Buildings account for 39 percent of carbon dioxide (CO2) emissions in the United States. CO2 is a greenhouse gas that greatly contributes to negative global climate change. Scientists predict that left unchecked, emissions of CO2 and other greenhouse gases from human activities will raise global temperatures by 2.5 F to 10 F this century. This could produce rising sea levels, more frequent floods and droughts, and increased spread of infectious diseases. A building's carbon footprint is the amount of CO2 it produces during its operations and activities.
Reducing carbon footprint is requisite in building design; here’s how
Managing and reducing carbon footprints as part of a low carbon strategy, with its inherent cost benefits and revenue opportunities, is increasingly important in building design. Building green is one of the best strategies to temper negative climate change because the technology to make substantial reductions in energy and CO2 emissions already exists.
Reducing a building’s carbon footprint reduces its running costs, improves employee morale, raises property values and improves LEED scores. Buildings become environmentally responsible, profitable and healthier places to live and work in. The following tips can help reduce a building’s footprint.
1. Start early
Evaluate and measure a building design’s carbon footprint as early in the process as possible. “That is when there are the most opportunities for reduction,” says Andrea Charlson, senior engineer of advanced technology and research, Arup, London. “At this stage, alternative layouts and materials can be considered and details can be refined to use less material. As the design progresses these opportunities diminish.” Part of this early planning involves a life cycle assessment on which carbon footprinting is based. “It is a process of considering all the flows (energy, water, materials, waste) in and out of a system to calculate its environmental impact,” says Charlson. “The result of a life cycle assessment for a product is a set of life cycle inventory data detailing the environmental impact per unit of the product. This information is becoming increasingly available through environmental product declarations direct from manufacturers. This data can then be combined with the material quantities used in the building to calculate its carbon footprint.”
2. HVAC
Since HVAC comprises 40 percent of all carbon emissions, incorporating the most efficient heating, ventilation and air conditioning systems, along with efficient operations and scheduled maintenance of such systems, reduces carbon footprint. Schedule heating and cooling systems to go on during pre-determined hours; let the system run hotter or cooler in off-hours, depending on the season. Most buildings are ventilated with outside air to keep the inside air fresh and odor free. This ventilation runs all of the time, even when it is not needed. This wastes energy because the outside air needs to be heated or cooled. Installing a low-energy humidifier instead of a typical electric steam humidifier will reduce a building’s carbon footprint. Also, equipping a building with sensors can measure indoor air quality and determine how much ventilation is needed. This means less electricity and natural gas will be needed for the HVAC system, which lowers energy bills and reduces the building’s carbon footprint.
3. Continuous insulation
Specify continuous insulation. ASHRAE 90.1 defines continuous insulation as insulation that is continuous across all structural members without thermal bridges other than fasteners and service openings. It is installed on the interior, exterior or is integral to any opaque surface of the building. “In a steel-framed building, thermal shorts reduce the assembly R-value of cavity-insulated wall systems by more than 50 percent,” says Gary Parsons, building scientist, Dow Building Solutions, Midland, Mich. “Continuous insulation saves energy and reduces the carbon footprint. It provides thermal, air, water and vapor control layers in one system and simplifies the construction process.”
Tanya Schnelzer, environmental manager at Firestone Building Products, Indianapolis, agrees, saying: “The most recent International Code Council (ICC) regulations for continuous insulation allow building owners to save millions of dollars in energy bills over the lifetime of a building. These savings are realized by increasing thermal performance and preventing thermal bridging through the use of continuous insulation.”
4. Lighting
Use state-of-the-art lighting and optimize daylighting. Lighting accounts for approximately 40 percent of the energy used in a typical commercial building. Solar thermal gain lowers carbon footprints, but too much solar gain in summer causes overheating and increases the need for cooling. Too little solar gain in winter increases the need for heating. Solar control window films can reduce carbon footprints by cutting energy expenditures by up to 30 percent.
