Search

A weather-based energy system consisting of a tri-generation unit, photovoltaics, and water-cooled chiller is proposed here for improving the energy and environmental performance. Together with capacities of other devices, the cooling ratio, and capacities of different types of chiller are optimized to find the ideal system configuration setting the energy and cost savings and renewable energy use as the objectives. In addition, daily and monthly operating modes with the optimal system composition are analyzed followed by a sensitivity analysis. The results show that increasing energy saving ratio improves the cost saving benefits, but the renewable energy penetration rate would decrease due to lower grid electricity consumption. The ideal system configuration in ratio optimization process has a higher gas turbine and chiller capacity resulting in higher performance than the system with capacity optimization process, or 2.7%, 1.6%, and 0.2%-unit higher of the considered indices. When increasing the specific cost of the chiller, cost saving ratio of the ideal system decreases, while the impacts on the energy savings and renewable energy use are lower. The analysis indicates that the price of grid electricity is the most sensitive factor, while the influence of carbon cost is slight. • Weather-based energy system with PV and water-cooled chiller. • Capacity and ratio optimization processes with three types of chiller. • Ideal energy, cost, and renewable benefits are 51.9%, 55.6% and 25.0%, with a cooling ratio of 69.1%. • The chiller reaches a yearly average COP of 7.5. [ABSTRACT FROM AUTHOR]

• Solar thermal and PV driven cooling/heating system with double-effect absorption heat pump is proposed. • Optimization against the specific exergo-environmental costs and cost saving ratio is performed. • Equivalent carbon and sulfur emission costs over the life-cycle chain are considered. • The ideal cost for cooling/heating is 1.10 $/kWh and 2.77 $/kWh with a cost saving ratio of 58.9%. • COP of cooling and heating is 4.5 and 1.04. 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. [ABSTRACT FROM AUTHOR]

District energy systems, in particular combined cooling, heating and power (CCHP) systems, can provide cost-effective energy products, reduce fossil fuel consumption and emissions. A gas-fired CCHP system is considered here employing an internal combustion engine, whose exhaust gas is split between an organic Rankine cycle unit and absorption heat pump. A simulation model of the system is constructed and validated. An emergy based exergo-environmental cost method is proposed here to optimize the exhaust gas allocation ratio based on specific working conditions considering the equivalent emissions of the whole life-cycle chain from an ecological view. The emergy consumption in each process stage is evaluated accompanied with a sensitivity analysis. The results show that the minimize specific system cost is 310050 seJ/J when 63% of the exhaust gas flows to the ORC-unit. The ICE and AHP are responsible for >98% of the emergy consumption, dominated by the operation of the system. The sensitivity analysis shows that heating is the most sensitive of all products against key parameter variations, while electricity is the least. Increasing the service period and the operating hours, the economic performance could be improved, while the transformity of emission enlarges the cost. • A novel natural gas-fired CCHP system allocating exhaust gas to drive ORC and AHP units. • Emergy based exergo-environmental optimization with ecological boundary. • Equivalent CO 2 and SO x emissions in life-cycle chain. • Sensitivity analysis against crucial parameters. [ABSTRACT FROM AUTHOR]

District energy systems based on renewable resources help to reduce greenhouse-gas emissions and fossil-fuel use. Here, a multi-generation energy system combining cooling, heating, and power is realized by employing organic Rankine cycle (ORC) and absorption heat pump (AHP) technologies, which enable cascading the utilization of solar heat. The AHP can operate steadily providing cooling, heating and hot water from solar thermal and geothermal sources. A modelling approach presented to evaluate the energy, exergy, economic, and exergo-economic performance of the above system. The results show that the AHP could reach a coefficient of performance (COP) between 1.38 and 2.37 depending on the mode of operation. The yearly energy and exergy efficiency of the tri-generation system is 56.5% and 9.6%, respectively. Compared to a separate system, the simple economic payback time of the tri-generation system is 3.5 years. The specific exergo-economic cost of electricity produced is 0.12 $/kWh, whereas the cost of hot water is much higher, or 0.31 $/kWh. The sensitivity analysis performed shows that the inlet and outlet temperatures of the AHP together with the yearly solar irradiance have the highest impact on the performance. This study provides a new direction on cost-effective utilization of renewable sources in district energy systems. • Cascading utilization of solar heat to generate multiple energy products. • Energy, exergy and economic performance assessment in different conditions. • Specific cost estimates of multi-products based on exergy analysis. • COP of absorption heat pump: 1.38 for cooling, 2.16 for heating, 2.37 for hot water. [ABSTRACT FROM AUTHOR]

