Outdoor Unit Of Air Conditioner Research Articles

Low-Frequency Discontinuous Noise Diagnosis and Reduction of Air Conditioner Outdoor Unit

Abnormal discontinuous low-frequency noise occurs in the outdoor unit when the air conditioner is operating at 86~96 Hz. This noise has the characteristics of low frequency, strong penetration, long transmission distance, and poor sound quality, which can cause serious noise pollution. In order to reduce the low-frequency noise of the outdoor unit of the air conditioner, the discontinuous noise frequency is first located by testing the time-domain and frequency-domain maps of the noise. It is then compared with the frequency of fan rotation noise and structural radiation noise. It is found that the discontinuous noise is caused by the coupling of fan rotation noise and structural radiation noise. It is found that low-frequency noise improvement is significant when the frequency difference between two noise peaks is greater than 8 Hz or when a single noise peak is less than 25 dB(A) by studying the methods of frequency modulation and amplitude modulation of noise peaks. By adjusting the fan speed from 930 rpm to 940 rpm, the problem of 94 Hz noise is solved. Then, through testing the natural frequencies of the pipe and shell, it is found that the natural frequencies of the pipe are close to the excitation frequencies. The structural radiation noise is mainly caused by the pipe. Modal analysis is conducted on the pipe. When the normal boundary with the condenser and the normal boundary with the valve of the pipe is constrained by springs, the simulated values are closer to the measured values. Finally, structural optimization design is carried out on the pipe. When the U-tube of the exhaust pipe is shortened by 30 mm, a 30 g mass block is added to the cold inlet pipe, and a 97 g mass block is added to the lower part of the valve pipe of the suction pipe. The discontinuous noise of the optimized prototype is significantly improved.

Effect of Added Natural and Artificial Sounds on Emotional Response and Indoor Soundscape to Residential Noises

This study investigated the effect of added natural and artificial sounds on emotional responses due to residential noises. The laboratory experiment conducted on three residential noise sources (child jumping and plumbing from upper unit and air conditioner outdoor unit) with different sound spectrum and temporal characteristics. In addition, combined sounds with residential, natural (one birdsong and three water sounds of waterfall, sea wave, and stream) and artificial sound (brown and white noise) were set. The experiment consisted of two sessions; self-assessment manikin and indoor soundscape assessment for each sound sources (single and combined residential noises) presented by headphone and woofer. As a result, most combined natural and artificial sounds resulted in more positive changes (higher valence and lower arousal score) than single residential noise. Among combined sounds, multiple natural sound (birdsong + stream) with residential noise showed significant difference from single residential noises such as air conditioner outdoor unit and plumbing noise. Meanwhile, eight affective attribute scale for indoor soundscape assessment showed two main perceptual dimensions and most added natural and artificial sounds had a role in increasing comfort.

Improving performance of air conditioning system by using variable-circuit heat exchanger: Based on the Chinese APF standard

For finned-tube heat exchangers, owing to the extremely different refrigerant pressure drop characteristics between condensation and evaporation processes, the optimum refrigerant circuits of these two conditions are different. However, for a typical heat pump type air conditioner, refrigerant circuit of the conventional heat exchanger (CHX) is fixed no matter what operation condition is conducted. To solve this problem, a modified variable-circuit heat exchanger (VCHX) is developed for air conditioner outdoor unit applications. The VCHX, for which the refrigerant circuit can be easily switched by using a globe valve, could provide better matching characteristics between refrigerant circuit and operation condition variations. With a developed simulation model, refrigerant circuit of the VCHX is optimized by using the entropy generation minimization theory. Then, comparative experimental works were conducted to investigate the performance of VCHX and CHX systems in detail. Experimental results show that the presented VCHX is more suitable for high heating capacity and low cooling capacity applications. Based on the Chinese APF (annual performance factor) Standard, the VCHX system yields 6.5% higher APF value over CHX system. Significantly, economic analysis indicates that the investment payback period of VCHX system is 1.46 year, which is much lower than the designed lifetime of a residential air conditioner. In general, the VCHX technique has a great application potential for improving the overall performance of a heat pump type air conditioner.

