Indoor Unit Research Articles

Development of a Heuristic Control Algorithm for Improving Energy Efficiency in Commercial Refrigerated Systems without Indoor Information

Despite the serious threat of global warming caused by carbon emissions, commercial refrigeration systems that generate cooling are unable to adjust their usage time. Therefore, it is essential to enhance the energy efficiency of refrigeration systems themselves. Recently developed refrigeration systems offer improved energy consumption efficiency as they utilize inverter-type outdoor units that can communicate with indoor units. However, traditional legacy refrigeration systems still suffer from poor energy efficiency because the existing indoor units cannot communicate with inverter-type outdoor units. Hence, this paper introduces a heuristic energy efficiency improvement algorithm for commercial refrigeration systems using legacy indoor units when an inverter-type outdoor unit is installed. In particular, to reduce the computational complexity of the process of selecting the optimal temperature difference and target low-pressure variables that can enhance energy efficiency, the algorithm employs the Monte Carlo method. Finally, the performance of the proposed heuristic energy efficiency improvement algorithm was evaluated in a laboratory environment to confirm its applicability.

Variable refrigerant flow heat pump model with estimated parameters and emulated controller based on manufacturer data

A new physics-based and modular variable refrigerant flow (VRF) heat pump model aimed toward multi-year simulations is presented. The model allows the simulation of any number of indoor units (IU), outdoor units (OU) and compressors. A parameter-estimation procedure and a control strategy both using available manufacturer data is proposed. The model is validated against data collected from a VRF system that services the first floor of the former ASHRAE Headquarters Building in Atlanta (USA), comprised of 22 IU, 2 OU, and 8 compressors. Results show that the model accurately predicts the total energy consumption over a two-month cooling period, with a relative error, normalized mean bias error, and coefficient of variation of the root mean square error of 1%, 1.6%, and 16.7%, respectively.

The data assimilation of volumetric velocity and temperature data to extract boundary conditions for high-fidelity simulation of the indoor air

The contemporary challenge of the air conditioning sector is to continuously improve the provided comfort conditions while reducing the energy consumption of the devices. This necessity can only be satisfied by improving research and design methods. Therefore, on the one hand, researchers worldwide develop and utilize experimental methods for more accurate measurements. On the other hand, researchers develop numerical methods to investigate design iterations effectively and quickly.The main idea of this study is to create a novel data assimilation method to utilize all the advantages of experimental and numerical methods to develop a high-fidelity investigation method of an indoor air model.In the present study, the three-dimensional velocity distribution at the split air conditioning indoor unit's outlet section was measured by using the Stereo Particle Image Velocity Measurement method. The temperature distribution at the outlet section of the split air conditioning indoor unit was also determined using the Meshed Infrared Thermography method. The data from these experimental measurements were assimilated to generate a highly realistic boundary condition of the steady-state and time-dependent Computational Fluid Dynamics (CFD) models. This is achieved for the first time in the literature.The results of these analyses compared with conventional CFD and the aforementioned experimental methods. The study's results show that the novel data assimilation approach (3.13% average error) is significantly more accurate than the traditional average boundary condition approach (13.19% average error).

Theoretical design and drainage characteristic of a C-type heat exchanger in duct air conditioner

The conventional duct air conditioner typically uses an A-type heat exchanger for indoor units, which has poor drainage behavior under wet conditions. In this research, a C-type heat exchanger is developed for drainage improvement. The innovative design employs a unitary fin and a curved profile instead of the sectional fin and linear profile. Theoretical calculations are conducted, determining that the droplet sliding time on the cycloid is the shortest among the curves. The C-type is then produced and subjected to dynamic dip testing to assess its drainage performance. Results reveal that it achieves steady drainage within 3 s and reduces residual water by 10.9% compared to the A-type. A CFD model is generated to simulate the drainage process, with a calculated deviation of less than 10% for residual water. Finally, the C-type prototype is installed in the duct unit for performance measurement under wet conditions. It exhibits a 7.12% increase in heat transfer capacity and a 12.74% increase in drainage rate under the basic condition. The lower evaporating temperature, higher inlet air temperature, higher relative humidity, and larger air volume flow rate contribute to the more apparent drainage enhancement of the C-type.

