Indoor Unit Research Articles

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.

Impact of bitumen terminal technology on atmospheric air

The article is devoted to evaluating the impact of technological factors on the average annual emissions into the atmosphere from the tanks of bitumen terminals. Bitumen terminals with a storage capacity of 2000 to 25000 m³,operating on two different technologies: with the use of day tanks and using a system of internal heating bitumen Kupol. Organised emissions from the tanks are assessed using two methodologies: the Russian methodology by JSC "SEI Atmosfera" and the American methodology according to document AP42. The results show a difference in average annual emissions of up to 3 times, obtained by different methods of calculation, regardless of the bitumen preparation technology. At the same time, the bitumen treatment technology in the Dome indoor units is more environmentally friendly as it reduces the number of product transfers within the terminal and hence the amount of operational emissions. Terminals with day tanks pollute the atmosphere up to 5 times more intensively than terminals using the internal heating technology.

Improved Thermal Performance of Combined Convection and Radiation Using Room Air Conditioner

This study aims to evaluate the indoor thermal environment within a detached residence in summer by applying combined convection and radiation air conditioning system using the refrigerant gas of room air conditioners (RACs). First, field measurements were performed in a detached residence at Hiroshima, Japan, in July and August 2021. Consequently, PMV values were generally maintained within the comfortable range during air-conditioning operation. The amount of heat generated by convection (via the RAC indoor unit) Qc and that by radiation (via the radiation panel) Qr were determined as 426 and 259 W, respectively, and the overall heat generated Qtotal was determined as 685 W. Applying the CFD model, thermal environment was compared varying the ratio between Qc and Qr with a constant Qtotal of 685 W. Results showed that the synergistic operation of a RAC and a radiant panel presented more comfortable PMV values than that of a single RAC application. Furthermore, the airflow from the RAC decreased with an increase in Qr ratio, and the chilled radiant panel provided a cooling effect around the dining area, where the airflow of the RAC was inadequate, thereby improving the thermal comfort.

Reducing energy consumption of heat pumps by introducing a thermal energy storage system

We proposed a short-term thermal energy storage system by applying Phase Change Materials (PCMs) in air ducts connected to an indoor air conditioning unit within a ceiling space. PCM tubes were arranged in a staggered layout in the air duct and cooled by chilled air from the air conditioning unit during “charging” mode, whereas the PCM tubes released cold energy to the room space without operation of the compressor during “discharging” mode. The charging mode allowed for an increase in the partial load ratio of the heat pump to prevent low-efficiency operation at <20% load, which can increase seasonal energy efficiency. We constructed an energy simulation program, where the heat exchange coefficient between the PCM tubes and air was varied with airflow rate and the temperature difference between the PCM and air, in accordance with results from CFD analysis. Switching between the charging and discharging modes was based on the outlet temperature (Tout) and 30% of the rated capacity of the indoor unit (Lr). The heat balance between the charging and discharging modes was improved by this change to the system control. A higher load factor and higher COP resulted in a 7.6% reduction in energy consumption.

Investigation of Fresh Air-Intake Split Air Conditioner Indoor Unit

Clean air is a necessity for physical and mental health. Today, many people cannot get enough fresh air because they have to live and work in closed environments. Especially in single-volume heating or cooling, the indoor air is reconditioned several times, and the air regresses to an insufficient level of air quality over time. The users can only overcome the situation by simply opening the windows and getting fresh air but unfiltered and unconditioned air. In this study, a fresh air supping unit was developed for split air conditioners to create healthier and more comfortable living environments. For the selection of the fan in the fresh air intake module, the amount of fresh air needed in the living room according to the ASHRAE standarts, the ability to change the fan speed, and the ability to overcome pressure drop caused by hose and filter were evaluated. In addition, a filter group was utilized in the unit against particles that may come from the outside environment. The prototype of the designed unit was produced and tested in terms of temperature and performance. The obtained results were investigated in detail.

