Building Cooling Heating And Power System Research Articles

Operation strategy optimization of BCHP system with thermal energy storage: A case study for airport terminal in Qingdao, China

Building cooling heating and power (BCHP) system is widely used in various public buildings, due to its high energy efficiency, low pollution emissions, high energy supply reliability and safety. Integrating thermal energy storage (TES) equipment with BCHP system proves to be an effective way to improve the system performance. However, some practical TES-BCHP systems show bad economic performance due to unreasonable operation. Thus to reduce the operation costs of TES-BCHP system through operation strategy optimization is important for realizing the advantages of TES-BCHP system compared to traditional systems. In this paper, the practical TES-BCHP system designed for the new airport terminal building energy supply in Qingdao, China is taken as the illustrative example. Aimed at minimizing the operation costs for such a system, the simplified system optimization model is established and the optimal operation strategy is determined through inverse problem and variation method. The preliminary results show that system operation strategy highly depends on the local natural gas price and electricity price. The optimal operation strategy for the studied case is as follows: (1) during the night, electrical chiller works at full capacity and the extra chilled water is stored in the water tank; (2) during the daytime, gas turbine is turned on and the absorption chiller is activated to produce low temperature water. Meanwhile, the water stored in the tank is discharged and the electrical chiller only works to make up for the insufficient part. Under such optimal operation strategy, electrical chillers, TES equipment and absorption chiller account for 51.4%, 27.3% and 21.3% of the total cooling loads respectively. In that situation, the operation costs can be reduced by 24% in a typical summer day. In off-design days, load ratio of the TES equipment increases with decreasing cooling demand, leading to 8.94×106 RMB operation cost saving in a whole summer season. It also indicates that the pay back period of incremental capital investment for TES-BCHP system is 5 years with 10% discount rate under present local energy policy. This work is of great significance in guiding the optimization operation for practical TES-BCHP systems.

Optimal phase change temperature for BCHP system with PCM-TES based on energy storage effectiveness

Integrating thermal energy storage (TES) equipment with building cooling heating and power (BCHP) system can improve system thermal performance. In this paper, a simplified model of TES-BCHP system is presented with phase change material (PCM). Moreover, a new index, energy storage effectiveness, is proposed and its relationship with primary energy consumption is established. To maximize energy storage effectiveness, the optimal phase change temperature of PCM-TES-BCHP system is obtained. The results show that the theoretically optimal phase change temperature is just the geometrical average value of ambient temperature and exhaust gas temperature from gas turbine for ideal PCM-TES equipment with infinite NTU. It also indicates that both energy storage effectiveness and optimal phase change temperature increase with increasing NTU. So improving the thermal performance of PCM-TES device is favorable for increasing energy efficiency and saving primary energy consumption. This work can provide guidance for the design of PCM-TES-BCHP systems.

Configuration Optimization with Operation Strategy of Solar-assisted Building Cooling Heating and Power System to Minimize Energy Consumption

This work designs a novel hybrid building cooling heating and power (BCHP) system incorporating with solar energy and natural gas. A basic natural gas BCHP system containing power generation unit, heat recovery system, hybrid cooling system and storage tank is integrated with solar photovoltaic (PV) and/or thermal collector. Optimization methodology with genetic algorithm (GA) is applied to optimize the configuration of the solar-assisted BCHP system for minimizing primary energy consumption. BCHP schemes are optimized in following electrical load (FEL) and following thermal load (FTL) operation strategies respectively. The result indicates that BCHP system in the FEL mode consumes less energy consumption than in the FTL mode to meet building demands. But the FTL mode would be superior to FEL mode at taking the surplus products from the hybrid BCHP system into consideration.

Pre-feasibility of building cooling heating and power system with thermal energy storage considering energy supply–demand mismatch

Natural-gas-driven building cooling heating and power (BCHP) system shows high energy efficiency and low greenhouse gases emission, but is of dissatisfactory performance under part load working conditions due to the non-synchronized and fluctuating thermal and electrical demands. Integrating thermal energy storage (TES) device with BCHP system proves to be an effective way to improve the performance of the whole system. In this paper, the applicability of TES–BCHP system is investigated according to the relationship between user load demands and system energy supply. Based on the supply thermal power ratio of the prime mover and the required one of users, a new parameter, the degree of mismatch (DM), is defined. Moreover, the analytical relationship between primary energy saving ratio (PESR) of TES–BCHP system and DM is established, under following thermal load (FTL) and following electrical load (FEL) respectively for three typical working conditions. The results show that the more DM approaches to unity, the higher PESR of TES–BCHP will be, and that the exportability of the co-generated electricity is favorable for energy saving. It also indicates that TES–BCHP is more applicable for those where the heating demand is dominant. This work is of great significance in further understanding the energy saving mechanism between TES and BCHP and guiding the design of practical TES–BCHP systems.