An Experimental Study omn Evaporative Condenser in Air Conditioning Systems Using R744

Nowadays, the use of refrigerants has low GWP and zero ODP applying refrigeration and air conditioning systems is an important concern. There has been a lot of research taking about refrigeration systems using R744. In this study, we focus on the use of the mix of water and air for an evaporative condenser through an experiment to study the heat transfer efficiency between water and the R744. The results of this study show that it is feasible to use water to cool down R744 to a subcritical state. The data obtained show that the R744 temperature at the outlet condenser gradually decreases with each change in the number of tube layers, the condensing pressure is stable at 73 bar with a pressure drop of 0.4 bar. The water temperature is stable between 26oC and 28oC, and the air outlet temperature from the indoor unit gradually decreases from 28oC to 16.8oC. With the 3 configurations of the condenser, the coefficient of performance gradually increases from 3.6 to 4.5 respectively.

Hybrid system development and application research for refrigerant leak inspection

Recently, record-breaking heatwaves due to global warming and abnormal weather have occurred in the summer, and sales and usage of air conditioners are rapidly increasing. Air conditioners are widely used all over the world and are recently expanding to centralized management system air conditioners. There are many customers requesting repairs due to leaking air conditioner refrigerant. However, the problem of refrigerant leakage is difficult to repair because it is difficult to quickly and accurately determine whether there is leakage on site. Air conditioner refrigerant leakage occurs in various parts such as outdoor units, indoor units, and connecting pipes, and there are cases of leakage due to minute defects, making it difficult to clearly determine whether there is leakage. Research was conducted to develop a hybrid system so that immediate judgment on these issues could be made in the field. A refrigerant leak diagnosis method was studied based on an acoustic emission sensor, and a refrigerant leak diagnosis procedure and hybrid diagnosis system were developed to detect refrigerant leak signals for each air conditioner component in consideration of the characteristics of the UV gas detector and each inspection method. It is expected that field diagnosis of air conditioning systems can be effectively applied using the procedure and diagnosis system developed through this study

Numerical investigation on flammability of R32 leakage in heat pump outdoor unit with CFD simulation

R32 is receiving significant attention as an alternative refrigerant owing to its higher operating efficiency and lower environmental impact; however, it is classified as flammable refrigerants. There have been some studies on R32 leakages about indoor unit rooms but extremely limited studies about outdoor unit rooms. The outdoor unit room is more cramped than the indoor one, and leakage easily occurs due to high-temperature and high-pressure operating conditions. In this study, the flammability risk was evaluated through a comprehensive R32 leak study in the outdoor unit room. Critical factors including the leak diameter, unit installation height, refrigerant charge, air infiltration, window opening, and room size were carefully selected, and parameter studies and correlation analysis were conducted. As the leak diameter increased from 2 to 8 mm, the R32 volume fraction increased from 7.7 to 46.3%, indicating that the leak diameter is the most significant factor in increasing the R32 volume fraction. Considering that the leak diameter is less than 1 mm in a typical leak accident and the leak occurs with a diameter of 2 mm or more in a catastrophic case, the risk of R32 leak was found to be low under the conditions. By increasing the window opening and unit installation height, the concentration of R32 can be lowered below the LFL, thereby reducing the flammable volume to close to zero.

Cause analysis and suppression method of the vortex at the impeller outlet of the multiblade centrifugal fan

AbstractIndoor air conditioning systems play a crucial role in regulating the environmental conditions of enclosed spaces. The noise generated by such systems can significantly impact human comfort. The multiblade centrifugal fan, as a crucial component of indoor air conditioners, has a significant impact on the performance of the air conditioner. The vortex, which is the primary noise source inside the fan, hinders the aerodynamic noise reduction of the indoor unit. During experimental research and numerical simulation of the indoor unit, the researchers identified the presence of a vortex flow at the outlet of the multiblade centrifugal fan. By analyzing the velocity vector of different cross‐sections in the fan, the researchers determined the formation mechanism and influencing factors of the vortex at the fan's outlet. The addition of fairing sheet plates on the volute wall was explored as a vortex suppression method, which proved effective in weakening and suppressing the vortex. The test results showed that under the same air volume, the noise reduction amplitude of the fan equipped with fairing sheet blades was 1.2 dB at an outlet static pressure of 30 Pa and 0.7 dB at an outlet static pressure of 100 Pa. The research findings suggest that the addition of the fairing sheet can effectively reduce the vortex's intensity, improve the performance of the multiblade centrifugal fan, and reduce the noise.

