Developing a physical BIM library for building thermal energy simulation

Insufficient interoperability resulting from complex data exchange between architectural design and building energy simulation prevents the efficient use of energy performance analyses in the early design stage. This paper presents the development of a Modelica library for Building Information Modeling (BIM)-based building energy simulation (ModelicaBIM library) using an Object-Oriented Physical Modeling (OOPM) approach and Modelica, an equation-based OOPM language. By using the ModelicaBIM library, our project investigates system interfaces between BIM and energy simulation, which can perform semi-automatic translation from the building models in BIM to building energy modeling (BEM) using a BIM's authoring tool's Application Programming Interface (API).The ModelicaBIM library consists of OOPM-based BIM classes and OOPM-based BIM structure. OOPM-based BIM classes represent building component information. OOPM-based BIM structure consists of test case models that demonstrate (i) how building information in BIM can be transformed to OOPM and (ii) how design operations in BIM, such as changing a building geometry and editing building components, can be translated into BEM. A case study for simulation result comparisons has been conducted using (i) OOPM-based BIM models in the ModelicaBIM library and (ii) LBNL Modelica Buildings library (a Modelica-based building thermal simulation library developed by Lawrence Berkeley National Laboratory). Our implementation shows that the ModelicaBIM library enables (i) objects in BIM to be translated into the OOPM-based energy models and (ii) existing OOPM library to be utilized as a simulation solver for BIM-based energy simulation.     

Mapping actual thermal properties to building elements in gbXML-based BIM for reliable building energy performance modeling

The ability to import building geometric and construction thermal data from building information models (BIM) has significant potential to reduce the time and uncertainty in building energy modeling process. In today's BIM-based energy modeling practice, thermal properties are mainly derived from generic building construction types in BIM. However, for energy modeling of existing buildings, such assumptions are often inaccurate as they do not account for diminishing thermal resistances of building materials instigated by their deteriorations. To improve the reliability of BIM-based energy modeling, we present a system, together with new methods for automated association and updating of actual thermal property measurements with BIM elements in gbXML schema. By leveraging collections of digital and thermal images and based on environmental measurements, our system first produces a 3D thermal model for the building under inspection and then derives the actual thermal resistances of the building assemblies at the level of 3D vertexes. By associating these measurements with their corresponding elements in gbXML, thermal properties of the BIM elements are automatically updated. Our experiments in real-world residential and instructional buildings show how actual thermal properties can be automatically associated with BIM elements and updated in gbXML. The proposed method shortens the gap between architectural information in BIM and the actual data needed for energy performance simulation, and enables reliable BIM-based energy analysis for retro-commissioning, continuous commissioning, and retrofit.     

Findings from a survey on the current use of daylight simulations in building design

This paper presents findings from a web-based survey on the current use of daylight simulations in building design. The survey was administered from December 2nd 2003 to January 19th 2004. One hundred and eighty five individuals from 27 countries completed the survey. The majority of respondents worked in Canada (20%), the United States (20%), and Germany (12%). Most participants were recruited through building simulation mailing lists. Their self-reported professions ranged from energy consultants and engineers (38%) to architects and lighting designers (31%) as well as researchers (23%). They worked predominantly on large and small offices and schools.Ninety one percent of respondents included daylighting aspects in their building design. Those who did not consider daylighting blamed lack of information and unwillingness of clients to pay for this extra service. Among those participants who were considering daylighting 79% used computer simulations. This strong sample bias towards computer simulations reflects that many participants had been recruited through building simulation mailing lists. Participants named tools’ complexity and insufficient program documentation as weaknesses of existing programs. Self-training was the most common training method for daylight simulation tools. Tool usage was significantly higher during design development than during schematic design. Most survey participants used daylighting software for parameter studies and presented the results to their clients as a basis for design decisions.While daylight factor and interior illuminances were the most commonly calculated simulation outputs, shading type and control were the most common design aspects influenced by a daylighting analysis. The use of scale model measurements had rapidly fallen compared to a 1994 survey, whereas, trust in the reliability of daylighting tools has risen. While participants named a total of 42 different daylight simulation programs that they routinely used, over 50% of program selections were for tools that use the RADIANCE simulation engine, revealing the program's predominance within the daylight simulation community.     

