Split Air Conditioner Research Articles

Performance evaluation of a mobile air conditioning unit: an exergetic approach

This study considers a public bus (having a capacity of 99 passengers and a volume of 69 m3) along with its vapour compressed mobile air conditioning (MAC) unit (utilising R134a as a refrigerant) together as a low exergy (so-called LowEx) system. The LowEx analysis, which has been mostly applied to buildings, and conventional exergy analyses method are utilised together (coupled up analysis method) to assess the performance of this system for the first time to the best of the authors' knowledge. Based on the LowEx analysis, total exergy efficiency and exergy flexibility factor are calculated to be 11.92% and 0.56 for the heating mode and 3.41% and 0.19 for the cooling mode, respectively. Furthermore, through on the conventional exergy analyses, the highest exergy efficiency belongs to condenser with 93.08% in the cooling mode, while it is 93.20% for the water heat exchanger in the heating mode, respectively.

Air Diverter System Prototypes for a Mobile Air Conditioner by Material Addition Method using 3D Printer

Air Diverter System Prototypes for a Mobile Air Conditioner by Material Addition Method using 3D Printer

Reducing Mobile Air Conditioner (MAC) Power Consumption Using Active Cabin-Air-Recirculation in A Plug-In Hybrid Electric Vehicle (PHEV)

Air conditioner power consumption accounts for a large fraction of the total power used by hybrid and electric vehicles. This study examined the effects of three different cabin air ventilation settings on mobile air conditioner (MAC) power consumption, such as fresh mode with air conditioner on (ACF), fresh mode with air conditioner off (ACO), and air recirculation mode with air conditioner on (ACR). Tests were carried out for both indoor chassis dynamometer and on-road tests using a 2012 Toyota Prius plug-in hybrid electric vehicle. Real-time power consumption and fuel economy were calculated from On-Board Diagnostic-II (OBD-II) data and compared with results from the carbon balance method. MAC consumed 28.4% of the total vehicle power in ACR mode when tested with the Supplemental Federal Test Procedure (SFTP) SC03 driving cycle on the dynamometer, which was 6.1% less than in ACF mode. On the other hand, ACR and ACF mode did not show significant differences for the less aggressive on-road tests. This is likely due to the significantly lower driving loads experienced in the local driving route compared to the SC03 driving cycle. On-road and SC03 test results suggested that more aggressive driving tends to magnify the effects of the vehicle HVAC (heating, ventilation, and air conditioning) system settings. ACR conditions improved relative fuel economy (or vehicle energy efficiency) to that of ACO conditions by ~20% and ~8% compared to ACF conditions for SC03 and on-road tests, respectively. Furthermore, vehicle cabin air quality was measured and analyzed for the on-road tests. ACR conditions significantly reduced in-cabin particle concentrations, in terms of aerosol diffusion charger signal, by 92% compared to outside ambient conditions. These results indicate that cabin air recirculation is a promising method to improve vehicle fuel economy and improve cabin air quality.

Investigating the influence of different speeds and directions of winds on the performance of split air conditioning systems

Air-cooled condensers are generally preferred in the condensing units of split air conditioning systems because of simple construction, lower operating costs, and water scarcity in many regions. This work presents a numerical analysis of the influence of winds at different speeds and directions on the performance of a split air conditioning system whose condensing unit is installed on the outer walls of buildings using mounting brackets. Commercially available simulation tools are used in this work to obtain airflow and thermal characteristics of the condensing unit as well as the performance of the air conditioning system. The simulation tools are validated at the original design point for correct and reliable simulation results. It is found that the temperature of air entering the condensing unit raises due to recirculation of the hot exhaust air caused by winds. The airflow rates in the condensing unit are reduced. This leads to an inefficient operation of the air conditioning system.

Performance evaluation and design considerations for a split air-conditioner with built-in thermal energy storage

