VAPOR COMPRESSION-TYPE REFRIGERATOR AND METHOD FOR CONTROLLING SAME

Abstract

The present invention is provided with an extraction device (40) including: a cooling unit for cooling gas that has been extracted from a condenser (5) and condensing condensed gas; and an exhaust pump (48) for discharging, to the exterior, uncondensed gas that has been isolated without having been condensed by the cooling unit. A current temperature difference, which is the difference between the current saturation temperature in the condenser (5) and the current outlet temperature of a cooling water heat transfer tube (5a), and a planned temperature difference, which is a planned value, are computed. Using information on an in-tube fouling temperature difference elevation, which is a difference between the saturation temperature in the condenser (5) and the outlet temperature of the cooling water heat transfer tube (5a) and which is predetermined assuming in-tube fouling of the cooling water heat transfer tube (5a), the temperature difference elevation due to the current in-tube fouling is computed. The extraction device (40) is operated if the elevation of the current temperature difference from the planned temperature difference is greater by a predetermined value or more than the temperature difference elevation due to the current in-tube fouling.

Claims

1. A vapor compression-type refrigerator, comprising: a compressor which compresses a refrigerant; a condenser which condenses the refrigerant compressed by the compressor; a cooling water heat transfer tube through which cooling water which performs heat exchange between the cooling water and the refrigerant in the condenser flows; an expansion valve which expands a liquid refrigerant introduced from the condenser; an evaporator which evaporates the refrigerant expanded by the expansion valve; an air bleeding device which bleeds gas from the condenser, and includes a cooling unit which cools the gas so as to condense the condensed gas and a discharge unit which discharges an uncondensed gas, which is separated without being condensed by the cooling unit, to an outside; and a controller which controls the air bleeding device, wherein the controller calculates a current temperature difference which is a difference between a current saturation temperature in the condenser and a current outlet temperature of the cooling water heat transfer tube, and a planned temperature difference which is a planned value, wherein the controller calculates an increase in a temperature difference caused by current in-pipe contamination using information on an increase in a temperature difference which is caused by in-pipe contamination and is a difference between a saturation temperature in the condenser predetermined by assuming the in-pipe contamination of the cooling water heat transfer tube and an outlet temperature of the cooling water heat transfer tube, and wherein in a case where an increase of the current temperature difference from the planned temperature difference is larger by a predetermined value or more than the increase in the temperature difference caused by the current in-pipe contamination, the controller operates the air bleeding device.

2. The vapor compression-type refrigerator according to claim 1, further comprising: a differential pressure sensor which detects a differential pressure between an inlet and an outlet of the cooling water heat transfer tube in the condenser, wherein the increase in the temperature difference caused by the in-pipe contamination is determined based on an increase of a current differential pressure obtained by the differential pressure sensor from the planned value.

3. The vapor compression-type refrigerator according to claim 2, further comprising: a cooling water flow rate sensor which measures a flow rate of cooling water which flows through the cooling water heat transfer tube, wherein the increase in the temperature difference caused by the in-pipe contamination is determined based on the flow rate obtained by the cooling water flow rate sensor.

4. The vapor compression-type refrigerator according to claim 2, further comprising: a cold water heat transfer tube through which cold water which performs heat exchange between the cold water and the refrigerant in the evaporator flows; and a cold water flow rate sensor which measures a flow rate of the cold water flowing through the cold water heat transfer tube, wherein the controller calculates a flow rate of the cooling water which flows through the cooling water heat transfer tube from a heat balance, based on the cold water flow rate obtained by the cold water flow rate sensor, a cold water inlet/outlet temperature difference of the cold water heat transfer tube in the evaporator, power input to the compressor, and a cooling water inlet/outlet temperature difference of the cooling water heat transfer tube in the condenser, and wherein the increase in the temperature difference caused by the in-pipe contamination is determined based on the cooling water flow rate.

5. A method for controlling a vapor compression-type refrigerator, the vapor compression-type refrigerator including a compressor which compresses a refrigerant, a condenser which condenses the refrigerant compressed by the compressor, a cooling water heat transfer tube through which cooling water which performs heat exchange between the cooling water and the refrigerant in the condenser flows, an expansion valve which expands a liquid refrigerant introduced from the condenser, an evaporator which evaporates the refrigerant expanded by the expansion valve, and an air bleeding device which bleeds gas from the condenser, and includes a cooling unit which cools the gas so as to condense the condensed gas and a discharge unit which discharges an uncondensed gas, which is separated without being condensed by the cooling unit, to an outside, the method comprising: calculating a current temperature difference which is a difference between a current saturation temperature in the condenser and a current outlet temperature of the cooling water heat transfer tube, and a planned temperature difference which is a planned value; calculating an increase in a temperature difference caused by current in-pipe contamination using information on an increase in a temperature difference which is caused by in-pipe contamination and is a difference between a saturation temperature in the condenser predetermined by assuming the in-pipe contamination of the cooling water heat transfer tube and an outlet temperature of the cooling water heat transfer tube; and operating the air bleeding device in a case where an increase of the current temperature difference from the planned temperature difference is larger by a predetermined value or more than the increase in the temperature difference caused by the current in-pipe contamination.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0022] FIG. 1 is a schematic configuration diagram showing a turbo refrigerator according to an embodiment of the present invention.