A mathematical model of critical releasable charge for R290 indoor leakage of split-type household air conditioners

The leakage of hydrochlorofluorocarbons and hydrofluorocarbons used as refrigerants will not only cause ozone depletion and global warming, but also pollute indoor air. Propane (R290) not only does not damage the ozone layer and has a negligible greenhouse effect, but also its charge is about 20–50% of that of hydrochlorofluorocarbons and hydrofluorocarbons, and the releasable charge is lower. In the previous study, a refrigerant pump-down method was proposed to control the R290 releasable charge of split-type household air conditioners (STHACs) under off-mode below the critical releasable charge (CRC) to prevent fires. CRC varies with leakage conditions, such as leak hole sizes, the distance between the installation height of the indoor unit (IDU) and the ignition source (dispersion distance), and the construction of IDU, etc. In this study, a mathematical model is developed to predict the CRCs for STHACs with different capacities and constructions under various leak conditions. The model is verified to have a deviation within 10% for the vast majority of data-points by ignition experiment and CFD model. For safety, the CRC prediction formula is optimized to under-predict CRCs properly, therefore, CRCs for various STHACs and leak conditions are determined to prevent the formation of flammable mixtures even directly under IDU, and the indoor air quality will also be improved. For the used 1 HP STHAC, the predicted CRC is 6.6 g under a 0.5 mm2 leak hole and a 0.7 m dispersion distance.

Experimental research on the performance and parameters sensitivity analysis of variable refrigerant flow system with common faults imposed in heating mode

Due to improper installation, operation, and maintenance, many common faults inevitably occur in the air conditioning systems. However, the same fault could demonstrate different characteristics under different load rates and fault levels; different faults may present similar fault phenomena. This paper reveals the quantitative impact of faults on system performance of VRF system with common faults imposed in heating mode through fault experiments. The system parameters sensitivity study has been carried out to understand the internal impact mechanism related to system parameters. This provides a reference for selecting characteristic parameters and fault decoupling variables and developing interpretable, professional, and reliable fault detection and diagnosis models. The results show that the outdoor unit fouling fault can cause the heating capacity to drop by 73.2%, and the indoor unit fouling can cause the system power to drop by 65.5%. The coefficient of performance drop is as high as 48.6%. The sensitivity study result shows that the system load rate is an influential parameter; it needs to be considered when characteristic parameters and fault decoupling variables are selected.

Experimental study of condensation characteristics and operation strategies of induction radiant air-conditioning system

To study the operation and condensation characteristics of an induction radiant air-conditioning system as a novel system that combines induction ventilation and radiant air conditioning, the characteristics of convection and condensation of an indoor terminal device radiant induction unit were studied. The mass transfer coefficient, condensation temperature, and condensation rate were analyzed experimentally. The time required to achieve a steady state indoor thermal environment was collected. The results indicated that the primary airflow rate and temperature mainly affected the mass transfer coefficient, condensation temperature, and condensation rate. When the indoor thermal environment reached a steady state, the heat transfer performance of the radiant induction unit was mainly affected by the primary air temperature. When condensation occurred, the primary airflow rate had a greater influence on the condensation rate. The start-up and response performances of the system were better than those of a traditional radiant air-conditioning system. In the condensation condition, reasonable control strategies maintain the primary air temperature and adjust the primary air flow rate, which can ensure sufficient heat transfer and stabilize the indoor thermal environment faster.

Parametric study for optimizing double-layer microchannel heat sink for solar panel thermal management

The most significant issue affecting the electric efficiency of solar panels is overheating. Concentration photovoltaic (CPV) modules work by converting approximately 80% of sunlight to heat; this may exceed the cell operating temperature limits. Therefore, thermal management is the best choice for keeping such panels working under specified conditions. Prior to producing an actual solar indoor unit, the current research primarily focuses on optimizing the heat sink dimensions that affect the cooling performance of the solar panel. Two parametric studies were employed to optimize the microchannel heat sink design. First, a two-dimensional numerical study was implemented to optimize the best channel height for more uniform flow inside a double-layer microchannel heat sink (DL-MCHS); the width of channels was kept as a constant value. Second, a three-dimensional conjugate heat transfer model for fluid flow in the optimized heat sink was used to optimize the inlet/outlet header length. To evaluate the overall CPV performance, a further numerical case study was carried out for the optimized designs at a wide range of inlet mass flow rates and steady-state heat flux. The findings indicated that a channel height of 0.5 mm and a header length of 20 mm were the best design points for the suggested heat sink. To assess the effectiveness of a solar/thermal module, the selected design points were applied to a 3D model. The maximum electricity efficiency measured was 17.45%, nearly 40% greater than the typical CPV/T system.

