CN202328574U - Air supply system of central air conditioner with two cooling coils - Google Patents

Abstract

The utility model provides a central air-conditioning air supply system with double cooling coils, which includes mutually independent return air cooling coils and fresh air cooling coils; the return air cooling coils are installed in the return air cooling coil heat exchange chamber, The heat exchange chamber of the air cooling coil is installed in the return air circulation pipe, and the return air cooling coil uses the first-temperature chilled water flowing through the coil to cool the return air flowing through the return air circulation pipe; the fresh air cooling coil is installed in the Fresh air cooling coil heat exchange room, the fresh air cooling coil heat exchange room is installed in the fresh air pipe, the fresh air cooling coil uses the second temperature chilled water flowing through its coil to dehumidify and cool the fresh air flowing in from the fresh air pipe ; The temperature of the frozen water at the second temperature is lower than the temperature of the frozen water at the first temperature; the air volume of the return air circulation pipeline is greater than the air volume of the fresh air pipeline. The utility model improves the refrigeration coefficient of the system and achieves the effect of energy saving.

Description

Double cooling coil central air-conditioning air supply system

technical field

The utility model relates to a central air-conditioning air supply system with double cooling coils.

Background technique

With the continuous progress of society and the continuous development of science and technology, people are now more and more concerned about the earth on which we live, and most countries in the world have fully realized the importance of the environment to our human development. All countries are taking active and effective measures to improve the environment and reduce pollution. Among them, the most important and urgent problem is the energy problem. In order to solve the energy problem fundamentally, besides finding new energy sources, energy saving is the key and the most direct and effective important measure at present.

Among the main energy consumers in my country, building energy consumption accounts for a large proportion. Statistics show that the proportion of building energy consumption in my country's energy consumption has reached 27.6%. In developed countries, building energy consumption generally accounts for 30-40% of total energy consumption. Therefore, with the development of the national economy and the improvement of people's living standards, my country's building energy consumption will inevitably continue to rise, and building energy conservation has a long way to go.

In building energy consumption, central air-conditioning system energy consumption generally accounts for 40-60% of the proportion. In the energy consumption of the central air-conditioning system, about 50-60% of the electricity load is consumed by chillers for cooling, about 25-30% of the electricity load is consumed by the transmission and distribution of chilled water pumps and cooling water pumps, and about 15-20% is used by The electrical load is consumed by the transmission and distribution of various fans. Due to the lack of advanced control technology and equipment, most of the current central air-conditioning systems still use the traditional manual management method and simple switch control equipment, which cannot realize the dynamic adjustment of the air-conditioning refrigerant flow following the change of the end load, causing a large number of problems during part-load operation. The waste of energy has made my country's building energy efficiency low, and the energy consumption per unit building area is 2 to 3 times higher than that of developed countries with the same climate conditions. Therefore, the energy saving of the central air-conditioning system is an important aspect of building energy saving, and it is of great significance to analyze and study the energy-saving optimization of the central air-conditioning system.

At present, large and medium-sized central air-conditioning systems generally adopt indirect refrigeration. The heat transfer process consists of five cycles: indoor air cycle, chilled water cycle, refrigerant cycle, cooling water cycle, and outdoor air cycle. The cooling coil is a device for heat exchange between indoor air and chilled water, and is an important part of the central air conditioning system.

In the traditional sense, the air supply system of the central air-conditioning room is only composed of a set of cooling coils. Such a set of cooling coils undertakes two tasks: cooling the explicit air generated by various electrical equipment brought by the return air of the air conditioning room. Load; remove the sensible and latent heat of the fresh air, that is, the dehumidification and cooling of the fresh air. Among them, the air volume of the former part is relatively large, accounting for 70-80% of the entire air volume. Usually the 7°C chilled water we use is only used for dehumidification of fresh air, and the 15°C chilled water is enough to complete the task of cooling the return air in the air-conditioning room. In the existing central air-conditioning system, 7°C chilled water is not only used for the dehumidification of fresh air, but also for the cooling of the return air in the air-conditioning room, which means that a large amount of chilled water cooling capacity is wasted.

The ideal refrigerant cycle is called the reverse Carnot cycle, that is, assuming that the temperature of the low-temperature heat source (that is, the object to be cooled) is T ₀ , and the temperature of the high-temperature heat source (that is, the ambient medium) is T _K , then the refrigerant (Freon, etc.) absorbs T ₀ in the thermal process, T _K in the exothermic process, that is to say, there is no temperature difference between the working fluid and the low-temperature heat source and high-temperature heat source in the heat-absorbing and exothermic process, that is, the heat transfer is carried out under isothermal conditions, and the compression And the expansion process is carried out without heat loss.

