Double-effect Absorption Heat Pump Research Articles

Renewable energy sharing based on the effect of energy supply from energy transportation and storage side on building load demand

Abstract To lower environmental-based operation costs, many literatures studied the relationship between the energy generation side (EGS) and building load (BL) demand side based on solar-based integrated energy systems (SIESs), without directly considering the effect of energy from energy transportation and storage side (ETSS) on BL demand, which may result in waste of solar energy extracted. To enhance energy utilization, this study proposed an analysis method that renewable energy source shares among different buildings was investigated based on the supply relationship between energy from the ETSS side and BL demand side. ETSS included an electric boiler/chiller (EB/C), double-effect absorption heat pump (AHP) and tank. According to the energy sources from ETSS and building loads for a hotel, a residence and a hospital on a heating/cooling day. The proposed analysis method was used to develop the potential of available renewable energy through energy sharing from the perspective of the energy consumption differences of the three buildings. The results presented that the potential of renewable energy utilization was further developed by reasonably operating the use and storage of energy sources from ETSS based on the optimization between energy sources from EGS and building loads. Energy source shares among different buildings with different energy consumption characteristics enhanced energy efficiency according to reasonably change the useable time of energy sources from tanks. When a building required a large number of energy sources, the buildings with low energy consumption directly shared renewable energy without considering the use of energy storage. This study can provide a reference for optimizing the design of integrated energy system (IES)-based architecture with different building loads.

Dynamic price optimization of a solar integrated cogeneration system considering uncertainties of building demands

Introducing renewable and high-efficiency devices into conventional cogeneration systems has the potentials to reduce fossil fuel consumption and mitigate environmental issues. This study aims to incorporate solar power and thermal energy into the power and waste heat generated by the gas turbine, respectively, while utilizing a double-effect absorption heat pump to meet the total heat demands. Following the creation of thermodynamic models, a trading mechanism is introduced involving an operating participant known as the product seller, which is analogous to electricity companies in power trading models. To maximize the interests of the participants with different confidence levels, the master-slave game is employed, using Genetic and Quadratic programming algorithms. The hourly outputs of devices and responded demands are evaluated based on the dynamic purchasing and selling price of products. The results indicate that the optimal interest of the cogeneration system is the lowest among all the participants. The power proportions from gas turbine and power grid exceed 60 %, while the contribution of gas turbine decreases by 11.0 % due to the lower heat demands caused by reduced confidence level. Overall, this study offers valuable insights into the market-oriented development of solar assisted cogeneration systems.

Indirect integration of a thermal–mechanical heat pump with a humidification-dehumidification desalination unit

Many previously developed integrated desalination and heat pump cycles have been observed to consume a significant amount of direct electricity supply, raising concerns about their cost effectiveness. To address this issue, this study has modified the performance and cost metrics of the double-effect absorption heat pump cycle combined with a humidification-dehumidification desalination system in terms of configuration. The novelties of the present study are to preheat seawater for desalination utilizing the waste heat of the absorption chiller and to design a doble-effect hybrid thermal–mechanical heat pump. Thermodynamic and thermoeconomic tools were applied to the system. The proposed cooling/desalination system was found to produce 23.23% more freshwater and 47.7% more cooling than a traditional combination. As a result, the current cogeneration unit achieved an energy utilization factor (EUF) of 6.96, which is approximately 17.89% higher than the conventional configuration. Compared to the base case, optimal steam extraction showed a significant improvement of 27.23% in exergy efficiency. Regarding cost metrics, the cost of freshwater was determined to be 2.051 $/m3. As a result, the humidifier has the highest attribution to the overall exergy destruction at 8.98 kW, which represents approximately 16.5% of the total exergy destruction rate.

Multi-objective optimization of an absorption solar-ground source heat pump considering the environmental and economic performance

ABSTRACT Solar heat pump has attracted more and more attention. This paper aims to improve the performance of an absorption solar-ground source heat pump (ASGSHP) through multi-objective optimization. Firstly, a double-effect absorption heat pump module is developed and a simulation model of the ASGSHP is established on TRNSYS platform. Secondly, considering both the economy and the environmental protection, the equivalent uniform annual cost (EUAC) and the environmental impact load (EIL) are taken as two objective functions. The non-dominated sorting genetic algorithm with elite strategy (NSGA-II) is applied to optimize the environmental and economic performance of the ASGSHP by TRNSYS and MATLAB joint. Pareto front of the multi-objective optimization of the ASGSHP system is obtained. Thirdly, using the TOPSIS decision-making method, the best optimization values for three optimization variables including the solar collector area, the storage tank volume and the setting temperature of the auxiliary heater are obtained. The optimization rate of the environmental impact load and the equivalent uniform annual cost of the optimal point selected by the TOPSIS decision-making method is 10.9% and 3.4%, respectively. The research results can provide the basic data and theoretical guidance for the further development and utilization of the solar-ground source heat pump.

