Double-heat-source partially-overlapped carbon dioxide heat pump system

Abstract

The utility model relates to a double heat source part cascade type carbon dioxide heat pump system which comprises a circulating water system, a carbon dioxide heat pump circulating system and a halogenated hydrocarbon working medium circulating system, and the circulating water system can exchange heat with the halogenated hydrocarbon working medium circulating system. The carbon dioxide heat pump circulating system comprises a first condensing heat exchanger and a second condensing heat exchanger which are sequentially connected, the first condensing heat exchanger is connected in a water return pipeline of the circulating water system in series, and the second condensing heat exchanger is connected in the halogenated hydrocarbon working medium circulating system in parallel. Heating return water is heated for the first time through the halogenated hydrocarbon working medium circulating system, the heating return water is heated for the second time through the carbon dioxide heat pump circulating system, and efficiency is improved. Partial cascade heat exchange is carried out between the halogenated hydrocarbon working medium circulating system and the carbon dioxide heat pump circulating system through a second condensation heat exchanger, waste heat is transmitted into the halogenated hydrocarbon working medium circulating system, and the second condensation heat exchanger is an evaporator of the halogenated hydrocarbon working medium circulating system and a condenser of the carbon dioxide heat pump circulating system.

Description

Technical Field

[0001] The utility model relates to the technical field of air-conditioning heat pumps, in particular to a dual-source partial cascade carbon dioxide heat pump system. Background Art

[0002] A heat pump is an energy-saving device that uses high-level electrical energy to convert low-level heat energy that cannot be directly utilized into high-level heat energy, and is mainly applied to heating or producing domestic hot water.

[0003] Carbon dioxide is an environmentally friendly natural refrigerant and is becoming more and more popular due to its excellent thermodynamic properties. It can extract heat from outdoor air and operate normally in an outdoor environment of -30°C. However, its critical temperature is about 31.3°C. Therefore, for an existing single-stage transcritical carbon dioxide heat pump system, the temperature of the medium exchanging heat with it on the condenser side needs to be lower than 31.3°C to meet the condition of liquefying carbon dioxide and realize the heat pump cycle. That is, when a single-stage transcritical carbon dioxide heat pump system is used in a heating system, the heating return water temperature needs to be lower than 31.3°C, and the lower heating water temperature is not conducive to improving the heating effect of users. An air-source heat pump using traditional halogenated hydrocarbon refrigerants as the refrigerant can only extract the heat energy of one of the low-temperature heat sources. And due to the restriction of the physical parameters of the refrigerant, the water outlet temperature of the unit generally does not exceed 60°C. Moreover, an air-source heat pump using halogenated hydrocarbons as the refrigerant has poor performance in adapting to outdoor low-temperature environments and cannot operate normally when the outdoor temperature is lower than -20°C. And the coefficient of performance in heating decreases severely at low temperatures, and the coefficient of performance in heating at low temperatures is not as good as that of a carbon dioxide heat pump system. However, the single-stage transcritical carbon dioxide heat pump system has the above-mentioned requirement for a lower heating return water temperature, which affects the heat dissipation effect at the end of the heating system. There is a heat pump form that completely cascades a traditional halogenated hydrocarbon heat pump and a carbon dioxide heat pump. The carbon dioxide heat pump extracts heat from the outdoor low-temperature environment and transfers the heat to the traditional halogenated hydrocarbon heat pump through an intermediate heat exchanger. The condenser of the traditional halogenated hydrocarbon heat pump heats the heating hot water. However, all heat transfer requires 2 compressors to do work, and the system efficiency is low. And due to the influence of the physical properties of halogenated hydrocarbons, the maximum heating water outlet temperature does not exceed 60°C. Summary of the Utility Model

[0004] (1) Technical Problems to be Solved

[0005] In view of the above-mentioned disadvantages and deficiencies of the prior art, the utility model provides a dual-source partial cascade carbon dioxide heat pump system.

[0006] (2) Technical Solutions

[0007] To achieve the above object, the dual heat source partial cascade carbon dioxide heat pump system of the present utility model includes a circulating water system, a carbon dioxide heat pump circulation system, a heat source system on the water source side, and a halogenated hydrocarbon refrigerant circulation system. Both the heat source system on the water source side and the circulating water system can exchange heat with the halogenated hydrocarbon refrigerant circulation system;

[0008] The carbon dioxide heat pump circulation system includes a first condensation heat exchanger and a second condensation heat exchanger connected in sequence. The first condensation heat exchanger is connected in series to the return water pipeline of the circulating water system, and the second condensation heat exchanger is connected in parallel to the halogenated hydrocarbon refrigerant circulation system.

