Ejector Heat Pump Research Articles

Experimental Analysis of a Polygeneration System: Assessment of the Thermal Sub-System

In this paper, the experimental results of the thermal sub-system of a reliable and cost-effective polygeneration solar system are presented. This polygeneration system produces heating, cooling, and electricity from solar energy, which is used in an existing test building. Heat is generated in four evacuated tube solar collectors (ETCs). The heat may be used for space cooling through a variable geometry ejector (VGE) heat pump. In order to reduce the mismatches between generation and consumption, two thermal storage tanks were added. The performance of a new thermal storage, with 400 L, able to store both sensible and latent heat, was tested. The heating performances of the test building were assessed. Ejector cycle tests were also performed, and the variation of the cooling coefficient of performance (COP) was calculated for different flow rates. For heating, the results showed that the heat storage was capable of heating the test building for 8 h, with temperatures between 22 °C and 26 °C. All results showed that this polygeneration prototype could be capable of meeting the heating and cooling needs when applied to a real building.

Searching for Suitable Binary Fluid for an Ejector Heat Pump for Domestic Water Heating

Abstract Water heating is a major source of energy consumption in the U.S. residential sector. Heat pumps can significantly increase the energy efficiency of water heating. An ejector heat pump (EHP) is a novel, thermally driven heat pump that uses an ejector as a thermocompressor. Choosing suitable working fluids is critical in developing high-performance EHPs. Therefore, this research screens binary fluid pairs (BFPs) for EHPs to produce domestic hot water at a high coefficient of performance (COP). The criteria for screening BFP candidates for EHP water heaters (EHPWHs) are established, and BFP candidates are shortlisted. This study identifies HFE7000, Novec649, HFE7100, HFE7200, and HFE7500 for the primary fluids and RE170, R600a, R600, and R1234ze(Z) for the secondary fluids. The thermodynamic model is employed to investigate the performance of EHPWHs using the shortlisted BFPs under various operating parameters, including the evaporation pressure of the primary working fluid in the high-temperature evaporator and the condensation temperature. The highest heating-cycle COP of 1.328 is achieved by an EHPWH operating with HFE7000/R600 at a condenser temperature of 50 °C and a pressure of 1.69 MPa in the high-temperature evaporator.

Performance assessment and working fluid selection for heat recovery ejector heat pump system in cold climatic conditions

The paper aims to analyze the performance and identify suitable working fluids for a new heat recovery ejector heat pump (HREHP) system. This system introduces a flue gas waste exergy recover circuit combined with the traditional ejector heat pump. Considering the factors of performance, environmental impacts, flammability, and fluid type, four working fluids are selected (i.e., R245fa, R365mfc, RE245fa2, and R1233zd(E)). Comparative study initially conducted to demonstrate the advantages of the proposed heat recovery ejector heat pump facility. Subsequently, the effects of the operational parameters on the novel system performance are investigated to derive design and operation criteria through energy and exergy analysis. Finally, sensitive analysis of generation temperature (Tg), flue gas temperature (Tfg,out), and supply water temperature (Tw) on the proposed system is carried out. Compared with traditional air source heat pump, the application of the HREHP shows higher energy efficiency and lower operating costs at lower ambient temperatures. The results indicate that the primary energy efficiency of the proposed system is 27.0 % and 35.56 % higher than that of conventional ejector heat pump cycle and air source heat pump cycle, respectively, at an ambient temperature of −10 °C. Besides, Tg has a stronger effect on the entrainment ratio and heating coefficient of performance; The primary energy efficiency is more sensitive to Tw variation. Lastly, the R365mfc and R1233zd(E) show good potential as the alternative for the R245fa. The design methods, evaluation methods, and operational characteristics obtained in this study can provide reference and guidance for the application of heat recovery ejector heat pump technology in practical engineering.