Super‐heating degree responsive control strategy of variable refrigerant flow air conditioning system for energy saving and stable operation

AbstractThe control strategy is important for variable refrigerant flow (VRF) air conditioning system to realize energy saving and stable operation. In this work, the super‐heating degree (SHD) responsive control strategy was developed to dynamically adjust the respective SHD target value (ΔTe,tar) of indoor units so as to adapt to the variable cooling load. The capacity code (Ecode) is introduced into the control model to quantify the reference target value of SHD. To responsively adapt to variable cooling load, the correction target values of SHD based on discharge temperature and deviation of the outlet air temperature are introduced in the SHD model for operation protection of the compressor and the consistency of refrigerant distribution. The enthalpy difference analogy method is developed to estimate the performance of the VRF system including cooling capacity, electric power, and energy efficiency ratio (EER). The performance was tested under the conditions of different ΔTe,tar. Experimental results demonstrate that the ΔTe,tar is an important factor to determine the operation frequency, which affects cooling capacity, power, EER, and operation status of the system. The cooling capacity and electric power at the ΔTe,tar of 9°C was about 55.2% and 63.5% lower than those at the ΔTe,tar of 1°C, and the corresponding EER was improved by 22.6%. To further verify the SHD control strategy, the VRF system was tested by the responsive control model under the condition that Ecode and ΔTe,tar were constantly automatically adjusted and changed with the actual indoor ambient temperature. Experimental results demonstrate that the VRF system can achieve a good and uniform cooling effect and realize energy saving and stable operation according to the responsive super‐heating degree control.

Radiological Patterns Integration with Duration of Illness in COVID-19 Pneumonia as ‘Evolved’ and ‘Evolving’ Radiological Phenotypes: A Single Center Experience

Background: Radiological phenotypes are radiological patterns or observable characteristics of COVID- 19 pneumonia. Methods: Prospective observational study, included 3000 COVID-19 RT-PCR confirmed cases with lung involvement documented and categorized on HRCT thorax at entry point as mild, moderate and severe as per lung segment involvement bilaterally and follow up CT thorax imaging at six months post discharge from hospital. Radiological phenotypes were categorized as ‘Evolved’ and ‘Evolving’ as per radiological features and analysed with inflammatory markers and interventions required in indoor setting including ventilatory support. Age, gender, Comorbidity, laboratory parameters and use of BIPAP/NIV in COVID-19 cases and outcome as with or without lung fibrosis were key observations. Statistical analysis is done by using Chi square test. Results: In study of 3000 COVID-19 RT PCR confirmed pneumonia, ‘Evolved’ and ‘Evolving’ radiological phenotype patterns were observed in 36.66% and 63.33% respectively. Duration of illness, laboratory parameters at entry point (CRP, IL-6, ferritin, LDH, D-dimer) & interventions required in indoor unit has significant association with Radiological phenotypes [p<0.00001] HRCT severity score at entry point & Post COVID-19 lung fibrosis or sequelae has significant association with radiological phenotypes. [p<0.00001] Conclusions: Radiological phenotypes have documented very crucial role in initial assessment of COVID- 19 pneumonia. Evolved and Evolving differentiation have documented important step in management of these cases in indoor and outdoor setting. J MEDICINE 2023; 24(2): 71-81

Operation characteristics based on a novel performance model based on capacity utilization rate of a variable refrigerant flow air conditioning system

In the context of a large market share, enhancing the actual performance of variable refrigerant flow (VRF) air-conditioning systems is of considerable importance. The operating states of indoor units (IUs) significantly influence the energy efficiency of a VRF system with multiple indoor terminals. Therefore, it is challenging to address accurate and concise representation of the operational characteristics of IUs for analyzing their impact on system performance. This study explored a novel performance index called capacity utilization rate (CUR) to illustrate the effect of IUs on system performance and developed a performance model based on this index. Simulation and experimental results demonstrated that energy efficiency and evaporating temperature decrease with a reduction in CUR under specific ambient temperatures and part-load rates. The proposed performance model was applied to real buildings in field tests to examine the operational characteristics of the VRF system. This research offers valuable insights for system design, performance simulation, and performance evaluation of VRF systems.