[0009] Optionally, the halogenated hydrocarbon refrigerant circulation system includes a first compressor, a third condensation heat exchanger, a first throttle valve, and a first evaporation heat exchanger connected in a circulating sequence;

[0010] The circulating water system is connected in series to the third condensation heat exchanger, the second condensation heat exchanger is connected in parallel to the first evaporation heat exchanger, and the heat source system on the water source side is connected in series to the first evaporation heat exchanger.

[0011] Optionally, in the halogenated hydrocarbon refrigerant circulation system, a first control valve is provided on the pipeline connecting the first evaporation heat exchanger, and a second control valve is provided on the pipeline connecting the second condensation heat exchanger.

[0012] Optionally, the heat source system on the water source side includes a solar collector and a circulating water pump, and the solar collector, the circulating water pump, and the first evaporation heat exchanger are connected in a circulating sequence.

[0013] Optionally, the heat source system on the water source side further includes a ground-coupled heat exchanger, and the ground-coupled heat exchanger is connected in parallel to the solar collector.

[0014] Optionally, a third control valve is provided at the inlet of the ground-coupled heat exchanger, and a fourth control valve is provided at the inlet of the solar collector.

[0015] Optionally, the carbon dioxide heat pump circulation system further includes a second throttle valve, a second compressor, and a second evaporation heat exchanger;

[0016] The second compressor, the first condensation heat exchanger, the second condensation heat exchanger, the second throttle valve, and the second evaporation heat exchanger are connected in a circulating sequence.

[0017] Optionally, a heating circulation pump is provided in the circulating water system.

[0018] (III) Beneficial effects

[0019] The halogenated hydrocarbon refrigerant cycle system first heats the heating return water in the circulating water system, and the high-temperature medium in the carbon dioxide heat pump cycle system secondarily heats the heating return water in the circulating water system, improving the efficiency of the entire system.

[0020] The cold inlet and cold outlet of the second condensation heat exchanger are connected in parallel in the halogenated hydrocarbon refrigerant cycle system. A partial cascade heat exchange occurs between the halogenated hydrocarbon refrigerant cycle system and the carbon dioxide heat pump cycle system through the second condensation heat exchanger, transferring the waste heat of the carbon dioxide heat pump cycle system to the halogenated hydrocarbon refrigerant cycle system. The second condensation heat exchanger is both the evaporator of the halogenated hydrocarbon refrigerant cycle system and the condenser of the carbon dioxide heat pump cycle system.

[0021] Part of the condensation heat of the carbon dioxide heat pump cycle is transferred to the halogenated hydrocarbon refrigerant cycle system through the second condensation heat exchanger, and another part of the condensation heat is directly used to heat the heating hot water through the first condensation heat exchanger. Utilizing the characteristic of the high condensation temperature of the first condensation heat exchanger, the supply water temperature is raised to 75°C, improving the heat dissipation effect at the end of the heating system. The halogenated hydrocarbon refrigerant cycle system only absorbs part of the heat, so the equipment capacity of the halogenated hydrocarbon refrigerant cycle system is smaller, reducing the cost of the entire system under the condition of the same heating capacity of the whole set of equipment.

[0022] The present utility model uses air and water source as dual heat sources. During partial load periods, air can be used as the heat source during the day. When the operating efficiency of the air source side is low at night, it is switched to use the water source as the heat source to improve the operating efficiency of the entire system. During the peak heating load period, a dual heat source simultaneous utilization operation mode is adopted to improve the operating stability and annual average operating efficiency of the whole set of systems. BRIEF DESCRIPTION OF THE DRAWINGS

[0023] Figure 1 It is a schematic diagram of the dual heat source partial cascade carbon dioxide heat pump system of the present utility model.