The benefits of thermal energy storage using phase change materials are well documented in the literature. Despite all the potential benefits of thermal energy storage, its commercial and widespread application remains limited. This is due to the high initial cost of phase change materials, extensive rework required in buildings, major modifications in HVAC systems, and the potential for leakage, fire and toxicity hazards. There is a strong need for a simple thermal energy storage solution which can be adopted by large number of consumers. Ductless split air-conditioners are portable, low cost, efficient and account for 70% of all air-conditioning systems sold worldwide each year. The present research provides a novel and low cost solution that incorporates thermal energy storage in these air conditioners, allowing them to run without electricity for 3 h. The paper deals with the detailed design aspects and engineering challenges that arise when incorporating thermal energy storage in these small units. A prototype air-conditioner with in-built thermal energy storage was developed, and all performance parameters presented have been validated through data obtained from the prototype. Our results indicate that thermal energy storage can be incorporated in split units in low cost and with minimal drop in overall energy efficiency of the system. Practical application: Incorporating thermal energy storage in split air-conditioners which enables them to run without grid for many hours has immense practical applications. Since around 50% power in any building is consumed by HVAC systems, being able to provide cooling during peak hours without using grid can significantly reduce load on the grid without compromising user comfort. For developing countries where load shedding is frequent, the users can run these air-conditioners without the use of generators or batteries thus saving costs and the environment.

Refrigerant migration during startup of a split air conditioner in heating mode

During winters, room air conditioners are generally expected to supply occupants with hot air rapidly following startup. In this study, the refrigerant migration characteristics during startup of a split air conditioner were experimentally investigated in heating mode. The transient refrigerant distribution inside main components was measured by using the quick-closing valve technique. The high and low side pressures and temperatures of the system were also investigated under the given operating conditions. All experiments were carried out in psychrometric rooms. On this basis, two control methods during the startup and shutdown process were proposed and tested. It was verified that increasing the refrigerant mass in the condenser prior to restarting can benefit the establishment of high pressure and supply occupants with air at a comfortable temperature more rapidly.

Energy Efficiency Study, Comparing, Commercial Grade Propane/Butane Blend; Refrigerant Grade Propane and Chlorodifluoromethane (CHClF2), Investigated in a Psychrometric Chamber

The current use of hydrochlorofluorocarbons (HCFCs) and hydrofluorocarbons (HFCs) as refrigerants will be phaseout and phasedown. Hydrocarbon (HC) refrigerants were introduced as potential replacements. These refrigerant grade hydrocarbons namely propane (R 290) and isobutane (R 600a) were on sale at premium prices. As Malaysia has capabilities to produce LPG, a study was conducted to find out the suitability of commercial liquefied petroleum gas (LPG) to be used as refrigerant. This study compares the efficiencies and cooling capacities of commercial grade LPG to refrigerant grade propane (C3H8) and chlorodifluoromethane (CHClF2) (R 22) in a split unit air conditioner installed in a psychrometric chamber. Results of experiments indicated that the commercial blends in the ratio of 80% propane and 20% butane provided the highest efficiency, but had the lowest cooling capacities; in contrast, the imported refrigerant grade propane despite value being purer, was not reflected in term of its efficiency; recorded the lowest. CHClF2 provided the highest efficiency and cooling capacity. LPG has the potential to replace R22 in split air conditioners despite losing 10 % in cooling capacities but instead gained 2.6% in energy efficiencies.

Investigation on thermal comfort of air carrying energy radiant air-conditioning system in south-central China

A field study of thermal environment and thermal comfort under air carrying energy radiant air-conditioning system (ACERS) and split air conditioner was conducted in south-central China. The results reveals that the ACERS can create a comfortable thermal environment with small vertical temperature gradient. Based on the regression equation of thermal sensation vote and operative temperature, it is found that the neutral temperature in ACERS is about 28 °C in summer and 18 °C in winter, while in split air conditioner, the temperature is about 26.1 °C and 19.3 °C. Besides, the comfortable temperature range for 80% acceptability in ACERS is 25.5–30.7 °C in summer and 13.8–22.2 °C in winter, and the corresponding range of split air conditioner is 23.9–28.3 °C and 16.7–21.8 °C. The results show that the ACERS has a larger temperature adjustment range compared to the split air conditioner and the thermal comfort stability of ACERS is better. The actual comfortable temperature range is wider than the theoretical value calculated by PMV-PPD equation, and the reason may be that people in their long-term life have been adaptable to the environment. This research is helpful for the design and operation of air-conditioning system in future and provides the theoretical basis for indoor temperature setting in this area.

