Numerical analysis of heat and mass transfer in a passive building component cooled by water evaporation

In this paper, the behaviour of a special roofing system is investigated. It is a passive building component that consists of a ventilated roof with a maintained wet lower surface of the cavity over which flows the external air. The authors have carried out numerical simulations of the thermal field, flow field and water vapour concentration of air within the duct for thermal performance evaluation purposes.In order to obtain an estimate of the thermal cooling flux on the wet surface, suitable procedures were coded and linked to a commercial program for computational fluid dynamics (CFX 4.4). An original approach to solve a coupled heat and mass transfer problem is presented. Results of numerical simulations of the temperature field and the values of the mean specific heat and mass fluxes of the wet lower surface are shown. Numerical problems that have been dealt with, due to particular physical phenomena such as boundary coupled fields and radiation between cavity surfaces, are highlighted.     

Thermal performance of a cool-pool system for passive cooling of a non-conditioned building

The thermal performance of a cool-pool system for passive cooling of a non-conditioned building is presented. The system consists of a water pond over the roof which is shaded in such a way that incident solar radiation does not reach the roof surface and the pond loses heat by convection and evaporation to its surroundings. Using periodic analysis, explicit expressions have been obtained for various performance parameters, namely room air temperature and water temperature and the amount of water evaporated from the system. Numerical calculations carried out for a typical day at New Delhi (28.6°N) show that the cool-pool system is more effective than the conventional evaporative cooling techniques such as water film and roof pond; the system also consumes less water in comparison with other evaporative cooling techniques.     

The thermal performance of a Roof-Pond integrated to a building for heating during Cold-Winter Desert climate conditions in Saudi Arabia

This study reports an experiment to investigate the feasibility of a passive heating roof-pond system on an existing room in the cold winter conditions of Riyadh, Saudi Arabia. Statistical analyses of data recorded during the winter season of 1996–97, are carried out to evaluate the thermal peformance of the proposed system. Total effective heating and the heating power of the roof pond system are computed and analysed. Results indicate that the roof-pond system is capable of maintaining warm indoor air temperature conditions. The statistical formulae for this system are presented and used to estimate the indoor daily average air Dry Bulb Temperature (DBT_Avg-indoor] created by the system. Validation of the proposed formulae is also presented.     

地区气候特征与气候适应性对节能住宅建筑热工设计的影响

以成都地区为例,从地区气候特征与气候适应性分析其对节能住宅建筑热工设计的影响,为节能住宅热工设计中的室内外气候计算参数的选择与确定,提供科学与实践的依据。     

Impact of passive climate adaptation measures and building orientation on the energy demand of a detached lightweight semi-portable building

The building energy demand for heating and cooling is changing due to climate change. The adoption of climate change adaptation measures at the building scale aims at limiting heating and cooling demands. In previous studies on adaptation measures little attention has been paid to lightweight semi-portable buildings, which are increasingly used to temporarily house the growing number of small households (1–2 persons) in peripheral and derelict areas. In this paper the impact of passive climate adaptation measures and building orientation on heating and cooling demands is assessed for a detached, lightweight, semi-portable residential building by means of building energy simulations (BES), considering two climate scenarios for the Netherlands: current climate and a future climate (2050). The results show that the most efficient adaptation measure consists in a combination of exterior solar shading and an increase of thermal resistance of the building envelope, which reduces the annual heating and cooling demand–averaged over eight building orientations – by 11% for the current climate and 15% for the future climate. The impact of building orientation varies according to the climate scenario. Compared to the average over the eight orientations considered, the annual cooling demand for a single orientation varies between about ?31% and +22% and between about ?24% and +18% for the current and future climate, respectively. For the case without adaptation measures, optimizing the building orientation leads to annual total energy savings of about 4% for the current and 3% for the future climate.     

