Evaluation of a turbine driven CCHP system for large office buildings under different operating strategies

Combined cooling, heating, and power (CCHP) systems use waste heat from on-site electricity generation to meet the thermal demand of the facility. This paper models a CCHP system for a large office building and examines its primary energy consumption (PEC), operational costs, and carbon dioxide emissions (CDE) with respect to a reference building using conventional technologies. The prime mover used in this investigation is a load share turbine, and the CCHP system is evaluated under three different operation strategies: following the electric demand of the facility, following the thermal demand of the facility, and following a seasonal strategy. For the various strategies, the percentages of total carbon dioxide emissions by source are presented. This paper explores the use of carbon credits to show how the reduction in carbon dioxide emissions that is possible from the CCHP system could translate into economic benefits. In addition, the capital costs available for the CCHP system are determined using the simple payback period. Results indicate that for the evaluated office building located in Chicago the CCHP operation reduces the operational cost, PEC, and CDE from the reference building by an average of 2.6%, 12.1%, and 40.6%, respectively, for all the different operational strategies.     

Analysis and optimization of the use of CHP-ORC systems for small commercial buildings

The use of combined heating and power (CHP) systems is increasing rapidly due to their high potential of reducing primary energy consumption (PEC), cost, and carbon dioxide emissions (CDE). These reductions are mainly due to capturing the exhaust heat to satisfy the thermal demand of a building. However, when the CHP system is operated following the electric load, the recovered exhaust heat may or may not be sufficient to satisfy the thermal demand of the facility. When the recovered exhaust heat is more than the heat required, the excess is usually discarded to the atmosphere. An organic rankine cycle (ORC) can be used to recover the surplus exhaust heat to generate extra electricity. Therefore, combining the ORC system with the CHP system (CHP-ORC) reduces the electricity that has to be produced by the CHP system, thereby reducing the total PEC, cost, and CDE. The objective of this paper is to study the energetic, economical, and environmental performance of a combined CHP-ORC system and compare its performance to a standalone CHP system and a reference building for different climate zones. A comparison of a CHP-ORC system operating 24 h with a system operating during typical office hours is also performed.     

三联供系统配置及运行策略的多目标优化分析

在满足建筑物冷热电负荷的前提下,建立了联供系统以年费用、一次能源消耗和二氧化碳排放要求的多目标函数,并利用权重系数将多目标转换为单目标优化模型。以上海市某能源中心的工程为例,得出了冷、热、电三联供系统的最优配置容量及运行策略。     

Analysis of a combined cooling, heating, and power system model under different operating strategies with input and model data uncertainty

Combined cooling, heating, and power (CCHP) system models have been used by many researchers to compare their performance with conventional systems. However, decisions based on the results of computer simulations need to take into account the uncertainty of these results to get insight into the level of confidence in the predictions. This paper presents an analysis of a CCHP system model under different operating strategies with input and model data uncertainty. However, the uncertainties that underlie the variation in input parameters such as the thermal load, natural gas prices and electricity prices are not readily available. Additionally, engine performance uncertainty can be difficult to characterize because of the nonlinearity of engine efficiency curves. This paper presents practical and novel approaches to estimating the uncertainty in these and other input parameters. A case study using a small office building located in Atlanta, GA, is described to illustrate the importance of the use of uncertainty and sensitivity analysis in CCHP system performance predictions, and how the primary energy consumption, operational cost, and carbon dioxide emissions are affected by the uncertainty associated with the model input parameters.     

冷热电联供系统能耗与CO2排放特性分析

建立了微型燃气轮机冷热电联供系统数学优化模型。基于上海某办公楼典型日负荷结构,以总运行费用最低为优化目标,采用模式搜索法对数学优化模型进行求解计算,分析了微型燃气轮机发电效率及空燃比对联供系统能耗与CO2排放特性的影响。研究结果表明微型燃气轮机发电效率及空燃比对联供系统能耗与CO2排放的影响趋势是一致的,可以通过调节微型燃气轮机发电效率及空燃比来充分发挥联供系统节能性和环保性的优势。     

三联供与冰蓄冷耦合的复合系统优化设计

本文建立了一个冷热电三联供与冰蓄冷耦合的复合系统优化数学模型,以年总运行成本最小为目标函数,综合考虑了经济性、环保性、节能性评价指标对系统的影响。最后以上海某综合型超高层建筑为研究对象,利用LINGO软件进行多目标优化计算,提出了三联供耦合冰蓄冷系统的设备优化容量以及全年运行策略优化方案,并分析了电、气价格及二氧化碳排放税对系统的影响。     

Passive designs and strategies for low-cost housing using simulation-based optimization and different thermal comfort criteria

An optimum design of low-cost housing offers low-income urban inhabitants great opportunities to obtain a shelter at an affordable price and acceptable indoor thermal conditions. In this paper, the design and operation of a low-cost dwelling were numerically optimized using a simulation-based approach. Three multi-objective cost functions including construction cost, thermal comfort performance and 50-year operating cost were applied for naturally ventilated and air-conditioned buildings. Thermal environment inside the house was controlled and assessed by two thermal comfort models. Optimization problems which consist of 18 design parameters and 6 ventilation strategies were examined by two population-based probabilistic optimization algorithms (particle swarm optimization and hybrid algorithm). Optimum designs corresponding to each objective function, differences in optimal solutions, energy saving by the adaptive comfort approach and optimization effectiveness were outlined. The optimization method used in this paper shows a considerable potential of comfort improvement, energy saving and operating cost reduction.     

