Refrigeration And Air Conditioning Research Articles

Finite element analysis of wire EDM process parameters on performance characteristics of Al–SiC hybrid composite with micro and nano reinforcements

Aluminum Hybrid Composites (AHC) microchannels find extensive applications in aerospace, refrigeration and air conditioning (RAC), microelectronics, automotive, biomedical, and marine industries due to their improved mechanical properties. The combination of lower density, high hardness, elevated thermal and electrical conductivity, superior elasticity, and heightened oxidizing ability at low temperatures makes machining aluminum hybrid composites challenging through orthogonal methods in an open environment. Therefore, it is imperative to investigate the impact of various machining conditions to determine optimal parameter values for microchannel fabrication in aluminum hybrid composite materials. This study aims to identify the ideal machining parameters for Al–SiC micro-SiC nano hybrid composites using wire electrical discharge machining. Four distinct process parameters (pulse on time, gap voltage, wire tension, and wire feed rate) and two response parameters (material removal rate (MRR) and surface roughness (SR)) were considered for process optimization. Additionally, finite element modeling was conducted for the aforementioned process, and the results were compared with experimental outcomes. Single-variable optimization yielded maximum MRR at 125 tons (μs), 25 SV (volt), 12 WT (kgf), and 2 WFR (m/min), and minimum SR at 125 tons (μs), 10 SV (volt), 12 WT (kgf), and 4 WFR (m/min). Single-variable optimization for simulations resulted in maximum MRR at 125 tons (μs), 40 SV (volt), 4 WT (kgf), and 6 WFR (m/min), and minimum SR at 110 tons (μs), 10 SV (volt), 12 WT (kgf), and 2 WFR (m/min). Precise modeling aids in minimizing unnecessary machining, enabling exploration of a broader range of experimental results, thereby promoting environmentally friendly and sustainable machining practices.

Survey and Review of Refrigerant Leakage Sources and Solutions in Malaysian Refrigeration and Air Conditioning (RAC) Systems

Survey and Review of Refrigerant Leakage Sources and Solutions in Malaysian Refrigeration and Air Conditioning (RAC) Systems

CFD analysis and optimization of thermal stratification in a Thermal Diode Tank (TDT)

Thermal stratification is a common and natural phenomenon in energy storage tanks. This paper presents a Computational Fluid Dynamics (CFD) analysis of thermal stratification within a novel cold energy storage, termed a Thermal Diode Tank (TDT). The TDT is a well-insulated water tank equipped with heat pipes for unidirectional heat transfer from water to the ambient air. When integrated into a Refrigeration and Air-conditioning (RAC) system, it provides cooling water to reduce the condensing temperature. The research problem revolves around the impact of thermal stratification on TDT performance and the identification of the optimal TDT structure when thermal stratification is present. Therefore, this study aims to employ CFD to simulate temperature profiles within a TDT, both with and without an obstacle. With validated models, parametric analysis has been conducted to determine the optimal TDT structure. Several design parameters have been investigated, including tank orientation, heat transfer capacity, the ratio of obstacle axial height to TDT height (ho/H), and the ratio of obstacle hole diameter to TDT diameter (do/D). Key findings reveal that a vertical tank orientation is more conducive to improving the TDT assisted RAC system performance than a horizontal one. Increasing the TDT's heat transfer capacity also positively contributes to the system performance. Parameters of an optimal TDT structure include a ho/H ratio of approximately 0.43 and a do/D ratio of 0.4. It is found that the do/D ratio should be at least 0.15 to obtain positive stratification. Furthermore, the presence of thermal stratification can increase the system's Coefficient of Performance (COP) by up to 10 %.

