Heat Pump Air Conditioning System Research Articles

Experimental investigation on frosting performance of a microchannel heat exchanger in heat pump system for electric vehicles

Frosting of outdoor heat exchangers deteriorates the heat transfer performance of the electric vehicle (EV) heat pump system. This study conducted frost experiments on the outdoor heat exchanger of an EV heat pump air-conditioning system, considering different flow configurations, tube arrangements, and frontal air volume. The purpose of the study was to establish the optimal tube arrangements and flow configurations for minimizing frost formation and maximizing system performance. The results indicate that a three-flow configuration outperforms a two-flow setup under frosting conditions. Specifically, a flow sequence of 14-21-35 increases the heat capacity by 15.05 %–20.64 % compared to that of the reverse flow order of 35-21-14. The flow sequence a-b-c represents the number of flat tubes along the refrigerant flow process. Additionally, the coefficient of performance (COP) increases by 1.19 %–3.55 %. Higher airflow reduces frost formation. A significant correlation exists between the refrigerant distribution within the heat exchanger and the corresponding frost distribution on the surface of the microchannel heat exchanger. The frost formation rate was slower for the flat tube vertical arrangement. Furthermore, horizontal tube arrangements were more conductive than vertical ones, providing a more uniform temperature distribution and higher heat transfer rates (an increase of up to 2.7% in heat transfer and 3.4% in heat capacity). The COP of the vertical arrangement was consistently higher than that of the horizontal arrangement by 1.4 %–3 %.

Impact of optimized gas-liquid separator on temperature and frost distribution in electric vehicle heat pump AC

In the context of low temperatures, the outdoor evaporator surface in an electric vehicle's heat pump air conditioning system tends to accumulate frost unevenly. This uneven frosting occurs due to the varying heat exchange capacity of the refrigerant's two phases within the evaporator. Any reduction in the heat exchanger's capacity would lead to a negative impact on system performance. To address these challenges, this study introduces a gas–liquid separator placed in front of the outdoor evaporator. The aim was to enhance both the outdoor evaporator's performance and the overall system efficiency while investigating frost formation and heat distribution in the outdoor evaporator within a heat pump air conditioning system. The research outcomes demonstrate that the gas–liquid separator can effectively enhance evaporating pressure by regulating the opening degree of the gas-phase bypass valve. Optimal performance is achieved with the gas-phase branch bypass valve set between 20% and 30%, ensuring a stable operational condition and higher evaporating pressure. Moreover, the incorporation of a gas–liquid separator could lead to significant improvements in system performance, with increases of 6.9% in heat capacity and 7.4% in COP observed. Additionally, this enhancement extends to the outlet air temperature, showing improvements ranging from 3.6% to 11.2%.

The comprehensive research on the transcritical CO2 thermal management system used in thermostatic transport vehicles

Natural fluid CO2 has become the preferred target of refrigerant alternative in the electrified transportation field in recent years to replace positive temperature coefficient (PTC) heaters, reduce energy consumption, and respect the international ban on Hydrofluorocarbons (HFCs) refrigerants. Thermostatic transport vehicles (TTVs) are well suited to exploit the benefits of CO2 due to their working conditions with a broad range of ambient temperatures, extensive transit distances, and substantial heating capacity requirements in cold climates. In this paper, a transcritical CO2 heat pump air-conditioning system used in TTV was constructed initially with proper control logic. Then following the assessment of the system’s steady-state performance, the dynamic operation process under high thermal inertia was thoroughly examined and analyzed in detail. Ultimately, the optimization of the dynamic response process was realized under varying heat flow boundary conditions. The primary results demonstrated that the rationally designed CO2 thermal management system performed admirably in various operating conditions, particularly in the heating mode where the coefficient of performance (COP) exceeded 3.2. Addressing the high-frequency fluctuation caused by the cargo thermal inertia, the temperature could be maintained with only two starts and stops within 3×105 seconds when the system control logic was refined. The optimized thermal management system of TTV efficiently allowed cargo to achieve the proper temperature as quickly as possible and sustain stability. This study provides an effective theoretical basis for the promotion of the transcritical CO2 thermal management system in the field of TTVs.

