Split-type Air Conditioning System Research Articles

An Investigation of the Acoustic Enclosure of an Air Conditioning Compressor Using Response Surface Analysis and Topological Rigidity Optimization

A novel split-type air conditioning system is introduced to balance usability and portability. Unlike conventional split-type systems, where the compressor is typically placed outside, this system situates the compressor within the indoor unit, which may expose users to compressor noise. There are prominent peaks in the compressor noise spectrum, particularly at the compressor operating frequency and its harmonics, notably the second and third harmonics. The research presents a multilayered acoustic enclosure specifically designed for air conditioning compressors to address this issue without modifying the compressor or indoor unit casing. In order to get better sound insulation performance, a response surface methodology (RSM) is applied to optimize the thickness ratio, open area ratio, and open area height of the acoustic enclosure with predefined thickness. In addition, topological optimization is employed to strengthen weak areas of the acoustic enclosure. Then, experimental trials using the proposed acoustic enclosure are conducted in a semianechoic chamber. Results demonstrate significant reductions in noise levels, including 7.99 dB(A), 5.69 dB(A), and 5.19 dB(A) reductions in the fundamental frequency, second harmonic, and third harmonic noise of the compressor’s operating frequency, respectively.

Eco-design of an air conditioning system decrease in carbon footprint

The appropriate use of energy is vital for the sustainable development of society in the different productive areas such as the industrial, commercial and domestic sectors, in this sense the machines must use suitable materials tending to reduce the contamination of water sources and soil, emission of carbon dioxide into the atmosphere due to energy consumption. In this context, the objective of the study focused on designing an air conditioning system based on the carbon footprint; life cycle analysis (LCA) and eco-designs were applied as a methodology, allowing to identify the categorization of the contaminant and its level of environmental impact, from the extraction of resources, manufacturing, distribution, use and final disposal. It was possible to evaluate the environmental impact referring to the functional unit of a split-type air conditioning system of 12,000 BTU of cooling capacity, obtaining as a result the carbon footprint with an annual carbon dioxide quantification of 722.8 tons of carbon dioxide. carbon (CO2), significantly representing the intensive use of the system and, on the other hand, the energy required for the manufacturing process of the refrigerant gas hydrofluorocarbons (HFC) R410 A.

Exergy and Energy Analyses of Dual-Temperature Evaporator Split AC System Incorporated A Capillary Tube and A Two-Phase Ejector

This study was aimed to investigate performance of a split type air conditioning (SAC) system applying exergy destruction method. A numerical model was established based on exergy destruction analysis of a Condenser Outlet Split-Split Air Conditioning (COS-SAC) system integrated with dual-temperature evaporator and incorporated capillary tube and ejector as expansion devices. An experimental test system was also established to experimentally validate the model. Two type of refrigerants R-290 and R-22 were involved in the evaluations. The Coefficient of Performance (COP) of the ejector COS-SAC system, exergy destruction, and exergy efficiency were determined and compared with those in the SAC system utilizing capillary tube. The results showed there was a significant improvement in the overall exergy efficiency of the COS-SAC systems. The COP of the COS-SAC system was also found to be better than the COP of the SAC system.

Experimental Study of HFC-32 Split-Type Air Conditioning Systems in Different Indoor Temperatures

Energy management has become one of the main issues in world energy scenario, every energy consumed system should be investigated and developed to increase its performance; especially air-conditioning systems which consumes more than half of the total power required by one air-conditioned building. In agreement with “Montreal Protocol on Substances that Deplete the Ozone layer”, HCFC-22 was stopped its production and its refrigerating system must take another refrigerant; HFC-32 as the working fluid. This work presented information about two 12,000 Btu/h HFC-32 split-type air-conditioning systems with the hermetically sealed swing compressor (so called Inverter compressor) and the hermetically sealed rotary compressor. Both systems were placed in two identical rooms where 3,500 Watt heaters were also set in the middle of the rooms and operated under the constant heat flux condition in two different indoor temperatures; 20 and 22 Celsius. From experiment results in both indoor temperatures, the system with the hermetically sealed swing compressor escorted better energy consumptions, Coefficient of Performances (COPs) and Energy efficiency ratios (EERs) than those of another system with the hermetically sealed rotary compressor by 29.70% and 31.86% at 20-and 22-Celsius room temperature, respectively. The performances of both HFC-32 systems in different indoor temperatures were variant. The double pipe heat exchangers (DPHXs) were also investigated in this work, the COPs of the system with the swing compressor and DPHX were higher than those of another system with the rotary compressor and DPHX by 65.17% and 75.88% at 20-and 22-Celsius room temperature, respectively. The information in this work was used in making decision on the A/C system selection, as well as, the A/C energy management to reduce total A/C power consumption in macro views.