[0024]

DESCRIPTION OF THE REFERENCE NUMERALS

[0025] 1: Second compressor; 2: First condensation heat exchanger; 3: Second condensation heat exchanger; 4: Second throttle valve; 5: Second evaporation heat exchanger;

[0026] 6: First compressor; 7: Third condensation heat exchanger; 8: First throttle valve; 9: First evaporation heat exchanger;

[0027] 10: First control valve; 11: Second control valve;

[0028] 12: Circulating water pump;

[0029] 13: Ground heat exchanger; 14: Solar collector;

[0030] 15: Third control valve; 16: Fourth control valve;

[0031] 17: Heating circulation pump. Detailed implementation manners

[0032] For better explaining the present utility model for easy understanding, the present utility model will be described in detail below in conjunction with the accompanying drawings through specific implementation manners. Among them, the orientation nouns such as "upper", "lower",... mentioned in this article are referred to Figure 1 for orientation.

[0033] Although the exemplary embodiments of the present utility model are shown in the drawings, it should be understood that the present utility model can be implemented in various forms and should not be limited by the embodiments described herein. On the contrary, these embodiments are provided to enable a clearer and more thorough understanding of the present utility model and to be able to fully convey the scope of the present utility model to those skilled in the art.

[0034] As Figure 1 shown, the present utility model provides a dual heat source partial cascade carbon dioxide heat pump system, which includes a circulating water system, a carbon dioxide heat pump circulation system, a water source side heat source system, and a halogenated hydrocarbon refrigerant circulation system. The halogenated hydrocarbon refrigerant circulation system is a circulation system represented by R134a (1,1,1,2-tetrafluoroethane) or R410a (a mixed refrigerant, a mixture composed of difluoromethane and pentafluoroethane). Among them, a heating circulation pump 17 is provided in the circulating water system for supplying hot water to the user side. Both the water source side heat source system and the circulating water system can exchange heat with the halogenated hydrocarbon refrigerant circulation system. The water source side heat source system transfers heat to the halogenated hydrocarbon refrigerant circulation system, and then the halogenated hydrocarbon refrigerant circulation system first heats the heating return water in the circulating water system. The carbon dioxide heat pump circulation system includes a first condensation heat exchanger 2 and a second condensation heat exchanger 3. The first condensation heat exchanger 2 and the second condensation heat exchanger 3 are preferably plate heat exchangers, and both include a hot inlet, a hot outlet, a cold inlet, and a cold outlet. In the pipeline of the carbon dioxide heat pump circulation system, the hot inlets and hot outlets of the first condensation heat exchanger 2 and the second condensation heat exchanger 3 are connected in sequence. The first condensation heat exchanger 2 is connected in series to the return water pipeline of the circulating water system. The circulating water flows in from the cold inlet of the first condensation heat exchanger 2 and flows out from the cold outlet. The high-temperature medium in the carbon dioxide heat pump circulation system secondarily heats the heating return water in the circulating water system, effectively increasing the temperature of the heating return water. The cold inlet and cold outlet of the second condensation heat exchanger 3 are connected in parallel to the halogenated hydrocarbon refrigerant circulation system. Heat exchange occurs through partial cascade between the halogenated hydrocarbon refrigerant circulation system and the carbon dioxide heat pump circulation system through the second condensation heat exchanger 3, and the waste heat of the carbon dioxide heat pump circulation system is transferred to the halogenated hydrocarbon refrigerant circulation system. The second condensation heat exchanger 3 is both an evaporator of the halogenated hydrocarbon refrigerant circulation system and a condenser of the carbon dioxide heat pump circulation system.

[0035] In this utility model, only part of the condensation heat of the carbon dioxide heat pump cycle is transferred to the halogenated hydrocarbon refrigerant cycle system through the second condensation heat exchanger 3, and the other part of the condensation heat is directly used to heat the heating hot water through the first condensation heat exchanger 2. By utilizing the characteristic of the high condensation temperature of the first condensation heat exchanger 2, the supply water temperature is raised to 75 °C, improving the heat dissipation effect at the end of the heating system. The halogenated hydrocarbon refrigerant cycle system serves to further cool the carbon dioxide vapor coming out after being cooled by the first condensation heat exchanger 2 to below 31.3 °C. Therefore, only the condensation heat of the low-temperature section of the carbon dioxide heat pump cycle is transferred to the halogenated hydrocarbon refrigerant cycle system. The heat is first used to heat the heating return water through the work cycle of the first compressor 6, and the carbon dioxide heat pump cycle directly uses the work cycle of the second compressor 1 to perform secondary heating on the heating return water, improving the efficiency of the entire system. Since the halogenated hydrocarbon refrigerant cycle system only absorbs part of the heat, the equipment capacity of the halogenated hydrocarbon refrigerant cycle system is relatively small, reducing the cost of the entire system under the condition that the heating capacity of the entire set of equipment is the same.

