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• HFC-152a was tested in a SL system and compared with baseline in a DX system. • The SL system showed heating performance attenuation compared with the DX system. • A heat exchanger was added in the SL system to use waste heat in the passenger cabin. • The COP of the improved SL system achieved the comparable level to the DX system. In mobile air conditioning (MAC) systems, the secondary loop (SL) structure was usually adopted when using flammable refrigerants such as R1234yf, R290 and R152a. The introduction of intermediate heat exchangers in SL system inevitably increased the temperature difference between the condensation side and the evaporation side, thereby increased the compressor power consumption and caused the performance attenuation. To overcome the attenuation, this study designed a heat recovery device which collects the waste heat from the passenger compartment to increase the evaporation temperature and reduce the compressor power consumption. Validation experiments were completed in a secondary loop heat pump (SLHP) MAC system using R152a and was compared with a baseline direct expansion (DX) system. According to experimental results, under the -10 °C outdoor temperature, the SLHP system showed performance attenuation compared with the DX system. With the increase in indoor temperature, the attenuation gradually increased to 8.96% at the indoor temperature of 20 °C. In this case, a heat recovery design was used in the SLHP system, which increased the coefficient of performance (COP) by 9.29% compared with the original SLHP system and achieved similar performance to the DX system. [ABSTRACT FROM AUTHOR]

• The leak pressure, leak hole size and wind speed are the three major parameters that affect R290 distribution. • Increasing the hole size and decreasing the wind speed will raise the maximum R290 concentration and the duration time. • A lower pressure indicates that the concentration rises slower but a maintained longer time. • Evaporator leakage is the most risky situation of the R290 MAC system. • The highest concentration and the duration time can be both significantly reduced by the SL system. The natural refrigerant R290 has been gradually investigated as an alternative refrigerant of R134a in the automobile air conditioning (MAC) systems at present. As an A3 class refrigerant, the application of R290 is associated with the greatest challenge of its flammable and explosive characteristics. This paper aimed to describe the distribution of R290 gas under different leakage conditions through experiments in the engine compartment and the passenger compartment. Our results showed that, evaporator leakage was the most risky situation of the system. In this case, R290 gas leaked to the passenger compartment, as a result, the R290 concentration in the environment was above the lower flammable limit (LFL). In the case of leakage in the engine compartment, the leak pressure, leak hole size, and wind speed were recognized as the three main parameters affecting R290 distribution. Moreover, increasing the hole size and decreasing the wind speed would raise the maximum R290 concentration as well as the duration in which the R290 gas concentration was above the LFL level. Additionally, a lower pressure suggested that the R290 concentration rose slower but it was maintained for a longer time above the LFL than that under high pressure situation. [ABSTRACT FROM AUTHOR]

• Air conditioning load reduction strategy in vehicles using recirculated air is provided. • Utilizing the recirculated air can extent the annual driving range by 11−30%. • Energy saving of heat pump heating in electric vehicle air conditioning is provided. The stock of electric vehicle is booming recently. However, the range of the electric vehicle is still a main barrier in its adoption. Air conditioning system is the second largest energy consumption device on vehicle, which will cause significant range reduction during operation. In this paper, the energy-saving effect of utilizing the recirculated air in air conditioning system is evaluated. The outside air ventilation rate based on CO 2 limits and windshield anti-fog requirements are calculated, and the energy-saving effect of this strategy in 30 cities across China is evaluated using an annual energy consumption model. It is found that utilizing the recirculated air can save 14–46% heating energy when using PTC heater, and 33–57% heating energy in heat pump AC system. Throughout a year, utilizing the recirculated air can extend the driving range by 11–30%. Image, graphical abstract [ABSTRACT FROM AUTHOR]

Highlights • R427A, R161 and R290 were firstly used to substitute R22 in EVI ASHP for heating. • Performances of four refrigerants were measured in high pressure ratio condition. • The capacity, COP, discharge temperature, IPLV (h) and LCCP were compared. • R290 is the most synthetically beneficial alternative. Abstract To help reduce the warming impacts, this study evaluates the drop-in performances of R-427A, R-161 and R-290 in R-22 air source heat pump with EVI (Economized Vapor Injection). The results show that the IPLV(H) of R-161 and R-290 arises 5∼8% relative to R-22 with EVI on. A reversal occurs between R-290 and the baseline with EVI on, making the IPLV(H) of R-290 superior to that of R-22 by 3.6∼5.2% from worse performance with EVI off. At -20/41°C condition, the capacity and COP of R-290 increase by 38% and 19%, respectively. Considering COP and discharge temperatures, R-290 is better-performed to replace R-22 in high pressure ratio conditions. Based on LCCP (Life Cycle Climate Performance) model, 11% of the equivalent CO 2 emission can be reduced by using R-161 and R-290. However, the discharge temperature of R-161 is high in the high pressure ratio condition. R-290 is the most synthetically beneficial alternative. [ABSTRACT FROM AUTHOR]

