Performance rating of glass windows and glass windows with films in aspect of thermal comfort and heat transmission

This article is about a study on glass window and glass window with film of different types in aspect of thermal comfort and heat transmission. Different types of glass window, clear glass, tinted glass, reflective glass, double pane glass, and low-e glass were investigated. Films with different spectral optical properties were then adhered to the glass windows of different types and studied. The analysis was done based on the outside design weather condition which selected from 12 years of Bangkok meteorological data. Predicted percentage of dissatisfied (PPD) was selected as the thermal comfort index. The relative heat gain (RHG) based on local weather condition was selected as the heat transmission index. The PPD can be subdivided into the PPD due to surface temperature effect and the PPD due to solar radiation effect. The analysis indicated that, for most of the glass windows considered except the reflective glasses, the values of PPD due to solar radiation effect were much larger than the values of PPD due to surface temperature effect. And the most discomfort condition occurred when using a clear glass as window. Adhered films to the glass windows caused the PPD due to surface temperature effect increase and cause the PPD due to solar radiation effect decrease. It was also found that the PPD values due to solar radiation effect for glass windows and glass windows with films were varied linearly with the total transmittance of glass windows and glass windows with films. The PPD values due to surface temperature effect were varied with the total absorptance of glass windows and glass windows with films in an almost linear fashion. The heat transmission index, RHG, based on chosen design weather condition can be subdivided into the RHG due to conduction effect and RHG due to solar radiation effect. The analysis indicated that the values of RHG due to solar radiation effect were larger than the values of RHG due to conduction effect for all glass windows and glass windows with films considered in this study. Adhered film to the glass windows resulted in lowering the relative heat gain due to solar radiation in the amount corresponding to the film properties. But the film had very few effect on the relative heat gain due to conduction. The relative heat gain values were varied linearly with the total transmittances of the glass windows and glass windows with films. The relative heat gain values were also varied inversely with the absorptances of glass windows and glass windows with films in a linear fashion.     

Energy simulations for glazed office buildings in Sweden

Highly glazed buildings are designed by architects to be airy, light and transparent with more access to daylight. Their energy efficiency, however, has become questioned. Therefore, energy simulations of single skin office buildings in Sweden were carried out, using a dynamic energy simulation tool. In order to study the impact of glass on the energy use during the occupation stage, office building alternatives with 30, 60 and 100% window to external wall area were studied. Other varied parameters were the building's orientation, the plan type (open and cell plan offices), the control set points and the façade elements (type and size of windows, type and position of shading devices, etc.). The main conclusion is that careful design is needed to ensure low energy use and good thermal comfort, especially for highly glazed office buildings. Careful design of glazed office buildings has to be based on detailed thermal simulations. Especially in fully glazed buildings (in which the façade is more “sensitive” to climatic conditions), proper combination of control set points, glazing and solar shading are crucial for the energy performance.     

Performance evaluation of a PV ventilated window applying to office building of Hong Kong

PV ventilated glazing technology for application in warm climate provides energy saving opportunities through the reduction in air-conditioning load, the daylight utilization, and the green electric power generation. In a working environment, the use of semi-transparent a-Si glazing is deemed better than the one with non-transparent c-Si solar cells. This paper reports an evaluation of its integrated performance using a small office room in Hong Kong as an example. An energy model of a PV ventilated window system is first introduced. Based on this together with the TMY weather data of Hong Kong and the daylight simulation capability of the EnergyPlus program, the overall performance analysis have been executed for different window orientations. It was found that a solar cell transmittance in the range of 0.45–0.55 could achieve the best electricity saving.     

Investigation on energy performance of double skin façade in Hong Kong

Double skin façade can be defined as a building façade covering one or several stories with multiple skins. The skins may be air tight or ventilated. With sophisticated study and design, buildings constructed with double skin façade can have better thermal performance than the conventional single skin façade. This paper reports the findings on the energy performance of double skin façade applied to a typical office building under the climatic condition in Hong Kong. An experimental setup was established and the measured data were used to verify the theoretical model developed via the EnergyPlus simulation program. The validated model was then used to evaluate the energy performance of double skin façade with various configurations including glazing type (clear, absorptive or reflective glass), glazing position (inner or outer pane) and glazing layers (single or double glazing material). The results indicate that a double skin façade system with single clear glazing as the inner pane and double reflective glazing as the outer pane can provide an annual saving of around 26% in building cooling energy, as compared to a conventional single skin façade with single absorptive glazing. However, the long payback period of 81 years makes the double skin façade system economically infeasible. Support and motivation are needed from the local government in order to foster successful and widespread application of the double skin façade system in buildings.     