Simulation of a radiation-enhanced thermal diode tank (RTDT) assisted refrigeration and air-conditioning (RAC) system using TRNSYS

The increasing demands for refrigeration and cooling have led to higher energy consumption and greenhouse gas emissions of Refrigeration and Air-conditioning (RAC) systems. To tackle this global challenge, a Radiation-enhanced Thermal Diode Tank (RTDT) has been proposed as an innovative and sustainable condenser-cooling approach to assist the RAC system to save energy. The RTDT is a passive cooling device that utilises a Radiation-enhanced Heat Pipe (RHP) to discharge heat in one direction, i.e., from the interior of a heat-insulated water tank to the surrounding area. In this paper, TRNSYS simulation was used to conduct a case study comparing the performance of the RTDT assisted RAC (RTDT-RAC) system with a reference Air-cooled RAC system under identical ambient conditions in Adelaide, Australia. The findings show that the RTDT-RAC system can save up to 40 % energy compared with the reference RAC system, with an increased Coefficient of Performance (COP) of 5.34. Moreover, a parametric analysis has also been conducted to study the impacts of weather conditions or regions, room temperature setpoints and RHP radiative surface areas on the RTDT-RAC system's performance. The results of the parametric analysis indicate that the regions with larger day and night ambient temperature differences demonstrate better energy-savings. Both a higher room temperature setpoint and an increased RHP radiative surface area can increase the energy-savings effectively. For a 50 m3 RTDT, to achieve energy-savings, the RHP radiative surface area is found to be at least 2.2 m2, while the optimal value is about 5 m2.

Viscosity measurement and correlation of saturated solutions of R-290 with three lubricants

As a natural refrigerant, propane (R-290) with a similar cooling capacity of R-22 is being increasingly widely attention in refrigeration and air conditioning (RAC). In the refrigeration cycle, the working fluid is actually a mixture of refrigerant/oil. To gain insight into the performance of vapor-compression refrigeration using R-290 as a refrigerant, the thermophysical properties of R-290/oil mixtures should be well known, especially the viscosity behavior. A self-designed double-capillary apparatus was applied to measure the viscosities of saturated solution for R-290 with three synthetic oils (PAG 68, POE 75 and PVE 68) from 303.15 to 348.15 K. The results show that the viscosities of three blends have the similar trend as rising solubility. The absorbed R-290 has a great impact on the oil viscosity in the low temperature region. Viscosities of R-290/oil mixtures could be well represented by the Eyring-MTSM model.

Performance Simulation Model of a Radiation-Enhanced Thermal Diode Tank-Assisted Refrigeration and Air-Conditioning (RTDT-RAC) System: A Novel Cooling System

This paper presents a novel technology to improve the energy efficiency of refrigeration and air-conditioning (RAC) systems by applying a condenser cooling approach. The approach is based on the integration of an innovative radiation-enhanced thermal diode tank (RTDT) with a RAC system. The thermal diode tank (TDT), consisting of heat pipes and an insulated water tank, is a passive device to generate cooling water at a minimum night ambient temperature. When the radiation-enhanced heat pipe (RHP) is equipped with the TDT, it becomes an RTDT, which could theoretically lower the water temperature below the ambient temperature. In this study, a radiation-enhanced thermal diode tank (RTDT) is proposed to supply cooling water to the RAC system. Simulation models for the proposed RTDT-assisted RAC (RTDT-RAC) system are developed in order to investigate the impacts of the tank size to cooling capacity (TS/Qc) ratio, day/night ambient temperature fluctuations on the system’s coefficient of performance (COP) and the energy saving percentage (ESP). The results show that a greater day/night ambient temperature difference and a larger TS/Qc value can both enhance the COP and ESP of the RTDT-RAC system. The optimal and threshold TS/Qc values were 1 m3/kW and 0.18 m3/kW, respectively. These findings demonstrate the potential of the RTDT-RAC system to achieve significant energy savings and provide valuable insights for the design and optimization of an RTDT-RAC system.