[0023] FIG. 2 is a control block diagram of a controller.

[0024] FIG. 3 is a graph showing a cooling water pressure loss with respect to a temperature difference at a cooling water outlet.

[0025] FIG. 4 is a flowchart showing a starting control and a stopping control of an air bleeding device according to the embodiment of the present invention.

[0026] FIG. 5 is a graph showing a starting timing and a stopping timing of the air bleeding device.

DESCRIPTION OF EMBODIMENTS

[0027] Hereinafter, an embodiment according to the present invention will be described with reference to the drawings.

[0028] As shown in FIG. 1, a turbo refrigerator 1 includes a turbo compressor 3 which compresses a refrigerant, a condenser 5 which condenses a high-temperature and high-pressure gas refrigerant compressed by the turbo compressor 3, an expansion valve 7 which expands a liquid refrigerant introduced from the condenser 5, and an evaporator 9 which evaporates the liquid refrigerant expanded by the expansion valve 7.

[0029] For example, as the refrigerant, a low-pressure refrigerant such as HFO-1233zd(E) is used, and a pressure of a low-pressure portion such as the evaporator during the operation becomes the atmospheric pressure or less.

[0030] The turbo compressor 3 is a centrifugal compressor and is driven by an electric motor 11 whose rotational speed is controlled by an inverter. An output of the inverter is controlled by a controller (not shown). Input power W of the electric motor 11 is measured by a watt meter 13 and a measurement result is sent to the controller (not shown).

[0031] The turbo compressor 3 includes an impeller 3a which is rotated around a rotary shaft 3b. Rotational power is transmitted from the electric motor 11 to the rotary shaft 3b via a speed increasing gear 15.

[0032] For example, the condenser 5 is a shell and tube type heat exchanger.

[0033] A cooling water heat transfer tube 5a through which a cooling water for cooling the refrigerant flows is inserted into the condenser 12. A cooling water forward pipe 6a and a cooling water return pipe 6b are connected to the cooling water heat transfer tube 5a. The cooling water introduced to the condenser 5 via the cooling water forward pipe 6a is introduced to a cooling tower (not shown) via the cooling water return pipe 6b, heat of the cooling water is exhausted to the outside, and thereafter, the cooling water is introduced to the condenser 5 again via the cooling water forward pipe 6a.

[0034] In the cooling water forward pipe 22a, a cooling water pump 20 which feeds the cooling water, a cooling water flow rate sensor 22 which measures a cooling water flow rate GWC, and a cooling water inlet temperature sensor 24 which measures a cooling water inlet temperature TWCI are provided. In the cooling water return pipe 6b, a cooling water outlet temperature sensor 26 which measures a cooling water outlet temperature TWCO is provided. In addition, a cooling water differential pressure sensor 28 which measures a differential pressure PD between an inlet and an outlet of the cooling water is provided between the cooling water forward pipe 6a and a cooling water return pipe 6b.

[0035] A condenser pressure sensor 29 which measures a condenser pressure Pc of the refrigerant in the condenser 5 is provided in the condenser 5.

[0036] Measurement values of the sensors 23a, 23b, 24, and 25 are sent to the controller.

[0037] The expansion valve 7 is an electric expansion valve and an opening degree of the expansion valve 7 is set to a predetermined degree by the controller.

[0038] For example, the evaporator 9 is a shell and tube type heat exchanger.

[0039] A cold water heat transfer tube 9a through which a cold water which performs heat exchange between the cold water and the refrigerant flows is inserted into the evaporator 9. A cold water forward pipe 10a and a cold water return pipe 10b are connected to the cold water heat transfer tube 9a. The cold water introduced to the evaporator 9 via the cold water forward pipe 10a is cooled to a rated temperature (for example, 7 C.) and is introduced to an external load (not shown) via the cold water return pipe 10b so as to supply a cold heat, and thereafter, the cold water is introduced to the evaporator 9 again via the cold water forward pipe 10a.