Potential emissions reductions from the use of dual-combined heat and power systems in different climate conditions

In this paper, the potential carbon dioxide emissions (CDE) reduction from the use of a combined heat and power system with two power generation units (D-CHP) is examined for a restaurant building in nine different climate conditions. The performance of the D-CHP system is evaluated on the basis of CDE and operational cost savings. In addition, the results from the D-CHP optimised scheme are compared with the optimised results of a base-loaded CHP (BL-CHP) system and a CHP system operated following the electric load (CHP-FEL). Results show that the D-CHP system produces greater savings over BL-CHP and CHP-FEL for most of the locations examined, whether optimised based on CDE or based on cost. Moreover, the effect of the emissions and cost spark spreads for each location on the D-CHP system performance is analysed. Results indicate that higher spark spreads are shown to yield greater savings for all CHP configurations.     

热电(冷)联产系统运行调节的双目标规划

针对热电（冷）联产系统的运行调节问题建立了包含经济性和节能要求的双目标规划模型,根据热、电、冷负荷的全年变化提出了合理的运行模式和运行方案,探讨了经济性和节能要求的权重变化对总目标函数的影响,分析了分时电价、燃料价格对系统运行策略的影响.     

Innovative method for energy management: Modelling and optimal operation of energy systems

This paper presents an optimal management control strategy for power systems in industrial plants. A dedicated code has been developed to perform system analysis and simulation. The energy/mass balances existing between building and power plant has been depicted through a mathematical model based on vector equations, taking into account the behaviour of each system component. The main result is the definition of the power plant component set points satisfying the energy load under predefined optimization criterion (i.e. system efficiency, costs, pollutant emissions). Input data are the industrial plant loads, both electric and thermal, the technical characteristic of the installations, and the cost of electricity and fuel. As a general result we show that the optimal management of a power plant is as significant as the efficiency of its components for energy saving purposes. In particular, the correlation between the component set point profiles and the energy/cost/pollution savings is highlighted. Yearly simulations are performed on an existing energy system of an industrial plant varying the frequency of energy load dataset. The considered time steps are month, half a day, 4 h and 1 h. The results demonstrate that the whole power plant management leads to a global reduction of the cost and that the availability of more detailed energy load dataset leads to better operation cost estimation. As expected, considering a large time-step, the variation of energy load is not appreciable.The energy saving potential of this method is demonstrated allowing the best plant management solution under different energy loads.     

热电冷联产系统节能性的(火用)分析

利用分析的方法,定义了等效发电效率,对常用热电冷联产系统形式的节能性进行了分析。认为相对于全国平均供电煤耗而言,热电冷联产系统的节能是有条件的,应选取合理的方式,优化设计和运行方案;相对于当前有些热电厂夏季负荷不足的情况,热电冷联产是节能的,在不同的情况下节能率在7.8%~39%之间。建议利用现有的热电联产条件,发展热电冷联产系统,提高现有热电厂的设备利用率和运行经济性。     

Optimal location and thickness of insulation layers for minimizing building energy consumption

This work aims to optimize the position and thickness of insulation layers in building external wall for climates in the coastal Mediterranean zone and in the inland plateau of Lebanon. A space and an air-conditioning system performance models are developed to predict the space and system loads and associated thermal comfort of occupants. A genetic algorithm is used for the optimization of the life cycle cost of the insulation based on energy load while including the productivity loss associated with thermal discomfort during transient periods. For continuous operation of building HVAC system, adding insulation reduces life cycle cost by 20% over current thermal code requirements. During intermittent operation, locating the insulation at the inner side of the walls results in 15% reduction in energy load compared to locating it on the outer wall. The optimum thickness varied between 3 cm and 5 cm depending on wall orientation climate season.     