Optimal Phase Change Temperature for Energy Storage Based on Fluctuating Loads in Building Cooling Heating and Power System

Abstract Natural gas driven Building Cooling Heating and Power (BCHP) system is encouraged to develop as small-scale energy supply system in recent year. Integrating Energy Storage System (TES) with tri-generation system can improve the energy efficiency and reduce the installed capacity for energy supply equipment. However, it has never been an easy task to reasonably design the TES-BCHP system, in terms of that it is hard to determine the suitable installed capacity of energy supply devices considering the fluctuating loads and the influence of TES. In this paper, a thermodynamic model of BCHP system with phase change material (PCM) energy storage is established. According to practical user loads and considering the correspondingly hourly changing flow rate in charge and discharge processes, a simplified method is proposed to determine the optimal phase change temperature for BCHP-TES, aiming to minimize the primary energy consumption of BCHP-TES system. An illustrative example shows that the optimal phase change temperature can be obtained for given loads. It also indicates that compared to infinite NTU for PCM-TES, the optimal phase change temperature will increase as well as the corresponding minimal primary energy consumption for finite NTU. This work is of great importance for PCM optimization of BCHP-TES system design.

Comparison of Thermal Performance of BCHP System with Latent Thermal Energy Storage in Different Locations

Building cooling, heating and power (BCHP) is an integrated energy system to provide the three energy commodities, which is characterized by cascading utilization of primary energy and high energy efficiency. Latent thermal energy storage (LTES) is a promising technology to smoothen the fluctuating loads, and improve the system efficiency due to the isothermal property during phase change process and the high energy storage density. This paper aims at studying the influences of LTES location on BCHP system, in the upstream or downstream of waste heat recovery unit, with consideration of partial load performance of equipment. Firstly, a general model is presented for a typical BCHP system working in winter, consists of gas turbine (GT), absorption heat pump (AHP), and LTES unit. Based on the assumption of infinite number of transfer unit (NTU) of LTES, the comparison of the two designs is conducted in terms of primary energy consumption (PEC) and equipment capacity for an office in Beijing. Then, the influences of the limited heat transfer area of LTES are analyzed. The results show that the addition of LTES can significantly reduce the PEC and equipment capacity because it enables the GT work efficiently. In addition, the choice of the LTES in the downstream of AHP is preferred when assuming infinite NTU of LTES. However, when considering the limited heat transfer area, the heat transfer temperature difference makes the downstream choice less advantageous.

Multi-criteria Performance Analysis of BCHP System Taking Reliability and Availability into Consideration

The failure of equipment or sub-system leads to disruption of building cooling, heating and power (BCHP) system. This paper analyzed the energetic, economic and environmental performances of BCHP system taking reliability and availability into consideration. The results indicate that the integrated performance of the optimized non-redundant BCHP system is the best while its availability of cooling and heating is lower than the separation production (SP) system. The redundant BCHP system increases 0.44% availability at the cost increase of 38 Yuan/kWh while its energetic and economic performances are worse.

Influence of Position of Thermal Energy Storage with Different Effectiveness on the Performance of BCHP System

Natural gas-driven Building Cooling Heating and Power (BCHP) system shows high energy efficiency and low emission. Nevertheless non-synchronized and fluctuating thermal and electrical demands lead to part load working conditions of the energy supply devices (prime mover and absorption chiller), resulting in low energy efficiency of the whole system. Integrating Thermal Energy Storage (TES) equipment to BCHP proves to be an effective way to improve the system performance. The location of the TES device in BCHP has a great impact on the performance of the whole system. In this paper, a simplified model of BCHP with TES system composed by a Gas Turbine (GT), an Absorption Chiller (AC) and a TES device of different heat exchange effectiveness is presented. Aiming to minimize primary energy consumption, the performances of BCHP systems with different TES locations (upstream and downstream the AC) are compared and analyzed. The preliminary results indicate that it is better for improving efficiency and reducing installed capacities of energy supply devices, to place TES close to users. Moreover, it is shown that the Relative Energy Saving Ratio (RESR) of BCHP with TES system is influenced by whether the co-generated power is merchantable to the power grids. This work is of great significance in further understanding the energy saving mechanism between TES and BCHP and guiding the design of practical BCHP with TES systems.

