Life cycle primary energy analysis of residential buildings

The space heating demand of residential buildings can be decreased by improved insulation, reduced air leakage and by heat recovery from ventilation air. However, these measures result in an increased use of materials. As the energy for building operation decreases, the relative importance of the energy used in the production phase increases and influences optimization aimed at minimizing the life cycle energy use. The life cycle primary energy use of buildings also depends on the energy supply systems. In this work we analyse primary energy use and CO₂ emission for the production and operation of conventional and low-energy residential buildings. Different types of energy supply systems are included in the analysis. We show that for a conventional and a low-energy building the primary energy use for production can be up to 45% and 60%, respectively, of the total, depending on the energy supply system, and with larger variations for conventional buildings. The primary energy used and the CO₂ emission resulting from production are lower for wood-framed constructions than for concrete-framed constructions. The primary energy use and the CO₂ emission depend strongly on the energy supply, for both conventional and low-energy buildings. For example, a single-family house from the 1970s heated with biomass-based district heating with cogeneration has 70% lower operational primary energy use than if heated with fuel-based electricity. The specific primary energy use with district heating was 40% lower than that of an electrically heated passive row house.     

Building energy-efficiency standards in a life cycle primary energy perspective

In this study we analyze the life cycle primary energy use of a wood-frame apartment building designed to meet the current Swedish building code, the Swedish building code of 1994 or the passive house standard, and heated with district heat or electric resistance heating. The analysis includes the primary energy use during the production, operation and end-of-life phases. We find that an electric heated building built to the current building code has greater life cycle primary energy use relative to a district heated building, although the standard for electric heating is more stringent. Also, the primary energy use for an electric heated building constructed to meet the passive house standard is substantially higher than for a district heated building built to the Swedish building code of 1994. The primary energy for material production constitutes 5% of the primary energy for production and space heating and ventilation of an electric heated building built to meet the 1994 code. The share of production energy increases as the energy-efficiency standard of the building improves and when efficient energy supply is used, and reaches 30% for a district heated passive house. This study shows the significance of a life cycle primary energy perspective and the choice of heating system in reducing energy use in the built environment.     

Primary energy implications of end-use energy efficiency measures in district heated buildings

In this study we explore the effects of end-use energy efficiency measures on different district heat production systems with combined heat and power (CHP) plants for base load production and heat-only boilers for peak and medium load productions. We model four minimum cost district heat production systems based on four environmental taxation scenarios, plus a reference district heat system used in Östersund, Sweden. We analyze the primary energy use and the cost of district heat production for each system. We then analyze the primary energy implications of end-use energy efficiency measures applied to a case-study apartment building, taking into account the reduced district heat demand, reduced cogenerated electricity and increased electricity use due to ventilation heat recovery. We find that district heat production cost in optimally-designed production systems is not sensitive to environmental taxation. The primary energy savings of end-use energy efficiency measures depend on the characteristics of the district heat production system and the type of end-use energy efficiency measures. Energy efficiency measures that reduce more of peak load than base load production give higher primary energy savings, because the primary energy efficiency is higher for CHP plants than for boilers. This study shows the importance of analyzing both the demand and supply sides as well as their interaction in order to minimize the primary energy use of district heated buildings.     

我国建筑耗能状况及有效的节能途径

简要分析了我国建筑能源消耗状况,从用能特点出发,对建筑物和建筑用能途径进行了新的分类,给出各类的现状、问题和节能潜力。在此基础上列出为实现建筑节能所需要的主要技术与产品研究领域和政策研究与保障机制。文中列出的关键技术研究为：基于模拟分析的建筑节能优化设计;新型建筑围护结构材料与部品;通风装置与排风热回收装置;热泵技术;降低输配系统能源消耗的技术;集中空调的温度湿度独立控制技术;建筑自动化系统的节能优化控制;楼宇式燃气驱动的热电冷三联供技术;燃煤燃气联合供热和末端调峰技术;节能灯、节能灯具与控制。有关政策与保障机制的研究问题为：建筑能耗数据的统计系统;住宅能耗标识方法与保障机制;大型公共建筑能耗评估与用能配额制;各种建筑用能装置的能耗标识标准与方法。     

