EP2196740A2 - Method for determining the performance of a cooling machine - Google Patents

Abstract

The method involves determining refrigerant temperatures (T1-T3) in an inlet region of a compressor (14) and outlet regions of a condenser (16) and an expansion valve (18) using temperature sensors (28, 30, 32) arranged in a closed loop (10), respectively. Enthalpies of the closed loop are calculated from the determined temperatures. Heat energy and electrical energy of cooling machine are calculated from difference of calculated enthalpies. A coefficient of performance of the cooling machine is determined from quotient of the calculated heating and electrical energies. An independent claim is also included for a cooling machine comprising an evaluation device.

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

To achieve the object, a method having the features of claim 1 or 4 is provided.

In the inventive method according to claim 1 are 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 aid of at least three temperature sensors , which are arranged in the circuit, determined at least 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 the Measurement of the refrigerant temperatures at three different points of the refrigerant circuit, a minimum of information about the refrigerant circuit is determined, which is required to determine the coefficient of performance of the chiller can.

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 an advantageous embodiment of the method, 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.

Alternatively, by means of a fourth temperature sensor additionally a fourth temperature can be determined and used to determine the coefficient of performance, wherein the fourth temperature is preferably determined in the region of the output of the compressor. By measuring the refrigerant temperature at the compressor outlet, this no longer needs to be calculated by a compressor model, but can be determined accurately. In this way, the figure of merit can be determined easier, faster and more accurately.

In the method according to claim 4 of the invention, at least two temperatures and a pressure of the refrigerant are determined to determine the coefficient of performance of a chiller with the aid of at least two temperature sensors and at least one pressure sensor, which are arranged in the refrigerant circuit. From the determined refrigerant temperatures and the determined refrigerant pressure enthalpies of the circuit and from differences between the enthalpies the heating power and the absorbed electric power of the chiller are calculated. The coefficient of performance of the chiller is then determined from the quotient of the calculated heating power and the calculated absorbed electrical power.

Also in this variant of the method according to the invention, the coefficient of performance of the chiller can be determined using a minimum number of sensors and in particular without an electricity meter and thus particularly cost. In this case, the determination of the coefficient of performance takes place exclusively on the basis of the measured values supplied by the two temperature sensors and the one pressure sensor, whereby here too knowledge of the system, in particular of the thermodynamic properties of the refrigerant and of the compressor, must be assumed.

According to an advantageous embodiment of the method according to claim 4, 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 first pressure in the region of the outlet of the evaporator is measured.

In addition, a third temperature can be determined and used to determine the coefficient of performance, wherein the third temperature is preferably determined in the region of the output of the compressor. Due to the additional measurement of a third temperature, it is possible to replace calculations that are required with the use of only three sensors for determining the enthalpies, in particular for determining the coolant temperature at the compressor output, by an actual measurement, whereby the determination of the coefficient of performance of the chiller easier, faster and with greater accuracy.

Alternatively or additionally, a second pressure can be determined and used to determine the coefficient of performance, wherein the second pressure is preferably determined in the region of the outlet of the condenser. Also, the measurement of the second pressure contributes to a faster and more accurate determination of the coefficient of performance of the chiller, by eliminating the need to calculate the pressure value without the direct measurement.

Further objects of the invention are also the chillers according to claim 8 or 11. With the help of these chillers, the inventive method can perform particularly well and achieve the above advantages accordingly

Fig. 1

eine schematische Darstellung einer ersten 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 zweiten Ausführungsform einer erfindungsgemäßen Kältemaschine;

Fig. 4

eine schematische Darstellung einer dritten Ausführungsform einer erfindungsgemäßen Kältemaschine;

Fig. 5

eine schematische Darstellung einer vierten Ausführungsform einer erfindungsgemäßen Kältemaschine;

Fig. 6

eine schematische Darstellung einer fünften Ausführungsform einer erfindungsgemäßen Kältemaschine; und

Fig. 7

eine schematische Darstellung einer sechsten Ausführungsform einer erfindungsgemäßen Kältemaschine.