Prevalence of asthma, allergic rhinitis and eczema in 6–7-year-old schoolchildren from Luanda, Angola

BackgroundEpidemiological data have shown that the prevalence of asthma, rhinoconjunctivitis and eczema in children is still increasing, namely in Africa. However, there are no epidemiological studies on asthma or allergic diseases in Angolan children. ObjectiveTo study the prevalence of asthma and other allergic diseases in Angolan children. MethodsDescriptive, observational, cross-sectional study, using the ISAAC study methodology, in the province of Luanda, Angola in 6–7-year-old children. Forty-six (8.3%) public schools were randomly selected. Data were analysed using the SPSS Statistics version 24.0 software. ResultsA total of 3080 children were studied. Results showed that the prevalence of asthma (wheezing in the previous 12 months) was 15.8%, that of rhinitis (sneezing, runny or blocked nose in the previous 12 months) was 19%, and that of eczema (itchy skin lesions in the previous 12 months) was 22%, without differences between sexes. Rhinitis was associated with a higher number of episodes of wheezing episodes, disturbed sleep and night cough, in children with asthma. Rhinitis, eczema, Split-type air conditioning system, antibiotic intake in the child's first year of life, frequent intake (more than once per month) of paracetamol and active maternal smoking were associated with a higher risk of having asthma, whereas electrical cooking was associated with a protective effect. ConclusionAsthma and allergic diseases are highly prevalent in children from Luanda. A strategy for preventive and control measures should be implemented.

Solutions of thermal performance problems of installing AC outdoor units in buildings light wells using mechanical ventilations

Split-type air-conditioning systems are widely deployed worldwide, due to their low costs, ease of operation and simplicity of control. From engineering perspective the installation of the outdoor components of the AC units should be done on the building façade, to ensure good air circulation around the units. However this may interfere with the architectural design and the aesthetics of the building block. Therefore alternative plant spaces for the installation of those units are often selected, which include light wells or the units being recessed. Installing those units in light wells may lead to units overheating that leads to low units’ performance or units troubleshooting. Two cases of mechanical ventilations solutions (by exhaust extraction or by fresh air supply), for this problem are suggested and investigate in this study using CFD modeling for different arrangements of the units in the light wells. The results show that (i) mechanical ventilation of the building light well is necessary in case of installing the AC outdoor units in it, (ii) in case of exhaust extraction ventilation, the AC units’ COP and power consumptions enhance as the installing level of the outdoor units increases and the opposite is true in case of fresh air supply ventilation, (iii) the outdoor units installed at lower levels (first two floors) in case of fresh air supply ventilation has bitter performance than the case of exhaust air ventilation and the opposite is true for units installed at higher levels, and (iv) the layouts arrangements of the outdoor units in light well has no effect on the units’ performance in case of using mechanical ventilation.

Monitoring results and analysis of thermal comfort conditions in experimental buildings for different heating systems and ventilation regimes during heating and cooling seasons

This paper focuses on the long-term monitoring of thermal comfort and discomfort parameters in five small test buildings equipped with different heating and cooling systems. Calculations of predicted percentage of dissatisfied people (PPD) index and discomfort factors are provided for the room in winter season running three different heating systems – electric heater, air-air heat pump and air-water heat pump, as well as for the summer cooling with split type air conditioning systems. It is shown that the type of heating/cooling system and its working regime has an important impact on thermal comfort conditions in observed room. Recommendations for the optimal operating regimes and choice of the heating system from the thermal comfort point of view are summarized.

Thermal comfort condition assessment in test buildings with different heating/cooling systems and wall envelopes

The main aim of this study is a comprehensive analysis of long-term monitoring data of thermal comfort and discomfort parameters in small identical test buildings equipped with different heating/cooling systems. Calculations of PPD index expressed the human perception of thermal comfort and such discomfort factors like draught rate and vertical air temperature difference are provided for the room in winter season running three different heating systems – electric heater, air-air heat pump and air-water heat pump, as well as for the summer cooling with split type air conditioning systems. It is shown that the type of heating/cooling system and its working regime has a significant impact on thermal comfort conditions in the room. Recommendations for the optimal operating regimes and choice of the heating system from the thermal comfort point of view are provided.