Development of a Value -Based Curriculum Model for the Environment in the Vocational College Standard Curriculum in the Field of Refrigeration and Air Conditioning: A Needs Analysis

This curriculum model is a value-based model of environmental sustainability built through the Vocational College Standard Curriculum of Refrigeration and Air Conditioning (VCSC_ RAC). Concerning that, this study proposes a Research, Design and Development (DDR) approach which is a multi-method development research approach. The study will go through three phases and use several different research tools in each phase. The involvement of study participants from expert groups and user groups consisting of field lecturers will be able to provide various inputs and consider aspects of the model’s needs in addressing the problem of the impact of refrigerants on the environment through VCSC_RAC. The purpose of this study is to identify the needs analysis for the development of this curriculum model. The study was conducted by survey method that is using questionnaires. Questionnaires were distributed to Vocational College (VC) lecturers in the field of Refrigeration and Air Conditioning (RAC) throughout Malaysia. Researchers have found that there is a need to build a value -based curriculum model for the environment. The findings of this study indicate the need for the curriculum model to be built through VCSC_RAC based on values towards the environment. The emphasis on the value aspect of the environment is very relevant so that the quality of teaching and learning in VC can be improved to provide students with values, awareness and responsibility towards the environment.

Estimation of greenhouse gas mitigation potential from refrigerant switching and energy efficiency improvement in Thai air conditioners

Thailand is an important manufacturing and export center of Refrigeration and Air Conditioning (RAC), especially wall-typed air conditioners (ACs). Environmentally friendly refrigerant such as Hydrofluorocarbons (HFCs) have become the future substitute potential due to their zero-ozone depleting potential (ODP) with lower global warming potential (GWP). In this paper, we focus on country-wide GHG mitigation potential from refrigerant switching from R-32 to R-290 in Thai air conditioners. We found that there are GHG mitigation opportunities with overall 1.48 MtCO 2eq from the switching in the year 2020 from two concept as follows; (i) GHG mitigation from refrigerant leakage results at around 0.50 MtCO 2eq, (ii) GHG mitigation from energy efficiency improvement result at around 0.98 MtCO 2. However, there are some safety concerns of R-290 which is flammable refrigerants, hence, the relevance government agencies have to be seriously considered especially the installation and operation of R-290 in Thai air conditioners. The well-designed capacity building and awareness for manufacturers, technical service, provider, and user have to be set. Technology transfer from industrialized country to Thailand is essential. All activities have to be implemented along with the Kigali Amendment which will be aligned with the national NDC Roadmap.

Radiation-enhanced thermal diode tank (RTDT) for refrigeration and air-conditioning (RAC) systems

A Thermal Diode Tank (TDT) is invented for energy conserving purposes that can passively produce cooling water at a minimum night ambient temperature. The TDT is an insulated water tank equipped with heat pipes, which provides unidirectional heat transfer from the TDT water to its surroundings. The conventional heat pipes dissipate heat mainly by convection heat transfer, which are termed Convective Heat Pipes (CHPs), and a TDT equipped with CHPs is a Convection TDT (CTDT). To promote the TDT performance in generating cooling water at a lower temperature, a Radiation-enhanced Heat Pipe (RHP) is proposed with a flattened hollow cuboid as its condenser section to radiate heat to the night sky, while maintaining the convection heat transfer with air. Such a Radiation-enhanced TDT (RTDT) is expected to have a better water-cooling performance than CTDT currently obtains, and could potentially cool the water below the minimum ambient temperature. In this paper, performance simulation models for both RTDT and CTDT have been developed and validated by the experiment. The results reveal that the RTDT generates colder water than CTDT does, and the heat transfer capacity of the RTDT is approximately twice as high as that of the CTDT if they are made from the same quantity of materials. It is found not advisable to promote the TDT performance by increasing the air circulation at the heat pipe condenser. However, analysis shows that increasing the heat pipe condenser area dominantly contributes to the enhancement of TDT performance, especially for RTDT.