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

Fig. 1

a schematic representation of a first 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 second embodiment of a refrigerator according to the invention;

Fig. 4

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

Fig. 5

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

Fig. 6

a schematic representation of a fifth embodiment of a refrigerator according to the invention; and

Fig. 7

a schematic representation of a sixth embodiment of a refrigerator according to the invention.

In Fig. 1 a first embodiment of a refrigerator 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.

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

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

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

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

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

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: $$\mathrm{Qel}\mathrm{/}\mathrm{m\; °}\mathrm{=}\mathrm{H}\mathrm{3}\mathrm{-}\mathrm{H}\mathrm{2}$$

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 $$\mathrm{Qh}\mathrm{=}{\mathrm{m}}^{\mathrm{°}}\mathrm{*}\left(\mathrm{H}\mathrm{3}\mathrm{-}\mathrm{H}\mathrm{1}\right)$$

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: $$\mathrm{COP}\mathrm{=}\mathrm{Qh}\mathrm{/}\mathrm{Qel}\mathrm{=}\left(\mathrm{H}\mathrm{3}\mathrm{-}\mathrm{H}\mathrm{1}\right)\mathrm{/}\left(\mathrm{H}\mathrm{3}\mathrm{-}\mathrm{H}\mathrm{2}\right)$$

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 shows a second embodiment of a refrigerating machine according to the invention, which 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 embodiment, 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 first 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 a third embodiment of a refrigerating machine according to the invention is shown, which differs from that with reference to Fig. 1 described first difference 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.

Thus, in this embodiment, the pressure P1 need not 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 with the aid of a compressor model, according to the equations (1) to (3), the enthalpies H1, H2 and H3 and from this according to equation (6) the coefficient of performance of the chiller can be determined.

In Fig. 5 a fourth embodiment of a refrigerating machine according to the invention is shown, which differs from the in Fig. 4 3 shows that a fourth temperature sensor 34 connected to the evaluation unit 26 is arranged in the region of the outlet of the compressor 14 in order to determine the refrigerant temperature T4 at the compressor outlet. Thus, unlike the third embodiment, the refrigerant temperature T4 at the compressor output need not be calculated by means of a compressor model in this embodiment, but it becomes similar to that in FIG Fig. 2 shown directly measured second embodiment. As in the above Embodiments, the pressure P2 from the refrigerant temperature T2 at the outlet of the condenser 16 is also calculated here.

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 a fifth embodiment of a refrigerating machine according to the invention is shown, which differs from the in Fig. 4 3 shows that a second pressure sensor 38 connected to the evaluation unit 26 is arranged in the region of the outlet of the condenser 16 in order to determine the refrigerant pressure P2 at the condenser outlet.

Thus, unlike the third embodiment, the pressure P2 in this embodiment 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 embodiment 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 a sixth embodiment of a refrigerating machine according to the invention is shown, which differs from the in Fig. 6 shown fifth embodiment in that a third temperature sensor 34 connected to the evaluation unit 26 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 fifth embodiment, therefore, the refrigerant temperature T4 at the compressor output need not be estimated with the aid of a compressor model in this embodiment, 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 (14)

