EP2196740B1 - Method for determining the performance of a cooling machine - Google Patents

Description

The present invention relates to a method for determining the coefficient of performance of a refrigerating machine, in particular a heat pump, comprising a refrigerant having a closed circuit in which an evaporator, a compressor, a condenser and an expansion valve are arranged.

The coefficient of performance (COP) of a chiller is the quotient of the heating power of the chiller and the recorded electrical power of the chiller. Conventionally, the electric power consumption of the refrigerating machine is detected by an electricity meter, while the heating power of the refrigerator is detected by a temperature and volume flow measurement on the water side of the refrigerant circuit, i. So behind the condenser, is determined.

Also known is a method in which, with the aid of two pressure sensors and three temperature sensors, the temperatures and pressures of the refrigerant are detected at different points of the circuit and used to calculate the coefficient of performance. By means of an electricity meter also the electrical power consumption of the chiller is detected. By multiplying the coefficient of performance with the recorded electrical power, the heating power of the chiller can then be calculated.

As problematic proves in the known methods or refrigeration that both the electricity meter and the pressure sensors represent a significant cost factor.

The EP 0 100 210 A2 discloses a method for determining a coefficient of performance of a refrigeration-conditioned air conditioner, in which four temperatures of the refrigerant are determined by means of at least four temperature sensors, from which enthalpies of the circuit can be calculated, which are used to determine the coefficient of performance COP of the refrigerator.

The US 5,735,134 A teaches a method of optimizing a coefficient of performance of an air conditioner using a single measured temperature or pressure value. This method assumes that the maximum performance index is already known, so that when measuring the temperature or pressure value, the ideal operating point of the air conditioning system can be set on the basis of previously known values.

The EP 1 914 481 A2 describes an apparatus and method for checking a refrigeration cycle. In this method, a so-called "figure of merit" is calculated, which is coupled to the efficiency, ie the performance of such a system. In the refrigeration cycle, temperatures and pressures of the refrigerant are determined by means of temperature and pressure sensors. From the determined temperature and pressure values enthalpies of the circuit can be determined, from which then an efficiency factor of the chiller is determined.

The JP 2004 176938 A discloses a method for controlling the coefficient of performance of a refrigeration system in which the coefficient of performance is determined by means of two temperature sensors and two pressure sensors.

The invention has for its object to provide a cost-effective method for determining the coefficient of performance of a chiller.

To solve the problem, a method with the features of claim 1 is provided.

In the method according to claim 1 of the invention for determining the coefficient of performance of a refrigerator, in particular a heat pump, comprising a refrigerant having a closed circuit in which an evaporator, a compressor, a condenser and an expansion valve are arranged, with the help of exactly three temperature sensors , which are arranged in the circuit, determined three temperatures of the refrigerant. From the determined refrigerant temperatures, enthalpies and pressures of the circuit are calculated, and from differences in the calculated enthalpies, both the heating power and the consumed electric power of the refrigerator are calculated. From the quotient of the calculated heating power and the calculated absorbed electrical power finally the coefficient of performance of the chiller is determined.

In other words, in the method according to the invention, the coefficient of performance of the refrigerating machine is determined exclusively on the basis of temperature values supplied by three temperature sensors arranged in the refrigerant circuit, assuming some knowledge of the thermodynamic properties of the system, in particular of the refrigerant and of the compressor becomes. By measuring the refrigerant temperatures at three different locations of the refrigerant circuit, a minimum of refrigerant circuit information necessary to determine the coefficient of performance of the refrigerator is determined.

Use of additional sensors, e.g. further temperature sensors or pressure sensors, which are typically about ten times more expensive than temperature sensors, is therefore generally not required. In particular, can be dispensed with the use of a costly electricity meter. The inventive use of a minimum number of temperature sensors thus makes it possible to determine the coefficient of performance of a chiller with a minimum cost.

