Absorption-compression Heat Pump Research Articles

Entransy based heat exchange irreversibility analysis for a hybrid absorption-compression heat pump cycle

Thermally-coupled hybrid absorption-compression heat pump cycle could achieve large temperature lift and high output temperature, which is promising for the decarbonization of industrial heat demand. However, the cycle also has many heat exchange processes, resulting in irreversible losses in different components and performance degradation. In this study, entransy dissipation is used for the heat exchange irreversibility analysis of different components in the cycle. Heat and mass transfer model and entransy dissipation model for combined heat and mass transfer components such as absorber and generator are proposed. By comparing with the exergy loss, it proved that the entransy dissipation calculation model is reasonable. In addition, the T-Q diagram obtained by entransy dissipation analysis visually illustrates the heat exchange processes in each heat exchange component, which shows that entransy dissipation analysis has the characteristics of focusing on heat exchange, process-oriented and visualization. Results of entransy dissipation analysis are then used to guide the heat exchange enhancement of different components, thus optimizing the performance of whole heat pump cycle. Reducing the heat exchange irreversibility in internal heat recovery part can obtain the maximize improvement on COP by 3.92 %. The effect of thermal coupling temperature on exergy based and entransy based parameters of the heat pump cycle is investigated. The entransy increment states the optimal coupling temperature as 73.9 °C, in agreement with the COP and exergy analysis results. Therefore, from entransy dissipation to entransy increment, entransy analysis is expected to be a powerful tool to guide from the heat transfer optimization to the thermodynamic system optimization.

Performance enhancement of hybrid absorption-compression heat pump via internal heat recovery

Heat pumps, especially the air-source systems, have been regarded as promising technology for deep decarbonization of thermal energy, but its industrial application is strongly constrained by its small temperature lift. Three-stage hybrid absorption-compression heat pump cycles have been proven as an effective way to achieve large temperature lift, but suffer from performance degradation under high temperature lift. In this study, different internal heat recovery configurations for the three-stage hybrid cycle are investigated for performance enhancement under high temperature lift. Results show that the three-stage hybrid cycles with internal heat recovery can reach output temperature of 100–190 °C with COP of 1.26–2.23, under the ambient temperature of 30 °C. By effectively recovering the condensation heat of absorption sub-cycle, the maximum output temperature and maximum temperature lift of three-stage hybrid cycles are increased by 10 °C and 20 °C, respectively, and the COP under 100 °C temperature lift is improved by 13 %. More importantly, sub-zero operation of the three-stage hybrid cycle is enabled by the internal heat recovery. The comprehensive enhancement of three-stage hybrid cycle with internal heat recovery shows the great potential in promoting the industrial application of air-source heat pump.

Numerical investigation of an oil-free liquid-injected screw compressor with ammonia-water as refrigerant for high temperature heat pump applications

• Thermodynamic analysis of liquid injection with varying ammonia-water mixtures. • Model of an oil-free twin screw compressor with injection, leakage, and heat losses. • Injection of lean solution with low ammonia content is best for oil-free compressor. • Injection flow of 10% of compressor's suction flow is enough for full wet compression. • Two injection ports are advantageous to ensure sufficient lubrication and sealing. This study investigates a numerical model of an oil-free twin screw compressor with ammonia-water mixture as refrigerant and liquid injection. The compressor was identified as main constraint to increase the heat sink temperature of absorption-compression heat pump systems past 120 °C. liquid injection can reduce superheating of the vapor during compression, while an existing liquid film can provide lubrication and sealing, enabling oil-free operation. A quasi-one-dimensional numerical model was developed using the Modelica language. It considers the effects of liquid injection flows and injection positions, leakages, heat losses, and variation in ammonia mass fractions. The results revealed a strong influence of occurring internal leakages, varying ammonia mass fractions of the injected solution and changing injection flows and positions on the evolution of temperature, pressure, and compression power. The injection with lower ammonia mass fraction is beneficial for reducing the discharge temperature, discharge pressure and compression power. The increase in injection flow led to a further reduction in the values obtained. Continuous wet compression, which is required for sufficient sealing and lubrication of the compressor, was achieved with injection at 360° at the beginning of the compression phase and an injection rate of about 10% of the compressor’s suction mass flow. By distributing the injection to two injection ports, wet compression can be supported and occurring under-compression and backflow can be reduced.