Prevalence of asthma and allergies in 13-14-year-old adolescents from Luanda, Angola.

The few epidemiological studies on asthma and allergic diseases performed in Africa have shown that the prevalence of these diseases is high or increasing. No such studies have been performed in Angola. To determine the prevalence of asthma and other allergic diseases in Angolan adolescents. This was a descriptive, observational, cross-sectional study in the province of Luanda, Angola, using the International Study of Asthma and Allergies in Childhood study methodology in adolescents aged 13 and 14 years. Twenty-three (12%) public schools were randomly selected. Data were analysed using the Statistical Package for the Social Sciences version 22.0 software. A total of 3128 adolescents were included. The prevalence of asthma (wheezing in the previous 12 months) was 13.4%. The prevalence of rhinitis (sneezing, runny or blocked nose in the previous 12 months) was 27% and that of eczema (itchy skin lesions in the previous 12 months) was 20%; both were more prevalent in girls. Rhinitis was associated with a greater number of episodes of night cough in adolescents with asthma. Rhinitis and eczema, a split-type air conditioning system, and frequent intake (more than once per month) of paracetamol were associated with a higher risk of having asthma. Asthma and related allergic diseases are a public health problem in adolescents from Luanda. Preventive and control measures should be implemented.

Experimental investigation of a vapor compression system with condenser air pre-cooling by condensate

Air conditioning systems contribute to the largest share of energy consumption in building sector. On the other hand, the systems produce reasonable amount of condensate, especially when operating in humid climates. The aim of this study is to minimize the energy consumption and improve the performance of air conditioning systems utilizing condensate. Experimental investigation has been carried out to improve the performance of an air-cooled vapor compression system by pre-cooling air entering the condenser using condensate. A pre-cooler is incorporated on a 1.5ton-cooling capacity split-type air conditioning system to lower the air temperature entering the condenser sensibly. Performances of the air conditioning system with and without air pre-cooling are compared and reported in this paper. The results show that pre-cooling the air by about 4°C before entering the condenser lowers the compressor discharge pressure. The decrease in the discharge pressure resulted in the decrease in compressor power consumption by 6.1% and the cooling effect of the system is enhanced. The combined effect of the increase in the cooling effect and decrease in compressor power resulted in an increase in the coefficient of performance (COP) and second law efficiency of the system by about 21.4 and 20.5%, respectively.

Explicit model predictive control of split-type air conditioning system

Domestic air conditioners are a major source of energy consumption. In this study, utilizing real-time data from a public domain, a cascaded hardware in loop approach to the control of room temperature is considered. An inner loop to control the supply air temperature by adjusting the electronic expansion valve using a second-order plus delay time model is proposed. The room temperature control is considered the outer loop. A simplified lumped parameter representation of the thermal dynamics of the building is modelled in MATLAB using ordinary differential equations. A constrained multi parametric model predictive controller (mpMPC) is designed for both the control loops. The constraints include safety limits on the superheat and manipulation rates for the inner loop and a rate constraint on the reference signal in the outer loop. Model uncertainties like ambient temperature and thermal load variations (representing an office space) are considered for hardware in the loop testing of the proposed strategy. From performance analysis, using power spent and thermal comfort quantization, it is observed that the mpMPC scheme outperforms traditional control strategies.

Study of Electricity Utilization in Beach Resort Hotel, Chonburi Province for Energy Conservation

