Refrigerant For Air-conditioning Systems Research Articles

Refrigerant Selection in Air Conditioning Systems Considering Thermodynamic, Environmental, and Economic Performance Using the BHARAT-II Multi-Attribute Decision-Making Method

A simple and effective multi-attribute decision-making method, named as "Best Holistic Adaptable Ranking of Attributes Technique (BHARAT)-II”, to choose the best refrigerant for air conditioning systems is presented. The thermodynamic properties of the refrigerants, and their environmental, and economic performances are also considered for the selection. Two case studies are provided to demonstrate the proposed multi-attribute decision-making method. The first case study addresses the problem of selecting the best refrigerant for residential split air conditioners out of 15 alternative refrigerants considering 12 selection attributes; the second case study addresses the problem of selecting the best refrigerant for automobile air conditioning systems by considering 14 alternative refrigerants and 13 selection attributes. The results of the proposed decision-making method are compared with those of other well-known multi-attribute decision-making methods such as EDAS, TOPSIS, and MOORA. The proposed method is shown to be simple to implement, providing a logical way for allocating weights to the selection attributes and is useful to solve the best alternative refrigerant selection problems of the residential as well as industrial refrigeration and air conditioning.

Indoor space risk assessment based on Co-analysis strategy in split room air conditioning

The use of environmentally friendly hydrocarbon refrigerants in air conditioning systems is being promoted worldwide as a proactive measure to combat global warming and ozone depletion. A comprehensive analysis of hydrocarbon refrigerant leakage and the resulting fire risk is essential for split room air conditioning (SRAC) systems. The study presents a novel Co-analysis strategy that integrates the operation of SRAC systems with the assessment of indoor space fire risk. Experiments involving the leakage and diffusion of R-290 in SRAC system have been conducted to substantiate the validity of the Co-analysis strategy. This model is used to analyze the dynamic parameters of leakage and distribution patterns of hazardous areas within the SRAC indoor unit. The study considers various leakage hole sizes (1 mm, 2 mm, 3 mm) under both cooling and heating operating modes. The results show the leaking refrigerant flow rate presents different attenuation types under cooling and heating modes. When the leakage hole diameter is less than 2 mm in the cooling mode, the concentration of R-290 in the space is below 50 % lower flammable limit. The comprehensive fire risk probability of the R-290 indoor unit is 1.0 × 10−11∼5.0 × 10−10 for the cooling model and 1.0 × 10−11∼9.0 × 10−10 for the heating model. Effective methodologies for mitigating risks and optimizing the system are also proposed. Based on the Co-analysis strategy, this study presents a scientifically grounded assessment of the fire risk associated with air conditioning uses flammable refrigerants inside buildings. The strategy aims to enhance building safety.

Synthesis and thermal properties of n-tetradecane phase change microcapsules for cold storage

Due to the high heat carrier density, latent heat functional fluid may be used as the secondary refrigerant in air conditioning system. In this study, two-step in-situ polymerization method is used to synthesis microcapsules of ploy (urea-formaldehyde) (UF), where n-tetradecane is used as core material and SDS as emulsifier. Microcapsules with excellent morphology and performance are obtained by adjusting the emulsifier mass fraction, stirring rate, polymerization PH value and core-shell mass ratio. The experimental results show that when the mass fraction of SDS is 1.2 wt%, the initial PH value is 3.5 and the core-shell mass ratio is 2: 1, phase change microcapsules have good dispersibility. The phase change enthalpy of the microcapsules reach to 178.1 J·g−1, whose encapsulation rate is up to 85.6%. A latent heat functional fluid is prepared using the synthesized microcapsules and the base liquid of water and absolute ethanol. When the ethanol mass fraction in the base fluid is about 74 wt%, the stable latent heat functional fluid is obtained. The thermal conductivity of the latent heat functional fluid increases with the increase of temperature, and decreases with the increase of the mass fraction of microcapsules. Its viscosity rises with the increase of temperature or the mass fraction of microcapsules.

