CN112484357A

CN112484357A - Low-pressure-ratio working condition heat pump system based on air-supplementing enthalpy-increasing circulation and control method thereof

Info

Publication number: CN112484357A
Application number: CN202011382695.6A
Authority: CN
Inventors: 吴建华; 李澳特; 雷博雯; 李佳宸
Original assignee: Xian Jiaotong University
Current assignee: Xian Jiaotong University
Priority date: 2020-11-30
Filing date: 2020-11-30
Publication date: 2021-03-12
Anticipated expiration: 2040-11-30
Also published as: CN112484357B

Abstract

The invention provides a low-pressure-ratio working condition heat pump system based on air-supplementing enthalpy-increasing circulation and a control method thereof, and solves the problem that the reliability of a compressor and the refrigerant charge amount are influenced due to the fact that the exhaust temperature of the existing heat pump system under the low-pressure-ratio working condition is low. The low-pressure ratio working condition heat pump system comprises a compressor, a condensing heat exchanger, a first throttling element, a second throttling element, an evaporating heat exchanger and an economizer; refrigerant and lubricating oil are filled in the heat pump system; the outlet of the compressor is connected with the inlet of the condensing heat exchanger, the outlet pipeline of the condensing heat exchanger is divided into two paths, one path is connected with the cold end inlet of the economizer through a first throttling element, and the other path is connected with the hot end inlet of the economizer; the cold end outlet of the economizer is connected with the air supplement port of the compressor for supplementing air; the hot end outlet of the economizer is connected with the inlet of the compressor through a second throttling element and an evaporation heat exchanger in sequence; the heat exchange area of the economizer is 1.2-2 times of that of the original economizer.

Description

Low-pressure-ratio working condition heat pump system based on air-supplementing enthalpy-increasing circulation and control method thereof

Technical Field

The invention belongs to the field of refrigeration, and particularly relates to a low-pressure-ratio working condition heat pump system based on air-supplementing enthalpy-increasing circulation and a control method thereof.

Background

Since the twenty-first century, energy conservation and environmental protection have become the development theme of refrigeration and air conditioning industry. The heating heat pump system mainly adopts HCFC22, HFC410A and the like as working media of the system. However, the problem of ozone layer destruction caused by the discharge of the refrigerant into the atmosphere, so that HCFC refrigerant enters a phase of elimination. Based on multi-target constraints such as environmental protection, safety, economy, energy efficiency conversion capability and the like, the types of the replaceable refrigerants are less and less. The natural refrigerant propane (R290) has the advantages of zero Ozone Depletion Potential (ODP), extremely low Global Warming Potential (GWP), environmental friendliness, low cost and the like, and is one of the choices of future refrigerants. However, the physical and chemical properties of propane have natural limitations.

Compared with freon refrigerant, propane (R290) refrigerant has the characteristics of small heat insulation index, low exhaust temperature and exhaust superheat degree and the like. The air temperature in winter in subtropical regions is averagely above 0 ℃, the operation pressure ratio of a compressor in a heating cycle is small, and the characteristics of low exhaust temperature and low exhaust superheat degree of a propane (R290) refrigerant are more obvious. The lower discharge superheat of propane (R290) affects the solubility of propane (R290) in the high back pressure compressor sump, as well as the viscosity of the R290/lube oil mixture, further affecting compressor reliability and refrigerant charge in the heat pump system.

The circulating system represented by a room air conditioner and a heat pump mostly adopts a high-backpressure rotary compressor, and has the advantages of simple structure, high efficiency, good reliability and the like. Unlike low back pressure rotary compressors, the oil sump of high back pressure rotary compressors is inside a high temperature, high pressure housing. The refrigerant dissolves in the oil pool in a large amount, resulting in a large difference between the viscosity of the mixture and the viscosity of pure oil when the refrigerant works. In order to guarantee the supporting effect of the friction pairs inside the rotary compressor, the working viscosity of the oil sump mixture must reach the minimum required viscosity. Above that, higher viscosity results in increased oil film shear stress, resulting in higher viscous drag losses and reduced compressor efficiency.

