Power grid balancing of energy systems with high renewable energy penetration by demand response

It is generally accepted that the integration of intermittent energy resources like wind energy and photovoltaics into an electricity system cannot exceed a limit of around 20% or 25%, see, e.g. [EWEA, 2005. Large-scale integration of wind energy in the European power supply: analysis, issues and recommendations. The European Wind Energy Association]. However, the decoupling of electricity generation and consumption cannot be implemented only by use of electricity storage. In the end, electricity is converted into many different energy services – quite often into thermal energy – which is better suited for storage. This article presents the results of investigations which studied the potential of those demand response activities for Germany. The investigations are based on both modelling of thermal storage devices and laboratory tests.     

Study on Auto-DR and pre-cooling of commercial buildings with thermal mass in California

This paper discusses how to optimize pre-cooling strategies for buildings in a hot California climate zone with the Demand Response Quick Assessment Tool (DRQAT), a building energy simulation tool. This paper outlines the procedure used to develop and calibrate DRQAT simulation models, and applies this procedure to eleven field test buildings. The results of a comparison between the measured demand savings during the peak period and the savings predicted by the simulation model indicate that the predicted demand shed match well with measured data for the corresponding auto-demand response (Auto-DR) days. The study shows that the accuracy of the simulation models is greatly improved after calibrating the initial models with measured data. These improved models can be used to predict load reductions for automated demand response events. The simulation results were compared with field test data to confirm the actual effect of demand response strategies. Results indicate that the optimal demand response strategies worked well for most of the buildings tested in this hot climate zone.     

Application of an energy management and control system to assess the potential of different control strategies in HVAC systems

The significant and continuous increment in the global electricity consumption is asking for energy saving strategies. Efficient control for heating, ventilation and air-conditioning systems (HVAC) is the most cost-effective way to minimize the use of energy in buildings. In this framework, an energy management and control system (EMCS) has been developed to schedule electricity end-uses in the campus of the Universidad Politécnica de Valencia (UPV), Spain. This paper presents an evaluation performed by using the EMCS of different control strategies for HVAC split systems. It analyzed the effect of different schedules for a common air-conditioning device and demand response strategies are tested in several situations. The economic saving is calculated taking into account the electricity contract clauses. Finally, a test is made for the control of a group of similar devices in order to reduce the maximum peak power in consumption and to obtain a flexible load shape with the HVAC loads. The studies are then extrapolated to a larger system, the whole University campus, for which energy and economic savings are quantified.     

Thermal optimization of multilayered walls using genetic algorithms

This paper reports on an optimization of a building wall using genetic algorithms. The double objective of optimization is maximizing thermal insulation and maximizing thermal inertia. If insulation is easily quantified with thermal resistance, inertia is a criterion not characterized with a single parameter. Using the quadrupoles method, we propose the thermal capacitance as a way to quantify the inertia of the wall. Walls realizing the best trade-off between the two conflicting objectives are presented in a Pareto front. Optimal walls composition shows that the best layers disposition is massive layer at indoor side and insulating layer at outdoor side. An important and new result obtained in this study is that the optimal thickness of the indoor side massive layer is Λ/4 where the thermal wavelength Λ is an intrinsic parameter of the layer material depending on the period of oscillations.     

Domestic electricity use: A high-resolution energy demand model

The pattern of electricity use in an individual domestic dwelling is highly dependent upon the activities of the occupants and their associated use of electrical appliances. This paper presents a high-resolution model of domestic electricity use that is based upon a combination of patterns of active occupancy (i.e. when people are at home and awake), and daily activity profiles that characterise how people spend their time performing certain activities. One-min resolution synthetic electricity demand data is created through the simulation of appliance use; the model covers all major appliances commonly found in the domestic environment. In order to validate the model, electricity demand was recorded over the period of a year within 22 dwellings in the East Midlands, UK. A thorough quantitative comparison is made between the synthetic and measured data sets, showing them to have similar statistical characteristics. A freely downloadable example of the model is made available and may be configured to the particular requirements of users or incorporated into other models.     

热环境、热舒适与空调节能

本文讨论了热环境、居室人与空调设备的相互作用关系及影响人体热舒适的主要环境参数(温度、风速、相对湿度、平均辐射温度);结合厦门夏季人居热环境实际状况,分析实现空调节能途径。     

Optimization of thin conical frusta for impact energy absorption

Experimental and numerical investigations were carried out to optimize thin-walled conical shells for their use in design for energy absorption. Geometrical parameters, such as bottom diameter, height, and semi-apical angle were considered to obtain the design space. The numerical analysis and impact experiments were designed using design of experiments (DOE). A three-level, second-order Box–Bhenken technique was used to select the design points from the design space. Various set of numerical simulations were carried out using LS-DYNA. To investigate the influence of flow stress of the material on the energy absorption, numerical simulations were carried out using frusta made of aluminium, zinc, and mild steel. From the numerical results, mathematical models were created using response surface methodology (RSM). With the help of impact experiments carried out on specimens made of zinc on a drop mass test rig, a mathematical model has been developed using RSM. The mathematical models developed using experimental data and the numerical data were used as objective functions for optimization of the design. The non-dominated sorting genetic algorithm code NSGA II was used to optimize the design. The mathematical models were also used to predict the energy absorbed and deformation. The influence of various design parameters on energy absorption has been analysed and is discussed.     

