Development of a numerical simulation system toward comprehensive assessments of urban warming countermeasures including their impacts upon the urban buildings'' energy-demands

One of the detrimental effects caused by the urban warming phenomena is the increase of energy consumption due to the artificial air-conditioning of buildings in summer. In greater Tokyo, the temperature sensitivity of the peak electricity demand reaches up to 3%/°C in recent years, and about 1.5 GW of new demand is required as the daily maximum temperature increases by 1.0 °C. This huge demand for summer electricity is considered to be one of the common characteristics of big cities in Asian countries. In order to simulate this increase in cooling energy demands and to evaluate urban warming countermeasures from the viewpoint of buildings' energy savings, a numerical simulation system was developed adopting a new one-dimensional urban canopy meteorological model coupled with a simple sub-model for the building energy analysis. Then, the system was applied to the Ootemachi area, a central business district in Tokyo. Preliminary verification of the simulation system using observational data on the outdoor and indoor thermal conditions showed good results. Simulations also indicated that the cut-off of the anthropogenic heat from air-conditioning facilities could produce a cooling energy saving up to 6% with the outdoor air-temperature decrease by more than 1 °C in the summer urban canopy over Ootemachi area.     

上海某高校研究生宿舍空调电耗特性研究

以上海某高校研究生宿舍空调电耗作为研究对象,统计分析了所有抽样房间(共12间,每间4人)全年空调电耗使用规律,并总结出典型日、典型月空调电耗指标以及与室外温度之间的关系。夏季空调电耗集中于7、8、9月,冬季空调电耗集中于12、1、3月(2月寒假放假)。全年男、女生宿舍单位面积空调电耗差异不大,但与夏季相比,冬季单位面积空调电耗较高。夏季单位面积空调电耗与日平均温度呈正相关,冬季单位面积空调电耗与日平均温度呈负相关,且冬季单位面积空调电耗受室外温度影响较小。     

City-block-scale sensitivity of electricity consumption to air temperature and air humidity in business districts of Tokyo,Japan

The sensitivity of electricity consumption to air temperature and air humidity are effective indicators in evaluating the impacts of countermeasures against urban heat islands. The impacts of these countermeasures vary in time and space and so sensitivities based on finer resolution data are needed. Using actual hourly electric power consumption data from the business districts of Tokyo, we calculated the sensitivity of electric power consumption using multiple regression analysis. The sensitivities appear from 07:00 to 23:00 local standard time (LST) during weekdays during both winter and summer, mainly from 09:00 to 17:00 LST. The sensitivities to air temperature during winter are approximately 0.7–1.1 (W/floor-m²)/°C on an average and those during summer are approximately 1.1–1.4 on an average; the sensitivities to air humidity are approximately 0.6–0.9 on an average. It was found that the sensitivities to air temperature are caused due to heating during winter and cooling during summer; further, the sensitivities to air humidity were caused by dehumidification not for conditioning the air humidity of the room but for the condensation around the air-conditioner's coils with cooling during summer.     

Experimental and numerical study of unsteady non-periodic wall heat transfer under step,ramp and cosine temperature perturbations

An experimental and numerical study of the transient non-periodic wall heat transfer problem is presented. A computer-controlled indoor/outdoor environment simulation system produces any desired variation of the air temperature, thus allowing measurement of the dynamic thermal behaviour of any test wall under the desired boundary conditions. Measurements of the temperature field within the wall, of the heat flow and of the convection coefficients at the wall surfaces are performed during step, ramp and cosine perturbations of the outdoor air temperature. The measurements are in very good agreement with the numerical predictions obtained by a developed finite difference solution procedure. The results showed that in building heat transfer applications, for example in air conditioning, the usual assumption of periodic outdoor conditions may lead to considerable errors in case of a significant temporary deviation of the temperature from periodicity.     

