Meeting and Exceeding Energy Standards with BIM Software

Building design professionals rely on building information models and other computer software as integrated tools for design and performance
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Sponsored by Vectorworks, Inc.
By Peter J. Arsenault, FAIA, NCARB, LEED AP
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ENERGY STAR for Buildings

Most people recognize the familiar blue and white ENERGY STAR symbol found on everything from appliances to computers, but many design professionals and building owners are also taking advantage of this program for buildings. ENERGY STAR for buildings is a national program administered by the U.S. Environmental Protection Agency (EPA) that looks at all aspects of energy use and conservation in buildings. In order to earn this certification, a building must show a predicted (i.e., energy model) or actual (i.e., utility bills) energy performance that produces a score of 75 or better, which represents at least 20 percent better energy performance than an established baseline for similar buildings. The program is specific to different building types and geographic regions, and it uses the Commercial Building Energy Consumption Survey (CBECS) as the data source for its baseline.

Some of the aspects of this program have become fairly mainstream tools for the energy-conscious design and construction of buildings. First, it identifies a distinction between the amount of energy consumed on-site in a building (e.g., utility meter readings) and the amount of raw energy that was required at the source to produce the delivered energy (e.g., fuel at a power plant). When normalized to be measured in basic, common units of energy such as British thermal units (BTUs), it is typical to find that the energy used in a building actually requires two to three times that amount at the source due to generation and transmission losses. Hence, the ENERGY STAR program brings attention to the multiplier effect of energy use reduction in buildings by identifying both source and site energy. It also provides direct mathematical calculations for the amount of carbon dioxide (measured in tons) that is produced at the source based on the amount of site energy used.

While this may all sound good at a high level, the question naturally becomes how to compare buildings fairly. Like all common building comparisons, breaking things down on a square-foot basis according to building type seems to be the most equitable, just as is commonly done for cost estimating. In the case of energy use, all building energy sources (electric, natural gas, etc.) are converted to BTUs for a uniform comparison. Then, the total number of BTUs required for the building over the course of a year are calculated and divided by the square footage of the building. This provides an annualized unit of comparison that is referred to as energy use intensity (EUI) and is expressed in terms of thousands of BTUs (kBTU) per square foot per year. So, for example, a building with an EUI of 75 is portrayed as requiring 75,000 BTUs for every square foot per year. If a similar type of building is constructed nearby and has an EUI of 37.5, then it has an energy use intensity that is half of the first one.

ENERGY STAR logo.

Image courtesy of ENERGY STAR

The ENERGY STAR program provides tools such as Portfolio Manager and Target Finder that rely on energy usage data calculated from building designs to both benchmark and predict energy impacts.

ENERGY STAR offers some free online calculators known as Target Finder and Portfolio Manager that allow design firms to quickly and easily identify data for their buildings. These include the building EUI, the ENERGY STAR score, the amount of site and source energy consumed, and the carbon dioxide savings potential. However, to run these numbers with any accuracy, the total building energy usage needs to be known. For existing buildings with a year’s worth of actual energy bills, that is a matter of tallying and entering the data. For buildings in design, it requires running a computer energy model based on the proposed design of the building. BIM data can once again inform the energy model, which can produce an overall energy usage profile for the year. That data can then be used as input for the ENERGY STAR calculations.

Net-Zero Energy Buildings and the Architecture 2030 Challenge

The modern concept of net-zero energy buildings (NZEB) has been around for at least the past few decades but has been defined in different ways. Some people mistakenly think it is a building that uses zero energy. While that may have been possible for cave dwellers and nomadic tribes, it is not what is intended here. Rather, it is the concept of reducing the demand for energy in a building to the point that on-site renewable energy sources (such as solar and wind power) can supply as much or more energy as the building consumes. ASHRAE has defined this concept further by stating that a true NZEB produces as much renewable energy as the source energy that it consumes. Fundamentally, everyone recognizes that modern buildings will require some energy to power devices and conveniences, but the way that power is produced can be more sustainable than relying on fossil fuels. It is also understood that most buildings will still be connected to a power grid or other utility infrastructure both to cover the times of the day or year when renewables aren’t available (i.e., no solar at night) or to sell excess energy back to the utility. Hence, for our purposes, we will define a net-zero energy building as one that produces the same or more on-site renewable energy in a given year than it consumes from outside fossil fuel sources. With this in mind, there are two national programs worth discussing.

The 2030 Challenge

Architecture 2030 is a non-profit organization founded by architect Edward Mazria, FAIA, in 2002. He has successfully publicized reliable data demonstrating that buildings account for nearly half of the overall energy usage in the United States and more than 70 percent of the electricity consumption. Hence, any strategy to save energy or reduce pollution emissions from fossil fuel usage will necessarily be directly impacted by working toward net-zero energy buildings. The specific strategy proffered by Architecture 2030 is contained in the 2030 Challenge. Simply stated, the 2030 Challenge is a series of design targets for buildings to gradually reduce their fossil fuel energy consumption. The current target is to design and renovate buildings to use 70 percent less fossil fuels than the regional average. The targets grow every five years to 80 percent less by the year 2020, 90 percent less by the year 2025, and 100 percent less (i.e., zero fossil fuel usage) by the year 2030. This goal is for all new buildings, as well as an equal amount of existing buildings, and for all types—residential, commercial, institutional, and industrial.

Graphic showing 2030 Districts.

Image courtesy of Architecture 2030

Overseen by the not-for-profit organization Architecture 2030, a program called 2030 Districts has produced a network of cities in the United States that are collaboratively creating and documenting hundreds of millions of square feet of buildings that are working toward the goal of net-zero energy use from fossil fuels.

How do we get there? By using the same principles we have been discussing: better building envelope design, holistic energy conservation, improved building system performance, plus on-site renewable energy generation. To get to net zero, however, we need to pay attention to all of the details of these things, going well beyond minimum code levels and even beyond LEED and ENERGY STAR levels. The phased approach over time is meant to allow the design and construction community the chance to ramp up practices and procedures and incorporate them into building projects. Some have suggested that this can be accelerated by having building owners simply purchase all of their energy from renewable suppliers over the utility grid. Architecture 2030 has responded with a very realistic approach that reflects the ability of the utilities to meet such a demand by indicating that no more than 20 percent of the energy needs of a building should be expected from off-site (utility company) renewable sources for electricity. The other 80 percent needs to be accounted for in design, system efficiencies, and on-site renewable energy. Architects and engineers who have pursued this goal have been successful by using computer analyses to account for the same design variables we have been discussing, as well as the specific parameters of the 2030 Challenge.

 

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Originally published in April 2017

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