Flammable refrigerant leakage hazards control for split-type household air conditioners

Propane (R290) is expected to be employed in air conditioners and heat pumps, whereas the flammability slows down its uptake. In this study, the leakage hazards control of an R290 split-type household air conditioner (STHAC) with 5 mm diameter finned-tube heat exchangers under off-mode were investigated through concentration measurement and ignition experiments. The critical releasable charges under which a fire may or may not occur at different installation heights were obtained and examined through ignition test. A refrigerant pump-down method was proposed to evacuate the R290 in the indoor unit (IDU) by the compressor to below the critical releasable charge under off-mode. Therefore, the leakage hazards would be enormously decreased, and it could be equally used for other flammable refrigerants or commercial refrigeration units. Besides, a deconvolution method was employed to correct the deviation of measured R290 concentration caused by response time. It is found that the critical releasable charge was 4.3 g and 8 g under a 1 mm leak hole at 1.8 m and 2.2 m installation height of IDU respectively with 1.5 m ignition height from the floor. A formula was proposed to acquire the number of compressor revolutions during the pump-down process. Moreover, the deconvolution method could effectively correct the deviation caused by the response time, but the deconvoluted concentration was still lower than the actual concentration due to the “averaging” effect at the inlet and sample cell of the detector, especially under a small releasable charge below 17.8 g.

Risk Factors Related to Residential Environment of Childhood Community Acquired Pneumonia

Introduction: Community-acquired pneumonia (CAP) is a lower respiratory tract infection occurring in a child who has not resided in a hospital or health care facility in the preceding 14 days. This study was done to determine the risk factors related to the residential environment of CAP among children under five.
 Methods: It was a case-control study conducted at the indoor and outdoor units of the Department of Pediatrics and EPI center of Rajshahi Medical College Hospital (RMCH); the study period was two years, from January 2017 to December 2018. The sampling method was purposive sampling. The sample size was 246 children aged 2-59 months, consisting of 123 cases and 123 controls.
 Result: A significant association was found between CAP and parental smoking (p =0.000, OR=3.33), overcrowding (p = 0.010, OR =1.96) , indoor air pollution (p = 0.004 ,OR =2.33 ) , exposure to cold & humidity ( p = 0.015 , OR =1.95 ) . The study had identified tobacco smoking of parents, overcrowding, exposure to cold & humidity, indoor air pollution as risk factors for CAP.
 Conclusion: CAP is an important cause of morbidity and mortality in under five children (2-59 months) in developing countries like Bangladesh. A huge amount of money is needed to treat the CAP. So, it will be a burden on family and country. However, early detection of the significant risk factors and necessary actions toward these factors help us prevent the development of CAP in under five children (2-59 months) and improve their quality of life.
 TAJ 2022; 35: No-1: 117-123

Optimal thermohydraulic design of the indoor unit of a split-type air conditioner

A CFD-based optimization process was used to design an air supply casing shape for the indoor unit (IDU) of a split-type air conditioner (SAC). The aim was to enhance the IDU performance, including the volume flow rate and total cooling capacity. To this end, the numerical results, including the pressure, velocity, temperature, and humidity ratio distribution, were used to evaluate the IDU performance. For the CFD-based optimal design, a 3D printer was used to manufacture an optimized casing in combination with four IDU geometric parameters. The optimal tongue gap, rear wall gap, and radii of curvature for the first and second segments were 2.2, 8.4, 56.7, and 98.8 mm, respectively. As a result, the measured and predicted volume flow rate and total cooling capacity of the optimized IDU increased by nearly 20% and 27%, respectively, compared with those of the original IDU. Moreover, the predicted and measured volume flow rates and total cooling capacities agreed well, with the relative errors of the IDU performance being less than 1% and 5%, respectively. In addition, the measured power consumption of the cross-flow fan of the optimized IDU was reduced by 19.4% compared with that of the original IDU.