[0040] In the cold water forward pipe 10a, a cold water pump 30 which feeds the cold water, a cold water flow rate sensor 32 which measures a cold water flow rate GWW, and a cold water inlet temperature sensor 34 which measures a cold water inlet temperature TWEI are provided. In the cold water return pipe 10b, a cold water outlet temperature sensor 36 which measures a cold water outlet temperature TWEO is provided. In addition, a cold water differential pressure sensor 38 which measures a differential pressure PDe between an inlet and an outlet of the cold water is provided between the cold water forward pipe 10a and a cold water return pipe 10b.

[0041] Measurement values of the sensors 32, 34, 36, and 38 are sent to the controller.

[0042] An air bleeding device 40 is provided between the condenser 5 and the evaporator 9. An air bleeding pipe 42 for introducing the refrigerant (condensed gas) including an uncondensed gas from the condenser 5 is connected to the air bleeding device 40. Moreover, a liquid refrigerant pipe 44 through which the condensed liquid refrigerant is introduced to the evaporator 9 is connected to the air bleeding device 40. In addition, a discharge pipe 46 through which the uncondensed gas is discharged to the outside is connected to the air bleeding device 40, and an exhaust pump (discharge unit) 48 is provided in the discharge pipe 46. An operation of the exhaust pump 48 is controlled by the controller.

[0043] Moreover, as shown by an arrow 49, cold heat for cooling the refrigerant including the uncondensed gas introduced into the air bleeding device 40 is supplied to the air bleeding device 40. As a cooling unit for supplying the cold heat, there is a refrigerator having a refrigeration cycle different from that of the turbo refrigerator 1, means for supplying the cold water, means for supplying the refrigerant into the turbo refrigerator 1, cooling means such as a peltier element, or the like. An operation of the cooling unit is controlled by the controller (not shown).

[0044] The controller 1 performs a control relating to the operation of the turbo refrigerator 1, and for example, a Central Processing Unit (CPU), a Random Access Memory (RAM), a Read Only Memory (ROM), a computer readable storage medium, or the like. In addition, for example, a series of processing for realizing various functions is stored in the storage medium or the like as a program form, and the CPU reads the program to a RAM or the like and executes information processing/calculation processing to realize the various functions. Moreover, the program may be installed in the ROM or other storage mediums in advance, may be supplied in a form stored in the computer readable storage medium, or may be distributed via wired or wireless communication means. The computer readable storage medium is a magnetic disk, a magneto-optical disk, a CD-ROM, a DVD-ROM, a semiconductor memory, or the like.

[0045] FIG. 2 shows a block diagram of the controller.

[0046] As described below, data for determining the operation of the air bleeding device 40 is stored in a storage unit 50.

[0047] The measurement values from the above-described sensors and the data from the storage unit 50 are input to an operation state calculation unit 52, and the operation state calculation unit 52 performs various calculations for determining the operation of the air bleeding device 40.

[0048] An operation state determination unit 54 performs determination of the operation of the air bleeding device from information obtained by the operation state calculation unit 52.

[0049] A control command unit 56 performs a command for starting or stopping the air bleeding device 40, based on an output from the operation state determination unit 54.

[0050] Next, a method for determining the starting or stopping of the air bleeding device 40 will be described with reference to FIG. 3.

[0051] In FIG. 3, a horizontal axis indicates an increase value of a temperature difference between the cooling water outlet temperature TWCO and a condenser saturation temperature TCs calculated from the condenser pressure Pc, from a planned temperature difference. A vertical axis indicates an increase of a cooling water pressure loss from a planned value, and indicates an increase in pressure difference between an inlet and an outlet of the cooling water heat transfer tube 5a caused by contamination of the cooling water. In this way, FIG. 3 shows in-pipe contamination temperature difference information indicating a heat resistance increasing by in-pipe contamination. The increase in pressure difference taking the contamination into account can be obtained by a preliminary test or the like.

[0052] In addition, for example, in a case where the increase of the differential pressure PDc measured by the cooling water differential pressure sensor 28 from the planned value is 4 kPa, according to FIG. 3, the increase in the temperature difference caused by a pressure loss due to the contamination is approximately 1 C. However, in actual, in a case where an increase of an inlet/outlet temperature difference (TWCO-TWCI) of the cooling water measured by the temperature sensors 24 and 26, from the planned value is 2 C., 1 C. of the difference in the temperature increase is considered degradation of condensability caused by the uncondensed gas. In a case where the temperature increase is a predetermined value or more, a command from the controller is performed so as to start the air bleeding device 40.

[0053] FIG. 4 shows a specific control of the air bleeding device 40.