Air-source hybrid absorption-compression heat pumps with three-stage thermal coupling configuration for temperature lift over 150 °C

Heat pump technology is promising for low-carbon heating supply. However, temperature lift of current technology is still insufficient to meet different industrial demands. Aiming at larger temperature lift, this paper extends the thermal coupling of absorption heat transformer (AHT) and vapor compression heat pump (VCHP) from two-stage configuration to three-stage configuration. Two different three-stage air-source hybrid absorption-compression heat pump cycles are proposed, and analyzed together with a modified two-stage one. Performance optimization, parameter analysis and second law analysis are carried out for the three hybrid heat pump cycles. The three-stage cycle coupling single-stage AHT with double-stage VCHP achieves the best COP of 2.10–1.32 under the temperature lift of 70.0–151.0 °C, while the two-stage one can only achieve COP of 1.10 and temperature lift of 129.0 °C. This enhanced performance is attributed to the less irreversible loss in throttling process. With both better performance and larger temperature lift, the proposed cycle is promising for the industrial application of air-source heat pump.

Development of a novel flexible multigeneration energy system for meeting the energy needs of remote areas

This paper introduces a flexibility concept in development of a novel multigeneration energy system driven by a renewable energy heat source. Nevertheless, the energy system can be upgraded to a highly productive system by incorporating other subsystems for achieving more production such as domestic hot water and freshwater. A novel design is proposed for a system comprising organic Rankine cycle, absorption compression heat pump, liquid natural gas to natural gas converting system, domestic water heater, and humidifier-dehumidifier desalination to exploit the Sabalan geothermal source for multigeneration purposes. Due to its high-efficient and environmentally friendly characteristics, n-pentane is utilized in the organic Rankine cycle. Also, the Ammonia-water is employed in the absorption compression heat pump subsystem. Energy, exergy, and thermoeconomic analysis is conducted on the plant along with multi-objective optimization based on the parametric study of key variants. According to the results, the novel step-by-step flexibility analysis can give a wide viewpoint to the designers to make the best multiple plant. The results of multi-objective optimization indicate that the freshwater production increases from 0.803 kg/s to 0.834 kg/s, the capacity of the domestic water heater rises from 1254 kW to 1265 kW, and the net output power surges up by 137.96 kW. However, the heating production falls from 1276 to 1088 kW. Furthermore, the total energy and exergy efficiencies increase by 6.43% and 4.47% with a 2.08 $/GJ reduction in the unit cost of the product.

Waste heat recovery at low temperature from heat pumps, power cycles and integrated systems – Review on system performance and environmental perspectives

Utilization of unused waste heat energy below 100 °C is a challenging effort. In spite of investing in energy retrieving technology, a considerable amount of heat energy is still dissipating to the surroundings. The recovery of LTWH through different technologies plays a pivotal role in several process industries and domicile application. Heat pumps are widely employed to retrieve low level heat energy and also aid in reducing greenhouse gas emission. Hybrid absorption-compression heat pump showed maximum of 95% waste heat recovery rate, where air-source and CO2 trans critical heat pump reduced energy consumption by 60–75% and centrifugal heat pumps generated 9700 kW capacity of heat. Most of the studies reported the effective performance of absorption heat pump units with heat source temperature lie in the range of 60–120 °C along with maximum energy and exergy production with minor irreversible energy loss. Nanofluids are emerging as a high-performance working fluid for heating and cooling applications. Silver/pentane nanofluids increased overall system efficiency and showed 14% less carbon footprint, which is considered as a most effective alternate to hazardous working fluids. The simultaneous production of potable water and electrical power generation through desalination system was reviewed. The techno-economic assessment of using heat pumps in low grade energy recovery and its integrated prototype were presented in this paper together with the environmental impact of working fluids used in the heat pumps and thermodynamic cycles.

Experimental investigation of a high-temperature heat pump for industrial steam production

Low-temperature flue gas heat recovery acts as an important way for energy saving and emission reduction in industry sectors. It is difficult to reuse low-temperature heat in the industrial production process, upgrading low-temperature heat using a heat pump is a promising approach to pursue. In this work, an experimental prototype of a high-temperature compression-absorption heat pump was conducted and investigated. Driving by low-grade waste heat and a small amount of electricity, using ammonia-water as a working fluid, this heat pump experimental prototype can produce high-temperature (more than 150 °C) process steam for industrial processes. The operation strategies of the experimental system are clarified and programmed into the control system. Two hours of automatic stable operation indicates the operation strategies are suitable for this high-temperature heat pump. The temperature and pressure of the produced steam are 154 °C and 0.53 MPa, respectively. The steam heat output of the heat pump experimental prototype reaches 70.15 kW, in which the electric heating share is 18.9% and the waste heat heating share reaches 81.1%. The experimental results indicate the hybrid heat pump is capable of recovering low-temperature (less than 170 °C) flue gas heat for process steam generation. This work provides a new approach to upgrade low-temperature waste heat for process steam production.

