The room air conditioner performance standard GB/T 7725—2022 will be published soon. The text structure, technical requirements and test methods of operation performance, APF test and calculation methods are revised greatly in the new standard, and the standby power, temperature control fluctuation, partial performance grading and so on are added. This standard is the basic standard for the design, manufacture and performance evaluation of room air conditioners in China, on the premise of combining the specific situation in China, keeping up with the technical changes of the latest relevant international standards, and ensuring the advancement of the standard.

The V-type heat exchanger is commonly employed in duct-type air conditioners, although the non-uniform distribution of airflow velocity in the low duct would result in limited heat transfer capacity. Based on the match between the fin width distribution and the airflow velocity distribution, a C-type heat exchanger with non-uniform fin width was developed for the non-uniform airflow. The heat transfer characteristics of C-type and V-type fins were compared, and capacity was predicted and validated via simulations and tests. The effects of air temperature, condensing temperature, air volume, and air velocity distribution on the heat transfer were investigated. Results show that theoretical heat transfer capacity is maximized when the fin width distribution is proportionate to the power of airflow velocity distribution. The heat transfer area of the C-type fin matches with the airflow velocity better than the V-type fin. The local heat transfer capacity of the C-type fin is greater in most zones, hence the total capacity is greater. The heat transfer increase of the C-type heat exchanger over the V-type is more than 10% across a wide range of working conditions.

Using the computational fluid dynamics software Star-CCM+, the indoor air flow of the four side air outlet embedded air-conditioning air deflector at different angles is numerically simulated, and the air volume of each outlet and the overall air volume are calculated. The numerical relationship between the angle of the air deflector and the air volume is obtained by using the numerical fitting method of MATLAB, and the quintic polynomial can accurately describe the relationship between the air volume and the static angle; Through the simulation of the velocity field and temperature field of the 1.5 m height plane, it is concluded that the indoor air flow can better meet the comfort requirements when the air deflector is at 40°.

Refrigerant flows directly into a few indoor units to make heat exchange with air through long pipes in a variable refrigerant flow system (VRF). Under circumstances of high temperature, VRF faces challenges in safety and reliability due to dramatic voltage fluctuation by electricity peak load and regional difference. The on-off dynamic operating behavior with high temperature and voltage fluctuation was mainly experimentally investigated for a VRF (24 HP), while some performances during the initial stable stage were also shown. Results showed that the VRF operates safely in accordance with the controlling logic of capacity requirement, outdoor environment temperature, internal pressure, voltage supply, etc.

By setting the temperature fluctuation of 3 P environment simulation room within 2℃ as the goal to achieve the effect of "no effect frost", the paraffin with phase change temperature of 46℃ is selected as the heat storage material, and the heat accumulator in line with the outer space of 3 P air conditioner is designed by theoretical calculation. Through experimental verification, the room temperature fluctuation, air outlet temperature and 24 h continuous heating operation attenuation of the heat storage defrosting system are analyzed. Compared with the traditional reverse defrosting system, the outdoor defrosting temperature fluctuation at 2℃ is compared. The experiment shows that the temperature fluctuation of the thermal storage defrosting system at 2℃ is as low as 1℃, significantly lower than 5.67℃ of the traditional reverse defrosting system, and the minimum air outlet temperature of the thermal storage defrosting system is above 39.1℃, which can meet the 24 h long-time operation and the fluctuation is less than 1℃.

In order to analyze the influence of structural parameters of rubber pad on its damping capacity, the mathematical model of structural parameters on the stiffness of rubber pad is established based on response surface methodology, and the influence of structural factors on stiffness is analyzed. The failure mechanism of rubber pad under actual using conditions is discussed, and a new structure considering robustness is proposed. Compared with conventional structures, this structure can effectively reduce the probability of damping failure during the use of rubber pads without affecting the original damping capacity, and improve the reliability of rubber pads.

During the progress of refrigerant alternative. R290 (propane) as a hydrocarbon refrigerant used in Room Air Condition (RAC) has been widely concerned. China has also regarded it as a long-term alternative substance, and also given preferential policies. Introduces the change of R290 refrigerant charge in the latest national standard, through the example, the paper further introduces how to calculate R290 Refrigerant charge and the minimum circulating air volume in the new national standard. Then, based on a 1.5 HP R32 APF1 DC INV. RAC system, finished the contrast test when the RAC system changes the refrigerant charge from the R32 to R290 and analyzed the performance results of the whole air conditioner. Finally, combined with the characteristics of R290 refrigerant, the goals and prospects of the future system development are put forward.