The heat Q ₀ absorbed by the refrigerant from the cooled low-temperature heat source:

The heat Q _K released by the refrigerant to the high-temperature heat source:

Among them, S ₁ = S ₂ , S ₃ = S ₄ , are the entropy values in the process of isentropic compression (work done on the system by the outside world) and isentropic expansion (system returns to its original state).

From energy conservation, it can be seen that the work W ₀ consumed by the refrigerant cycle is equal to the work consumed by compression minus the work obtained by expansion.

Refrigeration coefficient ε _K : the value of the refrigeration capacity obtained by consuming unit work. Then the refrigeration coefficient ε _K of the reverse Carnot cycle is:

In the reverse Carnot cycle, the refrigerant only exchanges heat with two heat sources. It can be seen from the above formula that the refrigeration coefficient of the reverse Carnot cycle has nothing to do with the nature of the refrigerant, but only depends on the temperature T of the low-temperature heat source (that is, the object to be cooled). ₀ and the temperature T _K of the high-temperature heat source (ie, the ambient medium). Decreasing T _K and increasing T ₀ can increase the refrigeration coefficient.

The ideal refrigerant cycle should be the reverse Carnot cycle. Although the reverse Carnot cycle is practically impossible, it can be used to evaluate the cooling efficiency of a real refrigerant cycle.

Generally speaking, for the refrigerant circulation system of central air conditioning, the low-temperature heat source (that is, the object to be cooled) is chilled water, and the high-temperature heat source (that is, the environmental medium) is cooling water; temperature, can increase the actual refrigeration coefficient of the central air-conditioning refrigerant circulation system.

The utility model will increase the cooling efficiency by increasing the freezing water temperature ( T ₀ ).

Contents of the invention

The technical problem to be solved by the utility model is to provide a double cooling coil central air-conditioning air supply system to overcome the shortcomings of the existing central air-conditioning air supply system that wastes a large amount of chilled water cooling capacity, and to provide an air supply system that effectively utilizes the chilled water cooling capacity. System, providing design solutions for central air-conditioning energy saving. For this reason, the utility model adopts the following technical solutions:

The central air-conditioning air supply system with double cooling coils includes two independent cooling coils: the return air cooling coil and the fresh air cooling coil; Indoors, the return air cooling coil heat exchange chamber is installed in the return air circulation pipe, and the return air cooling coil uses the first-temperature chilled water flowing through its coil to cool the return air flowing through the return air circulation pipe; the fresh air The cooling coil is installed in the heat exchange chamber of the fresh air cooling coil, and the heat exchange chamber of the fresh air cooling coil is installed in the fresh air pipe. The air is dehumidified and cooled; the temperature of the chilled water at the second temperature is lower than that of the chilled water at the first temperature; the air volume of the return air circulation pipeline is greater than the air volume of the fresh air pipeline.

On the basis of adopting the above-mentioned technical solution, the utility model can also adopt or adopt the following further technical solutions in combination:

The temperature of the chilled water at the first temperature is 11-17°C, the temperature of the chilled water at the second temperature is 4-10°C; the optimal temperature of the chilled water at the first temperature is 15°C, and the second temperature The optimal temperature of the chilled water is 7°C; the chilled water at the first temperature and the chilled water at the second temperature are transported by respective chilled water circulating pumps; the chilled water circulating pump is a variable frequency pump, which can adjust the chilled water circulating flow through frequency conversion .

The refrigerating capacity required for cooling the chilled water at the first temperature and the chilled water at the second temperature comes from the first refrigerant evaporator and the second refrigerant evaporator connected in parallel in the refrigerant circulation pipeline respectively; The pipeline is connected to the refrigerant compressor and the refrigerant condenser in turn, and then divided into the parallel branch of the first refrigerant evaporator and the parallel branch of the second refrigerant evaporator, and the two parallel branches are connected to the refrigerant compressor after being merged. the inlet end of the first refrigerant evaporator; the parallel branch of the first refrigerant evaporator is sequentially connected with the first expansion valve, the first refrigerant evaporator and the first evaporation pressure regulating valve; the parallel branch of the second refrigerant evaporator is sequentially connected with There is a second expansion valve, a second refrigerant evaporator and a check valve; through the regulation of the first evaporation pressure regulating valve, the evaporation pressure of the first refrigerant evaporator is higher than the evaporation pressure of the second refrigerant evaporator Pressure; through the one-way flow effect of the check valve, the gas with higher outlet pressure of the first refrigerant evaporator is prevented from flowing back into the second refrigerant evaporator; the first expansion valve and the second expansion valve are electronic Expansion valve or thermostatic expansion valve.