Identification of key factors for uncertainty in the prediction of the thermal performance of an office building under climate change

There is growing concern about the potential impact of climate change on the thermal performance of buildings. Building simulation is well-suited to predict the behaviour of buildings in the future, and to quantify the risks for prime building functions like occupant productivity, occupant health, or energy use. However, on the time scales that are involved with climate change, different factors introduce uncertainties into the predictions: apart from uncertainties in the climate conditions forecast, factors like change of use, trends in electronic equipment and lighting, as well as building refurbishment / renovation and HVAC (heating, ventilation, and air conditioning) system upgrades need to be taken into account. This article presents the application of two-dimensional Monte Carlo analysis to an EnergyPlus model of an office building to identify the key factors for uncertainty in the prediction of overheating and energy use for the time horizons of 2020, 2050 and 2080. The office has mixed-mode ventilation and indirect evaporative cooling, and is studied using the UKCIP02 climate change scenarios. The results show that regarding the uncertainty in predicted heating energy, the dominant input factors are infiltration, lighting gain and equipment gain. For cooling energy and overheating the dominant factors for 2020 and 2050 are lighting gain and equipment gain, but with climate prediction becoming the one dominant factor for 2080. These factors will be the subject of further research by means of expert panel sessions, which will be used to gain a higher resolution of critical building simulation input.     

The role of adaptive thermal comfort in the prediction of the thermal performance of a modern mixed-mode office building in the UK under climate change

Climate change is becoming a serious issue for the construction industry, since the time scales at which climate change takes place can be expected to show a true impact on the thermal performance of buildings and HVAC systems. In predicting this future building performance by means of building simulation, the underlying assumptions regarding thermal comfort conditions and the related heating, ventilating and air conditioning (HVAC) control set points become important. This article studies the thermal performance of a reference office building with mixed-mode ventilation in the UK, using static and adaptive thermal approaches, for a series of time horizons (2020, 2050 and 2080). Results demonstrate the importance of the implementation of adaptive thermal comfort models, and underpin the case for its use in climate change impact studies. Adaptive thermal comfort can also be used by building designers to make buildings more resilient towards change.     

Optimum lumped parameters for modeling building thermal performance

A least-squares method for choosing optimum lumped parameters for modelling the thermal performance of buildings is presented. A realistic passive solar-heated room is modelled with a one-time constant lumped model to better than 10% accuracy. This technique provides a simple method that can be used in the design or evaluation of the thermal performance of buildings such as those using passive solar heating.     

Estimating the impacts of climate change and urbanization on building performance

Over the past 15 years, much scientific work has been published on the potential human impacts on climates. For their Third Assessment Report in 2001, the United Nations International Programme on Climate Change developed a set of economic development scenarios, which were then run with the four major general circulation models (GCM) to estimate the anthropogenesis-forced climate change. These GCMs produce worldwide grids of predicted monthly temperature, cloud, and precipitation deviations from the period 1961–1990. As this period is the same used for several major typical meteorological year data sets, these typical data sets can be used as a starting point for modifying weather files to represent predicted climate change. Over the past 50 years, studies of urban heat islands (UHI) or urbanization have provided detailed measurements of the diurnal and seasonal patterns and differences between urban and rural climatic conditions. While heat islands have been shown to be a function of both population and microclimatic and site conditions, they can be generalized into a predictable diurnal and seasonal pattern. Although the scientific literature is full of studies looking at the impact of climate change driven by human activity, there is very little research on the impact of climate change or urban heat islands on building operation and performance across the world. This article presents the methodology used to create weather files which represent climate change scenarios in 2100 and heat island impacts today. For this study, typical and extreme meteorological weather data were created for 25 locations (20 climate regions) to represent a range of predicted climate change and heat island scenarios for building simulation. Then prototypical small office buildings were created to represent typical, good, and low-energy practices around the world. The simulation results for these prototype buildings provide a snapshot view of the potential impacts of the set of climate scenarios on building performance. This includes location-specific building response, such as fuel swapping as heating and cooling ratios change, impacts on environmental emissions, impacts on equipment use and longevity comfort issues, and how low-energy building design incorporating renewables can significantly mitigate any potential climate variation. In this article, examples of how heat island and climate change scenarios affect diurnal patterns are presented as well as the annual energy performance impacts for three of the 25 locations. In cold climates, the net change to annual energy use due to climate change will be positive – reducing energy use on the order of 10% or more. For tropical climates, buildings will see an increase in overall energy use due to climate change, with some months increasing by more than 20% from current conditions. Temperate, mid-latitude climates will see the largest change but it will be a swapping from heating to cooling, including a significant reduction of 25% or more in heating energy and up to 15% increase in cooling energy. Buildings which are built to current standards such as ASHRAE/IESNA Standard 90.1-2004 will still see significant increases in energy demand over the twenty-first century. Low-energy buildings designed to minimize energy use will be the least affected, with impacts in the range of 5–10%. Unless the way buildings are designed, built, and operated changes significantly over the next decades, buildings will see substantial operating cost increases and possible disruptions in an already strained energy supply system.     