中国城市热电厂区域热制冷对温室气体减排的作用

一些欧洲与亚洲国家已发展了满足建筑冬季供暖的区域供热系统,并以独立的电力压缩式制冷用于夏季空调的使用。存在两套并行的供暖与制冷空调系统意味着需要大量的初期投资。因此城市能源系统规划建设应考虑保持城市热电厂在夏季仍采用热电联产生产,实现热电厂区域热制冷以满足建筑在夏季的空调供冷,以使热电厂全年以高效率的热电联产方式运行。这种热电厂冷热联供系统为建筑提供了可持续的能源供应方案。本文以2004年的热电联产实际数据为依据,综合考虑我国的社会与经济发展趋势,对三种不同发展情景下通过发展热电厂夏季热制冷可实现的温室气体减排能力进行了分析预测。     

Development of system concepts for improving the performance of a waste heat district heating network with exergy analysis

The building sector is responsible for a great share of the final energy demand and national CO₂ emissions in countries like Germany. Nowadays, low quality thermal energy demands in buildings are mainly satisfied with high-quality sources (e.g. natural gas fired in condensing boilers). Exergy analysis, pursuing a matching in the quality level of energy supplied and demanded, pinpoints the great necessity of substituting high-quality fossil fuels by other low quality energy flows, such as waste heat. In this paper a small district heating system in Kassel (Germany) is taken as a case study. Results from preliminary steady-state and dynamic energy and exergy analysis of the system are presented and strategies for improving the performance of waste-heat based district heating systems are derived. Results show that lowering supply temperatures from 95 to 57.7 °C increases the final exergy efficiency of the systems from 32% to 39.3%. Similarly, reducing return temperatures to the district heating network from 40.8 to 37.7 °C increases the exergy performance in 3.7%. In turn, the energy performance of all systems studied is nearly the same. This paper shows clearly the added value of exergy analysis for characterising and improving the performance of district heating systems.     

Optimized control strategies for solar district heating systems

Solar district heating (SDH) systems are a proven concept for the supply of space heating and/or domestic hot water using solar energy as the main heat source. SDH systems with a high solar fraction include seasonal thermal storage and various subsystems with different time scales that must be managed by the supervisory control system. This paper presents the development of optimized control strategies for the Drake Landing Solar Community in Okotoks (Alberta, Canada). The proposed strategies, based on the application of model predictive control concepts, aim to further reduce the use of auxiliary energy for heating (gas) while also reducing the pumping energy (electricity). Perfect forecasts for the weather and the SDH loads are assumed in the study and a detailed TRNSYS model is used. Results show that the primary energy consumption can be reduced by 5% by updating the supervisory control strategies.     

太阳能-地源热泵联合供暖系统数值模拟研究

在北方寒冷地区的冬季,利用地源热泵机组(Ground Source Heat Pump Unit,GSHPU)为建筑物进行供暖是一种新型节能减排模式。由于在采暖期间从土壤中吸收了较多的热量,超过了土壤本身的热修复能力,会造成GSHPU的地埋管所在区域的土壤热稳定性能发生变化,使得其COP值下降,运行功耗增加。针对此问题,提出了太阳能-地源热泵联合供暖系统。该系统在冬季以太阳能热水系统(Solar Water Heating System,SWHS)的运行作为主要供热模式,GSHPU的间歇运行作为辅助供热模式,从而充分利用太阳能并解决阴天等气象因素所带来的集热量不足、供水温度低等的问题。在非供暖季期间,GSHPU停运,而SWHS通过热水循环,对GSHPU地埋管所在的土壤区域进行热量回补,使得土壤温度场稳定,从而确保GSHPU在冬季间歇运行时的高效性。以兰州地区某办公楼的太阳能-地源热泵联合供暖系统作为案例,基于TRNSYS软件,进行数值模拟和分析,验证了该系统的可行性,且节能效果明显。     

Analysis of an effective solution to excessive heat supply in a city primary heating network using gas-fired boilers for peak-load compensation

Through investigation of the Dengfeng heating network in the city of Daqing, China, for the 2007-2008 heating season, we found serious problems of excessive heat supply in the primary heating network. Therefore, we propose the application of gas-fired boilers in underperforming heating substations as peak-load heat sources to effectively adapt to the regulation demands of seasonal heat-load fluctuations and reduce the excessive heat supply. First, we calculated the excessive heat supply rates (EHSRs) of five substations using detailed investigative data. We then discussed the feasibility of the proposed scheme providing energy savings from both energetic and exergetic points of view. The results showed that the average EHSR of the five substations between January and March was 20.57% of the gross heat production but consequently reduced to 6.24% with the installation of the gas-fired boilers. Therefore, the combined heating scheme with coal as the basic heat-source and gas-fired boilers as peak-load heat sources is energy-efficient to some extent, although requires the use of natural gas. Meanwhile, the exergy decreased by 10.97%, which indicates that the combined heating scheme effectively reduces the primary energy consumption and pollutant emission of the heating systems.     

