Vapor Injection Heat Pump Research Articles

Performance analysis of vapor injection heat pump system for electric vehicle in cold startup condition

In this study, a vapor-injection (VI) cycle designed for indoor heating of electric vehicle (EV) was investigated for low temperature heating purposes. The heating capacity variation was observed both in mathematical and experimental ways to verify the influence of vapor injection at different injecting positions and under different intermediate pressure. From this study, the optimal injection position of the scroll compressor and intermediate pressure ratio were evaluated that maximizes heating capacity and coefficient of performance (COP) of the cycle. To validate the numerical results, the experiment was also conducted in the prototype of a vapor-injection (VI) heating system for electric vehicle. The experiment was carried out under the steady-state condition and the same parameters as those of numerical analysis were employed. The comparison between the results of numerical analysis and that of experiments showed a good agreement. For the increase of heating capacity, the optimal injecting port position was observed in specific value which was close to 300°. As the opening of the main expansion valve was decreased, the performance of the VI system generally got better but the system had much restricted intermediate pressure ratio in which the performance was drastically decreased. As a result, the optimal intermediate pressure ratio occurred in specific value below 0.25 in startup condition.

A Study on Electric Vehicle Heat Pump Systems in Cold Climates

Electric vehicle heat pumps are drawing more and more attention due to their energy-saving and high efficiency designs. Some problems remain, however, in the usage of the heat pumps in electric vehicles, such as a drainage problem regarding the external heat exchangers while in heat pump mode, and the decrease in heating performance when operated in a cold climate. In this article, an R134a economized vapor injection (EVI) heat pump system was built and tested. The drainage problem common amongst external heat exchangers was solved by an optimized 5 mm diameter tube-and-fin heat exchanger, which can meet both the needs of a condenser and evaporator based on simulation and test results. The EVI system was also tested under several ambient temperatures. It was found that the EVI was a benefit to the system heating capacity. Under a −20 °C ambient temperature, an average improvement of 57.7% in heating capacity was achieved with EVI and the maximum capacity was 2097 W, with a coefficient of performance (COP) of 1.25. The influences of injection pressure and economizer capacity are also discussed in this article.

Performance evaluation of a vapor injection heat pump system for electric vehicles

Battery-powered electric vehicles (EV) need an efficient electric heating system for extending the driving mileage. An air-source heat pump system offers an economical alternative for EV because it consumes less energy than a heating system using Joule heat and it can use the same components as an air conditioning system for cooling. However, its performance degradation is inevitable at very low ambient temperatures. Although vapor refrigerant injection is known as a good technology to overcome this problem in residential heat pump systems, the number of vapor injection heat pump studies for EV applications is quite limited. In this paper, considering the characteristics of EV application, the configuration of a vapor injection heat pump system for EV is introduced, and it was modeled, using a scroll compressor geometry-based thermodynamic analysis. The performance was estimated for cold ambient regions under the EV operational conditions.

Experimental investigation on vapor injection heat pump with a newly designed twin rotary variable speed compressor for cold regions

A newly designed twin rotary variable speed compressor was adopted to improve the heating performance of a vapor injection heat pump air conditioner (HPAC) at cold regions in this study. The performances of a R410A HPAC were measured and investigated. The results showed that an optimum intermediate pressure existed to achieve the maximum heating capacity and system COP for the injection cycle, and the heating capacity was enhanced effectively by increasing compressor frequency, however, at the cost of COP decrease. Comparative research on system performances between injection and non-injection cycles indicated that the newly designed compressor could improve the heating performance of the HPAC at low ambient temperatures. Specifically, the system's heating capacity was enhanced by 5.6%-14.4%, and COP improvement reached up to 3.5%. Vapor injection cycle was not suggested at high ambient temperatures due to its lower COP compared with non-injection cycles.

