Ultra-efficient phase-change energy storage and variable-load central air-conditioning system

Abstract

This invention provides an ultra-high-efficiency phase-change energy storage and variable-load central air conditioning system, comprising a refrigeration unit and a phase-change accumulator. The refrigeration unit operates at the highest COP. If the cooling capacity exceeds the load demand, the phase-change accumulator stores energy through phase-change. Conversely, if the cooling capacity falls short of the load demand, the phase-change accumulator releases stored energy to supplement the insufficient cooling capacity of the refrigeration unit. Users can formulate an operating strategy for the refrigeration unit based on normal usage statistics. This, combined with the phase-change accumulator, enables efficient operation of the refrigeration unit, effectively improving system energy efficiency and saving energy. This can result in savings of over 40%-70% compared to existing central air conditioning systems.

Description

Technical Field

[0001] The present invention relates to a central air-conditioning system, in particular to an ultra-high efficiency variable load central air-conditioning system utilizing phase change energy storage technology. Background Art

[0002] The power consumption (or power) of a refrigeration unit is evaluated by its refrigeration cycle's Coefficient of Performance (COP). COP refers to the ratio of a refrigeration unit's cooling output (or power) to its power consumption (or power) after completing a refrigeration cycle, or the unit's cooling efficiency. Different types of refrigeration units have different cooling efficiencies. Refrigeration units are generally classified into three categories based on the type of compressor: piston, screw, and centrifugal.

[0003] Reciprocating chillers are used in applications with smaller cooling capacity requirements, screw chillers are used in medium-sized enterprises, and centrifugal chillers are used in medium- to large-scale enterprises. Due to differences in compressor principles and structures, the COP (cost of ownership) of these three types of chillers varies significantly. With current technology, the COP of a reciprocating chiller is approximately 3-4 under standard operating conditions. The COP of a screw chiller can reach around 4-5, while the COP of a centrifugal chiller can reach as high as 5-6. Therefore, centrifugal chillers are relatively efficient. The average COP of a typical commercial building's central air conditioning water-cooled centrifugal unit, combined with a water pump and water tower, is only 4 at best.

[0004] from Figure 2 It can be seen that the COP increases with decreasing condensing temperature and increasing load. This suggests that, under normal circumstances, to maximize the unit's COP, users often prefer to operate the chiller at full load. However, in practice, due to weather conditions, the chiller often doesn't need to operate at full load for most of the year. It often operates at partial load, resulting in a lower cooling efficiency than its maximum achievable efficiency. Centrifugal chillers have different operating characteristics from piston and screw chillers. The use of a variable-speed motor significantly alters their COP curve. As shown in the left half of the figure above, at partial load, the unit's COP is significantly improved compared to conventional centrifugal chillers. This is a significant improvement. However, a closer look at the figure reveals that the COP improvement that can be achieved using a variable-speed motor has certain limitations. The maximum COP value must be achieved between 40% and 60% load. However, air conditioning systems typically operate outside this range during peak hours throughout the year. Therefore, simply using a variable-speed motor will not achieve optimal results. Summary of the Invention

[0005] In response to the above-mentioned deficiencies in the prior art, the present invention provides an ultra-high-efficiency phase-change energy storage and variable-load central air-conditioning system. By using a phase-change accumulator and employing an unbalanced strategy, the refrigeration main unit can operate efficiently in a partial load state while ensuring the overall load requirements.

[0006] The present invention achieves the above object by:

[0007] The ultra-high-efficiency phase-change energy storage and variable-load central air-conditioning system includes a refrigeration main unit and a phase-change accumulator. The cold water outlet of the refrigeration main unit is connected to the first-stage cold water delivery pipeline through a cold production circulating water pump. A cold capacity delivery variable frequency pump is also installed in series in the first-stage cold water delivery pipeline. The outlet of the cold capacity delivery variable frequency pump is then delivered to the user's air supply system through a second-stage cold water delivery pipeline. The outlet of the air supply system is connected to the return water delivery pipeline, and the return water delivery pipeline is connected to the water inlet of the refrigeration main unit; one end of the phase-change accumulator is connected to the first-stage cold water delivery pipeline between the cold production circulating water pump and the cold capacity delivery variable frequency pump through a pipeline, and one end of the phase-change accumulator is connected to the return water delivery pipeline through a pipeline; the system will control the cooling capacity of the refrigeration main unit, the flow rate of the cold production circulating water pump and the cold capacity delivery variable frequency pump as needed to realize the phase-change accumulator to store and release stored energy, as follows:

[0008] When the phase-change accumulator is storing energy, the delivery rate of the cold water delivery variable frequency pump is reduced and / or the flow rate of the cold water outlet of the refrigeration unit is increased, so that the water pressure in the first-stage cold water delivery pipe is greater than that in the return water delivery pipe. The cold water in the first-stage cold water delivery pipe flows into the phase-change accumulator through the pipe, causing the energy storage material in the phase-change accumulator to produce phase change energy. The cold water temperature rises and flows out of the phase-change accumulator through the other end and enters the return water delivery pipe.

[0009] When the phase change accumulator releases stored energy, the delivery rate of the cold water delivery frequency conversion pump is increased and / or the flow rate of the cold water outlet of the refrigeration main unit is reduced or even the refrigeration main unit is shut down, so that the water pressure in the return water delivery pipe is greater than that in the first-stage cold water delivery pipe. The water in the return water delivery pipe flows into the phase change accumulator through the pipe. The energy storage material of the phase change accumulator undergoes phase change and releases the stored energy, cooling the return water. After that, it flows out of the phase change accumulator through the other end and enters the first-stage cold water delivery pipeline. After being pressurized by the cold water delivery frequency conversion pump, it enters the second-stage cold water delivery pipeline and is delivered to the user's air supply system.

[0010] Wherein, two refrigeration hosts are connected in series to form a refrigeration host chain, and one or more refrigeration host chains are connected in parallel to form the refrigeration host group.

[0011] Among them, the cooling circulating water pumps are provided in one group or more, which are connected in parallel, with their inlets connected in parallel to the total cold water outlet of the refrigeration main unit, and their outlets connected in parallel to the first-stage cold water delivery pipeline.

[0012] Among them, the two refrigeration hosts in the refrigeration host chain are connected in series, and are divided into high-temperature refrigeration hosts and low-temperature refrigeration hosts. Specifically: for the evaporator circuit, the return water delivery pipeline is connected to the water inlet of the evaporator circuit of the high-temperature refrigeration host, the water outlet of the evaporator circuit of the high-temperature refrigeration host is connected to the water inlet of the evaporator circuit of the low-temperature refrigeration host, and the water outlet of the evaporator circuit of the low-temperature refrigeration host is connected to the cold production circulation water pump; for the condenser circuit, the cooling tower is connected to the cooling water pump through the condensing water pipe, the outlet of the cooling water pump is connected to the water inlet of the condenser circuit of the low-temperature refrigeration host through the condensing water pipe, the water outlet of the condenser circuit of the low-temperature refrigeration host is connected to the water inlet of the condenser circuit of the high-temperature refrigeration host, and the water outlet of the condenser circuit of the high-temperature refrigeration host is connected to the cooling tower.

[0013] Among them, the cooling water pumps are provided in one group or more, the cooling water pumps are connected in parallel, their inlets are connected in parallel to the outlet of the cooling tower, and their outlets are connected in parallel to the water inlet of the condenser circuit of the low-temperature refrigeration host.

[0014] Among them, the system's control strategy for storing and releasing energy in the phase change accumulator includes:

[0015] Energy storage strategy: When the cooling demand load is low, the refrigeration unit keeps operating according to the specified energy efficiency value in the load-energy efficiency curve, and the phase change accumulator is set to operate in the energy storage working state, so that the cooling capacity generated by the refrigeration unit is stored in the phase change accumulator;

[0016] Energy storage release strategy: when the cooling demand load is high and greater than the load generated by the refrigeration main unit maintaining operation according to the specified energy efficiency value in the load-energy efficiency curve, the refrigeration main unit still maintains operation according to the specified energy efficiency value in the load-energy efficiency curve, and the phase change accumulator is set to operate in the working state of releasing energy storage, so that the system can meet the cooling demand load; or when the refrigeration main unit is shut down, the phase change accumulator is set to operate in the working state of releasing energy storage, and the phase change accumulator provides and meets the cooling demand load.

[0017] The control strategy further includes:

[0018] The low-cost energy storage strategy is based on the power supply cost. When the power supply cost is at a lower value, the refrigeration main unit keeps operating according to the specified energy efficiency value in the load-energy efficiency curve, and sets the phase change accumulator to operate in the energy storage working state, so that the cooling capacity generated by the refrigeration main unit is stored in the phase change accumulator.

