BEM Links

The U.S. Department of Energy (DOE) Building Technologies Office (BTO) site with information about its energy modeling program.

The site includes information about the portfolio of DOE-developed software tools (including EnergyPlus and OpenStudio), BTO's plans and roadmap for future activities, publications and presentations by BTO, and links to other industry resources.

The BEM Library was developed in 2011 with the intention of it becoming a curated set of industry-vetted resources. Three sections of the library were created with each section providing targeted information for a specific stakeholder group type:

1. Owners and Managers
2. Practitioners
3. Financiers.

The site has not been actively maintained since its initial development. The section for Owners and Managers has the most complete content. The other sections have numerous gaps.

The BEMBook Wiki was developed in 2011 with the intention of capturing the energy modeling “body of knowledge” and providing topical access to energy modeling concepts. It was organized using an outline that groups modeling concepts into specific modeling or design phases of a project.

The site has not been actively maintained since its initial development. There are numerous links in the wiki that open to blank pages and it’s not clear which pages have content until you click the link, making navigation difficult.

Unmet Hours is a question and answer website for building energy modelers. Its design is based on a popular site for programmers called Stack Overflow. Unmet Hours allows users to post questions and other users to answer them. If multiple answers are provided, other users can “vote” for what they consider the best answer, and top answers rise to the top of a list. Users may also search for a topic and find previously posted Q&A’s relevant to their search.

The site has gained good traction over the years and is still actively developed and used by the modeling community. Most of the questions and answers are for the EnergyPlus and OpenStudio modeling tools.

Project Stasio aims to provide supporting content on inputs, outputs, and case studies for the first 3 (early stage) modeling cycles defined in ASHRAE Standard 209.

• Cycle 1: Simple box modeling
• Cycle 2: Conceptual design modeling
• Cycle 3: Load reduction modeling

Content is organized around “design questions.” The idea is that early-stage analysis should serve a specific purpose and answer a specific design problem. In this way, the analysis is actually useful to making a project design decision.

The website is developed/managed by the IBPSA-USA Architectural Simulations Subcommittee - content on Stasio has a focus on architects and owner/clients as consumers of the data so it is highly visual in nature. Content is crowdsourced - much of the existing content has been developed around design competitions that coincide with annual modeling conferences over the last 2 years (2018, 2019).

The IBPSA-USA-NY chapter created a wiki for energy modeling. Similar to the BEMBook Wiki, it is organized in an “outline” fashion but many of the topics were never populated with content. The site includes some useful calculation examples and rules of thumb. The examples are static (i.e. you can’t use them to perform your own calculations directly).

The site suffered from spamming and has not been actively maintained. Many of the links to external content (e.g. modeling guides in various jurisdictions) no longer work.

The DDx is a database for participating architecture firms to submit energy performance data and track progress towards the AIA 2030 Commitment. AIA offers the following description on its website:

The mission of the AIA 2030 Commitment is to support the 2030 Challenge and transform the practice of architecture in a way that is holistic, firm-wide, project based, and data-driven. By prioritizing energy performance, participating firms can more easily work toward carbon neutral buildings, developments and major renovations by 2030.

Joining the 2030 Commitment gives you access to the Design Data Exchange (DDx), a national framework created by AIA with simple metrics and a standardized reporting format for measuring progress. The confidential, easy-to-use DDx lets you pinpoint best practices and anonymously compare project performance in your firm and beyond. The research tool allows you to compare projects of similar type, size, climate, and a host of other attributes across the 2030 portfolio.

This site is a detailed guide on how to use the DDx for 2030 Commitment reporting. It includes screenshots, narratives, and videos to walk users through how to use the DDx. It is very specific to this workflow (not trying to teach modeling). Each input field has a description, and different use-cases for the reporting tools are described.

This is a massive website dedicated to providing information and training about whole building design processes. It is organized into 3 main sections:

1. Design Guidance
2. Project Management
3. O&M

Within each section are various “resource pages” - topic-specific pages with detailed write-ups, and extensive lists of links to available (external) resources. While this site does not provide training specific to BEM, it is a valuable resource for providing information about design principles that will be part of many BEM models.

The Framework for Design Excellence, formerly known as the COTE Top Ten, provides design guidance to architects. AIA states that the framework: “organizes our thinking, facilitates conversations with our clients and the communities we serve, and sets meaningful goals and targets for climate action."

