Split Air Conditioner Research Articles

A novel refrigerant-direct radiant cooling system: Numerical simulation-based evaluation

• A novel refrigerant-direct radiant cooling system is proposed. • The temperature distribution of the RDRC terminal surface is homogenous. • The mathematical and economic models of this terminal are established. • The sequencing of impact factors and the optimal structure are obtained. Split air-conditioners have deficiency in thermal comfort due to draught sensation and fan noise. The existing radiant cooling systems adopt chilled water as circulating medium, resulting in low energy efficiency because of the requirement of secondary heat exchange. To address these problems, a novel refrigerant-direct radiant cooling (RDRC) system is proposed. Experiments are conducted in a climate chamber to evaluate the thermal performance of this system. Results show that the RDRC terminal surface temperature is distributed homogenously and this system has excellent stability. The mathematical and economic models of this terminal are established and the mathematical model is validated with experimental data. The effects of different structural parameters on thermal and economic performances of the RDRC system are investigated, and then this terminal is optimized by orthogonal design method. The cooling capacity for per exterior area is considered as objective function and the initial cost less than 121.1 $ is taken as constraint condition. Results indicate that the fin height of 40.0 mm, the copper pipe diameter of 6.0 mm, the copper pipe spacing of 40.0 mm and the aspect ratio of 0.88 are recommended.

A study on the quantitative single and dual fault diagnosis of residential split type air conditioners in static operation using support vector machine method

l Fault diagnosis for single and dual failure for air conditioners using SVM method. l Based on the existing sensors only. l Machine learning based on the database obtained from refrigeration cycle simulation. l Failure mode was detected with an accuracy of higher than 88%. l Failure level was predicted within ±10% of actual data. Owing to the recent uprise in summer temperatures, the use of air conditioners has been increasing accordingly. Air conditioners consume a significant amount of energy, and defects in air conditioners usually could lead to even more consumption of energy. Hence, early detection of defects could not only enhance user satisfaction, but also conserve energy. In the present work, quantitative fault detection models for single- and dual-failure modes have been developed using a support vector machine technique based on refrigeration cycle simulation data including normal and defective conditions. The defect modes investigated in the present work include refrigerant shortage and degraded air flow rates for the evaporator and condenser of an air conditioner. The results indicate that the proposed method can predict the values of more than 95% of the defective parameters within ± 5 % for the single-failure mode, and more than 90% of the data within ± 10 % for the dual-failure mode.

Performance, environment, and cost‐benefit analysis of a split air conditioning unit usingHC‐290 andHCFC‐22

AbstractA widely used hydrochlorofluorocarbon (HCFC) refrigerant HCFC‐22 in the split air conditioner (AC) is being phased out in all countries under the Montreal Protocol. Propane (HC‐290) is a favorable substitute for HCFC‐22. The performance, environment impact and cost‐benefit analysis of a split AC unit operated with HCFC‐22 and HC‐290 has been carried out experimentally under different test conditions prescribed by IS 1391. The results showed that the variation in system performance was more significant for HCFC‐22 than for that of HC‐290 while varying the refrigerant charge. The experienced optimum charges that represent the maximum coefficient of performance (COP) was varied with the working environment and it was realized that, generally the optimum charge for HC‐290 was 50% lesser than that of HCFC‐22. The COP of the AC unit with HC‐290 was observed to be 5% more than that of HCFC‐22. However, the system capacity diminished by 7.8%. The operation of a split AC unit with HC‐290 produced up to 15.9% lesser CO2emission than that of HCFC‐22 under all the test conditions. The use of HC‐290 in an existing HCFC‐22 split AC system can save up to 12.22% of the life time total cost. Finally, it was inferred that the replacement of HCFC‐22 with HC‐290 in the split AC unit showed dominance in all aspects such as performance, emission, and life time total cost.

