Green: A State of Mind
Just about every building project these days is looking at green building products and systems. But it can be difficult to evaluate and determine just how "green" a product really is, or what is a green product for that matter. While the U.S. Green Building Council's Leadership in Energy and Environmental Design (LEED) rating system has, in general, helped familiarize many engineers with the co...
Just about every building project these days is looking at green building products and systems. But it can be difficult to evaluate and determine just how "green" a product really is, or what is a green product for that matter.
While the U.S. Green Building Council's Leadership in Energy and Environmental Design (LEED) rating system has, in general, helped familiarize many engineers with the concept of green building design, it isn't necessarily the ideal tool to fully assist in this evaluation process. Because the LEED rating system is based on checklists—and in several areas, is very prescriptive—it does not force designers to fully understand why one product or system is greener than another.
As defined by the USGBC, the goal of green building design is "to create buildings that meet the needs of current building occupants while being mindful of the needs of future generations." It's an open-ended definition that could include products made from recycled content, equipment that requires less energy to manufacture, products that improve indoor environmental quality by reducing toxic off-gassing or simply energy-efficient products or systems.
Consequently, there are many products to choose from, and engineers must weed out numerous claims being made by manufacturers to find those products that are legitimate and best for their particular project. Unfortunately, many "green" manufacturers are taking advantage of the green building movement to promote products that, in reality, are no greener than the next.
But before getting into a discussion about how to select green products, it's important to distinguish between two primary types of products. First, green building products are considered green by virtue of their material makeup or manufacturing process. The second category— performance-based green products —is defined by their unique application or use and their ability to improve the environmental performance of a facility.
For engineers in this situation, the good news is that there are a number of available green building products directories, some of which have been developed by design professionals themselves or by specifications consultants researching green building products for design professionals. One of the most widely used is the GreenSpec Directory, published by BuildingGreen, Inc., Brattleboro, Vt.
GreenSpec breaks out green products into six main categories:
Products that are made with salvaged, recycled or agricultural waste content.
Products that conserve natural resources.
Products that avoid toxic or other emissions.
Products that reduce environmental impacts during construction, demolition or renovation.
Products that save energy or water.
Products that contribute to a safe, healthy indoor environment.
The products contained in the first three directory categories are "green" in that their greenness is primarily based upon the material makeup or manufacturing process. The best way to evaluate and compare these products is by using what's called an environmental life-cycle assessment. An LCA compares the overall environmental impact of building materials from cradle to grave by evaluating resource extraction, manufacturing, installation, operations, maintenance and demolition/disposal.
Several computer programs are under development to assist in developing an environmental LCA comparison, but they are still limited in their comparison of materials and systems. Also, they generally do not adequately take into consideration regional differences, such as the effects on products of transportation, storage or differences in regional construction methods. These factors can have a significant impact on environmentally-sensitive projects.
The two most widely known environmental LCA programs are: Building Environmental and Economic Sustainability (BEES) version 2.0, developed by the National Institute of Standards and Technology; and the Athena Environmental Impact Estimator version 2.0, from the Athena Sustainable Materials Institute in Canada.
The products listed in the GreenSpec Directory are generally selected based on their environmental LCA. However, there is still a need for an independent third-party product certification based on these LCAs. That being said, there's a problem comparing products based on LCA: There must be some normalizing of different environmental impact categories—such as global warming, toxic emissions or greenhouse gases—and as of yet, there is no national environmental impact database to help normalize the impacts.
Until the controversy over the relative weighting of these different impacts is resolved, designers must rely on currently available certification programs that look at very discrete environmental impacts. These programs include: the Forest Stewardship Council (FSC) certification—for wood products that meet requirements for sustainably harvested building materials; Environmentally Preferable Product (EPP) certification—for certifying that composite wood panels contain 100% recycled or recovered content; and Green Seal certification—for commercial building products such as electric chillers, windows, doors, plumbing fixtures, paints and sealants.
In effect since the early 1990s, the Green Seal accreditation is slightly more comprehensive than the others. It provides an independent evaluation of the various environmental impacts for a particular product and then establishes manufacturing and operational performance standards that the products must meet to achieve certification. The program, however, has been slow to take off, and only a limited number of products have been certified through it.
So much for the first three product categories of GreenSpec. The products contained in the final three directory categories are considered performance-based, where greenness is primarily based upon energy performance, water utilization or indoor environmental quality. In other words, products are not considered green based on what they are made of or how they are manufactured, but rather, how they are used. A CO 2 sensor, for example, is not green because of the materials it is made of, but because it's used to monitor and control ventilation air. Of course, in due time performance-based green products will also be manufactured from environmentally appropriate materials. In fact, this is the ultimate goal of green building design.
One of the best-known performance-based green certification and labeling programs is Energy Star, a government-backed program introduced by the U.S. Environmental Protection Agency in 1992. Products covered under Energy Star ratings include commercial HVAC, commercial and residential lighting, roofing, transformers, windows, doors and skylights. The program generally provides an Energy Star label for a product that performs within the top 25% of the market.