Thermodynamic analyses on an ejector enhanced CO2 transcritical heat pump cycle with vapor-injection

In this paper, an ejector enhanced vapor injection CO2 transcritical heat pump cycle with sub-cooler (ESCVI) for heating application in cold regions is proposed. The thermodynamic analysis using energetic and exegetic methods is carried out to predict the performance characteristics of the ejector enhanced cycle, and then compared with those of the conventional vapor injection heat pump cycle with sub-cooler (SCVI). The simulation results demonstrate that the ejector enhanced cycle exhibits better performance than the conventional vapor injection cycle under the specified operating conditions. The improvements of the maximum system COP and volumetric heating capacity could reach up to 7.7% and 9.5%, respectively. Exergetic analysis indicates that the largest exergy destruction ratio is generated at the compressor followed by the evaporator and gas cooler. Additionally, the exergy efficiency of the ejector is introduced to quantify the effectiveness of the exergy recovery process, which may be a new criterion to evaluate the performance of the ejector enhanced vapor compression cycle.

과냉각 열교환기 용량 변화에 따른 인젝션 히트펌프의 성능 특성

One major breakthrough in the field of heating, ventilation and air conditioning has been the development of heat pumps. Heat pump systems offer economic alternatives for recovering heat from different sources for use in various industrial, commercial and residential applications. In recent years, the heat pump has been tipped to have a very good potential for hot water production. This paper investigated the performance of a vapor injection heat pump with the variation of sub-cooler capacity at heating mode. The heating capacity of the vapor injection heat pump slightly increased with an increment of sub-cooler capacity, while COP didn't increase continuously. The 20% capacity of sub-cooler comparing with system capacity could be used as a standard to select sub-cooler capacity.

Transient modeling of a flash tank vapor injection heat pump system – Part I: Model development

This two-part article explores the dynamic behavior of a flash tank vapor injection heat pump system from a numerical simulation perspective. Part I provides a first-principles model describing the transient heat transfer and flow phenomena of the system with detailed modeling techniques for each component. The vapor injection scroll compressor is analyzed with the internal heat transfer between the refrigerant and metallic parts taken into account. Lumped-parameter models are developed for the flash tank and expansion devices. Heat exchangers are modeled using a finite volume approach and accounting for the complex tube circuitry. The separated flow model without interfacial exchange is utilized for two-phase flows in order to incorporate an appropriate void fraction model so that a more accurate prediction for refrigerant mass distribution can be achieved. The modular nature of the component models allows flexibility in the system configuration. Transient simulations are carried out for start-up and shut-down operations. A detailed comparison of model predictions against experimental data is presented in the companion paper.

Transient modeling of a flash tank vapor injection heat pump system – Part II: Simulation results and experimental validation

This two-part article investigates the transient characteristics of a flash tank vapor injection system through modeling and experimental validation. The first part describes the detailed modeling techniques for each component, and the second part describes the transient simulations that are carried out for the overall system under start-up and shut-down operations and presents the results. After comparing the predictions of the proposed model with the experimental data, it was concluded that the proposed model can adequately capture the transient heat transfer and flow phenomena of the system. The dynamic system response when subjected to a step change in the opening of the upper-stage EEV (electronic expansion valve) was also investigated. It was found that EEV opening has a significant impact on the system performance and the liquid level in the flash tank, but exhibits little effect on the suction pressure. These findings were corroborated through experiments.

가스 인젝션을 적용한 전기자동차용 히트펌프의 난방성능 특성에 대한 실험적 연구

A heat pump has been considered as a thermal management unit for electric vehicles, including the heating and cooling of the cabin. However, the heat pump shows performance degradation at low outdoor temperatures or high compressor speeds. In this study, a R-134a heat pump for an electric vehicle was designed to improve system efficiency, by applying vapor injection with an internal heat exchanger. The heating performance characteristics of the vapor injection heat pump were analyzed at various compressor speeds and outdoor temperatures. The vapor injection heat pump showed 13.3% COP improvement over the non-injection heat pump, when the heating capacity was fixed at 5.2 kW. In addition, the heating capacity of the vapor injection system increased by 9.6%, as compared to the non-injection system.

