WHAT IS ENERGY MODELING?
To perform energy modeling, also known as building performance simulation or energy simulation, specific information is about the building design and equipment performance along with occupant energy requirements such as projected electrical load and desired indoor comfort levels. Local climate data is then applied to determine how it will interact with building heating and cooling requirements. The results come in the form of reports and graphs which estimate how that building will use energy. This information can then be used to estimate the annual operating costs of the building.
Energy modeling makes it possible for architects and building designers to aim for a specific energy efficiency goal, because these programs are designed for analyzing and understanding the complex behavior of building energy use. With these advances in computing technology, computer modeling has come into wide use for providing accurate and detailed appraisal of building energy performance. An iterative process can be used to compare different strategies and how they impact building energy use.
Different Types of Energy Simulation Software
Building energy simulation is important for the study of energy efficiency in buildings. Computer simulation programs are effective analytical tools for building energy research and evaluation of architectural design. Simulation tools have a wide range of capabilities:
- Basic concept and principles of building energy use
- Properties and energy usage of specialty spaces and occupancies
- Building design and simulation in a multidisciplinary environment (architecture + engineering)
- Focus on energy and demand, temperature, humidity and costs
Energy modeling is both an art and a science. Beyond selecting the specific software, an operator with strong experience is required to use it successfully. While software is the principal "tool" in the process, the operator must determine the data needed to build a model, how to build a model, how to examine the results. The operator must also know how to diagnose problems with a model and calibrate them realistically in order to ensure that results are not misleading.
Information on a wide range of available tools can be found in the Building Energy Tools Directory produced by the Department of Energy. Launched in 1996, it reviews over 300 different tools: www.energytoolsdirectory.gov or www.eere.energy.gov/buildings/tools_directory/
MODELING THE WEST BEND MUTUAL BUILDING ADDITION
As one of the utility’s commercial customers, West Bend called in the We Energies New Construction Program to perform energy modeling on the design for their new building addition. They were hoping to find energy efficiency measures that would cut future operating costs for the building, particularly strategies to reduce their peak load. The We Energies New Construction Program offers financial incentives for installing equipment that will lessen the building’s demand during peak energy usage.
The West Bend design team was ready. They submitted a set of detailed schematic design drawings and specifications to the engineer who would do the modeling, Lee DeBaillie, Technical Director at the Energy Center of Wisconsin. Lee was very pleased to receive such a complete package noting that the West Bend design team had really done their homework. He is certain their early design development efforts will lead to cost savings at other stages of the project.
The West Bend addition is a complex building for a multifaceted business. In addition to the variety of business functions needed such as computer rooms, office spaces, and conference and training rooms, West Bend provides amenities for its employees as well with its full service cafeteria and workout gymnasium, complete with shower rooms. These many functions require specialized mechanical equipment to keep the different spaces comfortable for both people and electronics. To evaluate the potential for reducing energy requirements and peak loads accurately, a sophisticated approach like energy modeling is needed. In addition to identifying economical cost-saving measures, the modeling data can also be used to calculate the environmental benefits of reduced energy consumption.
THE ENERGY MODELING PROCESS
Lee created two energy models for the West Bend project. The first he based on information from the specifications and building drawings he’d received from the design team. These drawings gave him a lot of detail about the building geometry, the proposed mechanical systems and the various uses of the building. After discussing the results of this preliminary model with the design team, Lee was able to help them establish a performance baseline and focus on specific systems and ideas to meet those objectives. The second model integrated this additional input, primarily from the architect and the mechanical and electrical design engineers.
Lee appreciated the opportunity to incorporate this additional feedback into a second model. Most projects that he’s modeled are on such a tight schedule that a second, more refined model is out of the question. He notes, "Usually you get one shot at it going into a bid situation and construction is starting. That’s the end of the malleable portion of the design process. In this case, because it was a large and high quality project there was quite a bit more time during the design phase to be able to explore different options. You have time to talk to people about what they’d like to see and change as the design proceeds. Then you’re able to capture those ands model a second time."
Lee also noted that West Bend is committed to building a facility that will last a long time and be efficient to operate. The schematic design reflected choices of high quality mechanical equipment and control systems in place to shut things off or turn things down. He knew the results of the first model would confirm that they already had a pretty efficient design. This allowed him to focus on more specialized systems and approaches in the second model.
The second model included evaluating an existing ice storage system that was scheduled for removal. Initially, an overhaul of the system made a strong economic case by significantly reducing peak demand, which also reduced operational costs and qualified the system for utility incentives. The system makes ice at night when electricity rates are low, and the ice is used to shave off the peak loads a building experiences during the hottest parts of the day. Unfortunately, after final pricing was received from the manufacturer regarding the ice system costs, it could not be justified in comparison to a high efficiency chiller system. By performing several iterations of the energy model, the design team was able to weigh several scenarios for cost effectiveness, and select the best one to meet the owner's needs.
There were some ideas that did not turn out to sufficiently save either energy or money. One was using domestic city water to cool the chillers in the chiller plant. A second design concept was recovering heat from the computer room and the commercial kitchen refrigeration to heat water for both kitchens and showers in the exercise room, but this proved to be uneconomical as well. Lee also found that increased daylight from skylights did not save enough to compensate for the heating and cooling losses they caused.