Effects of wind on the transmission heat loss in duo-pitched insulated roofs: A field study

This article presents measuring results of the thermal performance of duo-pitched tiled woodframe roof designs. The roofs have been monitored in a test building, exposed to the outside climate. The experiment was part of a programme to study the hygrothermal performance of highly insulated envelope parts in situ, in order to investigate whether a good thermal quality (U = 0.2 W/(m² K)) is achievable with current residential construction practices in Belgium. The results show the effect of wind on the thermal performance of duo-pitched roofs. The measured thermal properties of the roof components are compared to the design values, and related to the wind speeds and directions registered near the test building. The established thermal effects are explained using tracer gas tests to show the pattern of wind driven air flow in the roofs.     

Facade design optimization for naturally ventilated residential buildings in Singapore

Parametric studies of facade designs for naturally ventilated residential buildings in Singapore were carried out to optimize facade designs for better indoor thermal comfort and energy saving. Two criteria regarding indoor thermal comfort for naturally ventilated residential buildings are used in this study. To avoid the perception of thermal asymmetry, temperature difference between mean radiant temperature and indoor ambient air temperature should be less than 2 °C [F.A. Chrenko, Heated ceilings and comfort. J. Inst. Heat. Ventilating Eng. 20 (1953) 375–396; F.A. Chrenko, Heated ceilings and comfort. J. Inst. Heat. Ventilating Eng. 21 (1953) 145–154]. Thermal comfort regression model for naturally ventilated residential buildings in Singapore was used to evaluate various facade designs either. Facade design parameters: U-values, orientations, WWR (window to wall ratio) and shading device lengths are considered in the investigation. The building simulation results for a typical residential building in Singapore indicated that the U-value of facade materials for north and south orientations should be less than 2.5 W/m² K and the U-value of facade materials for north and south orientations should be less than 2 W/m² K. From the coupled simulation results, it was found that the optimum window to wall ratio is equal to 0.24. Optimum facade designs and thermal comfort indexes are summarized for naturally ventilated residential buildings in Singapore.     

夏热冬暖地区轻型绿化屋面隔热性能研究

绿化屋面能够改善屋面的隔热性能,提高热室热舒适度.而轻型绿化屋面具有成本低、重量轻、建造容易、维护简单等优点.通过轻型绿化屋面与普通屋面实测对比分析的方法,研究轻型绿化屋面的隔热性能.通过对2种屋面温度波变化情况以及与室外天气参数相关性的研究,得出了轻型绿化屋面的隔热效果非常显著的结论.     

Thermal performance evaluation of domed roofs

Domed roofs have been used in Iran and many other countries to cover large buildings such as mosques, shrines, churches, schools. They have been also employed in other buildings like bazaars or market places in Iran due to their favorable thermal performance. The aim of this research is to study about domed roofs thermal performance in order to determine how they can be helpful in reducing the maximum air temperature of inside buildings during the warm seasons considering all parameters like air flow around them, solar radiation, radiation heat transfer with the sky and the ground as well as some openings on the building. The results of the study show that the thermal performance of the investigated domed roof is better than the building with flat roof, particularly when the dome is covered with glazed tiles. In addition to their aesthetic values, domes covered with glazed tiles have thermal benefits of keeping the inside air of these buildings relatively cool during the summer. Moreover, openings cause passive air flow inside building, which is helpful for human comfort.     

复合防水蓄水屋面应用技术研究

屋面蓄水为夏热冬冷地区建筑顶层的隔热降温提供了条件。通过对苏州大学炳麟图书馆复合防水蓄水屋面隔热性能的测试分析,说明该类屋面能够改善建筑热工性能、降低室内空调能耗,是建筑节能的有效措施。     

Investigation of green roof thermal performance in temperate climate: A case study of an experimental building in Florianópolis city, Southern Brazil