The air supply system of the central air conditioner with double cooling coils adopts the air circulation mode to adjust the indoor temperature; the air circulation mode includes: the total cold air transported by the fan in the main air inlet duct is diverted to the air inlets of the air conditioners in each air conditioner room, and then flows into the air conditioner room. After passing through the air-conditioning room and flowing out from the air outlet of the air-conditioning room, it becomes the return air and enters the main return air duct; the total return air composed of all the return air entering the main return air duct is transported by the fan of the main return air duct and reaches the main return air duct. The end of the air duct is divided, and less than 30% of the total return air is discharged from the waste air duct to the outside through the damper of the waste air duct, and more than 70% of the total return air enters the return air circulation duct through the damper of the return air circulation duct and flows After passing through the heat exchange chamber of the return air cooling coil, it becomes cold return air; the fresh air flowing in from the fresh air pipe from the outside through the air valve of the fresh air pipe becomes cold fresh air after passing through the heat exchange chamber of the fresh air cooling coil; The total cold air mixed with the cold fresh air enters the main air intake duct and is transported by the fan of the main air intake duct.

The main air inlet duct fan and the main return air duct fan are frequency conversion fans, and the circulating air volume can be adjusted by frequency conversion.

Therefore, most of the frozen water is the first temperature frozen water, and the second temperature frozen water only accounts for a small part. An increase in the temperature of the chilled water means that the temperature difference between the chilled water (temperature T ₀ ) and the cooling water (temperature T _K ) decreases, which means that the cooling efficiency increases.

The central air-conditioning air supply system with double cooling coils adopts a variable air volume method to adjust the temperature of the air-conditioning room; the variable air volume method does not adjust the air supply temperature, but adjusts the temperature of the air-conditioning room by adjusting the air supply volume; The way to adjust the air supply volume is realized in the following way: the main air inlet pipe is connected with the main return air pipe through the air inlet of the air-conditioning room, the air-conditioning room, and the air outlet of the air-conditioning room. The air inlet damper is used to adjust the air supply volume of each air-conditioning room by changing the opening degree of the air inlet air valve of the air-conditioning room.

On the basis of the original single cooling coil air supply system of the central air conditioner, the utility model adds a set of independent cooling coil air loops, and realizes the separation of the return air cooling of the air conditioning room and the dehumidification and cooling of the fresh air supplemented from the outside. , Increase the temperature of the chilled water (first temperature chilled water) in the return air cooling coil, thereby increasing the refrigeration coefficient of the system and achieving the effect of energy saving. In order to realize the separation of the two sets of air circuits, it is necessary to generate two kinds of chilled water at different temperatures, that is, the first temperature chilled water and the second temperature chilled water. One refrigerant compressor simultaneously drives two refrigerant evaporators to produce chilled water at different temperatures. At the same time, by sending cold air to the air-conditioning room and adopting the variable air volume control method, the needs of users can be better met, and the pipelines for sending chilled water to the air-conditioning room are reduced, reducing the initial investment of the system.

The air supply system of the air-conditioning room of the utility model is especially suitable for use in central air-conditioning refrigeration, can realize energy-saving optimization of the system, and provide users with better services.

Description of drawings

Fig. 1 is a structural schematic diagram of a central air-conditioning air supply system with dual cooling coils of the present invention.

The symbols in the figure are as follows: 1. Return air cooling coil, 2. Return air cooling coil heat exchange chamber, 3. First temperature chilled water circulation pipeline, 4. Fresh air cooling coil, 5. Fresh air cooling coil heat exchange chamber. Exchange chamber, 6. Second temperature chilled water circulation pipeline, 7. First temperature chilled water circulation pump, 8. Second temperature chilled water circulation pump, 9. First refrigerant evaporator, 10. Second refrigerant evaporator, 11 . Refrigerant circulation pipeline, 12. Parallel branch of the first refrigerant evaporator, 13. Parallel branch of the second refrigerant evaporator, 14. First expansion valve, 15. Second expansion valve, 16. First evaporator Pressure regulating valve, 17, second evaporation pressure regulating valve, 18, check valve, 19, refrigerant compressor, 20, refrigerant condenser, 21, main air inlet pipe, 22, main air inlet pipe fan, 23, Main air inlet duct wind speed sensor, 24, main return air duct, 25, main return air duct fan, 26, waste air duct, 27, waste air duct damper, 28, return air circulation duct, 29, return air circulation duct wind Valve, 30, fresh air duct, 31, fresh air duct damper, 32, fresh air duct wind speed sensor, 33, air-conditioning room, 34, air-conditioning room air inlet, 35, air-conditioning room air inlet damper, 36 air-conditioning room air outlet.