Experimental study of ventilation performance of a novel integral-type air conditioner with heat recovery using R290

The leaking safety of air conditioner using R290 has been a research hotspot in recent years, one method to lower the risk of explosion after leakage is utilizing ventilation. For fresh air conditioner, it's common to use thermal anemometry and differential pressure flowmeters to measure ventilation flow rate. However, there is non-negligible error especially under low air volume flow rate conditions. In this paper, a novel integral-type air conditioner with heat recovery using R290 is proposed. And the relevant influencing parameters are analyzed and experimentally studied. The results show that tracer gas method is an effective way to measure ventilation flow rate, and the novel integral-type air conditioner can meet the needs of the ventilation standards. The air volume flow rates of indoor unit fan and outdoor unit fan are dominant factors affecting ventilation flow rate. The outlet area of exhaust air duct is more sensitive than the inlet area of fresh air duct in exerting influence on ventilation flow rate, while the indoor temperature has a mild impact on ventilation flow rate.

PEMANFAATAN ENERGI PANAS PADA MESIN PENGKONDISIAN UDARA 3/4 PK SEBAGAI MEDIA PEMANAS AIR MANDI

Air conditioning, commonly known as Air Conditioner (AC) is one type of cooling machine that is widely used by the community, almost in every home and heat energy is wasted in the surrounding environment from outdoor unit devices. The amount of heat energy released to the environment comes from the heat absorbed by the evaporator or indoor unit to the cooled room and added heat energy from the work of the compressor. The heat energy can be reused. The form of utilizing wasted heat energy is to add a pipe from the compressor to the condenser to heat the water. The working process of the AC machine is a closed cycle of the compressor, condenser, capillary tube and evaporator where the cooling medium will work continuously as long as the AC is turned on. Addition of a pipe to heat water for bathing purposes. The test results of the air conditioner using a water heater is an increase in the actual power that is equal to from 1,357 Kw to 1,447 Kw. The heat removed from the condenser decreased from 154.546 kJ/kg to 152.137 kJ/kg. The resulting temperature from a 20 liter water tank is 63.0 OC in 120 minutes.

Novel approach to typical air-conditioning behavior pattern extraction based on large-scale VRF system online monitoring data

The diversity of occupant air-conditioning (AC) behavior in buildings leads to significant discrepancies in building energy consumption. Thus, establishing models that reflect diverse realistic occupant AC behavior is crucial for the building performance simulations (BPS). Owing to the lack of large-scale samples, it is difficult to extract typical AC behavior patterns from existing studies. With advances in IT methods for data collection, large-scale on-site air-conditioning (AC) operation data of variable refrigerant flow (VRF) systems have become available. Therefore, based on the Big Data of 1200 indoor units (IDUs) of VRF systems, a novel method was proposed herein to establish realistic AC behavior models and extract typical patterns. The overall framework included three steps: data collection and preprocessing, large-scale occupant AC behavior model establishment, and typical behavior pattern extraction and evaluation. First, data preprocessing approaches were implemented to address data issues. Subsequently, based on Big Data, Bayesian parameter calibration was proposed to construct large-scale occupant AC behavior models. Afterwards, using the large-scale calibrated AC behavior models, the cooling demands of the population were simulated, and k-means clustering analysis was adopted to categorize the AC behavior into five groups representing different cooling demand levels and a typical model reflecting the group feature was selected. In the model validation, a hypothesis-based test was applied to confirm the validity of extracted typical patterns in reflecting the real distribution of district cooling demands. In the results, this study identified two occupancy patterns, i.e. “Daily occupied mode” (DOM) and “Night occupied mode” (NOM), and based on two occupancy types, five typical AC behavior patterns were extracted separately. From the typical patterns, it could be noticed that 90% of occupants had relatively low cooling demand less than 40 kWh/m2 during the cooling season. Moreover, comparing to the performance of fixed AC schedule model in district cooling demand evaluation, the extracted typical AC behavior patterns improved the accuracy up to 30.4% when calculating the bias between average modelled cooling demand and measured data. Additionally, the typical AC behavior models put forward in this study can be further integrated in BPS tools, which is promising for the simulation of cooling demand at building or district scale, and realizing AC technology evaluation in future engineering projects.

