Applied Mechanics and Materials Vol. 819

Abstract: Hydrocarbon refrigerants have been widely used to replace HFCs. As hydrocarbon, R-290 has no ODP (Ozone Depletion Potential) and negligible GWP (Global Warming Potential). This paper presents flow boiling heat transfer in small tube with R-290 and R-22. The test tube has inner diameter of 7.6 mm and length of 1.07 m. In order to determine the heat transfer coefficient, experiments were carried out for heat fluxes ranging from 10 to 25 kW/m², mass fluxes ranging from 204 to 628 kg/m²s, and saturation temperatures ranging from 1.87 to 11.9^o C. The study analyzed the heat transfer through the local heat transfer coefficient along the flow under the variation of these different parameters. In comparison with R-22, R-290 provides higher heat transfer coefficients. In the prediction of the heat transfer coefficients of R-22 and R-290, the correlation of Shah (1982) and Choi et.al. (2009) best fitted the present experimental result, respectively.

Abstract: This paper presents a steady-state modeling and parametric study on the characteristics of cooling loads for an automotive air-conditioning system. The model enables the hourly prediction of vehicular cabin cooling load profile at various operating conditions and types of vehicle. The model utilizes correlations and equations proposed by ASHRAE and previous researchers available in the open literature. A validation exercise indicates that the simulation results are within 5% of published results. In the parametric study, the effects of five parameters: vehicle surface color, number of passenger, cabin temperature, vehicle speed and angle of front wind screen on the hourly cooling load profile on a daily basis are investigated. It was found that an increase in number of passenger and vehicle speed, darker vehicle surface color and lower cabin temperature will increase the cooling load. Meanwhile, the angle of front wind screen does not significantly influence the cooling load profile. In conclusion, the cooling loads profile can be used for air-conditioning system improvement/optimization exercise. The generic model can be used for complete vehicle air-conditioning simulation program towards energy-efficient air-conditioning system for better overall performance, especially in the early stage of vehicle development.

Abstract: In this study, two experiments were performed, one with the conventional compression refrigeration cycle (CRC) and the other with an ejector refrigeration cycle (ERC). The CRC system for automotive air conditioning was designed, fabricated and experiments were conducted. The system was then retrofitted with an ejector as the expansion device and experiments were repeated for the ERC system. Calculations of the entrainment ratio, compressor compression ratio and coefficient of performance (COP) were made for each cycle. The calculations showed that ERC has some advantages over the CRC. In this study, an average improvement of 5% in COP has been obtained for the ERC compared with the CRC.

Abstract: A field study was done on the thermal comfort of seven air-conditioned university classrooms in the hot and humid climate of Malaysia. The aims of this paper are to investigate the perceptions of thermal comfort and the adaptation method of students in air-conditioned classrooms. In total, 189 respondents from the classrooms completed the questionnaire. A comparison was made between the Predicted Mean Vote (PMV) and the Thermal Sensation Vote (TSV) and it was found that the TSV values tended to be more sensitive than the PMV values. A variety of adaptation methods of the occupants in the classrooms are also presented. It was found that most of the occupants preferred to change the air-conditioning thermostat, probably because all the occupants had the opportunity to control the thermostat.

Abstract: An air conditioning (AC) system design requires two main aspects that should be taken into consideration, there are reducing energy consumption and ensuring thermal comfort. This paper present variable speed drive on compressor motor is being tested to reduce the energy consumption. Conventional AC system to use on/off controller where the compressor motor turns itself on and runs at maximum speed then turns back off to achieve the temperature setting. This controller consumes more energy, however, by using a variable speed drive, the compressor motor will constantly run at various speeds while achieving the temperature setting. A system that developed software to implement the controller algorithms was installed in a thermal environmental room with data acquisition to monitor the room temperature, energy consumption, energy saving and coefficient of performance. Measurements were taken during the one hour experimental period at a time interval of three minutes for temperature set-points of 22, 23 and 24°C with internal heat loads of 500, 700 and 1000 W. The proposed technique can save energy and thermal comfort in comparison with conventional on/off control. The experiment results indicate that the application of variable speed drive on compressor motor is better than conventional on/off.