Reliability and availability analysis of redundant BCHP (building cooling, heating and power) system

Failure of a component in BCHP (building cooling, heating and power) system may result in failure of a sub-system or of the whole system. The reliability and availability analysis of BCHP system is helpful to the designer to decide the redundancy in case of equipment failure. This paper presents the redundant design of BCHP system and its operation mode. The SSM (state-space method) combined to the probabilistic analysis of Markov model, is employed to analyze the reliabilities of three forms of energy supply including electricity, heat and cool in BCHP system. The failure rate, the repair rate, the availability and the MTBF (mean time to failure) of the redundant and non-redundant BCHP systems are deduced and analyzed respectively. Then, a numerical case for the reliability analysis of the redundant and non-redundant BCHP systems is compared to the SP (separation production) system. Finally, the calculation results indicate that the reliability of the redundant BCHP system compared to the SP system obviously increases, and the failure rates of the electricity, heat and cool supplies decrease 99.63%, 94.30% and 99.97% respectively.

Multi-objective optimization design and operation strategy analysis of BCHP system based on life cycle assessment

The promising energetic and environmental benefits of building cooling heating and power (BCHP) system are greatly dependent upon its design and operation strategy. In this paper, the energy and emission flows and different operation strategies of a BCHP system driven by gas engine are analyzed. Life cycle assessment (LCA) is employed to assess and compare the whole life energy saving potentials and pollutant emission reductions of BCHP system with the traditional energy system. Furthermore, energy consumption and three pollutant-related impacts, global warming, acid precipitation and respiratory effects, are selected as objective functions to optimize the gas engine capacity of BCHP system in different operation strategies. A numerical case of BCHP system for a commercial office building in Beijing, China is applied to obtain the optimum BCHP alternative in terms of the comprehensive energy and environment performance. The uncertainty of different evaluation criteria weights is also analyzed to show their influences on the optimal design and operation strategy. The results show that a reasonably sized BCHP system with an electric load-following strategy has the best performance under a wide interval of criteria weights, when the energetic and environmental benefits of producing excess electricity for nearby users are not considered.

Life cycle assessment of a solar combined cooling heating and power system in different operation strategies

A novel solar building cooling heating and power (BCHP) system driven by solar energy and natural gas is proposed in this paper. The performance of the presented system is greatly dependent upon the operation strategy. The primary energy consumption (PEC) and pollutant emissions of the solar BCHP system in following the electricity loads (FEL) and following the thermal loads (FTL) operation strategies are estimated based on life cycle assessment (LCA). Furthermore, three most important energy-related environment problems and human health issues, global warming, acid precipitation and respiratory effects, are considered to assess the environmental impacts of the system. In order to evaluate the comprehensive benefits achieved by the solar BCHP system in different operation modes, grey relation theory is employed to integrate the energetic benefits with environmental performances. Finally, a numerical case of the solar BCHP system for a commercial office building in Beijing, China is applied to compare the integrated performance in the FEL operation strategy with that of the FTL operation strategy. The results indicate that the energy saving and pollutant emissions reduction potentials of the FTL operation mode are the better than that of the FEL mode.

Sensitivity analysis of optimal model on building cooling heating and power system

The optimization of building cooling heating and power (BCHP) system is helpful to improve its comprehensive performance including energetic, economic and environmental aspects. However, the optimal results are closely dependent on the initial setting parameters. This paper deduces the energy consumption of BCHP system following the electrical load and presents the optimization problem of BCHP system that includes the decision variables, the objective function, the constraint conditions and the solution method. The influences of the initial parameters, which include the technical, economic and environmental parameters, the building loads and the optimization setting parameters, on the optimal decision variables and the performances of BCHP system are analyzed and compared. The contour curves of the performances of BCHP system in comparison to the conventional separation production (SP) system, and the sensitivity of the optimal decision variables to the initial parameters are obtained.

Influence analysis of building types and climate zones on energetic, economic and environmental performances of BCHP systems

The performance of building cooling heating and power (BCHP) system is obviously dependent upon the seasonal atmospheric conditions and the building types. This paper presents the energy flow analysis and the evaluation criteria of the redundant BCHP system and describes the optimal design method. The BCHP systems for four building categories (Hotel, Office, Hospital and School) in five climate zones (Severe Cold Zone, Cold Zone, Hot Summer and Cold Winter Zone, Mild Zone and Hot Summer and Warm Winter Zone) in China are compared and evaluated from energetic, economic and environmental aspects. The comparison results show that the BCHP system is generally suitable for the building, which operates for long time over the entire year, in the climate zone where buildings require more heat for space heating. Moreover, the influence analysis on BCHP capacity and operation strategy indicates that the capacity of power generation unit (PGU) is the most sensitive design parameter to influence the integrated performance of the BCHP system.