Experimental Study for the Effect of Pre-Cooling the Condenser Inlet Air of Split Type Air Conditioning Unit

The reduction of electric power consumption is considered to be a critical issue especially in the areas with elevated temperatures such as Iraq. In Basra city, the electric power consumption due to the air conditioning units (ACU) is so high. In this work, an evaporative cooling unit (ECU) is fabricated and tested where it is retrofitted with the condenser part of a split-type air conditioner. The experimental procedure was done in Basra engineering technical college located in west of Basra city. The present work is categorized in two cases. In case one, the system runs without using the ECU, while in case two the system is tested with ECU. The obtained results show that decreasing the inlet air temperature to the condenser will drop off the condensation and evaporation temperatures. Besides, it decreases the compression pressure ratio and increases the refrigerant mass flow rate. With this modification, it is found that the consumption power is decreased by 26% and COP increased by 90% compared with case one. The second law analysis of the modified system shows that using ECU will decrease most the exergy destruction and losses in the components. Only exergy destruction in the evaporator is increased. The system second law efficiency is improved by 69.5%.

Thermo-flow performance analysis of split air conditioner under high-speed winds around buildings

ABSTRACT Air-cooled condensers are predominantly used in condensing units of split air conditioning systems. These units are mostly installed on terraces or on outer walls of buildings. In case of tall buildings, the performance of air-cooled condenser is greatly affected by high-speed winds. Present work deals with a numerical study predicting the influence of high-speed winds on the performance of split air conditioning systems whose condensing units are installed on outer walls of buildings using mounting brackets. Simulation tools viz. ANSYS Fluent and VapCyc are employed in this work in order to obtain air flow and thermal characteristics of the condensing unit. Simulation results show that the thermo-flow performance of the split air conditioning system deteriorates significantly with high-speed winds due to an increase in the temperature of air entering the condensing unit and inferior air flow rates in the condensing unit. It is observed that the cooling capacity and coefficient of performance of the air conditioning system are reduced by 11% and 35%, respectively, when wind speed is 12.3 m/s in comparison with the baseline case.

Performance improvement in mobile air conditioning system using Al2O3/PAG nanolubricant

This paper presents the investigation of Al2O3/PAG nanolubricant performance for a compact vehicle mobile air conditioning (MAC) system. The Al2O3/PAG nanolubricant in this study is prepared by using two-step preparation method and stabilized using 4-Step UV–Vis Spectral Absorbency Analysis. An enhancement in the coefficient of performance (COP), reduction in compressor work, and enhancement in the cooling capacity of MAC employing Al2O3/PAG nanolubricant are recorded up to 31%, 26% and 32%, respectively, for 0.010% volume concentration. The current MAC performance is compared with MAC employing SiO2/PAG nanolubricant from previous study. The comparison shows that the Al2O3/PAG nanolubricant has better performance in term of cooling capacity, compressor work, and COP at an average of 6%, 8%, and 33%, respectively. Therefore, the finding from this study suggests Al2O3/PAG nanolubricant with a volume concentration of 0.010% as an optimum and best performance nanolubricant for MAC systems.

Experimental and Theoretical Study on the Cooling Performance of a CO2 Mobile Air Conditioning System

CO2 (GWP = 1) is considered as a promising natural alternative refrigerant to HFC-134a in mobile air conditioning (MAC) applications. The objective of this study is to investigate the cooling performance characteristics of a CO2 MAC system. A prototype CO2 MAC system, consisting of a CO2 electrical compressor, CO2 parallel flow microchannel heat exchangers, and an electrical expansion valve, was developed and tested. Factor analysis experiments were conducted to reveal the effect of outdoor temperature on the cooling performance of this CO2 MAC system. Compared with a conventional R134a MAC system, the prototype CO2 MAC system achieved comparable cooling capacity, but had COP reductions of 26% and 10% at 27 °C and 45 °C outdoor conditions, respectively. In addition, based on refrigerant properties, theoretical cycle analysis was done to reveal the impact of evaporator, gas cooler and compressor, on the system cooling performance. It is concluded that the increase of overall compressor efficiency or the decrease of gas cooler approaching temperature could greatly improve the COP of this CO2 MAC system.

Performance improvement of a split air conditioner by using an energy saving device

This study investigated the effect of an energy saving device (ESD) on the performance of a split-type air conditioner (SAC). The ESD was fabricated using a moisture-transferring and quick-drying textile (MTQDT), a condensate pipeline, and a distributor. The MTQDT was coated on the shell surface of the compressor to absorb the condensate expelled by a condensate pipeline and distributor to enable evaporative cooling of the compressor. The SAC was tested under various outdoor air conditions (29, 32, and 37 °C; 55% relative humidity) and under a fixed indoor air condition (26 °C; 50% relative humidity), and the performance of the SAC before and after ESD installation was compared. Results demonstrated that the MTQDT effectively improved compressor cooling and the efficiency of the SAC. Compared with the SAC without an ESD under the optimal condition, the shell temperature of the compressor, high-side pressure, and power consumption of the proposed SAC were 15.1 °C, 2.7%, and 9.2% lower, respectively. Moreover, the dehumidification capacity and energy efficiency ratio of the proposed SAC were 25.4% and 7.3% higher, respectively.