Optimal heating of large block of flats

District heating is used in many urban areas in Sweden. Almost always, the district heating utility is owned by the municipality and the municipality naturally encourages proprietors to connect their buildings to the grid, even if they cannot really force them to do so. The building owners are free to choose the best system, i.e. the cheapest one, for their need. Unfortunately, it is not always so easy to find the best solution. Mixed integer linear programming (MLIP) models might here come to help. By such computer programs it is possible to find the absolutely cheapest system of available alternatives, or even combinations among them. This paper shows how to design such a model and further how to closely depict the district heating, and electricity tariff. This is of course very important because the only interface between the proprietor of the building and the utility is found in this bureaucratic instrument. If the tariff is too high the building owners will choose other heating systems than district heating, or even worse, combining district heating with alternative base load sources. In Sweden, this has been of interest because ground-water coupled heat pumps can be profitable, operated by use of the relatively low electricity prices. In this paper we show that dual-fuel, and sometimes even triple-fuel systems, are of interest when the proprietor aims at minimising the cost for space and domestic hot-water heating.     

西藏自治区民用建筑采暖设计地方标准简介

标准结合西藏的能源供应模式和生态特点,提出通过主、被动式太阳能利用和建筑保温方法解决当地的采暖问题,主动式供暖系统以太阳能热水为主要热源;标准涉及供暖室内外计算参数的确定、热负荷计算、太阳能热水系统设计等方面,为当地民用建筑供暖制定了设计依据.     

Control of heating systems in residential buildings: Current practice

Heating is the most important energy consumer for households in Belgium. The primary energy consumption of a heating system is determined by the net energy demand of the building, but also by the efficiency of the equipment and the way it is used by the inhabitants.

To estimate the potential primary energy savings, today's situation should be analysed first. Therefore, the results of two surveys are combined to sketch current practice in Belgium. The most common systems in Western Europe, i.e. gas boilers combined with radiators, are then simulated to test their performance in dwellings with varied insulation quality. Typical internal heat gains and set temperature profiles are included, but the influence of the inhabitant behaviour on the heating efficiency is not studied as such.

The results show that current practice does lead to important energy losses, resulting in overall efficiencies as low as 30%, but improvements are possible by using intelligent controllers. However, correct boiler sizing and a sound combination of boiler and heat emitter control are still required to ensure high heating system efficiencies, especially for better insulated buildings with a high heat balance ratio.     

Optimierung geothermischer Energiesysteme am Beispiel eines städtebaulichen Entwicklungsvorhabens

Optimization of geothermal energy systems with an urban developement project. With an example of an urban development projekt in Bottrop‐Kirchhellen, Germany, a complete supply of a new urban district with geothermal energy will be presented. By thermal building simulations the heating load profiles of the buildings were determined and linked to geothermal simulations. However, the swaying of the heating loads in the buildings does not fit to the nearly constant heat flow from the ground. Hence, the profile of the loads should be smoothed by a combination of different heating systems and by the use of storage devices for an efficient use of geothermal energy.     

Conversion of electric heating in buildings: An unconventional alternative

To decrease the electric energy used for heating buildings it has become desirable to convert direct electrical heating to other heat sources. This paper reports on a study of the possibility of using an unconventional method for conversion to avoid installing an expensive hydronic system. The conversion method combines the ventilation and heating systems and uses air instead of water for distribution of heat within the building, taking advantage of thermal forces and the special properties of gravity currents. Full-scale tests have been carried out in a test apartment inside a laboratory hall where the conditions could be controlled. Temperatures and efficiency of ventilation have been measured to ensure that the demands with respect to thermal climate and air exchange were fulfilled. The results show that it is possible to use the method for heating and ventilation when converting the heating system, but further work has to be done to develop a detailed solution that works in practice.     