A novel peak shaving framework for coal-fired power plant in isolated microgrids: Combined flexible energy storage and waste heat recovery

Coal-fired power plants (CFPPs) not only bear the burden of peak shaving, but the mission of energy saving. However, the increasing peak-valley difference leads to the difficulties of peak shaving and the energy waste caused by the ineffective utilization of waste heat, which undoubtedly becomes a new problem for CFPPs. So, a new integrated system combining flexible energy storage and waste heat recovery in the CFPP is presented. The scheme consists of a double-effect absorption heat pump (D-AHP) with an integrated thermal electricity storage system (IT-ESS). Waste heat from flue gas is recovered by D-AHP, while IT-ESS is responsible for peak shaving. Firstly, comprehensive satisfaction is used for demand-side management. Subsequently, D-AHP is utilized to recover waste heat to meet the users' heating demand. Finally, steam is extracted during off-peak time to store energy for IT-ESS, while energy is released for peak shaving during peak time. Throughout the process, the proportional-integral-differential is applied to control the airflow into the IT-ESS. Numerical results indicate that the maximum peak-valley difference is decreased by 55.3 MW after the optimization of comprehensive satisfaction, and the response time for the airflow to reach the target value is only about 10% of one period with the PID control strategy. Besides, the scheme successfully satisfies the electricity demand and heating demand in isolated microgrids, and the round-trip efficiency of IT-ESS is 23.11%. Lastly, the daily revenue of the system is 1.40 million dollars and the payback period is 3.16 years.

Energy, environmental-based cost, and solar share comparisons of a solar driven cooling and heating system with different types of building

To reduce fossil fuel consumption and carbon emissions from building energy systems, a solar-based cooling and heating system is proposed here employing solar concentrating collectors, photovoltaics, double-effect absorption heat pump and thermal storage. The system is applied to five building types in a region with cold winter and hot summer. The system configuration is optimized using energy, environmental cost, and solar fraction as criteria. The results demonstrate that the solar system could produce at least 31.1% of the cooling/heating loads resulting in 73.3% and 64.2% energy and cost savings in a hospital. The coefficient of performance of the hybrid system ranges from 5.87 to 7.56 in cooling mode, and 1.22 to 1.65 for heating. The cost of devices is the most sensitive factor, and followed by the price of grid electricity. Increasing the renewable energy penetration rate could improve the energy performance, but decrease the cost saving ratio due to the lower carbon emissions.

Exergo-environmental cost optimization of a solar-based cooling and heating system considering equivalent emissions of life-cycle chain

Solar-driven energy systems can effectively reduce the fossil fuel use and pollutant emissions in the built environment. A solar-based cooling and heating (SCH) system employing solar thermal collectors, photovoltaics, a double-effect absorption heat pump, and an electric boiler/chiller is proposed to meet the energy demand of a community. The system and its components are optimized by simultaneously minimizing the specific exergo-environmental cooling/heating costs over the life-cycle and maximizing the cost saving ratio. Compared to the conventional exergo-economic and exergo-environmental optimization methods without life-cycle equivalent emissions, the results show that the system resulting from the proposed method has higher specific costs, or, 1.10 $/kWh for cooling and 2.77 $/kWh for heating, and the corresponding cost saving ratio is >0.02%-unit lower. The coefficient of performance of the hybrid system in the cooling and heating modes are 4.5 and 1.04, respectively. The specific heating cost shows the highest sensitivity against parameter changes. Increasing the capacity of the heat storage and price of grid power would increase the cost saving benefit, while increasing other parameters such as investment cost would decrease the saving ratio.