Using an ensemble machine learning methodology-Bagging to predict occupants’ thermal comfort in buildings

In this paper, an intelligent ensemble machine learning (EML) method - Bagging was developed for thermal perception prediction. Field data was collected in naturally ventilated (NV) and split air-conditioning (SAC) dormitory buildings in hot summer and cold winter (HSCW) area of China during the summer of 2016. The indoor physical measurement and subjective survey were conducted simultaneously during the field study.To determine the merit of the proposed Bagging approach, the performances of Bagging approach were compared against the artificial neural network (ANN) and support vector machine (SVM) regarding conventional statistical indicators, i.e., mean absolute error (MAE), root mean square error (RMSE), coefficient of determination (R2) and Pearson correlation coefficient (r). Several thermal indices, i.e., thermal sensation (TS), effective temperature (ET*), standard effective temperature (SET*) and predicted mean vote (PMV), were adopted to access the occupants’ thermal comfort and evaluate the model prediction.In our case study, the Bagging model's R2 for TS, PMV, ET* and SET* were 0.4986, 0.9892, 0.9920 and 0.9900, respectively. It shows higher accuracy than SVM and ANN models in thermal perception prediction and outperforms the classical PMV index in TS prediction. Results indicate the proposed Bagging model's prediction performance is reliable and is highly accurate to predict the thermal perception.

Effects of charge on the performance of R290 air conditioner with different expansion devices

Safety is a critical issue when considering R290 as a replacement for R22 in air conditioning and heat pump systems. The R290 charge mass in the domestic system is strictly restricted which means a small amount of leakage would be equivalent to a large percent of refrigerant loss. In this article, the effects of R290 refrigerant charge influences on a split air conditioning system with different throttling devices including capillary tube, thermostatic expansion valve (TXV), and electronic expansion valve (EEV) are experimentally investigated alongside with the indoor temperature, outdoor temperature and indoor air volume flow rates effects. Besides, the effects of superheat degree influences have been studied both theoretically and experimentally. The results suggested a larger superheat degree would have an optimum effect on R290 system performance.

Energy saving and economic analysis of a new hybrid radiative cooling system for single-family houses in the USA

Radiative cooling has received much attention as it generates “free” cooling to buildings and helps reduce energy consumption of mechanical air conditioning systems. However, most current radiative cooling materials either work for nighttime (nocturnal) cooling only or have high cost issues. A novel scalable-manufactured randomized glass-polymer hybrid metamaterial coated with silver has recently been developed and reported a 110 W/m2 cooling power on daily average. This metamaterial potentially provides passive cooling for both nighttime and daytime. Proposed is a hybrid diurnal radiative cooled-cold storage cooling system using this metamaterial for air conditioning purposes in single-family houses. Because single-family houses have a relatively low cooling load but high ratio of roof area to floor area, they are excellent end users of the hybrid radiative cooled-cold storage cooling system. The potential energy savings of the hybrid radiative cooled-cold storage cooling system in a typical two-floor single-family house with floor area of 204 m2 have been modeled using EnergyPlus for four locations in the U.S., including Orlando, FL, San Diego, CA, San Francisco, CA, and Denver, CO. In comparison with the electricity consumption of a split air conditioner alone, the hybrid radiative cooled-cold storage cooling system could save annual cooling electricity by 26% to 46% for the modeled locations, under a restriction of 8-year payback period. The corresponding simple payback periods for adoption of the hybrid radiative cooled-cold storage cooling system fall in a range of 4.8–8.0 years and the maximum acceptable incremental costs are $50.0/m2–$78.9/m2. The diurnal working hybrid radiative cooled-cold storage cooling system may provide a cost-effective solution for radiative cooling technology in residential building applications.

Study on model of household split air conditioning solution dehumidifier

Liquid desiccant technology in central air conditioning system is very promising, however, rare researchers proposed to carry out it on household liquid desiccant air conditioner. In this paper, a two-dimensional heat and mass transfer theoretical model of cross flow dehumidifier for household split air conditioner has been established, and it is shown that the model established has a good accuracy and the relative error is less than 3.72% by comparing the simulation results with the experimental data in the literature. Based on the model, a series of experiments are conducted and the experiment data is adopted to fit the correlation formula of NTUm and Le. The results show that the model established has a good reaction to the actual situation. Furthermore, the influence of air, solution inlet conditions on the dehumidification performance of the system has been discussed in the paper.