According to the invention, a first temperature in the region of the inlet of the compressor, a second temperature in the region of the outlet of the condenser and a third temperature in the region of the outlet of the expansion valve are measured. The refrigerant temperatures measured at these points of the refrigerant circuit are generally sufficient to determine the enthalpies of the circuit and ultimately to determine the coefficient of performance of the refrigerator.

Another object of the invention is also a chiller according to claim 2. With the help of this chiller, the inventive method can perform particularly well and achieve the above advantages accordingly.

Fig. 1

eine schematische Darstellung einer Ausführungsform einer erfindungsgemäßen Kältemaschine;

Fig. 2

ein Log p, H - Diagram des Kältemittels der Kältemaschine von Fig. 1 und den zugehörigen Kreisprozess;

Fig. 3

eine schematische Darstellung einer Variante einer Kältemaschine;

Fig. 4

eine schematische Darstellung einer weiteren Variante einer Kältemaschine;

Fig. 5

eine schematische Darstellung einer weiteren Variante einer Kältemaschine;

Fig. 6

eine schematische Darstellung einer weiteren Variante einer Kältemaschine; und

Fig. 7

eine schematische Darstellung einer weiteren Variante einer Kältemaschine.

Hereinafter, the present invention will be described purely by way of example with reference to an advantageous embodiment and with reference to the accompanying drawings. Show it:

Fig. 1

a schematic representation of an embodiment of a refrigerator according to the invention;

Fig. 2

a Log p, H - Diagram of the refrigerant of the chiller of Fig. 1 and the associated cycle process;

Fig. 3

a schematic representation of a variant of a refrigerator;

Fig. 4

a schematic representation of another variant of a refrigerator;

Fig. 5

a schematic representation of another variant of a refrigerator;

Fig. 6

a schematic representation of another variant of a refrigerator; and

Fig. 7

a schematic representation of another variant of a refrigerator.

In Fig. 1 an embodiment of a refrigerating machine according to the invention is shown. The refrigerator includes a closed circuit 10 having a refrigerant in which an evaporator 12, a compressor 14, a condenser 16, and an expansion valve 18 are disposed.

For determining the refrigerant temperature, a temperature sensor 28 in the region of the inlet of the compressor 14, a temperature sensor 30 in the region of the outlet of the condenser 16 and a temperature sensor 32 in the region of the outlet of the expansion valve 18 are arranged. The temperature sensors 28, 30, 32 are connected to an evaluation unit 26, which may be integrated into a controller of the refrigerator.

The chiller is described here in its function as a heat pump. Fig. 2 shows for this purpose a Log p, H - diagram of the refrigerant used in the refrigerator, wherein the pressure p of the refrigerant is plotted logarithmically as a function of enthalpy H. Also marked are the limits of saturated liquid 20 and saturated gas 22.

The point E in Fig. 2 indicates the state of the refrigerant after expansion by the expansion valve 18. In the evaporator 12, evaporation (EA) and overheating (AB) of the refrigerant take place.

The compressor 14 provides a compression (B-C) of the refrigerant, which is accompanied by a corresponding increase in temperature. For example, the temperature of the refrigerant may be raised from about + 10 ° C at the exit of the evaporator 12 through the compressor 14 to about + 90 ° C.

In the condenser 16 is a liquefaction (C-D) of the refrigerant, wherein the liquefaction temperature may be, for example + 50 ° C. The now liquid and only 50 ° C warm refrigerant is then expanded by the expansion valve 18 (D-E), where it cools, for example, to about 0 ° C.

Hereinafter, as T1, the temperature of the gaseous refrigerant at the inlet of the compressor 14, as T2, the temperature of the liquid refrigerant at the outlet of the condenser 16, as T3, the temperature of the expanded refrigerant at the outlet of the expansion valve 18 and T4 the Temperature of the gaseous refrigerant at the outlet of the compressor 14 is designated.

As P1, the evaporation pressure, i. that is, the pressure of the gaseous refrigerant at the outlet of the evaporator 12 and, as P2, the condensing pressure, i. that is, the pressure of the liquid refrigerant at the outlet of the condenser 16.