Green roofs have been investigated as a bioclimatic strategy to improve the energy efficiency of buildings. Quantitative data on this subject are still needed for many specific climatic conditions. This paper deals with the investigation of the green roof thermal performance of an experimental single-family residence in Florianópolis (SC, Brazil), a southern city with a temperate climate. Field measurements during a warm period (01-March-2008-07-March-2008) and during a cold period (25-May-2008-31-May-2008) included internal air temperature of rooms, internal and external surface temperature of three types of roofs (green, ceramic and metallic), heat fluxes through these roofs, green roof's temperature profile, water volumetric content in substrate layer and meteorological data. During the warm period, the green roof reduced heat gain by 92-97% in comparison to ceramic and metallic roofs, respectively, and enhanced the heat loss to 49 and 20%. During the cold period, the green roof reduced heat gain by 70 and 84%, and reduced the heat loss by 44 and 52% in comparison to ceramic and metallic roofs, respectively. From the derived data it has been confirmed that green roof contributes to the thermal benefits and energy efficiency of the building in temperate climate conditions.     

Suitable roof constructions for warm climates—Gazimağusa case

This research aims to find the suitable roof constructions for warm climates. The research has been carried out at Gazimağusa, North Cyprus. With the limited research budget 14 different roof constructions were selected and tested on a test house. These constructions included the types which are widely used in Cyprus and also the new ones. The roof constructions were tested under continuously air-conditioned and non-acclimatised regimes. They were also tested for the risk of condensation.Most of the research on similar aspects were done in terms of energy loss and gain. This research has been designed to study the roof constructions in terms of thermal comfort of the users. Naturally, the roof constructions which have the highest thermal resistance will result in lowest heat gain and loose. In this study instead of finding the roof constructions which gain the least amount of heat during the hottest days of summer or the ones which loose the least amount of heat during the coldest days of winter, it was aimed to find how much they provide thermal comfort throughout the year.In this respect, the roofs with thermal insulation showed the best performance. The location of the thermal insulation materials towards the inner surface of the section increased the performance. Inclined timber roof constructions on reinforced concrete ceiling save the buildings from solar bombarding in summer. However, to prevent the humidity accumulated, the attic space should be very well ventilated. On flat roofs, not only the thermal resistance of the roof section, but also the light reflectance of outside surface materials effected the thermal performance. Outside surface materials with very high light reflectance reduced heat gain in summer considerably.In buildings which are air conditioned in summer, there is condensation risk. The defects due to this condensation can be avoided by the use of thermal insulation materials which are not effected from water. There is also condensation risk for winter. However, it was found that this condensation can dry if the building is ventilated.     

Overcoming problems in house energy ratings in temperate climates: A proposed new rating framework

This paper first demonstrates that an efficient design for a house in conditioned operation mode differs from that for the same house in the free-running operation mode, and that this is a primary reason for the inability of current energy based rating schemes to adequately assess the performance of passive design in a temperate climate. We examine the Australian Nationwide House Energy Rating Scheme as an example of this problem. A new practical framework for a house rating scheme is then presented. In this proposed framework, the efficiency of a house design is evaluated with reference to its thermal performance in free-running mode, in addition to its projected energy loads in conditioned operation mode. The study uses simulation to evaluate the thermal performances of houses, and employs multiregression analysis to develop the framework. The reliability of proposed framework as compared to the current energy based rating scheme is demonstrated. By attributing more value to the performance of houses in the free-running than the conditioned operation, it is assumed that policy objectives for reducing energy demand for space heating and cooling in the residential building sector are more likely to be achieved.     