夏季大空间屋顶节能喷淋器的实验研究

针对大空间建筑模型进行喷淋效果实验,通过实验得到以下结论:由于Low-E玻璃材料在夏季具有较强的温室效应,未喷淋时,屋顶内表面平均温度为56.8℃,与环境平均温差为21.9℃,增加了空调的能耗。彩钢板屋顶具有较好的保温性能,未喷淋时,屋顶内表面平均温度为40.6℃,模型内部空间平均温度为38.9℃,该温度远低于Low-E玻璃模型温度,能耗比Low-E玻璃模型小。喷淋时,Low-E内层温度比外层温度低约5.4℃;彩钢板内外层温度在喷淋时两者相差不大,仅为0.5℃,喷淋对Low-E玻璃屋顶空调节能意义明显。     

Energy impact of indoor environmental policy for air-conditioned offices of Hong Kong

Air-conditioned office buildings are one of the biggest energy consumers of electricity in developed cities in the subtropical climate regions. A good energy policy for the indoor environment should respond to both the needs of energy conservation and the needs for a desirable indoor healthy environment with a reduction in carbon dioxide (CO₂) generation. This study evaluates energy implications and the corresponding CO₂ generation of some indoor environmental policies for air-conditioned office buildings in the subtropical climate. In particular, the thermal energy consumption in an air-conditioned office building was evaluated by the heat gains through the building fabric, the transport of outdoor fresh air for ventilation, and the heat generated by the occupant and equipment in the space. With the Monte-Carlo sampling technique and the parameters from the existing office building stocks of Hong Kong, the energy consumption profiles of air-conditioned office buildings in Hong Kong were evaluated. Energy consumption profiles were simulated for certain indoor environmental quality (IEQ) policies on indoor air temperature and CO₂ concentration settings in the offices, with other building parameters remaining unchanged. The impact assessment and the regression models described in this study may be useful for evaluation of energy performances of IEQ policies. They will also be useful for the promotion of energy-saving measures in air-conditioned office buildings in Hong Kong. This study presented a useful source of references for policymakers, building professionals and end users to quantify the energy and environmental impacts due to an IEQ policy for air-conditioned office buildings.     

Influence of air conditioners utilization on urban thermal environment

The urban heat island effect is essentially a kind of thermal pollution caused by artificial activity. Air conditioning units used in buildings release a great deal of heat into outdoors while they improve the indoor thermal environment. Therefore, it will cause a rise in the outdoor air temperature and worsen the urban thermal environment. A “box” model is presented in this paper; it is used to quantitatively determine the rise in outdoor air temperature caused by using domestic air conditioners in Wuhan. The results demonstrate the rise degree is 2.56 °C under inversion conditions and 0.2 °C under normal conditions, which indicates that thermal pollution is serious at stable atmosphere. To a certain extent, the rise of atmospheric temperature can be verified by the rise of lowest atmospheric temperature in Wuhan over recent years.     

Nonlinear coupling between thermal mass and natural ventilation in buildings

An ideal naturally ventilated building model that allows a theoretical study of the effect of thermal mass associating with the non-linear coupling between the airflow rate and the indoor air temperature is proposed. When the ventilation rate is constant, both the phase shift and fluctuation of the indoor temperature are determined by the time constant of the system and the dimensionless convective heat transfer number. When the ventilation rate is a function of indoor and outdoor air temperature difference, the thermal mass number and the convective heat transfer air change parameter are suggested. The new thermal mass number measures the capacity of heat storage, rather than the amount of thermal mass. The analyses and numerical results show that the non-linearity of the system does neither change the periodic behaviour of the system, nor the behaviour of phase shift of the indoor air temperature when a periodic outdoor air temperature profile is considered. The maximum indoor air temperature phase shift induced by the direct outdoor air supply without control is 6 h.     