Simulation Study on Performance of Solar-Powered Desiccant Wheel and Ground Source Heat Pump Air Conditioning in Qingdao

In China, a large amount of the total energy consumption is made up of building energy, particularly in humid regions. The conventional vapor compression refrigeration systems cannot effectively control the indoor humid and thermal environment. Therefore, this article proposes a solar-powered desiccant wheel and ground-source heat pump (SDW-GSHP) air conditioning system. The energy consumption of the system is mainly from sustainable sources of solar and geothermal energy, showcasing excellent energy efficiency and environmental friendliness. The desiccant wheel (DW) processes latent heat loads, and the GSHP processes the sensible heat load. The regeneration air of the DW is heated by a solar collector. The operational performance of the system was simulated by using TRNSYS during the typical summer week (15 July to 22 July) in Qingdao. The simulation results indicated that indoor temperature was maintained within 25.8–26.2 °C and the relative humidity was maintained in the range of 57–61%. The COP of the SDW-GSHP air conditioning system was 42.1% higher than that of the DW air conditioning system with electric heating regeneration, and electricity saved 43.7%.

Research on refrigerant charge determination under different compressor speed and its effects on the performance of transcritical CO2 air-conditioning heat pump system in electric vehicle

CO2 is assumed to be one of the most potential refrigerant alternatives for electric vehicles for its excellent properties. However, the charge determination of CO2 in current studies remain controversial. In this study, a transcritical CO2 air-conditioning heat pump system was established and experimentally tested to analyze the optimal charge amount. Based on two conflicting methods of charge determining proposed by the preceding research, this paper substantiated the existing controversy and subsequently proposed a more comprehensive method. The effects of different refrigerant charge on the system characteristics were investigated. The influence of the compressor speed on the optimal refrigerant charge and system characteristics was also analyzed. It was found that the optimal charge plateau occurred from refrigerant of 500 g–580 g at the compressor speed of 3000 r·min−1. However, the optimal charge declined with the increment of compressor speed from 3000 r·min−1 to 4500 r·min−1. Among three models, Hughmark's model was proved to be the most appropriate for the theoretical calculation of optimal charge within an error of 6.09%. Further study illustrates that refrigerant mass in high-pressure pipe and intermediate heat exchanger/accumulator (IHX/A) accounted for the main proportion about 52.6%–55.14%.

A dynamic simulation study of temperature and humidity independent control system for temperate semi-humid continental monsoon climate regions

A temperature and humidity independent control (THIC) system is a promising solution for hot and humid indoor working environments. This study proposes a dual-source heat pump air-conditioning (DSHPAC) system composed of a dual-source heat pump (DSHP) and air handling unit (AHU) as a THIC system. The proposed THIC system indirectly adjusts the cooling capacity of the high-temperature evaporator (Eva1) and low-temperature evaporator (Eva2) by controlling the refrigerant mass flow rate of the system to meet the cooling and dehumidifying requirements under different operational conditions. The proposed THIC system can switch among three operational modes by using the designed operational strategy, ensuring that the requirements for indoor temperature and humidity are met. In addition, the mathematical model and equilibrium equations of the THIC system are established. This study uses an office building in Xi'an on a typical summer day as a simulation case in dynamic simulations. The coefficient of performance (COP), cooling capacity, and compressor power consumption of the proposed DSHP system are analyzed. The results demonstrate that the COP of the proposed system increases with the temperature of Eva1 (TEva1), the COP of the proposed system varies from 1.76 to 3.62, and the cooling capacity increases from 1.19 kW to 3.38 kW when TEva1 increases from 6.24 °C to 36.4 °C. The analysis of different values of φR (refrigerant mass ratio) shows that the highest COP is achieved at φR = 0.1. The results prove the application potential of the dual-source heat pumps to the THIC air-conditioning systems.