Numerical and experimental investigation into effects of winglet shape on flow and noise performances of axial-flow fans for outdoor unit of air conditioner

In this study, the effects of winglet shape on the flow performance, efficiency, and aerodynamic noise of axial-flow fans, used as cooling fans in an outdoor unit of split-type air-conditioners, are numerically and experimentally investigated. Especially, a focus is placed on the coherent flow structures of the tip and leakage vortices: the former is generated from the fan blade tip near the leading edge, and the latter forms in the gap between the blade tip and the shroud. Two types of axial-flow fans are considered: one is with a blade-tip winglet, and the other is without the blade-tip winglet. The flow fields around the fans are simulated by numerically solving the three-dimensional unsteady incompressible RANS equations, and the radiated acoustic pressure is predicted using the Ffowcs-Williams and Hawkings equation. The validity of the numerical methods is confirmed through the predicted results with the measured ones. The flow field characteristics driven by the fans with and without the winglet are analyzed by comparing the detailed structure of the tip and leakage vortices in the gap flow region. In addition, the flow performance, efficiency, and sound pressure of the axial fans are characterized in association with the vortex structures. These results reveal that the winglet shape in the gap flow region has an adverse effect on the flow and acoustic performances of axial-flow fans by increasing the gap-vortex strength.

Development of flow-vibroacoustic coupled numerical methods for prediction of noise radiation due to flow-born vibration of compressor discharge piping system

The compressor and fan in air conditioner outdoor unit are the core component which deter-mines noise performance as well as cooling or heating performance. Among these, the com-pressor has larger contribution to the noise of outdoor units. For high efficiency air condition-er, the size and operating speed of compressor are smaller and faster. The high-speed com-pressor causes loud noise which is complaints for the customer. Traditionally, it is well-known that the vibration of compressor and connected duct is main noise source. However, as the compressor speed increases, the refrigerant flow in the compressor discharge duct also emerged as a major noise source. To reduce the compressor noise operating at high speed, it is necessary to analyze vibrational and acoustic characteristics of compressor discharge duct. This duct noise has the two-types source: structure born noise and flow induced noise. The structure born noise is generated by the duct vibration caused by compressor movement. For the flow induced noise, the static pressure field of refrigerant flow in the duct is vibrational source. In this paper, the compressor discharge duct noise considering two mechanisms was investigated. The refrigerant flow is solved using CFD and duct vibration and noise radiation are computed by FE-BE method.

Clustering the residential noise in apartment house based on spectral and temporal analysis

This study aimed to investigate how the residential noises cluster based on spectral and temporal characteristics of the noises in apartment houses. The type of noise was floor impact, air-borne, plumbing, transmitted outdoor unit of air-conditioner, traffic (road, rail, and air-craft noise), and construction noise. Duration of sound was edited to 5 s and sound pressure level was adjusted to be equal to be 50 dBA. K-means clustering analysis was performed to classify various sound sources, and the elbow method was used to confirm the number of clusters. As a result, residential noise sources were classified into twelves clusters according to spectral and temporal characteristics and difference in psychoacoustic parameters between clusters was also found. In addition, perceptual aspect of each cluster was investigated through sematic differential test.

Effects of bionic blades inspired by the butterfly wing on the aerodynamic performance and noise of the axial flow fan used in air conditioner

The axial flow fan, as a key part of the outdoor unit of air conditioner, has an important impact on the performance of air conditioner. In order to reduce the power consumption and aerodynamic noise of the outdoor unit, the outer edge profile with a depression structure, inspired by the effective control of butterfly wings for airflow, is reconstructed and adopted in the design of bionic blades. The effects of bionic blades with four different depression depths on the aerodynamic performance of the outdoor unit are investigated numerically. It is found that when the depression depth is 1.9 mm, the aerodynamic performance of the outdoor unit is the best. For the axial flow fan with the optimal design blade, the numerical simulation and experimental test on the noise of the outdoor unit are carried out. Based on the experimental results, the shaft power of the outdoor unit is reduced by 1% and the noise is reduced by 1.3 dB when the bionic blade with the depression depth of 1.9 mm is adopted. Based on the numerical results, the flow characteristics of the axial flow fan with the bionic blades is analyzed and the noise reduction mechanism of the depression structure is revealed. The studied results show that the depression structure with proper depth at the outer edge of the blades effectively changed the development and trajectory of the tip leakage vortex, which has a positive influence on the aerodynamic performance improvement and noise reduction of the axial flow fan.