[0036] The halogenated hydrocarbon refrigerant cycle system includes a first compressor 6, a third condensation heat exchanger 7, a first throttle valve 8, and a first evaporation heat exchanger 9 that are sequentially connected in a cycle. The third condensation heat exchanger 7 is similar in structure to the first condensation heat exchanger 2. The cold inlet and cold outlet of the third condensation heat exchanger 7 are connected in series in the circulating water system, and the second condensation heat exchanger 3 is arranged in parallel with the first evaporation heat exchanger 9. In the halogenated hydrocarbon refrigerant cycle system, a first control valve 10 is provided on the pipeline connecting the first evaporation heat exchanger 9 to control the on-off of the cold inlet and cold outlet of the first evaporation heat exchanger 9, and a second control valve 11 is provided on the pipeline connecting the second condensation heat exchanger 3 to control the on-off of the cold inlet and cold outlet of the second condensation heat exchanger 3. Specifically, the halogenated hydrocarbon refrigerant absorbs heat in the first evaporation heat exchanger 9 and / or the second condensation heat exchanger 3. The opening states of the first evaporation heat exchanger 9 and the second condensation heat exchanger 3 are switched and controlled through the first control valve 10 and the second control valve 11. After the halogenated hydrocarbon refrigerant absorbs heat from the two heat sources, it is compressed into a high-temperature and high-pressure steam by the first compressor 6. The high-temperature and high-pressure steam transfers the heat to the heating return water through the third condensation heat exchanger 7 to perform the first-stage low-temperature heating on the heating return water. The halogenated hydrocarbon refrigerant then condenses into a medium-temperature and high-pressure liquid, expands in volume through the first throttle valve 8 to become a low-temperature and low-pressure gas-liquid two-phase mixture, and then enters the first evaporation heat exchanger 9 and the second condensation heat exchanger 3 to absorb the heat on the heat source side. In this way, the heat of the two systems is transferred to the circulating water system, and the circulating water system uses the heat for indoor heating.

[0037] Further, the dual heat source partially cascaded carbon dioxide heat pump system further includes a water source side heat source system, and the water source side heat source system is connected in series with the heat inlet and heat outlet of the first evaporation heat exchanger 9. The water source side heat source system includes a solar collector 14 and a circulation water pump 12, and the solar collector 14, the circulation water pump 12 and the first evaporation heat exchanger 9 are sequentially connected in a cycle. Clean solar energy is collected by the solar collector 14 and serves as one of the heat sources of the water source side heat source system.

[0038] Furthermore, the water source side heat source system further includes a ground heat exchanger 13, and the ground heat exchanger 13 is connected in parallel with the solar collector 14 and is used to obtain geothermal heat as one of the heat sources of the water source side heat source system.

[0039] A third control valve 15 is provided at the inlet of the ground heat exchanger 13, and a fourth control valve 16 is provided at the inlet of the solar collector 14. The first control valve 10, the second control valve 11, the third control valve 15, and the fourth control valve 16 are all preferably electric control valves for easy automatic control. The third control valve 15 and the fourth control valve 16 respectively control the on / off of the solar collector 14 and the ground heat exchanger 13 to achieve their separate operation or parallel operation. Taking the ground source ground heat exchanger 13 and the solar collector 14 as examples, the heat source of the water source side heat source system can also be composed of various water source systems such as sewage sources and surface water sources. The temperature of the water source side such as the ground source, surface water source, and sewage source generally does not change much day and night, effectively avoiding the situation that the simple air source heat pump has a higher efficiency during the day when the temperature is high and a lower efficiency at night when the temperature is low.