Performance improvement of vapor compression heat pump with superhydrophobic finned-tube evaporator

Residential buildings frequently employ vapor compression heat pump for winter heating. Its advantages over electric and coal-fired heating include great energy effectiveness and low emissions. However, the outside evaporator's frosting negatively impacts the performance of heat pump systems in low-temperature and high-humidity environments. To ameliorate the frosting problem, a finned-tube heat exchanger with superhydrophobic surface wettability prepared by the wet chemical etching method was applied to a vapor compression heat pump in this study. The performance of a commercial evaporator unit and the superhydrophobic evaporator unit under five frosting conditions was investigated through experiments. The maximum heat transfer rate of the superhydrophobic heat exchanger unit was increased by 17%–44% compared with that of the commercial unit. The COP improvement of the superhydrophobic unit reached 11.2%, 14.3%, 18.8%, 20.9% and 31.9%, respectively. The total mass of frost formation of the superhydrophobic unit experienced a 59.2%–76.3% decrease. The operation time of the superhydrophobic evaporator unit before defrosting determination was significantly extended, reducing the number of defrosting times during a long-time operation. This study proves the advantages of superhydrophobic finned-tube evaporators used in heat pumps in terms of heat transfer performance and frost suppression performance, promoting the application of superhydrophobic finned-tube evaporators in heat pump air-conditioning systems.

Failure analysis and optimization of high-pressure pipe in carbon dioxide heat pump air conditioning system

Carbon dioxide heat pump air conditioning system is a promising technique due to its ODP of zero and GWP of one. However, high operating pressure induces extra challenges on refrigerant leak-proofness, limiting its practical applications. This study applied high-pressure metal pipes to enhance the leak-proofness of the CO2 heat pump system. The endurance of the metal pipes is increased by optimizing the thermal treatment process which can reduce the residual stress and optimize the grain size of the alloy. Based on a laboratory pipe leakage test, the failure mechanism was analyzed and clarified by macroscopic and microscopic inspection on the tested pipe. The results indicate that the cause of the leakage is the cracking of the metal corrugated pipe, which occurred at nearly half of the pipeline length. The failure mode of the corrugated pipe cracking is mainly bending fatigue damage caused by local stress concentration. At the same time, the unevenly distributed grain structure of the metal material is also one of the causes. By optimizing the thermal treatment process, the reliability of high-pressure metal pipes was improved. The gas tightness verification test results show that the average leakage rate can reach 0.00315 g/a. The temperature pulse cycle durability test can be conducted 250,000 times without leakage, which is five times better than before. The maximum tensile strength can reach 6.585 kN, and the bursting pressure can reach 85.79 MPa. This study demonstrates that the high-pressure metal pipes with optimized thermal treatment can overcome the leak-proofness challenge caused by the much higher pressure in carbon dioxide heat pump air conditioning system.

Research on Energy Consumption Model of Heat Pump Air Conditioning System for New Energy Vehicles Based on Digital Technology

Energy shortages and environmental degradation are issues that are getting more and more significant globally. New energy vehicles are being promoted by the state due to the advantages of low pollution and low fuel consumption. However, due to battery technology, the range of new energy vehicles cannot meet the needs of users. As the most energy-efficient auxiliary device, the energy consumption of air conditioning will significantly reduce the range of new energy vehicles. In low temperature environments, heating energy consumption will reduce the range of vehicles by more than 50%. Therefore, the research aims to reduce the energy consumption of air conditioning systems in new energy vehicles by reducing load demand and improving operating efficiency. The study designs a low-temperature heat pump air conditioning system based on digital technology and then uses a computational algorithm to construct an energy consumption model for the heat pump air conditioning system of a new energy vehicle. According to the test results, the system’s average increase in heat production after activating the enthalpy charge is 35% and its average COP is 0.14% lower than when switched off. At -5oC, the air outlet temperature of the system reaches up to 50.0oC. Summer cooling energy consumption increases exponentially with temperature, while winter heating energy consumption decreases linearly with temperature. In addition, the range decreases significantly as the ambient temperature deviates from the human comfort zone. The decline in the winter range is more severe than that in summer, moreover, the range of modern energy vehicles is reduced by 30% at an average winter temperature of -10oC. In summary, the low-temperature heat pump system offers greater performance. It is more useful in real-world applications and can offer a rational alternative to air conditioning’s energy-saving tactics.