Energy-Saving Potential of Thermal Diode Tank Assisted Refrigeration and Air-Conditioning Systems

Lowering the condensing temperature of the Refrigeration and Air-conditioning (RAC) system has been proven to effectively increase the system’s Coefficient of Performance (COP). This paper revolves around evaluating the energy-saving generated by applying a Thermal Diode Tank (TDT) in the RAC systems. The TDT is a novel invention, which is an insulated water tank equipped with gravity heat pipes. If the TDT was placed outdoors overnight, its inside water would theoretically be at the minimum ambient temperature of the previous night. When the TDT water is used to cool the condenser of RAC systems that operate during the daytime, a higher COP of this TDT assisted RAC (TDT-RAC) system could be achieved compared with the baseline system. In this study, a steady-state performance simulation model for TDT-RAC cycles has been developed. The model reveals that the COP of the TDT-RAC cycle can be improved by 10~59% over the baseline cycle depending on the compressor types. The TDT-RAC cycle with a variable speed compressor can save more energy than that with a fixed speed compressor. In addition, TDT-RAC cycles can save more energy with a higher day/night ambient temperature difference. There is a threshold tank size for a given TDT-RAC cycle to save energy, and the energy-saving can be improved by enlarging the tank size. A desk-top case study based on real weather data for Adelaide in January 2021 shows that 9~40% energy could be saved by TDT-RAC systems every summer day on average.

Experimental investigation and non-dimensional regression analysis of condensation heat transfer of R-600a over finned tubes

In this study, condensation heat transfer of R-600a (Iso-butane) has been analyzed experimentally over different finned tubes varying different parameters. These parameters like saturation pressure, wall sub-cooling temperature, fin geometry, refrigerant properties, and coolant flow rate are major factors affecting the performance of refrigeration and air-conditioning (RAC) systems. The parameters were varied within the range of operating conditions for most of refrigeration and air-conditioning systems. Based upon experimental data and exclusive analysis, best performing sets of different parameters have been concluded, and also a generalized correlation in non-dimensional form covering different parameters has been developed.

Urgensi Kepemimpinan dan Mentalitas Siap Berubah Terhadap Kinerja Pegawai di Musim Pandemi Covid-19

This research aims to examine the influence of transformational leadership on employee performance in the Refrigeration and Air Conditioning (RAC) industry employees in Bekasi with a mentality of being ready to change as a mediator. The data were collected through simple random sampling technique and the results of a questionnaire that returned and were valid for 132 samples. The data were processed by the SEM method using SmartPLS 3.0 software. From the results of this research, it is concluded that transformational leadership has no significant effect on employee performance, but transformational leadership has a significant and positive effect on the mentality of being ready to change as a mediator. This research also concludes that a mentality of being ready to change has a significant and positive effect on the relationship between transformational leadership and employee performance. The mentality ready to change in this study serves as a full mediator. This new research proposes a model for building employee performance among RAC industrial employees in Bekasi through the development of transformational leadership practices with a change-ready mentality as a mediating variable. This research can pave the way for developing a ready-to-change mentality in employees in the face of the pace of the fourth industrial revolution.

Performance investigation on refrigeration and air conditioning systems with multi-evaporator

Refrigeration and air conditioning (RAC) system Multi-evaporator structures are popularly applied in for efficient temperature and humidity control of multi-zone in underground buildings, light commercial and residential buildings, cold stores, et al., which can also attract and/or release heat from and/or to renewable sources. The increase on the system complexity makes it difficult to analyze the performance and to optimize its design and control. In this paper, a novel method, performance chart, is presented for the performance analysis and system optimization of multi-evaporator and RAC systems. The performance chart is generated by superimposing the performance curve of different evaporators of the indoor unit (IDUs), which can be applied to describe the performance of the whole RAC system by superimposing with the performance curve of outdoor units (ODUs). Based on the performance chart, the performance of multi-evaporator systems are analyzed at different conditions such as varying indoor temperatures, varying indoor air volumes, and varying IDUs’ capacities. The performance chart can give the reasonable and quantitative trends of multi-evaporator RAC system performance and guide the system design. These results showed that the performance chart can be used as a convenient tool for performance analysis and system optimization of multi-evaporator RAC systems.

