Combined Cooling, Heating And Power System Research Articles

Robust multi-objective optimization with life cycle assessment of hybrid solar combined cooling, heating and power system

Hybridization of solar energy technologies results in varieties of inherent characteristics of natural gas combined cooling, heating and power (CCHP) system. This work aims to propose a life cycle assessment-based robust multi-objective optimization model of hybrid solar-assisted CCHP system, which is driven by the complementarities of photovoltaic/thermal collectors and gas turbine. The environmental impact potentials including global warming, respiratory effect and acidification of hybrid system are assessed according to life cycle energy and emission inventory analysis. The optimal plan of hybrid system, using nondominated sorting genetic algorithm II, is implemented to minimize these environmental impacts, in which the robustness is incorporated as part of the search process of genetic algorithm. The sensitivity analysis of candidate Pareto solutions by transferring to linear programming sub-problem drives to the selection of new solutions with robustness requirements. A case study in a hotel building was presented to demonstrate the proposed optimization method. The key uncertain factors on optimization and system performances are discussed. The comparisons of partially and fully covered photovoltaic/thermal collectors indicate that the partially covered collectors lower the impacts of respiratory effect and acidification by 28.4% and 6.7%, respectively, by optimizing system configurations and energy compositions, and the optimum partially covered collectors with CCHP system is more cost-effective and feasible.

Energy, exergy, economic, and environmental (4E) analyses and optimization of a CCHP system with steam turbine

AbstractDue to finding solutions to reduce energy consumption and improve the electricity production efficiency in the power cycles, using the waste heat of power cycles in the combined generation systems can be a useful approach. Also, by using the wasted energy of the power generation cycles, the cooling and heating demands can be met. Therefore, this study presents energy, exergy, economic, and environmental evaluations of a new configuration of combined cooling, heating, and power (CCHP) or tri‐generation system with a steam turbine. This CCHP system includes a steam boiler, a steam turbine, a heat exchanger, a single‐effect absorption chiller, and pumps. Some important performance parameters such as electrical efficiency, combined electrical and cooling efficiency, combined electrical and heating efficiency, and tri‐generation efficiency, as well as exergy efficiency, are considered. Also, various output and environmental performance parameters such as percentage of operational cost reduction, percentage of fuel consumption reduction, percentage of pollutant emission reduction, and economic and technical issues based on different inlet temperatures and pressures of the steam turbine are investigated. In addition, the performance of the absorption chiller at different operating conditions has been investigated. This study shows that the usage of the CCHP system leads to reduction of 24.91% in carbon dioxide emission, 15.83% in fuel consumption, and 35.34% in operating costs compared with conventional systems. Also, the results show that there is a good improvement in the overall performance of the system with the tri‐generation efficiency of 82.46%.

A Reliability-Based Optimization Model for Operational Management of CCHP System

The combined cooling, heating, and power (CCHP) system has been explored extensively due to its ability to reduce the carbon dioxide emission and improve the energy-utilization efficiency. However, the existing studies associated with CCHP system rarely concerned for the system reliability, although it was capable of enhancing the stability of operational patterns. In this study, predefined reliability coefficient (i.e., r) was incorporated innovatively into a CCHP system optimization model in order to examine the influence of reliability level on model results. A variety of solutions under different r values were obtained, which effectively reflected the trade-off between system economy and reliability. The CCHP system of a hotel in Shanghai, China, was used as a study case for demonstration. The generated results indicated that the system cost would increase with the increase of reliability level; meanwhile, the user requirements in cooling, heating and electricity were ensured greatly. The successful application of proposed optimization model in real case is expected to be a good example for CCHP system management.