A new performance-based certification that is expected to have a major impact on green building design is the Greenguard Indoor Air Quality Certification program. The Washington, D.C.-based Greenguard Environmental Institute (GEI) has established performance-based standards to define and certify building products, furnishings and cleaning products with low chemical and particle emissions.
The Greenguard certification program is significant in that it uses a scientific third-party board to establish test methods and allowable emissions levels for standard interior products and building materials. All testing is required to be conducted by the manufacturer in accordance with standard ASTM testing protocols. Consequently, the GEI evaluates products on how they perform relative to chemical and particle emissions, regardless of the materials the products are made of or how the products are manufactured, making Greenguard certification a purely performance-based program.
Greenguard certified low-emitting products are one requirement in the USGBC's LEED for Commercial Interiors pilot program. GEI offers free access to its online product guide and indoor air quality resources.
Performance-based product certification is all well and good, but from an engineering standpoint, because most systems are judged based upon performance, some analysis is typically required to demonstrate a product's added value to the overall environmental goals of a project.
Engineers can make use of a number of software tools:
Energy modeling programs.
Dynamic thermal modeling programs.
Computational fluid dynamics (CFD) modeling programs.
Lighting analysis and energy modeling programs.
Energy modeling programs compare one system or piece of equipment to another so that users can select the most energy-efficient alternative and demonstrate system compliance with energy-efficiency performance standards.
One such standard, ASHRAE Standard 90.1, Energy Standard for Buildings Except Low-Rise Residential, is the normal performance standard for commercial facilities for HVAC, lighting and domestic water heating systems, as well as building envelope components such as walls, windows, roofs and shading systems. With energy modeling, it is important to have a performance goal. The LEED rating system uses 90.1 as its energy efficiency benchmark, and the LEED energy-efficiency credits provide engineers with energy reduction goals for their green projects.
The three most widely used energy modeling programs are: DOE-2 , which has been in use for 20-plus years and is now available with Windows-based input modules; EnergyPlus , a new program with its own graphical interface, introduced by the Dept. of Energy to improve on the features of DOE-2; and Trane Trace , a load estimating and energy modeling program. Trace has been popular with designers because it can be used in facility design for building loads and equipment selection.
Dynamic thermal and CFD modeling programs are used to demonstrate that proposed HVAC systems meet indoor environmental quality performance standards established for green building design. The two performance standards utilized for this include ASHRAE Standard 55-1992, Thermal Environmental Conditions for Human Occupancy, and Standard 62-1999, Ventilation for Acceptable Indoor Air Quality. These programs can help determine if comfort variables in a space, such as air temperature, wet-bulb temperature, mean radiant temperature and air velocity, meet established indoor comfort performance standards outlined in Standard 55. CFD modeling can also be used to verify ventilation effectiveness by modeling ventilation performance variables such as CO 2 levels to make sure they meet Standard 62. Two programs that have been used for commercial applications to calculate airflow, heat transfer and contamination distribution are Flovent version 4.1, distributed by Flowmerics, and Fluent version 6.1, distributed by Fluent Inc.
The net result of the new focus on green building design is that manufacturers are now taking note of the new independent standardized certification programs and rating systems being developed for green building products. However, the industry still has a long way to go before all manufacturers have their products' overall environmental impact and product performance verified, certified and included with their product literature. However, as acceptance of these independent certification programs grows, it is important for engineers to require verification that these certifications are being provided for the products they specify.
But simply specifying an energy-efficient piece of equipment is not enough. Engineers must be diligent about demonstrating the overall performance of the systems they design, and in so doing, they should always look for demand reduction strategies, opportunities for harvesting free energy, and ways to optimize basic system components.
Finally, it is important for engineers to follow up with commissioning, to verify that the building performs as designed and to work with building owners to operate and maintain them in order to guarantee that they continue performing at their highest level.
The following is a list of valuable web resources:
U.S. Green Building Council,
BuildingGreen, publisher of the GreenSpec Directory listing of 1,700 green products by CSI division. Portal also contains useful case studies, news and articles:
Forest Stewardship Council,
Composite Panel Assn.,
Greenguard Environmental Institute,
Windows and HVAC
While the specification of glass is not traditionally in the realm of the engineer, too often, many architects don't understand the relationship between glass and HVAC requirements. This usually results in the owner overspending on the HVAC system, paying higher operating costs and paying more for glass that is ineffective in terms of heat control. According to the California Energy Commission, 30% of a building's cooling requirements is a function of heat entering through existing glass. Solar heat gain through south and west facing windows is a serious problem for many buildings.
One cost-effective solution is spectrally-selective window film, which refers to the material's ability to transmit desirable daylight while blocking undesirable heat. It blocks heat as well as solar control glass does and offers the best ratio of visible light transmission to heat rejection. Even in new construction, the cost of solar control glass exceeds the cost of standard insulating glass to which a spectrally-selective film is later applied.
Newly constructed QuikTrip convenience stores were able to downsize HVAC by specing insulating glass and spectrally-selective film. Recently, 1.2 million sq. ft. of spectrally-selective film has been applied to existing glass on 17 buildings at Stanford University, significantly lowering air-conditioning operating costs.