CN101581518B - Transcritical CO2 energy-saving heat pump system of solar supplementary heat source - Google Patents

Abstract

A solar auxiliary heat source carbon dioxide transcritical energy-saving heat pump system is used to solve the problem of thermal energy recycling. The technical solution is: the system is composed of a solar heat collection auxiliary part and a transcritical carbon dioxide heat pump part, the two systems are connected by two expansion compressors, and the working medium of the whole system is carbon dioxide. The advantages of the present invention are reflected in the following aspects: 1. Energy saving: the present invention can effectively utilize solar energy as the driving energy of the system, greatly improving the COP value of system operation, and having the effect of saving energy; 2. Environmental protection: the refrigeration working medium of the whole system Both use CO ₂ , so there is no pollution to the environment; 3. Economical efficiency: the present invention only needs one-time investment, and the subsequent maintenance and investment costs are very small. Can be widely used in air conditioning, heating, refrigeration and other occasions.

Description

A solar auxiliary heat source carbon dioxide transcritical energy-saving heat pump system

technical field

The invention relates to a solar heat utilization technology, in particular to a heat pump system utilizing solar energy, and belongs to the technical field of heat exchange.

Background technique

The coal-based primary energy structure not only has low energy utilization efficiency, but also causes serious environmental pollution. 90% of SO ₂ emissions and 60% of NO _x emissions come from coal combustion. The impact of serious environmental pollution on the ecological environment has threatened the sustainable development of economy and society. With the rapid development of the economy, energy consumption is increasing day by day, and energy has gradually become a "bottleneck" restricting social and economic development. According to research reports, my country's building energy consumption accounts for more than 25% of the total social energy consumption, and in building energy consumption, air-conditioning energy consumption accounts for more than 50%, and the demand for building air-conditioning is increasing year by year. In this case, solar energy, as a kind of renewable energy, has been paid more and more attention by people. Solar energy is a huge clean energy. The solar radiant energy reaching the earth's surface every day is 5.57×10 ¹⁸ MJ, equivalent to 190 trillion tons of standard coal, which is about 1.56×10 ⁴ times the current total primary energy consumption in the world. Solar energy is valued by people for its inexhaustible, cheap, safe, no need for transportation, clean and pollution-free, etc. Solar energy utilization technologies such as photothermal, photoelectric, and photochemical are developing rapidly.

Due to the destruction of the ozone layer and the impact of the greenhouse effect, the use of natural refrigerants to replace synthetic refrigerants has attracted more and more attention from the refrigeration industry at home and abroad. Among several commonly used natural working fluids, CO ₂ is the most environmentally friendly refrigerant except water and air. _CO2 has many advantages as a refrigerant: its ODP = 0, GDP = 1; it is safe to use, non-toxic; good physical and chemical stability; large cooling capacity per unit volume, which is conducive to reducing the volume of the device; under supercritical conditions, It has good flow and heat transfer properties; moreover, _CO2 is readily available and inexpensive, and does not require recycling. In the carbon dioxide transcritical cycle, the exothermic process of carbon dioxide is carried out under supercritical pressure, and there is a large temperature drop. This temperature is especially suitable for heating domestic hot water. Carbon dioxide heat pump water heaters are currently recognized to be superior to R22, R134a and other conventional working fluid heat pump water heaters.

The expansion compressor is an expansion work recovery device. The expansion work of the expander is provided to the auxiliary compressor as input work to drive the compressor to complete the compression process. The use of expansion compressors is conducive to improving the performance coefficient of the entire system, so as to achieve the purpose of energy saving.

To sum up, if the effective use of solar energy, transcritical carbon dioxide heat pump system and expansion compressor can be integrated, it is an effective way to realize multiple functions such as high-efficiency heating and cooling.

Contents of the invention

The technical problem to be solved by the present invention is to provide a carbon dioxide transcritical energy-saving heat pump system with an auxiliary heat source of solar energy that effectively utilizes solar energy and greatly improves the COP value of the system operation cycle performance coefficient.