复合供能系统优化配置和运行策略研究

针对由微小型燃气轮机分布式供能系统和地下水地源热泵组成的复合供能系统,以北京市某典型医院为应用对象,分别以年总费用和天然气年节能率为优化目标,对系统在经济最优、以热定电和节能最优3种运行策略下的优化配置和运行规律进行了研究。结果表明,与电制冷机+燃气锅炉+市电的常规分供方案和地下水地源热泵+市电方案相比,复合供能系统具有经济、节能与电力调峰性能明显等综合优势;与联合循环+燃气锅炉+电制冷机模式相比,复合供能系统在传统的经济最优和以热定电运行策略下并不节能,但在节能最优运行策略下可实现节能。     

Simulation and optimization of the performance in the air-conditioning season of a BCHP system in China

Building cooling, heating and power generation (BCHP) is expected to play an important role in the sustainable energy strategy for buildings. However, in many cases the performance of BCHP systems is not as good as predicted and thus perplexes designers and building owners. In this paper the performance of a typical BCHP system is investigated using thermodynamic and thermoeconomic analyses based on the simulation of off-design operation and the performance optimization of the system with the help of a great number of real operation data of the system and the master data supplied by manufacturers. Two optimization problems using exergetic efficiency and gross benefit of the whole BCHP system, respectively, as objective functions are developed in virtue of curve fitting. Computations result in various graphs, which as references are helpful for judging whether or not the system operation is correct. The graphs show that only with enough high load rates can the system operation yield positive benefits. The simulation tells that the fuel cost of BCHP in China accounts for 70–80% of its total cost and therefore is the most important factor in spreading BCHP in the country.     

浅谈分布式区域冷热电联供系统

建筑节能已成为我国节能技术领域的重要议题。冷热电三联供技术是充分利用低品位热能的一种有效手段,该系统能源综合利用率高,一般均可达到70%以上。本文阐述了分布式区域冷热电联供系统的原理和特点,提出一种基于热气机的天然气能源岛系统。并指出充分推动分布式区域冷热电联供技术的应用,对于能源节约、环境保护、能源安全以及资本有效运作具有十分重要的意义。     

北京南站冷热电三联供系统探讨

介绍了北京南站冷热电三联供系统设计,包括方案选择、负荷计算、系统配置、运行策略、节能分析等。认为使用燃气内燃机比燃气轮机更具优势,建议在电力并网前提下采用以电定热原则确定系统设备容量配置。     

Thermally acceptable temperature drifts can reduce the energy consumption for cooling in office buildings

The energy consumption and cost in large office buildings can be reduced by allowing the indoor environment to deviate from the optimum comfort conditions to situations which are still acceptable by most occupants. One such strategy is to allow the indoor temperature to increase in the afternoon in summer. A computer program was developed to predict the thermal sensation and discomfort under transient conditions, and the detailed computer program BLAST was used to evaluate the indoor temperature, space cooling load, chilled water consumption and seasonal energy use. This paper presents a comparison performed for a reference office building in Montréal between a conventional design, with constant set-point temperature during the operating hours, and a new design, where the indoor temperature is allowed to increase after 3:00 p.m. The results show a reduction of seasonal consumption for chilled water between 34 and 40%, and a reduction of energy budget for HVAC systems of 11%.     

Optimal design and operation of a thermal storage system for a chilled water plant serving pharmaceutical buildings

A group of buildings in the pharmaceutical industry located in Southern Germany is experiencing a trend of growing cooling loads to be met by the chilled water plant composed of 10 chillers of greatly varying cost effectiveness. With a capacity shortfall inevitable, the question arises whether to install an additional chiller or improve the utilization of the existing chillers, in particular those with low operating costs per unit cooling, through the addition of a chilled water thermal energy storage (TES) system. To provide decision support in this matter, an optimization environment was developed and validated that adopts mixed integer programming as the approach to optimizing the chiller dispatch for any load condition, while an overarching dynamic programming based optimization approach optimizes the charge/discharge strategy of the TES system. In this fashion, the chilled water plant optimization is decoupled but embedded in the TES control optimization. The approach was selected to allow for arbitrary constraints and optimization horizons, while ensuring a global optimum to the problem.     

Optimal operation of a hospital power plant

In this paper the operation of an Academic Hospital installation is evaluated by simulation and optimization on a yearly base. A mathematical model has been developed, which is based on energy balances of the installed components. Manufacturer specifications of the components are used for calculating the parameters. The model is formulated using vector equations. Advantages of this type of model formulations are presented. The tools used for optimization are custom developed back-tracking methods for calculating a good starting point and a SQP optimization tool for finding the optimum. Detailed control strategies are calculated for three types of optimization strategies simulated. The simulation results show the impact of the choice of a control strategy on the optimized operation. The results are also applicable for on-line setpoint optimization.     

负荷不确定性对三联供系统配置和经济性的影响

利用围绕代表日负荷的概率分布来描述所有负荷的不确定性,以年总费用期望值为目标函数,建立了三联供系统的优化模型.根据一实例,系统地研究了负荷不确定性对三联供系统配置和经济性的影响.结果表明,负荷不确定性对三联供系统核心设备的配置影响不大,对辅助设备影响较大;随不确定性的增大,三联供系统初投资和运行费用都有所增加,系统经济优势有所下降.