Detection of R290 leaks in RACHP equipment using ultrasonic sensors

There is a growing need for cost-effective leak detection in smaller RACHP equipment that uses R290 and other flammable hydrocarbon refrigerants. Gas detection technology may not be suitable in many cases due to cost and reliability implications whilst detection with system parameters can suffer long response times. Ultrasonic leak detection can be an economical and reliable method. This study presents the development and testing of an ultrasonic leak detector using off-the-shelf components, within a conventional split type wall-mounted air conditioner indoor unit. Depending upon the chosen sensor, a fast and effective response to simulated “small” R290 leaks was achieved. Measurements of potential interference from environmental noise across ultrasonic frequencies suggests false alarms are unlikely. Such a leak detector was found to be potentially effective.

Heat and Moisture Management for Automatic Air Conditioning of a Domestic Household Using FA-ZnO Nanocomposite as Smart Sensing Material

Prior to the year 2000, air conditioning was not common in many cities throughout the world. However, today, 20 years later, air conditioning is common. This circumstance has a negative impact on the climate. Additionally, the situation regarding energy usage as a result of this is alarming. For a healthy and pleasant livelihood, indoor temperature and air flow must be controlled. False partitions with insulating layers have been used to regulate the temperature inside rooms, but they are unable to regulate the variation in humidity caused by the exchange of water between interior and exterior walls. In this manuscript, we provide a sensory system that can automatically detect relative humidity and temperature. Temperature is sensed at each layer of the false partition using an LM35-based integrated circuit and humidity is detected by an FA–ZnO nano-composite layer through an indoor false partition owing to changes in the material’s resistance. Depending upon the change in resistance based on the fluctuation in temperature, the corresponding current responds by arduino microcontroller, and thus triggers the automated ON and OFF switch for air conditioning. Living and non-living bodies both lead pleasant and healthy lives when indoor units are managed properly.

Explosion risk analysis of R290 leakage into a limited external space

R290 is considered as a promising alternative refrigerant to be used in household air conditioners. To promote the safety application of R290 in air conditioners, a numerical model of refrigerant leakage and diffusion in a limited space was developed, and the reliability of the model was verified by the experimental results on the concentration field of refrigerant leakage from a split air conditioner indoor unit. On this basis, the field strength characteristics of R290 leaking from holes with different diameters and shapes to the external space were investigated, and the explosion risk caused by R290 leakage was further analyzed. The results showed that when R290 leaked from circular leakage holes with different diameters or leakage holes with different shapes to the external space, respectively, Mach disks were formed in the flow area, and the location and size of the Mach disks had certain differences. For circular leakage holes, with the increase of the leakage diameter, the diameter of the Mach disk inside the flow area and the distance from the Mach disk to the leakage hole increased, and the range of the flammable area formed by the leaked R290 in the external space did not change significantly in the horizontal direction, but increased significantly in the vertical direction, which were 0.42 m, 0.84 m, 1.26 m, and 1.7 m, respectively. For leakage holes with the same area but different shapes, the diameter of the Mach disk formed by the gas leaking from the circular hole was larger, and the gas was distributed symmetrically in the horizontal direction with the jet axis as the center in the external space. The gas leaking from the triangular hole was approximately distributed in a triangular shape, and then it diffused along the three centerlines of the triangle. The gas leaking from the square hole diffused along the diagonal of the square in the horizontal direction, and finally the flow area gradually changed from a square to a circle. The gas leaking from the rectangular slit was elliptically distributed in the external space, and the gas mainly diffused along the long axis direction of the ellipse, and the diffusion of the short axis direction was not significant. The range of the flammable area formed by the gas leaking from holes of different shapes did not change significantly in the external space.