自然通风环境下办公建筑中庭空间热舒适性模糊优化研究

：随着绿色建筑设计理念深入人心,办 公建筑的中庭空间因其特有空间特质受到越来 越多的关注。通常办公中庭空间中的节能性与热 舒适性是一对矛盾体,而自然通风作为被动节能 技术之一,不仅能够促进中庭空间的内外空气 循环,改善室内空气质量,而且降低能耗和提升 热舒适性,较好地解决这一矛盾。以江雅园办公 楼中庭空间为案例进行研究,从中庭屋顶形态、 中庭高度及进风口开启方式三个变量因素出发, 引用模糊评估方法寻找出中庭空间自然通风热 舒适性最佳方案,结论显示在多个组合方案中 斜屋顶形态+进风口全部开启的方案热舒适性最 佳,同时也证明屋顶形态与通风方式的变化对自 然通风舒适性的影响较大,而中庭空间高度的变化对自然通风舒适性影响较小。本研究希望建立一套以风速和温度为评价指标的模糊体系,为自 然通风的热舒适性的评价提供一种客观的评估手段,从而为方案阶段的中庭空间设计提供一种 有效的优化方法。     

种植屋面隔热效果与种植密度相关性的实验研究

本文通过实测普通防水屋面与几类种植屋面的全天温度与热流变化情况,分析了种植屋面隔热性能的优劣,并总结出种植密度对屋顶热工性能的影响。     

Estimating the effect of using cool coatings on energy loads and thermal comfort in residential buildings in various climatic conditions

The impact from using cool roof coatings on the cooling and heating loads and the indoor thermal comfort conditions of residential buildings for various climatic conditions is estimated. The energy cooling loads and peak cooling demands are estimated for different values of roof solar reflectance and roof U-value. The results show that increasing the roof solar reflectance reduces cooling loads by 18–93% and peak cooling demand in air-conditioned buildings by 11–27%. The indoor thermal comfort conditions were improved by decreasing the hours of discomfort by 9–100% and the maximum temperatures in non air-conditioned residential buildings by 1.2–3.3 °C. These reductions were found to be more important for poorly or non-insulated buildings. For the locations studied, the heating penalty (0.2–17 kWh/m² year) was less important than the cooling load reduction (9–48 kWh/m² year). The application of cool roof coatings is an effective, minimal cost and easy to use technique that contributes to the energy efficiency and the thermal comfort of buildings.     

Thermal performance of insulated roof slabs in tropical climates

Reinforced concrete roof slabs can be an ideal alternative to traditional roofs considering the better cyclone resistance that can be offered due to the self weight. However, the concrete slabs do not perform satisfactorily in warm humid tropical climatic conditions and tend to act as heated bodies for the occupants in free running spaces. As a solution, a robust roof slab insulation system is proposed and its thermal performance was determined experimentally using small and large-scale models. With comfort models developed for the people acclimatized to tropical climatic conditions, it is shown that insulated roof slabs could provide acceptable indoor conditions while providing many valuable benefits such as cyclone resistance, regaining of land lost for the house and the possibility of creation of roof top gardens.     

Assessment of green roof thermal behavior: A coupled heat and mass transfer model

Green roofs have a positive effect on the energy performance of buildings, providing a cooling effect in summer, along with a more efficient harnessing of the solar radiation due to the reflective properties found inside the foliage. For assessing these effects, the thermodynamic model was developed as well as the thermo-physical properties of the green roof components were characterized. Its typologies and vegetation styles should also be studied. The proposed model is based on energy balance equations expressed for foliage and soil media. In this study, the influence of the mass transfer in the thermal properties and evapotranspiration were taken into account. We then added the water balance equation into our model and performed a numerical simulation. By assuming the outdoor conditions, the roof support temperature and the drainage water as inputs, the model evaluates the temperatures evolution at foliage and soil ground levels. A parametric study was performed using the proposed model to classify green roofs depending on the considered climate condition. Comparisons were undertaken with a roof slab concrete model; a significant difference (of up to 30 °C) in temperature between the outer surfaces of the two roofs was noticed in summer. The model was experimentally validated according to green roof platform, which was elaborated. The mass transfer effect in the subtract was very effective in reducing the model errors. Simulation results show that the use of vegetation in the roof building improves not only thermal comfort conditions, but the energy performance of a building.     