Feasibility and performance analysis of a hybrid GAX-based absorption-compression heat pump system for space heating in extremely cold climate conditions

Absorption heat pumps (AHPs) can be thermally activated by low-grade heat sources for space heating. The efficiency can be greatly improved by adopting GAX-based internal heat recovery, which lifts the heat source temperature demand and deteriorates the cold climate condition adaptability, and thus immensely limits the widespread application. In this paper, a hybrid GAX-based absorption-compression heat pump (ACHP) system is proposed to expand the geographical scope of application in extremely cold climate conditions, to lift the heat supply temperature, and more importantly to utilize heat sources of lower temperatures. A mathematical model was developed and validated in comparison with experimental and theoretical results from the literature. Feasible generation-evaporation temperature (Tg-Te) conditions to enable GAX were presented in detail. Coefficient of performance (COP), primary energy ratio (PER), heat supply temperature, heating capacity, and heat duty of main components were investigated concerning different working conditions. The possible sensible and latent heat recovery ratio of the GAX was explored. The results show that when Pr increases, the feasible Tg-Te area moves towards the lower Tg and Te sides. The system can be utilized for building floor heating with PER above 1.116, COP higher than 1.614, temperature lift (ΔTlift) up to 81.85 °C even when ambient air temperature (Tamb) is down to −40.6 °C, and for fan coil heating when Tamb is above −40.0 °C with PER above 1.074, COP over 1.615 and ΔTlift up to 85.92 °C. The system can utilize heat sources down to 80 °C by adjusting the working pressure ratio (Pr), highlighting the possibility of integration with solar collectors for heating purposes.

Identification of Existing Challenges and Future Trends for the Utilization of Ammonia-Water Absorption–Compression Heat Pumps at High Temperature Operation

Decarbonization of the industrial sector is one of the most important keys to reducing global warming. Energy demands and associated emissions in the industrial sector are continuously increasing. The utilization of high temperature heat pumps (HTHPs) operating with natural fluids presents an environmentally friendly solution with great potential to increase energy efficiency and reduce emissions in industrial processes. Ammonia-water absorption–compression heat pumps (ACHPs) combine the technologies of an absorption and vapor compression heat pump using a zeotropic mixture of ammonia and water as working fluid. The given characteristics, such as the ability to achieve high sink temperatures with comparably large temperature lifts and high coefficient of performance (COP) make the ACHP interesting for utilization in various industrial high temperature applications. This work reviews the state of technology and identifies existing challenges based on conducted experimental investigations. In this context, 23 references with capacities ranging from 1.4 kW to 4500 kW are evaluated, achieving sink outlet temperatures from 45 °C to 115 °C and COPs from 1.4 to 11.3. Existing challenges are identified for the compressor concerning discharge temperature and lubrication, for the absorber and desorber design for operation and liquid–vapor mixing and distribution and the choice of solution pump. Recent developments and promising solutions are then highlighted and presented in a comprehensive overview. Finally, future trends for further studies are discussed. The purpose of this study is to serve as a starting point for further research by connecting theoretical approaches, possible solutions and experimental results as a resource for further developments of ammonia-water ACHP systems at high temperature operation.

Proposal and assessment of a new solar space heating system by integrating an absorption-compression heat pump