The said problem of the present invention is solved by following technical scheme:

A solar auxiliary heat source carbon dioxide transcritical energy-saving heat pump system, the system uses carbon dioxide as the working medium, and its composition includes a solar heat collector, a first expansion compressor, a second expansion compressor, an air receiver, a gas cooler, and an evaporator and two electric motors respectively connected to the compressors of the first and second expansion compressors, wherein the solar heat collector is connected to the inlet pipeline of the expander of the first expansion compressor, and the carbon dioxide flowing out of the expander passes through the gas storage The compressor and the gas cooler are sent to the inlet of the compressor of the second expansion compressor, and the outlet of the compressor is connected to the inlet of the solar collector, and the above-mentioned components form a closed loop system of solar heat collection auxiliary heat source; the first expansion compression The compressor outlet of the machine sends carbon dioxide to the expander inlet of the second expansion compressor through the gas receiver and the gas cooler, the expander outlet is connected to the evaporator, and the evaporator outlet is connected to the compressor inlet of the first expansion compressor. The above components form another closed loop system of transcritical carbon dioxide heat pump.

In the above-mentioned solar auxiliary heat source carbon dioxide transcritical energy-saving heat pump system, a gas-liquid separator is arranged between the evaporator and the compressor inlet of the first expansion compressor.

In the above-mentioned solar auxiliary heat source carbon dioxide transcritical energy-saving heat pump system, electromagnetic valves are respectively provided at the two outlets of the three-way valve.

Aiming at the existing problems of energy utilization and environmental pollution, the present invention proposes a solar-assisted transcritical carbon dioxide energy-saving heat pump technology with an expansion compressor. A set of expansion compressors are installed in each of them, and the whole system uses carbon dioxide as the working medium. The advantages of the present invention are reflected in the following aspects:

1. Energy saving: the present invention can effectively use solar energy as the driving energy of the system, greatly improving the COP value of system operation, and achieving the effect of energy saving. When the system is just started or when the sunlight intensity is relatively weak, start the two motors. At this time, the COP of the system is also much larger than that of the single-stage transcritical carbon dioxide heat pump system. When the sunlight intensity is strong enough, the energy consumption of the motor will be smaller, and the COP of the system will be larger at this time. 2. Environmental protection: CO ₂ is used as the refrigeration working medium of the whole system, so there is no pollution to the environment. 3. Economic efficiency: In the long run, the present invention only needs a one-time investment, and the subsequent maintenance and investment costs are very small. Based on the above advantages and people's emphasis on energy saving and environmental protection, solar energy and green working medium carbon dioxide, and with the continuous research and improvement of the expansion compressor, its cost is continuously reduced, thus providing a technical basis for the wide application of the present invention. Can be widely used in air conditioning, heating, refrigeration and other occasions.

Description of drawings

Fig. 1 is a schematic diagram of the present invention;

Figure 2 is a p-h diagram of the circulatory system of the present invention.

The meanings of the labels in the figure are as follows: 1. solar heat collector; 2. the first expansion compressor; 2-1. the expander of the first expansion compressor; 2-2. the compressor of the first expansion compressor; 3. 1st electric motor; 4. Air receiver; 5. Gas-liquid separator; 6. Gas cooler; 7. Three-way valve; 8. Evaporator; 9. Second expansion compressor; 9-1. Second expansion compression 9-2. The compressor of the second expansion compressor; 10. The second electric motor; 11, 12. Solenoid valve.