Sustainability Analysis of Green Data Centers With CCHP and Waste Heat Reuse Systems

Data centers worldwide consume a large amount of energy and pose serious threats to the environment. Combined cooling, heating, and power (CCHP) and waste heat reuse (WHR) systems are two effective approaches to improve the data center energy efficiency. However, whether and to what extent the combination of them can bring further performance improvement have not been explored yet. Moreover, it is unclear how to manage the energy flow in such a hybrid system. In this article, we try to answer these questions by proposing a data center energy architecture that includes both CCHP and WHR technologies. We formulate the energy management problem as two optimization problems with different objectives. By analytically solving the optimization problems, two energy management strategies, namely, Following the electrical load with waste heat reuse (FEL-WHR) and operating cost-aware energy management with waste heat reuse (OCM-WHR), are developed. We evaluate the performance of proposed solutions by extensive simulations using a real-world workload trace from a production data center. Numerical results suggest that the CCHP and WHR technologies generally reduce the operating cost and are more environmental friendly. If the power generation efficiency of CCHP system is high, the impact of WHR will be more conspicuous (up to 8 percent improvement) and FEL-WHR is recommended because it achieves better sustainability at an operating cost comparable to OCM-WHR. Otherwise, WHR only improves the sustainability trivially, and the energy management policy should be carefully chosen according to the data center operator's objective.

Optimal Energy Scheduling for Data Center With Energy Nets Including CCHP and Demand Response

Internet data centers are growing rapidly in recent years and they operate with intensive energy activity. Combined cooling, heating and power (CCHP) brings new opportunities for reducing the electricity cost in internet data centers. The main objective of this study is to optimize the energy resources scheduling in the data center coupled energy nets considering the involvement of CCHP and different demand response techniques. In this paper, internet data center coupled energy nets are proposed, where power grid, solar photovoltaic, CCHP, and battery energy storage systems are the primary energy sources. The adjunct residential buildings and commercial buildings near the internet data centers are also included in the proposed energy nets, where different types of load and demand response characteristics are utilized. A two-stage optimized energy management model considering the coordinated operation of CCHP and demand response technologies is established for internet data center coupled energy nets. In the day-ahead stage, the control objective is to minimize system cost while satisfying various constraints. Consider the electricity tariff chance between day-ahead market and real-time market, real-time control is implemented to minimize the imbalance cost between two electricity markets. Case studies are conducted on a practical internet data center coupled energy nets in Foshan City, China. It is observed that the proposed control framework can optimally schedule the energy resources in the energy network to meet system demand and improve the energy efficiency. The economic evaluation demonstrates that the proposed control scheme reduces system daily cost by 22.01%.

Thermodynamic Analysis of Combined Cooling Heating and Power System with Absorption Heat Pump Based on Small Modular Lead-based Reactor

Small Modular Lead-based Reactor (SMLR) has generated great interest in academic research all around the world due to its good safety characteristics and relatively high core outlet temperature. In this paper, a Combined Cooling Heating and Power (CCHP) system with usage of absorption heat pump, which couples with a SMLR, was proposed to fulfill the energy demands in remote areas. Thermodynamic analysis was implemented to improve the performance of the CCHP system based on SMLR. To meet the remote areas’ energy needs, the main parameters and mass flow rate of a 35 MWth SMLR design were analyzed. The SMLR CCHP with absorption heat pump system can provide electric power 12.5MWe, heating 9.5MWh, and cooling 2.54MWc. The total energy utilization efficiency of the system can be 69.12 %. This work can provide a reference in the design and optimization of the CCHP system to meet the energy demands in the remote areas.

Operation Strategy Analysis and Configuration Optimization of Solar CCHP System

This paper proposed a new type of combined cooling heating and power (CCHP) system, including the parabolic trough solar thermal (PTST) power generation and gas turbine power generation. The thermal energy storage subsystem in the PTST unit provides both thermal energy and electrical energy. Based on the life cycle method, the configuration optimization under eight operation strategies is studied with the economy, energy, and environment indicators. The eight operation strategies include FEL, FEL-EC, FEL-TES, FEL-TES&EC, FTL, FTL-EC, FTL-TES, and FTL-TES&EC. The feasibility of each strategy is verified by taking a residential building cluster as an example. The indicators under the optimal configuration of each strategy are compared with that of the separate production (SP) system. The results showed that the PTST-CCHP system improves the environment and energy performance by changing the ratio of thermal energy and electric energy. The environment and energy indicators of FEL-TES&EC are superior to those of FTL-TES&EC in summer, and the results are just the opposite in winter. The initial annual investment of the PTST-CCHP system is higher than that of the SP system, but its economic performance is better than that of the SP system with the increase of life-cycle.

