Automated Building Energy Modeling and Assessment Tool (ABEMAT)

Highlights

• A new computer tool is developed using BIM and modified source code of EnergyPlus and OpenStudio.

• It resolves certain issues in BIM files, automatically, using a corrective tool developed in Python.

• The BIM to IDF conversion is performed automatically using ABEMAT and detailed outputs will be provided.

• Detailed outputs include the amount of heat transfer through every single wall, window, doors, roof, and floors.

• Comparison between EnergyPlus advanced outputs and ABEMAT's outputs yielded to similar results.

Abstract

Buildings contribute to about 40% of total annual energy consumption in the U.S. and saving a small percentage of that can lead to significant economic and environmental impacts. Building Energy Modeling (BEM) tools are important in reducing building's energy consumption. Most of the available tools only provide total energy consumption related to HVAC system, lighting, hot water, and appliances. While fine-grained data may be available in some computer tools, the process for obtaining these data is time-consuming, error-prone, and requires software-related skills.

This paper explains a developed tool that contributes in automation of building energy simulation and providing fine-grained outputs by using Building Information Modeling (BIM) and modified source code of energy simulation tools such as EnergyPlus and OpenStudio. This tool, which is referred to as ABEMAT (Automated Building Energy Modeling and Assessment Tool), receives gbXML file and provides users with the amount of heat transfer through every single building envelope component such as windows, doors, and walls through an automated process. ABEMAT's and EnergyPlus advanced outputs are compared for validation; the latter being a time consuming process and error-prone, which requires software-related skills compared to ABEMAT. Results showed similar findings indicating the functionality of ABEMAT in providing fine-grained outputs.

Introduction

Buildings consume about 40% of the total energy in the U.S. and to reduce such high level of energy consumption, multiple measures are needed. Building's design can be made to be more energy efficient by modifying building properties such as orientation, dimensions, and building envelope materials/details. In addition, the energy consumed during the use phase of buildings can be decreased by either monitoring the energy consumption and informing the residents or by energy retrofit of buildings, which could be benefitted by emerging tools such as energy smart homes and BEM tools. The tool developed in this study, ABEMAT, contributes to all of these measures. These measures and all the tools and technologies involved in their development are illustrated in Fig. 1, where all of these tools are shown to be interconnected and working together. For example, to evaluate the design of a building developed in a CAD tool in terms of energy performance, an energy simulation tool is required. In addition, energy smart homes can also be equipped with energy simulation tools in order to monitor and optimize the energy consumption. BIM's potential in improving the energy performance of buildings during the design and operation of buildings is also identified and discussed at length in other studies [1]. A brief introduction about the areas and tools involved in this research including BIM files, application of BIM in BEM, and building's energy retrofit is presented in this section.

BIM files may include data related to multiple aspects of buildings such as mechanical systems, electrical systems, schedules, structural, and architectural components. Two of the most prevalent BIM file schemas are Industry Foundation Classes (IFC) and Green Building Extensible Markup Language (gbXML). Application of BIM in different areas such as developing the 3D model of buildings, structural analysis, and energy modeling has been of interest and subject of some past studies [[2], [3], [4]]. Information related to the geometry, materials, HVAC system, and costs can be stored and transferred through these files, which makes the modeling process faster, less error-prone, and more toward automated process, while making it easier for different parties in design and construction process to communicate and facilitate visualizing data [5,1]. Other researchers have also identified the benefits of application of BIM in energy modeling during the design phase, which for example can lead to “rapid iterative comparison of design options” [6]. Both gbXML and IFC are capable of storing and transferring most of the data required for energy simulation such as defining thermal zones, material thermal properties, material thickness, and HVAC system properties [[7], [8], [9]]. However, there are some shortcomings in these file schemas related to the geometry of buildings, location, and domain of the application. For example, gbXML is only capable of transporting the data related to rectangular building geometry, while IFC works with other geometry types [[10], [11], [12], [13]]. Although these file schemas are capable of handling the data related to energy simulation, some of the tools being used for developing or importing these files are not capable to perform the process flawless and properly. Application of BIM in BEM can be explained in more details, where shortcomings can be identified and appropriate solutions developed.