Detailed ways

Referring to Fig. 1, the present invention comprises a solar heat collector 1, a first expansion compressor 2, a second expansion compressor 9, an air receiver 4, a gas-liquid separator 5, a gas cooler 6, an evaporator 8, three Through valve 7, electromagnetic valve 11, 12. and two motors M connected to the compressors of the first and second expansion compressors respectively, the above-mentioned components are connected through pipelines to form a carbon dioxide transcritical energy-saving heat pump system with solar auxiliary heat source, the system With carbon dioxide as the working medium. The solar heat collector 1 is generally placed on the roof. After being heated by the solar heat collector, the CO ₂ vapor enters the inlet of the expander 2-1 in the first expansion compressor 2 through the pipeline, drives the expander to do work, and enters the gas storage through the pipeline 4, mixed with the CO ₂ vapor from the compressor 2-2 in the gas receiver, after coming out from the outlet of the gas receiver, it enters the inlet of the gas cooler 6 through a pipeline, cools in the gas cooler to release heat, and then passes through The pipeline passes through the three-way valve 7 and the electromagnetic valve 11 successively, and enters the solar heat collector 1 for reheating after being compressed by the compressor 9-2 in the second expansion compressor 9, thus forming the solar heat collection auxiliary sealing part. The CO ₂ vapor is compressed by the compressor 2-2 in the first expansion compressor and enters the gas receiver 4 through the pipeline, and after being mixed with the exhaust gas of the middle expander in the gas receiver, it enters the gas cooler 6 through the pipeline to be cooled and released The heat, the _CO2 vapor coming out of the gas cooler passes through the pipeline through the other end outlet of the three-way valve 7 and the solenoid valve 12 in turn, and then drives the expander in the second expansion compressor 9 to drive the compressor connected to it to do work. The final _CO2 refrigerant enters the evaporator 8 for evaporation and refrigeration, and finally enters the compressor 2-2 in the first expansion compressor through the pipeline through the gas-liquid separator 5, thereby forming a transcritical carbon dioxide heat pump part. In the present invention, the expander and the compressor of the two expansion compressors are connected coaxially, and the compressor of the two expansion compressors is connected coaxially with the motor.

Fig. 2 is a ph diagram of the circulatory system of the present invention. The CO at the outlet of the evaporator ₈ is in a saturated state, and is compressed from point a to point b by the compressor in the first expansion compressor 2, and the superheated _CO vapor is expanded from point f to point b in the expander of the first expansion compressor 2 At point e, the _CO vapor from points b and e is mixed in the gas receiver to form point k, and then isobarically cooled to point c by the gas cooler 6, and then passed through the expander in the second expansion compressor 9 Isentropic expansion to point d, and finally, heat absorption in the evaporator to point a in a saturated vapor state. Point c to point e is the compression process of the compressor in the second expansion compressor, point e to point f is the heating and pressurizing process of the solar collector, point f to g is the external expansion of the expander in the first expansion compressor Work process. Where abkcda is the transcritical CO ₂ heat pump part, and efgkce is the solar thermal collection auxiliary cycle part.

The following takes a 321m ² villa in a community as an example for calculation and analysis: the cooling and heating specifications adopted in the design: 7/12°C in summer and 35/50°C in winter with floor radiation heating. Outdoor design parameters: the calculated outdoor dry bulb temperature of the air conditioner in summer is 33.2°C; the calculated outdoor wet bulb temperature of the air conditioner in summer is 26.4°C; the calculated outdoor temperature of the air conditioner in winter is -12°C; the calculated outdoor temperature of the heating in winter is -9°C. The interior design parameters are shown in Table 1.

Table 1 Interior Design Parameters

According to the characteristics of the structure and function of the villa, it is calculated that the summer air conditioning load of the building is 27.3kW, and the winter floor radiant heating and air conditioning load is 32.8kW.

For the convenience of analysis, cycle analysis is carried out under the following conditions: (1) The system cycle is in a steady state; (2) The indicated efficiency of the compressor is 0.9, the mechanical efficiency of the coupling is 0.98, and the efficiency of the expander is 0.8; ( 3) There is no heat exchange between the gas cooler, evaporator and the environment; (4) The heat transfer temperature difference of the gas cooler is 5°C, and the heat transfer temperature difference of the evaporator is 5°C; (5) The total loss of pipeline pressure is negligible .