Numerical simulation of earth-air heat exchanger application for Indonesian simple house air conditioning system

Research on an air-conditioning (AC) system that uses soil as a heat storage is still not widely conducted in Indonesia. The soil functions as a hot or cold storage medium by flowing fresh air through a heat exchanger due to its constant temperature tendency throughout a year. Earth-air exchanger (EAHE) application was simulated and got the results that soil with a volume of 12 m3 is potentially used as a heat exchange medium with a heat transfer surface area of 24.4 m2. The EAHE cooling capacity obtained is 1,002–1,282 watts depending on soil condition. Increasing the pipe diameter and airflow velocity decreases the average temperature difference by 42.9% per inch and 47.2% per m/s, respectively. Meanwhile, increasing the pipe thickness and soil depth increases the average temperature difference by 1.59% per millimeter and 6.06% per meter, respectively. The pipe interface distance recommended is greater than or equal to 200 mm. The EAHE can meet the Indonesian National Standard thermal comfort standard and ASHRAE breathing zone outdoor airflow for ventilation standard but can only meet 23.5%–30.0% of simple house-cooling loads. It consumes 75.8% lower energy and has an 139%–230% higher coefficient of performance than a split AC system.

Cooling performance enhancement for the automobile transcritical CO2 air conditioning system with various internal heat exchanger effectiveness

• CO 2 system with internal heat exchanger (IHX) were investigated. • An experiment to change IHX under different conditions was designed. • Effects of IHX on system performance and parameters were studied. • Effect of various IHX under a wide working condition was analyzed. • Energy and exergy analyses with different IHX were conducted. Carbon dioxide (CO 2 ) is one of the promising refrigerant substitutes in mobile air conditioning system. To enhance the cooling performance, this paper presented an experimental investigation on the influence of the various internal heat exchanger (IHX) effectiveness on a transcritical CO 2 mobile air conditioning system. An experimental apparatus with regulatable IHX effectiveness was set up and tested. The effects of IHX effectiveness on the cooling capacities and coefficient of performance (COP) were studied under various outdoor air temperatures (30, 35 and 40 ℃) and compressor speeds (2000 to 7000 rev·min −1 ). Optimal discharge pressure and cycle state parameters with various IHX effectiveness were analyzed. Based on exergy perspective, the irreversibility of the main components and the cycle were discussed to give further reference for system optimization. Results showed that using IHX enhanced the COP of CO 2 system by the rates from 14.5% to 18.5% at various outdoor air temperatures. With increasing IHX effectiveness, the COP enhancement decreased, and the discharge temperature easily increased to its restriction value. The compressor and gas cooler occupied the main exergy losses of the system with IHX. The results could provide reference for the design and optimization of the CO 2 mobile air conditioning system.

Performance Enhancement of Split Air Conditioner During Evaporative Cooling Application

The increase of condenser temperature and pressure in air-conditioning leads to decreased cooling capacity and the increase of power consumption. Evaporative cooling could improve the thermal performance of the system. In this study, the evaporative cooling module was installed before the condenser to reduce the inlet air temperature to the condenser unit. The impact of condenser air temperature on the air conditioning system's overall performance was determined by varying the cooling pad discharge water flowrate of 880, 1040, and 1200 mL/min. The cooling load of 2000 W was employed in this experiment. The obtained results were compared with the air conditioning without an evaporative cooling module. It shows that the coefficient of performance (COP) increases with the increase of discharge water flow rate. The highest COP obtained is 7.09 at the flow rate of 1200 mL/min. The compressor work reduces about 6.57 % as compared with the air conditioner without evaporative cooling application. Besides, the COP increases by 12. 95 % at the highest flow rate.

