Natural refrigerant freezing and air conditioner

Abstract

To improve a COP by optimization of cycles and addition of an expansion turbine coping with the current situation in which demand for air conditioners and freezers is increasing due to progress of global warming, fluorocarbon refrigerants with a high global warming coefficient are increasingly used, and it is feared that power consumption will increase due to the increased demand, and global warming will deteriorate by the disposal of refrigerants with a high warming coefficient at the time of disposal, and use of natural refrigerants in place of fluorocarbon refrigerants is desired though there is a risk of combustion and explosion in hydrocarbon system refrigerants and toxicity in ammonia, which makes their use be hesitated while in this respect carbon dioxide is thought to be desirable since there is no risk of toxicity, combustion or explosion in carbon dioxide though a disadvantage of a low COP remains.SOLUTION: Power recovery is achieved by optimization of cycles and an expansion turbine.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] Refrigeration and air conditioning equipment [Background technology]

[0002] Various types of refrigeration and air conditioning equipment have been developed to combat global warming and reduce energy consumption. However, most of them use fluorocarbon-based refrigerants, and refrigerants with low global warming potential are used during operation, but considering the disposal of refrigerants, it is desirable to use natural refrigerants. Among natural refrigerants, hydrocarbon refrigerants have a high COP and are being used in refrigerators with low charging volumes. However, due to concerns about flammability and explosiveness, their practical use in refrigerators with large refrigerant charging volumes is being hesitated. Ammonia has been used in refrigeration machines for a long time, but it is toxic, flammable, and explosive, and if released into the natural world, it is highly toxic to living organisms, so its practical use is limited to factories where it can be managed. Water refrigerants have large compressor sizes, making it difficult to put them into practical use. Air refrigerants have been put into practical use in fields where cold energy can be reused, such as sealed refrigerated warehouses, but in fields where a large amount of cold energy is required, a large temperature difference is required, and their practical use is limited to only a limited number of fields. The aim of this invention is to create a refrigeration and air conditioning system that uses natural refrigerants and has a high COP, with low global warming potential during operation and disposal. To achieve this, carbon dioxide was selected as the refrigerant. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent applications have been filed for JP 2000-146328 for a refrigeration and air conditioning system in which a bypass pipe is provided between a high pressure refrigerant pipe and a low pressure refrigerant pipe via an on-off valve and the on-off valve is opened and closed by a controller to reduce the load on the compressor, JP 2006-226563 for an evaporator for a carbon dioxide gas air conditioner which suppresses the accumulation of lubricating oil, and JP 2007-17061 for a gas cooler for a carbon dioxide gas air conditioner which has a reduced thickness in the direction of air flow. [Non-patent literature]

[0004] [Non-Patent Document 1] 1. Natural Refrigerant Promotion Site Ministry of the Environment 2. Promotion of Non-Fluorocarbon Global Environment International Environmental Cooperation Ministry of the Environment Summary of the Invention [Problem to be solved by the invention]

[0005] Below, we will take carbon dioxide, which is the safest of all natural refrigerants, as an example. The critical pressure of carbon dioxide is 7.38 MPa, and the temperature is 31.1°C, so the condensation pressure and temperature must exceed the critical pressure and temperature. The refrigerant in the condenser exchanges heat in a supercritical state, and the temperature drops even if the pressure is set constant. The diagram is different from that of a typical refrigeration and air conditioning system, as shown in Figure 1. Even if the compressor outlet is set to a high pressure, the temperature at the condenser outlet drops, making it difficult to dissipate heat sufficiently. If the pressure is increased to increase the amount of condensation heat, the compressor power increases and the COP decreases. The relationship between the pressure at the compressor outlet and the compressor power is shown in Figure 2. The medium pressure at the condenser outlet is relatively high, so the energy entering the expansion valve is large. When this medium is expanded by the expansion valve, it undergoes an equal enthalpy change, so the COP cannot be increased, but it is thought that the COP can be improved by recovering the power using an expander. [Means for solving the problem]

[0006] In order to utilize the unused energy of the high-energy medium that enters the expansion valve, an expander is installed on the other end of the compressor's rotating shaft instead of an expansion valve, and this energy is recovered as power for the rotating shaft, reducing the compressor's power and increasing the amount of evaporation energy. If the expander output is Le, the compressor input is Lc, the condensation energy is Lcon, and the evaporation energy is Lev, the heating COP and cooling COPc are expressed by the following formulas. COPh=Lcon / (Lc-Le), COPc=(Lev+Le) / (Lc-Le)The expander output Lev reduces the compressor power and increases the evaporation energy, improving the heating COPh and cooling COPc. Effect of the Invention

[0007] In conventional refrigeration and air conditioning units, the refrigerant undergoes an isoenthalpy change in the expansion valve, but in this system, energy is extracted from the refrigerant using an expander coaxial with the compressor, reducing the power required for the compressor while increasing the evaporation energy Lev and improving the cooling COPc.