Studi Kinerja Teoritis Pengkondisian Udara Menggunakan R32, R290 Dan R410a

The use of more environmentally friendly refrigerants in air conditioning systems has become a central demand and issue in the future. This article presents the simulation results of the comparison of the use of R32 (difluoromethane), R290 (propane) and R410A (difluoromethane+pentafluoroethane) on the performance of air conditioning systems. The thermodynamic analysis of the system using the two refrigerants used the CoolTools version 1.0 software at several variations of the evaporation temperature, with the condensation temperature held constant. The important quantities analyzed are heat release in the condenser, compressor power, and coefficient of performance. The results of this study indicate that the performance of air conditioning using R290 is higher than the use of R32 and R410A while the lowest coefficient of performance is owned by air conditioning using R410A. In addition, R290 is more environmentally friendly than R32 and R410A, so the use of R290 is highly recommended

Air conditioning cycle simulations using a ultrahigh-speed centrifugal compressor for electric vehicle applications

Electric vehicles (EVs) are an increasingly popular option to decrease global greenhouse emissions in the transportation sector. The largest limiting factor is their range, significantly decreased by the cooling load required. In conjunction with the shift to incorporating low-Global Warming Potential (GWP) refrigerants in cooling systems, it is critical to reexamine the design of traditional air conditioning (AC) systems. To this end, a model of a cooling system for an EV was created, while incorporating an ultrahigh-speed miniature centrifugal compressor, allowing for the performance comparison of multiple refrigerants. From these simulations, a centrifugal compression system using HFC-134a provided sufficient cooling capacity for the modeled vehicle (13.07 kW) with lower input power requirements (2.05 kW) than a commercial EV AC system. However, this requires improved heat exchanger efficiencies. A straightforward system design may be attainable with lower operating pressures utilizing the low-GWP HFO-1336mzz(Z) while achieving a nearly equivalent cooling capacity (12.39 kW) at reduced power requirements (1.86 kW). Performance and safety tradeoffs were examined for a variety of refrigerants and azeotropic mixtures. The use of azeotropic refrigerants increased the cooling capacity and energy efficiency compared with the individual components, but with the tradeoff of higher pressure and compressor exit temperatures. Overall, this effort provides specified conditions for EVs while being among the first to demonstrate the potential of low-GWP and low-Ozone Depletion Potential refrigerants in AC systems utilizing ultrahigh-speed centrifugal compressors.

Searching for suitable lubricants for low global warming potential refrigerant R513A using molecular-based models: Solubility and performance in refrigeration cycles

• Accurate molecular thermodynamic model for R513A/lubricants in refrigeration cycles. • Rigorous energetic investigation of refrigeration cycles with thermodynamic postulates. • PEC5 optimal lubricant for R513A, in view of solubility, miscibility and viscosity. • Procedure allowed quantifying impact of the presence of lubricant on the COP. • Presence of PEC5 in the mixture up to 5% weight led to COP decrease of 3%. Following environmental regulations, refrigerant R134a (Global Warming Potential GWP = 1430), commonly used in air conditioning applications, is required to be replaced by refrigerants with lower GWP. Among them, R513A is investigated as an excellent alternative, with a GWP reduction of 56% compared to R134a. However, further studies are needed in order to assess its use for this application. In this work, the molecular-based polar soft-SAFT equation has been employed to predict the vapour-liquid equilibria (VLE) of R513A and selected lubricants, searching for the optimal lubricant and their performance on a vapour compression refrigeration cycle. First, the binary VLE of the commercial lubricants from the Pentaerythritol Esters (PECs) and Polyethylene Glycol Dimethyl Ethers (PEGDMEs) families with R1234yf and R134a were assessed versus available experimental data, by developing the appropriate molecular models and parameters. Then, the models were used to predict the properties of the ternary mixtures containing the two refrigerants and the lubricants. PEC5 was found to be the optimal lubricant for R513A, considering a balance between solubility, miscibility and viscosity. Molecular modelling combined with thermodynamic and energetic analysis allowed to calculate the performance of a vapour compression refrigeration cooling cycle, quantifying the impact of the presence of the lubricant on the COP. The presence of PEC5 in the mixture was not significant, staying below a COP decrease of 3% in all cases considered, while for TrEGDME, its presence reduced the COP up to 6.1%. The procedure used here allows tuning the performance of the refrigerant/lubricant pair, in a step forward on the search for low GWP refrigerants in air conditioning systems.