The nexus between water, exergy, and economics in an optimal integrated desalination system with two configurations and four operation modes

Numerous integrated desalination systems have been proposed to satisfy the growing global demand for freshwater. However, the responses of various optimal configurations have rarely been subject to advanced combined analyses. Here, a parallel-feed multi-effect evaporative desalination unit is integrated with a series double-effect water-lithium bromide absorption heat pump using thermo-mechanical components to propose a novel flexible system. The proposed hybrid multi-modal cooling-heating-desalination system can be configured as a single compressor or a double-compressor. Both configurations can operate in four modes, producing chilled and tap water (mode I); hot and tap water (mode II); tap water (mode III); or chilled, hot, and tap water (mode IV). The energy, exergy, and economics of the proposed system are modeled in an iterative nonlinear thermo-mathematical program. The base models are compared using exergoeconomic and novel water-exergy nexus-based evaluation criteria, their sensitivity is examined under each operation mode, and the optimal configurations are determined by solving a many-objective optimization model. A non-dominated sorting genetic algorithm generation III is employed to solve the many-objective optimization problem. Exergy for water, exergy efficiency, and total product exergy costs, respectively, improved by 3, 3.6, and 3.7 times, while total annual costs decreased by 17.8–50.3% after optimization. Considering the nexus between exergy, water, and economics, the optimal single compressor configuration was recommended for hot and dry regions and the robust double-compressor configuration was recommended for cold climates or general trigeneration.

Experimental study and analysis on double effect absorption heat pump for efficient waste heat recovery

Experimental study and analysis on double effect absorption heat pump for efficient waste heat recovery

Energetic evaluation of a double-effect LiBr-H2O absorption heat pump coupled to a multi-effect distillation plant at nominal and off-design conditions

This paper presents the experimental characterization of a double-effect absorption heat pump (DEAHP) using lithium bromide-water (LiBr-H2O) which recovers the low-energy latent heat from the last effect of a multi-effect distillation (MED) plant. The experimental facility is located at the Plataforma Solar de Almería (PSA) and the test campaign has been performed with the aim to find the best operating strategies that minimize the energy consumption and maximize the energetic efficiency of the DEAHP-MED system taking also into account the distillate production of the MED unit. For this purpose, the impact of the variation of the input variables by which the DEAHP-MED system can be controlled (MED inlet hot water flow rate, MED inlet hot water temperature, the live steam flow rate and the DEAHP cooling water flow rate) on the coefficient of performance (COP), the performance ratio (PR) and on the total distillate production, has been analysed in two different coupling schemes between the DEAHP and the MED unit (indirect and direct). The results revealed that in direct mode, the rise in the live steam flow rate has the greatest impact on the distillate production and the increase of the MED inlet hot water flow rate and the DEAHP cooling flow rate on the COP. In the indirect mode, the rise in the MED inlet hot water temperature was the most influential in both parameters. The maximum COP, distillate production and PR was 2.08 ± 0.34, 2.42 ± 0.07 m3/h, and 18.53 ± 1.94, respectively in the direct mode and 2.04 ± 0.39, 1.92 ± 0.11 m3/h, 16.67 ± 3.42, respectively in the indirect mode. Moreover, empirical correlations that forecast the PR and the distillate production as a function of the COP were developed from the characterization results and were validated statistically by the coefficient of determination (R2) and the adjusted R2Radj2.

Dynamic modeling and simulation of a double-effect absorption heat pump

This paper presents a new dynamic model to study the transient thermochemical behavior of a double-effect absorption heat pump (DEAHP). It has been designed according to the experience with an experimental DEAHP totally integrated into a solar-assisted multi-effect distillation (MED) plant set up at CIEMAT – Plataforma Solar de Almería (PSA). The non-linear first-principles model was implemented using the equation-based object-oriented Modelica modeling language and is based on a mathematical formulation that describes the main heat and mass transfer phenomena in this kind of facilities. A modular and hierarchical modeling methodology has allowed a graphical modeling development. Submodels that wrap the different physical phenomena are interconnected between them, thus making a three level deep hierarchy. All the submodels have been calibrated and validated with experimental data. The numerical predictions show a good agreement with measured data.

Building integration of concentrating solar systems for heating applications

A new solar collection system integrated on the façade of a building is investigated for Dutch climate conditions. The solar collection system includes a solar façade, a receiver tube and 10 Fresnel lenses. The Fresnel lenses considered were linear, non-imaging, line – focused with a system tracking the position of the sun that ensures vertical incidence of the direct solar radiation on the lenses. For the heating system a double-effect absorption heat pump, which requires high temperature of the heating fluid, was used, working with water and lithium-bromide as refrigerant and solution respectively. The Fresnel lens system is connected with the absorption heat pump through a thermal energy storage tank which accumulates the heat from the Fresnel lens system to provide it to the high pressure generator of the absorption heat pump.