Building condition assessment using artificial neural network and structural equations

Building facilities condition assessment is considered a fundamental aspect of an effective decision-making maintenance management plan to fulfill service requirements. A noticeable dearth of studies is believed to have delivered condition assessment approaches for existing buildings; however, these approaches are still deemed premature, with some limitations in demand enhancement. This paper presents a novel physical condition assessment framework for existing educational buildings that contribute to the body of knowledge by offering a state-of-the-art approach incorporating an Artificial Neural Network (ANN) predictive model and a Structural Equation Model (SEM). The ANN predictive model aims to forecast the future condition-rating states for each facility component in various building spaces. Simultaneously, the SEM determines the proportionate weights of building facilities components. The primary objectives of this paper are to prioritize building components for maintenance purposes and record the potential effects of several parameters influencing the condition state of building components. These objectives can be achieved via four sequential modules: 1) scan to BIM module; 2) condition assessment prediction module; 3) proportionate weight determination module; and 4) entire space rating value module. Condition-monitoring data on six different buildings' internal components are analyzed to anticipate their future condition. The components carried out are: 1) wooden flooring tiles; 2) gypsum board ceiling tiles; 3) wooden doors; 4) wooden windows, 5) split air conditioner units; and 6) desktop computers. The overall coefficient of determination (R2) of the developed ANN models for the predicted six components conditions are 0.99, 0.99, 0.927, 0.88, 0.97, and 0.972, respectively.

Experimental Investigation of a Split Air Conditioning Using Condensate as Direct Evaporative Cooling

Split air conditioning systems produce reasonable amount of condensate which is usually not utilized and thrown away to the environment. On the other hand, it consumes a lot of energy during operation. The aim of this study is to investigate the improvement of air conditioning systems performance utilizing condensate. A direct evaporative cooling using condensate is incorporated on a 0.74 ton-cooling capacity of split air conditioning to decrease the air temperature before entering the condenser. Performances of the split air conditioning with and without direct evaporative cooling are compared and presented in this paper. The results show that the use of direct evaporative cooling using condensate into the air before passing through the condenser reduces the compressor discharge pressure. The decrease of the condenser pressure led to 4.7% and 7% reduction of power consumption for air conditioner without cooling load and air conditioner with 2000 W cooling load, respectively. The cooling effect and coefficient of performance (COP) increase with the decrease of compressor power. The use of direct evaporative cooling with condensate into the air before entering the condensing system can enhance the system performance and protect the environment.

Analysis and modeling of air conditioner usage behavior in residential buildings using monitoring data during hot and humid season

With split air conditioner (AC) becoming one of the most popular thermal comfort-related appliances in residential buildings in China, many issues, such as high energy consumption, have arisen. One crucial way to address these issues is to study the usage of split AC models, which can be greatly affected by occupant behavior. In this study, we conducted a large-scale field measurement among 34 residential buildings in eight cities distributed in three climate zones using wireless sensors during summer. The AC usage patterns in the three climate zones were analyzed, and models based on artificial neural networks and gradient boosting decision tree algorithms were developed for predicting AC on/off behavior. The results showed that the average usage duration and energy consumption of AC per day in the three climate zones were 7–10 h and 2.78–3.00 kWh, respectively, and that there was a large difference among different households. The AC usage patterns of households in the three climate zones had certain similarities. The models developed in this study showed higher performance and accuracy than the logistic regression-based model, and indoor relative humidity and CO2 concentration were found to significantly improve predicting accuracy. The models can generate an AC operation schedule as an input boundary condition to improve the accuracy of residential building energy consumption simulations in future studies.

Thermodynamic Performance Investigation of a Small-Scale Solar Compression-Assisted Multi-Ejector Indoor Air Conditioning System for Hot Climate Conditions

In year-round hot climatic conditions, conventional air conditioning systems consume significant amounts of electricity primarily generated by conventional power plants. A compression-assisted, multi-ejector space cooling system driven by low-grade solar thermal energy is investigated in terms of energy and exergy performance, using a real gas property-based ejector model for a 36 kW-scale air conditioning application, exposed to annually high outdoor temperatures (i.e., up to 42 °C), for four working fluids (R11, R141b, R245fa, R600a). Using R245fa, the multi-ejector system effectively triples the operating condenser temperature range of a single ejector system to cover the range of annual outdoor conditions, while compression boosting reduces the generator heat input requirement and improves the overall refrigeration coefficient of performance (COP) by factors of ~3–8 at medium- to high-bound condenser temperatures, relative to simple ejector cycles. The system solar fraction varies from ~0.2 to 0.9 in summer and winter, respectively, with annual average mechanical and overall COPs of 24.5 and 0.21, respectively. Exergy destruction primarily takes place in the ejector assembly, but ejector exergy efficiency improves with compression boosting. The system could reduce annual electric cooling loads by over 40% compared with a conventional local split air conditioner, with corresponding savings in electricity expenditure and GHG emissions.

