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• A simulation model of automobile CO 2 micro-channel gas cooler was developed and validated. • The inlet temperature of refrigerant has a great influence on heating performance of CO 2 gas cooler. • Unfavorable air temperature inhomogeneity appears on the airside outlet surface of gas cooler. • Expanding the depth of the gas cooler from 32 to 64 mm can improve the heating capacity by 29%. This study aims to investigate the supercritical heat transfer characteristics of compact micro-channel gas coolers applied in automobile CO 2 heat pump systems. A simulation model of automobile gas cooler was developed by using segment-by-segment method, and validated by experimental results. Using this model, under the typical heat pump operation conditions, the temperature distributions along the CO 2 refrigerant flow path were predicted, and the variation of heat transfer coefficient was analyzed. Furthermore, the impacts of operation conditions such as refrigerant inlet pressure and temperature, as well as configuration parameters such as depth and pass number on the heating performance were discussed. Results show that the established model has a good prediction accuracy for heating capacity of gas cooler. It is found that there is unfavorable air temperature inhomogeneity on the airside outlet surface of gas cooler. [ABSTRACT FROM AUTHOR]

Highlights • Performance of a novel CO 2 heat pump system with Series Gas Cooler (SGC) has been experimentally tested in both Air Conditioning (AC) and Heat Pump (HP) mode. • A numerical model of CO 2 SGC HP system has been established and validated with experiment results. • The impacts of ambient temperature, discharge pressure and degree of superheat (DSH) on the HP system has been studied using the numerical model. • A comparison between conventional CO 2 system and SGC HP system is carried out based on the model. Abstract The present study aims to investigate the performance a novel CO 2 heat pump system designed for electrical vehicle with Series Gas Cooler (SGC) configuration. A numerical model is developed, and experiments in both Air Conditioning (AC) and Heat Pump (HP) mode are performed to validate this model. Based on the validated model, the impacts of ambient temperature, discharge pressure and degree of superheat on the system are discussed. Additionally, a comparison between conventional CO 2 system and the novel SGC heat pump system is carried out using the developed model. The model can predict system capacity and COP with average errors of 5.1% and 6.0% in AC mode, and average errors of 7.2% and 5.8% are achieved in HP mode. The introduction of SGC into the heat pump system can bring an average increase by 33.7% for the system heating capacity, and an average increase by 35% is achieved for the system COP. [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]

This study investigated the heating performance characteristics of a CO 2 heat pump system for an electrical vehicle in a cold climate. Experimental tests evaluated the effects on system performance of outdoor temperature, outdoor air velocity, indoor temperature, indoor air flow rate, compressor speed, and EXV opening. The results of heating experiments when both the indoor and outdoor temperatures were −20 °C showed a coefficient of performance (COP) of 3.1 and a heating capacity of 3.6 kW. The COP was 1.7 when the outdoor, indoor air inlet, and outlet temperature were −20 °C, 20 °C, and 40 °C, respectively. Therefore, the heat pump using CO 2 refrigerant achieved good heating performance in a cold climate. Additionally, a new secondary loop heat pump was also compared with the conventional heat pump, and the test results show that use of the secondary loop heat pump reduced COP by 19%. [ABSTRACT FROM AUTHOR]

Highlights • A new modified autocascade heat pump system for electric vehicle heating in cold climate is proposed. • Both transcritical and subcritical cycle characteristics using CO 2 -propane are theoretically evaluated. • Results show the new system has much better performance than conventional cycle. • The feasibility of the ACHP system is verified and further optimization locations in the ACHP system is pointed out with exergy analysis. Abstract Heat pump and its efficiency are of great significance to the energy saving of electric vehicle in cold climate. This paper proposes a modified autocascade heat pump (ACHP) system using natural CO 2 -propane mixture. The main purpose is to enhance the heating performance compared with that of conventional heat pump. Using a thermodynamic model of the proposed ACHP cycle, the transcritical and subcritical cycle performance under various conditions are carried out from the perspective of first and second law of thermodynamics, and the transcritical operating characteristics of ACHP system is introduced for the first time. Additionally, an exergy performance comparison has been carried out. Results indicate that the ACHP system can produce more heating capacity, lower compression pressure ratio, lower heat rejection temperature for low ambient temperature conditions and it consumes less compressor work for all the temperature range researched. For transcritical ACHP cycle, the best COP is 2.7 obtained when CO 2 mass fraction is 0.8 at −20 °C, which is 12.3% higher than that of CO 2 single stage heat pump. For subcritical ACHP cycle, the best COP is 3.97 while heating capacity is much lower than that of transcritical cycle in the same condition. Finally, the exergy analysis confirms the feasibility of the ACHP system and points out exactly the further optimization locations in the ACHP system. [ABSTRACT FROM AUTHOR]

Vapor injection technology has been applied to improve the performance of heat pump systems at low ambient temperatures. However, little attention has been paid to the application of heat pump systems combined with the economized vapor injection for electric vehicles. In this study, the performances of two electric vehicle system configurations were compared, including the upstream injection and the downstream injection. The effects of the injection pressure, the compressor speed, the condenser and outdoor inlet temperatures on the overall system performance and specific operating parameters were measured and analyzed in detail. The results indicated that the downstream injection exhibited better system performance. At the compressor speed of 6500 rpm, the maximum heating capacity of the downstream injection was 18.6% and 8.9% higher than that of the upstream injection at the condenser inlet and outdoor temperatures of −2 °C and −12 °C, −7 °C and −18 °C, respectively. At the compressor speed of 4500 rpm, the COP of the downstream injection was 12.9% higher at the condenser inlet and outdoor temperatures of −7 °C and −18 °C. [ABSTRACT FROM AUTHOR]

To improve the efficiency of mobile air conditioning and to meet the need of protecting the environment, performance characteristics of the R1234yf heat pump were tested under various conditions in a cold climate. R1234yf is considered a promising replacement for R134a because of its low global warming potential (GWP). Many studies have examined the cooling performance of R1234yf, but little attention has been focused on its heating performance in cold climate. In this work, the system performance of R1234yf heat pump was analyzed and compared with that of R134a under different influencing factors such as charge, outdoor temperature, indoor temperature, outdoor wind speed, indoor air mass flow rate, compressor speed, inner condenser width, and economized vapor injection (EVI). The results obtained are presented in detail from the view of experimental analysis and comparison. [ABSTRACT FROM AUTHOR]