Detailed ways

Below in conjunction with accompanying drawing, the utility model is further described.

As shown in Figure 1, a double cooling coil central air-conditioning air supply system, its working process is: the refrigerant circulation pipeline 11 is connected with the refrigerant compressor 19 and the refrigerant condenser 20 in sequence, and then divided into the first refrigeration The parallel branch 12 of the refrigerant evaporator and the parallel branch 13 of the second refrigerant evaporator are connected to the inlet end of the refrigerant compressor 19 after the two parallel branches merge; the parallel branch 12 of the first refrigerant evaporator is sequentially connected with The first expansion valve 14, the first refrigerant evaporator 9 and the first evaporation pressure regulating valve 16, the parallel branch 13 of the second refrigerant evaporator are sequentially connected with the second expansion valve 15, the second refrigerant evaporator 10, the second Two evaporating pressure regulating valves 17 and check valves 18.

The evaporation pressure is the maximum pressure when the refrigerant changes from a liquid state to a gas state when the refrigerant temperature is constant. For a refrigerant, at a certain pressure, the evaporation temperature is fixed, that is to say, different evaporation temperatures can be generated by changing the evaporation pressure downstream of the refrigerant evaporator, so as to obtain different refrigeration effects and produce refrigeration at different temperatures. Water to meet the water temperature requirements of the return air cooling coil 1 and the fresh air cooling coil 4.

The evaporation pressure of the first refrigerant evaporator 9 corresponding to the chilled water at the first temperature is higher than the evaporation pressure of the second refrigerant evaporator 10 corresponding to the chilled water at the second temperature; The evaporation pressure of the first refrigerant evaporator 9 is the evaporation pressure that produces 15°C chilled water, and the evaporation pressure of the second refrigerant evaporator 10 is configured by the second evaporation pressure regulating valve 17 to be the evaporation pressure that produces 7°C chilled water. A check valve 18 is set to prevent the refrigerant from flowing from the first refrigerant evaporator parallel branch 12 (high pressure) to the second refrigerant evaporator parallel branch 13 (low pressure). The pressure behind the check valve 18 is the refrigerant compressor 19 suction pressure. It is worth mentioning that when we need to set the evaporation pressure after the second refrigerant evaporator 10 to be equal to the suction pressure of the refrigerant compressor 19, the second evaporation pressure regulating valve 17 becomes an optional component.

The cooling water and the refrigerant exchange heat in the refrigerant condenser 20, and the high-temperature, high-pressure refrigerant gas is condensed into a low-temperature, high-pressure refrigerant liquid in the refrigerant condenser 20, and heat is released. The low-temperature, high-pressure refrigerant liquid is throttled by the first expansion valve 14 and the second expansion valve 15, and then transformed into a low-temperature, low-pressure refrigerant liquid, and is respectively in the first refrigerant evaporator 9 and the second refrigerant evaporator 10 There is a heat exchange effect with the frozen water of the first temperature and the frozen water of the second temperature, the refrigerant evaporates and absorbs heat, and transforms into a low-temperature, low-pressure refrigerant gas, and at the same time generates 15°C first-temperature refrigeration in the first refrigerant evaporator 9 Water, in the second refrigerant evaporator 10 produces 7°C first temperature frozen water. Refrigerant compressor 19 compresses the low-temperature and low-pressure refrigerant gas to make it into high-temperature and high-pressure refrigerant gas acceptable to the refrigerant condenser 20. As for the main energy-consuming components, by changing the frequency of the refrigerant compressor 19, different cooling effects can be produced to meet the demands of different cooling loads.