To determine the coefficient of performance of the chiller, first the enthalpy H1 at the outlet of the condenser 16, the enthalpy H2 at the inlet of the compressor 14 and the enthalpy H3 at the outlet of the compressor 14 are determined.

$$\mathrm{H}\mathrm{2}=\mathrm{f}\left(\mathrm{P}\mathrm{1},\mathrm{T}\mathrm{1}\right)$$

$$\mathrm{H}\mathrm{3}=\mathrm{f}\left(\mathrm{P}\mathrm{2},\mathrm{T}\mathrm{4}\right)$$

The enthalpy H 1 is a function of the refrigerant temperature T 2 at the outlet of the condenser, the enthalpy H 2 a function of the refrigerant temperature T 1 at the inlet of the compressor 14 and the refrigerant pressure P 1 at the outlet of the evaporator 12 and the enthalpy H 3 a function of the refrigerant temperature T 4 at the outlet of the evaporator Compressor 14 and the refrigerant pressure P2 at the outlet of the condenser 16: $$\mathrm{H}\mathrm{1}=\mathrm{f}\left(\mathrm{T}\mathrm{2}\right)$$

$$\mathrm{H}\mathrm{2}=\mathrm{f}\left(\mathrm{P}\mathrm{1}.\mathrm{T}\mathrm{1}\right)$$

$$\mathrm{H}\mathrm{3}=\mathrm{f}\left(\mathrm{P}\mathrm{2}.\mathrm{T}\mathrm{4}\right)$$

At the in Fig. 1 In the embodiment shown, the determination of the temperatures T1, T2, T3 is carried out by measurement with the aid of the temperature sensors 28, 30 or 32. The temperature values T1, T2, T3 detected by the temperature sensors 28, 30, 32 are transmitted to the evaluation unit 26.

The evaluation unit 26 calculates the pressure P2 using the pressure equation of the refrigerant used from the received value for the temperature T2 at the outlet of the condenser 16 and the pressure P1 from the temperature value T3 at the outlet of the expansion valve 18. As a pressure equation, for example, the well-known Clausius-Clapeyron equation can be used.

Knowing the temperatures T1 and T2 and the pressure P1, the enthalpies H1 and H2 can now be determined by equations (1) and (2).

The enthalpy H3, since the temperature T4 is not known, is calculated from the compressor model.

For this, it is assumed that about 95% of the electric power consumed by the compressor 14 is induced in the refrigeration cycle. The electric power Qel received by the compressor 14 is not determined by an electricity meter, but calculated by a model describing the thermodynamic characteristics of the compressor 14, e.g. a 10-coefficient model.

By means of this model, not only the electric power consumed by the compressor 14 but also the refrigerating capacity Q0 of the compressor 14, the electric current I received by the compressor 14 and the mass flow m ° of the refrigerant flowing through the compressor 14 can be calculated.

The calculated values apply only to the documented operating point of the compressor 14 at either constant superheating or constant suction gas temperature, ie constant temperature T1 of the refrigerant at the compressor entrance. In order to calculate the values of the real operating point, the values must be corrected as a function of the real compressor input temperature T1.

The electric power Qel received by the compressor 14 is divided by the mass flow m ⁰ to determine the enthalpy difference H3-H2: $$\mathrm{Qel}/\mathrm{m\; °}=\mathrm{H}\mathrm{3}-\mathrm{H}\mathrm{2}$$

Since the enthalpy H2 from equation (2) is known, the enthalpy H3-H2 can be easily calculated from the enthalpy difference H3-H2.

