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Defining the required trackability level of the target condition for the testing facility reconditioning unit represents an unresolved challenge in improving the reproducibility of load-based tests and corresponding performance rating standards development. To enhance the reproducibility of such testing methodology, this paper presents and discusses a new feed-forward compensation technique based on the development of a transfer function model for the delay and offset characteristics of the psychrometric room's air temperature and humidity modulations with reference to the target signal from the room emulator. It is demonstrated that the proposed methodology enables offset and delay reduction in the trackability of the return air condition within 60 s at different testing conditions, enhances the reproducibility of the test results to limit performance deviations to within 2 %, and achieves closely matched controlled parameter modulations during load-based tests. [ABSTRACT FROM AUTHOR]

• Visualization experiment using a high-speed camera of a vertical sliding vane rotary engine. • Investigate the effect of compressor rotational speed on vane contact. • Effect of oil supply amount and temperature on vane chattering. • Influences of ratio of compressor discharge pressure and supply pressure on vane and cylinder contact. In this study, the impacts of various factors on the chattering phenomenon in sliding vane compressors, which is a crucial aspect that influences their performance and efficiency were explored. The analysis focused on the compressor rotational speed, pressure ratio, and operating temperature, considering both ambient and heated conditions. The aim was to provide a comprehensive understanding of the relationship between these factors and the occurrence of chattering at different operational intervals, as well as the vane sealing performance and adherence to the chamber wall. The methodology involved examining vane behavior and the chattering occurrence across three intervals under various conditions, specifically looking at oil films formation and sealing performance degradation. The experimental results provided notable insights into the chattering phenomenon. It was shown that as the pressure ratio increased and the compressor rotational speed decreased, the sealing performance deteriorated. Moreover, when operating under heated conditions, a decrease in oil viscosity leads to reduced friction between the vane and bearing, improving vane adherence compared to ambient conditions. The methodology and findings of this study provide insights into the chattering phenomenon in vane compressors by considering the interplay between various factors. The results emphasize the importance of optimizing the compressor oil refueling flow, rotational speed, pressure ratio, and operating temperature, to ensure proper lubrication and efficient interaction between the vanes and compression chamber walls for improved compressor performance and reduced operational challenges. [ABSTRACT FROM AUTHOR]

In a vapor compression refrigeration system, the oil enhances the efficiency of the compressor but impairs the performance of the heat exchanger. This paper focuses on the experimental study of the influence of oil quantity on the operational stability of CO 2 air conditioning system. The operational stability of the system under different oil charge quantity and operating conditions is studied. The experimental results indicate that when the oil circulation rate increases to a certain value, the adjustment of electronic expansion valve (EXV) opening or the compressor speed will cause system fluctuation and the outlet of evaporator gets close to no superheat. The critical oil circulation rate of the experimental system is about 9.2 %. The analysis of the fluctuation shows that it becomes more severe with the increasing of the refrigerant mass flow rate. When the mass flow rate increases from 210 kg∙ h −1 to 250 kg∙ h −1 at 7000 r min−1 of compressor speed, the fluctuation frequency increases from 0.072 Hz to 0.095 Hz. The occurrence of unstable phenomena has remarkable impact on system performance, the maximum difference of this system in instantaneous cooling capacity and COP during the fluctuation period is respectively 0.5 kW and 0.13. [ABSTRACT FROM AUTHOR]

Ice storage sphere systems are favored in the field of energy storage, however, the poor thermal conductivity of phase change materials (PCM) seriously weakens their wide application. Metal foam has been shown to enhance its heat transfer. In this paper, we investigate the impact of varying the filling radius ratio of foam metal to further improve energy storage performance and reduce costs in ice storage spheres. Computational fluid dynamics are employed to analyze the heat transfer and solidification processes. The enthalpy-porosity method is used to describe PCM solidification, while the local equilibrium thermal (LET) model characterizes heat transfer between the PCM and foam metal. The study explores temperature field variations, solid phase fraction changes, solidification times, and cold storage volumes, accounting for natural convection. By comparing solidification rates and other relevant parameters, the effect of foam metal filling on the solidification process is explored. Moreover, a new evaluation index is proposed, which can assess the overall performance of ice storage systems in real-time, considering market prices. The results show that natural convection is the primary heat transfer mode in pure PCM-ffild ice storage spheres, whereas smaller foam metal filling radii significantly inhibit natural convection, resulting in heat conduction as the dominant mode. Without specific requirements, an optimal fill radius ratio of 9/13 is determined. This paper offers a comprehensive understanding of cold storage employing various foam metal filling radios, contributing to advancements in efficient thermal energy storage systems. [ABSTRACT FROM AUTHOR]

• Performance of an AAC system was investigated for different types of compressors and refrigerants. • The COP of the R1234yf system with VCC and FCC is about 13.6% and 20.1% lower than the R134a one, respectively. • The exergy destroyed in the system with VCC is 1.7%... 52.7% lower than that with FCC. • The exergy destroyed in the evaporator and condenser for R1234yf is less than that for R134a. In this study, the performance of R1234yf as an alternative to R134a has been experimentally investigated in an experimental automobile air conditioning (AAC) system with variable (VCC) and fixed (FCC) capacity compressors. The AAC system was equipped with original components and instruments for mechanical measurements. The experiments were conducted for both types of compressors and refrigerants at various compressor speeds, air temperatures entering the evaporator and condenser and air speeds passing over them. The performance parameters of the AAC system have been evaluated by performing energy and exergy analysis based on the experimental data, and the results were presented in the form of comparative graphics. The experimental results show that the VCC compressor limits the refrigerant flow rate when the capacity control system is activated due to the decrease in the evaporator and condenser air inlet temperatures and the increase in the compressor speed. It was found that the coefficients of performance (COPs) of the R1234yf AAC system with VCC and FCC were approximately 13.6% and 20.1% lower than those of the R134a system with VCC and FCC, respectively. For both refrigerants, in the AAC system with VCC, the total exergy destruction rate per unit cooling capacity was 18.2% − 47.5% lower compared to the system with FCC. The R1234yf AAC system experiences lower exergy destruction in the evaporator and condenser compared to the R134a system, while it practices higher exergy destruction in the compressor and expansion device in comparison to the R134a system [ABSTRACT FROM AUTHOR]

This article presents the results of a novel concept of heat and cold decoupling from magnetocaloric materials (MCM) by unidirectional fluid flow. An experimental setup was developed to analyse the heat/cold decoupling and determine the optimal process parameters. Three different kinds of magnetocaloric material samples were analysed by using this setup. Comparing the measuring results to those of existing active magnetic regenerator (AMR) systems shows a very good performance and indicates a higher achievable thermal power output when using a unidirectional fluid flow. [ABSTRACT FROM AUTHOR]