The first temperature chilled water circulation pump 7 drives the circulation of the first temperature chilled water in the first temperature chilled water circulation pipeline 3; the return air cooling coil 1 is installed in the return air cooling coil heat exchange chamber 2, and the return air cooling coil heat The exchange chamber 2 is installed in the return air circulation pipe 28, and the return air cooling coil 1 utilizes the first-temperature chilled water flowing through the coil to cool the return air flowing through the return air circulation pipe 28; In the exchange room 2, the chilled water at the first temperature flowing through the return air cooling coil 1 and the return air recovered by the main return air duct 24 and discharged through the waste air duct 26 to a certain amount of waste air flow through the return air circulation duct 28 The heat exchange effect occurs, the temperature of the chilled water at the first temperature rises, and the return air flowing through the return air circulation pipe 28 is cooled to become cold return air. The main return air duct 24 is provided with a main return air duct fan 25 to provide power for the delivery of the total return air in the air-conditioning room.

The second temperature chilled water circulation pump 8 drives the circulation of the second temperature chilled water in the second temperature chilled water circulation pipeline 6; the fresh air cooling coil 4 is installed in the fresh air cooling coil heat exchange chamber 5, and the fresh air cooling coil heat exchange chamber 5 Installed in the fresh air duct 30, the fresh air cooling coil 4 utilizes the second temperature chilled water flowing through the coil to dehumidify and cool the fresh air flowing in from the fresh air duct 30; in the fresh air cooling coil heat exchange chamber 5, The chilled water at the second temperature flowing through the fresh air cooling coil 4 exchanges heat with the fresh air flowing in from the fresh air duct 30 through the damper 31 of the fresh air duct from the outside, and the temperature of the chilled water at the second temperature rises. It has the effect of cooling and dehumidification, and generates cold fresh air.

The total cold air formed by mixing the cold return air and the cold fresh air enters the main air intake duct 21 and is transported by the fan 22 of the main air intake duct.

The total cold wind delivered by the fan 22 of the main air intake duct is divided into the air-conditioning room air inlets 34 of each air-conditioning room 33, flows through the air-conditioning rooms 33 and flows out from the air-conditioning room air outlet 35, becomes return air and enters the main return air duct 24; the total return air composed of all the return air that flows into the main return air duct 24 is transported through the main return air duct fan 25 and then diverted after arriving at the end of the main return air duct 24, and the total return air below 30% is discarded The air duct damper 27 is discharged to the outside by the waste air duct 26, and more than 70% of the total return air enters the return air circulation duct 28 through the return air circulation duct damper 29.

The main air inlet duct 21 communicates with the main return air duct 24 through the air inlet 34 of the air conditioner room, the air outlet 33 of the air conditioner room, and the air outlet 36 of the air conditioner room. Independent air inlet air valves 35 of the air conditioner room are respectively installed at the air inlets 34 of the air conditioner room. The air supply volume of each air-conditioned room 33 is adjusted by changing the opening degree of the air inlet valve 35 of the air-conditioned room.

The fresh air duct 30 is provided with a fresh air duct wind speed sensor 32 and a fresh air duct damper 31 that can change the amount of fresh air entering. Under the condition that the fresh air duct 30 cross-sectional area A ₁ is known, the fresh air speed v ₁ ( t) The fresh air volume Q ₁ entering within a certain period of time (t1~t2) can be calculated, and the calculation formula is:

By adjusting the degree of opening of the air valve 31 of the fresh air duct, the amount of new fresh air can be changed. Correspondingly, the waste air duct 26 is provided with a waste air duct damper 27, and the return air circulation duct 28 is provided with a return air circulation duct damper 29. By changing the waste air duct damper 27 and the return air circulation duct damper 29 The opening degree can change the waste air volume and the return air circulation air volume; the main air intake duct wind speed sensor 23 is arranged in the main air intake duct 21, and the known condition of the cross-sectional area A of the main air intake duct ₂₁ The total air supply volume Q ₂ entering the air-conditioning room within a certain period of time (t1~t2) can be calculated through the measured air intake velocity v ₂ (t) , and the calculation formula is:

The fresh air ratio is the proportion of the fresh air volume to the total air supply volume, and the calculation formula is:

Different fresh air ratios can be realized by setting the opening degrees of the damper 27 of the waste air duct, the damper 29 of the return air circulation duct, and the damper 31 of the fresh air duct. For example, we can set the fresh air volume to account for 20% of the total air intake volume, then the waste air volume accounts for 20% of the total air supply volume, and the return air volume accounts for 80% of the total air supply volume. This ratio is not fixed and can be adjusted according to specific conditions to achieve the best results.