The framework consists of 10 measures, one of which is “Designing for Energy.” This measure features detailed discussions on the importance of energy benchmarking and goal setting at the beginning of a project, with energy modeling used to support reaching these targets.

This report outlines the case for using building performance simulation to inform decisions throughout the architectural design process. It provides an overview of the modeling process, guidance on how to integrate modeling in a firm, and numerous examples from case study projects that demonstrate how modeling informed the design.

These guides were developed to promote building energy efficiency and provide guidance on how to achieve levels of savings beyond code requirements. The zero energy Guides offer designers and contractors the tools needed for achieving zero energy buildings. The 50% Guides offer designers and contractors the tools needed for achieving a 50% energy savings compared to buildings that meet the minimum requirements of Standard 90.1-2004, and the 30% Guides offer a 30% energy savings compared to buildings that meet the minimum energy requirements of Standard 90.1-1999.

This chapter has sections on method development history, using models, uncertainty, thermal loads and model inputs, envelope components, HVAC components, terminal components, low-energy systems, natural and hybrid ventilation, daylighting, passive heating, hybrid inverse method, and model calibration.

This document is part of the EnergyPlus documentation. It provides a high level description of BEM concepts, and the components that make up a whole-building energy model. It is specific to e+. It also includes information about auxiliary e+ tools. There are some graphics that show how various building features are represented in a simulation model. Some formulas are included too.

This is a useful primer on BEM. After the introductory sections, the target audience is a technical modeler or engineer.

IBPSA-USA held an education survey in 2019. The >100 responses provide insight on training needs for the BEM community and preferred formats for delivery.

This document was developed to help owners and managers define and procure modeling services. It is presented in 3 sections:

1. Section 1: An Introduction to Building Energy Modeling - provides a brief overview of BEM, including its value, benefits, and common uses.
2. Section 2: Modeling Services - outlines service considerations related to timeliness, scope of work, simulation tools, and results.
3. Section 3: The Contracting Process - delivers specific resources to aid in contracting modeling services, developing the scope of work, and credentialing service providers.

Much of the content of this document was also incorporated into the “BEM Library” website.

In an appendix, there is a sample RFP for BEM services that serves as a template. It breaks down modeling tasks by project phase. This document came out before ASHRAE 209, so these tasks/phases are not completely aligned but in the same spirit.

In 2011, NREL performed a Job/Task Analysis (JTA) for Commercial Building Energy Modelers. The document describes tasks undertaken by modelers, and necessary knowledge, skills, and equipment needed to do the tasks. It was issued for public comment, but a final version was not published.

This technical support document for Architecture 2030's Zero Code describes several potential options for off-site procurement of renewable energy within the context of energy codes. It presents a process for evaluating and assigning a weight to each procurement method to value them compared to on-site generation or energy efficiency measures.

A searchable directory of technical papers from IBPSA-USA

A searchable directory of technical papers from IBPSA-World

The energy used to operate buildings is one of the most significant sources of greenhouse gas emissions. While it is possible to reduce emissions through climate-responsive design, many architects are not trained to do this. Filling an urgent need for a design reference in this emerging field, this book describes how to reduce building-related greenhouse gas emissions through appropriate design techniques. It presents strategies to achieve CO2 reductions, with an emphasis on control of energy flows through the building envelope and passive heating and cooling strategies. This new, revised edition is updated throughout, and includes a new chapter on building simulations.

CRC Press, 2017

This software-agnostic book, which is intended for you to use as a professional architect, shows you how to reduce the energy use of all buildings using simulation for shading, daylighting, airflow, and energy modeling. Written by a practicing architect who specializes in design simulation, the book includes 30 case studies of net-zero buildings, as well as of projects with less lofty goals, to demonstrate how energy simulation has helped designers make early decisions.

Within each case study, author Kjell Anderson mentions the software used, how the simulation was set up, and how the project team used the simulation to make design decisions. Chapters and case studies are written so that you learn general concepts without being tied to particular software. Each chapter builds on the theory from previous chapters, includes a summary of concept-level hand calculations (if applicable), and gives comprehensive explanations with graphic examples. Additional topics include simulation basics, comfort, climate analysis, a discussion on how simulation is integrated into some firms, and an overview of some popular design simulation software.

