Building information modeling (BIM) provides object-based parametric modeling and can take an object, along with all of the data describing its components, and place it in a computer model that is a virtual description, rather than a simple geometric description, of the object. There is an infinite variety in the amount and type of information BIM can contain, and as a result, it can assist designers in everything from choosing what type of electrical systems to use in a construction project to determining, through energy modeling, how that building actually will perform with regards to energy consumption when it is completed.
Energy modeling, according to Keith Elder, principal adviser for Coffman Engineers Inc., Seattle, represents the thermal dimension of a virtual model of a future building.
“At its essence, it is the hour-by-hour simulation of how the building is expected to perform during a representative year,” Elder said.
Energy modeling considers such factors as the building’s construction materials; its orientation; the heating, ventilating, air conditioning and lighting systems; and the behavior expected of the people occupying and operating the building.
The model allows design engineers to perform “what if” scenarios and helps the owner compare the economic performance of various competing energy-efficiency strategies. It is usually a simplified model of the building and contains just those components that affect energy performance, according to Forrest Lott, member of the Contract Documents Committee for the American Institute of Architects (AIA) and principal of Lott + Barber, Savannah, Ga.
“Energy modeling allows the design team to examine different options and calculate energy usage based on specific configurations,” said Mike Lambert, product manager for building electrical for Bentley Systems Inc., Exton, Pa.
Energy modeling and BIM
Unlike BIM, an energy model is a collection of computer information related to energy loads within a building.
“It’s an abstraction of a building that describes all of the characteristics of energy within it, including load information from sources of heat, such as equipment and lights, and data, such as the thermal value of insulation,” said Robert Middlebrooks, industry programs manager for Autodesk Inc., San Rafael, Calif.
The building performance analysis provided by energy modeling often is based on the data contained in the BIM model, which is how the two interrelate.
“The building performance analysis done through energy modeling is based on the data in the BIM model, allowing users to scale or resize the electrical systems, based on measurements input into the model,” said David Thirlwell, virtual design and construction manager, Current Builders, Pompano Beach, Fla.
In other words, the BIM model contains the information required for energy-modeling software to execute its analysis of the building’s potential energy performance.
There are a number of computer programs that perform energy modeling in accordance with the ASHRAE standard 90.1-2004 used by the Leadership in Energy and Environmental Design (LEED) to establish energy-modeling procedures.
“Energy modeling initially developed separately from BIM technology, but the industry is moving toward greater interoperability and compatibility between the two,” Lott said.
The greatest improvement to the technology, according to Elder, has been the increased speed of computers that made graphical input and output possible.
“In many cases, modelers can draw the building’s thermal environment and graphically delineate the thermal zones to be modeled,” he said.
Whichever energy-modeling software is used, its goal is to use the information provided by various sources, such as weather conditions and patterns and the energy characteristics of the building components, and then calculate how much thermal gain or loss will occur through windows, roofs, etc.
“For energy modeling to be successful, the software needs to know where the building is located, how it’s oriented and the external weather patterns of that location,” Lott said.
Couple that with the intended building design and materials information from BIM, and energy-modeling software can analyze the building’s projected performance. However, Lott said, to design a high-performance building, the models need to be compared to similar structures that were built to code minimums.
As a central repository for project data, BIM is a very powerful tool for the energy modeler, since energy simulations frequently require interdisciplinary information, such as architectural, mechanical and electrical data. Some BIM platforms are now incorporating energy-modeling tools, and this integration further leverages BIM’s ability to reduce the amount of time spent performing takeoffs and duplicating effort in the creation of the energy model.
“This not only saves time, but allows designers to see the implications of material choices, window placements, building orientation and mechanical and electrical systems in real time,” said Scott Mohr, principal for Coffman.
Generally, the more correct information that is present, the more helpful BIM can be to the energy-simulation process. If the model has been used to its full capacity as an interdisciplinary design tool, the modeler may choose to perform the simulations using tools provided in the BIM software. The modeler also may export the model to a third-party software provider.