Simulation of ventilated facades in hot and humid climates

The Hong Kong climate is sub-tropical with hot and humid weather from May to September and temperate climate for the remaining 7 months period. A mechanical ventilation and air-conditioning (MVAC) system is usually operated to avoid the high temperatures resulting in high peak cooling loads. The facade design has a significant influence on the energy performance of office buildings. This work evaluates different ventilated facade designs in respect to energy savings.Thermal building simulations (TRNSYS) were linked to nodal airflow network simulations (COMIS) for detailed ventilated double-skin facade performance. In order to validate the model, simulations were carried out for an office building in Lisboa; the results were compared with measured data from the same building. The simulation results of surface and air temperatures show good agreement with the measurements. The results of the study can be used to reduce surface temperatures by using different materials for the roller blind that is positioned in the cavity of the double-skin facade. The results can further be used to reduce the high peak cooling loads during the summer period. This may result in significant energy savings and a reduction in the system's cooling capacity. It proved that a careful facade design can play an important role in highly glazed buildings and provides potential for energy efficiency.     

中南地区建筑窗玻璃的热工性能模拟与选择

介绍了双层普通玻璃、单层Low-E低辐射玻璃及双层Low-E低辐射玻璃,并分析了其节能原理。用Opticals 5.0软件模拟了玻璃法向入射的太阳光学性能,针对中南地区的气候,用Window 5.0软件模拟了玻璃的热工性能。结果表明,单层Low-E玻璃具有较好的热工性能。考虑中南地区客观气候条件及成本因素,传热系数中等,太阳得热系数中等的单层Low-E玻璃是办公楼、酒店等建筑外窗玻璃的理想选择。计算了夏季7月21日建筑物不同朝向的单层普通玻璃和单层Low-E玻璃得热量,计算结果表明单层Low-E玻璃夏季节能效果明显。     

政府办公建筑能源审计分析

通过对山东省直机关办公建筑的能源审计,得到公建的能耗数据。对审计结果进行分析发现．外窗的窗框和玻璃对建筑能耗的影响较大．且建筑能耗呈逐年下降的趋势。该研究可为机关办公建筑节能降耗工作的开展提供参考。     

Comparison of low-energy office buildings in summer using different thermal comfort criteria

Sustainable low-energy office buildings attempt to harness the buildings architecture and physics to provide a high quality working environment with the least possible primary energy consumption. A promising approach to condition those buildings in summer employs the utilization of the building's thermal storage activated by natural heat sinks (e.g., ambient air, ground water or soil) through night ventilation or thermally activated building systems (TABS). However, a certain room temperature cannot be guaranteed as occupants may influence the room energy balance by window opening, internal heat gains or sun shading control. Between 2001 and 2005, monitoring campaigns were carried out over 2 or 3 years in 12 low-energy office buildings which are located in three different summer climate zones in Germany. These climate zones are defined as summer-cool, moderate and summer-hot. The weather at the building site and the room temperatures in several office rooms were monitored by different scientific teams. The raw data are processed for data evaluation using a sophisticated method to remove errors and outliers from the database and to identify the time of occupancy. The comfort in all office rooms in each building is evaluated separately. For data presentation, these separate comfort votes per office room are averaged using the median instead of the arithmetic mean in order not to overestimate extremely cold or hot room temperatures. A comfort evaluation in these 12 low-energy office buildings indicates clearly, that buildings which use only natural heat sinks for cooling provide good thermal comfort during typical and warm summer periods in Germany. However, long heat waves such as during the extreme European summer of 2003 overstrain passively cooled buildings with air-driven cooling concepts in terms of thermal comfort.     

Thermotropic glass with active dimming control for solar shading and daylighting

The effectiveness of an autonomous responsive dimming (thermotropic) glass panel fabricated with a transparent heating layer and an electrochromic layer to provide additional active dimming control is examined through preliminary experiments and simulations. Thermotropic glass consists of two panes of glass sandwiching a polymer gel that undergoes a transition from clear to cloudy at a threshold temperature. Winter temperatures can thus prevent the glass from dimming when required for solar shading. With appropriate control of the heating layer, however, the performance of the panel with respect to office solar-shading requirements is demonstrated to be superior to that without the heating layer, despite the simplicity of the system. The configuration requires relatively low electric power, utilizing solar radiation energy to maintain the cloudy state as required. In a different approach, application of electrochromic layer for active dimming control is proposed and verified in various aspects with wavelength characteristics considering simulation.     