This research investigated the standard electricity utilization in beach resort hotels based on a survey of four 4-star beach resort hotels in Chonburi, Thailand conducted in 2014. The main objective of the project was to know proportion of electricity in end-use category. Each hotel has total usable areas of 34,878.50, 24,706.56, 17,533.40 and 10,910.56 m2 with total air-conditioned areas of 17,364.45, 8,327.48, 5368.35 and 8,212.56 m2 respectively. The results showed that the hotel with most usable areas, air-conditioned space and using central air conditioning system has the minimum index value of electricity utilization for air conditioning system by compared with electrical consumption for air conditioning system per air-conditioned area equal to 72.36 kWh/m2/year. Unlike other three hotels with using split type air conditioning system that have this value equal to 89.92, 103.67 and 136.21 kWh/m2/year. Every hotel has the lowest proportion of electricity in lighting system compared with electrical consumption of air conditioning system and electric-mechanical system, which accounted for 5 – 10% of total electricity utilization and the maximum value of lighting density power is lower than 12 W/m2, which is considered the standard of Thailand Energy Conservation Promotion Act. Moreover, the study also found that the hotel with usable area most has annual electricity consumption for electric-mechanical equipment system that most in refrigerators, followed by pumps and other kitchen equipment, respectively which accounted for 53% of total electricity utilization. Finally, the results can also use as guidelines for designing beach resort hotels, Chonburi province for energy conservation, including the use of air conditioning systems appropriately.

Condensate as a water source from vapor compression systems in hot and humid regions

Water is one of the basic necessities in life and its preservation is essential, particularly in hot and humid regions. Air conditioning systems operating in these regions usually produce a considerable amount of condensate. In this paper, analytical and experimental investigations in determining the condensate from a vapor compression air conditioning system as an additional water source are presented. A split type air conditioning system (1.5tons) located in Dhahran, Saudi Arabia, where the dry bulb temperatures and relative humidity range from 25 to 50°C and from 15 to 90%, respectively, is used for the study during summer months. Based on the hourly data, the monthly condensate yields during June, July, August and September are 1.26, 1.29, 2.50 and 2.33kg/ton per CDD, respectively. The condensate is dominantly affected by the air humidity and temperature. The variation pattern of the condensate extraction is similar to that of the relative humidity. The collected condensate can be used as an additional water source. The chemical analysis of the condensate indicates that the water can be used for human consumption. The analytical model predictions of the condensate correlate well with the experimental data with a correlation factor of more than 90%.

Experimental Assessment of residential split type air-conditioning systems using alternative refrigerants to R-22 at high ambient temperatures

Steady state performance of residential air conditioning systems using R22 and alternatives R290, R407C, R410A, at high ambient temperatures, have been investigated experimentally. System performance parameters such as optimum refrigerant charge, coefficient of performance, cooling capacity, power consumption, pressure ratio, power per ton of refrigeration and TEWI environmental factor have been determined. All refrigerants were tested in the cooling mode operation under high ambient air temperatures, up to 55°C, to determine their suitability. Two split type air conditioner of 1 and 2 TR capacities were used. A psychrometric test facility was constructed consisting of a conditioned cool compartment and an environmental duct serving the condenser. Air inside the conditioned compartment was maintained at 25°C dry bulb and 19°C wet bulb for all tests. In the environmental duct, the ambient air temperature was varied from 35°C to 55°C in 5°C increments. The study showed that R290 is the better candidate to replace R22 under high ambient air temperatures. It has lower TEWI values and a better coefficient of performance than the other refrigerants tested. It is suitable as a drop-in refrigerant. R407C has the closest performance to R22, followed by R410A.

The performance study of a split type air conditioning system in the tropics, as affected by weather

The study of the effect of weather variation on a split air cooled ducted blower (ADB) air conditioner in an office building located in Malaysia is conducted. In the present study, the influence of weather variation on the performance of the ADB air-conditioning (AC) systems in terms of total cooling capacity and sensible heat factor (SHF) are studied. In addition, the impact of a suction line heat exchanger (SLHX) system when subjected to the climate change is analyzed. Based on the result, it is found that every 1°C increment in outdoor temperature will cause the COP and the total cooling capacity of the existing ADB system reduce by 2% while the SHF drops less than 2% from 2020 to 2080. Thus, the weather variation effect is a key factor in the AC systems’ initial design stage, which must be analyzed to preserve substantial of energy. Conversely, the SLHX system can improve the COP of the existing AC systems by about 2%, and the improvement is more significant when the outdoor ambient temperature is high. Besides, the SLHX system is strongly recommended for a machine cooling application since the SHF is higher by 4% compared to the normal AC system.

