A review of urban energy system models: Approaches,challenges and opportunities

Energy use in cities has attracted significant research in recent years. However such a broad topic inevitably results in number of alternative interpretations of the problem domain and the modelling tools used in its study. This paper seeks to pull together these strands by proposing a theoretical definition of an urban energy system model and then evaluating the state of current practice. Drawing on a review of 219 papers, five key areas of practice were identified – technology design, building design, urban climate, systems design, and policy assessment – each with distinct and incomplete interpretations of the problem domain. We also highlight a sixth field, land use and transportation modelling, which has direct relevance to the use of energy in cities but has been somewhat overlooked by the literature to date. Despite their diversity, these approaches to urban energy system modelling share four common challenges in understanding model complexity, data quality and uncertainty, model integration, and policy relevance. We then examine the opportunities for improving current practice in urban energy systems modelling, focusing on the potential of sensitivity analysis and cloud computing, data collection and integration techniques, and the use of activity-based modelling as an integrating framework. The results indicate that there is significant potential for urban energy systems modelling to move beyond single disciplinary approaches towards a sophisticated integrated perspective that more fully captures the theoretical intricacy of urban energy systems.     

太阳能热水系统的节能效益分析

一引言能源是人类社会存在与发展的物质基础。在环境日益恶化的压力下,发展和利用能源要以环保为根本出发点。大力发展可再生能源成为我国21世纪发展国民经济和建设小康社会刻不容缓的主要任务和战略目标。在可再生能源种类中,太阳能的利用前景最为广阔。     

太阳能供暖与制蒸馏水综合应用技术

在非供暖期,为了维护太阳能供暖系统的完好,避免太阳能集热器因干烧导致损坏,提出了一种太阳能供暖与制蒸馏水综合应用技术方案。通过对太阳能集热供暖设施进行技术改造,使太阳能集热装置在冬季用于建筑供暖,在非供暖期用于制蒸馏水,提高了太阳能集热系统的利用率。     

Modeling and identification of solar energy water heating system incorporating nonlinearities

Prediction accuracy is a fundamental modeling requirement. This work explores different models for a solar domestic water heating system located near Viña del Mar, Chile, in order to improve model prediction accuracy over some existing alternatives. The main approach is semi-physical modeling, which combines phenomenological modeling and system identification. The former helps to organize in a conceptual form the available system knowledge, and the latter allows to adjust that knowledge into a particular model structure for a working system. Thus, with semi-physical modeling we take advantage of a basic property of classical identification models: they are linear-in-the-parameters, but may contain nonlinear regressors. Hence, while physical knowledge suggests nonlinear data regressors, system identification adjusts linear weighting parameters. The models proposed here incorporate nonlinearities based on physical system knowledge and they include, among other inputs and disturbances, air wind speed (v) and air relative humidity (RH), signals not usually considered in these model structures. Specifically, this work shows model predictive accuracy of storage tanks temperature for three model types: semi-physical, state-space and, a combination of semi-physical and a feedforward neural network with one hidden layer and eight neurons. The best models found here, according to prediction accuracy, are of semi-physical nature, and are obtained using stepwise regressor elimination algorithms which retain disturbances such as v and RH. Additionally, final models are validated with classical statistical tests such as AIC and correlation analysis.     

太阳热水器与空气源热泵辅助加热集中供热水系统的工程设计

结合实例论述宾馆用太阳热水器与空气源热泵辅助集中供洗浴热水系统的工程设计方法,并着重介绍了空气源热泵的配置、布局、安装和控制.     

Performance investigation of thermal energy storage system with Phase Change Material (PCM) for solar water heating application

In order to harvest solar energy, thermal energy storage (TES) system with Phase Change Material (PCM) has been receiving greater attention because of its large energy storage capacity and isothermal behavior during charging and discharging processes. In the present experimental study, shell and tube TES system using paraffin wax was used in a water heating system to analyze its performance for solar water heating application. Energy and exergy including their cost analyses for the TES system were performed. Accordingly, total life cycle cost was calculated for different flow rates of the Heat Transfer Fluid (HTF). With 0.033 kg/min and 0.167 kg/min flow rates of water as HTF, energy efficiencies experienced were 63.88% and 77.41%, respectively, but in exergy analysis, efficiencies were observed to be about 9.58% and 6.02%, respectively. Besides, the total life cycle cost was predicted to be $ 654.61 for 0.033 kg/min flow rate, which could be reduced to $ 609.22 by increasing the flow rate to 0.167 kg/min. Therefore it can be summarized that total life cycle cost decreases with the increase of flow rate.     