Energy performance of a dual airflow window under different climates

Ventilated windows have shown great potential in conserving energy in buildings and provide fresh air to improve indoor air quality. This paper reports our effort to use EnergyPlus to simulate the energy performance of a dual airflow window under different climates. Our investigation first developed a network model to account for the two-dimensional heat transfer in the window system and implemented it in EnergyPlus. The two-dimensional assumption and the modified EnergyPlus program were validated by the measured temperatures of the window and the energy demand of a test cell with the window under actual weather conditions. Then EnergyPlus was applied to analyze energy performance of a small apartment installed with the dual airflow windows in five different climate zones in China. The energy used by the apartment with blinds windows and low-e windows was also calculated for comparison. The dual airflow window can reduce heating energy of the apartment, especially in cold climate. The cooling energy reduction by the window was less important than that by shading solar radiation. The dual airflow window is recommended for colder climate. If improving air quality is a major consideration for a building, the window can be used in any climate.     

Comparison of annual energy performances with different ventilation methods for temperature and humidity control

Stratum ventilation has been proposed to accommodate elevated indoor temperatures recommended by governments in East Asia. TRNSYS is used for computation of the space cooling loads, sensible and latent, as well as system energy consumption. Typical configurations of an office, a classroom and a retail shop in Hong Kong are investigated. Desiccant dehumidification with and without solar assistance is utilized for the air treatment under displacement ventilation and stratum ventilation, while simple reheating is adopted under mixed ventilation. Compared with mixing ventilation and displacement ventilation, stratum ventilation derives its energy saving potential largely from the following five factors: the reduction in ventilation, dehumidification and transmission loads, prolonged free cooling period and increased the COP of the chillers. For the office, the year-round energy saving is found to be substantial at 20% and 40% without the need for solar energy provision when compared with displacement ventilation and mixing ventilation respectively. For the classroom and retail shop, the year-round energy saving is at about 25% and at least 37% with the aid of solar energy provision when compared with displacement ventilation and mixing ventilation respectively.     

海南地区既有公共建筑围护结构节能改造分析

通过对海南地区既有公共建筑年代、类型,建筑窗墙比,外墙、外窗、屋顶构造等方面的详细调研,得出了海南地区既有公共建筑的节能现状。利用DeST-h软件对海南地区典型既有公共建筑进行节能诊断及改造效果分析,海南地区既有公共建筑围护结构热工性能较差,建筑能耗较高。建筑节能改造的潜力和重点在于降低外窗的综合遮阳系数和屋顶、外墙的太阳辐射吸收系数。经改造,办公建筑可较参照建筑节能4.28%~5.71%,酒店建筑可较参照建筑节能1.38%~15.21%。     

A holistic approach to energy efficient building forms

Minimizing energy consumption in buildings has become an important goal in architecture and urban planning in recent years. Guidelines were developed for each climatic zone aiming at increasing solar exposure for buildings in cold climates and at reducing solar exposure for buildings in hot climates. This approach usually plans for the season with the harshest weather; often forgetting that temperatures in cities at latitude 25° can drop below thermal comfort limits in winter and that temperatures in cities at latitude 48° often rise above thermal comfort limits in summer. This paper argues that a holistic approach to energy efficient building forms is needed. It demonstrates a generic energy efficient building form derived by cutting solar profiles in a conventional block. Results show that the proposed building form, the Residential Solar Block (RSB), can maximize solar energy falling on facades and minimize solar energy falling on roofs and on the ground surrounding buildings in an urban area in winter; thus maximizing the potential of passive utilization of solar energy. The RSB also supports strategies for mitigating the urban heat island through increased airflow between buildings, the promotion of marketable green roofs and the reduction of transportation energy.     

Predetermined overall thermal transfer value coefficients for Composite, Hot-Dry and Warm-Humid climates

This paper attempts to formulate Overall Thermal Transfer Value (OTTV) coefficients for Composite, Hot-Dry and Warm-Humid climates, the three main tropical climates in India. Four existing air-conditioned office buildings - two mid-rise and two high-rise were modeled as case studies using eQuest v.3.6, which is a DoE2.2, based building energy simulation tool. Based on the study of building envelope, loads, operation and HVAC system characteristics of these case study buildings, a hypothetical high-rise, 16 storey office building, octagonal in plan was created for parametric studies. 98 types of opaque exterior wall constructions and 93 types of glass constructions were varied sequentially in parametric runs to obtain results for hourly wall conduction, glass conduction and glass radiation heat flow in eight orientations for each of the climate type. These hourly results were processed to obtain annual heat gain intensities for each parametric case for all three modes of heat transfer. Regression analysis was used to obtain the OTTV coefficients - TD_eq, DT and SF for the three climates. A new OTTV equation is obtained and presented. The set of coefficients obtained were verified by calculating the OTTV for the four case study buildings, for various parametric runs. The computed OTTV for the four case study buildings exhibits good linear correlation with the annual space cooling plus heating energy use in three climates.     