Routledge, 2016

Mechanical and Electrical Equipment for Buildings, Twelfth Edition is the industry standard reference that comprehensively covers all aspects of building systems. With over 2,200 drawings and photographs, the book discusses basic theory, preliminary building design guidelines, and detailed design procedure for buildings of all sizes. The updated twelfth edition includes over 300 new illustrations, plus information on the latest design trends, codes, and technologies, while the companion website offers new interactive features including animations, additional case studies, quizzes, and more.

Wiley, 2014

Heating, Cooling, and Lighting is the industry standard text on environmental control systems with the emphasis on sustainable design. By detailing the many factors that contribute to the comfort in a building, this book helps architects minimize mechanical systems and energy usage over the life of the building by siting, building design, and landscaping to maximize natural heating, cooling, and lighting. This new fourth edition includes new information on integrated design strategies and designing for the Tropics. Resources include helpful case studies, checklists, diagrams, and a companion website featuring additional cases, an image bank, and instructor materials.

Wiley, 2014

Introducing the basics of architectural science, this book is an ideal reference, providing an understanding of the physical basis of architectural design. The knowledge gained from this book equips the reader with the tools to realize the full potential of the good intentions of sustainable, bioclimatic design.

Routledge, 2014

This textbook teaches the fundamentals of building energy modeling and analysis using open source example applications built with the US DOE’s OpenStudio modeling platform and EnergyPlus simulation engine.

The authors, all researchers at National Renewable Energy Laboratory and members of the OpenStudio software development team, present modeling concepts using open source software that may be generally applied using a variety of software tools commonly used by design professionals. The book also discusses modeling process automation in the context of OpenStudio Measures―small self-contained scripts that can transform energy models and their data―to save time and effort. They illustrate key concepts through a sophisticated example problem that evolves in complexity throughout the book.

The text also examines advanced topics including daylighting, parametric analysis, uncertainty analysis, design optimization, and model calibration. Building Energy Modeling with OpenStudio teaches students to become sophisticated modelers rather than simply proficient software users. It supports undergraduate and graduate building energy courses in Architecture, and in Mechanical, Civil, Architectural, and Sustainability Engineering.

Springer, 2018

ASHRAE Standard 209-2018, Energy Simulation Aided Design for Buildings except Low Rise Residential Buildings, defines minimum requirements for providing energy design assistance using building energy simulation and analysis.

This Standard does a great job of identifying when various modeling studies can be most impactful on a building’s design and operation.

The Standard defines seven design-phase modeling cycles, each with specific modeling goals coordinated with the typical design process. Three additional modeling cycles are defined for construction and operation phases, and include a design and post-occupancy performance comparison to help owners and modelers understand the impact of design phase modeling assumptions and inform future modeling efforts.

This standard provides the minimum requirements for energy-efficient design of most buildings, except low-rise residential buildings. It contains mandatory and prescriptive design requirements for many features and systems in a building. Of particular interest for energy modelers, the standard provides energy modeling guidelines for the Energy Cost Budget (ECB) Method (Section 11), and Performance Rating Method (Appendix G) which are widely used for code compliance and beyond-code programs like LEED.

Standard 55 specifies conditions for acceptable thermal environments and is intended for use in design, operation, and commissioning of buildings and other occupied spaces. It is not explicitly a modeling Standard, but thermal comfort is commonly evaluated by modelers using metrics like PMV and PPD from Standard 55. Adaptive comfort (often used to evaluate passive cooling strategies) is also a modeling analysis based on Standard 55.

Standard 62.1 specifies minimum ventilation rates and other measures for new and existing buildings that are intended to provide indoor air quality that is acceptable to human occupants and that minimizes adverse health effects. While it is not explicitly a modeling Standard, ventilation rates are a critical set of inputs for models.

COMNET is a modeling guideline that includes general modeling recommendations as well as a detailed compilation of over 400 building descriptors. Separate guidelines are available for the performance rating method (Appendix G) for the 2001, 2007, 2010 and 2016. It aims to provide much greater detail than ASHRAE 90.1 App. G in order to reduce ambiguity or need to interpret the intent of modeling rules.

It includes default modeling recommendations, default time-of-use energy tariffs, as well as advanced modeling tips. It also includes standardized report formats and an accompanying XML schema for the report data.