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Multi-objective optimization of CCHP system with hybrid chiller under new electric load following operation strategy

The performance of combined cooling, heating and power (CCHP) system is greatly affected by its operating strategy and design. In this paper, a new electric load following (NELF) strategy was developed. It is based on the alternation between absorption cooling and electric cooling according to the building energy requirements, for hybrid chiller based CCHP systems. A comparison of the new proposed strategy with the modified electric load following (MELF) and electric load following (ELF) strategies is performed. A multi-objective optimization approach based on genetic algorithm is carried out to predict the optimal capacity of CCHP systems. Performance criteria like primary energy consumption, annual total cost and carbon dioxide emission were considered as objective functions. The performances of these CCHP systems and operation strategies were examined and compared with the separated production (SP) system for a Mosque complex located in Algiers, Algeria. Results show that hybrid chiller CCHP based NELF strategy is the best choice, which can reduce the primary energy consumption by 34.45 GWh/year, annual total cost by 0.313 million €/year and carbon dioxide emission by 8.37 kton/year. Compared to the other configurations and strategies, the hybrid CCHP based NELF achieves better energetic, economic and environmental performance under the optimized conditions.

An Effective Operation Strategy for CCHP System Integrated with Photovoltaic/Thermal Panels and Thermal Energy Storage

The combined cooling, heating and power (CCHP) system is a promising energy-efficient technology to realize energy cascade utilization. With the integration of photovoltaic/thermal panels and thermal energy storage, the comprehensive performance of the system can be further improved. However, the performance is also affected by the operation strategy. This paper proposes an effective operation strategy to deal with the energy flow of the system well to achieve a better performance. The mathematical model of a CCHP system hybridized with photovoltaic/thermal panels and thermal energy storage is established in this paper. The optimal size of key components of the CCHP system is determined by the particle swarm optimization (PSO) algorithm. Case studies of four scenarios of a residential zone in Beijing are conducted to verify the effectiveness of the system structure and efficiency of the proposed method. The results show that by adding photovoltaic/thermal (PV/T) panels and thermal energy storage, the economic and energetic benefits can be effectively improved and the proposed operation strategy is effective.

Optimal design of hybrid combined cooling, heating and power systems considering the uncertainties of load demands and renewable energy sources

The uncertainties such as loads and renewable energy sources have significant impacts on operational performances of hybrid combined cooling, heating, and power (CCHP) systems. A multi-objective stochastic optimization model of a hybrid CCHP system is proposed, which contains a gas turbine, photovoltaic/thermal collectors, an absorption chiller/heater, a ground source heat pump, and storage devices of battery and water tank. Energy hub models of energy converters and storage devices considering the off-design characteristics of the components are constructed. The uncertainties of solar irradiance and building loads are expressed in a parametric method with probability distributions. Considering the uncertainties with system reliability, the hybrid CCHP system is optimized to achieve the best energetic, economic, and environmental benefits using the non-dominated sorting genetic algorithm-II. The Pareto frontiers obtained from the case study indicated that a lower system reliability results in more energy-saving and greenhouse emission reduction benefits. When the system confidence level decreases from 0.99 to 0.50, the hybrid CCHP system compared to the conventional separate production system averagely saves 13.7% primary energy and reduces 8.0% carbon dioxide emission. However, the annual cost saving rate will be reduced with the decrease in system confidence level and increase in uncertainty. The sensitivity analysis of Pareto frontiers on key economic parameters is performed and the results demonstrated that the annual cost saving rate is more sensitive to natural gas price, and the investment cost of solar collectors has a stronger impact than gas turbine.