Highlights • A propane heat pump system is proposed as a solution for electric vehicle. • The heating performance of the propane heat pump system was studied. • Different technical solutions have been compared. • Propane heat pump system will be the most competitive solution for electric vehicle. Abstract To solve the problem of driving mileage reduction for electric vehicles during winter resulting from high power consumption for heating and to deal with the global warming issues, propane heat pump is proposed as a novel solution in this paper for the first time. The heating performance characteristics of a mobile propane heat pump system for electric vehicles in cold climate under various operation conditions have been experimentally studied. Different technical solutions for heat pump are also compared in the research. According to the results, propane (R290) system is the strongest competitor at an outdoor ambient temperature above −10°C among all the strategies while CO 2 system may have small advantages when the ambient temperature is −20°C. However, due to CO 2 's poor cooling COP (Coefficient of performance) at high ambient temperature and its high operating pressure, propane heat pump system will be the most competitive solution for electric vehicles. [ABSTRACT FROM AUTHOR]

Electronic expansion valve (EEV) takes advantages of its fast response, wide working range and accurate control and is been widely used in CO 2 heat pump and air-conditioning system while the CO 2 mass flow characteristics is the most crucial parameter for EEV. Different from other refrigerants, at the inlet of EEV, CO 2 maintains at supercritical state. In this study, the effects of inlet pressure, inlet temperature, outlet pressure, EEV flowing area and EEV geometries on CO 2 mass flowing through EEVs have been investigated under a wide operation range for three different EEVs. Meanwhile, a new empirical correlation has been developed to predict the mass flow rate of CO 2 flowing through EEVs based on the experimental data. The proposed dimensionless correlation shows a good agreement with the test data. Approximately 91.8% of the experimental data within a relative deviation of ±5% for all EEVs. The average deviation and standard deviation of the predictions are 0.36% and 1.93% respectively. [ABSTRACT FROM AUTHOR]

This study investigates four influence factors of flow distribution in multi-circuit evaporators with distributor, including distributor inlet tube length, inclination angle, uneven airflow, and feeder tube length. Experimental tests and numerical simulations were carried out to evaluate the effect of these factors on superheat uniformity and refrigerant distribution performance. Additionally, a feeder tube compensation method for optimizing refrigerant distribution is presented that involves pressure drop fine-tuning of the feeder tube in each circuit coupled with a main expansion device to obtain more uniform superheat performance at all circuit outlets. To adopt this method, a model was developed to predict the best feeder tube length for each circuit. Experimental results show that when using feeder tubes with predicted lengths in condition of uneven airflow, the superheat uniformity was improved significantly, and up to 35% evaporator cooling capacity could be enhanced when airflow non-uniformity coefficient ( F a i r ) was 0.6. [ABSTRACT FROM AUTHOR]

Highlights • The capacities of R452B and R447B are 0.7–5% and 6–15% lower than those of R410A. • The attenuation with the ambient temperature of R452B is slower than that of R410A. • The COPs of R452B and R447B are higher than those of R410A. • The optimal injection pressure ratio is 0.35–0.45. • R452B and R447B are more appropriate for the high water temperature conditions. Abstract R410A has been widely applied in air-to-water heat pumps for space heating, but its phase-out process is accelerated due to the high GWP. This paper investigates the heating performances of low GWP HFO mixtures (R452B and R447B) as substitutions in a sub-cooler vapor injection cycle. The results illustrate that the capacities of R452B and R447B systems are lower by 0.7–5% and 6–15% in the measured conditions, respectively. The attenuation with the ambient temperature of R452B is slower than that of R410A, while R447B is faster. The COP improvements of R452B are 4–9% and 1.4–2.4% with and without vapor injection, respectively. The COP increases of R447B are 3–12% and 0.4–3.8% with and without vapor injection, respectively. In view of injection characteristics, the optimal injection pressure ratios of R452B and R447B are slightly higher. Synthetically R452B and R447B perform more excellent in the high outlet water temperature conditions and R452B is also suitable for low ambient temperatures. [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]