As a check, the refrigerant temperature T4 at the compressor output is obtained from the intersection of the enthalpy line H3 with the line of the pressure P2 in the log p, H diagram of FIG Fig. 2 calculated.

die Heizleistung Qh der Kältemaschine berechnet. Die von dem Verdichter 14 aufgenommene elektrische Leistung Qel wurde bereits mit Hilfe des Verdichtermodells ermittelt und ist gemäß Gleichung (4) proportional zu der Differenz der Enthalpien H3 und H2.From the difference of the calculated enthalpies H3 and H1 is then according to the equation $$\mathrm{Qh}={\mathrm{m}}^{\mathrm{°}}*\left(\mathrm{H}\mathrm{3}-\mathrm{H}\mathrm{1}\right)$$

calculates the heating capacity Qh of the chiller. The electrical power Qel received by the compressor 14 has already been determined with the aid of the compressor model and is proportional to the difference of the enthalpies H3 and H2 according to equation (4).

To determine the coefficient of performance COP or the efficiency of the chiller, finally, only the quotient of the heating power Qh and the electric power Qel needs to be formed: $$\mathrm{COP}=\mathrm{Qh}/\mathrm{Qel}=\left(\mathrm{H}\mathrm{3}-\mathrm{H}\mathrm{1}\right)/\left(\mathrm{H}\mathrm{3}-\mathrm{H}\mathrm{2}\right)$$

By integrating the coefficient of performance over time, it is also possible to determine from the coefficient of performance the annual working factor of the chiller. Accordingly, the heating power Qh and the electric power Qel can be integrated over time to indicate the heating energy and the absorbed electric power. The power consumption of ancillary equipment, such as Pumps, electronics, etc., can be incorporated into the calculation by suitable parameters.

In Fig. 3 a chiller is shown, which does not belong to the invention and differs from the embodiment described above in that a connected to the evaluation unit 26 fourth temperature sensor 34 is disposed in the region of the output of the compressor 14 to determine the refrigerant temperature T4 at the compressor output. In this refrigerating machine, therefore, the refrigerant temperature T4 at the compressor outlet need not be estimated with the aid of a compressor model, but it is measured directly.

According to the above embodiment, the evaluation unit 26 calculates the pressure P2 using the pressure equation of the refrigerant used from the received value for the temperature T2 at the outlet of the condenser 16 and the pressure P1 from the temperature T3 at the outlet of the expansion valve 18. Subsequently, according to equations (1) to (3), the enthalpies H1, H2 and H3 are determined from the measured temperatures T1, T2, T4 and the calculated pressures P1, P2, and the coefficient of performance is determined therefrom according to equation (6). In Fig. 4 is shown a further refrigerator, which does not belong to the invention and from the reference to Fig. 1 described embodiment in that instead of the third temperature sensor 32, a pressure sensor 36 is arranged in the region of the outlet of the evaporator 12, there to measure the pressure P1 of the refrigerant. The pressure sensor 36 is connected to the evaluation unit 26 in order to transmit the measured refrigerant pressure P1 to it.

In this refrigerator, the pressure P1 thus does not need to be calculated from the refrigerant temperature T3 at the outlet of the expansion valve 18, but it is measured directly. Only the pressure P2 is to be calculated using the pressure equation of the refrigerant used from the temperature T2 at the outlet of the condenser 16, and the refrigerant temperature T4 at the compressor output is as based on Fig. 1 explained using a compressor model, so that according to the equations (1) to (3) the enthalpies H 1, H 2 and H 3 and from this according to equation (6), the coefficient of performance of the chiller can be determined.

In Fig. 5 is another refrigeration machine shown, which does not belong to the invention and from the in Fig. 4 different in that a connected to the evaluation unit 26 fourth temperature sensor 34 is disposed in the region of the output of the compressor 14 to determine the refrigerant temperature T4 at the compressor output. Unlike the chiller of the Fig. 4 Thus, the refrigerant temperature T4 at the compressor output in this chiller need not be calculated with the aid of a compressor model, but it is similar to the in Fig. 3 shown directly measured chiller. As with the refrigerators described above Here, too, the pressure P2 calculated from the refrigerant temperature T2 at the outlet of the condenser 16.

From the measured temperatures T1, T2, T4 and the measured pressure P1 and the calculated pressure P2, the enthalpies H1, H2 and H3 are then calculated according to equations (1) to (3) and the coefficient of performance determined therefrom according to equation (6).