A study of alternative refrigerants for the refrigeration and air conditioning sector in Mauritius

The most frequently used refrigerants in the refrigeration and air conditioning (RAC) sector in Mauritius are currently hydrochlorofluorocarbons (HCFC) and hydrofluorocarbons (HFC). However, because of their strong influence on global warming and the impact of HCFCs on the ozone layer, refrigerants such as ammonia (NH3), carbon dioxide (CO2) and Hydrocarbons (HC), having minimal impact on the environment, are being considered. So far, HCs have only been safely used in domestic refrigeration. Ammonia has been used mainly for industrial refrigeration whereas CO2 is still under study. In this paper, a comparative study of the various feasible alternatives is presented in a survey that was undertaken with major stake holders in the field. The retrofitting possibility of existing equipment was assessed and safety issues associated with each refrigerant were analysed. The major setback of hydrocarbons as a widely accepted refrigerant is its flammability which was considered as a major safety hazard by the majority of respondents in the survey and the main advantages are the improved equipment coefficient of performance (COP) and better TEWI factor. This resulted in a 12 % drop in energy consumption. Despite the excellent thermodynamic properties of ammonia, its use has mainly been confined to industrial refrigeration due to its toxicity. In Mauritius, the performance of ammonia in air conditioning is being evaluated on a pilot basis. The major setback of carbon dioxide as a refrigerant is the high operating pressure which is considered a safety hazard. The high initial investment cost and the lack of qualified maintenance technician is also an issue. The use of CO2 is mainly being considered in the commercial refrigeration sector.

Re-Evaluation of the UK's HFC-134a Emissions Inventory Based on Atmospheric Observations.

Independent verification of national greenhouse gas inventories is a vital measure for cross-checking the accuracy of emissions data submitted to the United Nations Framework Convention on Climate Change (UNFCCC). We infer annual UK emissions of HFC-134a from 1995 to 2012 using atmospheric observations and an inverse modeling technique, and compare with the UK's annual UNFCCC submission. By 2010, the inventory is almost twice as large as our estimates, with an "emissions gap" equating to 3.90 (3.20-4.30) Tg CO2e. We evaluate the RAC (Refrigeration and Air-Conditioning) model, a bottom up model used to quantify UK emissions from refrigeration and air-conditioning sectors. Within mobile air-conditioning (MAC), the largest RAC sector and most significant UK source (59%), we find a number of assumptions that may be considered oversimplistic and conservative; most notably the unit refill rate. Finally, a Bayesian approach is used to estimate probable inventory inputs required for minimization of the emissions discrepancy. Our top-down estimates provide only a weak constraint on inventory model parameters and consequently, we are unable to suggest discrete values. However, a significant revision of the MAC servicing rate, coupled with a reassessment of non-RAC aerosol emissions, are required if the discrepancy between methods is to be reduced.

Exploring policy strategies for mitigating HFC emissions from refrigeration and air conditioning

The growing demand for cooling throughout the world, possibly increased by global climate change, requires the implementation of policies to mitigate the related greenhouse gas (GHG) emissions from energy and refrigerant use in the refrigeration and air conditioning (RAC) sector. This article aims to contribute to the discussion on strategies to reduce HFC emissions from RAC by looking at their different temporal effects, caused by stock-flow dynamics. From scenario modeling, we find that containment strategies are often most effective in reducing HFC emissions in the short run, whereas phase out strategies have more potential in the long run. Further findings suggest that early and quick implementation of phase out strategies could lead to important reductions in cumulative HFC emissions, because stock build up is prevented. This timing effect is less pronounced for containment strategies. Lastly, emissions from disposal, if unabated, can lead to equally large emissions annually as those from use. Preference for several short-term benefits of containment strategies might lead to sub optimal emission reduction strategies, endangering long term GHG emission reduction.