[0019] Beneficial effects of the present invention: The usual operating mode of the refrigeration host is to adjust the output cooling capacity of the refrigeration host according to the load change. Therefore, when the load is at a low value, the refrigeration efficiency COP of the refrigeration host will drop rapidly. In order to achieve the efficient operation of the refrigeration host under different loads, that is, variable load conditions of the entire refrigeration system, a phase change accumulator is added to the system to realize phase change energy storage and release of stored energy; the refrigeration host group will operate at the highest refrigeration efficiency COP. If the cooling capacity at this time is higher than the load demand, phase change energy storage is realized through the phase change accumulator. On the contrary, when the cooling capacity cannot meet the load demand, the phase change accumulator releases the stored energy to supplement the insufficient cooling capacity of the refrigeration unit. The user can formulate an operating strategy for the refrigeration host group based on normal usage statistics, and make the refrigeration host group operate efficiently with the cooperation of the phase change accumulator, thereby effectively improving the energy efficiency of the system operation and saving energy, saving more than 40%-70% compared with the existing central air-conditioning system. In addition, users can also keep the refrigeration unit running efficiently during the night when electricity is cheap, based on electricity costs, and store the cooling capacity in the phase-change accumulator, releasing it during the day, thereby further reducing operating electricity costs. Furthermore, the overall design of the phase-change accumulator in the central air-conditioning system of the present invention is simpler and more efficient. The phase-change accumulator can be operated in different working states of storing or releasing stored energy simply by coordinating the flow rate or operating pressure of the cooling circulating water pump and the cooling capacity delivery variable frequency pump. This simplifies the design and reduces the number of control valves required, making the system operation more stable and reliable, reducing the occurrence of failures, and thus reducing the maintenance cost of the system operation. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The present invention will be further described below with reference to the accompanying drawings:

[0021] Figure 1 It is a structural schematic diagram of the present invention;

[0022] Figure 2 This is a load-energy efficiency COP curve diagram of the refrigeration host of the present invention at different cold water temperatures. DETAILED DESCRIPTION

[0023] like Figure 1 As shown, the ultra-high-efficiency phase-change energy storage variable-load central air conditioning system includes a refrigeration unit and a phase-change accumulator. The refrigeration unit can utilize existing central air conditioning chillers, such as piston, screw, or centrifugal types. The interior of the phase-change accumulator consists of a large number of phase-change thermal energy storage plates filled with eutectic salt cold storage material. The plates also have channels for cold water to flow through, exchanging heat with the plates, causing the eutectic salt cold storage material to undergo phase change, storing or releasing stored energy.

[0024] The cold water outlet of the refrigeration main unit is connected to the first-stage cold water delivery pipeline through the cold production circulating water pump. A cold capacity delivery variable frequency pump is also installed in series in the first-stage cold water delivery pipeline. The outlet of the cold capacity delivery variable frequency pump is then delivered to the user's air supply system through the second-stage cold water delivery pipeline. The outlet of the air supply system is connected to the return water delivery pipeline, and the return water delivery pipeline is connected to the water inlet of the refrigeration main unit; one end of the phase change accumulator is connected to the first-stage cold water delivery pipeline between the cold production circulating water pump and the cold capacity delivery variable frequency pump through a pipeline, and one end of the phase change accumulator is connected to the return water delivery pipeline through a pipeline. The usual operating mode of the refrigeration main unit is to adjust the output cooling capacity of the refrigeration main unit according to the load change. Therefore, when the load is at a low value, the cooling efficiency COP of the refrigeration main unit will drop rapidly. To maintain efficient operation of the refrigeration unit under varying load conditions, this system incorporates a phase-change accumulator (PCA) to store and release stored energy. The refrigeration unit operates at its highest COP. If the cooling capacity exceeds the load demand, the PCA stores the stored energy. Conversely, if the cooling capacity falls short of the load demand, the PCA releases the stored energy to supplement the insufficient cooling capacity of the refrigeration unit. Users can develop an operating strategy for the refrigeration unit based on typical usage statistics. This, combined with the PCA, allows for efficient operation of the refrigeration unit, effectively improving system efficiency and saving energy by over 40%-70% compared to existing central air conditioning systems. Furthermore, users can adjust electricity costs by maintaining efficient operation of the refrigeration unit during nighttime hours when electricity is cheaper, storing cooling capacity in the PCA and releasing it during the day, further reducing electricity costs.