The central air-conditioning air supply system with double cooling coils of the utility model can realize overall optimal configuration. The first expansion valve 16 and the second expansion valve 17 of the throttling device used in the central air-conditioning refrigerant cycle are preferably electronic expansion valves, and the refrigerant compressor 19 used is an inverter compressor that can realize frequency conversion regulation. The first temperature chilled water circulation pump 7 and the second temperature chilled water circulation pump 8 of the central air conditioner are frequency conversion pumps, and the chilled water volume can be changed by changing the power supply frequency of the water pumps; the main air inlet duct fan 22 and the main return air duct fan 25 are frequency conversion fans, The air supply volume of the main air intake duct 21 can be changed by changing the power supply frequency of the fan. When the user load changes, by changing the frequency of the refrigerant compressor 19, the first temperature chilled water circulation pump 7, the second temperature chilled water circulation pump 8, the main air inlet duct fan 22 and the main return air duct fan 25, the system can be prevented from running in a fixed state. Working at the working point, the reduction of frequency means the reduction of energy consumption, and the best energy-saving effect can be achieved under the premise of meeting the needs of users. At the same time, this is an overall optimized configuration. The intelligent optimization algorithm is used to determine the operating frequency of each variable frequency equipment, so as to avoid the impact of the energy consumption of other electrical equipment when the energy consumption of a certain equipment is reduced, so that the overall performance of the system can be improved. consumption is minimized.

The above-mentioned specific embodiments are used to explain the utility model, and are only preferred embodiments of the utility model, rather than limiting the utility model. Within the spirit of the utility model and the scope of protection of the claims, the utility model is made Any modification, equivalent replacement, improvement, etc., all fall into the protection scope of the present utility model.

Claims (4)

1. Double cooling coil central air-conditioning air supply system, characterized in that it includes two sets of independent cooling coils: the return air cooling coil and the fresh air cooling coil; the return air cooling coil is installed on the return air cooling coil In the tube heat exchange room, the return air cooling coil heat exchange room is installed in the return air circulation pipe, and the return air cooling coil uses the first-temperature chilled water flowing through its coil to cool the return air flowing through the return air circulation pipe; The fresh air cooling coil is installed in the heat exchange chamber of the fresh air cooling coil, and the heat exchange chamber of the fresh air cooling coil is installed in the fresh air pipe. The incoming fresh air is dehumidified and cooled; the temperature of the chilled water at the second temperature is lower than that of the chilled water at the first temperature; the air volume of the return air circulation pipe is greater than the air volume of the fresh air pipe. 2. The double cooling coil central air-conditioning air supply system according to claim 1, characterized in that the temperature of the first-temperature chilled water is 11-17°C, and the temperature of the second-temperature chilled water is 4-10°C. °C; the optimum temperature of the first temperature chilled water is 15°C, and the optimum temperature of the second temperature chilled water is 7°C; the first temperature chilled water and the second temperature chilled water are respectively The water circulation pump is used for transportation; the chilled water circulation pump is a frequency conversion pump, which can adjust the chilled water circulation flow through frequency conversion. 3. The double cooling coil central air-conditioning air supply system according to claim 2, characterized in that the cooling capacity required for the cooling of the first temperature chilled water and the second temperature chilled water comes from the refrigerant circulation pipeline respectively The first refrigerant evaporator and the second refrigerant evaporator are connected in parallel; the refrigerant circulation pipeline is connected with a refrigerant compressor and a refrigerant condenser in turn, and then divided into the parallel branch of the first refrigerant evaporator and the second refrigerant evaporator. The parallel branch of the refrigerant evaporator is connected to the inlet end of the refrigerant compressor after the two parallel branches are merged; the parallel branch of the first refrigerant evaporator is connected with the first expansion valve, the first refrigerant evaporator and the The first evaporation pressure regulating valve; the second expansion valve, the second refrigerant evaporator and the check valve are sequentially connected to the parallel branch of the second refrigerant evaporator; through the regulation of the first evaporation pressure regulating valve, The evaporation pressure of the first refrigerant evaporator is higher than the evaporation pressure of the second refrigerant evaporator; through the one-way flow effect of the check valve, the gas with higher outlet pressure of the first refrigerant evaporator is prevented from flowing back into the second refrigerant evaporator. Two refrigerant evaporators; the first expansion valve and the second expansion valve are electronic expansion valves or thermal expansion valves. the 4. The double cooling coil central air-conditioning air supply system according to claim 1, 2 or 3, characterized in that the main air inlet duct fan and the main return air duct fan are frequency conversion fans, which can be adjusted by frequency conversion Circulation air volume. the

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