Dynamic analysis and operation simulation for a combined cooling heating and power system driven by geothermal energy

The geothermal energy is a renewable energy resource, which is viewed as a promising alternative to fossil energy. Powered by geothermal energy, the combined cooling heating and power (CCHP) system can potentially become an option for efficient energy supply. However, the operation of the CCHP system is subject to energy demand and temperature degradation of geothermal water. To capture the dynamic characteristics and off-design performance of CCHP system under different working conditions, the dynamic mathematical models of a CCHP system is established and a control strategy is proposed. On this basis, the effect of heating/cooling load on the dynamic behavior of the CCHP system is analyzed and the effect of temperature degradation of geothermal water on the off-design performance is investigated. The results indicate that the lower heating/cooling load leads to greater overshoot and longer settling time in the dynamic process. The settling time of Cooling-Power mode is much longer than that of Heating-Power mode. As the temperature of geothermal water decreases from 120 °C to 108 °C, the heating capacity of the CCHP system decreases by 28.87% and the cooling capacity decreases by 14.72%.In addition, the operation simulation shows that the CCHP system can precisely track hourly heating and cooling load of the student dorm building.

Investigating the effects of integrating an absorption heat transformer with a combined cooling, heating and power system: A thermodynamic and economic analysis

Regarding the significance of low-temperature heat sources in combined cooling, heating, and power (CCHP) systems, it is necessary to find practical and economical ways to maximize the efficient use of available energies. Integrating the auxiliary cycle with the main system and changing the configuration are among the useful solutions to achieve this purpose. In this work, a combination of both solutions is presented, accordingly, an absorption heat transformer cycle (AHT) is integrated with a conventional CCHP system, which is made of organic Rankine cycle, absorption refrigeration cycle, and a heat exchanger. Three conventional CCHP systems with sequential (Configuraion1), parallel (Configuraion2) and a combination of sequential and parallel (Configuraion3) configurations are considered. It is shown that among the Configuraion1, Configuraion2, and Configuraion3, Configuraion1 has the highest energy efficiency; therefore, it is selected to be compared with the proposed integrated system with AHT. This integration affects the outputs production and also energy consumption; therefore, four different modes (standpoints) are taken into account to compare the production of power (mode A), cooling (Mode B), heating (mode C), and energy consumption (mode D) of these two systems. Also, from the exergy, environmental, and economic aspects, these two systems are compared. Regarding mode D, it is indicated that the energy and exergy efficiencies, energy consumption and carbon emission of the proposed system are improved 17.68%, 17.68%, 15.03%, and 15.02%, respectively. It is noted that for the heat source stream temperature range of 90 °C–120 °C, the proposed system has better performance than the Configuration1. Despite the additional costs of integrating AHT with the CCHP system, the proposed system has 517018.1 US$/year cost saving (which is 32.65% of the investment cost of Configuration1) if biomass is used as a heat source, which indicates its higher economic advantage than the Configuration1. Also, comparing the proposed system with Configuration1, the amount of power, cooling and heating productions are improved 27.98%, 102.15%, and 36.87%, respectively.

A Birandom Chance-Constrained Linear Programming Model for CCHP System Operation Management: A Case Study of Hotel in Shanghai, China