[0025] The system will control the cooling capacity of the refrigeration main unit, the flow rate of the cooling circulation pump and the cooling capacity delivery variable frequency pump according to the needs to realize the phase change accumulator to store and release the stored energy. The specific operation process is as follows:

[0026] When the phase-change accumulator is storing energy, one approach is to reduce the cooling capacity required by users, such as when the number of users in the air supply system decreases or the air supply system's load decreases due to lower ambient temperature. In this case, the cooling capacity of the variable frequency pump will also decrease accordingly. Another approach is to actively increase the number of operating refrigeration units in the refrigeration unit and simultaneously start more cooling circulating water pumps to increase the cooling capacity output of the refrigeration unit. Both of the above situations will cause the water pressure in the first-stage cold water delivery pipe to be greater than that in the return water delivery pipe. The cold water in the first-stage cold water delivery pipe flows into the phase-change accumulator through the pipe, causing the energy storage material in the phase-change accumulator to produce phase-change energy. After the phase-change energy is stored, the temperature of the cold water rises and flows out of the phase-change accumulator through the other end into the return water delivery pipe, where it mixes with the return water from the air supply system and flows back to the water inlet of the evaporator of the refrigeration unit.

[0027] When the phase-change accumulator releases stored energy, one scenario is when the number of users in the air supply system decreases but suddenly increases, and the cooling capacity of the refrigeration unit cannot meet demand. Another scenario is when the phase-change accumulator has sufficient stored energy to meet supply, and the refrigeration unit has been completely shut down. At this time, the water pressure in the return water pipeline is greater than that in the first-stage cold water pipeline. The water in the return water pipeline flows through the pipeline into the phase-change accumulator, where the energy storage material in the phase-change accumulator undergoes a phase change and releases the stored energy, cooling the return water. The water then flows out of the phase-change accumulator through the other end and enters the first-stage cold water pipeline. It is then pressurized by the cold water delivery variable frequency pump and enters the second-stage cold water pipeline for delivery to the user's air supply system.

[0028] The above energy storage and release working processes show that the overall design of the phase-change accumulator is very simple and efficient. The phase-change accumulator can be operated in different working states of energy storage or energy release simply by coordinating the flow rate or working pressure of the cooling circulating water pump and the cooling capacity delivery variable frequency pump. This simplifies the design and reduces the number of control valves required, making the system operation more stable and reliable, reducing the occurrence of failures, and thus reducing the maintenance cost of the system operation.

[0029] The existing central air conditioning refrigeration unit group usually adopts a parallel connection of multiple refrigeration units. The cold water outlet of the evaporator circuit of each refrigeration unit is equipped with a cooling circulation pump to control the cold water flow of each refrigeration unit. Similarly, the condenser circuit of each refrigeration unit is also equipped with a cooling water pump. Since the cooling circulation pump and the cooling water pump will generate a certain amount of power consumption during operation, especially when the cooling load is small, the proportion of the above power consumption to the overall power consumption will increase significantly. And referring to Figure 2 According to the load-energy efficiency COP curve, the operating efficiency of the refrigeration host is related to the cooling water temperature. The lower the cooling water temperature, the higher the energy efficiency COP. To further improve the energy efficiency of the refrigeration host, the present invention preferably uses two refrigeration hosts connected in series to form a refrigeration host chain. One or more refrigeration host chains are connected in parallel to form the refrigeration host group. Specifically:

[0030] The two refrigeration hosts in the refrigeration host chain are connected in series and are divided into a high-temperature refrigeration host and a low-temperature refrigeration host.

[0031] For the evaporator circuit, the return water pipeline is connected to the water inlet of the high-temperature refrigeration unit's evaporator circuit, the water outlet of the high-temperature refrigeration unit's evaporator circuit is connected to the water inlet of the low-temperature refrigeration unit's evaporator circuit, and the water outlet of the low-temperature refrigeration unit's evaporator circuit is connected to the cooling circulating water pump. Similarly, there are one or more cooling circulating water pumps, connected in parallel, with their inlets connected in parallel to the total cold water outlet of the cooling unit group, and their outlets connected in parallel to the first-stage cold water delivery pipeline. In other words, the number of cooling circulating water pumps activated is determined solely by the required cooling capacity and is unrelated to the cooling unit.