• Heat pump condenser waste heat utilization reduces thermal pollution. • The system simultaneously produces cool air, fresh water, and hot water. • Novel duct design to accommodate the integrated system occupies less floor area. • The system plays in hot and humid climates more efficiently. Throughout the functioning of an air conditioner working on the principle of vapor compression (VCR system), the heat which is taken up by its evaporator, is thrown away by its condenser. The heat rejected by the condenser is frequently wasted, and it actually causes thermal pollution by increasing the temperature of the surrounding air. Aside from this, freshwater shortage is a severe issue in many regions. With the use of the waste heat of VCR system, it is intended to combine the air conditioning and humidification-dehumidification (HDH) water desalination, and to address these problems. The system supplies potable water, cool air, and warm water whilst avoiding the thermal pollution. Though the integration of the cooling and the desalination units has attracted the interest of some scholars, the duct construction in the current work is the new idea. In this study, the required spray water temperature in humidifier is found considering the human comfort inside the cabin. The impacts of ambient conditions, temperature of saline water, and efficiency of the humidifier on output and performance parameters are explored. The thermodynamic model developed in this research is validated by experimental studies. For the provided operating conditions, the gained output ratio (GOR), the cooling performance (CP), the energy performance coefficient (COEP), and the exergetic efficiency are 2.26, 0.70, 1.94, and 18.67%, respectively. [ABSTRACT FROM AUTHOR]

• A three-dimensional simulation for in-depth analysis of desiccant wheels. • Mass and energy balances are coupled with species transports and reaction kinetics. • Time-dependent and steady-state analyses of reaction, temperature, and water distributions. • Parameter optimization to achieve higher thermal efficiency and moisture removal. Hitherto air-conditioners have severe shortcomings because of the inherent need to maintain the cooling coil temperature significantly below the air's dew point. Their energy efficiency can be improved by employing desiccant wheel dehumidifiers that offer independent humidity control. Although numerous experimental and theoretical studies have evaluated desiccant wheels' performance, no existing investigation yields a detailed account of its localized temperature and humidity distributions. Therefore, a new three-dimensional mathematical model was developed to study the time-dependent and steady-state temperature, humidity, and reaction distributions. The model predicted the performance with the maximum discrepancy of ±10% in both temperature and humidity ratio. It also revealed that the countercurrent airflow configuration has a more uniform reaction distribution than the concurrent configuration. The parametric analysis using the model revealed that higher regeneration temperatures require smaller regeneration angles. With the regeneration temperatures ranging between 110 and 50 °C, the optimal regeneration angles span 120–180°. Additionally, the dehumidification performance could be easily improved by increasing the wheel's rotation speed at low desiccant mass since coating more desiccant on the wheel is costly and inconvenient. [ABSTRACT FROM AUTHOR]

• CYCLE_D-HX: vapor-compression cycle model w/ thermodynamic & transport properties. • CYCLE_D-HX: screen refrigerants & design systems w/ tube-based forced-convection HX. • Tests with R-134a, R-410A, R-513A, R-450A, Tern-1, R-1234yf, R-32, R-452B, R-454B. • COP and volumetric capacity predicted within 3%; for basic cycle. • Low-GWP refrigerants evaluated using simulations w/ optimized HXs and compressor. CYCLE_D-HX is a semi-theoretical model that simulates the performance of a vapor-compression cycle with forced-convection heat exchangers for specified temperature profiles of the heat source and heat sink. In this study, we validated CYCLE_D-HX using experimental measurements from a small (< 4 kW capacity) heat pump test apparatus operated in cooling mode. The tested refrigerants included the medium-pressure refrigerant R-134a and candidate replacements with a lower global-warming potential (GWP): R-513A, R-450A, Tern-1 (R-134a/1234yf/1234ze(E) 49.2/33.8/17.0 mass fraction,%), R-515B, and R-1234yf. We also tested high-pressure refrigerant R-410A and candidate replacements with lower-GWP: R-32, R-452B, and R-454B. The model generally agreed with experimental results, with COP and volumetric capacity overpredicted by (0 – 3)% for the basic cycle, and by (0 – 5)% for the cycle with the liquid-line/suction-line heat exchanger (LLSL-HX). We applied the model to evaluate the performance of the refrigerants in a system with optimized refrigerant circuitries in the evaporator and condenser. The simulations showed the lower-GWP medium-pressure refrigerants, including some non-flammable blends, had COP (0.2 – 2.3)% less than R-134a. The lower-GWP high-pressure refrigerants, which all have the '2L' flammability rating, had COP (2.3 – 3.2)% higher than R-410A. [Display omitted] [ABSTRACT FROM AUTHOR]

• Thermophysical and tribological analyses of nanolubricant carried out for Air conditioning (AC) application. • Nanodiamond (ND) and POE experiments examined vol.% from 0.05 to 0.5% with temperature ranges of 10 to 100°C. • ND/POE nanolubricant properties data validated and correlated for density, thermal conductivity, and viscosity. • 0.1 vol.% of ND/POE nanolubricant yielded the optimum minimum coefficient of friction (COF) • ND/POE nanolubricant showed potential for AC compressor improvement. Compressor oil lubricant plays a vital role in enhancing the performance of air conditioning (AC) systems. Thermophysical and tribological properties, as well as physical stability, of Polyolester (POE) oil dispersed with nanodiamond (ND) have been evaluated experimentally to determine its suitability and feasibility for utilization as a nanolubricant in AC compressors. Thermophysical properties correlations were developed for the ND/POE nanolubricant with volume percentage and temperatures ranges of 0.05 to 0.5% and 10 to 100°C, respectively. The density, thermal conductivity, and viscosity were found to increase with increasing ND particle concentration and reduced with increasing preparation temperature. The developed thermophysical properties correlations showed relatively accurate predictions with a maximum mean absolute error (MAE) of 6%. The nanolubricant at 0.1 vol.% showed the lowest coefficient of friction (COF) to improve the frictional power losses. The ND/POE nanolubricant exhibited a well-dispersed stability using both the photograph image capturing approach and ultraviolet-visible spectroscopy (UV-vis) analysis. As a result of the enhanced thermal, tribological and stability qualities, prolonged lifespan and cool operation of AC compressors are anticipated when utilizing POE oil containing up to 0.1 vol.% of ND. [ABSTRACT FROM AUTHOR]

• A combined generator including a double function of ammonia vapor generation and purification is developed and integrated in an NH 3 -H 2 O absorption chiller. • The impact of operating parameters at the inlet of the combined generator is investigated. • A design of experiments is defined to determine the effects of operation conditions on the combined generator performances. • The impact of the solution mass flowrate and the heating temperature on the machine performance is investigated. The present experimental work investigates the impact of an innovative falling-film and plate combined generator, associating vapor production and purification, on the performance of an NH 3 –H 2 O absorption chiller of 5-kW cooling capacity. The impact of the flooding of the lower part of the exchanger on the performance of the machine is investigated: It decreases the COP by 33% and cooling capacity by 38%. Solution sub-cooling at the combined generator inlet improves the purity of the ammonia vapor produced, but degrades the performance of the chiller. A design of experiments is defined to characterize the performance of the combined generator, which is highly impacted by the solution mass flowrate and concentration. Then, two correlation forms are used to predict the performance, and the adapted NTU model yields better results. Finally, for an air-conditioning application, a low solution mass flowrate allows the energy consumption to be reduced by approximately 15% but it requires a higher temperature for the heat source; while the increase in the solution mass flowrate degrades the performance but enables the machine to self-regulate at a low heat source. [ABSTRACT FROM AUTHOR]