Thermal performance of a non-air-conditioned building for passive solar air-conditioning: Evaluation of roof cooling systems

A periodic heat transfer analysis has been presented to predict the dynamic thermal behaviour of a non-air-conditioned building with evaporative cooling systems over the roof. Three different cases of evaporative cooling systems, namely, open roof pond, moving water layer over the roof, and water spray over the roof, have been studied in detail to assess their effectiveness for passive space air-conditioning. The effects of air ventilation, furnishings and ground heat conduction have been incorporated in the present analysis. Numerical computations using typical data of a harsh summer day in the Delhi climate, have been made to assess the analytical results quantitatively.It was found that the maximum cooling is achieved by water spray over the roof. However, the roof pond system with stationary water is more effective in stabilizing the fluctuations of indoor temperature as well as heat flux entering through the roof. Furthermore, with the increase in the number of air changes per hour, the time variation of indoor air approaches to that of outdoor air in phase as well as in magnitude.     

严寒地区民用建筑热工设计二级分区指标适用性分析

严寒地区分布范围广、气候条件复杂,现行标准规范以基准温度18℃的采暖度日数（HDD18）作为分区指标,将严寒地区划分为3个二级气候区。为分析该指标的适用性,通过EnergyPlus软件模拟并地较典型建筑在严寒地区61个城市的年累计热负荷差异,对比部分城市之间的气候特征,分析城市的HDD18与建筑年累计热负荷的关系,探讨HDD18分区指标的适用地区。结果表明：在HDD18相近的条件下,西部高海拔地区城市的建筑年累计热负荷显著低于东部城市;HDD18与建筑年累计热负荷仅在太阳辐射量及夏季温度差异较小的地区呈线性关系;HDD18作为分区指标,适用于太阳辐射及夏季温度差异小的地区,严寒地区宜结合太阳辐射等因素划分二级分区。     

Analysis of thermal performance of building attached sunspace

The thermal performance of a sunspace attached to a living room located in Amman-Jordan has been investigated. Six configurations that differ by the ratio of glazed surface area to opaque surfaces area are studied. A novel configuration that utilizes an inclined front surface is thermally investigated. The effect of orientation of the sunspace, opaque wall and floor absorption coefficients and number of glass layers on the thermal performance is evaluated. Results show that the sunspace reduces the heating load during the winter, while it creates a serious overheating problem during summer. The contribution of reducing heating requirements increases with increasing the ratio of glazed surface to opaque surface area. Also, the optimal contribution was obtained when the sunspace was oriented to the south. Two passive cooling techniques are proposed and evaluated to overcome the summer overheating problem. Additionally, a passive heating technique is proposed to minimize the thermal losses during winter nights. Internal shading and night ventilation successfully minimize the overheating problem. Employing the three passive techniques with sunspace, results show that as high as 42% reductions in annual heating and cooling load can be achieved. Utilizing an inclined front surface with double layer of glass can further reduce heating and cooling load requirements.     