Research on heat pump air conditioner compressor speed control strategy based on whale algorithm

Accurate control of compressor speed is crucial for enhancing the heating performance of heat pump air conditioning systems and extending the driving range of electric vehicles. Based on traditional PID control and fuzzy PID control strategies, a control system utilizing the WOA-PID (Whale Optimization Algorithm)fuzzy control strategy is proposed to regulate the compressor speed and achieve optimal passenger compartment temperature control.The results demonstrate that, compared to traditional PID control and fuzzy PID control, the WOA-PID fuzzy control strategy results in significantly reduced overshooting of the passenger compartment temperature, as well as increased COP (Coefficient Of Performance)values. Specifically, when the target temperature is set at 18 °C, the WOA-PID fuzzy control strategy achieves a temperature overshoot amount of only 0.01 °C, and increases the COP by 0.10 and 0.01 compared to traditional PID control and fuzzy PID control, respectively. Similarly, when the target temperature is set at 25 °C, the WOA-PID fuzzy control strategy achieves a temperature overshoot amount of only 0.08 °C, and increases the COP by 0.14 and 0.07 compared to traditional PID control and fuzzy PID control, respectively. These improvements optimize the maximum overshooting amount and adjustment time of the passenger compartment temperature, effectively enhancing the heating performance of the system.

Research to estimate energy efficiency of a ventilation and air conditioning heat pump system inside a production premise with ventilation air recovery

Research to estimate energy efficiency of a ventilation and air conditioning heat pump system inside a production premise with ventilation air recovery

Energy-saving Optimization of Frequency-variable Heat Pump Air Conditioning System for Electric Vehicles Based on a Genetic Algorithm

Energy-saving Optimization of Frequency-variable Heat Pump Air Conditioning System for Electric Vehicles Based on a Genetic Algorithm

Exergy analysis of heat pump air conditioning systems for pure electric vehicle use with low-GWP refrigerants

The exergy analysis of low-global warming potential (GWP) alternative refrigerants, R1234yf, R152a and R744 for heat pump air conditioning (HPAC) systems used in pure electric vehicles (EVs) is conducted via simulation. The results reveal that the system exergy efficiencies (SEEs) of R1234yf-HPAC and R152a-HPAC under identical cooling or heating capacity are similar due to their close thermodynamic properties. The largest exergy destruction component in R1234yf- and R152a-HPACs is the compressor. While for R744-HPAC, the compressor and expansion valve cause major exergy destruction. Moreover, the results also indicate that the SEE of R744-HPAC is at least 20 % lower than that of R1234yf-HPAC when producing identical cooling capacity, while it is on average twice that of R1234-HPAC when producing identical heating capacity. Furthermore, the measures to improve SEE of HPAC systems with different refrigerants are discussed by examining the effects of varying operating conditions. It is suggested to lower compressor speed under both cooling and heating conditions, increase condenser airflow or reduce evaporator airflow of R1234yf-, R152a- and R744-HPACs under cooling condition; for cabin heating, it is advisable to increase the evaporator airflow or decrease condenser airflow for R1234yf- and R152a- HPACs and enlarge condenser airflow for R744-HPAC to elevate SEE.

An ejector-assisted integrated thermal management of electric vehicles switchable between heating and cooling (reversible AC/HP)

Electric vehicles have become increasingly widespread in recent years due to environmental issues and limited natural resources, and the related thermal management strategies are receiving growing notice. A heat pump air conditioning system for cabin and battery pack thermal regulation (both heating and cooling) is proposed and studied under different operating conditions. The attention of the present study is more directed towards the heating mode of operation; cabin air conditioning in winter and electric aircraft application. Due to environmental considerations and restrictive laws, environmentally friendly refrigerants are also considered as alternatives for R134a. To improve the system's performance, an ejector is placed before the compressor and the refrigerant temperatures in the evaporator and chiller are set to be different. The performance of the proposed system is studied for both heating and cooling modes to compare with the basic system (without ejector). An exergy analysis is also carried out to further analyze the thermodynamic characteristics of the system. The results indicate that the proposed system's COP is improved for both cooling and heating modes under all operating conditions. For the heating mode, the highest COP was equal to 4.36 for R600a, and the COP improvement was between 8 and 47 % based on the different operating conditions. For the cooling mode, the highest COPs were equal to 5.20 and 5.17 for R600a and R1234ze(E) atTevap=Tchil=5°C respectively. The COP improvement for R600a was equal to 14 % atTevap=Tchil=−25°C, and it increases as the chiller temperature is raised. The exergy analysis also indicate that the highest exergy destruction occurs in the compressor and throttling valves. Moreover, R600a and R1234ze(E) show a better overall performance compared to other refrigerants. R600a and R1234ze(E) resulted in the least total exergy destruction of approximately 41 kW for the cooling mode and 51 kW for the heating mode. The exergy efficiency for R600a and R1234ze(E) was equal to 64 and 63 % respectively for both the cooling and heating modes.