Abstract: An automotive air conditioning system that uses thermal expansion valve (TEV) as an expansion device. The pressure drop from the condenser and evaporator pressure is considered an isenthalpic process (constant enthalpy), where this process causes energy loss (entropy generation) in the expansion process. The ejector recovers energy losses, which was previously lost in the expansion valve, and an ejector can be used to generate isentropic condition in the expansion process. The use of an ejector as an expansion device in this study can reduce power consumption of the compressor and increase cooling capacity of the evaporator. The experiments were conducted with temperature set-points of the conditioned space of 21, 22 and 23°C with internal heat loads of 100, 200 and 400 W. Measurements were taken during the one hour experimental period at a time interval of five minutes. The experiment results indicate that the ejector system is better than TEV and save fuel.

Abstract: The automotive air conditioning is one of the important things to be discovered and analyses to maximize the coefficient of performance (COP). The effects of the global warming in a surrounding world give a big impact on performance of air conditioning system in the vehicle. The significant of these issues make the ambient temperature changing. The ambient temperature it’s different according to the type of the place. The different ambient temperature will effect on the performance of air conditioning system. This study will analysis the energy consumption, temperature distribution and COP at various ambient temperature (30, 35 and 40°C), internal heat load (0, 500,700 and 1000 W) and engine speed (1000, 1500 and 2000 rpm) using HFC-R134a as the refrigerant. Measurements were taken during the 30 minute experimental period for temperature set point which 21°C. The results showed that the performance of the automotive air conditioning system decreases when ambient temperature, internal heat load and compressor speed increased.

Abstract: Reducing fuel consumption and ensure occupants thermal comfort are two important considerations when designing a vehicle air conditioning system. By using direct current electric compressor, speed of compressor can be controlled by changing the frequency of the inverter. Fuzzy logic controller (FLC) was developed to imitate the performance of human expert operators by encoding their knowledge in the form of linguistic rules. The system is installed to a 5-door compact car with 1.2cc four-cylinder engine with data acquisition system to monitor the temperature of the cabin, coefficient of performance (COP) and fuel consumption. Temperature set-point of 22°C with original belt-driven, on/off and FLC electric direct current compressor at one hour experimental periods. The experimental results indicate that the FLC can save more fuel compared to on/off controller and belt-driven compressor.

Abstract: Propane (HC-290) is one of hydrocarbons often called as a green refrigerant. As a result, in the long term, this refrigerant is able to be used as a substitute refrigerant to HCFC-22. Generally, the amount of charging HC-290 to replace HCFC-22 based on the density ratio of the refrigerants, for instance, the ratio of liquid density at-10°C between HCFC-22 and HC-290 is 40.59%. Also, most investigations reported that the refrigeration system performances of HC-290 were better compared to HCFC-22 without varying the refrigerant charging of HC-290. By varying the refrigerant charging of HC-290 in a freezer, the performances can be optimized. This study presents an experimental investigation of the impacts on the performances of a freezer when the refrigerant charging of HC-290 is varied replacing HCFC-22. Three performances are reported in the present study, namely: cooling capacity, input power and COP. The first experiment was performed on a freezer using HCFC-22 as working fluid and the amount of refrigerant charging was 450 gram. Furthermore, the tests were carried out using HC-290 with six charging conditions: viz.: 30, 35, 40, 45, 50 and 55% of the mass of HCFC-22. The results showed that when refrigerant of HC-290 was charged 45% (mass) of HCFC-22, the freezer yielded the biggest increase in the cooling capacity and COP.

Abstract: This paper reviews the progress made in outdoor wind environment and outdoor ventilation at pedestrian level in urban area for the past few decades until today. The focus is on the effect of wind on people at pedestrian level and how the urban geometry can influence the flow field around the building. Section 1 explains the effect of natural wind environment on comfort and safety of the pedestrian. Section 2 describes the characteristic of pedestrian wind and flow pattern around the building due to the building geometry arrangement.