• The characteristics of refrigeration and air conditioning systems in Colombian health sector. • The health sector is interested in promoting adequate refrigeration and air conditioning systems. • The importance of a good design that integrates environmental criteria, regulatory compliance, and energy efficiency. • It is important to perform cost benefit analyses in the selection of refrigeration and air conditioning systems. Refrigeration and air conditioning systems play a fundamental role in the health sector by maintaining necessary climatic conditions through the control of temperature and humidity, and maintaining a clean and germ-free environment that can contribute to the well-being of the patients and prevent the spread of diseases. The health sector is ranked fifth among the highest greenhouse gas emitting sectors worldwide. Thus, the objective of this study is to analyze the challenges and barriers to improving refrigerant and air conditioning systems to reduce the environmental impacts of the Colombian health sector. A sample of 230 answers was obtained from the individual surveys, and 14 focus groups were developed, with an average of 10 to 12 attendees per group. The results indicated that the health sector is interested in promoting adequate refrigeration and air conditioning systems, although different challenges were observed related to knowledge, awareness, qualified personnel, and financial restrictions. Other barriers include the costs and a lack of funding for these systems and a lack of information and knowledge on the latest technologies. The main recommendations for policymakers are associated with the design of guides and materials on the matter, the design of communication and outreach campaigns, the certification and recognition of entities that carry out efficient and environmentally friendly management processes for refrigeration systems, and promote financing instruments and information describing the associated benefits. These results are important for policymakers to promote adequate and efficient strategies and programs for achieving technological changes in refrigeration and air conditioning systems. [ABSTRACT FROM AUTHOR]

• This article focuses on designing FAM Z05 Zeolite-water and silica gel-water adsorption beds. • PVA glue for coating Zeolite with a weight of 1.2 kg, and PVP glue for coating Zeolite with a weight of 1.4 kg were applied on two adsorption beds. • The effect of three different hot water temperatures on the performance of the system was studied. • In this article, the performance of the system at five cycle' times of 20, 25, 30, 35 and 40 minutes was evaluated. The main purpose of this work is to focus on comparing a FAM Z05 Zeolite-water and silica gel-water for designing two adsorption beds and evaluating the performance of the system. Two adsorption beds are tested in this study, the first one is using Polyvinyl acetate (PVA) glue for coating Zeolite with a weight of 1.2 kg, the second one is using polyvinylpyrrolidone (PVP) glue for coating Zeolite with a weight of 1.4 kg. The cooling water temperature of 25 °C and the chill water temperature of 20 °C are fixed during the experimental work, whereas three different hot water temperatures of 60, 70 and 80 °C are tested and changed, and five cycle' times of 20, 25, 30, 35 and 40 minutes are changed to investigate their effects on the performance of the system. The test results show that the Coefficient of Performance (COP) on PVA glue at hot water of 70 °C is higher than that on PVP glue and this can be explained by the fact that the PVP glue blocks the porosity of the Zeolite and then deactivates the active nucleation sites which results in decreasing the adsorption of the water vapor. It is also observed that COP increases with increasing the cycle time. In addition, comparing the performance of the Zeolite adsorption bed with PVA glue to the silica-gel adsorption bed, the desorption temperature is much lower, and SCP at hot water of 80 °C is better than other types of coating glues. [ABSTRACT FROM AUTHOR]

• A novel rotary compressor of multiple vanes and a rotating cylinder is introduced. • The compressor is deemed to be energy efficient yet low in gas pressure pulsations. • Mathematical models are formulated to describe its operational characteristics. • A prototype is instrumented and tested in an R134a refrigeration system. • Good agreement is obtained between the predicted and measured mass flow rates. This paper presents a new variant of the Revolving Vane (RV) compressor, suitable for applications that require high cooling capacity yet low pressure pulsation. By adding supplementary free sliding vanes into the original RV mechanism, the compressor produces multiple discharge cycles per revolution, and hence, it can be configured to produce high volumetric capacity with lower pressure pulsations which are expected to lower the discharge noise level. In this paper, the working principles and the theoretical modelling of the multi-vane RV compressor are presented. A functional prototype has been designed, fabricated, instrumented and tested at the industrial grade compressor performance test bench, using refrigerant R134a as the working fluid. The prototype has operated at 1000 to 2000 rpm and attained pressure ratios of 5.3. The prototype's mass flow rates and volumetric efficiency were successfully measured and correlated with the predictions from numerical simulations. Discrepancies between the predicted and the measured mass flow rates are within ±15%. [ABSTRACT FROM AUTHOR]

• Electric vehicle air conditioning operating points and cooling loads provided. • Ultrahigh-speed centrifugal compression system simulated using low-GWP refrigerants. • Greater cooling loads generated at lower input power requirements. • Requires improved heat exchangers to handle condenser and evaporator temperatures. • Azeotropic refrigerants offer higher cooling capacity at higher pressures. 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. [ABSTRACT FROM AUTHOR]

• Air conditioning refrigeration achieves by guiding refrigerant vapor to mid-absorber. • Parallel PR cogeneration KC matches heat source well in cascade boiler and generator. • Leading generator dilute solution to low-pressure absorber has better performance. • Performances are improved by optimizing solution concentrations and boiler superheat. • Refrigeration/power ratio extends to 1.192 with boiler bubble point Δ t rises to 60 K. A parallel power/refrigeration cogeneration Kalina cycle (PPR-KC) system with adjustable refrigeration/power ratio that developed on the basis of the triple-pressure Kalina cycle system was analyzed. The PPR-KC system can produce refrigeration with temperature ranging in either air conditioning or ice making by switching the exhaust refrigerant vapor to the mid-pressure absorber or to the low-pressure one. The influences of the dilute solution from generator to the destination of either mid-pressure absorber (plan A) or low-pressure absorber (plan B) via recuperators on the performances of the PPR-KC system for air conditioning were investigated. The results show that the PPR-KC system matches well the heat source in cascade arranged boiler and generator thus showing excellent thermal performance by optimizing the solution concentrations, boiler superheat and other parameters. Under the given temperatures of heat source 400°C and cooling water 30°C respectively, the variation trends of the cycle parameters and performances of both plan A and plan B are presented. The power recovery efficiency of plan B is about 1.6% higher than that of plan A. When boiler bubble point temperature difference increases from 20 K to 60 K the refrigeration/power ratio of plan B climbs from 0.475 to 1.192. [ABSTRACT FROM AUTHOR]

Desiccant coated heat exchanger (DCHE) has shown great potential for dehumidification in vapor compression cooling systems and has been widely concerned in the research field of air conditioning, as well as heat and mass transfer in recent years. This paper is aimed at providing fundamental knowledge and research progresses on DCHE for dehumidification and cooling. Initially, DCHE dehumidification is chosen as the research object in this review due to its superiority of the principle by comparing with other two typical dehumidification processes, which are condensation dehumidification and rotary-wheel dehumidification. Then, intermittent dehumidification and continuous dehumidification as two operation modes of DCHE are compared. Finally, the variation characteristics of temperature and humidity during operation are discussed. The current studies of DCHE are reviewed from four aspects, including desiccant coating, cooling source, regeneration heating source and basic heat exchanger. The performance analysis of DCHE is then conducted, according to the different effects of above aspects acting on dehumidification performance, cooling performance and energy efficiency of DCHE. The ongoing researches indicate that the rational construction of DCHE is an effective way to achieve its multi-objective performance optimization. The significant progress of DCHE lays the foundation for applications on other fields. However, further research is required in the field of the selection of desiccant coatings and the structure of heat exchangers to broaden its application market. [ABSTRACT FROM AUTHOR]

