Hybrid Absorption-compression Heat Pump Research Articles

A mass-coupled hybrid absorption-compression heat pump with output temperature of 200 °C

Heat pump technology is a promising solution for energy saving and emission reduction in industry. However, current technologies with limited temperature lift are not sufficient to meet the industrial heat demands. Aiming at efficient heat supply over 200 °C, this work proposes a hybrid absorption-compression heat pump cycle with mass coupling between LiBr-water type II absorption heat pump and water vapor compression heat pump, which could reduce the working pressure of compressor. Water injection is applied in the compressor for performance improvement. Detailed performance analysis is carried out for the hybrid heat pump cycle, showing an optimized COP of 3.01 under the temperature lift from 150 °C to 200 °C. Besides, the proposed system is capable of achieving temperature lift of 50 °C for heat source between 100 °C and 164 °C. Greater application superiority occurs at higher temperature output. The proposed cycle broadens the working domain of heat pump.

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.

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.

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.

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.

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.

Experimental results of an absorption-compression heat pump using the working fluid ammonia/water for heat recovery in industrial processes

The full potential of hybrid absorption-compression heat pumps, which can cover heating demands at temperatures of around 100 °C and provide additional cooling in industrial processes, has yet to be exploited. Although research has also been conducted on alternative systems, the natural working pair NH3 and H2O still has numerous advantages, being a very economic and thermodynamically well-suited refrigerant for this application. Striving for the development of a heat pump system that can cover a large range of heating demands at a temperature of about 80 °C and create useful cooling power in industrial processes, a test rig was designed and built at the Institute for Thermodynamics at the Leibniz University in Hanover. According to the targeted heating power of 50 kW, the components of the system are chosen based on a simulation model that solves mass, energy and component-specific balance equations for each of the parts simultaneously. This simulation is later used to compare and evaluate experimental data. Constant parameters are water-inlet temperatures at the heat source of 59 °C and at the heat sink of 50 °C. Depending on the mass flow of ammonia-poor solution and the condensation pressure, the heating capacity and the COP of the test rig are investigated. The range of the poor solution mass flow is from 0.21 kg/s to 0.31 kg/s, while the absorption pressure is varied between 13.5 bar and 16.5 bar. The COP of heating reaches a maximum of 2.5, providing more than 40 kW of heating power at a maximum internal temperature lift of 43 K.

A high-temperature hybrid absorption-compression heat pump for waste heat recovery

An absorption-compression heat pump is a promising way to recover low-temperature waste heat efficiently in industrial applications. In this paper, an advanced ammonia-water absorption-compression heat pump is proposed to recover the sensible heat of flue gas below 150 °C to generate saturated steam at 0.5 MPa (151.8 °C). The sensible heat is cascade utilized in the hybrid heat pump system. The high-temperature waste heat is recovered to generate pure ammonia vapor in the rectifier, and the low-temperature heat is used to evaporate the ammonia liquid. In the ammonia vapor compression process, the gas compression process is combined with a liquid compression process, leading to the clear decrease in power consumption. The simulation results indicate that the coefficient of performance and exergy efficiency of the proposed system reaches 5.49 and 27.62%, which is almost two times and 4.69% higher than that of the reference system, respectively. Subsequently, a sensitivity analysis is conducted to optimizing the key parameters, and the optimums values are obtained. Finally, an economic analysis is adopted to evaluate the economic performance of the proposed system. The payback period of the proposed system is 6.26 years compared to the reference system. This study may provide a new way to produce saturated steam by efficiently using the low-temperature waste heat.