The daylighting dashboard – A simulation-based design analysis for daylit spaces

This paper presents a vision of how state-of-the-art computer-based analysis techniques can be effectively used during the design of daylit spaces. Following a review of recent advances in dynamic daylight computation capabilities, climate-based daylighting metrics, occupant behavior and glare analysis, a fully integrated design analysis method is introduced that simultaneously considers annual daylight availability, visual comfort and energy use: Annual daylight glare probability profiles are combined with an occupant behavior model in order to determine annual shading profiles and visual comfort conditions throughout a space. The shading profiles are then used to calculate daylight autonomy plots, energy loads, operational energy costs and green house gas emissions. The paper then shows how simulation results for a sidelit space can be visually presented to simulation non-experts using the concept of a daylighting dashboard. The paper ends with a discussion of how the daylighting dashboard could be practically implemented using technologies that are available today.     

Simplified daylighting energy savings for non-daylighting building energy simulation programs

The California Legislature mandated the California Energy Commission (CEC) to establish and periodically update energy efficiency standards for new buildings. To this end, a sensitivity analysis was conducted by the Standards Development Office of the California Energy Commission for nonresidential buildings. The purpose of this parametric analysis was to determine which variations in building parameters actually have significant energy impacts.A “generic” building model was developed and implemented in conducting this sensitivity analysis. The generic model was used as an analytical tool in modeling the energy impact of building parameter variations, as well as architectural and mechanical energy-saving measures on the energy use of each module. It is recognized that the level of significant energy impact is equivalent to, or bounded by the accuracy of the energy analysis tools in predicting energy usage in actual buildings. For the computer program used, DOE 2.1A this accuracy is within ±5%.Since DOE 2.1A and most of the other building energy simulation programs do not have daylighting algorithms, another calculation tool was used to determine daylight availability and lighting power reduction on an hour-by-hour basis for each orientation. This is accomplished with a daylight reduction factor (DRF).Quicklite, a simplified daylighting program, calculated footcandle (lux) levels based on outdoor ambient light levels, physical room dimensions and properties. To assess the impact of the Quicklite calculated footcandle (lux) levels on artificial lighting use, a control scheme was assumed, and a DRF was calculated based on annual sky conditions by climate zone.Once the DRF values are known for each orientation, the electric lighting schedule can be modified. A new profile number, representing the proportion of installed lighting switched on at that hour, replaced the daily lighting schedules when daylighting was utilized (09:00 – 17:00). To test this methodology, a sensitivity analysis was conducted between DOE 2.1A with Quicklite modifications and DOE 2.1B which has a daylighting preprocessor. The results displayed a 3.6% variation in total energy use.We conclude that daylighting calculations for design days using simplified programs can be used to approximate daylighting energy savings in building energy simulation programs that allow zoned lighting schedules but do not calculate daylight contributions.     

云南地区卷烟工厂采光优化设计

卷烟工厂具有建筑面积大、室内进深大的特点。加之考虑到工艺和视觉工作要求,工厂对室内光环境要求较高。以云南某卷烟复烤联合工房为例,运用Ecotect建立原自然采光设计方案的建筑模型,导入Desktop Radiance进行采光系数计算,分析原设计方案中存在的问题,提出自然采光设计方案优化结果;分析优化方案对室内照明能耗和空调能耗的影响,同时,提供自然采光产品的性能参数指标。提出自然采光模拟分析技术在卷烟工厂采光优化设计中的研究与运用思路。     

A parametric approach for performance optimization of residential building design in Beijing

During the early design stage of green residential buildings, there are tremendous potential of using parametric optimization to achieve preferable green performance, such as building energy consumption efficiency, daylighting, ventilation and thermal comfort. Taking residential design features into consideration, this paper presents an optimization workflow and effects based on a case study of a residential building project in Beijing. Firstly, 27 design parameters related to residential spatial form and building envelope were selected for the optimization. The simulation results of the cooling and heating load were taken as the optimization objects. Secondly, optimized schemes were obtained from 6246 simulation results, with 1925 verified simulation results proving that the optimized result is reliable. Finally, analysis was performed to establish the correlations between design parameters and performance in order to create the easy access for architects to determine design parameters depending on the performance sensitivity of each parameter. Analysis results showed that parametric optimization of spatial form and building envelope at the design stage is a feasible approach to reducing energy consumption in residential building design.