可实现快速制热和除霜的蓄能型空气源热泵系统的实验研究

提出一种可快速制热和除霜的蓄能型空气源热泵系统,并在室外温度约-0.7℃,相对湿度约95%的雨雪天气条件下进行实验测试,结果表明,结霜过程中蓄热器可有效阻止室内机出风温度的下降,除霜过程中新系统的压缩机出力大,效率高。除霜用时比常规除霜缩短68%,除霜能耗比常规除霜减少51.4%,除霜末期室内机出风温度为28℃,比常规系统高22℃,几乎没有吹冷风感;新系统开机快速制热效果十分显著,其6 min的制热量相当于常规开机制热10 min的制热量,新系统显著提高了空气源热泵的供热效果。     

Performance of a coupled cooling system with earth-to-air heat exchanger and solar chimney

Buildings represent nearly 40 percent of total energy use in the U.S. and about 50 percent of this energy is used for heating, ventilating, and cooling the space. Conventional heating and cooling systems are having a great impact on security of energy supply and greenhouse gas emissions. Unlike conventional approach, this paper investigates an innovative passive air conditioning system coupling earth-to-air heat exchangers (EAHEs) with solar collector enhanced solar chimneys. By simultaneously utilizing geothermal and solar energy, the system can achieve great energy savings within the building sector and reduce the peak electrical demand in the summer. Experiments were conducted in a test facility in summer to evaluate the performance of such a system. During the test period, the solar chimney drove up to 0.28 m³/s (1000 m³/h) outdoor air into the space. The EAHE provided a maximum 3308 W total cooling capacity during the day time. As a 100 percent outdoor air system, the coupled system maximum cooling capacity was 2582 W that almost covered the building design cooling load. The cooling capacities reached their peak during the day time when the solar radiation intensity was strong. The results show that the coupled system can maintain the indoor thermal environmental comfort conditions at a favorable range that complies with ASHRAE standard for thermal comfort. The findings in this research provide the foundation for design and application of the coupled system.     

分级相变储放热系统在日光温室中的应用效果

针对北方日光温室夜间室内低温问题,该文以收集利用温室内白天富余太阳能为目标,在理论分析相变材料特性的基础上,开发基于管材封装方式的两级相变储放热系统,并通过对比试验,在北京地区的日光温室中开展冬季应用效果试验。结果表明,所开发系统对冬季室内空气温度和土壤温度均有良好的增温效果。其中,空气温度方面,在试验周期内,试验温室夜间（17:00—次日08:00期间）平均室内气温比对照温室平均提高1.0 ℃,最低气温平均提高1.2 ℃;在晴天、多云不同天气条件下,试验温室的夜间平均气温分别提高1.3、1.2 ℃,最低气温分别提高1.5、1.7 ℃;在两天一夜未盖保温被的阴雪天气条件下,试验温室的室内气温全程高于对照温室,最大温差仍有1.9 ℃。在土壤温度方面,晴天和多云天气下,试验温室10和15 cm处的土壤温度平均提高0.6和0.8 ℃,研究表明所开发系统具有良好的持续储放热能力,能改善日光温室的冬季热环境。     

提高空调房间设定温度的节电效果分析

面对当前严峻的节电形势,提出了“合理提高空调房间温度来节约空调用电”的倡议。本文分析了这种节能措施的机理和节能效果的影响因素,同时以北京市为例分析了这种措施能够带来的节电效果和社会效益,并进一步提出了其他空调节能的途径。     

A numerical simulation tool for predicting the impact of outdoor thermal environment on building energy performance