A method for determining the coefficient of performance of a refrigerating machine, in particular a heat pump, comprising a refrigerant having a closed circuit (10), in which an evaporator (12), a compressor (14), a condenser (16) and an expansion valve (18) arranged are in what process
at least three temperatures (T1, T2, T3) of the refrigerant are determined with the aid of temperature sensors (28, 30, 32) arranged in the circuit (10),
from the determined refrigerant temperatures enthalpies (H 1, H 2, H 3) of the circuit (10) are calculated,
from differences of the calculated enthalpies the heating power (Qh) and the absorbed electric power (Qel) of the chiller are calculated and
from the quotient of the calculated heating power (Qh) and the calculated absorbed electrical power (Qel) the coefficient of performance (COP) of the chiller is determined. Method according to claim 1,
characterized in that
a first temperature (T1) in the region of the inlet of the compressor (14); a second temperature (T2) in the region of the outlet of the
Condenser (16) and a third temperature (T3) in the region of the output of the expansion valve (18) is determined. Method according to claim 1 or 2,
characterized in that
a fourth temperature (T4) is determined and used to determine the coefficient of performance, wherein the fourth temperature (T4) is determined in particular in the region of the output of the compressor (14). A method for determining the coefficient of performance of a refrigerating machine, in particular a heat pump, comprising a refrigerant having a closed circuit (10), in which an evaporator (12), a compressor (14), a condenser (16) and an expansion valve (18) arranged are in what process
at least two temperatures (T1, T2) of the refrigerant are determined with the aid of temperature sensors (28, 30) arranged in the circuit (10),
at least one pressure (P1) of the refrigerant is determined with the aid of at least one pressure sensor (36) arranged in the circuit (10),
from the determined refrigerant temperatures and the determined refrigerant pressure, enthalpies (H1, H2, H3) of the circuit (10) are calculated,
from differences of the calculated enthalpies the heating power (Qh) and the absorbed electric power (Qel) of the chiller are calculated and
from the quotient of the calculated heating power (Qh) and the calculated absorbed electrical power (Qel) the coefficient of performance (COP) of the chiller is determined. Method according to claim 4,
characterized in that
a first temperature (T1) in the region of the inlet of the compressor (14), a second temperature (T2) in the region of the outlet of the condenser (16) and a first pressure (P1) in the region of the outlet of the evaporator (12) is determined. Method according to claim 5,
characterized in that
a third temperature (T4) is determined and used to determine the coefficient of performance, wherein the third temperature (T4) is determined in particular in the region of the output of the compressor (14). Method according to claim 5 or 6,
characterized in that
a second pressure (P2) is determined and used to determine the coefficient of performance, the second pressure (P2) in particular in the region of the outlet of the condenser (16) is determined. Chiller, in particular for carrying out a method according to one of claims 1 to 3, comprising a closed circuit (10) having a refrigerant, in which an evaporator (12), a compressor (14), a condenser (16), an expansion valve ( 18) and at least three temperature sensors (28, 30, 32) for determining temperatures of the refrigerant are arranged, wherein the temperature sensors (28, 30, 32) for determining the coefficient of performance (COP) of the chiller with an evaluation device (26) are connected, which is designed to determine from the determined temperatures of the refrigerant (T1, T2, T3) the coefficient of performance (COP) of the circuit (10). Chiller according to claim 8,
characterized in that
a first temperature sensor (28) in the region of the inlet of the compressor (14), a second temperature sensor (30) in the region of the outlet of the condenser (16) and a third temperature sensor (32) in the region of the output of the expansion valve (18) is arranged. Chiller according to claim 8 or 9,
characterized in that
a fourth temperature sensor (34) is arranged in the region of the output of the compressor (14) and connected to the evaluation device (26). Chiller, in particular for carrying out a method according to one of claims 4 to 7, comprising a closed circuit (10) having a refrigerant, in which an evaporator (12), a compressor (14), a condenser (16), an expansion valve ( 18), at least two temperature sensors (28, 30) and at least one pressure sensor (36) for determining the temperatures (T1, T2) and the pressure (P1) of the refrigerant are arranged, wherein the temperature sensors (28, 30) and the pressure sensor ( 36) for determining the coefficient of performance (COP) of the refrigerating machine are connected to an evaluation device (26) which is designed to determine the coefficient of performance (COP) from the determined temperatures (T1, T2) of the refrigerant and the determined pressure (P1) of the refrigerant of the circuit (10). Chiller according to claim 11,
characterized in that
a third temperature sensor (34) in the region of the output of the compressor (14) is arranged and connected to the evaluation device (26). Chiller according to claim 11 or 12,
characterized in that
a second pressure sensor (38) is arranged in the region of the outlet of the condenser (16) and connected to the evaluation device (26). Chiller according to one of claims 8 to 13,
characterized in that
the evaluation device (26) is designed to calculate from the determined temperatures or pressures of the refrigerant enthalpies (H1, H2, H3) of the circuit (10) and from the calculated enthalpies (H1, H2, H3) the heating power (Qh) and calculate the consumed electric power (Qel) of the refrigerator to determine therefrom the coefficient of performance (COP) of the circuit (10).

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