Transient analysis of closed loop solar water heating system (effect of heat exchangers)

This paper presents a general and more realistic model of the transient behaviour of a forced circulation solar water heating system with and without heat exchangers in the collector loop and storage tank. The analysis has been presented for a constant flow mode. The effects of heat exchanger length and various water heating system parameters on its performance have been studied. Numerical calculations have been made for a typical cold day (26 January 1980) at Delhi.     

Analysis of a solar water heating system with n-tanks in series

A straightforward analysis of a solar water heating system with n-tanks connected in series has been presented. The long-term performance of the system has also been studied. On the basis of numerical calculations made for four successive days, the following conclusions have been drawn:

1. (1) The fluctuation in temperature variation decreases with increase of the number of tanks connected in series.

2. (2) The variation becomes smooth after the second successive day, which is more desirable from the point of view of users.

     

国内外家用分离式太阳能热水系统浅析

通过国内外分离式太阳能热水系统形式及部件对比,阐述了国内外分离式太阳能热水系统的差异。     

太阳能供暖二级水箱变容积蓄热系统能量及?分析

太阳能供暖系统中的固定容积单水箱蓄热系统,在太阳能波动供给和建筑热负荷波动需求之间存在不匹配及灵活性不足的问题。为更高效地利用太阳能,本文对二级水箱温度分层变容积蓄热太阳能供暖系统建立了MATLAB数学模型,包括集热循环、充热循环、取热循环和供热循环四部分及相应的控制策略,并运用Trnsys进行了模型验证。提出了在某时间段内,实际参与充热、取热或同时充热与取热的水箱体积为有效蓄热体积的概念。定义了集热比、有效蓄热体积平均温度、水箱热量取充比和热损比等参数对系统进行了分析与评价。研究表明:与传统的太阳能供暖固定容积单水箱温度分层蓄热系统相比,在整个供暖季,二级水箱变容积蓄热系统的热损失减少了17.2%,取充比增加了6.3%,?效率提高了6.6%,辅热能耗减少了9.5%;在供暖初期,二级水箱变容积蓄热系统的水箱温度响应时间缩短了54.9%,可更灵活快速地用于供热。二级水箱变容积蓄热系统有利于调节供暖季不同时期的供需匹配,具有良好的节能效果,可进一步为太阳能供暖系统的设计与应用提供指导。     

Dimensioning of the solar heating system in the zero energy house in Denmark

The paper describes the project for a Zero Energy House constructed at the Technical University of Denmark. The house is designed and constructed in such a way that it can be heated all winter without any “artificial” energy supply, the main source being solar energy. With energy conservation arrangements, such as high-insulated constructions (30–40 cm mineral wool insulation), movable insulation of the windows and heat recovery in the ventilating system, the total heat requirement for space heating is calculated to 2300 kWh per year. For a typical, well insulated, one-storied, one-family house built in Denmark, the corresponding heat requirement is 20,000 kWh. The solar heating system is dimensioned to cover the heat requirements and the hot water supply for the Zero Energy House during the whole year on the basis of the weather data in the “Reference Year”. The solar heating system consists of a 42 m² flat-plate solar collector, a 30 m³ water storage tank (insulated with 60 cm of mineral wool), and a heat distribution system. A total heat balance is set up for the system and solved for each day of the “Reference Year”. Collected and accumulated solar energy in the system is about 7300 kWh per yr; 30 per cent of the collected energy is used for space heating, 30 per cent for hot water supply, and 40 per cent is heat loss from the accumulator tank. For the operation of the solar heating system, the pumps and valves need a conventional electric energy supply of 230 kWh per year (corresponding to 5 per cent of the useful solar energy).     

集中式太阳能热水系统管道和水箱在高层建筑中的实践

在高层建筑上采用集中式太阳能热水系统时,因部分管道处于高空露天的苛刻环境中工作,管道易发生堵塞、冻结和腐蚀等问题,造成系统的失常或瘫痪.因此,安全可靠的管道设计施工、健全有效的管理规章制度是系统安全运行的保证,也是太阳能热水系统的关键技术之一.     

相变储能太阳能热泵系统的试验研究

文章建立了相变储能太阳能热泵系统试验平台,介绍了系统的运行方式以及各个部分的运行原理,选取典型日进行试验,并对试验数据进行分析。分析结果表明:相变储能太阳能热泵系统能够满足北方农村的供暖需求,可以保证白天室内的温度达到22℃,COP的最大值为6.3;太阳能热泵系统停止工作后,相变储能箱可以保证室内温度达到供暖的需求温度7 h,起到了"削峰填谷"的作用,运行费用显著降低;相变储能太阳能热泵系统解决了单纯电加热供暖方式费用高、能耗高的问题,具有显著的节能性。     