In cold regions, solar space heating is a clean and promising method that can be used to reduce the consumption of fossil fuels and electricity; however, the heat supply cost is extremely high because of the high investment, low energy efficiency, and short operating time. In this paper, a new system is proposed to improve the thermodynamic and economic performance of solar space heating in this paper. An absorption-compression heat pump is integrated with a conventional solar heating system in which the temperature of the collected heat is decreased by 20 °C to 30 °C, to increase the solar collection efficiency. The low-temperature heat collected by the solar collector is upgraded through the absorption-compression heat pump to generate high-temperature heat for space heating in winter and low-pressure process steam for industrial applications in other seasons. The thermodynamic performance of the proposed system is investigated through a numerical simulation. The results show that the efficiency of the solar collector increased by 39.50%, its annual effective operating time reached 2682 h, which is approximately four times that of a conventional solar heating system, and the annual solar energy utilization ratio increased from 4.82% to 43.74%. The payback period of the proposed system decreases to 5.69 years when the natural gas price equals 7.25 cents/kWh, which is 9.35 years shorter than that of the reference system. Furthermore, parameter optimization is performed on the solar collector area, storage tank volume and heat pump capacity. A minimum payback period of 5.44 years is obtained when the solar collector area, storage tank volume and heat pump capacity equal 170 m2, 11.17 m3 and 18.35 kW, respectively. This work provides a new way to utilize solar energy more efficiently and economically.

An air-source hybrid absorption-compression heat pump with large temperature lift

High-temperature heat pump is gaining more and more research attention due to the efficient heat supply for industrial uses, which includes waste heat-source, water-source, and air-source types. Although air heat source has lower energy grade, its superior availability is attractive. However, large temperature lift is necessary to fill in the gap between the low temperature ambient air and high temperature supply, which cannot be fulfilled by current heat pumps. In this study, a novel air-source hybrid absorption-compression heat pump is proposed to address this issue, in which the compression sub-cycle and absorption sub-cycle are thermally coupled for stepped temperature lift. Compared with the conventional air-source heat pump, a large temperature lift (over 90 °C) and relatively good thermodynamic perfectibility (0.34) are obtained. As the temperature lift increases from 70 °C to 110 °C, the coefficient of performance changes from 1.7 to 1.2. Moreover, heat recovery between the two sub-cycles is achieved to reduce the heat exchange capacity with air, thus saving air–liquid heat exchanger area and cost. Via the integration of relatively mature technologies, the proposed system provides a feasible and efficient way to upgrade ambient heat for industrial uses, and it is technologically available in different capacities.

A novel distributed energy system using high-temperature proton exchange membrane fuel cell integrated with hybrid-energy heat pump

Distributed energy systems based on proton exchange membrane fuel cell (PEMFC) pave a promising technological pathway to achieve carbon neutrality. The waste heat from PEMFC can be well recovered for cooling/heating, but additional systems are required if the available waste heat is not enough to meet the building cooling/heating demands. To achieve a dynamic supply–demand match efficiently and flexibly, this study proposes a novel PEMFC distributed energy system integrated with a hybrid-energy heat pump (HEHP). It can flexibly switch between a single absorption heat pump under sufficient waste heat and a hybrid absorption-compression heat pump under deficient waste heat. The integrated PEMFC-HEHP system is characterized and optimized using a validated model under different working conditions and hybrid configurations. The equivalent power density and fuel cell efficiency can be improved by 18.5% and 7.9% with supply temperatures of −10–10 °C for cooling, and be improved by 54.8% and 20.3% with supply temperatures of 40–60 °C for heating. Optimization yields a maximum equivalent power density of 4.341 kW/m2 in cooling mode and 5.357 kW/m2 in heating mode, compared to 3.290 kW/m2 of the individual PEMFC system. A higher absorption fraction enhances the PEMFC equivalent power while a higher compression fraction improves the HEHP cooling/heating capacity, the hybrid configuration needs to be determined by comprehensively considering the required cooling/heating loads and the available waste heat. The results can facilitate the better development of PEMFC distributed energy systems.

Integrated high temperature heat pumps and thermal storage tanks for combined heating and cooling in the industry

• Study of an integrated heat pump and thermal storage tank system of a new dairy. • Utilization of high temperature heat pumps with natural refrigerants. • Conducted energy and performance analysis for an energy-intensive week. • Energy and emission savings through extensive waste heat recovery. • Good process integration with total system coefficient of performance of 4.1. This study investigates the integrated heat pump system of a green-field dairy located in Bergen, Norway. The purpose of the study is to determine the energy consumption and system performance. The dairy features a novel and innovative solution of a fully integrated energy system, employing high temperature heat pumps such as the hybrid absorption-compression heat pump (HACHP) with natural refrigerants to provide all temperature levels of heating and cooling demands. To evaluate the performance an energy analysis has been performed based on available process data for a comparatively energy-intensive week in February. The results have shown that the integrated system is able to meet the occurring demands. Furthermore, the specific energy consumption with 0.22 kWh l −1 product can outperform the annual average value of the replaced dairy even under difficult conditions. However, it is expected that the specific energy consumption will be further reduced on an annual basis. Through measures such as the extensive use of waste heat recovery accounting for 32.7% of the energy used, energy consumption was reduced by 37.9% and greenhouse gas (GHG) emissions by up to 91.7% compared to conventional dairy systems. Simultaneous, the process achieves a waste heat recovery rate of over 95%. Furthermore, demand peaks were compensated and a system coefficient of performance (COP) of 4.1 was achieved along with the identification of existing potential for further improvements.