According to Steve Fronek, PE, LEED Green Associate, vice president of technical services at Wausau Window and Wall Systems in Wausau, Wis.: “Open plan offices and light-colored interior finishes help distribute daylight more deeply within the building. High-performance curtainwall systems with integrated sunshades and light shelves can increase natural light. Properly executed daylighting strategies can reduce HVAC peak loads with corresponding reductions in mechanical equipment capacity and carbon footprint.” For a sound daylighting strategy, product information on window properties such as U-factor, solar heat gain coefficient and condensation resistance is available. “However, the relative importance of these properties depends on site-specific and building-specific conditions,” says Fronek.
5. Recycled content
Specify recycled content building and interior materials. Choose recyclable building materials that have less negative effect on the environment. Support green suppliers and vendors that embrace green practices. “Metal building systems are the ideal product for sustainability and green as steel is the most recycled material on the planet,” says Wes Brooker, marketing development manager, American Buildings Co., Eufaula, Ala. “Recycled steel reduces mining waste by 97 percent, air pollution by 86 percent and water pollution by 76 percent. Producing steel through recycling also uses significantly less energy than conventional steelmaking. The typical metal building is manufactured from at least 70 percent recycled steel.”
Margaret A. Davis, PE, director strategic services, Metallic Building Co., Houston, touts metal’s recyclable merits saying, “Steel is 100 percent recyclable, sustainable and less is needed for building a frame; therefore it is an excellent framing material to help reduce a building’s total carbon footprint.”
6. Water usage
A major factor contributing to the carbon footprint of a building is the amount of energy expended to supply, treat and use its water. Water-oriented strategies significantly reduce energy use and greenhouse gas emissions. Designing for water conservation, efficiency and reuse are among the largest and most cost-effective energy and carbon reduction strategies available. Specify plumbing equipment that prevents leaks-or “real water losses”-the most troubling element of what water efficiency experts call “non-revenue water.”
Installing efficient fixtures and appliances can reduce water usage. Specify high-efficiency toilets with reduced average flush volumes compared to conventional toilets. Use rainwater as a valuable water source. Design buildings to harvest rainfall and create outdoor spaces that rely primarily on precipitation for irrigation. Rainwater harvesting and xeriscaping can result in 50 percent savings in outdoor water use. Rainwater harvesting has a low environmental footprint because it’s not pumped long distances. Water for flushing toilets, irrigation and washing machines does not need to be potable, so using rainwater direct from a building’s roof lowers carbon footprint.
7. Renewable energy
A building’s carbon footprint can be reduced by sourcing its operational energy from environmentally responsible sources, or by generating renewable energy on-site. Using the walls or roof of a building for solar air heating, solar electric photovoltaic (PV) systems or solar water heating can permanently eliminate part of the demand for conventional energy. “This is the next phase of where large-scale CO2 reductions from the building sector will be realized, because you can only reduce so much energy usage, without having to actually generate it at some point and hopefully from carbon-free sources like solar,” says Victoria Hollick, principal at Conserval Systems Inc., Buffalo, N.Y. “Solar systems work by fulfilling a certain percentage of the building’s heating or electric load. A solar air heating system will generate heat energy to provide space heating or to heat the ventilation/make-up air for the building. A solar PV system will generate electricity that can be used to offset the building’s conventional electric source. Solar water systems generate thermal energy to offset the heating of water.” Metal roofs are a good host for solar PV because they are very durable and have lifetimes that meet or exceed the 25- to 30-year expected life of the solar PV system.
8. Location
A building’s location will have a direct impact on its overall carbon footprint. “Highly efficient buildings should be oriented along an east-west axis, maximizing north- and south-facing glazing,” says Fronek. Where a building is built will impact the carbon footprint and the potential for carbon buildup in the landscape. Is the building situated by a degraded or a pristine ecosystem? Can an ecosystem be restored in the process of developing the building? Also, siting the building near public transportation reduces its carbon footprint.
Bob Zabcik, director of research and development, NCI Group Inc., Houston