• Refrigerant place on the market (POM) in Europe will suffer a significant cut in 2021. • Up to 2020, European refrigerants POM has been respected, despite the sustained demand. • Meeting the 2021 quota will be challenging due to inertia in the adoption of POM mitigation measures. • Industrial, stationary and commercial refrigeration will concentrate more than half of the total refrigerant demand, measured in CO 2 e. The European Union (EU) Regulation on fluorinated greenhouse gases (F-gases) has encouraged to reduce gradually the number of hydrofluorocarbons (HFC) that can be placed on the market (POM) to 21% of the baseline level in 2030. However, to this day, the EU refrigeration, air conditioning and heat pump (RACHP) market is still dominated by these substances. This study describes a methodology to estimate the refrigerant demand by refrigeration, air conditioning, and heat pumps available to the EU customers until 2030. The work is based on the most relevant current statistical data, refrigerant distribution (R134a, R404A, R407C and R410A), and future technology acceptance and trends. The study presents a refrigerant demand grow scenario and provides a basis for a closer market follow-up to facilitate refrigeration industry stakeholders' decision-making. The results indicate that by 2021 will be challenging to accomplish the fluorinated gas quota considering the current HFC phase-down process. However, by 2030, the transition is possible in the EU, assuming the additional measures to mitigate the leakage from already installed equipment will be taken. By that time, natural refrigerants, including CO 2 , ammonia, and hydrocarbons, can dominate the market. However, the share of HFC or HFC/HFO mixtures in operation is still significant (R32 or mixtures with similar behaviour, and R404A low flammability alternatives). Consequently, industrial and commercial refrigeration (large scale applications) will concentrate approximately half of the GWP weighted CO 2 e, negligible direct emissions for domestic refrigeration or mobile air conditioning, dominated by natural refrigerants pure HFO refrigerants, respectively. [ABSTRACT FROM AUTHOR]

In warm and humid climates, a primary source of building energy consumption is dehumidification of conditioned air supplied to the building spaces. The system analyzed utilizes a selective membrane to remove water vapor from ambient air instead of a vapor compression cycle or a desiccant. This work analyzed a membrane dehumidification system with a focus on the system energy performance. A system performance goal was set by the project sponsor for an inlet air condition of 32.2 °C and 90% relative humidity, an outlet condition of 12.8 °C and 50% relative humidity and a total cooling load of 3.52 kW resulting in a target COP latent for the system of 3.34. Models of the basic system components were used to develop the system, analyze operating parameters and predict performance. The results indicate that the system requires two optimizations to meet the target performance: condenser pressure optimization and the use of multiple membrane segments operating at different pressures. Subsequently, a model was developed to analyze the performance of the final system configuration under a variety of operating conditions and yielded a maximum COP latent of 4.37 for membrane properties comparable to those of the earliest membrane module tested. This may be compared with a COP of about 3.5 for current refrigeration technology at these conditions. The best small membrane sample produced to date would increase the COP latent of the membrane system to well above 8, suggesting that the membrane system has high promise. Uncertainty analysis was also performed to assess the simulation results. [ABSTRACT FROM AUTHOR]

• Allocation principle of NTU m in the HPLDAC system is theoretically deduced. • The nonlinearity of the iso φ line of air affects the allocation principle. • Only when the total NTU m below 10, does the allocation principle matter. • This study suggests equal allocation cannot always lead to the optimal performance. Heat and mass transfer capacities of dehumidifier and regenerator significantly affect the performance of a heat pump driven liquid desiccant air-conditioning (HPLDAC) system. When the dehumidifier and regenerator have the same air flow rates, an equal allocation of the total usable number of mass transfer units (NTU m) between the dehumidifier and regenerator is an intuitive choice. However, whether the equal allocation can result in the optimal system performance is still a pending question. Thus, the optimization principle of NTU m allocation between dehumidifier and regenerator in the HPLDAC system is theoretically deduced and illustrated in this study. The results reveal the equal allocation is recommended when the nonlinearity of the iso φ line is insignificant, whereas allocating more NTU m to the dehumidifier than regenerator is recommended when the nonlinearity of the iso φ line is significant. When the NTU m values of the dehumidifier and regenerator are large enough, further increases of the NTU m values show limited effect on performance improvements of the dehumidifier and regenerator. Only when the total NTU m is below 10, does the NTU m allocation optimization play an important role in the system performance improvement, and is a pre-estimation necessary for achieving the optimal system performance. [ABSTRACT FROM AUTHOR]

Refrigerant charge is one of the most important factors affecting the performance of the transcritical CO 2 automotive air conditioning system. In the presented study, a transcritical CO 2 automotive air conditioning system test bench was set up, and the effect of normalized charge on the temperature, pressure and system performance were studied. A novel standard for judging the appropriate normalized charge was proposed. Meanwhile, the pressure-enthalpy diagrams under different charge was shown. Moreover, the influence of the ambient temperature and the compressor frequency on the charge characteristic were also experimentally studied and analyzed. Results revealed that the discharge temperature, the suction temperature and the temperature before the EXV were the optimal parameters to judge the charge characteristic. As the ambient temperature and compressor speed increased, the required charge amount decreased. It was concluded that the optimal normalized charge range of the transcritical CO 2 air-conditioning system was recommended to be set between 0.111 and 0.321. The results provide good guides in charge of automobile air conditioning system. [ABSTRACT FROM AUTHOR]

• Energy-efficient 1-Decanol-Expanded graphite composite (CPCM) was prepared. • CPCM has 84.99% of 1-Decanol, and it reduces the chiller operating time by 81.85%. • Thermal conductivity of CPCM is 16.33 times higher than that of 1-Decanol. • CPCM is having high freezing temperature (∼4.1 °C) and zero degree of supercooling. • Utilisation of CPCM paves the way for efficiently storing and recovering cold energy. Performance of a typical ice-based cold thermal energy storage system (CTESS) is immensely affected by its supercooling nature and low freezing temperature (0 °C). In this study, 1-Decanol (PCM) was recognised as a potential replacement for ice as it is cost-effective as well as having zero degree of supercooling, and high freezing temperature (5 °C). High thermal conductivity PCM-Expanded graphite (EG) composite (CPCM) was prepared by incorporating the PCM into the porous structure of EG. The thermal conductivity, specific heat, and thermal cycling stability of CPCM were studied. Further, the charging and discharging characteristics of CPCM were investigated in a 64 mm diameter spherical capsule at -3 °C and 13 °C wall temperatures, respectively. CPCM has an incorporation efficiency of 84.99%, and its thermal conductivity is 16.33 times higher than that of PCM. CPCM and PCM have good thermal reliability for 1000 cycles. The freezing temperature of CPCM is ∼4.1 °C higher than that of ice and its charging time is 81.85% lower than that of PCM, which signifies that the chiller operating time can be reduced by 81.85% to store the specified amount of energy in CPCM. Further, the time-averaged charging and discharging rate of CPCM is 5.51 and 5.97 times higher than that of PCM, respectively. Experimental results concede that CPCM is having high freezing temperature (∼4.1 °C), zero degree of supercooling and enhanced energy storage characteristics, which ensure that the utilisation of CPCM paves the way for efficiently storing and recovering the energy. [ABSTRACT FROM AUTHOR]