[0054] First, as in Step S1, it is assumed that the turbo refrigerator 1 is normally operated. In this case, the air bleeding device 40 is stopped.

[0055] In addition, as in Step S2, the controller determines whether or not the following Expression is satisfied.

(TDactTDsp)TDf>TDset1 (1)

[0056] In Expression (1), TDact is a difference (measurement value) [ C.] between the saturation temperature of the condenser pressure Pc and the cooling water outlet temperature TWCO. Here, TDact=TCsTWCO is established.

[0057] TCs is a condenser pressure saturation temperature [ C.] and is given as a function of the condenser pressure Pc.

[0058] The cooling water outlet temperature TWCO is the measurement value measured by the cooling water outlet temperature sensor 26.

[0059] In Expression (1), TDsp is a difference (set value) [ C.] between the condenser saturation temperature and the cooling water outlet temperature under a normal state. Here, the normal state means that there is no uncondensed gas in the condenser 5 and the cooling water heat transfer tube 5a is free from the contamination.

[0060] TDsp is expressed by Expression TDsp=f(Qr), which is a function of a refrigerator load factor Qr (=Qact/Qsp). Here, Qact is a measured value [kW] of refrigerating capacity and Qsp is rated refrigerating capacity [kW].

[0061] In Expression (1), TDf is the increase (set value) of the temperature difference of the cooling water heat transfer tube 5a caused by the in-pipe contamination. Here, TDf is expressed by Expression TDf=f(PDc).

[0062] PDc means an increase of the cooling water pressure from a planned value and a differential pressure increase [kPa] between the inlet and the outlet of the cooling water heat transfer tube 5a. PDc is expressed by Expression PDc=PDcactPDcsp.

[0063] PDcact is a differential pressure [kPa] between the inlet and the outlet of the cooling water heat transfer tube 5a measured by the cooling water differential pressure sensor 28.

[0064] PDcsp is a specification value [kPa] of a pressure loss of the cooling water heat transfer tube 5a with respect to the flow rate and means a pressure loss in a state where the cooling water heat transfer tube 5a is free from the contamination. Accordingly, PDcsp is a function of the cooling water flow rate GWC [m.sup.3/h].

[0065] In Expression (1), TDset1 is a set value by which it is determined that the operation of the air bleeding device 40 is required and is predetermined by a preliminary experiment or the like.

[0066] As understood from Expression (1), in a case where the increase in the temperature difference obtained by subtracting the influence (TDf) of the cooling water heat transfer tube 5a from the in-pipe contamination from the increase (TDactTDsp) of the temperature difference between the condenser saturation temperature and the cooling water outlet temperature TWCO from the planned value is equal or more than TDset1 which is the set value, it is determined that performance degradation caused by the uncondensed gas in the condenser 5 is large, and the air bleeding device 40 is operated.

[0067] Accordingly, in a case where Expression (1) is satisfied, the step proceeds to Step S3, and the controller starts the air bleeding device 40. In this case, power is supplied to the air bleeding device 40 at the first time.

[0068] In addition, as in Step S4, the controller determines whether or not the following Expression is satisfied.

(TDactTDsp)TDf<TDset2 (2)

[0069] If Expression (2) is satisfied, the controller stops the air bleeding device 40 (Step S5).

[0070] In addition, TDset2 is set to a value which is smaller than TDset1 by a predetermined temperature. Accordingly, as shown in FIG. 5, the temperature differences are given to the conditions for starting the air bleeding operation and stopping the air bleeding operation such that the air bleeding operation is not frequently started and stopped.

[0071] According to the present embodiment, the following effects are exerted.

[0072] It is focused that influences of both the in-pipe contamination and staying of the uncondensed gas are applied to the increase of the current temperature difference TDact which is the difference between the current saturation temperature in the condenser 5 and the current outlet temperature TWCO of the cooling water heat transfer tube 5a, from the planned value.

[0073] Meanwhile, the increase TDf of the temperature difference caused by the in-pipe contamination can be ascertained by a preliminary experiment in which the cooling water flows through the cooling water heat transfer tube 5a, or the like.

[0074] Accordingly, a value obtained by subtracting the increase TDf in the temperature difference caused by the current in-pipe contamination from the difference between the current temperature difference TDact and the planned temperature difference TDsp can be estimated as a decrease in the condensing performance caused by the staying of the uncondensed gas.

[0075] Accordingly, in a case where the difference between the current temperature difference TDact and the planned temperature difference TDsp is larger by the predetermined value than the increase TDf in the temperature difference caused by the current in-pipe contamination, it is determined that the condensing performance is decreased by the staying of the uncondensed gas, and the air bleeding device 40 is operated. Accordingly, it is possible to operate the air bleeding device 40 only in the case where the uncondensed gas of a predetermined amount or more stays in the condenser 5, it is possible to suppress wasteful energy consumption, and thus, it is possible to realize the turbo refrigerator 1 having the improved overall efficiency.