Predictions of European refrigerants place on the market following F-gas regulation restrictions

• Refrigerant place on the market (POM) in Europe will suffer a significant cut in 2021. • Up to 2020, European refrigerants POM has been respected, despite the sustained demand. • Meeting the 2021 quota will be challenging due to inertia in the adoption of POM mitigation measures. • Industrial, stationary and commercial refrigeration will concentrate more than half of the total refrigerant demand, measured in CO 2 e. The European Union (EU) Regulation on fluorinated greenhouse gases (F-gases) has encouraged to reduce gradually the number of hydrofluorocarbons (HFC) that can be placed on the market (POM) to 21% of the baseline level in 2030. However, to this day, the EU refrigeration, air conditioning and heat pump (RACHP) market is still dominated by these substances. This study describes a methodology to estimate the refrigerant demand by refrigeration, air conditioning, and heat pumps available to the EU customers until 2030. The work is based on the most relevant current statistical data, refrigerant distribution (R134a, R404A, R407C and R410A), and future technology acceptance and trends. The study presents a refrigerant demand grow scenario and provides a basis for a closer market follow-up to facilitate refrigeration industry stakeholders' decision-making. The results indicate that by 2021 will be challenging to accomplish the fluorinated gas quota considering the current HFC phase-down process. However, by 2030, the transition is possible in the EU, assuming the additional measures to mitigate the leakage from already installed equipment will be taken. By that time, natural refrigerants, including CO 2 , ammonia, and hydrocarbons, can dominate the market. However, the share of HFC or HFC/HFO mixtures in operation is still significant (R32 or mixtures with similar behaviour, and R404A low flammability alternatives). Consequently, industrial and commercial refrigeration (large scale applications) will concentrate approximately half of the GWP weighted CO 2 e, negligible direct emissions for domestic refrigeration or mobile air conditioning, dominated by natural refrigerants pure HFO refrigerants, respectively.

Modeling and Optimizing the Parameters of Condensers in Split Type Room Air Conditioners

Split type room air conditioners (RACs) are very common nowadays. In Bangladesh, RAC manufacturers employ trial-error prototyping techniques in their design to increase the efficiency of RACs and the profitability of the plant. Computer modeling can be a great help to reduce the cost in the R&D stage to find the optimum design of RACs. In this study, modeling of heat transfer in the condenser of split type RACs employing the techniques of Computational Fluid Dynamics (CFD) was performed. To reduce the computational load the geometry was divided into small sections and geometric symmetries were also taken into account. For the simulation, the geometry and other relevant data were set in such a way so that they commensurate closely with real industrial data. An example data set for validation of simulation results were obtained from an AC manufacturer company, Elite Hitech Industries Ltd. The geometry was built using meshing techniques. Copper and aluminum were selected as materials for tubes and fins, respectively. R-22 was chosen as the refrigerant. Heat transfer and fluid flow were modeled using non-isothermal flow in a multi-physics environment. The main assumptions employed are laminar flow, extra coarse mesh size, constant air inlet temperature, perfect insulation between system and surroundings, and thin layer fins. The temperature distribution and heat transfer efficiency in the condenser, the impact of different refrigerant flow arrangements in the tubes have been studied in detail. This study leads to the finding of efficient refrigerant flow arrangements from the viewpoint of maximum heat transfer.
 Chemical Engineering Research Bulletin 21(2020) 20-25

Air Conditioning System Performance of a City Hotel Appraised for Energy Use Efficiency

This paper presents results of a study on split air conditioning (AC) performance of a city hotel in Bali, Indonesia. The study applied a practical global approach to appraising the performance of existing AC systems and their installation in a city hotel. The results obtained indicate that improper AC system selection and installation potentially reduces their energy performance which include COP (coefficient of performance), EER (energy efficiency ratio), and SEI (system efficiency index). The finding also shows that improper system selection and installation has damaged 54 unit compressors of 90 AC systems installed in a particular building within three years’ period. Overall number of compressors that have been damaged in three years can reach 76 units accounted for about 23.1% of the total AC systems installed in the hotel. It is also found a reduction on AC system cooling capacity.