Thermodynamic analysis on feasible operating region of two-stage hybrid absorption-compression heat pump cycles

Abstract Ammonia-water hybrid absorption-compression heat pump (HACHP) based on Osenbruck cycle is a promising high-temperature heating technology. However, in the case of large temperature rise, the HACHP is faced with the problem that the compressor discharge temperature is too high, which greatly limits its application. In order to solve this problem, this paper introduces three two-stage HACHP cycles and thermodynamic analysis is conducted respectively. Results show that under the constraints of high pressure of 5000 kPa, compressor discharge temperature of 180 °C and vapor water mass fraction of 5%, the single-stage HACHP cycle cannot meet the heating requirement with the temperature lift of 40K, while three two-stage HACHP cycles can easily meet the needs of heating with the temperature lift of 40 K. When HACHP with flash tank intercooler is especially used, the heating with the temperature lift of 50 K can be achieved. Furthermore, this paper gives some typical combinations of ammonia mass fraction and circulation ratio for realizing high-temperature heating.

Hybrid absorption-compression heat pump with two-stage rectification and subcooler

Conventional hybrid absorption-compression heat pumps are difficult to efficiently upgrade waste heat to a heating temperature of above 90 °C. In this paper, to solve this problem, two novel approaches, namely a two-stage rectification and a subcooler, are specially proposed for the hybrid heat pump. By designing a two-stage rectification to reduce the suction temperature of compressor, thereby lowering its discharge temperature, commercially available normal-temperature compressors can be employed in the hybrid heat pump for high-temperature heating. By utilizing a subcooler proposed to reduce the irreversible loss during the throttling process, the energy efficiency of the hybrid heat pump is improved. Moreover, the hybrid heat pump with multi-stage subcoolers is also proposed and analyzed. Thermodynamic analysis exhibits that, at a heating temperature of 120 °C and a solution heat exchanger effectiveness of 0.8, the hybrid heat pump with a two-stage rectification and a subcooler brings about an energy efficiency improvement of 17.4% in comparison to the conventional one.

Proposal and Assessment of an Engine-Based Distributed Steam and Power Cogeneration System Integrated with an Absorption-Compression Heat Pump

Internal combustion engine-based poly-generation systems have been widely used for energy savings and emissions reductions. To maximize their thermodynamic and environmental performance potentials, the efficient recovery of flue gas and jacket water heat is essential. In a conventional internal combustion engine-based steam and power cogeneration system, the low-temperature (less than 170°C) heat from flue gas and jacket water is usually directly discharged to the environment, which dramatically reduces the thermal and economic performance. In this work, a high-temperature heat pump is employed to recover this part of low-temperature heat for steam generation. The sensible heat of the flue gas and jacket water is cascade utilized in a steam generator and a heat pump. Simulation results show that the process steam yield of the proposed system is almost doubled (increased by 703 kg/h) compared to that of an engine-based cogeneration system without a heat pump. The proposed system can reduce natural gas consumption, CO2 and NOx emissions by approximately 199,069 m3, 372.64 tons and 3.02 tons per year, respectively, with a primary energy ratio and exergy efficiency of 72.52% and 46.28%, respectively. Moreover, the proposed system has a lower payback period with a value of 5.11 years, and the determining factors that affect the payback period are natural gas and electricity prices. The total net present value of the proposed system within its lifespan is 2,441,581 USD, and an extra profit of 785,748 USD can be obtained compared to the reference system. This is a promising approach for replacing gas boilers for process steam production in industrial sectors.