This paper covers a basic model for analyzing the performance of the Claridge-Culp-Liu dehumidification process. The fundamental process efficiency limit for dehumidification is close to COP Carnot , but for the eight dehumidification cases examined, the limiting or ideal energy use required is 26% to 56% that of a Carnot condensing system as shown in an earlier paper. The model presented in this paper is used to show the membrane system performance reduction caused by finite membrane area, finite water vapor permeance, non-zero air permeance, non-zero system air pressure drop, non-ideal compressors, vacuum pumps, and condensers. The performance of a "conservative" membrane system based on the use of existing components is computed for eight specific conditions along with that of a "target" system that assumes expected component performance after additional future component development. The "conservative" membrane system would use 36% to 66% as much energy as a system with a COP=7 chiller to produce the same dehumidification for the eight cases examined while the "target" system would use 15% to 40% the energy of a system with a COP=7 chiller. In addition to the significant energy reduction over conventional technology, the membrane system offers the advantages of: 1) no HFC refrigerant use; 2) direct isothermal control over humidity ratio setpoint; 3) maximum capacity occurs at design conditions; and 4) system generates pure water extracted from air as a by-product. [ABSTRACT FROM AUTHOR]

• A novel semi-coupled solid desiccant heat pump system is proposed. • A mathematical model of the novel system is established. • Some of the designed parameters is optimized with the model. • Novel system can supply air with lower temperature and temperature variation. Solid desiccant heat pump system (SDHP) can handle sensible and latent heat load simultaneously with high coefficient of performance (COP). However, in such system, supply air temperature is relatively high and unstable due to the frequent switch between desiccant coated heat exchanger as evaporator and condenser. In order to overcome these drawbacks, the concept of semi-coupled solid desiccant heat pump (SCSDHP) system is proposed in this paper, then a mathematical model is established to investigate the feasibility of this novel system. Calculation shows that under ARI (Air-conditioning and Refrigeration Institute) summer condition silica gel coating with density of 0.25 kg m −2 is optimal, and area ratio between desiccant coated evaporator and conventional evaporator of 1:1 is recommended. Furthermore, compared with conventional SDHP system, supply air temperature can be 4.5~7°C lower and the variation range of supply air temperature decreases by 16~21°C. Also, effects of main operating parameters including the temperature and relative humidity of outdoor air on the performance of SCSDHP system are investigated. [ABSTRACT FROM AUTHOR]

• The transient characteristic and flow of the scroll compressor is studied using CFD. • Gas is under compressed in downside chamber and over compressed in upside chamber. • The pressure difference between the two chambers is caused by the discharge timing. • A novel discharge port is proposed to improve the compressor efficiency by 2.4%. • The largest pressure unbalance between the upside and downside chambers reduces 50%. Scroll compressor is a key component of the air conditioner/heat pump system in electric vehicle. This paper focuses on the impacts of discharge port design on the transient performance and flow mechanism of the scroll compressor. A three-dimensional unsteady computational fluid dynamic model is established and validated. The computational domain includes inlet duct, scroll working chamber, discharge port, check valve, plenum chamber and outlet duct. R134a is used as the working fluid. The impacts of the position of the conventional circular port on the transient characteristic and flow loss mechanism of the scroll compressor are studied. It is found that large pressure difference between the two central chambers is resulted from discharging time difference of the two chambers. It inevitably leads to under compression in downside chamber and over compression in the upside chamber at designed condition. The conventional circular discharge port cannot address this problem. Therefore, a novel discharge port with a tail is proposed to retard the discharge time of the downside chamber and advance that of the upside chamber. It is found that the isentropic efficiency of the scroll compressor is improved by 2.4%. The maximum pressure unbalance between the upside chamber and downside chamber is reduced by 50%. [ABSTRACT FROM AUTHOR]

• The performance of an air-conditioning unit with an add-on device was investigated. • The add-on was found to reduce the radial velocity, hence streamlining the flow. • An overall performance enhancement of 5.4% was found when using the add-on device. Performance measurements of an air-conditioning system was performed with and without a Passive Add-on Device installed on top of its condenser unit. This device has a cylindrical shape with fixed radial blades, combining characteristics that streamline the flow, while changing its rotational speed. In addition to the thermodynamic measurements, the flow velocity distributions at the outlet of the condenser fan unit (no Add-on Device case) as well as at the outlet of the Add-on Device were both measured using hot-wire anemometry. The Add-on Device increased flow rotation as well as uniformity of axial velocity, while reducing the radial velocity component. By streamlining the flow, the Add-on Device led to enhancements by 5.4% in terms of overall coefficient of performance of the tested air-conditioning unit, within the range of tests conducted in the present work. [ABSTRACT FROM AUTHOR]

• A solar thermal absorption cooling system was implemented in an isolated school. • Optimal operational strategies were determined to cover the cooling needs. • The balance of plant is the most expensive aspect of the project. • If the proposed strategies are not used, the air conditioning needs are not met. In this work, we present the simulation study of a LiBr-H 2 O solar thermal absorption air conditioning system, installed in an isolated primary school in the community of Puertecitos, Mexico. The collection system consists of 110 m2 of evacuated tube solar collectors that produce the thermal energy needed to activate the chiller, while four cooling coils of 8.75 kW each cool the classrooms of the school with the chilled water produced. The characteristics of the system's equipment are used and a simulator is developed to determine the optimum operational strategies, given the conditions to which it will be subjected before the start-up of the plant. This is intended to ensure the comfort conditions of the students within the classrooms during the weekly class periods. The results show that the installed system is capable of satisfying the cooling needs of the school with the simulated strategies, but for a stable operation, periods of time must be dedicated for the recovery of energy inside the thermal storage tank. Some experiences are mentioned, both of the start-up and economic, related to an installation in an isolated community. The cost of the balance of plant was the highest with 36% of the total project, followed by the chiller and the solar field with 25 and 18%, respectively. The preliminary experimental results obtained during the implementation of the system are presented, where some of the operational strategies resulting from the simulation study can be confirmed. [ABSTRACT FROM AUTHOR]

Hydrofluoroolefins (HFOs) have been attracting increasing attention over the recent decade, and some of them are regarded as candidates for next-generation refrigerants. In this paper, the flammability characteristics of forty-eight HFOs and blends have been relatively comprehensively and systematically summarized, for a variety of experimental conditions on the basis of the results reported in academic journal papers, professional books, conference proceedings, technical reports, patent applications, material safety data sheets, and presentations. The following flammability characteristics of HFOs are reviewed, including the lower flammability limit, upper flammability limit, burning velocity, minimum ignition energy, hot surface ignition temperature, autoignition temperature, thermal decomposition temperature, heat of combustion, product of combustion, etc. Besides, a new correlation equation has been suggested to roughly indicate the burning velocity and heat of combustion rankings of the fluorinated hydrocarbons once their basic molecular characteristics are known. In addition, the experimental methods, influencing factors, inerting mechanism, and developing tendency of the flammability of the HFO refrigerants are discussed. The details presented are expected to be useful for researchers working in the field of heating, ventilation, and air conditioning and refrigeration. [ABSTRACT FROM AUTHOR]