Analysis and optimization of subcritical two-stage vapor injection heat pump systems

Two of the major problems of heat pump systems working in extreme conditions are the loss of efficiency of the system and the high compressor discharge temperatures. One possibility in order to overcome these issues is to perform the compression in two stages. In this frame the use of vapor injection two stage cycles represent an economic and effective solution. This study analyzes the influence of design parameters and injection conditions for two different configurations of two stage cycles, for four refrigerants (R407C, R290, R22 and R32). Design parameters, such as the displacement ratio, are optimized in terms of COP in ideal conditions for both injection systems. A deeper analysis taking into account the efficiencies of the compressor is done finding that two stage systems could reach improvements of 30% in terms of COP compared with one stage systems and that a bad design of this type of systems could represent a loss of improvement between 6% and 10%. Finally a method to control the system at any operating point in order to make it works in its optimum is done. From all the analysis, guidelines for the optimum design and control of such systems are obtained in terms of capacity, Coefficient of Performance (COP), seasonal performance factor and discharge temperature criteria.

On-field measurement method of vapor injection heat pump system

This paper examines air-to-air injection heat pumps (HPs) and proposes a method to determine both heating capacity and coefficient of performance (COP) in situ, allowing analyses of already-installed setups and long-term observation. Due to the uncertain nature of air enthalpy measurements, this method instead uses refrigerant enthalpies calculated from pipe contact temperatures and steady-state energy balances to determine the COP. However, these energy balances are highly dependent on the hypothesis that the working fluid remains strictly monophasic in certain locations, which is not always true in practice. A parametric variable analysis is conducted on the refrigerant vapor quality to calculate the deviation in the COP due to diphasic conditions at the compressor inlet, injection port, and condenser and flash tank outlets. A final in situ COP uncertainty is presented, due to both the measurement and vapor quality uncertainties.

가스인젝션을 적용한 이산화탄소 열펌프의 난방성능 향상에 관한 해석적 연구

ABSTRACT: In this study, a simulation model for a CO 2 heat pump using vapor injection was developed and validated. It was used to predict the improvement of the heating performance of the CO 2 heat pump at various operating conditions. The simulation results showed consistent results with the measured data. The heating performances of the vapor injection and non-injection heat pumps were compared by varying the outdoor temperature and compressor frequency. The heating capacity of the vapor injection heat pump was 40% higher than that of the non-injection heat pump at the outdoor temperature of -8℃. The performance of the vapor injection heat pump was consistently higher than that of the non-injection heat pump even when the compressor frequency was reduced to 35 Hz at the outdoor temperature of -3℃.Keywords: CO 2 heat pump(이산화탄소 열펌프), Vapor injection(가스인젝션), Simulation(시뮬레이션) †Corresponding author Tel.: +82-2-3290-3366; fax: +82-2-921-5439 E-mail address: yongckim@korea.ac.kr 기 호 설 명

Simulations on the performance of a vapor-injection heat pump for different cylinder volume ratios of a twin rotary compressor

In residential air-source heat pump systems, the refrigerant injection technique has rapidly developed in recent years due to its outstanding performance at low ambient temperatures. A numerical simulation model of a flash tank vapor-injection heat pump with a twin rotary compressor is newly presented in this paper. The performance of the twin rotary compressor with refrigerant injection was simulated using a loss and efficiency model. The model was validated by comparing the predictions with measured data. In addition, the model was used to analyze the performance characteristics of the vapor-injection heat pump according to the cylinder volume ratio of the twin rotary compressor. Based on the simulation results, optimum cylinder volume ratios were suggested for various design conditions, including for the fixed first cylinder volume, the fixed total cylinder volume, and the fixed heating capacity.

Transient and steady-state experimental investigation of flash tank vapor injection heat pump cycle control strategy

Recent research on vapor injection technique has been mostly focused on performance improvement using different system configurations. The flash tank cycle typically shows better performance than the internal heat exchanger cycle. However, the flash tank cycle control strategy is not yet clearly defined. In this study, a novel cycle control strategy is proposed for an R-410A vapor injection flash tank heat pump system and its feasibility was experimentally investigated. The proposed novel cycle control strategy utilized an electronic expansion valve (EEV) for the upper-stage expansion and a thermostatic expansion valve for the lower-stage expansion, and applied an electric heater in the vapor injection line to introduce superheat to the injected vapor by providing a control signal to the upper-stage EEV. Both transient and steady-state system behaviors were studied. The proposed cycle control strategy was found to be able to provide reliable control to the system.