Applications of BIM in building energy modeling (BEM) consists of multiple components such as BIM files and conversion of BIM file to a readable file for energy simulation tools. Each of these components can experience shortcomings and issues during the process. The main core of the process includes using a BIM file for Building Energy Modeling (BEM) shown in Fig. 2, which can be referred to as BIM-to-BEM interoperability process (BBIP) or simply BIM-to-BEM. Some studies have addressed adoption of BIM-to-BEM approach in design phase of buildings to optimize it [[14], [15], [16]]. The challenges and issues in BBIP are identified in some studies to discuss the shortcomings related to CAD tools and mapping information to a BIM file, the process of mapping data from a BIM file to a readable file for BEM tools, and the interoperability issues during translating data for an energy simulation engine [8,[17], [8], [18], [19], [20], [21]]. On the other hand, there are solutions suggested and used by some researchers to resolve these issues, including adding supplementary library or using middleware tools [22,23]. such as using middleware tools, which work between BIM and BEM tools, adding the missing information manually, and linking the files to database servers to add the required information missing during the process [[24], [25], [26], [27]]. Adopting a middleware corrective tool is the same approach used in this study using Python, which will be explained in more details subsequently.

As shown in Fig. 1, energy retrofit can be another approach in reducing the energy consumption of existing buildings [28]. Energy retrofit can target different components of buildings such as HVAC system, electrical system, appliances, and envelope. In this study, ABEMAT is focused on building envelope including both opaque and transparent components such as walls and windows, respectively. Different computer tools can be adopted prior to performing energy retrofit, and the data provided by these energy simulation tools can contribute to evaluating the existing conditions of buildings in order to improve the decision making process of energy retrofit. Current energy simulation tools such as OpenStudio, DesignBuilder, and BEopt, which are used in energy retrofit of buildings, allow consideration of multiple criteria in choosing suitable energy retrofit scenarios [31,32,34]. Most of these tools only provide accumulated energy-related data, for example the whole-house energy consumption or the total heat transfer through all the components in one thermal zone [29,30,33]. Even if the detailed outputs are provided by an energy simulation tool, they are not presented in existing commercial computer tools or they are not easy to access. The process to obtain such data can be time consuming, error-prone, and requires software-related skills. It would be of great interest to have detailed energy consumption of each building envelope component such as the amount of heat transfer through a specific window or exterior wall as opposed to the total heat transfer through all windows and walls in a fast, easy, and more accurate approach. ABEMAT can provide such data by saving the amount of heat (gain or loss) transfer, through each building envelope component and floors in separate text files for walls, windows, floors, roofs, and doors.

As shown in Fig. 1, energy smart homes can also contribute to reducing energy consumption in buildings, for example through smart control of appliances and energy monitoring and the incentive impacts of informing residents about their energy consumption. Shortcomings also exists in energy smart homes, as these homes are typically neither equipped with energy simulation tools within their processing units, nor are the adopted simulation tools capable of providing fine-grained or detailed energy consumption data. Therefore, application of tools such as ABEMAT can contribute to providing fine-grained data on heat transfer through building envelope components to users in an automated and fast way, which is more compatible with emerging technologies and tools such as energy smart homes. Moreover, application of BIM-enabled tools such as ABEMAT in energy smart homes can in future facilitate data management and visualization obtained from data acquisition tools, which is also noted by other researchers [35].

The tool introduced in this paper, which is focused on building envelope components and floors, automates the whole process of building energy modeling, simulation, and providing fine-grained outputs by using BIM and modifying or using the source code of existing tools in energy simulation such as EnergyPlus and OpenStudio. As a result, it is referred to as Automated Building Energy Modeling and Assessment Tool (ABEMAT). The overview of its process and contributing components are presented in Fig. 2, which indicates that several tools and components are involved in its process. The process within ABEMAT includes the following major steps:

• Receive a gbXML file, which can be generated by any BIM tool such as Revit.

• Use a corrective tool developed by using Python to resolve some of the issues occurring during file conversion.

• Call the subroutines and functions defined in OpenStudio by using Ruby to convert the gbXML file to Input Data File (IDF) for EnergyPlus (E+)

• Perform energy analysis by adopting a modified EnergyPlus using C++ to provide detailed information on heat transfer through building envelope components such as windows and walls and saves them in separate text files for further use.

The methods used in order to develop each component in ABEMAT are explained in details under the methodology section. Different programming languages including C++, Python, and Ruby are used to develop the new tool or modify an existing tool such as EnergyPlus or OpenStudio. Ruby is an open source programming language, which can be used for modifying existing subroutines in OpenStudio. Python is also a high-level programming language, which has built-in functions making it a proper option for working with text files such as gbXML.ABEMAT is only capable of reading gbXML files at this point, and its outputs are saved in text files. In order to verify the outputs and process within ABEMAT, a computer model was also developed in this study base don Revit with EnergyPlus used as the energy simulator. The process and results are explained further subsequently. ABEMAT can be further enhanced to include more aspects in energy efficient and green buildings to include more detailed data related to natural ventilation, carbon emissions, and solar/day lighting. Follow-up studies exploring available BIM software can further contribute to this area [36].