Analysis of the Influence of EXV on Heat pump air conditioning system based on AMESim

Analysis of the Influence of EXV on Heat pump air conditioning system based on AMESim

The influences of the oil circulation ratio on the performance of a vapor injection scroll compressor in heat pump air conditioning system intended for electrical vehicles

Heat pump air conditioning (AC) based on a vapor injection scroll compressor has proven to be a promising solution to the current driving range limitations of electric vehicles (EV), especially in freezing climates. The lubricating oil inside the compressor is critical in promoting sealing and cooling, but it also exhibits a low performance under extreme working conditions. In addition, the effects of oil retention on compressor behavior and the optimal charge amount at low temperatures require further investigation. This paper adapts a second refrigerant calorimeter method to study the effects of different injection pressures on compressor performance. The results indicate that the mass flow rate, discharge temperature, compressor power consumption, and volume efficiency performance would increase significantly compared with the non-vapor injection (NV). The effects of oil circulation rate (OCR) on the performance of a vapor injection scroll compressor under two low-temperature operating conditions were also studied. The flow and heat transfer parameters were analyzed, and heating capacity was found to increase and decrease with enlarged OCR. The highest coefficient of heating performance (COP) was obtained at an OCR of 3.5% with a vapor injection pressure of 0.28 MPa. Compared with the non-vapor injection (NV) condition, the heating capacity and COP of the system at the same pressure of 0.28 MPa were increased by 6.2% and 1.8%, respectively. At extremely low temperatures, the heating capacity and COP were maximized at an OCR of 5.5% and an injection pressure of 0.45 MPa. Compared with that of NV, the heating capacity and COP of the heating system at the injection pressure were increased by 6.7% and 2.6%, respectively. The compressor discharge temperature decreased obviously with the increasing OCR. An empirical formula was devised to calculate the heating capacity for varying OCR.

Evaluation of energy-saving potential and cabin thermal comfort for automobile CO2 heat pump

Currently, the heat pump air conditioning system is extensively used in Electric Vehicle (EV). However, most previous simulation studies focused on one-dimensional (1D) system performance rather than three-dimensional (3D) cabin thermal comfort. This study proposed a novel control strategy for the operation of a one- and three-dimensional coupling transcritical CO2 heat pump air conditioning system based on the weighted Predicted Mean Vote (PMV) model. The mathematical characterizations of the multiple thermodynamic systems were achieved by one-dimensional calculation and the cabin thermal environment was described by three-dimensional simulation. The weighted predicted mean vote value was calculated by real-time interactive three-dimensional cabin thermal environment parameters while providing control signals for the one-dimensional refrigeration system. The simulation comparison revealed the influence of the weighted Predicted Mean Vote control strategy on the system’s thermodynamic parameters and energy-saving potential. Results showed that the compressor power consumption of the Predicted Mean Vote control strategy was reduced by 9.1%-33.7%, compared with the method of presetting specific temperatures. The proposed one- and three-dimensional coupling method of cabin thermal management establishes the structured correlation between heat pump air conditioning system and cabin thermal environment. The weighted Predicted Mean Vote control strategy reduces the system power consumption within the thermal comfort range of the passengers, and it provides a novel idea for cabin thermal management during practical engineering.

