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Greening EPA Glossary
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Acid Rain: The result of sulfur dioxide (SO2) and nitrogen oxides (NOx) reacting in the atmosphere with water and returning to earth as rain, fog, or snow. For more information, visit EPA's Acid Rain Web site.
Air Handling Unit: A type of heating and/or cooling distribution that channels warm or cool air to different parts of a building. Equipment includes a blower or fan, heating and/or cooling coils, and related equipment such as controls, condensate drain pans, and air filters. Does not include ductwork, registers, grilles, boilers or chillers.
Air Side Economizer: An air economizer cycle reduces the load on the chilled water system by increasing the flow of outside air above the minimum required for ventilation when the outside air temperature is favorable in comparison to return air temperature. Also known as free cooling. For example, in cooling season, if there is cool, dry air outside, it will be drawn into the building to cool it, instead of using chillers to provide cooling.
Autoclave: A device that uses steam to sterilize equipment and deactivate bacteria, viruses, fungi, and spores.
Boiler Feed Water: Input water utilized by a boiler.
Building Automation System (BAS): A system that optimizes the start-up and performance of HVAC equipment and alarm systems. A BAS greatly increases the interaction between the mechanical subsystems of a building, improves occupant comfort, lowers energy use, and allows off-site building control.
Carbon dioxide (CO2): A colorless, odorless, non-poisonous gas that exists in trace quantities (less than 400 parts per million) within ambient air. Carbon dioxide is a product of fossil fuel combustion. Although carbon dioxide does not directly impair human health, it is a greenhouse gas that traps terrestrial (i.e., infrared) radiation and contributes to the potential for global warming.
Chlorofluorocarbons (CFCs): A family of inert, nontoxic, and easily liquefied chemicals used in refrigeration, air conditioning, packaging, insulation, or as solvents and aerosol propellants. Because CFCs are not destroyed in the lower atmosphere, they drift into the upper atmosphere, where their chlorine components destroy ozone.
Cogeneration: The generation of electricity and the capture and use of otherwise wasted heat energy byproducts. Cogeneration is also referred to as a combined heat and power (CHP) system.
Combined Heat and Power (CHP): The generation of electricity and the capture and use of otherwise wasted heat energy byproducts. A CHP system is also referred to as cogeneration.
Cooling Tower Blowdown Water: Water released from a cooling tower to maintain proper water mineral concentration.
Cooling Tower Make-Up Water: Water added to a cooling tower to replace water lost to evaporation or blowdown.
Deionize (DI): To remove ions from a solution using an ion-exchange process.
Delivered Product: Green power fed into the same electric transmission and distribution system that serves the end user. Review the Green Tags vs. Delivered Product (PDF) (3 pp, 233K, About PDF) document to understand the difference between the two green power options: delivered product and renewable energy certificates.
Direct Digital Controls (DDC): The application of microprocessor technology to building environmental controls. DDC systems make it possible to control heating and cooling functions with software that takes into account a wide range of variables, thereby achieving greater efficiency.
Evapotranspiration: The loss of water from the soil both by evaporation and by transpiration from the plants growing in the soil.
Extensive Garden: Extensive gardens have thinner soil depths and require less management and less structural support than intensive gardens. They do not require artificial irrigation. Plants chosen for these gardens are low-maintenance, hardy species that do not have demanding habitat requirements. The goal of an extensive planting design is to have a self-sustaining plant community.
Green Roof: Also known as rooftop gardens, green roofs are planted over existing roof structures, and consist of a waterproof, root-safe membrane that is covered by a drainage system, lightweight growing medium, and plants. Green roofs reduce rooftop and building temperatures, filter pollution, lessen pressure on sewer systems, and reduce the heat island effect.
Green Infrastructure: An adaptable term used to describe an array of products, technologies, and practices that use natural systems – or engineered systems that mimic natural processes – to enhance overall environmental quality and provide utility services. As a general principal, Green Infrastructure techniques use soils and vegetation to infiltrate, evapotranspirate, and/or recycle stormwater runoff.
Green Tags: See renewable energy certificates.
Grey Water: Non-drinkable water that can be reused for irrigation, flushing toilets, and other purposes.