[0040] The carbon dioxide heat pump cycle system further includes a second throttle valve 4, a second compressor 1, and a second evaporation heat exchanger 5. The second compressor 1, the first condensation heat exchanger 2, the second condensation heat exchanger 3, the second throttle valve 4, and the second evaporation heat exchanger 5 are sequentially connected in a cycle. Specifically, the carbon dioxide working medium absorbs heat from the outdoor air through the second evaporation heat exchanger 5 and evaporates into a low-temperature and low-pressure superheated steam, which is compressed into a high-temperature and high-pressure steam by the second compressor 1. The carbon dioxide steam first passes through the first condensation heat exchanger 2 to perform secondary high-temperature heating on the heating cycle return water heated by the halogenated hydrocarbon working medium cycle system, transferring most of the heat to the heating cycle return water. Since the temperature of the carbon dioxide steam in the first condensation heat exchanger 2 is relatively high, the heating cycle return water can be heated to a relatively high temperature. The carbon dioxide steam then enters the second condensation heat exchanger 3, and transfers the low-temperature section heat of the carbon dioxide to the halogenated hydrocarbon working medium cycle system through the second condensation heat exchanger 3. The second condensation heat exchanger 3 is both an evaporator of the halogenated hydrocarbon working medium cycle system and a condenser of the carbon dioxide heat pump cycle system. After two-stage heat exchange, the carbon dioxide steam condenses into a medium-temperature and high-pressure liquid, enters the second throttle valve 4, expands in volume to become a low-temperature and low-pressure gas-liquid two-phase mixture, and then enters the second evaporation heat exchanger 5 to absorb heat from the outdoor air. In this way, the cycle is repeated, and part of the heat absorbed from the outdoor low-temperature air is directly transferred to the heating cycle water through the first condensation heat exchanger 2, and part is transferred to the halogenated hydrocarbon working medium cycle system, indirectly transferring the heat to the heating cycle water for indoor heating.

[0041] The carbon dioxide heat pump cycle system only transfers part of the low-temperature section heat to the low-temperature stage heating halogenated hydrocarbon working medium cycle through the second condensation heat exchanger 3. The temperature of the high-temperature section carbon dioxide steam is relatively high, and this part of the heat is directly used to heat the heating cycle water, improving the heating efficiency of the system and the temperature of the heating cycle water. The carbon dioxide is evaporated and cooled by the halogenated hydrocarbon working medium in the second condensation heat exchanger 3, and a relatively low cooling temperature can be achieved, avoiding the adverse requirements for the temperature of the heating return water when directly exchanging heat with the heating cycle water.

[0042] The water source side and the air source side of the dual-source partially cascaded carbon dioxide heat pump system can work simultaneously, or can adopt multiple operation modes such as a single heat source working mode and a timed switching working mode according to operation parameters such as the outdoor air temperature, the water source side temperature, and the indoor required heating quantity. During the winter heating period, the outdoor temperature varies greatly between day and night. The coefficient of performance value of the traditional single air source heat pump is also greatly affected by the outdoor atmospheric temperature, and its operating efficiency decreases with the decrease of the outdoor air temperature. The efficiency is higher during the day when the air temperature is high and lower at night when the air temperature is low. While the water temperature of the water source side such as the ground source, surface water source, and sewage source generally does not change much day and night and is hardly affected by the outdoor air temperature. The present utility model uses air and water as dual heat sources. During partial load periods, air can be used as the heat source during the day, and when the operating efficiency of the air source side is low at night, it can be switched to use water as the heat source to improve the operating efficiency of the entire system. During the peak heating load period, the operating mode of using both dual heat sources simultaneously can also be adopted, improving the operating stability of the entire system and the annual average operating efficiency.

[0043] In the description of the present utility model, it should be understood that the terms "first" and "second" are only used for descriptive purposes and cannot be understood as indicating or implying relative importance or implicitly specifying the quantity of the indicated technical features. Thus, the features defined with "first" and "second" may explicitly or implicitly include one or more of such features. In the description of the present utility model, the meaning of "a plurality of" is two or more, unless otherwise specifically and clearly defined.

[0044] In the present utility model, unless otherwise clearly specified and defined, the terms "installed", "connected", "connected to", "fixed", etc. should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or integrated; it can be a mechanical connection or an electrical connection; it can be directly connected or indirectly connected through an intermediate medium; it can be the internal communication of two components or the interaction relationship between two components. For those of ordinary skill in the art, the specific meanings of the above terms in the present utility model can be understood according to specific circumstances.