In Fig. 6 is another refrigeration machine shown, which does not belong to the invention and from the in Fig. 4 different in that a connected to the evaluation unit 26 second pressure sensor 38 is disposed in the region of the output of the condenser 16 to determine the refrigerant pressure P2 at the condenser output.

Unlike the chiller of the Fig. 4 Thus, the pressure P2 in this chiller need not be calculated using the pressure equation of the refrigerant used from the temperature T2 at the outlet of the condenser 16, but it is measured directly. Only the refrigerant temperature T4 at the compressor output is in this chiller as based on Fig. 1 calculated using a compressor model.

The enthalpies H1, H2 and H3 are then calculated from the measured temperatures T1, T2 and the measured pressures P1, P2 and the calculated temperature T4 according to equations (1) to (3), and the coefficient of performance is determined therefrom according to equation (6).

In Fig. 7 is another refrigeration machine shown, which does not belong to the invention and from the in Fig. 6 differs in that a connected to the evaluation unit 26 third temperature sensor 34 is arranged in the region of the output of the compressor 14 in order to determine the refrigerant temperature T4 at the compressor outlet. Unlike the chiller of the Fig. 6 Thus, the refrigerant temperature T4 at the compressor output in this chiller need not be estimated with the aid of a compressor model, but it is measured directly.

From the measured temperatures T1, T2, T4 and the measured pressures P1, P2, the enthalpies H1, H2 and H3 are then calculated according to equations (1) to (3), and the coefficient of performance is determined from equation (6).

LIST OF REFERENCE NUMBERS

10

circulation

12

Evaporator

14

compressor

16

condenser

18

expansion valve

20

Limits of saturated liquid

22

Limits of saturated gas

26

evaluation

28

temperature sensor

30

temperature sensor

32

temperature sensor

34

temperature sensor

36

pressure sensor

38

pressure sensor

H 1

enthalpy

H2

enthalpy

H3

enthalpy

T1

temperature

T2

temperature

T3

temperature

T4

temperature

P1

print

P2

print

Claims (2)

1. A method for the determination of the coefficient of performance of a refrigeration machine, in particular of a heat pump, which includes a closed circuit (10) which has a refrigerant and in which an evaporator (12), a compressor (14), a condenser (16) and an expansion valve (18) are arranged, in which method
   three temperatures (T1, T2, T3) of the refrigerant are determined using only three temperature sensors (28, 30, 32) arranged in the circuit (10);
   enthalpies (H1, H2, H3) of the circuit (10) are calculated from the determined refrigerant temperatures;
   the heat output (Qh) and the taken up electrical power (Qel) of the refrigeration machine are calculated from differences of the calculated enthalpies; and
   the coefficient of performance (COP) of the refrigeration machine is determined from the quotient of the calculated heat output (Qh) and the calculated taken up electrical power (Qel), wherein a first temperature (T1) is determined in the region of the inlet of the compressor (14); a second temperature (T2) is determined in the region of the outlet of the condenser (16); and a third temperature (T3) is determined in the region of the outlet of the expansion valve (18).
2. A refrigeration machine, in particular for the carrying out of a method in accordance with claim 1, which includes a closed circuit (10) which has a refrigerant and in which an evaporator (12), a compressor (14), a condenser (16), an expansion valve (18) and only three temperature sensors (28, 30, 32) are arranged for the determination of three temperatures of the refrigerant, wherein the three temperature sensors (28,30, 32) for the determination of the coefficient of performance (COP) of the refrigeration machine are connected to an evaluation device (26) which is designed to determine the coefficient of performance (COP) of the circuit (10) from the three determined temperatures of the refrigerant (T1, T2, T3),
   wherein a first temperature sensor (28) is arranged in the region of the inlet of the compressor (14), a second temperature sensor (30) is arranged in the region of the outlet of the condenser (16) and a third temperature sensor (32) is arranged in the region of the outlet of the expansion valve (18).

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