Designing to Comply with Code

Once a decision is made to follow the provisions of either the IECC or ASHRAE 90.1, how do architects tend to incorporate and demonstrate the needed energy code compliance? The answer varies by project and by firm, but there are two fundamental options. The first is a “prescriptive” compliance path, which amounts to essentially following checklists of traits or characteristics of specific building components (i.e., walls, windows, HVAC equipment, etc.) meeting certain minimum performance or efficiency requirements.

Since this is a fairly restrictive process that relies primarily on very conventional construction techniques, many firms tend to prefer the second option, which is based on performance. In this case, a building is considered as a single system rather than a collection of discrete parts. The code doesn’t dictate design, but it requires any building to demonstrate that its overall performance meets or exceeds code minimum overall performance comparable to meeting the prescriptive levels.

Under a simple performance approach, design trade-offs are allowed in the building envelope so that, for example, a building with less insulation in the walls than prescribed in the code can potentially make up for it with better windows or more insulation in the roof, as long as the overall building energy performance is met. For simple trade-offs of this nature, a computerized analysis using free ComCheck or ResCheck software from the U.S. Department of Energy is common and suitable based on either the IECC or ASHRAE 90.1. However, for more involved designs where the construction systems may not be completely conventional, or where glazed areas make up more than 30 to 40 percent of the building wall area, or where trade-offs involving mechanical or electrical systems are needed, then a full, computerized energy model is required to demonstrate code compliance. Under this scenario, the entire building and all of its systems must be modeled by computer, first in a baseline version where all prescriptive conditions are met and then in a version based on the proposed design. When comparing the two, the design must demonstrate that it will cost less in terms of energy than the baseline version, all other things being equal.

Fortunately, most architectural and engineering firms use computer-based design programs for their projects, including a growing number that rely on building information models. With this technology, architects can assign the specific design attributes of all of the building components and assemblies into a virtual, three-dimensional model. Since the model is made up of BIM objects that can be fully defined by architects, they include embedded data that can automatically update itself if dimensions or other aspects of an object are revised during design. This data can also include the full scope of a product’s materiality in terms of form, texture, color, and other attributes. Beyond the individual objects, the entire building can be modeled as a whole within the computer software. This allows for the three-dimensional geometry to be fully documented and for the computer to perform complex spatial calculations in a fraction of the time it would take to do by hand.

Image courtesy of Vectorworks, Inc.

Many architectural firms use three-dimensional BIM software to both visualize building designs and take advantage of the embedded data in the architect-specified BIM objects.

The embedded data and associative capabilities can also be used within the BIM program to perform some fundamental energy calculations or to assess things that affect energy, such as daylighting and solar heat gain. Either way, the BIM software and processes are direct ways to help designers provide the needed information to run a full energy model and demonstrate code compliance. It should be noted, however, that the most effective time to perform this analysis is not at the end of the construction document stage, but rather all throughout the design process, starting at the earliest stages. Most BIM and energy modeling software make it easy to try different variations or iterations of a design to see the comparative impacts of a given decision on energy usage in a building. That means a series of quick, schematic level mass and glazing studies can reveal design combinations or schemes that improve or impair energy performance. It also means that the designers can learn early what works best for their specific building project in its particular location and easily make informed design adjustments as required. Waiting until later to learn that a building does not perform as hoped will likely involve a lot more reworking of the design and documentation by the architects and engineers involved—a potentially time-consuming and costly process for the team.

International Green Construction Code

In 2012, the ICC released a new code document that addresses green building design beyond the basic energy-efficiency requirements of the IECC. The International Green Construction Code (IgCC) is the first model code to include sustainability measures for the entire construction project and its site with the expectations of making buildings more efficient, reducing waste, and having a positive impact on health, safety, and community welfare. It addresses conservation of natural resources, materials, energy, and water, as well as indoor air and environmental quality. While it uses the “model code” approach of the ICC, it also provides communities with the ability to modify the code to suit their particular local conditions. As such, it allows variation and electives for minimum and advanced levels of performance through both prescriptive and performance options. While it is a stand-alone document, it is important to note that it does not replace the IECC or other building codes, but rather is designed as an overlay to the ICC family of codes. Most states consider this an optional or voluntary code for jurisdictions to consider, thus far with a comparatively lower rate of adoption than other codes.