[0045] In the present utility model, unless otherwise clearly specified and defined, the first feature being "on" or "under" the second feature can be that the first and second features are in direct contact, or the first and second features are indirectly in contact through an intermediate medium. Moreover, the first feature being "above", "over" and "on" the second feature can be that the first feature is directly above or obliquely above the second feature, or merely indicates that the first feature has a higher horizontal height than the second feature. The first feature being "under", "beneath" and "under" the second feature can be that the first feature is directly below or obliquely below the second feature, or merely indicates that the first feature has a lower horizontal height than the second feature.

[0046] In the description of this specification, the descriptions of terms such as "one embodiment", "some embodiments", "embodiment", "example", "specific example", or "some examples" mean that the specific features, structures, materials, or characteristics described in connection with the embodiment or example are included in at least one embodiment or example of the present utility model. In this specification, the schematic representations of the above terms do not necessarily refer to the same embodiment or example. Moreover, the specific features, structures, materials, or characteristics described may be combined in any one or more embodiments or examples in a suitable manner. In addition, without contradiction, those skilled in the art can combine and combine the different embodiments or examples described in this specification and the features of different embodiments or examples.

[0047] Although the embodiments of the present utility model have been shown and described above, it can be understood that the above embodiments are exemplary and should not be construed as limiting the present utility model. Those of ordinary skill in the art can make changes, modifications, substitutions, and variations to the above embodiments within the scope of the present utility model.

Claims

1. A dual heat source partially cascaded carbon dioxide heat pump system, characterized in that, The dual heat source partially cascaded carbon dioxide heat pump system includes a circulating water system, a carbon dioxide heat pump cycle system, a heat source system on the water source side, and a halogenated hydrocarbon refrigerant cycle system. The heat source system on the water source side and the circulating water system can both perform heat exchange with the halogenated hydrocarbon refrigerant cycle system; The carbon dioxide heat pump cycle system includes a first condensation heat exchanger (2) and a second condensation heat exchanger (3) connected in sequence. The first condensation heat exchanger (2) is connected in series to the return water pipeline of the circulating water system, and the second condensation heat exchanger (3) is connected in parallel to the halogenated hydrocarbon refrigerant cycle system.

2. The dual heat source partial cascade carbon dioxide heat pump system according to claim 1, characterized in that The halogenated hydrocarbon refrigerant cycle system includes a first compressor (6), a third condensation heat exchanger (7), a first throttle valve (8), and a first evaporation heat exchanger (9) connected in a circulating sequence; The circulating water system is connected in series to the third condensation heat exchanger (7), the second condensation heat exchanger (3) is connected in parallel to the first evaporation heat exchanger (9), and the heat source system on the water source side is connected in series to the first evaporation heat exchanger (9).

3. The dual-source partially cascaded carbon dioxide heat pump system according to claim 2, wherein In the halogenated hydrocarbon refrigerant cycle system, a first control valve (10) is provided on the pipeline connecting the first evaporation heat exchanger (9), and a second control valve (11) is provided on the pipeline connecting the second condensation heat exchanger (3).

4. The dual heat source partially cascaded carbon dioxide heat pump system according to claim 2, wherein The heat source system on the water source side includes a solar collector (14) and a circulating water pump (12). The solar collector (14), the circulating water pump (12), and the first evaporation heat exchanger (9) are connected in a circulating sequence.

5. The dual heat source partially cascaded carbon dioxide heat pump system according to claim 4, characterized in that, The heat source system on the water source side further includes a ground-coupled heat exchanger (13), and the ground-coupled heat exchanger (13) is connected in parallel to the solar collector (14).

6. The dual heat source partial cascade carbon dioxide heat pump system according to claim 5, wherein, A third control valve (15) is provided at the inlet of the ground-coupled heat exchanger (13), and a fourth control valve (16) is provided at the inlet of the solar collector (14).

7. The dual heat source partially cascaded carbon dioxide heat pump system according to claim 1, characterized in that, The carbon dioxide heat pump cycle system further includes a second throttle valve (4), a second compressor (1), and a second evaporation heat exchanger (5); The second compressor (1), the first condensation heat exchanger (2), the second condensation heat exchanger (3), the second throttle valve (4), and the second evaporation heat exchanger (5) are connected in a circulating sequence.

8. The dual heat source partial cascade carbon dioxide heat pump system according to claim 1, wherein A heating circulating pump (17) is provided in the circulating water system.

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