The AQUASOL System: Solar Collector Field Efficiency and Solar-Only Mode Performance

Water scarcity is a global problem that will be of capital importance during the first half of this century, when seawater desalination will often be the only way to achieve sustainable development. Despite significant energy efficiency improvements during recent years, seawater desalination is still an intensive energy consumer; therefore, in the current instability of oil prices and environmental requirements, the sustainability of this technological solution inevitably passes through continued improvement of energy efficiency of the physical processes involved, as well as the use of renewable energy resources such as solar energy. In 2006, the “Enhanced Zero Discharge Seawater Desalination Using Hybrid Solar Technology” Project (AQUASOL) concluded with the erection of a complete solar desalination facility at the Plataforma Solar de Almeria (Spain) for the main purpose of developing an improved-cost, energy-efficient multi-effect distillation (MED) solar desalination technology. The system was designed to make the following three desalination operating modes feasible: (a) solar-only: the energy to the first distillation effect comes exclusively from thermal energy from the solar collector field, (b) fossil-only: a double-effect absorption heat pump powered by gas supplies all of the heat required by the distillation plant, and (c) hybrid: the energy comes from both the heat pump and the solar field. In this paper, solar-only mode system performance is presented and discussed. Optimum working conditions achieved in the solar-only mode were in the range of 64–67°C of MED first cell inlet temperature, which implies specific thermal energy consumption from around 58 kW hth/m3 to 62 kW hth/m3 and a performance ratio of 11.1–10.4, respectively.

Design recommendations for a multi-effect distillation plant connected to a double-effect absorption heat pump: A solar desalination case study

This paper deals with the design of a solar thermal desalination system based on a multi-effect distillation (MED) plant connected to a double-effect absorption heat pump (DEAHP). To date, the only two demonstration projects employing this technology worldwide have been implemented at the PSA (Almería, Spain). Two different prototypes of a DEAHP (LiBr–H 2O), manufactured by the French company ENTROPIE, were connected to an existing multi-effect distillation unit (nominal PR 10.5) in 1991 and 2005, respectively. This paper presents the first experimentally validated design proposal for a solar desalination system based on MED-DEAHP technology. The overall performance ratio, experimentally measured at the Plataforma Solar de Almería test facilities, was 20, which results in a 50% of reduction of the required solar field area compared to a solar MED system.

Connection of absorption heat pumps to multi-effect distillation systems: pilot test facility at the Plataforma Solar de Almería (Spain)

Theoretical analysis demonstrates that coupling a double effect absorption heat pump (DEAHP) cycle to a multi-effect distillation (MED) process shows higher overall performance than other conventional heat pumps like steam ejectors. However, only two demonstration facilities have been implemented worldwide to date, both of them at the Plataforma Solar de Almeria (Spain). The first experience (1992) allowed the expected performance results to be achieved, but some operational problems showed that the technology was not mature enough for its commercial implementation. This paper reports on the assessment of a second heat pump prototype (2005) more successful than the first one. Advances in both the DEAHP unit and design layout of the desalination system as a whole have led to proven reliability of the DEAHP/MED concept, which has an overall performance ratio of 20 with stable and fully automatic operation. It requires a 180°C saturated steam supply which can be provided by solar linear-focusing concentrators. This is a 100% increase over the performance ratio of the MED unit, thus becoming the most efficient solar distillation technology.

Experimental assessment of connection of an absorption heat pump to a multi-effect distillation unit

Theoretical analysis of integrating an absorption heat pump cycle in a multi-effect distillation (MED) process has shown better performance than with other types of heat pumps conventionally used as thermocompressors. However, to date, only two pilot facilities have been implemented worldwide. Both of them have been developed and tested in the framework of two different research and demonstration projects carried out at the Plataforma Solar de Almería (Spain). Two different double-effect absorption (LiBr–H 2O) heat pump (DEAHP) prototypes were coupled to an existing 14-effect MED unit. This paper reports the results of the experimental assessment of integrating the second prototype in the process. Although the initial design of the DEAHP prototype was based on fitting it to the MED unit power demand and their direct connection, the prototype was unable to achieve steady operation in this configuration. However, the indirect connection of both units by means of two auxiliary tanks was successful. An overall performance ratio of 20 was measured; therefore, integration of the DEAHP doubles the performance ratio of the MED unit alone, although the temperature of the external heat input required is increased from 70 °C to 180 °C.