Organic Rankine cycle-ejector heat pump hybrid system using low GWP zeotropic mixtures for trigeneration application

This paper presents a comprehensive study focused on improving the thermal efficiency and performance of an organic Rankine cycle (ORC) combined with an ejector heat pump (EHP) for trigeneration application. The utilization of zeotropic mixtures with low global warming potential (GWP) was proposed as a solution to address the inherent inefficiencies of the ORC at low-temperature heat sources and to enhance the coefficient of performance (COP) of the ejector refrigeration cycle. A thermodynamic model was developed to predict system performance, utilizing low-temperature heat sources such as solar or geothermal energy, along with zeotropic mixtures. The model was validated with the available literature data, demonstrating very good agreement. Five zeotropic fluid mixtures were preliminary studied, and the optimal mass fractions identified. Detailed investigations were then carried out for two of these mixtures, R1233zd(E)/propane and butane/propane, which exhibit low GWP and ozone depletion potential (ODP). The influence of generator temperature and entrainment ratio on system efficiency metrics, exergy, and COP were evaluated for these mixtures. Conclusions are drawn based on the two optimized zeotropic mixtures for maximum thermal efficiency. For R1233zd(E)/propane mixture with mass fractions 0.75/0.25 and butane/propane mixture with mass fractions 0.5/0.5 at generator temperature of 75 °C and entrainment ratio of 0.5, the systems achieved a heating capacity of 1607.9 kW and 2847.9 kW, a cooling capacity of 1037.5 kW and 1280.3 kW, and a net power output of 59.2 kW and 136.3 kW. Other related performance and efficiency parameters are included in the paper. These findings indicate the feasibility of utilizing these systems for trigeneration application. Additionally, a comparative analysis with a regenerative ORC highlighted the ORC-EHP hybrid system's advantages, including enhanced heating efficiency, cooling capacity, and overall COP.This research contributes valuable insights to advance the efficiency and sustainability of combined cooling, heat, and power systems, fostering the progression of innovative energy solutions.

Thermodynamic analysis of a two-stage binary-fluid ejector heat pump water heater

Thermodynamic analysis of a two-stage binary-fluid ejector heat pump water heater

Thermodynamic analysis of a modified booster-assisted ejector heat pump cycle with dual condensers

This paper proposes a modified booster-assisted ejector heat pump (MBEHP) cycle with dual condensers for heat pump dryer applications. Based on a basic booster-assisted ejector heat pump (BEHP) cycle, a low-temperature condenser is introduced between the conventional condenser (i.e. high-temperature condenser) and the evaporator to realize the dual-pressure condensation that can provide heat duty at two different temperatures for heating up dryer air. In this case, improvement on cycle performance could be achieved through the use of such dual condensers in the MBEHP cycle. The benefits from the MBEHP cycle are evaluated by using the first and second laws of thermodynamics, and performance comparisons with the BEHP cycle are also presented. The results show that when R134a is used as the refrigerant, the heating coefficient of performance COPhw and COPh of MBEHP cycle under the typical operating condition increase by 50.34 % and 16.97 % compared with those of BEHP cycle, respectively. The performance of MBEHP cycle is superior to that of BEHP cycle under all given operating conditions, especially under severe operating conditions such as high condensing temperature and low evaporating temperature. In typical operating condition, the total exergy destruction of MBEHP cycle is 12.70 % lower than that of BEHP cycle, but the ejector has the maximum optimization potential. Moreover, the heating capacity Qc and the COPhw of MBEHP cycle are 42.49 % and 12.79 % higher using R1234ze(Z) than using R134a, hence R1234ze(Z) is the most suitable refrigerant to replace R134a in the MBEHP cycle among R1234yf, R1234ze(E) and R1234ze(Z).

Experimental Performance Analysis of Ejector Heat Pump-Water Heater Under Transient Conditions

Net-zero energy buildings are on the agenda of international community due to reducing energy consumption in the building, thus dropping carbon emissions and negative environmental effects. One of the solutions is to utilize heat pumps to decrease energy consumption in the building. In this study, the idea of ejector utilization in a heat pump system was investigated in an experimental test facility by comparison to a conventional heat pump system (without an ejector). The experimental facility, which utilizes hot and cold water as the heat source, can operate in two modes: The ejector heat pump water heater (EHP-WH) and heat pump water heater (HP-WH). The system was tested in transient conditions and the effect of ejector utilization on the system was determined. Results indicate that EHP-WH mode (COP between 5 and 6) had an average of 5.5% higher COP value than HP-WH mode (COP between 4.5 and 5.5). Furthermore, the heating capacity obtained in EHP-WH mode was 30% higher than in HP-WH. Additionally, the water cooler loop’s water temperature was 64.5% higher in EHP-WH mode than in HP-WH. Finally, it is determined that the ejector positively impacts on the performance of HP-WH system.