Phototypology as a method of displaying the formation of the urban environ-ment in a modern photobook

Purpose. To figure out the directions of development and origins of the modern photonbook on the examples dedicated to the effect of the Soviet culture on the formation of the post-Soviet urban environment.Methodology. In the process of research, the following methods were used: art analysis, analysis of theoretical and historical preconditions for the development of the typology of a modern photobook that displays the urban environment; synthesis, generalization and systematization of the received information; methods of induction, deduction and comparative analysis.Results. It is shown that photobooks, dedicated to the influence of Soviet heritage on the formation of urban environment and landscape, continue the traditions established by the Dusseldorf School of Photography with some differences affected by the rise of publishing and design technologies. It is determined, that the characteristic feature of a modern photobook is a wider freedom in the choice of the target objects, angles of view, shots. But the concept of documenting the same or similar objects remains. Minimalism in the design of the indoor unit and cover, concise use of several options for repeating modular grids - the trends that unite the latest published photobooks.Scientific novelty. Typological features and principles of the design of one of the actual directions of the modern photobooks are revealed, which tend to continue the traditions of photographic typology as a form of presenting a photo project. Distinctive features in the formation of the design of such photobooks, associated with the development of modern digital technologies of photography and layout, are defined.Practical significance. A retrospective art analysis of photobooks, dedicated to the reflection of the urban environment, was conducted. The research is an important link in the further study of the history of the development of the photobook, as the implementation of the creative project of the photographer.

Improving operation management performance of air conditioners in offices using data envelopment analysis

Heating, ventilation, and air conditioning (HVAC) systems account for the bulk of a building's energy use, which means that potentially significant energy savings can be made by efficiently modifying how those systems are operated. Although several studies have demonstrated that optimizing the operation of HVAC equipment in combination with sensor readings can reduce potentially wasteful processes, such efforts are limited to buildings that have or can incorporate additional sensors. As an alternative approach, this paper aims to identify potentially wasted energy and provide suggested improvements for buildings that do not have installed sensors, which is important because such suggestions can extend the scope of energy reduction measures. More specifically, we hypothesized that comparing differences in user operations would make it possible to identify potentially wasteful operating times. Accordingly, we began our study by identifying target days and days for improvement using data envelopment analysis and then detected operational differences by comparing their operating times. Our new method was then applied to variable refrigerant flow systems in an office building as a case study. The obtained results showed that the potential for energy reduction was about 7.5%. These results, which helped determine the appropriate times for automatically shutting down each indoor unit, proved effective in implementing energy reduction measures. The novelty of this paper is that it clarified the energy waste that can be detected based on operating times, which is expected to lead to the development of additional options for energy reduction measures, thereby allowing building owners to implement more effective actions based on the sizes and conditions of their buildings.

Experimental and Numerical Study of Cross-flow Fan in Air-conditioner Indoor Unit

The cross-flow fan is an essential component of an air-conditioner indoor unit, and its aerodynamic performance seriously affects the performance and heat exchange efficiency of air-conditioning. The internal flow of the cross-flow fan is studied by PIV measurements combined with the three-dimensional unsteady simulation. It is observed that the internal flow of the cross-flow fan is unevenly distributed along the axial direction, and it presents prominent three-dimensional characteristics. Due to the influence of the end-wall, the eccentric vortex is strong in the middle and weak at both ends. Therefore, a pressure gradient along the axial direction in the eccentric vortex area, resulting in axial fluid transport inside the eccentric vortex. At the exit of the impeller, there is a small recirculation zone near the end-wall, which grows continually as it moves downstream in the diffuser section, thereby blocking the outlet. This paper further proposes a structure optimization, which effectively enhances the eccentric vortex near the end-wall and reduces the recirculation zone in the diffuser section, resulting in a 2.1% increase in the flow rate of air-conditioner indoor unit and a 0.8dB reduction in noise level. It is indicated that the structure optimization strategy based on the understanding of three-dimensional flow is beneficial to the internal flow and effectively improves the aerodynamic performance and the aeroacoustics performance of the whole air-conditioner indoor unit.

R290 leakage hazards assessment of a 1 HP split-type household air conditioner by concentration detection and ignition experiment

Propane (R290) is a promising alternative natural refrigerant for refrigeration, air conditioning and heat pump systems to replace hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs), but its highly flammable and explosive properties require specific attention and hinder the replacement process. A fire and/or an explosion may occur once R290 leaks. This paper evaluated the fire hazards of a 1 HP split-type household air conditioner (STHAC) with a charge of 260 g to 350 g not only by measuring the R290 concentration distribution 1.5 m above the floor after a leakage occurred in the indoor unit (IDU) under various situations, but also by ignition experiment to examine the validity of concentration distribution results. A new method for reducing fire hazards was provided by installing a check valve near the gas-liquid separator with a solenoid valve installed after the capillary to prevent the transference of refrigerant from the condenser to the evaporator, which was validated to effectively decrease the fire hazards. The effects of charge, leak hole diameter and valve arrangement on the R290 concentration profiles were studied. It was found that under a fast-leaking rate, a fire occurred though the maximal concentration was 73% LFL detected by infrared gas detectors. This indicated that the detected R290 concentration may be lower than the actual concentration at a fast-leaking rate, and the ignition test was probably the most accurate method for fire hazards assessment. The low-risk application boundaries of the 1 HP STHAC were confirmed both by concentration detection and ignition test.