[0032] For the condenser circuit, the cooling tower is connected to the cooling water pump via a condenser pipe. The outlet of the cooling water pump is connected to the water inlet of the condenser circuit of the low-temperature refrigeration main unit via the condenser pipe. The outlet of the condenser circuit of the low-temperature refrigeration main unit is connected to the water inlet of the condenser circuit of the high-temperature refrigeration main unit, and the outlet of the condenser circuit of the high-temperature refrigeration main unit is connected to the cooling tower. Similarly, there is one or more cooling water pumps, which are connected in parallel. Their inlets are connected in parallel to the outlet of the cooling tower, and their outlets are connected in parallel to the water inlet of the condenser circuit of the low-temperature refrigeration main unit.

[0033] In order to coordinate with the system's hardware configuration and achieve efficient operation of the central air-conditioning system under variable load, the inventors have also developed the system's operating strategy as follows:

[0034] Energy storage strategy: When the cooling demand load is low, the refrigeration main unit keeps operating according to the specified energy efficiency value in the load-energy efficiency curve, and sets the phase change accumulator to operate in the energy storage working state, so that the cooling capacity generated by the refrigeration main unit is stored in the phase change accumulator.

[0035] Energy storage release strategy: when the cooling demand load is high and greater than the load generated by the refrigeration main unit maintaining operation according to the specified energy efficiency value in the load-energy efficiency curve, the refrigeration main unit still maintains operation according to the specified energy efficiency value in the load-energy efficiency curve, and the phase change accumulator is set to operate in the working state of releasing energy storage, so that the system can meet the cooling demand load; or when the refrigeration main unit is shut down, the phase change accumulator is set to operate in the working state of releasing energy storage, and the phase change accumulator provides and meets the cooling demand load.

[0036] The low-cost energy storage strategy is based on the power supply cost. When the power supply cost is at a lower value, the refrigeration main unit keeps operating according to the specified energy efficiency value in the load-energy efficiency curve, and sets the phase change accumulator to operate in the energy storage working state, so that the cooling capacity generated by the refrigeration main unit is stored in the phase change accumulator.

[0037] According to tests conducted by the inventors, the central air-conditioning system provided by the present invention can improve energy efficiency by more than 40%-70% compared with existing air-conditioning systems. For specific comparison data, please refer to the following Table 1.

[0038] Table 1 Comparison of energy efficiency and energy saving of different central air-conditioning systems

[0039] Air conditioning type Energy efficiency Energy efficiency added value Power consumption (10,000 kWh) Absolute amount of energy saving (10,000 kWh) Energy saving ratio (%) Old central air conditioning 2.0 0.0 300.0 0.0 0.0 New central air conditioning 2.2 0,2 272.7 27.3 9.1 Central air conditioning with energy efficiency of 3.0 (commonly used in hotels) 3.0 1.0 200 100 33.3 Central air conditioner designed by the present invention 7.0 5.0 85.7 214.3 71.4

Claims

1. Ultra-high efficiency phase change energy storage variable load central air conditioning system, characterized by: The system comprises a refrigeration main unit and a phase-change accumulator. The cold water outlet of the refrigeration main unit is connected to the first-stage cold water delivery pipeline through a cold production circulating water pump. A cold capacity delivery variable frequency pump is also installed in series in the first-stage cold water delivery pipeline. The outlet of the cold capacity delivery variable frequency pump is then delivered to the user's air supply system through a second-stage cold water delivery pipeline. The outlet of the air supply system is connected to the return water delivery pipeline, and the return water delivery pipeline is connected to the water inlet of the refrigeration main unit. One end of the phase-change accumulator is connected to the first-stage cold water delivery pipeline between the cold production circulating water pump and the cold capacity delivery variable frequency pump through a pipeline, and one end of the phase-change accumulator is connected to the return water delivery pipeline through a pipeline. The system will control the cooling capacity of the refrigeration main unit, the flow rate of the cold production circulating water pump and the cold capacity delivery variable frequency pump according to needs to realize the phase-change accumulator to store and release stored energy, as follows: When the phase-change accumulator is storing energy, the delivery rate of the cold water delivery variable frequency pump is reduced and / or the flow rate of the cold water outlet of the refrigeration unit is increased, so that the water pressure in the first-stage cold water delivery pipeline is greater than that in the return water delivery pipeline. The cold water in the first-stage cold water delivery pipeline flows into the phase-change accumulator through the pipeline, causing the energy storage material in the phase-change accumulator to produce phase change energy. The cold water temperature rises and flows out of the phase-change accumulator through the other end and enters the return water delivery pipeline. When the phase change accumulator releases stored energy, the delivery rate of the cold water delivery frequency conversion pump is increased and / or the flow rate of the cold water outlet of the refrigeration main unit is reduced or even the refrigeration main unit is shut down, so that the water pressure in the return water delivery pipe is greater than that in the first-stage cold water delivery pipe. The water in the return water delivery pipe flows into the phase change accumulator through the pipe. The energy storage material of the phase change accumulator undergoes phase change and releases the stored energy, cooling the return water. After that, it flows out of the phase change accumulator through the other end and enters the first-stage cold water delivery pipeline. After being pressurized by the cold water delivery frequency conversion pump, it enters the second-stage cold water delivery pipeline and is delivered to the user's air supply system.