청감실험을 통한 실내에서의 저주파 소음의 단일수치평가량 제안

In this study, new single number quantities (SNQs) based on 1/3 octave band sound pressure levels and low-frequency noise criteria were proposed to evaluate low-frequency noise in indoor spaces. The suitability of the proposed SNQs (D<SUB>max</SUB> and D<SUB>sum</SUB>) was assessed through correlation analysis with other existing SNQs (L<SUB>Ceq</SUB> and L<SUB>Zeq</SUB>) and confirmed by an auditory experiment conducted for construction and air-conditioner outdoor unit noise to be infiltrated from outdoor to indoor spaces. The result showed that the proposed SNQs were highly correlated with the existing SNQs in the range of 0.81 to 0.95. The auditory experiment also revealed that the proposed SNQs had a high correlation with subjective annoyance in the range of 0.81 and 0.89 out of the total range of presentation levels, and a similar correlation with existing SNQs for each presentation level. The proposed SNQs will be able to identify the major frequency bands in terms of annoyance and help assess and establish countermeasures at the site of the low-frequency noise.

Development of Residential Fuel Cell "Ene-Farm Mini"

Tokyo Gas Co., Ltd. has launched residential distributed power generation system “ENE-FARM” which is a micro-CHP system in 2009. The number of cumulative sales reached 300,000 in Japan and 130,000 in Tokyo Gas in FY2019. In order to further spread of “ENE-FARM”, the world's smallest residential fuel cell "ENE-FARM mini" manufactured by Kyocera Corporation was released in October 2019.“ENE-FARM mini” has been developed with the concept to minimize the system size, optimize the rated power of the system with ensuring the power generation efficiency, add the function of continuous power generation during blackout, utilize the IoT technologies, and reduce the cost for installation work.To minimize the system size, the SOFC system integrated of the cell stack and the reformer was adopted. The cell stack’s size was reduced by lowering the rated power to 400 W. The lowered power is also suitable to the recent energy demand decreasing by the spread of energy saving house. The system was introduced to minimize the size of the hot water tank to 20 L, much smaller compared to the conventional “ENE-FARM”. As a result, the size of the whole system is minimized to the point of the smallest in the world, as small as the size of the air conditioner outdoor unit. It is expected to meet more demands from the customers who were not able to afford the large space for the installation due to the limited space available in their residences.In order to lower the rated power to 400 W power with securing the power generation efficiency, it is challenge to secure the heat required for power generation. Hot Box covering the cell stack was designed to achieve high thermal insulation by reducing the heat dissipation loss. As a result, the high power generation efficiency of 47% (LHV) was achieved due to maintain high-temperature conditions.Moreover, the function of continuous power generation during blackout was introduced to “ENE-FARM mini”. Although the blackout occurs during power generation, it is capable to supply the power to the emergency outlet and the boiler, as long as the city gas lines are operating. Therefore, it is possible for users to operate some of the household appliances through the emergency outlet. The hot water supply system and the floor heating system can be functional if the water lines are operating.“ENE-FARM mini” was compatible with the IoT system. Many features such as the usage amount of gas, electricity, water and utility costs can be easily checked on the user’s smartphones. The users also can remotely control many systems such as the hot bath and the floor heating system. Additionally, the usability was improved by implementing the smart speaker compatibility.It is the critical challenge to reduce the cost for installation work. The minimized and weight saved system made it possible to carry the whole assembly with a subcompact car. It only requires two persons to carry and install the system even in a narrow space with a depth of 500 mm. Because the center of gravity point was set to be lower, the base components could be compact and lightweight. The typical weight of the base components was about 27 kg which consists of two components of 13.5 kg. Therefore, the base components can be carried by only one person. It leads to simplify the installation work and reduce the cost for installation.We will continue to contribute to the comfortable living of customers, the preservation of the global environment, and the enhancement of resilience through the spread of "ENE-FARM". Figure 1

Investigation study on the flow-induced noise by winglet and shroud shape of an axial flow fan at an outdoor unit of air conditioner

Axial flow fans of outdoor units are equipped with specially shaped winglets and shroud for reduction of the flow-induced noise. In this study, the unsteady state flow field and the characteristics of the flow-induced noise according to the application of the sweptback tip winglets and 30 % covered shroud in an axial flow fan of an outdoor unit of air conditioner were experimentally and numerically analyzed. To analyze the unsteady flow field, large eddy simulation (LES) reflecting the geometry of complicated outdoor unit was performed; and the LES results were used by simplified Ffowcs Williams and Hawkings (FW-H) equation in order to calculate the noise numerically. As a result, asymmetric flow characteristics inside the outdoor unit by the mount and the shape of blade tip and shroud were found to cause inconsistent movement of the tip leakage vortex, which was revealed to change the characteristics of the flow-induced noise.