Exergy Investigation of R410A as a ‘Drop In’ Refrigerant in a Water-Cooled Mechanical Vapor Compression Cycle

The urge to replace hydrofluorocarbons which possess high global warming potentials has taken center stage in the air conditioning industry due to both international and local policies such as the Kigali Amendment and Japan’s revised Fluorinated Gas law. This has prompted the exploration of novel refrigerants as well as their mixtures to create high performance environmentally friendly alternatives. These refrigerants can be integrated into existing systems as ‘drop in’ refrigerants, which provide a simpler and low cost substitution process to replace environmentally harmful refrigerants such as R410a. R410a is currently a widely used refrigerant in air conditioning systems, but is to be phased out of use under the Kigali Amendment by the late 2040s. Thus to compare the suitability of replacing this refrigerant with environmentally friendly ‘drop in’ alternatives, a preliminary baseline investigation on a mechanical vapor compression chiller with R410a is conducted via performance and exergy indicators. The testing procedure utilized Air Conditioning, Heating and Refrigeration Standard 551/591 which revealed an optimum charge amount of 0.70 kg with a peak performance near 88% of full capacity. The heat exchanger overall heat transfer coefficients showed varying trends, whilst the exergy destruction was as expected highest for the compressor.

Стабилизация хладагента как энергоэффективное решение поддержания параметров микроклимата серверных помещений

Among all known methods for energy saving based renewable energy sources, those aimed at improving the quality of equipment regulation are of particular importance. The use of renewable energy sources ensures an increase in energy saving; however, the equipment used in engineering systems should also be reliable. At present, almost every office building has a special facility for server equipment. Such facilities are rarely furnished with devices for removing excess heat, which may hinder stable operation of computer equipment and shorten its service life. In the present study, the energy efficiency of a method for stabilising the refrigerant in air conditioning systems operating on freon is experimentally verified. The stabilisation of the refrigerant is based on bringing the gas-liquid freon in the circuit to a uniform state prior to its entry in the thermostatic expansion valve (TEV). A refrigerant stabilisation device was embedded in the circuit of the on/off type split system, the working substance in which was R410A. During 3 months, the temperature of the server mobile station and the power consumption of the split system were monitored in real time, 24/7. On the basis of the obtained results, the energy saving was calculated. The test results were independent of external factors. Reasons for a more efficient cooling of the split system by bringing the refrigerant to a homogeneous state with a decrease in its temperature prior to its entry in the TEV were investigated. It is shown that, in the evaporator, freon requires more time and energy for the phase transition, which process consumes more heat from the facilities under cooling.

Phase change materials development from salt hydrate for application as secondary refrigerant in air-conditioning systems

Salt hydrate for application as secondary refrigerant in the air-conditioning system are selected based on the slurry forming according to the evaporator temperature 5°C–12°C. Research development of salt hydrate for application is done in three stages, namely; the study of the properties, flow, and heat transfer characteristics, also applications in air-conditioning systems. The study of the properties of the phase change materials is in the form of latent heat, freezing and melting temperature, thermal stability properties, viscosity, and rate of corrosion. The study of flow and heat transfer characteristics determine the effect of salt hydrates on the pressure drop and heat transfer in a heat exchanger. Studies on the application of the air-conditioning system is made to use a type of cooling room air-handling units and fan coil unit. The results of the researches for each of two stages are described in the discussion of the current article. The characteristics of salt hydrates from Na2HPO4 and CaCl2 are fitted to be applied as secondary refrigerant. This material has high latent heat value and matched phase change temperature, as well as a very low corrosion rate. This material also demonstrates excellent heat transfer performance, in which an increase as much as 18.62% for salt hydrate from calcium chloride and 13.9% for salt hydrate from disodium hydrogen phosphate. For its flow characteristics, there was a less significant increase on pressure drop for Na2HPO4.

Limited options for low-global-warming-potential refrigerants

Hydrofluorocarbons, currently used as refrigerants in air-conditioning systems, are potent greenhouse gases, and their contribution to climate change is projected to increase. Future use of the hydrofluorocarbons will be phased down and, thus replacement fluids must be found. Here we show that only a few pure fluids possess the combination of chemical, environmental, thermodynamic, and safety properties necessary for a refrigerant and that these fluids are at least slightly flammable. We search for replacements by applying screening criteria to a comprehensive chemical database. For the fluids passing the thermodynamic and environmental screens (critical temperature and global warming potential), we simulate performance in small air-conditioning systems, including optimization of the heat exchangers. We show that the efficiency-versus-capacity trade-off that exists in an ideal analysis disappears when a more realistic system is considered. The maximum efficiency occurs at a relatively high volumetric refrigeration capacity, but there are few fluids in this range.