Experimental performance of ejector heat pump operating in the sub-critical mode

Ejector heat pump (EHP) is an efficient-energy technology with a promising potential to replace the vapor compression cycle in heating and cooling applications. It can be powered by low-grade waste heat and uses environmentally friendly working fluids. EHP has also become a viable solution in research seeking cooling applications. However, little attention has been paid to using EHP for heating purposes. In order to investigate this, a steam EHP for domestic water heating was designed and built. The coefficient of performance (COP) is evaluated at various operating and design conditions in sub-critical operational modes to achieve higher condensation temperatures. Two primary nozzles with a throat diameter of 1.5 mm and 2.0 mm were investigated. The primary nozzle is movable along the ejector’s axis, allowing investigation of its positional effects on the EHP’s COP. Experimental measurements revealed that using a smaller throat diameter results in a high COP and low back pressure. The EHP COP and back pressure increase when the LTE temperature increases. Using a throat diameter of 1.5 mm, the EHP COP increases as the nozzle exit position (NXP) becomes closer to the constant area section. A COP of 2.42 and a back pressure of 4.28 kPa are achieved at a high-temperature evaporator (HTE) temperature of 130 °C and a low-temperature evaporator (LTE) temperature of 30 °C using a primary nozzle with 1.5 mm.

System COP of Ejector-Based Ground-Source Heat Pumps

Compared to mechanical compressors, ejector-based refrigeration systems can make direct use of many forms of thermal energy, including waste heat, solar thermal, or biogases. It is known that SE systems have a lower thermal efficiency compared to mechanical compressors because of their lower performance at high compression ratios. In the present work, binary fluid ejector heat pumps with high efficiency are presented based on a proper selection of the binary fluids and the ejector geometry for specific operating conditions of a ground-source heat pump cooling system (GSHP). The existing literature on ejector-based refrigeration systems considers the thermal COP and does not account for many energy losses across the system. In the present paper, the system COP of an ejector-based GSHP that accounts for all energy exchange processes is determined. A method for the calculation of the work done by the boiler feed pump, the refrigeration expansion valve, and the ground loop circulation pump is presented. The influence of the condenser temperature on the entrainment process and the system COP is also discussed. The estimated overall system COP for the three top-ranked binary fluid candidates under various operating conditions was found to range from 1.55 to 3.06.

Techno-economic analysis of a PV/T waste heat–driven compound ejector-heat pump for simultaneous data centre cooling and district heating using low global warming potential refrigerants

A comprehensive techno-economic evaluation is evaluated based on an innovative compound ejector-heat pump system with PV/T (photovoltaic thermal) waste heat-driven. The aim of the system is simultaneous data centre cooling and waste heat recovery for district heating to reduce residential greenhouse gas emissions. The new system avoids the ejector pump by combining PV/T waste heat with an evaporative-condenser as an ejector driving force, considering several low global warming potential alternatives to R134a. The simulation indicates that the proposed system presents a remarkable difference in all investigated refrigerants’ overall system coefficient of performance (COP). Particularly, R515B presents the highest increase in COP, 54% and 49% in cooling and heating modes, respectively. It also provides the highest electricity consumption reduction, 84.1 MWh yearly. Moreover, the system improves the data centre power usage effectiveness (PUE) index from 10 to 19%. In financial terms, the shortest payback period (6.3 years) is obtained with R515B, followed by R515A and R1234ze(E).