• Performance of a two circuits CO 2 train AC system has been experimentally tested under different operating conditions. • An introduction of a numerical model of CO 2 train AC system has been presented. • Effects of operating conditions on the train AC system have been discussed in detail. • An error analysis between the test and the numerical has been presented. • A related equation between the gas cooler outlet temperature and the optimum high pressure is presented. This paper aims to investigate the effects of different operating parameters on the performance of a transcritical CO 2 air conditioning system for trains. Similar designs of automotive CO 2 air conditioning system are used in the train system such as internal heat exchanger (IHX) to improve the system efficiency. Experimental results are presented for the performance characteristics of the CO 2 train air conditioning system with two independent circuits under different test conditions such as different refrigerant charge amount, compressor working frequency, indoor air volume flow rate and outdoor chamber temperature. Two different operating modes of the two circuits are also included in this research. For mode I while only one circuit is working, the test results show that the maximum cooling capacity and coefficient of performance (COP) is 24.3 kW and 2.7, during 55 Hz and 40 Hz compressor working frequency conditions respectively. Also, the cooling capacity and COP reach the minimum, 16.2 kW and 1.5, when the outdoor chamber temperature is 45°C. For mode II while both two circuits are working, the results show that the cooling capacity and COP are 42.0 kW and 2.4, respectively. The system performance error between the test and numerical modeling which directs the design of the system is within ±5%. Furthermore, an optimum high pressure control algorithm for the transcritical CO 2 cycle of the train AC system is also presented. [ABSTRACT FROM AUTHOR]

• A domestic dehumidifier model is validated and presented. • Geared domestic dehumidifiers with TXV metering can perform better than capillary systems. • TXV equipped dehumidifiers less likely to experience slugging or frosting. • Economiser dehumidification rate dominant contributor to geared system. Small refrigerative dehumidifiers have shown energy efficiency improvements when operating with air-side gearing. However, the geared domestic dehumidifier has not previously been investigated experimentally for a wide range of airflow settings typical of domestic dehumidifier operation, or with different throttling schemes, and the efficiency of these systems is not well understood under household conditions. In this work, we measure the performance of a commercial domestic dehumidifier, adapted for laboratory testing, in ungeared and geared modes at a wide range of airflows and with both capillary and thermostatic expansion valve throttling to understand how the system performance is effected, for air volume flow rates of 29 L/s - 48 L/s. The measurements show that both capillary and thermostatic expansion valve equipped domestic dehumidifiers can improve energy efficiency in the geared operation mode, but the capillary equipped system is more prone to frosting and wet compression, degrading performance. [ABSTRACT FROM AUTHOR]

• An analysis of an AC system was carried out to evaluate peripheral fin condensers. • Three other types of fins were simulated for comparison purposes. • The condenser with peripheral fin provided higher UA and cooling capacity. • An average reduction of 10.5% of R-290 charge was achieved. The use of hydrocarbons as refrigerants has increased substantially in the past decades due to more severe regulations on direct and indirect carbon dioxide emissions. However, safety standards related to flammable fluids limit the amount of propane (R-290) used in air-conditioning (AC) systems. In this study, an experimentally validated numerical model for a split-type AC system is employed and, for the first time, an air-side peripheral fin geometry is used in the condenser in an attempt to reduce the refrigerant charge for a given system cooling capacity. To establish a fair basis for comparison, plain, wavy and louvered fins were also investigated in the model. A more realistic assessment of the system performance was achieved by considering the POE ISO 22 oil circulation ratio (OCR) in the computation of the physical properties of the mixture. The results have shown that, for the simulated range, heat exchangers with peripheral fins provided higher values of thermal conductance (UA) and cooling capacity than other types of fins. A substantial decrease in the R-290 mass (as high as 12.13%) was observed when peripheral fin condensers were employed. [ABSTRACT FROM AUTHOR]

• A test rig for refrigerant pipe pressure drop measurement is presented. • Standard correlations are not suitable to calculate refrigerant pipe pressure drop. • CFD predicts single-phase flow pressure drop with an accuracy of less than 30%. • One-dimensional models significantly underestimate the pressure drop of up to 55%. This study investigates the pressure drop in refrigerant pipes of a CO 2 automotive air conditioning unit. A test rig to measure the pressure drop of arbitrarily shaped pipes is presented. As boundary conditions at the inlet of the test section, mass flow, pressure and enthalpy of the refrigerant are independently adjustable to values that cover the whole operating range of a CO 2 automotive air conditioning system for cars in the premium segment. Numerical analysis using CFD and a one-dimensional modelling tool is carried out. The pressure drop for the suction pipe reaches values of up to 500 mbar. CFD simulation predicts the pressure drop with an error of 25.7% for single-phase flow whereas the deviation using one-dimensional models is 46.5%. During two-phase flow the error increases to 55.8% with one-dimensional models and 42.4% using CFD. [ABSTRACT FROM AUTHOR]

• Simulations of different hybrid desiccant A/C systems. • Absorption used for both cooling and dehumidification. • Proposed hybrid configuration significantly increases performance. • Proposed hybrid configuration allows improves control of supply air state. Air conditioning (A/C) systems serve two main functions: temperature and humidity control of the conditioned space. This work focuses on a hybrid A/C system consisting of a liquid desiccant system (LDS) and an absorption chiller. An efficient deep-dehumidification hybrid A/C system (EDHACS) configuration is proposed. It is designed to enhance both performance and control. A detailed simulation study of the EDHACS has been conducted, and selected results are described in this article. Liquid desiccant systems (LDS) are exceptionally good at air dehumidification, and hence capable of handling the latent heat load. In conventional air conditioning (A/C) systems, this task is achieved by over-cooling the air below its dew point, which leads to both thermodynamic and practical inefficiencies. An optimal A/C system may be hybrid, consisting of a chiller to handle the sensible load and a low-grade heat driven liquid-desiccant-system (LDS), potentially with storage capability, to handle the latent load. The hybrid system has the added advantage of allowing independent control of temperature and humidity, thereby providing much-improved thermal comfort. Simulation results show that the EDHACS outperforms any other hybrid configuration that was tested. Its dehumidifier is split in two to take advantage of both the ambient and the chiller cooling capacity as heat sinks. By minimizing absorbent circulation between the two dehumidifiers, two distinct dehumidifier temperature levels are maintained, thereby further improving performance – resulting in increased COP and capacity values, and lower supply air temperatures. [ABSTRACT FROM AUTHOR]

In this study, the performances of a new configuration of the desiccant dehumidifier with cut-segmental silica-gel baffles and water cooling (DDSBWC) for air conditioning connected to HDH desalination unit was experimentally investigated. The proposed configuration consists of two subsystems: (i) new configuration of DDSBWC for air conditioning, which use to achieve the conditions of thermal comfort. The DDSBWC aims to improve the quality of supply cooling air by using dehumidification with the cooling process; (ii) HDH desalination unit utilized to produce freshwater. Experimental results showed that use the DDSBWC improve the dehumidification process, the average dehumidification capacity in DDSBWC reached to 10.2 g water kg dry-air −1 (0.3264 g water g silica-gel −1). This will improve the performance of the air conditioner. Within the period 9:00 am till 6:00 pm the supply air temperature, supply air relative humidity, cooling capacity, cooling COP, hourly distillate water production, and overall COP vary between 17.4–18.3 °C, 65–68%, 696–937 W, 0.40–0.622, 3.2–3.6 L h−1, and 0.40–1.584, respectively. The percentage improvement in the overall COP as compared to the cooling COP varied between 0–162.6%. The results showed that a suggested configuration is a perfect choice in hot and humid areas to achieve thermal comfort and freshwater production. [ABSTRACT FROM AUTHOR]