Investigation of Various Mixtures of HC290/HC600 Refrigerants in Adiabatic Capillary Tube Used in Split-Type Air-Conditioner

: According to Montreal Protocol, HCFC22 (hydro chlorofluorocarbon), a commonly used refrigerant in domestic refrigeration and air-conditioner, must be phased out owing to its environmental problem. Several natural substances including ammonia, carbon dioxide, water and hydrocarbon (HC) such as propane (HC290) and butane (HC600) and their mixtures have immerged as close substitute. Literature showed that pure HC refrigerant may not be suitable enough because of the difference in operating pressure and volumetric cooling capacity when compared with HCFC22. The main objective of this study is to theoretically investigate different ratios of HC refrigerants HC290/HC600 mixtures flowing through adiabatic capillary tube using homogenous model. In this study, the percentage by volume of HC290 was varied from 30 to 40 % in a step of 5%. The pressure at the two extreme ends and temperature along the capillary tube, using HCFC22 refrigerant, which was used as benchmark, was experimentally determined in the air-conditioning (AC) system. Comparing the model results with the experimental data showed that HC refrigerants HC290/HC600 in ratio 35%/65% gave 2.95% minimum error and thus it can be used as a substitute to HCFC22 in the split-type AC system.

A211 ビル用マルチエアコンの革新的省エネ制御の研究開発(OS-7: 次世代ヒートポンプ・冷凍システム(5))

The Purpose of our research is to improve the energy efficiency of multi split type air conditioning systems for buildings operated under low thermal load conditions. For this purpose, we develop an innovative energy-saving A/C controller that enables an optimum operation of A/C and the heat recovery VRV systems. By combining the COP data of A/Cs obtained by those tests and the field data measured in a real building, the annual energy consumption of the A/C system was estimated to examine the energy-saving effect of the new A/C controller. As a result of this estimation, it was ascertained that the new A/C controller could attain 50% higher annual average COP IN comparison with that of the conventional controller.

Application of a closed-loop oscillating heat pipe with check valves (CLOHP/CV) on performance enhancement in air conditioning system

The objective of this paper was to study the application and working fluid type of a closed-loop oscillating heat pipe with check valves on energy consumption in split type air conditioning system. In the experiment, the CLOHP/CV was fabricated from the copper tube with the diameter of 2.03 mm. In the usual range of 20–27 °C indoor design temperature and 50% relative humidity. R134a, R22 and R502 refrigerant was used as working fluid in the CLOHP/CV set for this study. In comparison of the type with a conventional air conditioning system and that with the CLOHP/CV air conditioning system, the results have shown that; the new cooling load had increased 3.6%, the latter gave the highest value of 14.9%, 17.6% for COP and EER, respectively. The highest value of heat flux was 5.19 kW/m 2 with R134a was used as the working fluid, at overall operating temperature. The results of this study are expected to guideline as they improve the performance of the air conditioning system in buildings, which reduce its energy consumption.

Stack-Driven Ventilation in Two Interconnected Rooms Sharing a Single Opening and Connected to the Exterior by a Lower Vent

This paper describes the transient ventilation of two interconnected rooms. One of them has a negative buoyancy source located at ceiling level, similar to an overhead split type air-conditioning system with ductless distribution, whereas the other has a vent at floor level. The flow evolution from short- and long-term analytical models was determined and confirmed with scale-model salt bath experiments. The short-term model predicts the depth of the dense-layer ‘first front’ until it reaches the ceiling of the first room, and the long-term model predicts the density evolution of the fluid until it reaches a steady value. The advance of the first front depends on the location of the interior opening but is independent of the size of the exterior vent. The long-term density evolution depends on both parameters. As the interior opening is lowered, the volume implicated in the dynamics decreases and the dense fluid density increases at a higher rate. Furthermore, increasing the size of the exterior vent causes a turbulent exchange flow to develop through that vent, which inhibits the increase of the average density by introducing ambient fluid to the rooms.

Study on Running Performance of a Split-type Air Conditioning System Installed in the National University Campus in Japan

Split-type air conditioning systems, or heat pump systems with multiple indoor and outdoor units, are becoming very popular for room cooling and heating of small or middle-sized non-residential buildings in Japan. However, their running performance is yet to become known due to the difficulty of measuring the actual amount of heat transferred by the system. Mixed irregular flow of vapor and liquid refrigerant prevents building engineers from obtaining accurate heat flow data between indoor and outdoor units. This study introduces an alternative method to calculate heat transferred by the system from air volume and enthalpy measured with simple sensors attached to the indoor units. Experimental results on a national university campus in suburban Tokyo showed unexpectedly low COP values both in summer and winter mainly due to the prevailing low partial load factors under 20-30% of the system capacity.