Raising the Bar with LEED and ENERGY STAR

While the codes set the basic, required level of performance, many design professionals and building owners have been interested and committed to doing more than the minimum. Over the past 20 years or so, two significant voluntary programs have emerged for buildings that promote energy and building performance that is better than code minimums.

Images courtesy of U.S. Green Building Council

The LEED program allows buildings to be designed and recognized at different levels of certification for green buildings.

Leadership in Energy and Environmental Design (LEED)

The U.S. Green Building Council (USGBC) was established in April 1993 when representatives from 60 design firms and several nonprofits gathered in the board room of The American Institute of Architects (AIA) in Washington, D.C., for the council’s founding meeting. Their stated mission was to promote sustainability-focused practices in the building and construction industry. That has been achieved through a membership that reflects an open and balanced coalition spanning the entire building industry. The flagship program of the USGBC is the green building rating system known as LEED, which was first unveiled in 2000 and has since become an international standard for environmentally sound buildings. The premise behind it is that an objective third party reviews information submitted by design and construction teams to ascertain a building’s level of sustainability and then issues a certification accordingly. Currently, hundreds of thousands of square feet are certified under the program around the world each day.

In addition to energy use, the LEED program addresses a full range of sustainability categories in buildings, including the site, water use, materials and resources, indoor environmental quality, and others. Different versions have been developed in an open, reviewed process with custom variations for different building types, such as schools, hospitals, homes, data centers, etc. In all cases, obtaining certification requires meeting some basic prerequisite requirements under the different categories and then demonstrating how the building achieves points in the scoring system (essentially on a scale of one to 100) under different credits available in each category. Depending on the number of total points achieved, a building can be recognized at the Certified (basic), Silver, Gold, or Platinum levels.

The latest release of the system is LEED version 4 (LEEDv4), which requires higher levels of energy conservation than prior versions. Under the Energy and Atmosphere credit category, the prerequisite for a building to be considered is a demonstrated improvement of 2 to 5 percent (depending on building type) in energy conservation compared to a baseline building using ASHRAE Standard 90.1 (2010 edition). This means that the building has to be slightly better than code just to be eligible for the program. After that, the design can earn between one to 20 points (the largest single potential area for earning points in LEED) based on demonstrating additional energy use reduction from between 6 to 50 percent of the baseline; the more reduction, the more points. In order to qualify, a full energy model is required following the guidelines of the LEED program and ASHRAE 90.1—some of which can be a little different than the IECC guidelines. Once again, this is where having the basic data in a computerized BIM model can save time and money while fostering creativity in design. The core information and design criteria can be the focus of design and exported as needed to other programs to demonstrate the needed performance.

In addition to the pure energy usage, the Environmental Quality category addresses things that are important in their own right but can also influence energy use. As such, they need to be addressed in the building design from multiple vantage points with multiple variables, which makes them particularly appropriate for computerized analysis. Daylighting and Views in this category addresses how the building design provides occupants with views to outside and allows natural daylight inside. These traits are good for people but may also mean that electric lights can be dimmed or turned off when conditions are right, thus requiring less electricity use in the building. Conversely, too much sunlight might cause the building to heat up more than desired and require more energy to run air-conditioning systems. The key is in finding a balanced design, which is where multiple computer simulations can be invaluable.

Image courtesy of Vectorworks, Inc.

Computer analysis using three-dimensional BIM simulations can identify natural and artificial lighting levels in building designs that can contribute directly to the building’s energy efficiency.

Increased ventilation is another condition of good indoor environmental quality since having plenty of fresh air in places where people are located is both desirable and healthy. Of course, that means the fresh air needs to be conditioned for temperature and humidity like the rest of the air inside the building, which requires energy. Some of the techniques in this situation include better controls to require ventilation only when people are present in rooms or heat exchange systems that condition incoming ventilation air by reusing the temperature of the outgoing air. Indeed, some basic levels of these things are mandatory provisions of the IECC, but LEED allows and encourages more creative and inclusive approaches. These might include the use of “solar chimneys” that induce natural ventilation air flows instead of requiring electric fans. It might also involve night cooling techniques where a building is flushed with fresh air overnight to cool it down so less air-conditioning is needed in the morning. Any of these techniques need to be simulated on a computer and shown how they are effective for providing the needed levels of ventilation while reducing the need for electrical energy. BIM models and associated software can be critical in producing the needed simulation and documentation for these areas.