Challenges in recovery and recycling of refrigerants from Indian refrigeration and air-conditioning service sector

Abstract India is a large producer and user of chlorofluorocarbons (CFCs) in the refrigeration and air-conditioning (RAC) sector. Government of India has taken several steps to restrict the production and consumption of CFCs. Refrigerant conservation through recovery, recycling (R&R) and reclamation is one way of reducing emissions and encouraging timely phase out of CFCs in developing countries. CFC recovery, recycling and reclamation have been mandated in many developed countries. However, this practice is yet to make an impact in India although it is practiced in MAC sector to some extent. India is planning for the final phase out of CFCs in the RAC service sector, in which R&R will be one of the components. A model has been developed to assess the economics of R&R for some typical parameters in developing counties like India. The model suggests that the enterprises recycling 1500 kg/a will break even within 1 year for all scenarios. However, R&R may not be cost effective for small workshops and low volume refrigerant vendors until either the price of CFC goes up or the cost of R&R unit is subsidized. A nationwide survey on RAC service sector revealed that in India, there are very few enterprises handling more than 500 kg/a. Therefore, there is a need to provide the RAC service sector with adequate and innovative financial incentives. This paper attempts to study the issues related to R&R for various sub-sectors of RAC in developing countries with an emphasis on cost effectiveness. India is used as a model for this study.

Ozone friendly HFC134a/HC mixture compatible with mineral oil in refrigeration system improves energy efficiency of a walk in cooler

In the event of chlorofluorocarbon (CFC) phase out, identifying a long term alternative to meet all our requirements in respect of system performance and service is an important area for research in the refrigeration and air conditioning (RAC) sector. Even though HFC134a and the HC blend (containing 55.2% HC600a and 44.8% HC290) have been reported to be substitutes for CFC12, they have their own drawbacks in energy efficiency, flammability and serviceability aspects of the system. HFC134a is not miscible with mineral oil, and hence, polyol ester oil is recommended, which is highly hygroscopic in nature. This hygroscopicity demands stringent service practices, which otherwise results in moisture entry into the system. On the other hand, the HC blend has flammability issues, and hence, the charge quantity in systems is limited by safety standards. This work focuses on experimentally studying the performance of an ozone friendly refrigerant mixture (containing HFC134a/HC600a/HC290) in a walk in cooler, operating with an open type compressor with mineral oil as lubricant. To have a realistic comparison of the new mixture performance, tests were conducted with the conventional refrigerant (CFC12) for the system behaviour, such as no load pull down time, motor power, energy consumption, ON and OFF cycle time, temperature distribution along the coil and COP. The performance of the system with the new mixture was studied and compared. The oil miscibility of the new mixture with mineral oil was also studied and found to be good. It is observed that the mixture has better performance, resulting in 28.6% less energy consumption than CFC12. The enhancement in COP was 6–10%.

Applications of fault detection and diagnostic techniques for refrigeration and air conditioning: A review of basic principles

During the 1990s a number of different prototype Refrigeration and Air Conditioning (RAC) Fault Detection and Diagnostic (FDD) systems have been developed and subsequently presented in various research publications. This interest in RAC FDD systems is generally a result of the potential benefits, such as reducing equipment downtime and avoiding energy wastage, these systems can bring to new and existing RAC installations. With the exception of a few reports produced by the International Energy Agency (IEA) Annex 25, no other publications or texts exist that bring together the various FDD concepts directly associated with RAC applications. However, the reports produced by the IEA are far from comprehensive enough to be of use to typical industry personnel. Therefore, the aim of this review is to present RAC personnel with a clearer understanding of the fundamental principles associated with the application of RAC FDD. The paper will initially highlight various relevant areas before presenting examples of typical FDD systems applicable to RAC systems.