Environmental impact analysis of BCHP system in different climate zones in China

The operation performance of building cooling, heating and power (BCHP) system is dependent on the seasonal atmospheric conditions. This paper presents the environmental impact models of separation production (SP) system and BCHP system respectively. Three most important energy-related environmental issues, global warming, acid precipitation and stratospheric ozone depletion, are considered to evaluate the environmental impact of BCHP system for a commercial building located in five climate zones, China. Because the global emissions of BCHP system are related to the central power plant that provides the additional electricity to building, the environmental impacts by coal-fired and gas-fired power plants are compared and discussed. The results indicate that the emission reduction potential of BCHP system over SP system in hot summer zone and mild zone is larger than in severe cold zone when the coal-fired power plant is used. Contrarily, BCHP system in severe cold zone reduces more emissions than in hot summer zone when the gas-fired power plant provides the additional electricity.

Particle swarm optimization for redundant building cooling heating and power system

An optimal and redundant building cooling heating and power (BCHP) system can yield economical savings, but more importantly can save energy as well as reduce the emission of pollutants. This paper presents the energy flow analysis of the conventional separation production (SP) system and the redundant BCHP system. Four decision variables (the capacity of power generation unit (PGU), the capacity of heat storage tank, the on–off coefficient of PGU and the ratio of electric cooling to cool load) to be optimized are selected in consideration of the design and the operation strategy of BCHP system. An objective function to simultaneously measure the energetic, economical and environmental benefits achieved by BCHP system in comparison to SP system is constructed and maximized. Particle swarm optimization algorithm (PSOA) is employed to search the optimal solutions. A case study of BCHP system with thermal storage unit and hybrid cooling system is presented to ascertain the feasibility and validity of the optimization method.

Optimization design of BCHP system to maximize to save energy and reduce environmental impact

The energetic and environmental performances of building cooling heating and power (BCHP) system are closely dependent on its design and operation strategy. This paper analyzes the energy consumptions of a conventional separation production (SP) system and a BCHP system respectively and constructs their corresponding environmental impact models. Furthermore, three energy-related environmental issues, global warming, acid precipitation and stratospheric ozone depletion, are assessed in the proposed emission model. To maximize the benefits (energy-saving and emission-reducing) achieved by the BCHP system in comparison to the SP system, genetic algorithm (GA) is employed to optimize the capacity of BCHP system in consideration of its operation mode. A numerical case of BCHP system for a hotel building is applied to ascertain the effectiveness of the optimal method and demonstrate the performances of the optimal BCHP system.

Uncertain programming of building cooling heating and power (BCHP) system based on Monte-Carlo method

Uncertainty of building energy demands has large influence on accuracy of building cooling heating and power (BCHP) programming model. Uncertain programming model is proposed to optimize BCHP system with consideration of uncertainty of energy demands. Monte-Carlo method (MCM) and mixed-integer nonlinear programming (MINLP) are integrated in the model (M–M model for short). MCM can be used to simulate the uncertainty of energy demands avoiding dimension disaster and complex calculation. Correlation between different energy demands can also be considered in the model. And facility scheme and operation strategy can be optimized simultaneously in MINLP model. A numerical example is calculated with the M–M model. Convergence rate of expected values of the variables optimized in the model is high. Influence of energy demand uncertainty is studied with investigation of expected values, standard deviations of evaluation indicators and facility capacities. Sensitivity of the parameters to energy demand uncertainty is much different. It is unnecessary to consider uncertainty of energy demands when evaluating system feasibility with indicators of annual cost saving rate and annual natural gas saving rate, for they are influenced only a little by uncertainty of energy demands. While uncertainty of energy demands must be considered when studying parameters related to assistant facilities, which are very sensitive to the uncertainty. The result is valuable for designing strategy of facility scheme.

Experimental investigation of adsorption chiller for Micro-scale BCHP system application

Building cooling, heating and power (BCHP), is an attracting cogeneration system for its economic and environmental friendly qualities. Therefore, it is meaningful to develop Micro-scale BCHP (MBCHP) system based on adsorption chiller and internal combustion gas engine for the use of residential and light commercial buildings. To guide the optimum matching and operation of adsorption chiller in MBCHP system correctly, this paper deals with the performance of adsorption chiller under varying heating conditions. Experimental results show that the value of COP is high in the operation mode of varying hot water inlet temperature with mass recovery in no heating pattern (VTNH). With the hot water inlet temperature of 65 °C, the value of COP is as high as 0.40 in VTNH mode. Under electricity output conditions from 6.0 to 8.3 kW in MBCHP system, VTNH mode is especially preferred when cooling demand is with priority.