As known in the art, the lubricating oil used in the R290 air conditioner and the heat pump system mainly includes Mineral Oil (MO) completely miscible with the R290 refrigerant, polyol ester synthetic oil (POE), and polyethylene glycol synthetic oil (PAG) partially miscible with R290. Compared with partial intersolubility lubricating oil, the lubricating oil system with complete intersolubility has better oil return characteristic and less influence on the heat exchange performance of the heat exchanger, but the high solubility of R290 in the oil pool can greatly reduce the viscosity of the mixture in the oil pool. Meanwhile, the lubricating oil which is completely mutually soluble is adopted, so that the charging amount of the R290 refrigerant is not reduced. Although the solubility of the R290 refrigerant in the partially miscible lubricating oil is low, the maximum solubility requirement is still exceeded due to the low discharge temperature of the R290 compressor.

In the prior art, the method for improving the exhaust temperature is to improve the degree of superheat of air suction through regenerative cycle, so that the degree of superheat of exhaust is improved. For a heat pump system, the ambient temperature is low, and the highest suction temperature can only reach the ambient temperature, so the suction superheat degree cannot be increased to the minimum required temperature to ensure the solubility of the refrigerant in the oil pool and the viscosity of the mixture, and the efficiency of the evaporator is also influenced, so the regenerative cycle is not suitable for a low-pressure specific heat pump system.

In addition, in the current heat pump system, the vapor-supplying and enthalpy-increasing technology is generally used for reducing the exhaust temperature or increasing the heating capacity of the heat pump system. When the exhaust temperature is reduced, two-phase refrigerant is supplemented into the cylinder; when the heating capacity is increased, saturated gaseous refrigerant or gaseous refrigerant with low superheat is generally supplemented into the cylinder. The vapor-supplying enthalpy-increasing cycle mainly comprises a Flash Tank Cycle (FTC) and an economizer cycle (IHXC), wherein the flash tank cycle is generally saturated gas, and the economizer cycle is a gaseous refrigerant with low superheat degree.

Disclosure of Invention

The invention aims to solve the problems that the exhaust temperature of a heat pump system under the existing low-pressure-ratio working condition is low, so that the reliability of a compressor and the filling amount of a refrigerant are influenced, and provides a low-pressure-ratio working condition heat pump system based on air-supply enthalpy-increasing circulation and a control method thereof.

In order to achieve the purpose, the invention adopts the following technical scheme:

a control method of a heat pump system under a low pressure ratio working condition is characterized in that the heat pump system is an air-supplementing enthalpy-increasing heat pump system and comprises a compressor, a condensing heat exchanger, a first throttling element, a second throttling element, an evaporating heat exchanger and an economizer; the heat pump system is filled with refrigerant and lubricating oil; the outlet of the compressor is connected with the inlet of the condensing heat exchanger, the outlet pipeline of the condensing heat exchanger is divided into two paths, one path is connected with the cold end inlet of the economizer through a first throttling element, and the other path is connected with the hot end inlet of the economizer; the cold end outlet of the economizer is connected with the air supplementing port of the compressor for supplementing air; the hot end outlet of the economizer is connected with the inlet of the compressor sequentially through the second throttling element and the evaporation heat exchanger; controlling the intermediate air supplement superheat degree of the air supplement enthalpy increasing heat pump system according to the following corresponding relation to realize the improvement of the exhaust temperature: when the lubricating oil is mineral oil MO and the viscosity grade ISO VG is 80-90, the gas supplementing superheat degree is more than 19K; when the lubricating oil is mineral oil MO and the viscosity grade ISO VG is 90-100, the gas supplementing superheat degree is more than 17K; when the lubricating oil is mineral oil MO and the viscosity grade ISO VG is 100-120, the gas supplementing superheat degree is more than 16K; when the lubricating oil is polyester synthetic oil POE and the viscosity grade ISO VG is 50-60, the air-supplementing superheat degree is more than 23K; when the lubricating oil is polyester synthetic oil POE and the viscosity grade ISO VG is 60-70, the air-supplementing superheat degree is more than 21K; when the lubricating oil is polyester synthetic oil POE and the viscosity grade ISO VG is 70-80, the air-supplementing superheat degree is more than 19K; when the lubricating oil is polyethylene glycol synthetic oil PAG and the viscosity grade ISO VG is 35-43, the air-supplementing superheat degree is more than 17K; when the lubricating oil is polyethylene glycol synthetic oil PAG and the viscosity grade ISO VG is 43-52, the air-supplementing superheat degree is more than 16K; when the lubricating oil is polyethylene glycol synthetic oil PAG and the viscosity grade ISO VG is 50-60, the air supplementing superheat degree is more than 14K.