Thermal expansion and contraction are common properties of engineering materials. The change of component length and volume caused by temperature change may lead to air conditioner failure. Such as the air-conditioning internal gear movement mechanism, due to temperature difference caused by uneven thermal deformation and stuck, or caused by excessive clearance, so skidding unable to drive, loss of its function. Or the air-conditioning outside the guide plate movement mechanism, heat deformation against the face frame, unable to guide the wind. And among them the most difficult problem, is the problem of abnormal sound caused by thermal expansion and cold contraction, is the difficulty of the air conditioning industry. Based on the principle of thermal expansion and contraction, the optimization of structure design, control logic, material optimization and production process are studied by using dimension chain analysis, the problem of heat expansion and cold contraction of the air conditioner is solved by optimizing the theoretical design and practical application.

Aiming at the heat dissipation requirement of the the integration and lightweight electronic control components such as the intelligent power module (IPM), the heat sink of the IPM module is designed. After establishing the numerical model of the heat sink and the electronic control system, the influence factors such as IPM heat sink fin orientation, fin spacing, and fin surface treatment methods on the temperature rise of the intelligent power module are explored. The simulation results indicate that the heat dissipation efficiency of the fins which is parallel to the direction of gravity is 9% better than the vertical direction of gravity fins. The average temperature of the heat sink decreases first and then increases with the increase of the fin, the optimal fin spacing is exist. In addition, compared with the fin surface protrusion process, the blackening of the fin surface has a greater impact on the IPM temperature, the heat dissipation efficiency improved by 16.6%. Finally, the designed optimal fin structure is experimentally verified with better performance, and higher economic benefits.

As the core part of fine storage of refrigerator, the electric damper is widely used in air-cooled refrigerator. During the reset process, the redundant reset steps conflict with the zero mechanical limit, resulting in abnormal noise of the damper, affect user experience. In view of this abnormal noise, by studying the mechanism of abnormal noise, a damper structure which can eliminate abnormal noise is designed. A micro pressure sensor is added to the damper structure, and the corresponding control strategy is designed. The test shows that this design can effectively reduce the reset times of the damper and eliminate the abnormal noise in the reset process.

Refrigeration system design is one of the cores of refrigerators. Due to the different design concepts of various manufacturers, the current layout of refrigerator refrigeration system is more diverse. Based on the same conditions, four different layout schemes of refrigeration system are designed on the same box: back vertical, bottom, middle beam transverse, top, by means of theoretical calculation and flow field simulation, the comparison of ability and cost is to illustrate the advantages and disadvantages of each layout, and to provide some reference for future refrigerator design and refrigeration system layout.

Aiming at the problem of limited sound source localization model performance caused by the insufficient number of measured data samples, an indoor sound source localization method based on transfer learning is proposed. The method uses a convolutional neural network to build a transfer learning model, pre-trains a large amount of simulated data, and re-trains a small sample of measured data on the basis of the pre-trained model, so as to achieve indoor sound source localization with small sample data. Experiments based on the TAU Spatial Sound Events 2019 dataset show that the transfer learning model can achieve high-accuracy azimuth prediction for different small sample measured data, and the localization performance is better than the traditional convolutional neural network model, has certain value for the application of transfer learning theory in indoor sound source localization.

Aiming at the problem of abnormal sound and vibration caused by workers' installation errors in refrigerator production, a method of refrigerator sound and vibration fault diagnosis based on improved variational modal decomposition-support vector machine (IVMD-SVM) is proposed to realize the fault self-check for sound and vibration of refrigerators. First, use the collector to obtain the acoustic and vibration signals of the refrigerator under different working conditions, and then perform variational modal decomposition, feature extraction and other preprocessing on the acoustic and vibration signals to obtain the feature data set, which is divided into training set and test set, and then use the training set. Set the training SVM model, and finally apply the trained model to the test set, and output the fault identification result. The results show that the method has high diagnostic accuracy (95.6%, 96.8%), and is a sound-vibration fault diagnosis method for refrigerators suitable for actual working conditions.

Reciprocating vacuum pump working noise, sound quality is not good. In order to improve the sound quality of vacuum pump during operation, the pipe noise of air outlet of reciprocating vacuum pump is studied. Firstly, the near field noise at the outlet of the vacuum pump was collected to obtain the frequency domain characteristics of the vacuum pump noise. It was found that the noise at the outlet of the vacuum pump was mainly concentrated in the 0~4000 Hz frequency band. Then, the noise reduction scheme was designed for the frequency segment, and the muffler series was adopted to eliminate the passing frequency of transmission loss curve, and the Virtual Lab software was used to simulate the performance of the series muffler. Finally, the design scheme was installed at the outlet of the vacuum pump to verify the noise, and the experimental verification of gas flow loss was carried out. The results show that the noise reduction effect of the series muffler on the outlet of the vacuum pump is more than 25 dB(A), and the gas flow loss is 9.8%. The research results can be used for reference to improve the sound quality of vacuum pump.