ENERGY AND COST SAVING POTENTIAL OF HOTEL AIR CONDITIONING USING MAGNETIC BEARING CHILLER IN JAKARTA

The use of magnetic bearing chillers in hotel air conditioning systems is an opportunity for energy or cost savings. This study will compare the electrical energy consumption and cost analysis of the centralized air conditioning system using magnetic bearing chiller that uses variable flow to another air conditioning system such as the centralized air conditioning using constant flow chiller and the VRF split air conditioning system at Hotel A in Jakarta. The calculation of energy consumption for each air conditioning system is carried out for a year. Meanwhile, the cost analysis will be carried out using the life cycle cost method for 20 years. The air conditioning system which has the least energy consumption and has the lowest life cycle cost is the best air conditioning system for this hotel building. The maximum cooling load that occurs in Hotel A is 3,281 kW. From the results of energy calculations and cost analysis, a centralized air conditioning system with magnetic bearing chiller with variable flow is the best choice to Hotel A or similar building to Hotel A, with IKE (Intensitas Konsumsi Energi) value of 84 kWh/(m2.year), and a total cost of 78,873,678,478.00 IDR for a period of 20 years.

CFD simulation of HC-290 leakage from a split type room air conditioner

HC-290 is one of the alternatives to HCFC22 in room air-conditioners. With the phase-down schedules in Kigali Amendment, it is imperative to use HC-290. However, there are concerns about its flammability in the event of a leak from the AC indoor unit (IDU). IEC 60335-2-40 has been revised to extend the capacity ranges for A2L refrigerants and is being further revised with a focus on A2 and A3 refrigerants. In real-life situations, furniture and occupants are present inside the room and these may positively or negatively influence the dispersion of any leaked HC-290. CFD simulation of dispersion of leaked HC-290 has been carried out for a variety of scenarios. The variables include leakage rates, IDU installation heights, IDU blower ON or OFF and types of furniture. Furniture, in general, appears to promote mixing, thereby reducing HC-290 stratification. The maximum concentration occurs on the side where the leak is directed by the momentum of the jet from IDU. There is no significant effect on the concentration distribution by the type and size of furniture with legs, although solid furniture has some marginal effect due to reduction of room free volume. The average concentration of HC-290 in the room is slightly more when the solid furniture like cupboards are placed some distance away from the IDU. The highest concentration at 30 cm above floor level, is 44% of LFL when the blower is ON, while it is 62% when the blower is OFF.

Active Filtering and Exchange of Indoor Air by Means of Mobile Air Conditioners to Avoid Infection by The SARS Cov-2 Virus

In not actively ventilated rooms such as in schools, air exchange is insufficient, particularly during win- ter. Under the presence of COVID-19 or to reduce the CO2 concentration, the air must be filtered and refreshed as well as possible. A tracer clearance experiment using a mobile air conditioner e.g. from KRONE Kälte + Klima VertriebsmbH Germany is supposed to determine to what extent. In Szabadi [1].

A simulation and experimental study of an innovative MAC/ORC/ERC system: ReverCycle with an ejector for series hybrid vehicles

This paper presents the simulations and experiments for the development of a hybrid and reversible mobile air conditioning, organic Rankine cycle (ORC), and ejector refrigeration cycle (ERC) system. This flexible and compact system may be the solution to the introduction of waste heat recovery in passenger cars. The cycle fuel economy is calculated for series hybrid electric vehicles (SHEVs). A global vehicle model is used to simulate the annual weather conditions of different climatic regions. The reference driving cycle is the Worldwide Harmonized Light Vehicle Test Cycle.The cycle fuel economy is maximized in temperate and cold climatic regions. In the hypothesized engine cold-start initial condition, the SHEV ReverCycle maximum fuel economy is 1.2% in Paris. In the hot-start initial condition, the SHEV ReverCycle maximum fuel economy is 2.2% in Moscow. The experimental results of the ReverCycle proof of concept are then presented. The maximum measured net efficiency in the ORC mode is 3.9%. The ERC mode can satisfy cabin cooling requirements at an ambient temperature below 20 °C. The estimated fuel economy in the ERC mode is 1.4%.