Further, the control of the air-supplementing superheat degree is realized by changing the heat exchange area of the economizer, at the moment, the heat exchange area of the economizer is increased, and the air-supplementing superheat degree is correspondingly increased.

Meanwhile, the invention also provides a low-pressure ratio working condition heat pump system based on air-supply enthalpy-increasing circulation, which comprises a compressor, a condensing heat exchanger, a first throttling element, a second throttling element, an evaporating heat exchanger and an economizer, wherein the compressor is connected with the condensing heat exchanger; the heat pump system is filled with refrigerant and lubricating oil; the outlet of the compressor is connected with the inlet of the condensing heat exchanger, the outlet pipeline of the condensing heat exchanger is divided into two paths, one path is connected with the cold end inlet of the economizer through a first throttling element, and the other path is connected with the hot end inlet of the economizer; the cold end outlet of the economizer is connected with the air supplementing port of the compressor for supplementing air; the hot end outlet of the economizer is connected with the inlet of the compressor sequentially through the second throttling element and the evaporation heat exchanger; the heat exchange area of the economizer is 1.2-2 times of that of the original economizer.

Further, the heat exchange area of the economizer is 1.2-1.5 times of that of the original economizer.

Further, the compressor is a high back pressure compressor; the refrigerant is a hydrocarbon refrigerant; the base oil of the lubricating oil is mineral oil MO, polyester synthetic oil POE or polyethylene glycol synthetic oil PAG.

Further, the high back pressure compressor is a high back pressure rotary compressor; the hydrocarbon refrigerant is propane refrigerant; the base oil of the lubricating oil adopts mineral oil MO with the viscosity grade of ISO VG80-ISO VG120, or adopts polyester synthetic oil POE with the viscosity grade of ISO VG50-ISO VG80, or adopts polyethylene glycol synthetic oil PAG with the viscosity grade of ISO VG35-ISO VG 60.

Compared with the prior art, the invention has the following advantages:

1. the system adopts an economizer cycle with high air supplement superheat degree, and improves the exhaust temperature by controlling the air supplement superheat degree, so that the temperature of the oil pool is improved, the solubility of the refrigerant in the oil pool is reduced, the refrigerant filling amount is further reduced, and the problem of insufficient circulation amount caused by excessive refrigerant dissolution is solved; meanwhile, the viscosity of the mixture in the oil pool is ensured, so that the reliability of the compressor is ensured.

2. The system and the method transfer the heat at the outlet of the condenser to the outlet of the economizer through an air-supplying enthalpy-increasing technology, the temperature at the outlet of the condenser is reduced (the supercooling degree is increased), and the superheat degree at the outlet of the economizer is increased (the air-supplying superheat degree is increased), so that the supercooling degree of the air-conditioning system is improved, and the heating capacity and the energy efficiency ratio of the heat pump system are improved.

3. The system adopts the economizer cycle with high air supplement superheat degree, and increases the supercooling section at the outlet of the condensing heat exchanger, thereby improving the supercooling degree of the system, increasing the superheat degree at the outlet of the economizer, fully dissolving the lubricating oil in front of the inlet of the first throttling element and preventing the throttling element from being blocked due to lubricating oil mass.