Performance of a Mid-Size Net-Zero Energy Solar House

The University of Alabama at Birmingham (UAB) was one of 16 collegiate teams from around the world that participated in the U.S. Department of Energy Solar Decathlon 2017 competition. An interdisciplinary team of students from across the university was engaged in a 2-year long process to design and build a house that is powered completely by solar power. The house was equipped to run all the typical appliances of an average modern house at similar levels on a conventional power grid. The net-zero house was built and tested on the UAB campus. Considering Birmingham’s weather, a safe room was built to ensure the safety of occupants during events of extreme weather, such as a tornado. A ductless HVAC unit consisting of an inverter-type 3-speed outdoor unit supplied refrigerant to four high-wall indoor units providing the primary source of space conditioning. To achieve a model of efficiency and cost effectiveness, the house incorporated a heavily insulated envelope and precise glazing protection. The roof, floor framing and walls had R-30 batt and foam insulation. With a design informed by southern vernacular language, the building is oriented to maximize solar access and to use roof planes for shading the majority of the year. Peak power generation of the panels was recorded at 9.6 kW. The home has a centralized energy management system that can provide access to energy consumption data and allow control of lighting, appliances, and plug loads remotely. Energy modeling showed that the annual electricity consumption for heating and cooling with variation in wall types were 8470 to 11,661 kWh. For the month of October, it was calculated varying from 683 to 763 kWh, with varying air changes per hour from 0 to 1.5.

Airflow to disperse refrigerant leaks from hydrocarbon refrigeration systems✰

Whilst R290 is currently used to a limited extent in room air conditioners there is a desire for wider application due to its excellent performance and negligible global warming potential. The product standard IEC 60335–2–40 specifies requirements to limit the allowable refrigerant charge in such a way that it obstructs the wider use of R290. Airflow of an indoor unit can be used to dilute a refrigerant leak, enabling substantially greater charge quantities to be used. A numerical model based on entrainment theory was developed and supported by analysing the behaviour of experimentally simulated releases under various conditions with indoor unit airflow. The work determines the minimum airflow rate necessary to prevent formation of a flammable concentration within the room. Further, the work includes determination of appropriate response time and leak rate to initiate airflow once a leak has begun. The developed methodology can equally be applied to commercial refrigeration units and other flammable refrigerants.

Research on Optimization of Climate Responsive Indoor Space Design in Residential Buildings

This paper first analyzes the climate characteristics of five typical cities in China, including Harbin, Beijing, Shanghai, Shenzhen and Kunming. Then, based on Grasshopper, Ladybug and Honeybee analysis software, according to the indoor layout of typical residential buildings, this research extracts design parameters such as the depth and width of different rooms and their window-to-wall ratios etc., to establish a climate responsive optimization design process with indoor lighting environment comfort, with heating and cooling demand as the objective functions. Meanwhile, based on Monte Carlo simulation data, ANN (Artificial Neural Network) is used to establish a prediction model to analyze the sensitivity of interior design parameters under different typical cities’ climatic conditions. The study results show that the recommended values for the total width and total depth of indoor units under the climatic conditions of each city are both approximately 14.97 m and 7.88 m. Among them, under the climatic conditions of Harbin and Shenzhen, the design parameters of residential interiors can take the recommended value of UDI optimal or nZEB optimal. While the recommended values of window-to-wall ratios for the north bedroom, master bedroom and living room in Shanghai residential interiors are 0.26, 0.32 and 0.33, respectively. The recommended value of the window-to-wall ratio of the master bedroom in Kunming residences is 0.36, and that of the remaining rooms is between 0.15 and 0.18. The recommended values of window-to-wall ratios for the master bedroom and living room in Beijing residences are 0.41 and 0.59, respectively, and that for the remaining rooms are 0.15. The multi-objective optimization process based on parametric performance simulation used in the study can effectively assist architects in making energy-saving design decisions in the preliminary stage, allowing architects to have a case to follow in the actual design operation process.