[Display omitted] • Solar-driven adjustable tri-generation system for building heating and cooling. • Energy, exergy, and adjustable performance in variable conditions is explored. • Energy levels and investment recovery are considered in exergo-economic optimization. • Optimal solar heat allocation ratio is 0.86 with a minimum exergy cost of 0.83 $/kWh. Solar-driven trigeneration system producing cooling, heating and power (CCHP) is an effective way to increase the utilization rate of solar energy. Here, a novel adjustable CCHP system is proposed by employing parabolic trough collectors (PTC), Organic Rankine Cycle (ORC), absorption chiller (AC) and electrical chiller/heater (EC/H) to meet building cooling and heating demand. A full thermal simulation model of the system is constructed and validated. The thermal and adjustable performance of a hybrid system with variable solar irradiance and solar thermal allocation ratio is explored by carrying out energy, exergy and heat to electricity ratio. Considering the energy levels of products and investment recovery coefficient of units at the end of service life, a modified exergo-economic method is utilized to optimize the thermal allocation ratio among the system components based on a specific working condition converted from yearly building parameters. The thermal analysis shows that except for the energy efficiency with increasing allocation ratio, the irradiance and allocation ratio have positive impacts on energy, and exergy performance, and the proposed system has a higher adjustable performance with a higher heat to electricity ratio than other studies. The exergo-economic optimization shows that 86% of the solar heat is fed to the ORC-unit at optimum point with an unit exergy cost of 0.826 $/kWh. Compared to conventional exergo-economic method, the specific costs of the products are lower owing to the function of cost recovery coefficient. This research illustrates a new way to effectively utilize solar thermal energy for district energy systems. [ABSTRACT FROM AUTHOR]

• Novel district heating system with photovoltaic/thermal collector and geothermal heat pump. • Sustainability evaluation model with energy, environment, economic and social indicators. • Comprehensive parametric system analysis with 11 indicators and weight factors. • The ideal solar subsystem is a photovoltaic/thermal collector with 100% photovoltaic coverage ratio. District heating systems assisted by renewable energy harness local energy sources, save fossil fuels, and reduce greenhouse gas emissions. Here, geothermal and solar resources are integrated into district heating through a geothermal heat pump and an absorption heat pump by employing vapor-compressor and absorption cycles, respectively. A quantitative sustainability assessment model was constructed for the resulting hybrid district heating systems. Indicators on energy, environment, economic, and societal aspects were used to evaluate the composite sustainability index of hybrid systems with information entropy method. The results demonstrate that a district heating system coupled to compound parabolic concentrator-photovoltaic/thermal solar collector system with 100% photovoltaic coverage ratio is the ideal system for the case study when the annual cost saving ratio is given the highest impact in the composite sustainability index. A detailed analysis on the annual cost saving ratio shows that a higher ambient temperature, solar beam irradiance and grid electricity price would have a positive impact on the annual cost saving ratio. It can be concluded that the quantitative sustainability evaluation approach proposed helps to select the ideal hybrid system. [ABSTRACT FROM AUTHOR]

• Novel combined heat and power system integrated with GSHP. • Multi-criteria optimization methodology for energy, environment, economic, and adjustment analysis. • Allocation ratios of mixed water from ICE were optimized to maximize multi-criteria performance. • The comprehensive parametric system analysis was carried out. Hybrid fossil/renewable energy combined heat and power (CHP) systems harness local energy sources, save fossil fuels, and reduce greenhouse gas emissions. Here geothermal energy is integrated into a natural gas driven CHP system by employing both vapor-compressor and absorption cycles through a geothermal heat pump (GSHP). To increase the performance of the heat pumps, the mixed hot water from the internal combustion engine (ICE) is used to preheat the evaporator. Using a multi-criteria optimization method based on energy, economic, environmental and adjustable factors, the optimal allocation ratio of hot water from the ICE is analyzed to maximize the performance of the hybrid CHP system for a specific case building. The necessary thermodynamic models of the system components needed for the optimization are presented. The results demonstrate that the increasing allocation ratio of mixed water for the heat pumps raised the output and coefficient of performance (COP). At optimal allocation ratio maximizing the performance of the CHP system against a set of criteria, the optimum energy saving ratio (ESR), carbon dioxide emission reduction ratio (CDERR), annual cost saving reduction (ACSR), and adjustable ratio are 30.26%, 53.20%, 40.80% and 6.40%, respectively. The hybrid CHP system also shows much higher flexibility than other relevant systems. [ABSTRACT FROM AUTHOR]