Drawings

FIG. 1 is a schematic diagram of a conventional single stage compression economizer cycle system;

FIG. 2 is a schematic of the comparative pressure enthalpy for a conventional economizer cycle versus a single stage cycle;

FIG. 3 is a schematic diagram of the contrast pressure enthalpy of the regenerative cycle and the single-stage cycle;

FIG. 4 is a schematic diagram of the comparative pressure enthalpy for the high make-up air superheat economizer cycle and the single stage cycle of the present invention;

FIG. 5 is a schematic representation of three different lubricants and solubility variations of the present invention;

FIG. 6 is a schematic diagram of the viscosity change of three different lubricants and refrigerants according to the present invention.

Reference numerals: 10-compressor, 20-condensing heat exchanger, 30-first throttling element, 40-economizer, 50-second throttling element, 60-evaporating heat exchanger.

Detailed Description

The invention is described in further detail below with reference to the figures and specific embodiments.

The invention provides a low-pressure-ratio working condition heat pump system based on air-supplementing enthalpy-increasing circulation and a control method thereof, wherein the air-supplementing enthalpy-increasing circulation is used for increasing the exhaust temperature, so that the high performance, the high energy efficiency and the high reliability of a propane heat pump system under the working condition of low pressure ratio are ensured.

As shown in fig. 1, the heat pump system based on the air-make-up enthalpy cycle under the low pressure ratio condition of the present invention includes a compressor 10, a condensing heat exchanger 20, a first throttling element 30, a second throttling element 50, an evaporating heat exchanger 60, and an economizer 40; refrigerant and lubricating oil are filled in the heat pump system; the outlet of the compressor 10 is connected with the inlet of the condensing heat exchanger 20, the outlet pipeline of the condensing heat exchanger 20 is divided into two paths, one path is connected with the cold end inlet of the economizer 40 through the first throttling element 30, and the other path is connected with the hot end inlet of the economizer 40; the outlet of the cold end of the economizer 40 is connected with the air supplement port of the compressor 10 for supplementing air; the hot end outlet of the economizer 40 is connected to the inlet of the compressor 10 sequentially through the second throttling element 50 and the evaporative heat exchanger 60. The economizer 40 of the present invention is connected to two sections of piping for heat exchange, one section being the piping from the first throttling element 30 to the air supply port of the compressor 10, and the other section being the piping from the condensing heat exchanger 20 to the second throttling element 50. The heat exchange area of the economizer is 1.2-2 times of that of the original economizer, and preferably, the heat exchange area of the economizer 40 is 1.2-1.5 times of that of the original economizer.

The heat pump system is an economizer circulating system, preferably a single-stage compression economizer circulating system; the compressor is a high back pressure compressor, which is preferably a high back pressure rotary compressor. The air conditioning system uses a hydrocarbon refrigerant, which is preferably R290 (propane) refrigerant. The air conditioning system is filled with lubricating oil, the lubricating oil and the refrigerant form a refrigerating machine oil mixture in an oil pool at the bottom of the compressor, and the base oil of the lubricating oil is mineral oil MO, polyester synthetic oil POE and polyethylene glycol synthetic oil PAG. The base oil of the lubricating oil is selected as mineral oil MO, preferably having a viscosity grade of ISO VG80-ISO VG120 (i.e. the kinematic viscosity of the lubricating oil is 80-120cSt at 40 ℃). The base oil of the lubricating oil is selected from polyester-based synthetic oils POE, preferably with a viscosity grade of ISO VG50-ISO VG80 (i.e. the kinematic viscosity of the lubricating oil is 50-80cSt at 40 ℃). The base oil of the lubricating oil is selected from polyethylene glycol based synthetic oil PAG, preferably with a viscosity grade of ISO VG35-ISO VG60 (i.e. the kinematic viscosity of the lubricating oil is 35-60cSt at 40 ℃).

The air conditioning system controls the air supplementing superheat degree according to the type and viscosity grade of the filled lubricating oil, and the corresponding relation is as follows:

in the table, A is the heat exchange area of the economizer in the traditional economizer cycle, and the refrigerant added into the cylinder at the outlet of the economizer is generally saturated gaseous refrigerant or gaseous refrigerant with small superheat degree.