Outdoor thermal comfort: Analyzing the impact of urban configurations on the thermal performance of street canyons in the humid subtropical climate of Sydney

The quality of outdoor space is becoming increasingly important with the growing rate of urbanization. Visual, acoustic, and thermal balance degradation are all negative impacts associated with outdoor comfort in dense urban fabrics. Urban morphology thus needs assessment and optimization to ensure favorable outdoor thermal comfort (OTC). This study aims to evaluate the thermal performance of streets in residential zones of Liverpool, NSW, Australia, and tries to improve their comfort index (Physiological Equivalent Temperature) to reveal optimum urban configurations. This evaluation is done by investigating the following urban design factors affecting OTC using computational simulation techniques: street orientation, aspect ratio, building typology, and surface coverage. Our findings reveal that street canyon orientation is the most influential factor (46.42%), followed by aspect ratio (30.59%). Among the influential meteorological parameters (air temperature, wind speed, humidity and solar radiation), wind velocity had the most significant impact on the thermal comfort of the outdoor spaces in this coastal region, which typically experiences intense airflow. The results of our analysis can be utilized by multiple stakeholders, allowing them to understand and extract the most vital design factors which contextually influence the thermal comfort of outdoor spaces. Outdoor thermal comfort has a direct effect on the health and wellbeing of occupants of outdoor spaces.     

Modeling the heat diffusion process in the abiotic layers of green roofs

Green roofs have been increasingly installed to alleviate some common environmental problems. The thermal benefit of living vegetation on rooftop has been extensively studied. The individual and joint contribution of the non-living green roof layers, namely soil, rockwool (water storage) and plastic drainage layers, to thermal performance of green roof has seldom been assessed. This study evaluates the insulating and cooling effects of these abiotic materials. A one-dimensional theoretical model was developed to assess the heat diffusion process in the layers. The model was validated with empirical results from three experimental plots. A calibration procedure was successfully applied to determine key model parameters. The model can capture the most critical features of temperature variations and thermal performance of common abiotic green roof materials. The appreciable water-retention capacity of rockwool plays the dual role of supplying water to the soil to enhance evaporative cooling, and increasing the specific heat capacity of the green roof. The plastic drainage sheet with ample air spaces serves as an excellent thermal insulator. The model remains robust despite seasonal and weather variabilities. Our research findings contradict with some researches in the temperate region that the thermal dissipation in green roofs with dense vegetation is lower than thermally insulated bare roofs. The theoretical model could be used to simulate the micro-environmental conditions and predict the thermal performance of different materials to improve green roof design.     

CFD modelling and thermal performance analysis of a wooden ventilated roof structure

Thermal comfort and energy saving are objectives of key significance that building design must meet. Since a low energy building can be obtained as a result of the good realization of all its components, roofs call for particular attention as they represent a large part of a building’s total surface area. In this paper the benefit of using ventilated roofs for reducing summer cooling load is investigated. The investigation has been conducted comparing a ventilated roof assembly with different channel heights (3 cm, 5 cm, and 10 cm) to the same non ventilated structure, assuming buoyancy-driven airflow. Direct comparison between the open and the closed roof structures as a function of different cavity heights and outside environmental conditions is presented. To provide fundamental information about the thermal performance of these building envelope components, the computational fluid dynamics (CFD) model has been used to develop correlations for the characterization of the airflow and heat transfer phenomena in the ventilation cavity which have been implemented in a whole year energy simulation software. The present analysis shows a conflicting discrepancy among the indexes of performance describing the actual energy saving potential of a ventilated roof.     