This document is intended to be a reference manual for the Appendix G Performance Rating Method (PRM) of ANSI/ASHRAE/IES Standard 90.1-2016 (Standard 90.1-2016). The procedures and processes described in the PRM reference manual (PRM-RM) are designed to provide consistency and accuracy by filling in gaps and providing additional details needed by users of the PRM. Note that this document has been created independently from ASHRAE and Standing Standard Project Committee (SSPC) 90.1 and is neither sanctioned nor approved by either of those entities.

2016 Version

2010 Version

The NACM Reference Manual lays out the modeling procedures for CA’s Title 24, Part 6 energy code, following the performance compliance approach. It provides detailed modeling rules for the proposed and standard design including input types, ranges, defaults, restrictions, etc. The intended audience is software developers, who wish to have their software tools certified for use as a compliance tool, and practitioners, who wish to understand that basis of comparison against the standard design (code minimum).

EDAPT is a platform that facilitates the development and submission of energy models to utility incentive program administrators. This site provides information on utilities that use the EDAPT system, instructions for performing utility incentive calculations (whole-building simulations using OpenStudio), and documentation requirements.

CABEC provides training and education for various groups of professionals who work with CA’s Title 24 energy code. Their online training tool includes recordings of webinars. The webinars are free to attend, but recordings are free for members only or at a small cost for non-members. Offerings can be filtered by “energy modeling” and the results include numerous Title 24 compliance modeling topics.

A collection of free energy code training, tools and resources for those who need to understand and meet the requirements of California’s Title 24 Energy Code. Not specifically focused on energy modeling, but provides information on the energy code requirements, and processes.

Program information for California’s utility incentive program. Project teams can earn monetary incentives for implementing strategies that demonstrate energy savings using building simulations.

Program information for New Jersey’s utility incentive program. Project teams can earn monetary incentives for implementing strategies that demonstrate energy savings using building simulations.

Program information for Austin Energy's utility incentive program. Project teams can earn monetary incentives for implementing strategies that demonstrate energy savings using building simulations.

Program information for Energy Trust of Oregon's utility incentive program. Project teams can earn monetary incentives for implementing strategies that demonstrate energy savings using building simulations.

Program information for Connecticut’s utility incentive program. Project teams can earn monetary incentives for implementing strategies that demonstrate energy savings using building simulations.

Program information for SMUD's utility incentive program. Project teams can earn monetary incentives for implementing strategies that demonstrate energy savings using building simulations.

Offers online training courses in eQuest, TRACE, OpenStudio, and LEED modeling. Courses and bundles are charged as monthly subscription (subscription applies to individual courses/bundles).

This site is built on an e-learning platform that allows for anyone to be an instructor, post a course, and charge a fee. There are currently 9 available courses. It includes detailed courses on eQuest and OpenStudio. There are also several other shorter courses with low or no cost.

This site includes a series of pre-recorded webinar training courses. The courses are largely hands-on training/tutorials with a heavy emphasis on grasshopper and ladybug tools.

This site includes a series of pre-recorded webinar training courses. The library of courses is available to paid IBPSA-USA members.

Pacific Gas & Electric offers numerous training courses across much of California. Many of them are recorded and offered as on-demand trainings (via the web). At the link above, you can see all available training courses, and filter by subject. One may apply a filter for building modeling or building science. Of note on this site is a series of building science trainings.

These trainings are led by John Straube from Building Science Corp. The content is much broader than modeling, but does provide very detailed info on how building enclosures work. There are many hours of video content available for this topic. It covers topics such as air barriers, thermal bridging, windows, curtain walls, shading, moisture control, and more. While this is probably information overload for many modelers, it is a great resource for understanding the science of heat transfer through the envelope.

14 short videos (5-10 min each) describing building physics concepts such as heat and moisture transfer. Led by Professor Carl-Eric Hagentoft, Chalmers University of Technology, Sweden

9 short videos (~5 min each) with basic information for getting started using EnergyPlus

Many short videos (5-10 min each) and playlists focused on how to use the SketchUp Plugin and the OpenStudio Application

1 long video (3+ hours)

This is a software-neutral, instructor-led training that covers the fundamentals of building energy modeling and explains how to use modeling to guide design decisions, with an emphasis on HVAC.