The exergo-economic analysis of two novel combined ejector heat pump/humidification-dehumidification desalination systems

Two novel integrated cycles including ejector heat pump (EJR-HP)/humidification-dehumidification (HDH) desalination were investigated. The first scheme (EJR-single) uses the rejected heat of the HP condenser for heating both seawater and dry air streams of the HDH cycle. In the second scheme (EJR-double), the condenser rejected heat only heats the air, and the system includes double HDH units that use the rejected brine of the first HDH as the feed sweater of the second unit. Based on the results, the novel EJR cycles have better exergy efficiency (ηex), gained output ratio (GOR), and lower fresh water cost (COW) over the base cycle without EJR. Moreover, the GOR and ηex of the EJR-double cycle (7.10, 1.1%, respectively) are 1.88% and 12.45% higher than the EJR-single cycle, respectively. However, the electricity consumption of the EJR-single cycle is higher than the other EJR cycle due to higher pumping power. Due to the higher investment costs of the EJR-double scheme, the COW was obtained as 5.33 $/m3 which is slightly higher than that of the EJR-single cycle (5.18 $/m3). The increase of dehumidifier effectiveness (εdh) from 0.87 to 0.97 decreases the COW of the first and second schemes to 4.20 $/m3 and 4.30 $/m3, respectively.

System development and simulation investigation on a novel compression/ejection transcritical CO2 heat pump system for simultaneous cooling and heating

The problems that the expansion work cannot be recovered and the heat source of the evaporator is insufficient have been found in the previous experimental research, and thus this paper proposes a novel compression/ejection transcritical CO2 heat pump system for simultaneous cooling and heating. An ejector and a water source evaporator are added to the novel system, which realizes the improvement of the compressor inlet grade and the utilization of multiple heat sources. The feasibility of the novel system is verified at first, by numerically analyzing the system operating characteristics variation tendency. The simulation results show that COPtotal of the novel system can reach 11.7 in the compressor frequency of 30 Hz and the discharge pressure of 8000 kPa. In addition, the novel system is compared with the basic transcritical CO2 heat pump system and the transcritical CO2 ejector heat pump system in the exergy, energy and economic aspects. The dual-evaporator design helps the novel system achieve the highest total COP. The simulation results show that the novel system owns 12% higher exergy efficiency over the ejector system, and yields the shortest payback period of 1.10 years among the three considered systems.

Numerical study on operating characteristics of direct-fired ejector air source heat pump

Of the absorption heat transformer that useful to solve the problem of low-temperature heat utilization, the ejector heat pump is a good candidate because of its simple structure, flexible setting and single pure working fluid. This study aims to characterize the behavior of a novel design which replaces the traditional compression heat pump cycle with an ejector heat pump cycle and adds a waste heat recovery system to recover the heat in the flue gas. The evaluation approach takes into consideration four indices (the heating capacity per unit area of the system qh, gas consumption per unit heating capacity EC, gas heat utilization rate GUR and comprehensive heating coefficient R). The results show that the performance of this new designed system is good enough. Moreover, the influence of air and circulating water parameters on the performance of the system is studied, and it is pointed out that air parameters are the most important factors affecting the performance of direct-fired ejector air source heat pump.

Thermodynamic Analysis of a Two-Stage Binary-Fluid Ejector Heat Pump Water Heater

Thermodynamic Analysis of a Two-Stage Binary-Fluid Ejector Heat Pump Water Heater

Energy, exergy, and environmental (3E) analysis of a compound ejector-heat pump with low GWP refrigerants for simultaneous data center cooling and district heating

This work presents an energy, exergy, and environmental evaluation of a novel compound PV/T (photovoltaic thermal) waste heat driven ejector-heat pump system for simultaneous data center cooling and waste heat recovery for district heating networks. The system uses PV/T waste heat with an evaporative-condenser as a driving force for an ejector while exploiting the generated electric power to operate the heat pump compressor and pumps. The vapor compression system assessed several environmentally friendly strategies. The study compares eleven lower global warming potential (GWP) refrigerants from different ASHRAE safety groups (R450A, R513A, R515A, R515B, R516A, R152a, R444A, R1234ze(E), R1234yf, R290, and R1243zf) with the hydrofluorocarbon (HFC) R134a. The results prove that the system presents a remarkable overall performance enhancement for all investigated refrigerants in both modes. Regarding the energy analysis, the cooling coefficient of performance (COPC) enhancement ranges from 15% to 54% compared with a traditional R134a heat pump. The most pronounced COPC enhancement is caused by R515B (a 54% COPC enhancement and 49% heating COP enhancement), followed by R515A and R1234ze(E). Concerning the exergy analysis, R515B shows the lowest exergy destruction, with the highest exergy efficiency than all investigated refrigerants.