Thermoeconomic assessment of a heat pump-enhanced steam and power cogeneration system under design and off-design conditions based on energy level-based exergy cost allocation method

Thermoeconomic analysis is considered a strong tool for cogeneration systems to optimize operation and set prices. In this paper, an absorption-compression heat pump enhanced steam and power cogeneration system is proposed, in which a heat pump is used to upgrade low-temperature waste heat and generate steam. The thermoeconomic performance of the proposed system is investigated under design and off-design conditions using a new thermoeconomic analysis approach with energy level-based cost allocation. As a result, the unit exergy costs of electricity and steam under the design conditions are 2.249 kW/kW and 1.714 kW/kW, respectively. The cost of electricity is higher than that of steam, and this result is opposite to that obtained by a conventional thermoeconomic method (2.063 kW/kW and 2.339 kW/kW, respectively). The costs of electricity and steam increase along with the decreasing engine load under off-design conditions, and the cost of electricity is always higher than that of steam. Finally, the thermoeconomic analysis method with energy level-based cost allocation can obtain more reasonable results and is more suitable for cogeneration systems.

Performance enhancement of a conventional multi-effect desalination (MED) system by heat pump cycles

Multi-effect desalination (MED) systems are highly promising for high salinity seawaters at large scales, and hence are used broadly in desalination plants. Despite the fact that the MED systems can be driven by various renewable or waste heat energies, many of the available renewable technologies are expensive in some parts of the globe. Hence, proposing and developing high-efficient mechanical-based MED units can be an encouraging alternative. In pursuance of this objective, two innovative mechanical-driven MED units are devised, simulated and the results are compared with those of the conventional MED-MVC (mechanical vapor compression) unit. For this aim, absorption-compression heat pump (ACHP) and vapor compression heat pump (VCHP) systems are used for integrating with the MED unit. Under a constant input power of 1845 kW it is found that proposing the MED-VCHP system instead of the conventional MED-MVC system improves gain-output-ratio (GOR), performance ratio (PR), freshwater rate, specific work consumption (SWC), exergy efficiency, exergy destruction rate, and exergy of loss by 1%, 12.86%, 12.64%, 11.45%, 10.78%, 3.3%, and 10.86% respectively. However, the unit cost of distilled water (UCDW) of the MED-VCHP system is around 6.7% higher than that of the MED-MVC system. Also, the MED-VCHP system uses less exergy of fuel than the MED-MVC system due to its high seawater exergy. Furthermore, it is found that one can decrease the overall exergy loss rate from 145.4 kW to 129.6 kW when the MED-VCHP system is used instead of the MED-MVC system.

Working domains of a hybrid absorption-compression heat pump for industrial applications

Absorption-compression heat pumps are especially suitable for high-temperature heat production, however, its performance at different conditions are highly influenced by the choice of ammonia-rich solution mass fraction and circulation ratio. This paper revealed the working domains of a hybrid absorption-compression heat pump for high-temperature (>130 °C) saturated steam production and obtained its optimized thermodynamic performance at different conditions. For saturated steam production, a supplied heat temperature up to 160 °C can be obtained using commercially available components with a thermal benefit compared to a gas boiler. For hot water or air production, the supplied temperature can be even higher. Moreover, a new heat coefficient of performance is proposed to evaluate the heat pump systems with both heat and power consumption. There are optimal heat coefficient of performance values for the circulation ratio and ammonia-rich solution mass fraction for the hybrid system. The results indicated that setting the ammonia-rich solution mass fraction less than 0.6 and the circulation ratio more than 0.7 is a better choice for the hybrid system in actual application. Finally, the hybrid heat pump system was used to improve the thermal performance of a saturated steam and power cogeneration system driven by an internal combustion engine. This work provides a useful guidance for the hybrid absorption-compression heat pump in actual application.

Performance comparisons of NH3/ionic liquid absorption–compression heat pump for increasing the utilization of geothermal energy

Geothermal energy is becoming increasingly attractive to mitigate global energy and environment crisis. Various hybrid heat pump systems were introduced for increasing the utilization of geothermal energy, and then the absorption–compression heat pump (ACHP) using novel NH3/IL (ionic liquid) mixtures was analyzed. The property model of NH3/IL mixtures and the thermodynamic model of the ACHP cycle were established. Parameter studies showed that there was an optimal pressure ratio to achieve the highest coefficient of performance (COP). The optimal pressure ratio increased and the highest COP decreased as the allowed absorption pressure decreased. In addition, a higher pressure ratio was needed to produce a larger temperature lift. A higher absorber temperature (heat sink) led to a lower COP, while a higher generation temperature (heat source) was beneficial to a higher absorber temperature. Among the investigated ILs, [OMIM][BF4] (1-octyl-3-methylimidazolium tetrafluoroborate) yielded the highest heating COP with the lowest pressure ratio.