Biophysical properties and thermal performance of an intensive green roof

Green roofs have been increasingly enlisted to alleviate urban environmental problems associated with urban heat island effect and stormwater quantity and quality. Most studies focus on extensive green roofs, with inadequate assessment of the complex intensive type, subtropical region, and thermal insulation effect. This study examines the physical properties, biological processes, and thermal insulation performance of an intensive green roof through four seasons. An experimental woodland installed on a Hong Kong building rooftop was equipped with environmental sensors to monitor microclimatic and soil parameters. The excellent thermal performance of the intensive green roof is verified. Even though our site has a 100 cm thick soil to support tree growth, we found that a thin soil layer of 10 cm is sufficient to reduce heat penetration into building. Seasonal weather variations notably control transpiration and associated cooling effect. The tree canopy reduces solar radiation reaching the soil surface, but the trapped air increases air temperature near the soil surface. The substrate operates an effective heat sink to dampen temperature fluctuations. In winter, the subtropical green roof triggers notable heat loss from the substrate into the ambient air, and draws heat upwards from warmer indoor air to increase energy consumption to warm indoor air. This finding deviates from temperate latitude studies. The results offer hints to optimize the design and thermal performance of intensive green roofs.     

The effects of roof covering on the thermal performance of highly insulated roofs in Mediterranean climates

While the EU Directive 2002/91/CE on the Energy Performance of Buildings (EPBD) clearly establishes regulations for the thermal insulation of buildings for saving energy in winter, the summer strategy is described by a little more than qualitative provisions. As a consequence, in the national requirements, the high insulation of the building envelope is considered as the principal strategy to control energy consumption even in summer, regardless of the different climates. This approach leads to a homologation of the building trade, and imposes construction technology and materials which do not adhere to the traditional way of making buildings, like in Southern Europe. Here, the “over insulation” of buildings runs the risk of reducing the effectiveness of traditional passive cooling strategies (thermal mass, air permeability of the roof covering, roof ventilation) and could have adverse effects on internal comfort. In this paper, we focus on the effects of over insulation on the thermal performance of roofs in summer, by analyzing experimental data from monitoring a full-scale mock-up in Italy. Results show how an increase in insulation thickness reduces the effectiveness of traditional passive cooling strategies, as an effect of the thermal decoupling between the interior and the upper layers of the roofs.     

Thermal analysis of vaulted roofs

In hot arid regions, cooling buildings by passive techniques is very important regarding energy saving and the need to keep clean the environment. In such areas, domed and vaulted roofs are widely used for centuries, such as in the Middle East region and central part of Iran. In this article analysis is made to explore east–west direction of wind flow around north–south vaulted roofs and flat roof buildings. Combined convection and solar radiation over the roofs is considered to studying thermal performances of vaulted roofs and comparing their heat transfer with flat roofs. Two-dimensional RNG k–? turbulence model is incorporated to predict turbulent flow field as well as separation and recirculating patterns around the vaulted roofs and flat roof buildings. Solar radiation distribution over the roofs is determined based on an appropriate model applicable to hot arid regions of Iran. Pressure differences above the vaulted roof are compared with flat roof for various rim angles and different wind speeds. Heat transfer to the building with respect to time is determined for a certain inside ceiling design temperature, various wind flows and vault shapes, and results are compared with corresponding flat roof. It was found that daily average heat flux for all vaulted roofs, except vaulted roof of rim angle 180° is less than flat roof and it reduces further by increasing wind speed.     

Key elements of and material performance targets for highly insulating window frames

The thermal performance of windows is important for energy efficient buildings. Windows typically account for about 30-50 percent of the transmission losses though the building envelope, even if their area fraction of the envelope is far less. The reason for this can be found by comparing the thermal transmittance (U-factor) of windows to the U-factor of their opaque counterparts (wall, roof and floor constructions). In well insulated buildings the U-factor of walls, roofs and floors can be between 0.1 and 0.2 W/(m² K). The best windows have U-factors of about 0.7-1.0. It is therefore obvious that the U-factor of windows needs to be reduced, even though looking at the whole energy balance for windows (i.e., solar gains minus transmission losses) makes the picture more complex.In high performance windows the frame design and material use are of utmost importance, as the frame performance is usually the limiting factor for reducing the total window U-factor further. This paper describes simulation studies analyzing the effects on frame and edge-of-glass U-factors of different surface emissivities as well as frame material and spacer conductivities. The goal of this work is to define material research targets for window frame components that will result in better frame thermal performance than is exhibited by the best products available on the market today.