Theoretical Analysis of a Single-Stage Gas-Fired Ejector Heat Pump Water Heater

Abstract Ejector-driven systems have the ability to operate at high efficiencies, utilizing recycled thermal energy as a power source. For a typical ejector heat pump (EHP) system, the increase of the condenser temperature reduces the coefficient of performance (COP). In addition, if the condenser temperature is higher than the critical temperature, the ejector may not function. In this situation, the condenser temperature must be reduced, and an additional heater will be utilized to heat the production water from the condenser temperature to the desired temperature. In this study, a single-stage gas-fired EHP is investigated and thermodynamically modeled to optimize the system COP for the purpose of heating water by utilizing the thermal energy from the ambient air. The effects of the high-temperature evaporator (HTE) and low-temperature evaporator (LTE) on the ejector critical back pressure and the EHP system performance are examined for a HTE temperature range of 120–180 °C and LTE temperatures of 15.5, 17.5, and 19.5 °C. Results show that an optimized COP for the EHP system exists and is dependent on HTE and LTE temperatures and the primary nozzle throat diameter. In addition, it is found that the peak EHP COP does not necessarily coincide with a large ejector COP. From this study, a maximum EHP COP of 1.31 is achieved at a HTE temperature of 170 °C and LTE temperature of 19.5 °C with a total heating capacity of 15.98 kW.

Conventional and Advanced Exergoeconomic Analysis of a Compound Ejector-Heat Pump for Simultaneous Cooling and Heating

This work focused on a compound PV/T waste heat driven ejector-heat pump system for simultaneous data centre cooling and waste heat recovery for district heating. The system uses PV/T waste heat as the generator’s heat source, acting with the vapour generated in an evaporative condenser as the ejector drive force. Conventional and advanced exergy and advanced exergoeconomic analyses are used to determine the cause and avoidable degree of the components’ exergy destruction rate and cost rates. Regarding the conventional exergy analysis for the whole system, the compressor represents the largest exergy destruction source of 26%. On the other hand, the generator shows the lowest sources (2%). The advanced exergy analysis indicates that 59.4% of the whole system thermodynamical inefficiencies can be avoided by further design optimisation. The compressor has the highest contribution to the destruction in the avoidable exergy destruction rate (21%), followed by the ejector (18%) and condenser (8%). Moreover, the advanced exergoeconomic results prove that 51% of the system costs are unavoidable. In system components cost comparison, the highest cost comes from the condenser, 30%. In the same context, the ejector has the lowest exergoeconomic factor, and it should be getting more attention to reduce the irreversibility by design improving. On the contrary, the evaporator has the highest exergoeconomic factor (94%).

Thermodynamic analysis and parametric optimization of ejector heat pump integrated with organic Rankine cycle combined cooling, heating and power system using zeotropic mixtures