Due to its capability to reduce fuel consumption and increase energy efficiency, the combined cooling, heating, and power (CCHP) system has obtained great concern during the last decade. A large number of deterministic and stochastic optimization models were proposed for supporting the operation management of the CCHP system, but few studies noticed that users’ demands in the real world may be subjected to twofold randomness with incomplete or uncertain information. In this study, a birandom chance-constrained linear programming (BCCLP) model is developed for identifying optimal operation strategies under random uncertainties. Compared with traditional stochastic programming models, the BCCLP model made the improvement through describing the energy demands as the birandom variables firstly, instead of traditional random variables. This way effectively avoided potential imbalance between energy supply and demand caused by oversimplified expression of uncertain parameters. A gas-fired CCHP system of a hotel in Shanghai, China, was used as a study case for demonstration. A variety of operation strategies are obtained under specific constraints-satisfaction conditions. It is concluded that the BCCLP model was capable of generating the cost-effective operation strategies and evaluating the tradeoffs between system economy and reliability. The influence imposed by some critical parameters on the system performance was examined through the sensitivity analysis, which provided the important guidance to the design and operational management of other similar CCHP systems in the future.

WITHDRAWN: Multi-objective thermoeconomic optimization of innovative CCHP system driven by solar energy integrated with thermal energy storage

Abstract An efficient innovative combined cooling, heating and power (CCHP) system driven by solar energy with thermal energy storage is proposed and investigated. The system is a modified configuration of Rankine and ejector refrigeration cycles, integrated in such a way that it can operate on complete CHP or CCP modes by regulating the extracted mass flow ratio from the power turbine. Another interesting feature is employment of environmentally-friendly working fluids, namely CO2 and N2O. To enhance the system performance booster compressor is employed in refrigeration loop to increase the cooling production and thermoelectric generators are used to recover some part of the cycle waste heat. Feasibility analysis, parametric investigation and multi-objective thermoeconomic optimization are conducted to examine the system performance at all the range of practical operating/design conditions. The results indicated better performance of N2O compared to CO2 as the working fluid in terms of power generation, exergy efficiency and L C O E for all the operating conditions. Under the optimal operation obtained by multi-criteria optimization, thermal efficiency and L C O C H E values, respectively are 40.32% and 15.32 $/GJ for N2O working fluid. In addition, a comparison with similar previously proposed CCHP systems has indicated superiority of present CCHP system at the similar operating conditions.

Research on Benefit Analysis of CCHP-WSHP System in Vehicle to Building

This paper proposes a combined cooling, heating and power (CCHP) system, which comprehensively uses water source heat pump (WSHP) system and vehicle to build (V2B) mode. The CCHP-WSHP-V2B could efficiently solve the problems when a CCHP or a WSHP operates independently. And it can acquire better system performance. In this mode, the CCHP system can flexibly exchange electricity with electric buses and coordinate electricity demand. The water source heat pump can supplement the cooling load and heating load of the system. Furthermore, a case study based on a hotel building is established and studied to verify the effectiveness of the model. The results of the case study show that the primary energy saving ratio, carbon dioxide emission reduction ratio, and annual total cost saving ratio comparing with the separate production system are 36.09%, 43.06%, and 25.47%, respectively.

Energetic, economic, and environmental assessment of a Stirling engine based gasification CCHP system

Due to the tar contamination caused by the gasification process of biomass, the internal combustion engine (ICE) based gasification cogeneration systems require complicated gas cleaning devices to purify producer gas. In this paper, a Stirling engine based gasification combined cooling, heat and power (CCHP) system was introduced, which has the capability of mitigating tar condensation and contamination. The gasification CCHP system, including the gasification system, the Stirling engine system, and the absorption chiller system, can provide electricity, heat and cooling for a commercial building. The effects of the equivalence ratio on syngas composition and cold gas efficiency of the gasification process were analyzed herein. The optimal systems in Singapore and Shanghai can save respectively 75.9% and 70.5% levelized total cost compared to a conventional reference system. The Stirling engine based CCHP system had advantages over the ICE systems on overall consideration of the levelized total cost and the primary energy saving ratio. The monthly energetic, economic and environmental performance of the CCHP systems was evaluated under different modes and the above two systems’ primary energy saving ratios, operation cost reduction ratios and CO2 equivalent reduction ratios respectively reached 0.886, 0.462 and 0.701 in Singapore and 0.908, 0.535 and 0.710 in Shanghai in annual operation. The outcomes of this paper contribute to the design and deployment of such a CCHP system, and the developed models and analysis framework can be extended to different climate areas.