Domestic solar water heating system in Oman: Current status and future prospects

The excessive usage of fossil fuels worldwide is causing environmental problems. One solution to these problems is the exploitation of available renewable energy resources, including solar energy. This exploitation of renewable energy resources becomes essential to meet the large energy demand that resulted in depletion of fossil fuel resources, fuel price uncertainty and volatility, and growing concerns about global warming. Oman is located in a geographical region with an abundant and reliable supply of solar energy throughout the year. This paper presents a thorough financial, economic and technical analysis of using Solar Water Heaters (SWHs) in residential units. It was found that using SWHs in all governorates of Oman can save up to 1859 GWh of electrical energy annually, which is equivalent to the annual energy produced by a power station of 212 MW size. Moreover, the net annual reduction in CO₂ emission exceeds 1.227 million tons. In addition, the economic feasibility of installing SWHs in residential units is presented. The study shows that the dissemination of SWHs in Oman requires setting policies that motivate people to use them. Besides, subsidies to SWHs customers and/or investors will help making the price of these devices more affordable to the public.     

Breaking the mould: solar water pumping—the challenges and the reality

Solar (photovoltaic) powered water pumping has the potential to bring sustainable supplies of potable water to millions of people in developing countries. Unfortunately, in many cases the application of the pump technology ignores the sociological and economic needs of the users, leading to lack of maintenance, inappropriate financing schemes, inadequate system management and, ultimately, failure of the pump. This paper investigates some of the issues involved in solar water pumping projects, describes the positive and negative effects that they can have on the community and, in proposing an entirely new type of pump, considers what steps could be taken to ensure future sustainability.     

典型采暖地区太阳能在建筑节能中应用方法分析

一前言全球范围内能源与环境危机在我国的表现日益突出,我国已有的400多亿m~2城乡建筑面积中,约99%属于高耗能建筑,而且多以化石能源及其延伸产品为主,随着我国房地产市场的突飞猛进,这一现象还在不断加剧,从全社会能源消耗状况来看,30%的能源总耗属于建筑能耗,这一现象严重制约了我国经济的进一步发展,为此,近年来国家已将降低建筑能耗作为一项战略性工作来抓,将未来建     

基于远程无线监控的太阳能和热泵集中供热水系统设计

针对目前集中供热水系统存在的不足,利用太阳能和空气源热泵作为热源,采用GSM网络技术开发设计出基于远程无线监控的集中供热水系统。太阳能为主加热热源,当太阳能加热温度达不到设定温度时,由空气源热泵进行辅助加热。利用GSM网络进行远程无线数据收发,将现场控制设备的状态和故障信息发送给监控中心和设备管理人员、维修维护人员手机,监控中心或设备管理和维修维护人员将现场设备控制指令通过GSM网络发送给现场控制器,控制现场设备运行。系统节能、环保,实现了远程全自动化监控,无人值守,降低了投资运营成本。经实际应用表明,系统性能稳定可靠,效果良好。     

太阳能和锅炉烟气余热联合的供热系统及其经济性

某供热系统因实际可用热功率与用热设备功率有较大差距，导致不能满足供热需求，系统运行压力低，锅炉疲劳运行，经济性差，为此提出将太阳能集热系统和锅炉烟气余热利用系统与现系统并网的措施，阐述了系统设备构成及运行控制，经济性分析表明节煤效果显著。     

A small-scale silica gel-water adsorption system for domestic air conditioning and water heating by the recovery of solar energy

A small-scale silica gel-water adsorption system with modular adsorber, which utilizes solar energy to achieve the cogeneration of domestic air conditioning and water heating effect, is proposed and investigated in this paper. A heat recovery process between two adsorbers and a mass recovery process between two evaporators are adopted to improve the overall cooling and heating performance. First, the adsorption system is tested under different modes (different mass recovery, heat recovery, and cogeneration time) to determine the optimal operating conditions. Then, the cogeneration performance of domestic cooling and water heating effect is studied at different heat transfer fluid temperatures. The results show that the optimal time for cogeneration, mass recovery, and heat recovery are 600 s, 40 s, and 40 s, respectively. When the inlet temperature of hot water is around 85°C, the largest cooling power and heating power are 8.25 kW and 21.94 kW, respectively. Under the condition of cooling water temperature of 35°C, the obtained maximum COP_c, COP_h, and SCP of the system are 0.59, 1.39, and 184.5 W/kg, respectively.     

Nuclear energy development in China: A study of opportunities and challenges

With rapid economic development, China faces a great challenge to meet its increasing energy demand. Currently, China's energy supply is dominated by coal consumption, while natural gas and oil are in relative short supply. At the same time, nuclear energy is a relatively clean energy without green-house gas emissions. Considering the growing cost of fossil energy and the limited resources in China, oil supply security, coal mining disasters, the domestic environment pressure, and global climate warming, nuclear energy is an inevitable strategic option.