Introduction to EnergyPlus Seminar - PowerPoint Slides, developed in 2012 by GARD and DOE

Presentations and exercises on five building physics topics: Insulation, Thermal Mass, Internal Gains, Infiltration, and Daylighting. Suitable for self-study or for use in a university course. Presentations cover general building physics concepts then show how to model them EnergyPlus. Developed in 2010 by GARD and IIT.

NREL also maintains a listing of OpenStudio training providers that include university and international training options.

The Society of Building Science Educators (SBSE) is an association of university educators and practitioners in architecture and related disciplines who support excellence in the teaching of environmental science and building technologies. SBSE's goal of promoting and supporting quality instruction in building science is realized through a broad range of practical activities.

“The Joint Committee on Building Science Education is a coalition of university and other peer organizations that is working closely with academic and research organizations and the US Department of Energy to facilitate excellence in building science education.”

This website has many links to building science resources and publications including teaching resources. Not organized by topic, but rather a list of resources grouped into broader categories. Much of the content is academic focused. There is not a specific focus on BEM, but this information is relevant to explaining the building performance concepts that BEM simulates.

This site is a listing of ~200 available building simulation software tools. Originally hosted by DOE, now by IBPSA-USA. Vendors can submit the product descriptions, capabilities, screenshots, etc. and submissions are added after a staff review. The site includes good capabilities for filtering results based on search criteria.

One filter is for available BEM training options (see this link).

EnergyPlus is free, open-source, and cross-platform—it runs on the Windows, Mac OS X, and Linux operating systems. Its development is funded by the U.S. Department of Energy’s (DOE) Building Technologies Office (BTO). Along with OpenStudio, EnergyPlus is part of BTO’s building energy modeling program portfolio.

DOE releases major updates to EnergyPlus twice annually.

OpenStudio® is a cross-platform (Windows, Mac, and Linux) collection of software tools to support whole building energy modeling using EnergyPlus and advanced daylight analysis using Radiance. OpenStudio includes graphical interfaces along with a Software Development Kit (SDK).

The graphical applications include the OpenStudio SketchUp Plug-in (for importing geometry models), OpenStudio Application, ResultsViewer (for plotting time-series data) and the Parametric Analysis Tool for studying the impact of various combinations of design options).

The SDK allows software developers to programmatically define and run models using C++, Ruby, and C#.

IES <VE> is a suite of tools for performing building analysis. For whole-building simulation analysis, it uses its proprietary, hourly simulation engine, Apache. The whole-building energy analysis also utilizes shading calculations, Radiance (for daylighting analysis), and a graphical interface for designing detailed HVAC system and control models.

The software includes several features for visualizing the energy modeling results. It also has a series of wizards for walking users through various modeling workflows including compliance with energy codes (e.g. ASHRAE 90.1 Appendix G)

Sefaira is an early-stage whole-building energy modeling software for performing energy, daylight, thermal comfort, and HVAC sizing analysis. It is part of Trimble's SketchUp Studio software package.

Energy simulations use U.S. DOE's EnergyPlus and OpenStudio. Daylight analysis uses the Radiance engine.

DesignBuilder comprises a core 3-D modeler and 11 modules which work together to provide in-depth analysis for buildings. The whole-building simulations utilize the EnergyPlus engine. Other modules allow for energy code compliance and LEED modeling, daylight analysis, a graphical interface to define HVAC systems and controls, and optimization capabilities.

Ladybug Tools is a collection of free computer applications that support environmental design and education. The tools connect 3D Computer-Aided Design (CAD) interfaces to a host of validated simulation engines including EnergyPlus and Radiance.

The tools can perform energy, daylight, and climate analysis. Ladybug Tools runs within parametric visual scripting interfaces, enabling the exploration of design spaces and the automation of tasks.

Cove.Tool is a cloud-based program in which subscribers input building features and design options—for example, glazing, shading, and insulation—and project parameters, such as job location and construction schedule. The software then performs a series of automated simulations to pinpoint the combinations of parameters that offer the required performance within the prescribed budget. (Cove stands for COst Versus Energy.)

According to the company founders, Cove.Tool reduces a project’s initial cost by an average of 2 to 3 percent, or can improve building performance by 40 percent in exchange for a 3 percent cost premium.

TRNSYS (pronounced 'tran-sis') is an extremely flexible graphically based software environment used to simulate the behavior of transient systems.