Optimum operational conditions of a rotary regenerator using genetic algorithm

The optimum operational conditions of an air-to-air rotary regenerator (also called air preheater or heat wheel) for air conditioning applications which was designed and manufactured in Energy Systems Improvement Laboratory (ESIL) has been investigated in this paper. The performance of such a rotary regenerator was modeled and the numerical values of modeling output were verified with the experimental data obtained from the equipment testing. In the next step, the optimum operational conditions of the rotary regenerator were obtained using genetic algorithm optimization technique subject to a list of constraints. The objective function in the optimization technique was the thermal effectiveness, while the design parameters (decision variables) were volumetric flow rates of cold and hot air streams, matrix rotational speed, and the exchanger frontal area (heat transfer surface area). The apparatus was tested under the optimized operating conditions and the results were compared with the results obtained numerically applying genetic algorithm optimization. The experimental value for the effectiveness showed an acceptable closeness (2.07%) with the corresponding value obtained from the system modeling and optimization. The economic analysis of energy savings by the designed and manufactured regenerator showed a pay back period about 3 years.     

基于弹塑性动力分析的结构非线性响应及抗震设计

回顾与总结了结构在大震作用下的非线性动力反应分析成果 ,包括结构整体分析模型 ,构件单元模型 ,恢复力模型以及运动方程的求解等问题。基于平面杆系模型 ,针对结构在多遇及罕遇地震下的弹塑性时程响应计算结果及其与现行规范设计结果的对照 ,对今后结构非线性抗震设计提出了建议     

冬季空调间歇运行室内温度特性及节能潜力的理论与实验研究

本文通过对冬季空调房间空调开关机过程试验得到的室内环境温度数据进行分析,建立了温度变化的理论模型,分析结果表明,房间内气温随时间呈指数规律变化,且时间越长,室内温度越趋于稳定。通过对开关机过程中室内PMV值进行计算,在对人体热舒适影响不大的条件下,得到了试验房间空调间歇运行较佳的启停时间组合方式,与常规连续运行方式相比节能潜力最高可达40%。     

Three-years operation experience of a ground source heat pump system in Northern Greece

The paper presents the basic parameters and the energy flows of a ground source heat pump system (GSHP) used for air conditioning the New City Hall of Pylaia (Thessaloniki area—Northern Greece). The building is a typical public one, with an air-conditioned area of 1350 m². The ground source heat pump installation is the largest in Greece, and its operation is monitored with the aid of a DAQ system. The energy flows presented in the paper are based on DAQ recordings of the first 3 years of system's operation. It is proved that the energy demand of the system is significantly lower, compared to that of conventional heating and cooling systems. The seasonal COP of the system has not yet been stabilized, gradually increasing, as it is expected due to the operation of the ground heat exchanger.     

Performance evaluation of a PV ventilated window applying to office building of Hong Kong

PV ventilated glazing technology for application in warm climate provides energy saving opportunities through the reduction in air-conditioning load, the daylight utilization, and the green electric power generation. In a working environment, the use of semi-transparent a-Si glazing is deemed better than the one with non-transparent c-Si solar cells. This paper reports an evaluation of its integrated performance using a small office room in Hong Kong as an example. An energy model of a PV ventilated window system is first introduced. Based on this together with the TMY weather data of Hong Kong and the daylight simulation capability of the EnergyPlus program, the overall performance analysis have been executed for different window orientations. It was found that a solar cell transmittance in the range of 0.45–0.55 could achieve the best electricity saving.     

Adaptive optimal control model for building cooling and heating sources

An adaptive optimal control model for building cooling and heating sources is presented with the aim of achieving global optimization and satisfying the requirements of time and accuracy in HVAC system control. The adaptive optimal control model includes the optimal control model, parameter identification and optimization algorithm. First, the penalty function is constructed to transform constrained optimization problem into unconstrained optimization problem, and then, the fuzzy self-tuning forgetting factor method is developed for parameter identification. In the end, the genetic algorithm (GA) is used to find the optimum values for the discrete and continuous variables. Optimization is applied for the building cooling source system in a publishing house located in Changsha, China. The optimization is expected to reduce the energy consumption of the cooling source system by 7%.     

电荒、节能与热舒适研究

电力资源短缺是目前我国面临的重大问题,而空调负荷是造成电网压力大、电力供应严重不足的主要原因之一。人体热舒适研究涉及到空调舒适温度、空调设备运行控制、气流组织优化、节能等方面,其研究成果可直接或间接应用于降低空调能耗。热舒适研究可能成为解决电力紧张的方法之一。     

Seasonal thermal energy storage – the HYDROCK concept

A method for seasonal storage of heat or cold in the bedrock (the HYDROCK concept) is presented and its thermal performance discussed. It involves the use of a fractured bedrock at shallow depths (ca. 50–250 m), where existing fractures are stimulated or new fractures artificially created and used as flow-paths for a heat/cold carrier (usually water). The fracture surfaces are used as heat exchangers and the bedrock is loaded and unloaded to suit the energy needs. Propants are injected into the fractures to keep them open and reduce the energy needed for pumping water through the system. Field tests confirm that stacked parallel fractures can be produced by hydraulic fracturing. The thermal performance of the store is modelled and compared with a ducted ground heat store. It is shown that the HYDROCK store may yield 10–20% more energy during extraction than a ducted ground heat store for similar amounts of injected energy. This indicates that the HYDROCK concept is competitive as a seasonal energy store and may be of particular importance as an alternative energy source where existing methods cannot be economically justified. Electronic Publication