筑幕墙热工性能试验测试系统的研制和应用

随着对建筑幕墙性能检测认识的进一步深化和国内幕墙公司不断承接境外的工程,这对我们的检测工作提出了与国际接轨的要求。建筑幕墙的热工性能的检测成为当前幕墙检测中重要的一个环节,其中,热循环试验和冷凝试验是建筑幕墙热工性能检测的重要组成部分。美国AAMA501.5-98和欧洲CWCT建筑维护系统的标准第18项都对这些检测做了相应的规定。本文介绍了热循环试验和冷凝试验的原理、结构和控制方法,并简要介绍了试验的情况。     

A new stable finite volume method for predicting thermal performance of a whole building

Discretised governing equations involving only temperatures and heat fluxes at both surfaces of a solid wall layer were obtained by combining a new stable finite volume scheme for the two inner nodes of the wall layer with the surface diffusion equations (discretised by third order equations). The finite volume scheme for the inner nodes of the layer is proved to be stable with its truncation error being O(Δx⁴,Δx²Δt²)$O(\mathrm{\Delta }{x}^4,\mathrm{\Delta }{x}^2\mathrm{\Delta }{t}^2)$. A special analytical solution for a solid wall was used to evaluate different schemes for the inner nodes, showing that the new proposed scheme performs better than all other schemes for time steps of 3600 and 600 s. Finally, this scheme was used to simulate a whole house and the predicted zonal air temperature, and surface temperatures agreed well with measured values.     

某火力发电厂主厂房框排架结构扭转性能研究

以某火力发电厂主厂房为原型,建立整体结构的空间计算模型,对其分别进行模态分析和水平双向地震作用下的弹塑性时程分析。结合拟动力和伪静力试验研究,探讨框排架结构的空间变形性能及塑性铰的分布特点。针对此类结构特点引起的严重地震扭转效应,提出减小扭转的措施,改善了火力发电厂主厂房在高烈度地震作用下的动力性能,为工程设计提供参考依据。     

某住宅建筑大阶砖隔热屋面热工性能分析

测试分析了某住宅建筑屋面的热工性能参数,并通过测试数据,研究了其热工性能,测试结果为评价该类建筑屋面的热工性能及其节能计算提供了基本实验依据。     

Hysteresis effects on the thermal performance of building envelope PCM-walls

This work presents a numerical study of the combined effects of the hysteresis temperature difference, peak melting temperature, and thickness of a building envelope PCM-wall on its thermal performance in air-conditioning and non-air-conditioning conditions. The study was carried out considering complete melting-freezing daily cycles of the PCM in a climate exhibiting both hot and cold thermal discomfort. A time-dependent one-dimensional heat conduction code, which uses the effective specific heat method to simulate the heat transfer through the PCM was developed. Insights into the effects of the hysteresis phenomenon were obtained; it was found that hysteresis improves the thermal performance of PCM-walls. The higher the hysteresis temperature difference the better the thermal performance, but there is a limit in the improvement of the thermal performance, which is achieved when the entire phase change process takes place at temperatures outside of the thermal comfort zone. Maximum improvements from 4% to 29% for air-conditioning and from 4% to 30% for non-air-conditioning, for a BioPCM wall with thicknesses from 6 mm to 18 mm, were found. Suggested criteria to achieve the maximum possible thermal performance of PCM-walls given a thickness and use condition were obtained. This work proposes the basis of a methodology to optimize simultaneously any pair of variables of a PCM-wall for different use conditions (AC, nAC, or a combined use of AC and nAC).     

Conflicts in passive building performance: Retrofit and regulation of informal neighbourhoods

Urbanization growth in developing countries raises concerns regarding these countries' ability to consider slums, underdeveloped communities, and neighbourhoods in economic, health, and climatic goals. This research proposes a methodology that integrates algorithmic design and analysis strategies to define, study, and measure key parameters that affect the rehabilitation of these areas. Construction scenarios and design dimensions are analysed to establish design and comfort thresholds, and alternatives are simulated and tested to identify possible improvements. The methodology includes an optimisation step integrated in the workflow that maximizes thermal comfort, minimizes costs, and ensures fairness in the rehabilitation of large sets of buildings. This step identifies improvements in thermal comfort for different construction scenarios from which a two-staged rehabilitation plan is defined. The first stage comprises a sensitivity analysis to identify building materials regarding their improvement and cost of application, and the second defines the most suitable construction scenarios considering the results from the optimisation process for each building. Additionally, we research and document guidelines regarding the parameters tested for building design, revealing the existing conflicts between performance objectives, and the architect's role in their prioritization.