Effect of a casing fence on the tip-leakage flow of an axial flow fan

The effect of a casing fence on the tip-leakage flow of an axial flow fan is investigated using large eddy simulation. A fence is attached on the shroud near the trailing edge of an axial flow fan used in an outdoor unit of air conditioner. The Reynolds number is 547,000 based on the blade tip radius and tip velocity. At the design condition, the fan efficiency is increased by the casing fence. The roles of the fence are to block backward leakage flows near the shroud and to weaken the movement of the tip-leakage vortex (TLV) in the azimuthal direction. Also, the fence reduces the double-leakage tip-clearance flow generated at the aft part of the blade tip due to the TLV-blade interaction, reducing the strength of the tip-separation vortex. Consequently, the tip leakage and total pressure losses are reduced, and the efficiency is increased. The pressure fluctuations on the aft part of the blade tip of the pressure surface caused by the TLV-blade interaction are also significantly reduced by the fence, indicating reduction of the noise source. According to the interaction between the fence and backward leakage flow induced by the TLV, the fence significantly and slightly increases the aerodynamic performances at the design and peak efficiency conditions, respectively, but reduces them at an overflow condition.

Increasing the efficiency of split type air conditioners/heat pumps by using ventilating exhaust air

The article presents the possibility of using exhaust air from ventilation system to increase the efficiency (SCOP, COP, SEER and EER) of commonly used air conditioners with the function of a heat pump. These types of devices are very popular both in residential and in public buildings. The topic discussed in the article is very important, because the widespread increase of the energy efficiency of these devices significantly influences national electricity consumption. The possibility of increasing their efficiency by directing the exhaust air from the ventilation system to the heat exchanger of the air conditioner outdoor unit has been analysed. It has been shown that the use of the simple design solution described in the article allows for a significant increase of the efficiency of these devices (seasonal efficiency even up to 35% at 100% share of exhaust air), reducing the energy consumption and increasing their capacity and operation range. By increasing the share of exhaust air it is possible to ensure year-round operation of the device and even 100% coverage of heat demand.

The influence of axial-flow fan trailing edge structure on internal flow

Axial-flow fan with advantages such as large air volume, high head pressure, and low noise is commonly used in the work of air-conditioner outdoor unit. In order to investigate the internal flow mechanism of the axial-flow fan with different trailing edge structures of impellers, four kinds of impellers were designed, and numerical simulation and experiment were deployed in this article. The pressure distribution on the blades surface and distribution of vorticity in impellers were obtained using numerical simulation. Distribution of blade loading and velocity at the circumference are discussed. The relationship between the wideband noise and the trailing edge was established based on the experiment results. The results show that after the optimization of the trailing edge structure, the distribution of vorticity near the trailing edge of the blade is more uniform, especially at the trailing edge of 80% of the chord length of the suction surface. From the blade height position of 70% to the impeller tip, the pressure on the surface rapidly increases due to the tip vortex and the vortex shedding on the blade edge occurred in the top region of impeller. The pressure fluctuation amplitude at the trailing edge structure of the tail-edge optimization structure is smaller. In the distribution of blade loading, the three tail-edge optimization structures have smaller pressure fluctuations and pressure differences at the trailing edge structure. It is extremely important to control the fluctuation amplitude at the trailing edge. The amplitude of low-frequency sound pressure level of optimizing the trailing edge structure decreases obviously in the range of 50–125 Hz, and the optimization structure of trailing edge has an obvious effect on low-frequency wideband noise.