A CCHP system based on ORC cogenerator and adsorption chiller experimental prototypes: Energy and economic analysis for NZEB applications

In this work, the study of a novel solar driven Combined Cooling, Heating and Power (CCHP) system is carried out. In particular, the system is composed of a 60 m2 flat plate solar thermal collectors field, a 10 kWe photovoltaic plant, a 2 m3 Thermal Energy Storage (TES), a 3 kWe micro-Organic Rankine Cycle (micro-ORC) prototype, a 4.4 kWc thermally driven Adsorption Chiller (AC) coupled with a 6 kWc auxiliary Heat Pump (HP). It has been conceived for residential applications and has been integrated with a real bioclimatic nearly zero energy building (NZEB). The building-plant system has been modelled in TRNSYS environment and studied for three Italian locations, spread along the peninsula, with three different climates, Messina, Milano and Rome. An energy, environmental and economic analysis have been carried out. The system has been assessed on hourly basis and the sensitivity analysis has demonstrated that performances are sensitive to location. In particular, the effectiveness of the system is greatly affected by solar radiation and weather condition. The CCHP system works for about 2400 h during the whole year on average with global efficiencies ranging from 32% to 42%. The plant is generally suitable for air conditioning applications in residential sector only with a government’s financial support. A medium value of Pay Back Time of 6 years has been found with a medium Net Present Value of 50 kEUR. In conclusion, this study has highlighted the potential of solar driven micro-CCHP systems based on advances technologies for residential applications.

Thermodynamic evaluation of CCHP system based on biomass gasification by exploring the feasibility of using CO2 as gasification agent

The initial purpose of adopting combined cooling heating and power (CCHP) system is to achieve cascade utilization of fuel energy as well as stepping into low-carbon society. In this study, CO2 is used as gasification agent instead of conventional option of using steam in the biomass gasification unit for reducing CO2 emissions and increasing energy efficiency. To determine the thermodynamic feasibility during the process, exergy analysis has been performed within the whole process as well as its individual units. From the analytical results, it discloses that gasification and combustor irreversibilities yield the highest exergy destruction in the CCHP system, which account for 44.19% and 20.79% of the overall exergy destruction, respectively. Exergy analysis emphasises that both losses and irreversibilities can contribute to loss of efficiency system performance. Additionally, focusing on the influences of key parameters on system performance has been highlighted as well. The outcomes suggest that the optimum gasification temperature and CO2/C are 825 °C and 0.25 respectively. Under the optimal design parameters, the energy efficiency and PESR can reach 53.25% and 10.17% in summer respectively. In addition, a preliminary economic analysis is involved and the financial feasibility of this CCHP system is further demonstrated.

Investigation of the effects of operating parameters of an internal combustion engine on the performance and fuel consumption of a CCHP system

In the present study, a combined cooling, heating and power (CCHP) system with a gas internal combustion (IC) engine prime mover, called EF7, has been proposed. A numerical model has been presented to evaluate the performance of the system, and for the first time, the effects of operating parameters of the IC engine, such as the combustion start angle, combustion duration, compression ratio and rotational speed, on the performance and fuel consumption of the CCHP system have been studied. Results show that the minimum specific fuel consumption required for power generation is achieved when combustion starts close to top dead centre (TDC) (i.e. 20° before TDC), and combustion duration is up to 5° after TDC. Additionally, for providing heating load, the minimum specific fuel consumption is achieved when combustion occurs further from TDC (i.e. 50° before TDC), and the combustion duration is about 10°. The minimum specific fuel consumption needed for cooling load is obtained when combustion occurs close to TDC (20° before TDC), and combustion duration is about 70°. The findings of this research will help in the design of optimum IC-based CCHP systems capable of providing demand loads with the minimum fuel consumption as well as reducing pollutants.