Development and application of a life cycle greenhouse gas emission analysis model for mobile air conditioning systems

Mobile air conditioning (MAC) is potentially a huge source of greenhouse gas (GHG) emissions in China from a life cycle (LC) perspective as the vehicle population increases in the future. The MAC-GHG-LCA model is developed to calculate LC GHG emissions from MAC systems, covering life-span refrigerant leakage (direct emissions) and emissions caused by energy use in MAC system production and operation (indirect emissions). Using R152a and R1234yf as alternative refrigerants instead of R134a in MAC systems can decrease LC GHG emissions by 22–32% and 17–29%, respectively. Their GHG reduction benefits mainly result from their lower global warming potential (GWP) values though the indirect emissions are only slight lower or even higher than R134a. Using R744 can offer reduction in 2050 though it will cause an increase of 20% in 2020. Total LC GHG emissions from MAC systems of the whole light duty vehicle (LDV) fleet in China will be 159 million tonnes of CO2-equivalent in 2050 in the scenario where R134a will be the only refrigerant adopted, about 3 times that in 2015. It is found that alternative low-GWP refrigerants can help reduce LC GHG emissions from MAC systems effectively. The shift from conventional cooling and heating technology to advanced heat pump technology in electric vehicles (EVs) can reduce electricity use in MAC system operation and reduce LC GHG emissions from the MAC systems in EVs.

The Effect of Compressor Speed Variation and Vapor Injection on the Performance of Modified Refrigeration System

This work presents an experimental and numerical investigation of vapor compression refrigeration system performance with variable speed compressor and vapor injection. A test rig of 5 ton capacity split air conditioner equipped, with frequency inverter to control the speed of scroll type compressor, and a secondary capillary tube to expand the refrigerant in the vapor injection circuit are used to conduct the experimental work. Three different vapor injection mass ratios (2, 3, and 4%) are investigated with variable compression speed for frequency range from 35 to 60 Hz. TRNSYS-16 is the software is used to simulate a single zone building conditioned with the modified split air conditioner. The results showed that, the reduction of the compressor speed to the frequency of 35Hz leads to an improvement of the COP by 36% and reduces the power consumption by 18%, compared to the conventional refrigeration system. The usage of the vapour injection with variable speed compressor has improved the COP of the modified system by 47% at 35 Hz and 2% vapour injection ratio. The average improvement in cycle capacity at different compressor speeds is about 24.6%, 28.77% and 34.28% respectively for the vapor injection ratios of 2%, 3& and 4%. It was observed that the reduction of compression speed can extend the compressor lifetime by reducing the ON/OFF cycle of the system at a speed of 35Hz and 2% vapor injection by 17.3%, compared to the conventional system. While at a speed of 60Hz, the ON/OFF cycle has increased by 9.3 and 12% for 2% and 4% injection ratios, respectively. The comparison between the numerical and experimental results of the modified system with vapor injection ratio 2% and 35 Hz compressor speed has displayed an increase in the numerical results around 2.57% for COP, 5.8% for cooling capacity and 5.68% for compressor power consumption.

Assessment of leakage and risk reduction of R290 in a split type household air conditioner

R290 (propane) is a famous hydrocarbon substance, but the flammable and explosive characteristics require safety precautions for its use. In fact, R290 is also a refrigerant with low global warming potential (GWP) and excellent thermodynamic properties. However, the application of R290 in split type household air conditioners (STHAC) is hindered by unpredictable gas leakages into the room. This paper evaluates the fire hazard of R290 as a refrigerant in STHAC and provides a new method of installing a solenoid valve near the capillary to reduce the fire risk by decreasing the R290 leaking rate. The approach uses a numerical model to analyze the major parameters effect on the concentration distribution of R290 in the room after leakage from the STHAC indoor unit, as well as a series of experimental tests for verification. The influence of different charge quantities, leakage hole diameters and air flows on the R290 concentration distribution in the room were compared and discussed. The new method was also validated by experiments. The results showed that the fire hazard only occurs during the fast-leaking period and that the most likely flammable region is underneath the location of the leak. In addition, the flammable hazards can be assessed by the huge noise generated by the R290 leakage.