TRNSYS is made up of two parts. The first is an engine (called the kernel) that reads and processes the input file, iteratively solves the system, determines convergence, and plots system variables. The second part of TRNSYS is an extensive library of components, each of which models the performance of one part of the system. The standard library includes approximately 150 models ranging from pumps to multizone buildings, wind turbines to electrolyzers, weather data processors to economics routines, and basic HVAC equipment to cutting edge emerging technologies. Models are constructed in such a way that users can modify existing components or write their own, extending the capabilities of the environment.

Trane analysis software packages are created for designers and engineers responsible for assessing system design and function for new construction or existing buildings anywhere in the world.

The software tools are used to analyze energy efficiency to determine eligibility for LEED credits, determine HVAC system selection impact on operating costs, and perform HVAC system sizing.

TRACE 700 uses Trane's proprietary simulation engine. The newest version, TRACE 3D Plus, uses DOE's EnergyPlus simulation engine and allows for a 3D representation of the building geometry.

HAP is designed for consulting engineers, design/build contractors, HVAC contractors, facility engineers and other professionals involved in the design and analysis of commercial building HVAC systems. The program is a powerful tool for designing systems and sizing system components as well as modeling annual energy performance and energy costs.

Tas is a building modeling and simulation tool capable of performing hourly dynamic thermal simulation. It has BIM data import & export options, and it consists of modules that can be used for energy code analysis, thermal comfort analysis, HVAC system analysis, and daylight analysis.

eQUEST® is a freeware building energy use analysis tool that provides professional-level results with an affordable level of effort. eQUEST was designed to allow you to perform detailed comparative analysis of building designs and technologies by applying sophisticated building energy use simulation techniques but without requiring extensive experience in the "art" of building performance modeling. This is accomplished by combining schematic and design development building creation wizards, an energy efficiency measure (EEM) wizard and a graphical results display module with a complete up-to-date DOE-2 (version 2.2) building energy use simulation program. You can read the eQUEST Overview to get a more complete summary of the features and capabilities of this excellent program.

CBECC-Com is an open-source BEM software that automatically creates a code baseline building for code compliance of nonresidential buildings following California's Title 24, Part 6 energy code. It utilizes DOE's EnergyPlus engine to perform simulations.

CBECC-Res is an open-source BEM software that automatically creates a code baseline building for code compliance of residential buildings following California's Title 24, Part 6 energy code. It utilizes the California Simulation Engine (CSE) perform simulations.

EnergyPro integrates with CBECC-Com and CBECC-Res to perform Title 24 compliance analysis for California projects. It has additional modules for performing LEED and utility incentive calculations.

Free, easy-to-use, graphic-based computer program that displays climate data in dozens of ways useful to architects, builders, contractors, and homeowners, including temperatures, humidity, wind velocity, sky cover, and solar radiation in both 2-D and 3-D graphics for every hour of the year in either Metric or Imperial units.

Estimates the energy production and cost of energy of grid-connected photovoltaic (PV) energy systems throughout the world. It allows homeowners, small building owners, installers and manufacturers to easily develop estimates of the performance of potential PV installations.

Target Finder is a benchmarking tool for new buildings, using CBECS 2012 as a baseline.

The Zero Tool is used to compare a building’s design or an existing building’s energy use intensity (EUI) with similar building types, understand how a building achieved its EUI (via energy efficiency, on-site renewable energy, and/or green power purchases), and set EUI targets. Based on CBECS 2003.

Weather data for more than 2100 locations are available in EnergyPlus weather format — 1042 locations in the USA, 71 locations in Canada, and more than 1000 locations in 100 other countries throughout the world. The weather data are arranged by World Meteorological Organization region and Country.

In building design and retrofits, the terms energy efficiency measure (EEM) and energy conservation measure (ECM) refer to a specific change that can be made to a building to reduce its energy use. As an example, if you are retrofitting an existing building and one of the ECMs suggested by the design team is "Add insulation to the roof", then the modeler must apply this change to their model to calculate the energy impact.

In OpenStudio, a "Measure" is a set of programmatic instructions (such as an Excel macro) that makes changes to an energy model to reflect its application. In the above example, the measure might find the default construction used by roof surfaces in the model, copy this construction and add insulation material to the outside, then set the new construction with added insulation as the default construction to be used by roof surfaces. Measures can be written specifically for an individual model, or they may be more generic to work on a wide range of possible models.