Comparative analysis of sizing procedure for cooling and water heating cascade heat pump applied to a residential building

An appropriate design strategy suitable for the purpose of a building should be considered to apply a cascade heat pump system for multiple functions to buildings. The purpose of this study is to propose a sizing process and evaluate a capacity calculation simulation of air-to-air/water cascade heat pump systems applied in residential buildings that supply indoor cooling and hot water. A simulation study was performed by dividing the capacity calculation method suitable for the building conditions into two cases when this multi-functional cascade heat pump system was applied to a residential building. Case 1 was a sizing method that considered a low-cycle heat pump for indoor cooling. The existing heat pump sizing method for the hot-water supply used in the previous study was set to Case 2. The heat pump simulation and heat calculations were conducted based on thermodynamic theoretical equations. A simulation tool capable of dynamic thermal load analysis was used for model building. Detailed building information was entered in accordance with design standards. The results showed that Case 1 completely satisfies both the cooling and hot-water supply performance of the heat pump compared to Case 2. Based on Case 1, when the temperature of the intermediate heat exchanger was 10 °C higher than the outdoor temperature, the air volume of the indoor unit and the outdoor unit was found to be 941 m3/h at an appropriate air volume rate. In addition, the energy consumption was also the lowest at 2.29 kW h, and the maximum system COP of 6.0 was achieved.

Numerical study on the effects of circuits on thermal-hydraulic performance in an indoor unit with small diameter in air conditioner

The distributed parameter method is adopted to establish a simulation model of the indoor unit of a split-type household air conditioner with a diameter of 5 mm. The circuits of forward and reverse cross are proposed, and the effects of different circuits on the thermal-hydraulic performance of heat exchanger are revealed. Compared with the prototype, the heat load of the forward and reverse cross is increased more obviously. The forward and reverse cross can realize the strengthening of the heat load by changing the spatial distribution of heat load and temperature difference. The forward and reverse cross under the cooling condition can improve the temperature difference of the second row. The heat loads of the two-phase zone and the vapor phase zone increase to a certain extent. Under the cooling condition for circuit-3, the heat load is increased by 6.65%, and the pressure drop in refrigerant side is slightly increased. Under the heating condition for circuit-3, the heat load and pressure drop in refrigerant side are similar to that of the prototype. Meanwhile, the circuit-3 has the most obvious improvement effect on the non-uniformity of pressure drop under different conditions.

Easy-to-treat and difficult-to-treat radiological phenotypes in coronavirus disease 2019 pneumonia

INTRODUCTION: Radiological phenotypes are observable radiological patterns or characteristics. Robust data are available regarding the role of high-resolution computed tomography (HRCT) in coronavirus disease 2019 (COVID-19) pneumonia. We evaluated the role of radiological phenotyping in assessing severity and predicting the response to therapy, as well as its association with outcomes in COVID-19 pneumonia. METHODS: This prospective observational study included 3000 COVID-19 reverse transcription polymerase chain reaction-confirmed cases with lung involvement who underwent thoracic HRCT on hospital admission and were categorized as mild, moderate, or severe according to lung segment bilateral involvement (mild 1–7, moderate 8–15, and severe 16–25). Follow-up thoracic CT imaging was also conducted 6 months after hospital discharge. Response to treatment phenotypes was categorized as “easy to treat” or “difficult to treat” based on the response and interventions required in indoor settings, including ventilatory support. Age, gender, comorbidities, laboratory parameters, the use of bilevel-positive airway pressure/noninvasive ventilation, and outcomes (with or without lung fibrosis) were key observations. The Chi-square test was used for statistical analysis. RESULTS: Easy-to-treat and difficult-to-treat radiological response phenotypes were observed in 20% and 80% of the cases, respectively. There were significant associations between the radiological phenotypes and the duration of illness at hospital admission. The duration of illness (<7 days, 7–14 days, and >14 days) could predict the radiological phenotype (P < 0.00001). Laboratory parameters at hospital admission (C-reactive protein, interleukin-6, ferritin, lactate dehydrogenase, and D-dimer) were significantly associated with the radiological phenotypes (P < 0.00001), as were interventions required in indoor units (P < 0.00001). The HRCT severity score at admission was significantly correlated with the radiological phenotype (P < 0.00001). Post-COVID lung fibrosis or sequelae were also significantly associated with the radiological phenotype (P < 0.00001). CONCLUSION: Easy-to-treat and difficult-to-treat phenotypic differentiation had a crucial role during the initial assessment of COVID-19 cases on hospitalization and was used for planning targeted intervention treatments in intensive care units. In addition, phenotypic differentiation had an important role in analyzing the radiological sequelae and predicting final treatment outcomes.