[0008] In other words, the compressor power is reduced by the amount of expander output and the evaporation energy is increased, so both the heating COP and the cooling COP are increased. When the refrigerant is carbon dioxide, the expander output is estimated to be about 30% of the compressor power. [Brief description of the drawings]

[0009] [Figure 1] Cycle diagram of a refrigeration and air-conditioning unit that uses carbon dioxide as a refrigerant and temperature change during the condensation stage [Diagram 2] Relationship between compressor outlet pressure and compressor power for carbon dioxide gas refrigeration and air conditioning systems [Diagram 3] System diagram of Example 1 [Figure 4] Changes in compressor power, expander output, COPh, and COPc due to compressor outlet pressure DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] The compressor shown in the system diagram compresses the medium and the heat contained in the medium needs to be released in the condenser, but in the case of a medium with a low critical point temperature, the temperature of the latent heat is not as high as when other media are used, making it difficult to release to the outside air, and heat release at supercritical pressure is required. When the pressure is increased to above the critical pressure of 7.38 MPa and heat is released from the condenser, the temperature of the medium inside the condenser drops, and if it falls to the same temperature as the outside air temperature, heat release becomes impossible. At that time, if you try to improve the situation by increasing the pressure temperature at the compressor outlet, the compressor power increases and the COP drops.

[0011] With this type of medium, a large amount of energy enters the expansion valve installed at the outlet of the condenser, and although it would be desirable to utilize this energy, there have been no examples of this being used yet. This is thought to be because there is no method for recovering the energy, and it has not been possible to find a use for or a way to utilize the recovered energy.

[0012] Instead of an expansion valve, an expander is used to recover energy, and the recovered energy is used to reduce the compressor driving power. This expander is equipped with an expander rotor blade on one end of the compressor rotating shaft. The energy of the medium entering the expander is about half the compressor power, and because of its high density, the outer diameter of the expander rotor blade is about half the size of the compressor impeller. At this time, the compressor and expander have the same rotation speed, so if the compressor rotation speed and expander rotation speed based on the compressor discharge pressure are estimated to be consistent, it is estimated that the two rotation speeds will be consistent. EXAMPLES

[0013] A system diagram of the first embodiment is shown in Fig. 3. This refrigeration and air conditioning system uses carbon dioxide gas as a working medium, which is a natural refrigerant with no flammability or explosiveness, the highest level of safety, and a small global warming potential of 1, and uses a compressor equipped with expander blades at the other end of a rotating shaft equipped with a compressor impeller of an oil-free turbo compressor. In Fig. 3, the refrigerant sucked into the compressor 100 becomes high temperature and high pressure and enters the condenser 200, where it is cooled by outside air, etc., and enters the expansion turbine 400. In the process of expanding with the blades, the enthalpy decreases and energy is absorbed, and the power is used to drive the impeller of the coaxial compressor, reducing the power of the compressor. [Industrial Applicability]

[0014] To provide a refrigeration and air conditioning system that uses carbon dioxide as a refrigerant, which is the safest natural refrigerant and has a small global warming potential. This refrigeration and air conditioning system does not emit refrigerants with a high global warming potential during use or disposal, and is neither flammable nor explosive, making it the safest and most excellent refrigeration and air conditioning system that does not pollute the environment during use or disposal.

[0015] This refrigerant, carbon dioxide, has excellent environmental friendliness, but its critical temperature is low, and unless it operates at supercritical pressure, it cannot release a large amount of heat, resulting in a low COP, and increasing the compressor outlet pressure increases the compressor power, leading to a drop in COP. In order to solve this problem, instead of the expansion valve provided at the condenser outlet, an expander capable of absorbing energy is provided, which recovers energy, reduces the compressor power, increases the evaporation energy, and improves the COP. This invention provides a refrigeration and air conditioning system that is environmentally friendly and has high energy utilization efficiency. [Explanation of symbols]

[0016] 100 compressor 110 compressor inlet 120 compressor outlet 200 condenser 310, 315 journal gas bearings; 320, 325 pressure balanced thrust gas bearings; 330 permanent magnet rotor; 350 rotating shaft; 400 expander; 410 expander inlet; 420 expander outlet; 500 evaporator

Claims

1. Refrigeration and air conditioning equipment characterized by using carbon dioxide as a refrigerant

2. 2. The refrigeration and air conditioning system according to claim 1, further comprising a turbo compressor having a dynamic pressure gas bearing.

3. 3. The refrigeration and air conditioning device according to claim 2, characterized in that an impeller of a centrifugal compressor is provided at one end of a rotating shaft, and a rotor blade of an expander is provided at the other end.

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