As shown in fig. 2, which is a schematic diagram of the enthalpy of a conventional economizer cycle compared with the enthalpy of a single-stage cycle, the gas supplied by the conventional economizer cycle is a saturated refrigerant gas or a low superheat refrigerant gas, which not only does not increase the discharge temperature, but also decreases the discharge temperature, thereby seriously affecting the reliability of the heat pump system. Fig. 3 shows a schematic diagram of the pressure enthalpy of the regenerative cycle and the single-stage cycle. Although the exhaust temperature of the regenerative cycle can be increased by increasing the degree of superheat of the suction gas, the suction gas temperature cannot be higher than the ambient temperature, the range of the exhaust temperature required by the cycle cannot be reached, and the heating capacity and the energy efficiency ratio of the regenerative cycle are not improved as much as those of an economizer cycle.

FIG. 4 is a schematic of the enthalpy of the high superheat make-up economizer cycle versus the stand-alone cycle for the present invention. The high-air-supply superheat economizer circulates through the increase of the heat exchange area of the economizer, increases the air-supply superheat degree, and therefore the purpose of improving the exhaust temperature is achieved, the heat of the outlet of the condensation heat exchanger is utilized, the supercooling section of the condensation heat exchanger is increased, lubricating oil in front of the first throttling element can be fully dissolved into the refrigerant, the oil return of the system is guaranteed, and the heating capacity and the energy efficiency ratio of the system are improved.

Fig. 5 and 6 show solubility versus viscosity profiles for three different lubricants and refrigerants.

Fig. 5 is a graph showing the solubility of refrigerant in lubricating oil as a function of the superheat of the oil pool, which is the difference between the temperature of the oil pool and the saturation temperature of the refrigerant at the pressure of the oil pool. It can be seen from the figure that the solubility of the refrigerant in the three lubricating oils is reduced along with the increase of the superheat degree of the oil pool, and under the same superheat degree of the oil pool, the solubility of the refrigerant in the mineral oil and the solubility of the refrigerant in the polyester synthetic oil are not greatly different and are all larger than the solubility of the refrigerant in the polyethylene glycol synthetic oil. For the heat pump system, the exhaust temperature of the compressor can be improved due to the improvement of the air supply superheat degree, so that the temperature of an oil pool of the compressor is improved, and the superheat degree of the oil pool can be maintained in a range of extremely low (less than 15%) of the solubility of a refrigerant. Therefore, the problem of insufficient circulation amount caused by excessive dissolution of the refrigerant can be solved, the refrigerant filling amount of the system is reduced, and the reliability of the system is ensured.

Figure 6 is a graph of the refrigerating machine oil mixture viscosity as a function of pool superheat, from which it can be seen that the three lubricating oil and refrigerant refrigerating machine oil mixture viscosities eventually reach a relatively plateau region with increasing pool superheat and subsequently decrease. The air-supplementing superheat degree provided by the air-conditioning system can fully ensure that the viscosity of the refrigerating machine oil reaches a proper range (2-5cSt), thereby ensuring the lubrication and the sealing of the compressor.

Claims

1. A control method of a heat pump system under a low pressure ratio working condition is characterized in that the heat pump system is an air-supplementing enthalpy-increasing heat pump system and comprises a compressor (10), a condensing heat exchanger (20), a first throttling element (30), a second throttling element (50), an evaporating heat exchanger (60) and an economizer (40); the heat pump system is filled with refrigerant and lubricating oil; the outlet of the compressor (10) is connected with the inlet of the condensing heat exchanger (20), the outlet pipeline of the condensing heat exchanger (20) is divided into two paths, one path is connected with the cold end inlet of the economizer (40) through the first throttling element (30), and the other path is connected with the hot end inlet of the economizer (40); the cold end outlet of the economizer (40) is connected with the air supplement port of the compressor (10) for supplementing air; a hot end outlet of the economizer (40) is connected with an inlet of the compressor (10) sequentially through a second throttling element (50) and an evaporative heat exchanger (60); the method is characterized in that: controlling the intermediate air supplement superheat degree of the air supplement enthalpy increasing heat pump system according to the following corresponding relation to realize the improvement of the exhaust temperature:

when the lubricating oil is mineral oil MO and the viscosity grade ISO VG is 80-90, the gas supplementing superheat degree is more than 19K;

when the lubricating oil is mineral oil MO and the viscosity grade ISO VG is 90-100, the gas supplementing superheat degree is more than 17K;

when the lubricating oil is mineral oil MO and the viscosity grade ISO VG is 100-120, the gas supplementing superheat degree is more than 16K;

when the lubricating oil is polyester synthetic oil POE and the viscosity grade ISO VG is 50-60, the air-supplementing superheat degree is more than 23K;

when the lubricating oil is polyester synthetic oil POE and the viscosity grade ISO VG is 60-70, the air-supplementing superheat degree is more than 21K;

when the lubricating oil is polyester synthetic oil POE and the viscosity grade ISO VG is 70-80, the air-supplementing superheat degree is more than 19K;

when the lubricating oil is polyethylene glycol synthetic oil PAG and the viscosity grade ISO VG is 35-43, the air-supplementing superheat degree is more than 17K;

when the lubricating oil is polyethylene glycol synthetic oil PAG and the viscosity grade ISO VG is 43-52, the air-supplementing superheat degree is more than 16K;

when the lubricating oil is polyethylene glycol synthetic oil PAG and the viscosity grade ISO VG is 50-60, the air supplementing superheat degree is more than 14K.

2. The control method of the low pressure ratio heat pump system according to claim 1, wherein: the control of the air-supplementing superheat degree is realized by changing the heat exchange area of the economizer, at the moment, the heat exchange area of the economizer is increased, and the air-supplementing superheat degree is correspondingly increased.

3. The control method of the low pressure ratio heat pump system according to claim 2, wherein: the heat exchange area of the economizer is increased by 1.2-2 times.

4. The control method of the low pressure ratio heat pump system according to claim 3, wherein: the heat exchange area of the economizer is increased by 1.2-1.5 times.

5. A low-pressure ratio working condition heat pump system based on air-supplementing enthalpy-increasing circulation comprises a compressor (10), a condensing heat exchanger (20), a first throttling element (30), a second throttling element (50), an evaporating heat exchanger (60) and an economizer (40); the heat pump system is filled with refrigerant and lubricating oil; the outlet of the compressor (10) is connected with the inlet of the condensing heat exchanger (20), the outlet pipeline of the condensing heat exchanger (20) is divided into two paths, one path is connected with the cold end inlet of the economizer (40) through the first throttling element (30), and the other path is connected with the hot end inlet of the economizer (40); the cold end outlet of the economizer (40) is connected with the air supplement port of the compressor (10) for supplementing air; a hot end outlet of the economizer (40) is connected with an inlet of the compressor (10) sequentially through a second throttling element (50) and an evaporative heat exchanger (60); the method is characterized in that: the heat exchange area of the economizer (40) is 1.2-2 times of that of the original economizer.

6. The low pressure ratio working condition heat pump system based on the vapor-supplementing enthalpy-increasing cycle of claim 5, characterized in that: the heat exchange area of the economizer (40) is 1.2-1.5 times of that of the original economizer.

7. The low pressure ratio working condition heat pump system based on the vapor-filling enthalpy-increasing cycle is characterized in that: the compressor (10) is a high back pressure compressor; the refrigerant is a hydrocarbon refrigerant; the base oil of the lubricating oil is mineral oil MO, polyester synthetic oil POE or polyethylene glycol synthetic oil PAG.

8. The low pressure ratio working condition heat pump system based on the vapor-supplementing enthalpy-increasing cycle of claim 7, characterized in that: the high back pressure compressor is a high back pressure rotary compressor; the hydrocarbon refrigerant is propane refrigerant; the base oil of the lubricating oil adopts mineral oil MO with the viscosity grade of ISO VG80-ISO VG120, or adopts polyester synthetic oil POE with the viscosity grade of ISO VG50-ISO VG80, or adopts polyethylene glycol synthetic oil PAG with the viscosity grade of ISO VG35-ISO VG 60.