Schematic diagram of ejector heat pump integrated with organic Rankine cycle combined cooling, heating and power (ORC-CCHP) system and mass fractions of (R141b/R134a) in ORC and heat pump loop, merits: great temperature glides in the high-temperature evaporator and high-temperature condenser, beneficial to generate plentiful refrigeration capacity in the heat pump loop. • Comprehensive thermal efficiency is proposed to achieve energy utilization potential substantially. • Mass fractions of zeotropic mixture, generator temperature and entrainment ratio are optimized. • R141b/R134a(55%/45%) achieves optimum mass fractions in ORC and heat pump loop. • Comparative analysis of basic ORCs, ORC with post ejector, ORC with ejector heat pump, EORC is conducted. • Ejector heat pump integrated with ORC-CCHP system is thermodynamiclly feasible and economically attractive. To improve the coefficient of performance ( COP ) of ejector refrigeration cycle (ERC), a novel ejector heat pump integrated with organic Rankine cycle combined cooling, heating and power system (ORC-CCHP) using zeotropic mixtures is established in this study. The comprehensive thermal efficiency is proposed considering exergy efficiency and heat recovery efficiency simultaneously. Results show that the entrainment ratio can be determined with the objective of exergy efficiency, while generator temperature and mass fraction of zeotropic mixture are optimized with the comprehensive thermal efficiency. With the optimized entrainment ratio of 0.2 and generator temperature of 351.15 K, R141b/R134a (55%/45%) achieves the power efficiency of 4.21%, refrigeration efficiency of 14.6% and COP of 1.12, which are considerably higher than those of pure R141b or R134a. Meanwhile, R141b/R134a with optimum mass fractions in ORC and heat pump loop can generate plentiful refrigeration capacity, great temperature glides in the high-temperature evaporator and high-temperature condenser. The comparative analysis of basic ORCs, ORC with post ejector, ORC with ejector heat pump, ORC combined with ejector (EORC) is carried out. The ejector heat pump integrated with ORC-CCHP system is thermodynamically feasible and economically attractive, thanks to optimized system parameters and optimum compositions of zeotropic mixture, giving support of new applications of ERC coupled with positive and reverse Carnot cycles.

Thermal performance of an absorption-assisted two-stage ejector air-to-water heat pump

A gas-fired air-to-water ejector heat pump (EHP) for domestic hot water production is proposed and analyzed thermodynamically. The COP of the EHP is improved by using binary fluids (HFE7500 and water), and the high backpressure in the primary ejector (first-stage) is actively controlled by either a second-stage ejector and/or a LiBr-H2O absorption subsystem. A thermodynamic model is established for analysis and performance evaluation. A case study shows the backpressure of the first-stage ejector is reduced by 53.5%, and the backpressure control using the second-stage ejector increases the system COP by 21.0% compared with that using LiBr-H2O absorption. Parametric studies are conducted to investigate the roles of the first-stage ejector, the second-stage ejector, and the LiBr-H2O absorption subsystem. The first-stage ejector plays a dominant role in the EHP system performance. The EHP’s heating COP can reach 2.0 with an entrainment ratio of 0.12 in the first-stage ejector. EHP performance can be improved with a high entrainment ratio and a low-temperature primary working fluid in the first-stage and second-stage ejectors, a low condensation temperature in the first-stage ejector, and a high generating temperature and a low concentration of the LiBr-H2O solution.

A comparative assessment of space-conditioning technologies

With recent technological developments, many space-conditioning technologies have undergone significant breakthroughs. This investigation provides an updated quantitative comparison of 14 air-source heat pump technologies for residential or commercial space conditioning. These technologies are subdivided into three categories based on the working material, which can be solid-state, two-phase, or gaseous. Thermodynamic models are implemented for each technology and three figures of merit – primary-energy-based COP, exergetic efficiency, and power density – are calculated for cooling and heating mode operation. Solid-state technologies (thermoelectrics, thermionics, elastocaloric, magnetocaloric, and electrocaloric), two-phase technologies (vapor absorption, adsorption, ejector heat pump, membrane heat pump, and conventional vapor compression), and gas cycles (Stirling, Brayton, Bernoulli, vortex tube, and thermoacoustics) are analyzed on a common basis, with proper accounting of realistic thermal resistances and estimates of component requirements, rather than just computing idealized performance. Vapor compression outperforms all the not-in-kind technologies in cooling mode; however, in heating mode, vapor absorption with the ammonia-water working pair outperforms vapor compression by ~ 4.3%, 50.2%, and 49.3% when comparing primary energy COP, exergetic efficiency, and power density, respectively. Elastocaloric and thermoelectric devices demonstrate high power density in heating mode, exceeding that of vapor compression by 83.3% and 46.1%, respectively.