Based on the above theoretical calculation formulas and initial assumptions, a theoretical analysis of a solar-assisted transcritical _CO2 heat pump system with an expansion compressor is carried out. Table 2 shows the physical parameters of the main state points of the transcritical CO ₂ heat pump cycle.

Table 2 The physical parameters of the main state points of the transcritical _CO2 heat pump cycle

status point t(°C) p(MPa) h(KJ/Kg) s(KJ/K·Kg) p(Kg/m ³ ) a 2 3.669 430.4 1.837 103.7 b 69.97 9 465.5 1.837 207.6 c 40 8 403.3 1.659 278.4 d 2.001 3.669 381.5 1.659 128.4

Theoretical calculation analysis shows that: when the area of the solar heat collector is ^25m2 , the heat absorption per square meter is 1KW, and the total heat release of the gas cooler is 50KW, the COP of the system of the present invention is 4.79, and its performance coefficient is obviously higher than that of the single stage _CO2 transcritical heat pump system.

In order to make the pressure at the inlet of the gas cooler reach the critical pressure of _CO2 , a medium-temperature solar collector should be used, and its normal operating temperature range is 100°C to 180°C. At this time, the pressure range at the inlet of the expander in expansion compressor A is 12MPa ~14MPa.

When the whole system has just started or the intensity of sunlight cannot meet the needs, it is necessary to start the first motor 3 and the second motor 10. At this time, the input power of the motor 10 is relatively large; when the intensity of sunlight meets the needs, the input of the motor 10 can be adjusted. Smaller work, the motor 3 can be directly turned off.

The solenoid valves 11 and 12 can respectively adjust the flow of refrigerant as required.

The auxiliary part of solar heat collection and the transcritical carbon dioxide heat pump part share a gas cooler 6, and the heat released by the gas cooler can be freely distributed and utilized by users according to their needs, so as to achieve the purpose of heating, hot water or heating + hot water. The cooling medium can be water, air, etc.

The evaporator 8 in the transcritical carbon dioxide heat pump part absorbs heat from the outside to achieve the purpose of cooling, supplying cold water or cooling + cold water, and can be reasonably designed and installed according to user needs. The cooling medium can also use other substances, such as water, air and so on.

Claims (3)

1. A solar auxiliary heat source carbon dioxide transcritical energy-saving heat pump system, the system uses carbon dioxide as the working medium, and is characterized in that: the composition includes a solar heat collector (1), a first expansion compressor (2), a second expansion compression machine (9), gas receiver (4), gas cooler (6), evaporator (8) and two motors connected to the compressors of the first and second expansion compressors respectively, wherein the solar heat collector Connected to the inlet pipeline of the expander of the first expansion compressor, the carbon dioxide flowing out of the expander is sent to the inlet of the compressor of the second expansion compressor through the air receiver and the gas cooler, and the outlet of the compressor is connected to the solar collector Heater inlet, thus forming a closed loop system of solar heat collection auxiliary heat source; the compressor outlet of the first expansion compressor sends carbon dioxide to the expander inlet of the second expansion compressor through the air receiver and gas cooler, and expands The outlet of the evaporator is connected to the evaporator, and the outlet of the evaporator is connected to the inlet of the compressor of the first expansion compressor, thereby forming another closed loop system of a transcritical carbon dioxide heat pump. 2. The solar auxiliary heat source carbon dioxide transcritical energy-saving heat pump system according to claim 1, characterized in that: an air compressor (2-2) is installed between the evaporator (8) and the inlet of the first expansion compressor (2-2). Liquid separator (5). 3. The solar auxiliary heat source carbon dioxide transcritical energy-saving heat pump system according to claim 2, characterized in that: the gas cooler is respectively connected to the compressor inlet and the expander inlet of the second expansion compressor through a three-way valve (7). Electromagnetic valves are respectively arranged at the two outlets of the through valve.

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