“But if the BIM has been used as little more than a three-dimensional computer-assisted design (CAD) tool, the modeler may find it easier to reference the BIM for architectural information but not attempt to perform energy calculations in the BIM,” said Brian Emtman, Coffman’s mechanical engineer and a LEED Accredited Professional.
The benefits of using BIM coupled with energy modeling are a faster, easier, more accurate analysis and the ability to perform repetitive analyses to find the best solutions. According to Lott, BIM easily can answer the questions the energy model needs for analysis through its database of design and specification information.
“In addition, because the BIM model is easy to alter, it’s easy to run multiple energy analyses to determine the optimal design for a building,” he said.
One of the best advantages of BIM and energy modeling, according to Middlebrooks, is that this allows the relationship of spaces and zones within a building to be organized to directly reflect the actual design of the building.
“BIM models generally evolve to reflect different choices in the design or equipment,” he said.
The technology also allows the design team to really understand the impact of different design or system options, such as building orientation or the use of daylighting or other technologies, and to take a more integrated design approach encouraged by such programs as LEED. Since the models produced by BIM and energy-modeling software help the design team determine the most appropriate systems that will achieve the building’s desired performance levels, it’s easier to avoid over-engineering.
“The three-dimensional model provides the electrical contractor and design team the projected results that allow them to most efficiently design the electrical system,” Thirlwell said.
By enabling designers to improve their decisions about energy-savings systems and helping them focus their efforts on the systems that consume the most energy, BIM and energy modeling help to support sustainable design, Lott said.
“There are new sustainable standards that designers are trying to comply with, such as carbon footprints or the AIA 2030 Challenge, and energy modeling enables them to determine if the design intent of the building meets those standards,” Lott said.
BIM and energy modeling also support sustainable design through their ability to explore multiple options, perform analyses and quickly determine the optimal design conditions.
“The earlier in the design process the team can make decisions regarding energy efficiency, the more successful and sustainable will be the outcome,” Middlebrooks said.
Electrical contractors and energy modeling
Energy modeling is primarily the domain of the mechanical engineer who inputs the information about building loads, performance characteristics and thermal transfer into the model and then runs the performance analysis to determine the sizes of the heating and cooling equipment and ductwork for the building.
“Most electrical contractors don’t have any real involvement with energy-modeling analysis,” Middlebrooks said.
However, he added, it’s important for the electrical contractor to understand the design and how building loads have been incorporated into the model and realize that any configuration changes will have a direct impact on the building’s performance.
Lott, however, believes energy modeling allows the design/build electrical contractor to help the design team determine issues, such as watts per square foot, and to determine the best quality of lighting that uses the least energy.
“The contractor can help the design team to inform the options that are analyzed by the energy model in terms of energy usage and load,” Lott said.
Paul Jones, principal at Coffman, agrees that contractors that don’t use the energy-modeling software itself can still play a key role by offering alternatives throughout the design process.
“This brainstorming is critical to the success of a truly integrated design effort,” he said.
Mainstream acceptance of BIM and energy modeling is increasing rapidly, and more electrical contractors, according to Lambert, are engaging in the technology.
“Entire building energy analysis would still probably be the domain of the architect or engineers of a project, but the contractor will increasingly need to be able to provide or input data concerning the specific systems it is designing or is responsible for,” Lambert said.
The next steps for BIM will be advancement of the software, especially for the electrical design; better integration of all the disciplines involved; and the ability to answer the questions of function, performance and constructability.
“The challenge, however, will be clarifying the liability issues related to the ownership and use of the models during the various phases of the project,” said Greg Routh, BIM manager for Coffman.
As BIM and a building’s characteristics become more closely linked and the ability to get quicker feedback is refined, BIM will provide more integrated solutions between building design and energy performance, Middlebrooks predicted.
Electrical contractors need to be ready as interoperability between energy modeling and BIM increases.
“Expect more tools to be developed for the contractor to use to analyze the design of daylighting systems and to perform power distribution analysis and even control system simulations,” Lambert said.
BREMER, a freelance writer based in Solomons, Md., contributes frequently to ELECTRICAL CONTRACTOR. She can be reached at 410.394.6966 or firstname.lastname@example.org.