Computer modeling and benchmarking software tools are as invaluable as a blower door or duct blaster when evaluating the impact of building energy use on the environment.  And the impact is enormous – each year, nearly half of all energy produced in the U.S. goes to operate the buildings we live and work in every day.

Software tools help building performance professionals quickly identify the most cost-effective energy-saving measures.  Seasoned auditors may be able to “eyeball” a building and provide a rough estimate of potential savings from improvements.  Modeling software analyzes numerous variables like hourly weather changes, and generates predicted savings quickly and accurately.

Building an accurate model can be a challenge, however.  Energy loads, particularly for residential buildings, are notoriously difficult to quantify with great precision.  Occupant behavior is hard to capture in a model, but it has a big impact on a home’s energy usage.  Do the occupants do three loads of laundry per week?  Ten?  Do they keep the thermostat set at 65 degrees?  Or 70?  The building envelope in existing homes presents its own set of challenges.  It’s hard to accurately measure the level and quality of insulation behind the walls.

Developed by building performance professionals who understand that creating a model of energy usage is complex, Performance System Development’s TREAT is one example of modeling software with a nationwide reach. The foundation for TREAT is SUNREL, the state-of-the-art hourly energy model developed by the Department of Energy’s National Renewable Energy Lab (NREL).  SUNREL is based on fundamental models of physical behavior and enables TREAT to accurately estimate the energy consumed by a particular building by calculating the interactions among a building's occupants, its envelope, and its environment.

Software tools can dramatically reduce the time it takes to complete a model, automating much of the process of defining spaces, zones, surfaces and appliances.  Some tools allow auditors to identify inputs that stay the same from project to project, such as fuel rates, weather, and heating and cooling season dates.  Setting up custom defaults for a variety of values, including building air-tightness, shielding class, calculation algorithms, etc., can also save time and help build a more accurate model.

Modeling software can also consider the effects of the interaction of several upgrades in a group, providing maximum accuracy and helping promote a more comprehensive approach to energy efficiency.  A robust tool can calculate how changing a single feature might alter the energy savings for other features.  Contractors can confidently share the information with building owners, show solid savings to investment ratios (SIR), and help customers choose the best investment options for their property.

Software is not without pitfalls, however.  Modeling tends to overestimate how poorly a building performs, and in turn the amount of potential savings realized by improvements.

TREAT allows auditors to “true up” their model using the building’s utility bills.  Matching actual fuel bills with the energy model tells an honest story of occupant behavior so variables can be adjusted to improve the accuracy of the model.  Even if billing records are incomplete, TREAT can create estimates for missing data.  Plus, TREAT uses hourly weather data for more precise predictions, and incorporates gains from solar radiation, lights, and appliances.  Accurate models help an auditor make informed recommendations for retrofits, and give the homeowner peace of mind when making decisions.

Multi-family and commercial buildings present another set of challenges.  A much larger capital investment by the owner is at stake, so ensuring accuracy in predicted savings is crucial.  There’s much more data and stakeholders, and projects can vary greatly in size and complexity. The buildings can be very complex and vary greatly by construction type and equipment.  In multi-family buildings, there may be limited access to and/or insufficient funds to investigate all apartment units.  Also, for buildings that are not master metered, it is typically difficult to get access to even 30% of the direct utility meters.

The first step in reducing the overall energy use among a portfolio of buildings is assessing how the buildings are currently using energy.  Benchmarking tools can provide unparalleled support for this step by allowing comparison between all portfolio buildings based on the total energy, as well as the individual heating, cooling, and baseload components.  Resulting reports allow quick identification of buildings that are under-performing and can help determine the best candidates for an audit.

Energy modeling increases the confidence that actual savings realized by a retrofit will match that of the predicted savings.  The consistency provided by software tools reduces investment risk, ensuring that stakeholders base their investment decisions on the same financial assumptions.  Software tools can also make an auditor’s job easier by tracking multiple projects and properties.

Modeling software allows an integrated approach, providing energy savings and model calculations at various levels. For instance, auditors and contractors can provide homeowners and building managers options, which can be compared side by side to highlight payback and savings differences.  Improvement packages can be designed to fit different budgets or payback periods.  Another powerful selling point is that TREAT is particularly good at providing guidance for home performance projects.  In fact, NYSERDA uses it for just this purpose.  The software is approved by the Department of Energy for use in Weatherization Assistance Programs in all residential building stock – from mobile homes to multi-family buildings – and passes HERS BESTEST, a benchmark for validating building energy simulation programs.*

The “Better Buildings Initiative” outlined by President Obama in February includes tax incentives and financing opportunities for commercial retrofits. Under the plan, by 2020, commercial building space in the United States will be made 20 percent more energy efficient through cost-effective upgrades – a lofty goal.  The plan complements initiatives already underway, including the $20 billion American Recovery and Reinvestment Act (ARRA) investments in programs like the Weatherization Assistance Program, Better Buildings, and the Energy Efficiency and Conservation Block Grant, which aim to retrofit 600,000 residential homes.  The case for investing in building efficiency is a strong one, made stronger by the verified energy savings a software tool can provide.

The use of building performance software can help us get there.

See http://www.psdconsulting.com/software/treat/hers

About the Author
Lauren McFeeley is a writer at Performance Systems Development, a software and services firm based in Ithaca, New York, dedicated to advancing the marketplace for building energy efficiency.