[0076] The in-pipe contamination in the cooling water heat transfer tube 5a is generated by deposits in the heat transfer tube, the deposits narrow a flow path in the heat transfer tube, and thus, the differential pressure PDc between the inlet and the outlet of the cooling water heat transfer tube 5a is higher than the planned value. Accordingly, the in-pipe contamination temperature difference TDf is determined based on the differential pressure increase PDc, and thus, it is possible to accurately estimate the in-pipe contamination.

[0077] The increase TDf of the temperature difference caused by the in-pipe contamination is dependent on the increase PDc from the planned differential pressure, and the differential pressure PDc is dependent on the cooling water flow rate GWC. Accordingly, the increase TDf of the temperature difference caused by the in-pipe contamination is determined based on the cooling water flow rate GWC obtained by the cooling water flow rate sensor 22. Accordingly, it is possible to accurately estimate the in-pipe contamination.

[0078] Moreover, the present embodiment can be modified as follows.

MODIFICATION EXAMPLE 1

[0079] In the present embodiment, the cooling water flow rate GWC is measured by the cooling water flow rate sensor 22. However, in a case where the cooling water flow rate sensor 22 is not present, the cooling water flow rate GWC can be estimated as follows.

[0080] The cooling water flow rate GWC is obtained by the following Expression from a heat balance of the entire turbo refrigerator 1 using the cold water flow rate sensor 32.

GWC=(W+Qact)/(TWCOTWCI)Cpcwew (3)

[0081] Here, W is input power [kW] of the electric motor 11 measured by the watt meter 13. TWCO is the cooling water outlet temperature measured by the cooling water outlet temperature sensor 26 and TWCI is the cooling water inlet temperature measured by the cooling water inlet temperature sensor 24. Cpcw is a specific heat [kWh/kg C.] of the cooling water and pcw is a specific weight [kg/m.sup.3] of the cooling water.

[0082] In Expression (3), Qact is the measured value [kW] of the refrigerating capacity and is expressed by the following Expression.

Qact=(TWEITWEO)GWEcpewew (4)

[0083] Here, TWEI is the cold water inlet temperature measured by the cold water inlet temperature sensor 34 and TWEO is the cold water outlet temperature measured by the cold water outlet temperature sensor 36. GWE is the cold water flow rate measured by the cold water flow rate sensor 32, Cpew is a specific heat [kWh/Kg C.] of the cold water, and pew is a specific weight [kg/m.sup.3] of the cold water.

[0084] In a case where the cooling water flow rate sensor for measuring the cooling water flow rate GWC is not present, it is possible to calculate the cooling water flow rate GWC from the heat balance by Expression (3), based on the cold water flow rate GWE obtained by the cold water flow rate sensor 32, the cold water inlet/outlet temperature difference (TWEITWEO), the power W input to the turbo compressor 3, and the cooling water inlet/outlet temperature difference (TWCITWCO). Accordingly, the cooling water flow rate sensor 22 is omitted, and thus, it is possible to reduce the cost.

[0085] Moreover, in a case where the cold water flow rate sensor 32 is not prevent, it is possible to calculate the cold water flow rate as the following Expression (5) using the differential pressure PDe measured by the cold water differential pressure sensor 38 and a loss factor e of the cold water heat transfer tube 9a.

GWE=ePDe.sup.1/2 (5)

[0086] In addition, in the above-described embodiment, for example, the turbo refrigerator 1 is described. However, the present invention can be applied to any refrigerator as long as it is vapor compression-type refrigerator.

REFERENCE SIGNS LIST

[0087] 1: turbo refrigerator (vapor compression-type refrigerator)

[0088] 3: turbo compressor

[0089] 3a: impeller

[0090] 3b: rotary shaft

[0091] 5: condenser

[0092] 7: expansion valve

[0093] 9: evaporator

[0094] 11: electric motor

[0095] 13: watt meter

[0096] 20: cooling water pump

[0097] 22: cooling water flow rate sensor

[0098] 24: cooling water inlet temperature sensor

[0099] 26: cooling water outlet temperature sensor

[0100] 28: cooling water differential pressure sensor

[0101] 30: cold water pump

[0102] 32: cold water flow rate sensor

[0103] 34: cold water inlet temperature sensor

[0104] 36: cold water outlet temperature sensor

[0105] 38: cold water differential pressure sensor

[0106] 40: air bleeding device

[0107] 48: exhaust pump (discharge unit)