Method for achieving hydraulic balance in typical Chinese building heating systems by managing differential pressure and flow

Hydraulic unbalance is a common problem in Chinese district heating (DH) systems. Hydraulic unbalance has resulted in poor flow distribution among heating branches and overheating of apartments. Studies show that nearly 30% of the total heat supply is being wasted in Chinese DH systems due to a lack of pressure and flow control. This study investigated using pre-set radiator valves combined with differential pressure (DP) controllers to achieve hydraulic balance in building distribution systems, and consequently save energy and reduce the emissions. We considered a multi-storey building modelled in the IDA-ICE software, along with a self-developed mathematical hydraulic model to simulate its heat performance and hydraulic performance with various control scenarios. In contrast to the situation with no pressure or flow control, this solution achieves the required flow distribution and close-to-design room temperatures, as well as 16% heat savings, 74% pump electricity savings, and proper cooling of supply water. The energy consumption savings would therefore have positive environmental impacts, and be reflected in seasonal reductions of 2.1 kg/m² CO₂, 0.02 kg/m² SO₂, and 0.01 kg/m² NO_x for 3rd step energy efficiency buildings in Beijing.     

集中供热系统不同调峰供热方式的技术经济性分析

本文主要分析了分布式调峰供热方式在集中供热系统应用中的技术经济性。通过节能性和经济性对比分析可知,相对于集中调峰供热方式,分布式调峰供热方式可以降低集中供热系统的供热能耗,提高承担基础负荷的集中热源的满负荷运行小时数、提高集中热源的供热效率,同时可以降低一次供热管网的初投资、减少一次供热管网的热损失。     

瑞典集中热泵系统区域供热供冷经验以及在中国的和谐化应用

20世纪80年代,瑞典开始将热泵系统区域供热作为一项重要市政基础建设进行大规模的安装,在短短几年内,大型热泵站在瑞典中型以上城市得以运行,10年后,使用热泵系统实现区域供冷的热潮相继而至,最初通常与区域供热相结合,一直以来,瑞典都是世界上成功应用热泵技术实现区域供热供冷的领军国家,致力于完善建设并且国际化的推广本土经验,当今．节能减排和新型环保型能源的应用成为中国在快速发展进程中的关键词．成就了将热泵1区域供冷技术以及在欧洲的应用经验引入中国的大好时机,本文将介绍集中热泵系统供热供冷系统的优点,瑞典的热泵系统成功经验以及此项技术在中国因地制宜的和谐化应用,     

地源热泵--建筑节能新技术

在建筑供热空调中采用热泵技术可以有效地提高一次能源利用率，减少温室效应气体CO2和其他大气污染物的排放。本文阐述了利用热泵供热比锅炉直接燃烧供热节能的原理，对主要的热泵供热形式，特别是地源热泵的技术特征、适用范围和经济性作了较详细的介绍。     

Comparison of natural gas driven heat pumps and electrically driven heat pumps with conventional systems for building heating purposes

Electrically driven heat pumps achieve good efficiencies for space heating. If heat pumps are driven directly by a combustion engine instead of an electric motor, losses attributed to the production and transport of electricity are eliminated. Additionally, the use of the combustion engine's heat leads to a reduced temperature difference across the heat pump. This article presents annual efficiencies of these systems and compares internal combustion engine and electrically driven heat pumps in terms of primary energy consumption and CO₂ emissions. Because heat pump performance depends strongly on the heating circuit's flow temperature level, the comparison is performed for air-to-water and geothermal heat pump systems in two cases of maximum flow temperatures (40 °C and 60 °C). These temperature levels represent typical modern buildings with large heating surfaces and older buildings with high-temperature radiators, respectively. In addition to the different heat pump setups, conventional space heating systems are included in the comparison. The calculations show that natural gas-driven heat pumps achieve about the same efficiency and CO₂ emissions as electrically driven heat pumps powered with electricity from the most modern natural gas-fired combined cycle power plants. The efficiency of such systems is about twice that of conventional boiler technologies.     

我国供热节能中的问题和解决途径

分析了我国集中供热系统热利用效率低,运行能耗高的主要原因,并讨论了目前分户计量、按热量收费改革的问题。认为根据目前居住特点,这种热改方式不适合在我国推广。应采取按楼计量、楼内按面积分摊的方式。这可以激励围护结构的保温改造,并在技术上和经济上都可行。为了解决由于系统设计不当和调节不当导致局部过热造成的热损失问题,提出在楼的热入口采用换热或混水,在楼内实行“大流量、小温差、低水温”的供热方式,使每栋楼可在不同的入口水温下运行,以有效减少由于散热器面积不匹配、建筑内局部热源、系统流量不均等原因造成的局部过热现象,提高集中供热系统的热利用效率。