Optimization of flow performance by designing orifice shape of outdoor unit of air-conditioner

Optimization of flow performance by designing orifice shape of outdoor unit of air-conditioner

Aerodynamic performance improvement of up-flow outdoor unit of air conditioner by redesigning the bell-mouth profile

To improve the aerodynamic performance of an up-flow outdoor unit in a split-type air conditioner, experimental and numerical investigations on the propeller fan system of the outdoor unit are performed. Based on the prototype analysis, the propeller fan has a complex vortical flow field near the rotor tip. The vortex structures cause blockage effect on the through flow and have influence on the aerodynamic performance of the outdoor unit. The bell-mouth configuration is redesigned to control the vortex structures. It is shown that the redesigned bell-mouth can weaken the tip vortex and reduce the blockage effect. The redesigned bell-mouth is fabricated and installed on the outdoor unit with 2-blade fan to perform experimental validation. The measured results demonstrate that the aerodynamic efficiency of the outdoor unit is improved by 1.2% with use of the redesigned bell-mouth. The 3-blade fan solution is also attempted to provide more work capacity to enhance the flow rate.

Experimental and numerical study of electronic module-cooling heat sinks used in a variable frequency air-conditioner outdoor unit

In variable-frequency Air Conditioner (AC), sizes of frequency controlling electronic module and its supplemental heat sink are much restrained and they are also tightly packed. Heat removal in such a limited space is difficult, and effective and compact heat sinks are required. The study has focused on heat sink thermal performance with different geometries and configurations. To allow for interaction of heat sink and fan, both numerical and experimental investigations are conducted in a real AC outdoor unit environment. An increase in heat sink base area significantly improves its thermal performance; fin height and pitch influence convective surface and also sweeping stream behavior and a good compromise is needed to enhance convective heat transfer. A proper tuning of heat sink configuration is effective to improve convective stream and subsequently enhance thermal performance. Heat sink geometry and configuration produces insignificant influence on fan aerodynamic and aeroacoustic performance, and AC system performance.

Prediction and measurement of axial flow fan aerodynamic and aeroacoustic performance in a split-type air-conditioner outdoor unit

The study has focused on outdoor unit noise reduction by fan geometry modification with the refined numerical and experimental approaches. The outlet louver, electric motor and its support are included to refine the flow and acoustic model and a hybrid method incorporating CFD and CAA is used to predict the noise behavior. The fan performance curve is well-predicted; the moderate acoustic power is obtained on the outlet louver, motor support and motor exhibiting a significant contribution to overall noise behavior. The aeroacoustic test is conducted in an anechoic chamber and the obtained results are compared with the semi-anechoic chamber ones, and the unremarkable differences are produced, which indicate the ground floor being of some influence. Both modified fan geometries are effective to reduce the noise but the flanging outer-edge blade is more effective. The noise directivities of three geometry fans are investigated both numerically and experimentally and the produced asymmetric characteristics are analyzed.

에어컨 실외기 토출그릴 형상 최적화

The aerodynamic and aeroacoustic performance of discharge grille of outdoor unit of air-conditioner was investigated in this study. Discharge grille is one of outdoor unit's important parts to affect the flow rate and Overall Sound Pressure Level(OSPL). New type of discharge grille was suggested based on the results of numerical simulation. To simulate the flow pattern near the propeller fan, commercial flow solver FLUENT was used. Sliding mesh method was used for rotating propeller fan and initial condition for unsteady model was calculated by Multiple Reference Frame(MRF) method. To minimize the interaction noise between fan blade wake and discharge grille, new discharge grille has radial rib which is aligned with trailing edge of fan blade. And inclined radial rib was adopted for reducing flow rate drop in discharge grille. The optimization of inclined angle of radial grille was performed experimentally.

Numerical Study on Structural Improvement of the Grill Fixed at the Outlet of the Air Conditioner Outdoor Unit

This paper presents the techniques to numerically simulate the inner flow field of the air conditioner outdoor unit with Fluent. The results are verified experimentally and proved to be mesh-independent. The possibility of improvement to increase the flow rate by modifying the grill’s structural parameters is shown through analyzing the numerical results. The gill’s structure is improved using the flow field information got from numerical simulation and the improvement helps to increase flow rate by 4.1% and reduces the turbulent intensity near the grill significantly.

에어컨 실외기용 축류홴의 성능에 관한 연구: 유동 특성

The aerodynamic performance of axial flow fans for outdoor unit of air-conditioner is investigated by numerical and experimental approaches in this study. The pressure drop and volumetric flow rate are compared each other in several different conditions and fan speeds. It is shown that the predicted fan performances are quite well matched with the experimental results. It is also shown that the curvature of the fan arc and hub height have significant influences on the flow distribution after hub. By the results of this study, it can be suggested that several ways to improve the aerodynamic performance of the axial flow fan can be found using the numerical analysis.