Saving Energy in Historic Buildings: Balancing Efficiency and Value.

Energy modeling and life-cycle costing can help identify simple steps to make a historic building more energy efficient addressing both preservation and sustainability concerns. This article originally appeared in vol. 41, no. 1, of APT Bulletin, journal of Association for Preservation Technology International. APT is a cross-disciplinary membership organization dedicated to promoting best technology for conserving historic structures and their settings, including preservation. More information is available at www.apti.org. By now slogan of National Trust for Historic Preservation that the greenest building is one already built is widely known. In an era of increased environmental awareness and rising fuel prices, however, question is how can historic building stock be made more energy efficient in a manner respectful of its historic integrity and character. The other challenge is to find those improvements that, in quest to save energy (and, by extension, money), do not in long run cost more than they save. There are an increasing number of sustainable in marketplace today, but not all are good investments, provide tangible benefits, or are appropriate approaches for historic buildings. Often common sense, trained historic and/or aesthetic judgment, and studies and assurances of those marketing solutions are used to determine what interventions are appropriate, In addition, practical and objective analysis tools are needed in process, and that is benefit of including energy modeling and life-cycle costing in assessing potential changes. These calculation tools can help all of those involved in a project to understand which solutions truly offer energy and operating-cost savings. Energy Modeling The use of computers to simulate annual energy consumption began as a result of energy crisis in 1970s. After United States Department of Energy (DOE) was created by President Jimmy Carter, algorithms were developed to simulate annual energy consumption of a building. These calculations were refined and further developed over years, with DOE-2 simulation algorithms gaining wide acceptance in industry throughout 1990s. Currently, use of these energy-modeling tools has become standard for any project that is pursuing Leadership in Energy and Environmental Design (LEED) certification from United States Green Building Council. There are many energy-modeling software programs in use today, including Energy Plus, developed jointly by University of Illinois and Lawrence Berkeley National Laboratory.1 The basic concept of energy model is to virtually create (or, in case of preservation, recreate) a building, delineating not only its physical form but also other performance and usage variables. The simulation process includes a virtual model of building geometry, building materials and their characteristics, and types of mechanical systems and lighting, along with other systems that may consume energy. The patterns of occupants and their activity levels are added to virtual model, and finally weather-data files that reflect particular locale are referenced for a complete hour-by-hour simulation of a typical meteorological year.2 Depending on size of building, creating this baseline model can be a process that takes 40 hours for a small, straightforward building, such as a suburban office building, to hundreds of hours for a large, complex edifice, such as a monumental campus building. Regardless of project size, process is typically same, although larger buildings tend to leverage effort and cost of model to greater effect since improvements can produce larger energy savings. Once baseline information has been entered and an existing-conditions model created, it is then possible to calculate building's current energy-use footprint and to track what percentage of that consumption can be attributed to each of building's components. …