CRYOGENIC AIR CONDITIONING OF MOTOR VEHICLES

Cryogenics is the branch of physics and engineering that involves the study of very low temperatures (below 123 K), how to produce them, and how materials behave at those temperatures. It is frequently applied to low temperature refrigeration applications such as in the study of physical phenomena of materials at temperature approaching absolute zero and in the liquefaction of gases. Liquefied gases such as liquid nitrogen and liquid helium are used in many cryogenic applications. Using liquid nitrogen as a refrigerant reduces chloro-fluorocarbon (CFC) emission in atmosphere and it is an eco-friendly technique. This paper deals with usage of liquid nitrogen in air conditioning of motor vehicles. First the preparation of liquid nitrogen is discussed, followed by its storage and working as a refrigerant in air conditioning system. This is followed by its advantages and draw backs.

Experimental Investigation on Friction and Wear of Coated Vane under the Environments of Lubricants and CO<sub>2</sub> as a Refrigerant

The CO2 was investigated as an alternative refrigerant to replace HFC (hydrofluorocarbons) refrigerant in air conditioning systems due to the environmental concerns. Because new compressors with CO2 are going to be operated under the high pressure, the tribology of sliding surfaces in the compressor becomes very important. To develop new compressor, especially rotary type, the friction and wear characteristics of sliding surfaces between a vane and a roller in the rotary compressor were evaluated in this paper. Several hard coatings, such as TiN, CrN and WC/C, were applied on vane surfaces in order to improve the tribological characteristics, and their performances were evaluated experimentally. Two types of lubricants were used, namely POE (polyol ester) oil and PAG (polyalkylene glycol) oil. The vane-on-disk type sliding tests were performed with an exclusive high pressure wear tester. From the tests, wear volumes of vane surfaces applied various coatings were compared. Test results showed that WC/C and CrN coatings showed good tribological properties. Also, the results of the sliding tests showed that using PAG oil has an advantage over POE oil in CO2 environment.

Tribological Studies on Scuffing Due to the Influence of Carbon Dioxide Used as a Refrigerant in Compressors

Because hydrofluorocarbon (HFC) refrigerants in air-conditioning systems are known to have a negative effect on the environment, carbon dioxide (CO2) is a candidate as a replacement refrigerant. Research work related to CO2 as a refrigerant has been focused primarily on its thermodynamic performance, whereas work in the area of tribology related to carbon dioxide is absent. In this study, the effects of CO2 used as a refrigerant on the tribological behavior of surf aces in contact in such systems were investigated. Controlled experiments were performed at constant loads in environments of CO2 and the conventional HFC refrigerant, R134a, as well as under conditions of step-increasing loads in the presence of refrigerant (CO2 or R134a) and polyalkylene glycol lubricant. The experiments were performed on a high-pressure tribometer that is particularly suited for tribological testing of compressor contact interfaces. The tribological behavior of contacting surfaces in a CO2 environment was nearly identical to that in an R134a environment when tested under the same operating conditions.

Gas Viscosity of Difluoromethane from 298.15 to 423.15 K and up to 10 MPa

Chlorodifluoromethane (HCFC-22) has been used mostly as a refrigerant for air-conditioning systems, but it is scheduled to be phased out by 2030 due to its ozone depletion properties. Difluoromethane (HFC-32) has no ozone depletion potential (ODP) since there are no chlorine atoms in the molecule and has been considered as a substitute for HCFC-22. The gas viscosity of difluoromethane was measured using an oscillating disk viscometer of the Maxwell type from 298.15 to 423.15 K at pressures up to 10 MPa. The results were fitted to an empirical equation as a function of temperature and density. Intermolecular force constants of the Lennard-Jones 12-6 potential were determined. In addition, the experimental density was compared with the calculated values from various equations of state previously reported.

Alternatives for R22 and R502: the next challenge in CFC and HCFC replacement.

Increasing concern over the possible depletion of stratospheric ozone by all chlorine-containing refrigerants is driving the fluorochemical industry to identify replacements for HCFCs such as R22 (CHClF 2). As a pure fluid this is currently used as the major refrigerant in air conditioning systems and in an azeotrope with R115 (CF 3CF 2Cl) for supermarket refrigeration. This paper describes candidates for fluorocarbon replacements for R22 and R502 and indicates how the selection can be made to ensure low environmental impact yet satisfying the equipment manufacturers' requirements for nonflammability and good performance. These factors will be related to molecular structure.