In order to improve the power density of the air conditioner, it is necessary to increase the operating frequency of the switching tube to reduce the volume of the passive device. Based on the working principle of Power Factor Correction (PFC), the root cause of power device heating after HIGH frequency PFC is analyzed. By improving the control method and selecting more matched power devices, the power dissipation was reduced, which was verified by using an air conditioner with 7.2 kW of refrigeration capacity as the load of PFC for experiments. Compared with the existed technical solutions, the IGBT temperature of the PFC circuit can be reduced by more than 15℃ after using the control method and the design scheme, and the temperature of the fast recovery diode can be reduced by more than 10℃.

In order to solve the problem of the large number of desktop devices and the complicated charging connection, a wireless power supply device based on magnetic resonance technology is designed, which mainly includes transmitting coil, transmitting circuit, receiving coil and receiving circuit. The natural resonant frequency of the transmitting coil is consistent with that of the receiving coil. TMS320F28335 chip of TI company is used to control 4-channel SiC MOS to provide inverter power. The receiving end uses a rectifier DC/DC circuit composed of a power chip GS3671 to convert the AC power output from the receiving coil into a stable DC power supply that can be used by the load. Through the tests of different coil diameters, distances and relative positions, the receiving coil designed can stably drive the load within the range of 0~15 cm from the desktop, and ensure a transmission efficiency of more than 80%.

Sensors ore important sensing device for home appliances to achieve intelligence, sensors play a very important role. As a mature sensor device, gas sensor is only used in the field of home appliances in the fields of air purifiers, fresh air conditioners and other fields. With the introduction of sensor arrays and intelligent algorithms, gas sensors also have more potential application scenarios in home appliances. First, briefly introduces the principle of gas sensors and recognition algorithm, expounds the potential applications of gas sensors and arrays in intelligent scenarios such as preservation, cooking, and health monitoring in the field of home appliances. Then, puts forward the problems of life, drift and consistency faced by gas sensors in home appliances. Finally, looks forward to the future development and puts forward suggestions to promote the application development: (1) strengthen the research of gas sensor array; (2) strengthen the cooperative development of home appliance companies and sensor companies; (3) strengthen data accumulation in home appliance application scenarios.

For a wide variety of detergent products, how to accurately identify the concentration of detergent has become a new hotspot and difficulty in the research field of intelligent washing machines. Through the research and analysis of the detergent identification method, it is concluded that the change of the conductivity of the solution can indirectly reflect the change of the detergent concentration. Based on the conductivity identification principle of the quadrupole method, the detergent concentration identification module is designed and tested. The results verify the feasibility, accuracy and stability of the identification method.

The energy collecting ring is the key to achieve higher thermal efficiency. The multi scheme design of the energy collecting ring of a certain type of burner is studied by experiments and numerical simulation. The results show that the thermal efficiency of the energy collecting ring with double-layer convex shaped can be increased by about 10% compared with the case without energy collecting ring. Compared with the energy collecting ring with double-layer concave shaped, the thermal efficiency of the energy collecting ring with double-layer convex shaped can be increased by about 3%. At the same time, the influence of the key design parameters of the energy collection ring on the thermal efficiency and CO emission is analyzed.

In order to achieve intelligent detection of the ambient voltage of an air purifier, a BP neural network model based on the temperature rise curve to predict the ambient voltage is constructed by using the sigmoid activation function. The results showed that when there were 27~53 neurons in the input layer and 25 neurons in the implicit layer, the prediction ability of the ambient voltage was better. The correlation coefficient between the actual value of the environmental voltage and the predicted value of the training set is 0.996, the model error range is -2.24%~5.26%, the relative error of the evaluation of the new data is small, and it has good predictability, and the results show that the voltage identification model can be used to intelligently predict the ambient voltage.

The operational energy efficiency of multi-unit air conditioner can be effectively improved by adjusting the control strategies of suction pressure and oil return frequency combined with suction line length, so it is necessary to be able to obtain the suction line length online during the operation of multi-unit air conditioners. An online evaluation algorithm for suction line length of multi-unit air conditioners is proposed, where a generalized heat balance method for compressor based on isentropic efficiency is established to iteratively calculate the mass flow rate of refrigerant, a method of the equivalent length of suction line was theoretically derived, and the correlation between the suction length and equivalent length was developed based on experimental data. The experimental results show that the online evaluation algorithm of suction line length can effectively distinguish between long and short piping under full load and partial load conditions, and the piping length calculation error is less than 20% for over 90% working conditions.