A building affects its surrounding environment, and conversely its indoor environment is influenced by its surroundings. In order to obtain a more accurate prediction of the indoor thermal environment, it is necessary to consider the interactions between the indoor and outdoor thermal environments. However, there is still a lack of numerical simulation tools available for predicting the interactions between indoor and outdoor microclimate that take into account the influences of outdoor spatial conditions (such as building forms and tree shapes) and various urban surface materials. This present paper presents a simulation tool for predicting the effect of outdoor thermal environment on building thermal performance (heating/cooling loads, indoor temperature) in an urban block consisting of several buildings, trees, and other structures. The simulation tool is a 3D CAD-based design tool, which makes it possible to reproduce the spatial forms of buildings and constructed surface materials in detail. The outdoor thermal environment is evaluated in terms of external surface temperature and mean radiant temperature (MRT). Simulated results of these temperatures can be visualized on a color 3D display. Building heating/cooling loads and indoor air temperature (internal surface temperature) can also be simulated. In this study, a simulation methodology is described, and a sensitivity analysis is conducted for a wooden detached house under different outdoor conditions (building coverage, adjacent building height, surrounding with trees or no-trees). Simulation results show that the simulation tool developed in this study is capable of quantifying the influences of outdoor configurations and surface materials on both indoor and outdoor environments.     

Experimental investigation of a multi-function heat pump under various operating modes

Heat pumps have been spotlighted as efficient building energy systems because they have great potentials for energy reduction in building air conditioning and reducing CO₂ emission. In this study, a multi-function heat pump which has the functions of heating, cooling, and hot water supply was designed and its performance was investigated according to operating modes. In the cooling-hot water mode, the capacity and COP were enhanced as compared to other modes because the waste heat from the outdoor heat exchanger was utilized as useful heat in the indoor heat exchanger. In the heating and hot water supply mode, the compressor speed should be increased to get appropriate heating and hot water capacities. For all operating modes, the system could be optimized by adjusting the superheat.     

Earth-to-air heat exchangers for Italian climates

The European Energy Efficiency Building Directive 2002/91/CE, as well as other acts and funding programs, strongly promotes the adoption of passive strategies for buildings, in order to achieve indoor thermal comfort conditions above all in summer, so reducing or avoiding the use of air conditioning systems.In this paper, the energy performances achievable using an earth-to-air heat exchanger for an air-conditioned building have been evaluated for both winter and summer. By means of dynamic building energy performance simulation codes, the energy requirements of the systems have been analysed for different Italian climates, as a function of the main boundary conditions (such as the typology of soil, tube material, tube length and depth, velocity of the air crossing the tube, ventilation airflow rates, control modes). The earth-to-air heat exchanger has shown the highest efficiency for cold climates both in winter and summer.The possible coupling of this technology with other passive strategies has been also examined. Then, a technical-economic analysis has been carried out: this technology is economically acceptable (simple payback of 5–9 years) only in the cases of easy and cheap moving earth works; moreover, metallic tubes are not suitable.Finally, considering in summer a not fully air-conditioned building, only provided with diurnal ventilation coupled to an earth-to-air heat exchanger plus night-time ventilation, the possible indoor thermal comfort conditions have been evaluated.     

Theoretical and testing performance of an innovative indirect evaporative chiller

An indirect evaporative chiller is a device used to produce chilled water at a temperature between the wet bulb temperature and dew point of the outdoor air, which can be used in building HVAC systems. This article presents a theoretical analysis and practical performance of an innovative indirect evaporative chiller. First, the process of the indirect evaporative chiller is introduced; then, the matching characteristics of the process are presented and analyzed. It can be shown that the process that produces cold water by using dry air is a nearly-reversible process, so the ideal produced chilled water temperature of the indirect evaporative chiller can be set close to the dew point temperature of the chiller’s inlet air. After the indirect evaporative chiller was designed, simulations were done to analyze the output water temperature, the cooling efficiency relative to the inlet dew point temperature, and the COP that the chiller can performance. The first installation of the indirect evaporative chiller of this kind has been run for 5 years in a building in the city of Shihezi. The tested output water temperature of the chiller is around 14–20 °C, which is just in between of the outdoor wet bulb temperature and dew point. The tested COP_r,s of the developed indirect evaporative chiller reaches 9.1. Compared with ordinary air conditioning systems, the indirect evaporative chiller can save more than 40% in energy consumption due to the fact that the only energy consumed is from pumps and fans. An added bonus is that the indirect evaporative chiller uses no CFCs that pollute to the aerosphere. The tested internal parameters, such as the water–air flow rate ratio and heat transfer area for each heat transfer process inside the chiller, were analyzed and compared with designed values. The tested indoor air conditions, with a room temperature of 23–27 °C and relative humidity of 50–70%, proved that the developed practical indirect evaporative chiller successfully satisfy the indoor air conditioning load for the demo building. The indirect evaporative chiller has a potentially wide application in dry regions, especially for large scale commercial buildings. Finally, this paper presented the geographic regions suitable for the technology worldwide.     