A novel internally hybrid absorption-compression heat pump for performance improvement

Heat pump technologies play significant roles in building energy saving and emission reduction. Combing the opposite characteristics of the electrical and absorption heat pumps, a novel internally hybrid absorption-compression heat pump was proposed for performance improvement. The thermodynamic models for the hybrid heat pump using two cycles (single-effect and generator-absorber-heat-exchange) were built for component design and performance simulation with various refrigerant distribution ratios. Results show that a higher absorption-side refrigerant ratio generally makes the primary energy efficiency less sensitive and the capacity more sensitive to working condition. In the heating mode, a higher absorption-side refrigerant ratio brings about a higher efficiency when the evaporator inlet temperature is below 16 °C and 20 °C for the two cycles. In the cooling mode, a lower absorption-side refrigerant ratio contributes to a higher efficiency. The hybrid absorption-compression heat pumps can realize flexible heating/cooling capacity ratios to accommodate the design heating/cooling loads as necessary. Generally, a higher absorption-side refrigerant ratio is preferred in colder conditions owing to the higher heating efficiency and the higher heating/cooling capacity ratio, well matching the heating-dominant building loads. This study focuses on the principle and performance of the novel hybrid heat pump, the applications in actual buildings will be conducted through year-round simulations in future studies.

Numerical study of a hybrid absorption-compression high temperature heat pump for industrial waste heat recovery

The present paper aims at exploring a hybrid absorption-compression heat pump (HAC-HP) to upgrade and recover the industrial waste heat in the temperature range of 60°C–120°C. The new HAC-HP system proposed has a condenser, an evaporator, and one more solution pump, compared to the conventional HAC-HP system, to allow flexible utilization of energy sources of electricity and waste heat. In the system proposed, the pressure of ammonia-water vapor desorbed in the generator can be elevated by two routes; one is via the compression of compressor while the other is via the condenser, the solution pump, and the evaporator. The results show that more ammonia-water vapor flowing through the compressor leads to a substantial higher energy efficiency due to the higher quality of electricity, however, only a slight change on the system exergy efficiency is noticed. The temperature lift increases with the increasing system recirculation flow ratio, however, the system energy and exergy efficiencies drop towards zero. The suitable operation ranges of HAC-HP are recommended for the waste heat at 60°C, 80°C, 100°C, and 120°C. The recirculation flow ratio should be lower than 9, 6, 5, and 4 respectively for these waste heat, while the temperature lifts are in the range of 9.8°C–27.7 °C, 14.9°C–44.1 °C, 24.4°C–64.1°C, and 40.7°C–85.7°C, respectively, and the system energy efficiency are 0.35–0.93, 0.32–0.90, 0.25–0.85, and 0.14–0.76.

On the development of high temperature ammonia–water hybrid absorption–compression heat pumps

Ammonia–water hybrid absorption–compression heat pumps (HACHP) are a promising technology for development of efficient high temperature industrial heat pumps. Using 28 bar components HACHPs up to 100 °C are commercially available. Components developed for 50 bar and 140 bar show that these pressure limits may be possible to exceed if needed for actual applications. Feasible heat supply temperatures using these component limits are investigated. A feasible solution is defined as one that satisfies constraints on the COP, low and high pressure, compressor discharge temperature, vapour water content and volumetric heat capacity. The ammonia mass fraction and the liquid circulation ratio both influence these constraining parameters. The paper investigates feasible combinations of these parameters through the use of a numerical model. 28 bar components allow temperatures up to 111 °C, 50 bar up to 129 °C, and 140 bar up to 147 °C. If the compressor discharge temperature limit is increased to 250 °C and the vapour water content constraint is removed, this becomes: 182 °C, 193 °C and 223 °C.

Technical and economic working domains of industrial heat pumps: Part 2 – Ammonia-water hybrid absorption-compression heat pumps

The ammonia-water hybrid absorption-compression heat pump (HACHP) has been proposed as a relevant technology for industrial heat supply, especially for high sink temperatures and high temperature glides in the sink and source. This is due to the reduced vapour pressure and the non-isothermal phase change of the zeotropic mixture, ammonia-water. To evaluate to which extent these advantages can be translated into feasible heat pump solutions, the working domain of the HACHP is investigated based on technical and economic constraints. The HACHP working domain is compared to that of the best available vapour compression heat pump with natural working fluids. This shows that the HACHP increases the temperature lifts and heat supply temperatures that are feasible to produce with a heat pump. The HACHP is shown to be capable of delivering heat supply temperatures as high as 150 °C and temperature lifts up to 60 K, all with economical benefits for the investor.