with a circuit in which a refrigerant is pumped by means of a compressor (4), the compressor (4) having an instantaneous electrical power consumption (P _el ) and an instantaneous mass flow (n) of the Promotes the refrigerant, the refrigerant also having a low pressure (p _in ) and a suction gas temperature (T _in ) on a suction side of the compressor (4) and a high pressure (p _off ) and a hot gas temperature (T _off ) on a pressure side, and power consumption ( P _el ), mass flow (n), low pressure (p _in ), suction gas temperature (T _in ), high pressure (p _out ) and hot gas temperature (T _out ) represent operating parameters and at least some of these operating parameters are recorded during operation, characterized in that from the values of these operating parameters determine the current isentropic actual efficiency (η _is ) of the compressor (4) and from this or from an actual variable derived therefrom a current actual state of the compressor (4) is concluded, with the actual Efficiency (η _is ) the actual electrical power requirement is inferred as a derived actual variable and the actual state is inferred by a comparison with a target electrical power requirement. procedure after claim 1 , characterized in that the actual efficiency (η _is ) from low pressure (p _in ), suction gas temperature (T _in ), high pressure (p _out ) and hot gas temperature (T _out ) is determined. Method according to one of the preceding claims, characterized in that the actual efficiency (η _is ) is compared with a setpoint efficiency (η _is,setpoint ) and, if there is a deviation by a predetermined threshold value (g) of, for example, 5%, indicates a bad state of the compressor (4) is closed and an error warning is issued. procedure after claim 3 , in which the desired efficiency (η _is,soll ) is determined, in particular on the basis of a mass flow (m) and the electrical power consumption (P _el ) of the compressor (4). procedure after claim 3 , characterized in that the desired efficiency (η _is,soll ) is independent of the compressor (4) used. Method according to one of the preceding claims, characterized in that the remaining service life of the compressor (4) is determined on the basis of the actual efficiency (η _is ) or the actual variable derived therefrom, such as the actual power requirement. Method according to one of the preceding claims, characterized in that the determined actual state is used to deduce a remaining service life of the compressor (4) and for this purpose in particular the time profile of the determined actual efficiencies (η _is ) or the actual variable derived therefrom is taken into account becomes. Method according to one of the preceding claims, characterized in that the actual efficiency (η _is ) and the actual state of the compressor (4) are determined by means of a decentralized evaluation unit (12) as part of the refrigerant system (2). Procedure according to one of Claims 1 until 7 , characterized in that the determination of the actual state of the compressor (4) and, if necessary, also the determination of the actual efficiency (η _is ) within a central evaluation unit (12) that is remote from the refrigerant system (2). Device for monitoring a refrigerant system (2), which has a circuit in which a refrigerant is circulated by means of a compressor (4) during operation, wherein during operation the compressor (4) has an instantaneous electrical power consumption (P _el ) and a momentary mass flow (n) of the refrigerant and, furthermore, during operation, the refrigerant has a low pressure (p _in ) and a suction gas temperature (T _in ) on a suction side of the compressor (4) and a high pressure (p _off ) on a pressure side of the compressor (4). ) and a Hot gas temperature (T _out ) and power consumption (P _el ), mass flow (m), low pressure (p _in ), suction gas temperature (T _in ), high pressure (p _out ) and hot gas temperature (T _out ) represent operating parameters and the refrigerant system ( 2) has devices for detecting at least some of these operating parameters during operation, characterized in that an evaluation unit (12) is provided, which is set up in such a way that it calculates the current isentropic actual efficiency (η _is ) of the compressor from the values of these operating parameters (4) determined and from this or from an actual variable derived therefrom a current actual state of the compressor (4) is concluded, the actual efficiency (η _is ) being used to infer the actual electrical power requirement as a derived actual variable and the actual state is inferred by a comparison with a target electrical power requirement.

Images