The Claridge-Culp-Liu Dehumidification Process is a novel and efficient approach to removing water vapor from air using a combination of membrane separation, vacuum compression and sub-atmospheric condensation. The basic theory of this process is to separate water vapor from moist air flowing across one side of a membrane by applying a partial vacuum to the opposite side of the membrane and then compressing the water vapor to its saturation pressure at the wet-bulb temperature of the ambient air so as to facilitate condensation. This process has a fundamental efficiency limit that approximates the Carnot limit, but for eight different ideal dehumidification-only cases examined herein, the process requires only 26–56% the energy required by a Carnot vapor-compression system. Furthermore, the limiting energy required by an ideal 5-stage membrane system is 16–31% that of a Carnot system for the same cases. Of special importance, the ideal Claridge-Culp-Liu Dehumidification Process requires less than 5% of the energy required by an ideal desiccant process for all cases treated. The Claridge-Culp-Liu Dehumidification Process can also be combined with evaporative cooling to provide dehumidification and sensible cooling with the temperature and humidity controlled independently. Of special importance, this system uses no HFC refrigerants, and it generates pure water as a by-product. [ABSTRACT FROM AUTHOR]

• The 1st oblique-tube condenser coil manufactured by controlled atmospheric brazing. • Thermal-hydraulic performance matching with Daikin's circular-tube coil. • Slender oblique tubes with plain fins reduce air-side pressure drop by 20.9–30.9%. • Discussion of the number of tubes per pass for the most energy-saving design. • Adjustment of air velocity and water flow rate for heat transfer augmentation. This paper presents new development of aluminium oblique-tube condenser coils with plain fins manufactured by controlled atmospheric brazing (CAB) for air-conditioning applications. The CAB technique provides good quality joints and thermal contact between oblique tubes and fins for more effective heat transfer. Performances of seven oblique-tube coils with different numbers of tubes per pass (i.e. 1, 2, 3, 4, 5, 7 and 14) were assessed against those of a commercial circular-tube coil with corrugated fins. The contribution of the slender oblique tubes with plain fins reduced air pressure drop penalties by 20.9–30.9% for 1–3 m/s air velocity. Thermal performance of the 1-tube-per-pass coil surpassed that of the commercial coil albeit not energy-saving. On the other hand, the 4-tube pass coil when matching with the heat transfer performance of the 3- and 2-tube-per-pass coils and the circular-tube coil saved water-side pump energy as high as 27.9%, 36.3% and 38.7%, respectively. [ABSTRACT FROM AUTHOR]

Abstract Typical electric vehicle thermal management system with air conditioning and battery cooling is introduced with different refrigerant flow control devices. Electronic expansion valve (EXV) and thermal expansion valve integrated with shut off valve (TXV+SOV) are adopted in such a dual evaporators cooling system as refrigerant flow control valve to investigate the benefits of EXV compared to TXV+SOV by testing. Test result shows the EXV has significant benefits of proper refrigerant distribution with less system fluctuation to avoid the dissatisfaction of customer. With the TXV+SOV control, due to mal-distributed refrigerant flow between air conditioner evaporator and battery chiller, air conditioner blow off temperature variation can reach 8°C which will significantly affect the comfort of passenger cabinet. While with EXV control, air conditioner blow off temperature is very stable. Stable control of EXV also contributes to system efficiency improvement than the TXV+SOV by saving the energy up to 20%. [ABSTRACT FROM AUTHOR]

Highlights • A CO 2 ejector system is proposed for independent indoor temperature and humidity control. • The CO 2 ejector refrigeration cycle shows 12–60% better COP compared with an isenthalpic expansion one. • Quasi-steady state investigation explains operating characteristics of the CO 2 ejector system. • Energy performance of a CO 2 GOS GCHP ejector system is predicted, and COP values vary from 3.0 to 6.1. Abstract This study presents a single CO 2 vapour-compression system for independent cooling and dehumidification of indoor air conditioning systems. A CO 2 gas cooler outlet split (GOS) ejector system is introduced to generate two levels of evaporating temperature, and therefore indoor air temperature and humidity can be controlled independently. The two-phase ejector improves energy efficiency of the CO 2 transcritical system by recovering expansion work loss. The steady state analysis shows that the COP of the CO 2 ejector system is 12–60% better than that of standard isenthalpic expansion one when the humidity load ratio covers 10–50% of the total thermal load. Moreover, transient performances of the CO 2 GOS ejector system under different indoor load conditions are simulated. It proves that the hybrid GOS GCHP ing system offers a solution to the future air conditioning sector to use the environmentally friendly CO 2 as long term working fluid. [ABSTRACT FROM AUTHOR]

Highlights • The air conditioning systems with/without a vapor–liquid heat exchanger are compared. • EER at cooling mode and COP at heating mode are improved by 9.8% and 7.4%, respectively. • Various benefits are identified at the variable operating conditions. • The enhancement mechanisms of the vapor–liquid separation evaporation are proposed. Abstract Air conditioning system consumes a large percentage of energy and its efficiency becomes important in this energy-conscious era. In this paper, a heat exchanger with vapor–liquid separation is applied to air conditioning system (system-B), it is experimentally compared to the baseline system with a conventional heat exchanger (system-A). The results indicate that at cooling mode the system-B has an improvement of EER by 9.8%, while at heating mode, it exhibits a higher heating capacity and lower power consumption, and COP is enhanced by 7.3%. Under variable operating conditions at heating mode, the system-B gets benefits over system-A from various perspectives. Moreover, the study of automatic defrosting of system-B shows well-functioning and the results meet the corresponding requirements. Finally, the mechanisms of how the vapor–liquid separation enhances heat transfer coefficient during evaporation are proposed. It is suggested that its implementation in air conditioning system brings large potential of performance improvement. [ABSTRACT FROM AUTHOR]

It is challenging and difficult for a conventional On-Off controlled single evaporator direct expansion (DX) air conditioning (A/C) system to deal with the variable latent load, unless complicated and costly supplementary measures to supply variable dehumidification ability are provided. Therefore, based on multi-evaporator air conditioning technology, a standalone DX based enhanced dehumidification air conditioning (EDAC) system with two evaporators was proposed to provide variable dehumidification ability. This paper reports on the development of a steady-state physical-based mathematical model for such an EDAC system. Firstly, a detailed description on the configuration of the EDAC system is presented, followed by reporting the development and experimental validation of the steady-state model for EDAC system. Thirdly, using the validated EDAC model, a follow-up detailed modeling study was carried out to both demonstrate that the EDAC system was able to provide variable dehumidification ability and optimize the sizing of the two evaporators used in the EDAC system. The modeling study results indicated that the EDAC system could produce variable dehumidification capacity. The modeling study results also suggested that a lower ratio of surface areas for the two evaporators in an EDAC system was beneficial to enlarging its variation ranges of both total cooling capacity (TCC) and equipment sensible heat ratio (E SHR). [ABSTRACT FROM AUTHOR]

