Building Cooling Heating And Power Research Articles

Optimal phase change temperature for building cooling heating and power 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 composed of a gas turbine, an absorption chiller and TES equipment with PCM is presented. To evaluate the energy saving effect of PCM-TES, a new index, energy storage effectiveness, is proposed and its relationship with primary energy consumption is established. Aimed at maximizing the energy storage effectiveness, the optimal phase change temperature of the 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 number of transfer units. It also indicates that both energy storage effectiveness and optimal phase change temperature in-crease with increasing number of transfer units. So improving the thermal performance of PCM-TES device is favorable for increasing energy efficiency and saving primary energy consumption accordingly. This work is of great importance in guiding the optimization design of practical phase change temperature of the PCM-TES-BCHP systems.

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.

A simplified model to study the location impact of latent thermal energy storage in building cooling heating and power system

Introducing the thermal energy storage (TES) equipment into the building cooling heating and power (BCHP) system proves to be an effective way to improve the part load performance of the whole system and save the primary energy consumption. The location of TES in BCHP has a great impact on the thermal performance of the whole system. In this paper, a simplified model of TES-BCHP system composed of a gas turbine, an absorption chiller/an absorption heat pump, and TES equipment with phase change materials (PCM) is presented. In order to minimize the primary energy consumption, the performances of BCHP systems with different PCM-TES locations (upstream and downstream) are analyzed and compared, for a typical hotel and an office building respectively. Moreover, the influence of the thermal performance of PCM-TES equipment on the energy saving effect of the whole system is investigated. The results confirm that PCM-TES can improve the energy efficiency and reduce the installed capacities of energy supply equipment, and that the optimal TES location in BCHP highly depends on the thermal performance of the TES equipment and the user load characteristics. It also indicates that: 1) the primary energy saving ratio of PCM-TES-BCHP increases with increasing NTU of TES; 2) for the studied cases, downstream TES location becomes more preferable when user loads fluctuate greatly; 3) only downstream TES can reduce the installed capacities of absorption chiller/absorption heat pump. This work can provide guidance for PCM-TES-BCHP system design.

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.

Adequacy assessment of power systems incorporating building cooling, heating and power plants

Electric power systems have been changing from the conventional and traditional electric units to the efficient, economical, less-polluting and reliable ones. Building cooling, heating and power (BCHP) systems can yield these goals and save energy as well as improve the reliability of the system. However, for significant integration and the use of large amount of BCHP generation in electric power systems, some approaches should be followed in order to study the reliability of the BCHP systems. In this study, we focused on the reliability aspects of power systems incorporating BCHP systems in the local distribution systems. The Markov method based on the state-space analysis is used to investigate the impacts of implementation of BCHP systems on the power systems’ reliability. The Markov method is well suited to analyze the reliability of systems based on a continuous stochastic process. The Roy Billinton test system and the IEEE reliability test system are used to illustrate the results. Case studies show the effects of BCHP systems on general adequacy of electric power systems. Various case results demonstrate the efficiency and effectiveness of the proposed method.

Applicability of TES-BCHP System Based on the Degree of Mismatch between User Load Demands and Energy Supply

Integrating thermal energy storage (TES) device with building cooling heating and power (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 supplied 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 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 different working conditions. The preliminary results show that the more DM approaches to unity, the higher PESR of TES-BCHP will be. It also indicates that TES-BCHP is more applicable for those where the heating demand is dominant.

Energy Efficiency of Existing Buildings: Optimization of Building Cooling, Heating and Power (BCHP) Systems

The enhancement of the energy efficiency of existing buildings represents an important task, specifically addressed by the European Directives. Among the currently available technologies to achieve this issue, the combined generation of heat and power (CHP) is found. Its higher efficiency with respect to the separate production of heat and power mainly depends on the occurrence of a profitable use of the cogenerated heat. This technology is now rapidly spreading because of its benefit from both the energy and the environmental sustainability points of view. However, in order to properly size the CHP system capacity and operation strategy, some specific design rules have to be identified. In particular, the CHP systems optimal design requires the building energy loads to be known on a hourly time scale. In the present paper a simplified procedure for estimating the hourly energy load for space heating and cooling of existing buildings is applied to the assessment of building cooling, heating and power systems energy performance. The results, obtained for a complex nine storey building located in six representative climates, point out that the suggested method allows to estimate the primary energy savings index with an approximation error, averaged over the considered combined generation system capacity range, less than 2.8% and 3.3% in continuous and time scheduled plant operation, respectively.

A simple method to determine the optimal gas turbine capacity and operating strategy in building cooling, heating and power system

The gas turbine capacity and operating strategy selection of Building Cooling, Heating and Power (BCHP) systems play an important role in the system operating performance, leading to different primary energy consumption for the same building load. However, the optimal design problems of those two factors have not been solved very well. This paper presents a new simple method to determine the optimal gas turbine capacity and operating strategy. The gas turbine electricity efficiency, the Coefficient of Performance (COP) of absorption heat pumps, and the demand heat/power ratio are found to be the key factors. There exists two values of the critical gas turbine efficiency. More primary energy will be consumed when the selected gas turbine electricity efficiency is below the smaller critical value compared with the separated generation. When the selected gas turbine electricity efficiency is between the two critical values, the hourly optimal operating strategy and the gas turbine capacity can be determined by Following the Thermal Load (FTL). Otherwise, the optimal gas turbine capacity should be sized by Following the Electricity Load (FEL) with the consideration of the actual given conditions. Based on this method, some typical cases with or without TES are analyzed. The results agree well with the conclusions drawn in the current published papers. This method gives a new aspect to understand BCHP analytical design, and can be applied in the engineering area.

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.

Theoretical Analysis on the Solid Sensible and Latent Heat Storage in Building Cooling Heating and Power Systems

Thermal Energy Storage (TES) is an important technology to balance the hourly energy supply and demand in Building Cooling Heating and Power (BCHP) systems, aiming to lower primary energy consumption. The solid sensible TES and latent TES, which are relatively developed, have the potential to be generalized in BCHP systems. However, design problems such as what are the key parameters or how to get the optimal value for this specific application remain unclear. The objective of this paper is to give a theoretical method to solve those two problems. The fixed storage period constraint is taken into consideration, which was important but not considered in the published articles. Firstly, a new evaluation index called the non-dimensional cooling capacity is defined to evaluate the thermal performance of TES. Secondly, the key non-dimensional design parameters are found based on the mathematical model. Finally, the sensitivity analysis of those parameters is studied. The results can be applied to further understand TES in BCHP systems and are helpful to design BCHP systems.

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.

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.