Optimization of energy consumption for indoor climate control using Taguchi technique and utility concept

In this research work, results on optimization of parameters related to energy consumption for indoor climate control of a building enclosure are discussed. The analysis is carried out for a building unit maintained at comfort level using Mitsubishi 1.5 ton of refrigeration split air conditioner. A mathematical model based on energy balance and experimental trials were used to compute energy consumption for space cooling/heating conditions. For the purpose of optimization, six control variables at three levels have been chosen from environment, thermo-physical properties, and geometrical variables. Taguchi optimization was carried out using L27 orthogonal arrays to obtain an experimental test strategy for cooling and heating modes, which gives rise to two sets of parameters. With the implementation of utility concept, a single set of optimum level parameters were obtained for both heating and cooling mode operations. Taguchi technique predicted 1.606 kW and 1.252 kW as optimum energy consumption for space cooling and heating modes, respectively with 95% confidence level. Inside humidity ratio, overall heat transfer coefficient and wall to window ratio are predicted as the most influencing parameters for both cooling mode and heating mode operations by the Taguchi method and utility analysis.

Experimentally evaluation of split air conditioner integrated with humidification-dehumidification desalination unit for better thermal comfort, produce freshwater, and energy saving

The present experimental study aims to achieve the better indoor thermal comfort, produce freshwater, and energy saving. To investigate this idea, split air conditioner was integrated with solar assisted humidification-dehumidification (HDH) desalination unit, the HDH desalination unit was designed to produce the freshwater and also used as a pre-cooling unit to cool the condenser of split air conditioner in order to reduce a power consumption, increases the cooling capacity, and COP. To obtain the effect of utilizing the HDH desalination unit as pre-cooling unit on a performance of the split air conditioner, two operating cases were suggested to run the HDH unit and the split air conditioner. In the first operating case, the HDH unit was operated separately from the air conditioner. In the second operating case, the HDH unit was connected to the condenser of air conditioner to cool the condenser. Is this case the cold air leaving from the dehumidifier of the HDH desalination unit was used to cool the condenser of the split air conditioner. The results show that when the HDH desalination unit combined with the split air conditioner, (i) the saving in power consumption of air conditioner reached 18.4%, (ii) COP for the air conditioner improved by 48.5%, (iii) accumulative freshwater production reached 36.49 L day−1, and (iv) the improvement in GOR for utilizing the proposed hybrid system reached 60.9%.

A thermal comfort-driven model predictive controller for residential split air conditioner

In the wake of rising cooling electricity demand in the residential building sector, there is a need to contemplate how the residential air conditioners (ACs) are operated. This study explores the residential split AC's capacity regarding its ability to provide thermal comfort to the occupants instead of just cooling through the implementation of thermal comfort-driven model predictive control (MPC). The proposed control technique is illustrated by implementing it in a real residential house. To integrate thermal comfort feedback into the controller while optimizing AC's set-point, a real-time co-simulation methodology has been developed, using EnergyPlus and Simulink. A data-driven model is used in the MPC framework to predict the set-point of AC, accounting for the environmental variables as measured disturbances and thermal comfort index, i.e., predictive mean vote (PMV) as a constraint on output. A Raspberry Pi-Arduino-based embedded system is developed to actuate the AC's set-point during real-time co-simulation. Experimental data is used to develop the numerical model of the system. The simulation study has been performed to observe the proposed control technique's value addition over the base cases. Simulation data shows that AC operated with the proposed control technique consumes (8.8–17.5%) less cooling energy compared to the base cases.