     

Adding advanced behavioural models in whole building energy simulation: A study on the total energy impact of manual and automated lighting control

Behavioural models derived from on-going field studies can provide the basis for predicting personal action taken to adjust lighting levels, remedy direct glare, and save energy in response to physical conditions. Enabling these behavioural models in advanced lighting simulation programs, such as DAYSIM and the Lightswitch Wizard, allows for a more realistic estimate of lighting use under dynamic conditions. The current downside of these approaches is that the whole building energy impact of manual changes in blind settings and lighting use, including its effect on heating and cooling requirements, is not considered. A sub-hourly occupancy-based control model (SHOCC), which enables advanced behavioural models within whole building energy simulation, is presented. The considered behavioural models are the Lightswitch2002 algorithms for manual and automated light and blind control, while the investigated whole building energy simulation program is ESP-r.The enhanced functionality is demonstrated through annual energy simulations aiming at quantifying the total energy impact of manual control over lights and window blinds. Results show that building occupants that actively seek daylighting rather than systematically relying on artificial lighting can reduce overall primary energy expenditure by more than 40%, when compared to occupants who rely on constant artificial lighting. This underlines the importance of defining suitable reference cases for benchmarking the performance of automated lighting controls. Results also show that, depending on the proportion of buildings occupants that actively seek out daylighting, reduced lighting use through automated control may not always produce anticipated savings in primary energy for indoor climate control. In some cases, reduced lighting use is shown to even increase primary energy expenditure for indoor climate control, trimming down initial primary energy savings in lighting alone. This reveals the superiority of integrated design approaches over simpler daylighting guidelines or rules of thumb.     

Evaluation of user interaction with daylighting simulation in a tangible user interface

We present a study of a tangible user interface for design and simulation applied to architectural daylighting analysis. This tool provides an intuitive way for architects and future occupants of a building to quickly construct physical models and interactively view in them a projected simulation of resulting daylighting.A user study was conducted of both architecture students and non-architects in a set of analysis and design exercises. The study investigates the effectiveness of this interface as an educational tool, the precision and accuracy of the constructed physical models, and its effectiveness for creative design exploration. The four part study investigates users' intuitions about daylighting and their interaction with the tangible user interface for analysis of an existing space. These exercises revealed and corrected misconceptions in many of the participants' intuitions about daylighting, and overall the participants praised the ease-of-use of the tool and expressed interest in this simulation tool for daylighting analysis in architectural design.     

Integrating energy consciousness in the design process

The design process for an intelligent, energy conscious building which was built, along with the design tools that were applied, is presented. The building, situated in the hot–humid climate of Rehovot, Israel, houses the laboratories and offices of the Weizmann Institute's Environmental Science and Energy Research Department. Alternative bio-climatic design options were proposed and evaluated throughout the detailed design stage. A building energy performance index (BEPI) was established for each alternative. This index reflects the total amount of energy consumption for heating, cooling, ventilating and lighting used per square meter of floor area. Thermal modeling for the different design alternatives were carried out by means of an hourly dynamic simulation model. The model solves simultaneously the heat transfer equations through all exterior walls, taking into account the thermal mass of each external wall as well as internal partitions. The model was extended to include hourly calculations of daylighting and geometrical shading coefficient of the windows, as well as automated and `smart' control strategies.     

外窗尺寸对办公建筑采光影响因素研究

外窗作为建筑重要的外围护结构,不仅会影响建筑采光,同时,还会影响建筑照明、空调、供暖能耗。在相同外窗面积条件下,为获得更好的采光效果,可以在不增加空调及供暖能耗的前提下有效减少建筑的照明能耗,进而降低整体建筑能耗。通过计算机模拟分析办公建筑外窗尺寸对有效采光宽度、有效采光深度、有效采光面积的影响,总结出不同吊顶高度下的采光效果指标的查询图标,供外窗设计参考。     

Optical and thermal performance of glazing with integral venetian blinds

Shading devices have long been used to control solar gain and daylighting through windows. The optimal design and use of such devices requires a detailed knowledge of their optical and thermal properties, including their variation with the angle of incidence of the solar radiation. We describe the experimental methods used to characterise two types of double-glazing units (DGU) incorporating Venetian blinds. The first consists of a DGU with an adjustable blind located in the space between the panes. The second incorporates a fixed blind element bonded between two glass sheets. The spectral bi-directional transmittance functions (BRTF) were measured for a range of incidence angles, using the Cardiff goniospectrometer. The thermal properties were measured with an illuminated hot box. These measurements are laborious, and it is desirable to develop simple models, that could be used for product development to estimate the effect of changing the properties of the blind material and its design, without the need to make detailed measurements on each variation. A model is described, that calculates the properties of the DGU using as input the optical properties at normal incidence of the component elements (glass and the blind’s slats). The model is applied to the variable blind DGU, varying the angle of rotation of the blind. Despite the simple nature of the model, it is shown to satisfactorily predict the properties of the DGU. The model can easily be incorporated in building energy simulation programs.     