2. The ultra-high efficiency phase change energy storage and variable load central air conditioning system according to claim 1 is characterized by: Two refrigeration hosts are connected in series to form a refrigeration host chain, and one or more refrigeration host chains are connected in parallel to form the refrigeration host group.

3. The ultra-high efficiency phase-change energy storage and variable load central air conditioning system according to claim 1 is characterized in that: The cooling circulating water pumps are provided in one group or more, which are connected in parallel, with their inlets connected in parallel to the total cold water outlet of the refrigeration main unit, and their outlets connected in parallel to the first-stage cold water delivery pipeline.

4. The ultra-high efficiency phase-change energy storage and variable load central air conditioning system according to claim 2 is characterized in that: The two refrigeration hosts in the refrigeration host chain are connected in series, and are divided into a high-temperature refrigeration host and a low-temperature refrigeration host. Specifically: for the evaporator circuit, the return water delivery pipeline is connected to the water inlet of the evaporator circuit of the high-temperature refrigeration host, the water outlet of the evaporator circuit of the high-temperature refrigeration host is connected to the water inlet of the evaporator circuit of the low-temperature refrigeration host, and the water outlet of the evaporator circuit of the low-temperature refrigeration host is connected to the cold production circulating water pump; for the condenser circuit, the cooling tower is connected to the cooling water pump via a condensing water pipe, the outlet of the cooling water pump is connected to the water inlet of the condenser circuit of the low-temperature refrigeration host via a condensing water pipe, the water outlet of the condenser circuit of the low-temperature refrigeration host is connected to the water inlet of the condenser circuit of the high-temperature refrigeration host, and the water outlet of the condenser circuit of the high-temperature refrigeration host is connected to the cooling tower.

5. The ultra-high efficiency phase-change energy storage and variable load central air-conditioning system according to claim 4 is characterized in that: The cooling water pumps are provided in one group or more, which are connected in parallel, with their inlets connected in parallel to the outlets of the cooling towers, and their outlets connected in parallel to the water inlets of the condenser circuits of the low-temperature refrigeration main unit.

6. The ultra-high efficiency phase-change energy storage and variable load central air conditioning system according to claim 1 is characterized in that: The control strategy for the system to store and release energy in the phase change accumulator includes: Energy storage strategy: When the cooling demand load is low, the refrigeration unit keeps operating according to the specified energy efficiency value in the load-energy efficiency curve, and the phase change accumulator is set to operate in the energy storage working state, so that the cooling capacity generated by the refrigeration unit is stored in the phase change accumulator; Energy storage release strategy: when the cooling demand load is high and greater than the load generated by the refrigeration main unit maintaining operation according to the specified energy efficiency value in the load-energy efficiency curve, the refrigeration main unit still maintains operation according to the specified energy efficiency value in the load-energy efficiency curve, and the phase change accumulator is set to operate in the working state of releasing energy storage, so that the system can meet the cooling demand load; or when the refrigeration main unit is shut down, the phase change accumulator is set to operate in the working state of releasing energy storage, and the phase change accumulator provides and meets the cooling demand load.

7. The ultra-high efficiency phase-change energy storage and variable load central air conditioning system according to claim 6, characterized in that: The control strategy also includes: The low-cost energy storage strategy is based on the power supply cost. When the power supply cost is at a lower value, the refrigeration main unit keeps operating according to the specified energy efficiency value in the load-energy efficiency curve, and sets the phase change accumulator to operate in the energy storage working state, so that the cooling capacity generated by the refrigeration main unit is stored in the phase change accumulator.

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