Experimental study of electronic expansion valve opening on the performance of electric vehicle heat pump system at different compressor speeds

The good matching of the electronic expansion valve (EXV) opening and compressor speed in an electric vehicle heat pump air conditioning system is significant for improving the whole system performance. The matching of EXV opening and compressor speed and its effect on system performance was experimentally investigated and analyzed. The results showed that at various compressor speeds, the condensing pressure increased and the evaporating pressure decreased to a small extent with the decrease of EXV opening, thus increasing the pressure ratio. The condensing pressure had a jump phenomenon at a specific EXV opening, and the corresponding jump opening was different at each compressor speed. The COP reached the optimal values of 2.4, 2.6, and 2.1 at the EXV opening of 110, 100, 90 steps, respectively, due to the synergistic effect between compressor speed and EXV opening. Moreover, it was found that the changing trend of COP was consistent with that of condenser outlet temperature. The compressor speed and EXV opening had a more significant impact on condensing pressure than evaporating pressure. The influence of compressor speed on each performance parameter was greater than that of EXV opening, while the EXV opening significantly influenced the subcooling degree. Under different compressor speed conditions, changing the single adjustment step of EXV according to the influence of EXV on each parameter can realize the rapid and accurate control of the heat pump system performance, which can provide a reference for the formulation of relevant control strategies and the reduction of the system energy consumption.

THERMODYNAMIC EFFICIENCY OF HEAT PUMP AIR CONDITIONING SYSTEM BASED ON VERTICAL GROUND HEAT EXCHANGER

An analysis of literary sources in which heat pump heating and air conditioning systems were studied over the past 10 years was carried out. It was determined that research for heat pumps using vertical soil heat exchangers was conducted more in the empirical plane. The authors analyzed the effectiveness of using existing systems that work for heating and air conditioning in different countries. The results of many studies are given, which show that, in fact, the use of ground heat pumps in a temperate climate only in the heating mode entails the exhaustion of the thermal potential and the impossibility of its use in the future. Theoretical studies at the system design stage are not sufficiently presented, and the issue of predictioning the efficiency of the use of such systems is not disclosed. In this regard, it is proposed to investigate the energy efficiency of the heat-pump air conditioning system based on vertical soil heat exchangers. A heat pump air conditioning system based on a vertical soil heat exchanger is considered. Two research tasks were defined: analysis of efficiency in active and passive modes of conditioning. A thermodynamic analysis of the efficiency of the proposed scheme was carried out. The main operating parameters of the system at nodal points are defined. With the help of balance equations, the framework of the system's operation in passive and active modes according to the main parameters is determined. Graphical dependences of energy efficiency indicators on the determining parameters of the system were constructed and analyzed. It is shown at which parameter values the system has optimal operating costs. The results of the study are compared with those for the split system. The advantages and disadvantages of using the proposed solution are determined. It was determined that the heat pump system using soil heat for air conditioning with a vertical soil heat exchanger has stricter requirements for the thermal insulation of the air conditioning object than the system based on the air heat pump.

Heating performance of heat pump air conditioning system for battery electric vehicle with different refrigerants

To improve the heating performance of Heat Pump Air Conditioning System (HPACS) of Battery Electric Vehicle (BEV) and reduce the greenhouse effect of refrigerants, the performances of multiple refrigerants in different modes and conditions are analyzed in this paper. Based on Worldwide Harmonized Light Vehicles Test Cycle (WLTC) dynamic conditions, the impact of heating on battery State of Charge (SOC) is analyzed in HPACS and Positive Temperature Coefficient (PTC) combined heating mode. To better evaluate the contribution of refrigerants to the greenhouse effect, Total Equivalent Warming Impact (TEWI) is used to evaluate multiple refrigerants. The results show that heating capacity increases with the increment of compressor power and air velocity. As compressor power decreases and air velocity increases, COP increases. R32 and R744 are the optimal refrigerants. When the ambient temperature is between −10°C and −15°C under WLTC conditions, the SOC reduction of R32 system is 20.8%–21.1% less than that of R134a system. When the ambient temperature is between −20 and −25°C, the SOC reduction of R744 system is 21.4%–21.6% less than that of R134a system. And the carbon dioxide emissions of R32 and R744 systems are 35.1%, 66.9%, 39.2%, and 55.5% less than that of R134a system, respectively.