The electric vehicles (EVs) are drawing much attention worldwide due to low fuel consumption and local pollution. However, the range of EVs is still not parallel to that of internal combustion engine vehicles. Moreover, the EV's range suffers a significant decrease in cold and hot climate due to the climate control load of the air conditioning system. These two combined making the range extension strategies a hot spot in EV research. In this paper, the review on EV range extension strategies is provided. First, the climate control load reduction strategies are reviewed. The characters of heating load in cold climate and the reduction methods are introduced. Second, the review on heat pump heating is conducted based on the different structures of heat pump systems. The combination of load reduction and heat pump heating seems to be a promising way in solving the range reduction problems. [ABSTRACT FROM AUTHOR]

The main purpose of this work is to enhance the energy efficiency of CO 2 automobile air conditioning system. Theoretical analysis demonstrated that the mixture of CO 2 and propane can improve its performance, thus, experiments have been carried out to see effects of various CO 2 -propane mass fractions of 100/0, 90/10, 80/20, 70/30, 60/40, 50/50 on the system performance at different ambient temperatures and gas cooler frontal air velocities. Experimental results show similar trends with those from the theoretical results. It has been shown that under the same compressor speed, system COP reaches highest at 60% of CO 2 mass fraction, which is 29.4% higher than pure CO 2 system and even achieves equal level of the R134a system, the optimum pressure and discharge temperature are reduced up to a maximum of 40% and 47   °C during the research range. Furthermore, comparison was carried out under the same cooling capacity by adjusting compressor speed for different mass fraction of CO 2 , results demonstrate that the use of CO 2 -propane mixtures yields a maximum COP rise of 22%even when cooling capacity is kept constant. A new optimum high pressure control algorithm for the transcritical CO 2 -propane mixture cycle has been developed based on the experimental data within a deviation of 5%. [ABSTRACT FROM AUTHOR]

The present paper aims to evaluate the performance characteristics of a split air conditioner working with R-417A under different indoor and outdoor operating conditions. A test facility was constructed and experiments were carried out to achieve the research objectives. The indoor conditions were varied in a wide range of air temperature (21–31.4 °C), air relative humidity (40.3%–61.9%) and air velocity (2.8–4.7 m s −1 ) while the outdoor conditions were changed in range of air temperature (35–51.2 °C) and air relative humidity (40.8%–81.2%). Experimental results showed that the increase in the indoor air temperature causes an enhancement in the system coefficient of performance by about 59.7%, while increasing the outdoor air temperature decreases the system coefficient of performance by about 51.6%. The system cooling capacity using R-417A was lower than that of R-22 by about 33.2% at indoor air temperature of 24.5 °C. [ABSTRACT FROM AUTHOR]

The merits of an alternative refrigerant are established based on many attributes including environmental acceptance, chemical stability in the refrigeration system, low toxicity, flammability, efficiency and volumetric capacity. In an earlier work, these criteria were used to screen a comprehensive database to search for refrigerants with low global warming potentials (GWP). The present paper summarizes the screening process and presents the performance of the “best” replacement fluids for small and medium-sized air-conditioning, heating, and refrigeration applications. In addition to considering cycle calculations based only on thermodynamic properties, a simulation model that included transport properties and optimized heat exchangers was used to assess the performance potentials of the candidate fluids. The need for this more detailed modeling approach is demonstrated for systems relying on forced-convection evaporation and condensation. The study shows that the low-GWP refrigerant options are very limited, particularly for fluids with volumetric capacities similar to those of R-410A or R-404A. The identified fluids with good COP and low toxicity are at least mildly flammable. Refrigerant blends can be used to increase flexibility in choosing tradeoffs between COP, volumetric capacity, flammability, and GWP. The probability of finding “ideal”, better-performing low-GWP fluids is minimal. [ABSTRACT FROM AUTHOR]

Kigali's amendment on Montreal Protocol has recognized the great impact of hydrofluorocarbons (HFCs) on climate change. In the European Union, the Regulation (EU) No. 517/2014 (F-gas Regulation) controls the use of HFCs in several applications. This paper reviews the recent investigations performed because of F-gas Regulation, with focus on lower global warming potential (GWP) synthetic alternatives. The GWP limit and the date of prohibition have an influence on the studies found for each application. The major relevance of the studies has been observed on mobile air conditioners for pure hydrofluoroolefins (HFOs), possibly caused by the earlier control. Additionally, a great number of studies have been found for stationary refrigeration systems using several mixtures and residential air conditioners using R32. An important number of articles investigate synthetic alternatives for domestic refrigerators given the flammability barriers for hydrocarbons in some countries. Despite higher GWP allowance on cascade supermarket systems, few articles are available on this topic. Given the extent of the current studies and the rate of new refrigerant developments, an increase in studies using the new synthetic mixture is expected in the coming years. [ABSTRACT FROM AUTHOR]

For predicting the performance of variable refrigerant flow multi-split air conditioning (VRF) systems with arbitrary layouts under various operating conditions, a general simulation model for VRF systems based on graph theory was proposed. In the present study, the directed graphs and adjacent matrixes were established to describe the systems with arbitrary layouts under cooling and heating modes, and a diagonal matrix was developed to describe the operating number of indoor units; the general description matrix of VRF systems under various operating conditions was expressed as the multiplication of the adjacent matrixes and the diagonal matrix. The component models meeting the simulation accuracy requirement were presented. A tailor-made iteration algorithm using graph-based traversal method was developed to solve the system model. The proposed simulation model for VRF systems was validated experimentally, and the model deviations of the heat capacity, temperature and pressure are within 3%, ±3 °C and ±5%, respectively. [ABSTRACT FROM AUTHOR]

This study presents a theoretical investigation into integration of phase change materials (PCMs) with an adsorption cooling system in order to provide 24-hour air conditioning. A latent heat storage unit containing PCM is used to store solar energy during the daytime, and at nighttime the conserved thermal energy and an auxiliary heater drive the adsorption chiller. The system adopts a cooling channel to reduce the air temperature. The air flow to the channel is provided by use of fans and at different fresh air ratios (FR). Room temperature and the room's maximum cooling demand for which thermal comfort can be achieved are estimated. In addition, the effects of different parameters on room temperature and solar fraction are studied. It is indicated that an optimum ACH value exists for which the room temperature is the lowest. Also, rise of ACH and FR decrease solar fraction and increase auxiliary energy consumption. It is found that when ACH = 4 and FR = 20%, daily solar fraction is 0.76 and 217 MJ of auxiliary energy is required during the 24 hours. Under this condition, thermal comfort is achieved for a maximum cooling demand of 4000 W during the 24 hours. [ABSTRACT FROM AUTHOR]

When ice slurry is employed for air conditioning, there is gap of 5–7 °C between the melting point of the ice and the cooling water temperature. However, TBAB hydrate slurry made from an aqueous TBAB solution can remove the gap because it has a more suitable melting point. Furthermore, the slurry is relatively a high latent heat of fusion and good fluidity. So, the slurry is the most promising material for air conditioning. However, it is expected that TBAB hydrate in the slurry strongly adheres to surface of a metal such as copper. However, to date, there have been no quantitative studies of the adhesion forces, so in the present work adhesion forces of TBAB hydrates to copper surface at 3 and 5 °C were measured varying TBAB solution concentrations. And the adhesion force and its surface temperature-dependency were investigated based on surface energies and observations of hydrates crystals. [ABSTRACT FROM AUTHOR]