Laboratory research on combined cooling, heating and power (CCHP) systems

Combined cooling, heating and power (CCHP) systems offer the potential for a significant increase in fuel use efficiency by generating electricity onsite and recycling the exhaust gas for heating, cooling, or dehumidifying. A challenge for CCHP system is the efficient integration of distributed generation (DG) equipment with thermally-activated (TA) technologies. The China Ministry of Science and Technology and Tsinghua University launched the 863 Hi-Tech Program in 2007 to focus on laboratory and demonstration research to study the critical issues of CCHP systems, advance the technology and accelerate its application. The research performed at the Building Energy Research Center (BERC) Laboratory focuses on assessing the operational performance and energy efficiency of the integration of current DG and TA technologies; developing and verifying mathematical models of the individual devices and all the systems. The test laboratory is a flexible test-bed for the configuration of DG (presently a 70-kW natural gas-fired internal combustion engine (ICE) with various heat recovery units, such as an flue gas-to-water heat recovery unit (FWRU), a jacket water heat recovery unit (JRU), liquid desiccant dehumidification systems (LDS), an exhaust-gas-driven double-effect absorption heat pump (EDAHP), and a condensation heat recovery unit (CRU)). In the winter, the exhaust gas from the ICE is used in the FWRU or used to drive the EDAHP directly, and the exhaust gas from the EDAHP is used in the CRU. The water flows from the CRU can be directed to the evaporator side of the EDAHP as the low-grade heat source. The water flows from the condensation side of the EDAHP, in conjunction with the jacket water flows from the JRU, is used for heating. In the summer, the exhaust gas from the ICE is used to drive the EDAHP for cooling directly, the exhaust gas from the EDAHP is bypassed to the exit via automated damper controls. The waste heat of the jacket water is used to drive the liquid desiccant dehumidification systems, to realize the separate control of heat and humidity. The automated damper is used in order to test various configurations and operating modes. The testing results show that the operating parameters and efficiencies of the overall system depend on different configurations. Under certain combinations of CCHP, the efficiency of the overall system can be as high as 90% (based on lower heating value of the natural gas).

Assessment of an absorption heat pump coupled to a multi-effect distillation unit within AQUASOL project

An absorption heat pump coupled to a multi-effect distillation unit is able to recover part of the thermal energy rejected in the distillation process, thus increasing its performance ratio. At the beginning of the nineties, a pilot plant installed at the Plataforma Solar de Almería (CIEMAT, Spain) showed a consumption of 108 kJ/kg of distilled water at 180 °C, thus resulting in a performance ratio of 21.3 while that of the distillation unit was about 10. A new precommercial prototype of double effect absorption heat pump has been designed and implemented within the framework of AQUASOL European Project that is being carried out since 2002. This is an ambitious research and demonstration project which complements all previous research activities of the Plataforma Solar de Almería related to solar multi-effect distillation. The research phase of the project has been successfully concluded and the test facility has been erected.

Application of absorption heat pumps to multi-effect distillation: a case study of solar desalination

The coupling of a double-effect absorption heat pump and a multi-effect distillation unit was demonstrated at the Plataforma Solar de Almería (CIEMAT), Spain, within a solar desalination research project. Improvements that were identified have been implemented in a new prototype within the framework of the European project entitled AQUASOL (March 2002 – February 2006). The prototype, which will be tested during the demonstration phase of this project, is expected to consume about half of the multi-effect distillation unit but at a higher temperature, 180 °C. This paper points out different advantages of coupling an absorption heat pump to a multi-effect distillation system which could significantly increase the competitiveness of both conventional and solar powered multi-effect distillation plants. In addition, this paper shows that intensive research should be carried out for optimising and assessing such a desalination system.

Process intensification applied to an aqueous LiBr rotating absorption chiller with dry heat rejection

This paper describes the development and operation of a rotating double effect absorption heat pump, which uses an aqueous lithium bromide solution as the absorbent and dry heat rejection. The design principles are outlined including the operation of the major components and the ways in which the integration of the processes has been achieved. The operation of the fluid management system is described. Experimental performance data are presented from laboratory testing for the machine operating as a chiller.