Double skin façades for warm climate regions: Analysis of a solution with an integrated movable shading system

The analysis of a glass double skin façade equipped with integrated movable shading devices is presented, employing three different modelling levels: optics of materials, fluid dynamics of the double skin façade and building energy balance; the aim is to optimize both winter and summer energy performance. The model is developed for a façade oriented towards the south and taking into account the climatic data of central Italy; the solar radiation path with its multiple reflections at the different interfaces have been taken into account employing a ray tracing method. Simulations have been validated by the comparison with data of a similar experimental apparatus and they show that the winter configuration of the proposed façade allows a satisfactory solar heat gain in spite of the presence of shading systems. In summer, the solar heat is mainly absorbed by the external part, and even if a natural convection occurs, there is no significant influence on the inner skin and on the internal environment, thus reducing building cooling requirements. The façade performance was compared with traditional enclosures such as glazed and opaque walls in an office room in central Italy, showing that in the entire year the façade proposed significantly improves the building energy behavior, especially compared to opaque walls and when the configuration with air recovery is considered.     

Assessment of pre-heating air through a double window system on different building location and weather condition

Double windows are a currently adopted construction system in Portuguese dwellings. Simple changes enable this construction system to pre-heat the ventilation air. The air coming from the outside circulates goes upward through the channel between windows where it is pre-heated before entering the building. Heat that escapes from inside through the inner window and solar radiation, heats up the air between the two windows. This paper presents the performance of such passive system and focuses on the design aspects of this system and its building integration in function of weather conditions. One type of building is used where the window is located on different facades, thus, different orientations. Four different weather conditions are chosen, from mild to cold winters. The methodology used is based on previous validated parametric studies. Results indicate that the ventilated double window system offers an alternative to cold natural ventilation in any cold region and any facade orientation. The colder the location, the higher the pre-heating of the incoming air. This study expects to help designers to conceive ventilated double windows duly adapted to local climate where natural ventilation is an important design consideration and where energy consumption must be reduced.     

不同类型玻璃在北京地区的节能研究

分别采用5种不同传热系数和遮阳系数的外窗玻璃,利用建筑能耗模拟软件eQUEST模拟北京地区某办公建筑的能耗,研究分析在北京地区玻璃的传热系数和遮阳系数对办公建筑逐月冷热负荷的影响;在全年能耗方面,6mm白玻+12mm空气+6mm白玻、6mm Low-E玻璃+12mm空气+6mm白玻、4mm超白玻+13.5mm气凝胶+4mm白玻、气凝胶玻璃(遮阳型)相对于12mm白玻的节能率分别为2％、11％、1％、13％,通过分析比较得出气凝胶玻璃这一新型建筑材料具有较好的节能效果.     

建筑节能与玻璃

公共建筑与居住建筑是建筑整体构成的主要部分。建筑物的节能,以外围护结构节能为主;外围护结构节能由屋面、外墙、外窗节能构成。由于现代建筑设计中,外窗占外墙的比例越来越大,导致通过窗户造成的能源损耗约占整体建筑的1/3~1/2。因此,窗户的节能性十分重要。窗户由窗框、玻璃组成,玻璃约占整体窗户的80%~90%,窗玻璃的隔热性能至关重要。阐述了太阳光辐射热能的性质及各种玻璃的节能性,着重介绍了镀膜玻璃及相关节能效果,对建筑节能设计有一定的参考价值。     

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.     

Modelling sheltering effects of trees on reducing space heating in office buildings in a windy city

Using statistical weather analysis, computational fluid dynamics and thermal dynamic simulation, a systematic method was developed to assess quantitatively the effects of a shelterbelt on space heating, particularly with regard to the energy consumption and CO₂ emission. It was then applied to estimate the heating loads of two typical office buildings in a windy city located at 57.2North, with and without a shelterbelt. Firstly, the statistical analysis of weather data was carried out to identify the prevailing wind direction during a typical winter heating season in the location. It was to ensure the windbreak planted rightly to maximise its sheltering benefits for the buildings in its leeward. This analysis, which revealed the main weather features in the location, would help to better comprehend the results of the thermal modelling and gain insight of how the load responses to the climate. In the second part, CFD modelling predicted wind reduction due to the shelterbelt under various wind directions. The predicted data were then used to prepare two sets of weather data, the original weather file and the revised one, in which the wind data had taken into account the reduction effect of the windbreak. The third part was a dynamic thermal modelling study where two types of office buildings were selected as the representative offices in Edinburgh for the assessment of sheltering effect on energy saving and CO₂ reduction. The predicted savings over a heating season due to the shelterbelt were in a range of 16–42% and the actual values in space heating were about 2.2 kWh m⁻² for new office buildings and 14.5 kWh m⁻² for offices converted from conventional houses without insulation improvement. These significant savings were due to the local weather that is typically known as long windy winter with many cloudy days.