Urban heat island characteristics in London during winter

This paper presents results characterising the urban heat island intensity (UHI) in London during the peak winter season. Most UHI studies focus on the phenomenon during the summer as this is the period when temperature peaks are observed. However, for urban planning mitigation strategies and building energy demand design, the heating season should be also considered, since proposed measures to alleviate the summer UHI might have a negative effect during the winter or intermediate seasons.The study carries out trend and regression analysis by controlling climatic and geographical variations in the data set following a methodology developed for studying summer UHI [Kolokotroni, M., Giridharan, R., 2008. Urban heat island intensity in London: an investigation of the impact of physical characteristics on changes in outdoor air temperature during summer. Solar Energy 82, 986-998]. It was found that average nocturnal UHI of winter periods are of similar magnitude to the summer periods but the peak winter UHI trends are not as regular as summer giving a first indication that the effect of climate and urban parameters is different. The regression analysis in this research uses six on-site variables namely aspect ratio, surface albedo, plan density ratio, green density ratio, fabric density ratio and thermal mass to carry out impact investigation in six data sets, categorised by three geographical location within London and three sky conditions and regional wind velocity. The above variables do not explain the changes in outdoor temperature as much as they did during summer period models. However, unlike summer, the winter climate control models have the same R² indicating that most of changes in outdoor temperature are caused by climate factors and not the on-site variables.     

水上和水下提取次表层海水冷量的对比和分析

夏季的酷热迫使人们耗费大量能源以维持狭窄的温度环境,城市空调负荷节节攀升;近在身边的海中,表层以下巨大的水团静静地安卧,闲置着天然的冷量.冷媒水与海水在海中进行换热,是实现水下直接提取海洋冷量的构想.与陆上提取冷量方案的对比,可以证明其技术优势和节能效果.水下取冷方案甚至可应用于高盐度海区,并提高海水与冷媒水的换热温差,以提升海水冷量利用率;采用自来水作为冷媒水,不需要对海水进行处理,也不会出现管道堵塞的故障;作为空调系统回水的自来水,又可用作其它工业或生活用途.该方案在提供相同冷媒水流量的条件下,输水耗功减少幅度达到90%.     

冬季特朗贝墙内置卷帘对墙体热性能的影响

对大连地区某被动式太阳实验房进行实验研究,通过对玻璃幕墙内壁面温度、夹层内空气温度、特朗贝墙墙体温度等相关参数及室外气象参数等的实测,定量地分析了冬季夜间特朗贝墙采用卷帘保温的效果。并且通过有限空间自然对流换热理论计算分析,提出了更为合理的卷帘安装位置,最后根据围护结构响应因子BER指标,讨论了使用卷帘对提高室内热舒适性的影响。     

变频多联空调能量特性的建模和仿真

为评价变频多联空调(VRV)的能耗特性,基于美国能源部动态建筑能耗模拟软件EnergyPlus开发了VRV的能耗计算模块。利用一实际建筑作算例,在不同室内设定温度、不同室内机开停台数的情况下对变频多联空调系统的性能系数和部分负荷比以及室外温度和机组能耗的关系进行了计算分析,并与文献中的实验结果作了对比验证。结果表明,所开发的计算模块能够较好地分析变频多联空调系统的能耗特性。