基于光热性能的南向遮阳措施节能降耗模拟研究

采用模拟耦合计算室内照度与窗体能耗的方法,以上海为研究区域,针对朝南方向,分析了水平、垂直遮阳板以及卷帘等不同装置引起的照明能耗和制冷能耗之和,并由此评价其节能降耗的效果.结果表明,当灯具光效大于41.2 Lm/W时,遮阳卷帘引起的综合能耗较小;而当光效小于上述数值时,水平遮阳板更好.这两种遮阳措施下室内的照度分布相对...     

Autozoner: an algorithm for automatic thermal zoning of buildings with unknown interior space definitions

In this paper, we present a general algorithm to automatically convert arbitrary building massing models into multi-zone building energy models (BEM). The algorithm follows current guidelines for thermal zone discretization of BEMs when actual interior space boundaries are yet undefined. Envisioned applications are for rapid model generation during schematic building design as well as for urban massing studies. We present an argument that current recommendations for separating core from perimeter zones effectively follow a straight-skeleton subdivision. Following a step-by-step explanation of the procedure, a number of example building shapes of varying complexity are shown to demonstrate the algorithm's robustness and suitability for automated multi-zone BEM generation. Going forward, it is recommended that the algorithm is adopted by software developers to ensure more consistent thermal model production within the building simulation community.     

Development of an optimal daylighting controller

A new lighting and daylighting control strategy is modeled and evaluated against conventional lighting and daylighting controls. The new lighting and daylighting control strategy can be incorporated in an energy management and control system (EMCS) to operate and control lighting fixtures in any indoor space. The new daylighting control can also be modeled and integrated in detailed building energy simulation tools. Through a validation analysis, it was found that the new control strategy provides more energy savings than conventional daylighting controls. Moreover, the validation analysis has indicated that existing daylighting control simulation analysis tools could overestimate lighting energy savings associated with daylighting controls. Moreover, it was also found that if calculated solar and illuminance data are used instead of measured solar radiation data, the errors in predicting lighting energy use when daylighting controls are utilized can be significant.     

Integrating thermal comfort field data analysis in a case-based building simulation environment

Despite the obvious importance of thermal comfort in the design of indoor environments, it has not been effectively integrated with design support tools. The reasons can be attributed in part to an absence of modular and flexible software architecture that facilitates dynamic data transfer between building performance simulation modules. Research has shown that the mathematical models of thermal comfort sometimes fail to accurately describe or predict thermal comfort in workplace settings even when the values of environmental and personal parameters are known. Thus, there is a critical need to provide a thermal comfort evaluation framework that, in addition to the algorithmic implementation of mathematical thermal comfort prediction models, would make use of the empirical knowledge base accumulated over the last 20 years from field experiments around the world. This paper first talks about an integrated simulation environment SEMPER that allows for multiple performance evaluation including thermal comfort analysis from a shared object model of building. Then, it discusses the results of a detailed thermal comfort analysis performed to find the reasons for the discrepancy between the predicted and observed values and the factors responsible for such discrepancy. Finally, the paper shows how the results of the empirical thermal comfort analysis can be used in designing better thermal environments.     

Whole building energy simulation and energy saving potential analysis of a large public building

This article explores how to use EnergyPlus to construct models to accurately simulate complex building systems as well as the inter-relationships among sub-systems such as heating, ventilation and air conditioning (HVAC), lighting and service hot water systems. The energy consumption and cost of a large public building are simulated and calculated for Leadership in Energy and Environmental Design (LEED) certification using EnergyPlus. American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) baseline model is constructed according to ASHRAE 90.1 standard and the comparison of annual energy consumption between ASHRAE baseline model and proposed model is carried out. Moreover, an energy efficiency (EE) model is built based on the design model. Meanwhile, other energy conservation measures (ECMs) such as daylighting dimming and occupant sensors are considered. The simulation results show 4.7% electricity consumption decrease but 6.9% gas consumption increase of the EE model compared to ASHRAE baseline model. In summary, the annual energy cost of the EE model is reduced by 7.75%.