Ground Source Heat Pump (GHP): Electrically powered systems that tap the stored energy of the earth. These systems use the earth's relatively constant temperature to provide heating, cooling, and hot water for homes and commercial buildings.
Heating, Ventilation, and Air Conditioning (HVAC): Controls the ambient environment (temperature, humidity, air flow, and air filtering) of a building and must be planned for and operated along with other data center components such as computing hardware, cabling, data storage, fire protection, physical security systems, and power.
Heat Island Effect: This phenomenon describes urban and suburban temperatures that are 2° to 10°F (1° to 6°C) warmer than nearby rural areas. For more information, visit EPA's Heat Island Web Site.
Heat Pipe: A device that can quickly transfer heat from one point to another. Heat pipes are often referred to as the "superconductors" of heat, as they possess an extraordinary heat transfer capacity and rate with almost no heat loss.
Heat Recovery System: Process by which the exhaust air preheats the supply air when the outdoor air is cooler than the inside air. When the outside air is warmer than the inside air, the exhaust air will cool the supply air. This system saves energy depending on the season and only operates for sensible heat recovery.
Hydrochlorofluorocarbons (HCFCs): Compounds containing carbon, hydrogen, chlorine, and fluorine. They were originally intended as replacements for CFCs, but are only a temporary solution because they still contain chlorine and have the potential to destroy stratospheric ozone.
Intensive vs. Extensive Gardens: Intensive gardens have thicker soil depths and generally require more management and artificial irrigation systems. The plants chosen for these gardens must thrive in the specific roof environment they inhabit. Intensive gardens are heavier than extensive gardens, requiring more structural support. Extensive gardens have thinner soil depths and require less management and structural support. They do not require artificial irrigation. Plants chosen for extensive gardens are low maintenance, hardy species and do not have demanding habitat requirements. The idea of an extensive planting design is to have a self-sustaining plant community.
Irrigation: Supplying water to grass, trees, and other plants.
Lab Process Water: Water used for laboratory experiments and procedures.
Low Impact Development (LID): A sustainable landscaping approach that can be used to replicate or restore natural watershed functions and/or address targeted watershed goals and objectives.
Mercury: A naturally occurring element that is found in air, water, and soil. It exists in several forms: elemental or metallic mercury, inorganic mercury compounds, and organic mercury compounds. Mercury is used in thermometers, fluorescent light bulbs, and some electrical switches. For more information, visit EPA's Mercury Web site.
Methane (CH4): A greenhouse gas that is emitted during the production and transport of coal, natural gas, and oil or from the decomposition of organic wastes in municipal solid waste landfills and the raising of livestock. Although CO2 is more prevalent in the atmosphere, methane is over 20 times more effective in trapping heat than CO2 over a 100-year period. For more information, visit EPA's Methane Web site.
Net Metering: A method of crediting customers for electricity that they generate on site in excess of their own electricity consumption. Customers with their own generation offset the electricity they would have purchased from their utility. If such customers generate more than they use in a billing period, their electric meter turns backwards to indicate their net excess generation. Depending on individual state or utility rules, the net excess generation may be credited to their account (in many cases at the retail price), carried over to a future billing period, or ignored.
Nitrogen Oxides (NOx): A group of gases that cause acid rain and other environmental problems, such as smog and eutrophication of coastal waters. Burning fossil fuels such as coal and gasoline releases NOx into the atmosphere. For more information, visit EPA's Air and Radiation Web site.
Onsite Renewable Energy Generation: Electricity generated by renewable resources using a system or device located at the site where the power is used. Onsite generation is a form of distributed energy generation.
Operations and Maintenance (O&M): The activities related to the performance of routine, preventive, predictive, scheduled, and unscheduled actions aimed at preventing equipment failure or decline with the goal of increasing efficiency, reliability, and safety.
Particulate Matter: A complex mixture of extremely small particles and liquid droplets. It is made up of a number of components, including acids (such as nitrates and sulfates), organic chemicals, metals, and soil or dust particles.
Photovoltaic (PV): A system that converts sunlight directly into electricity using cells made of silicon or other conductive materials. When sunlight hits the cells, a chemical reaction occurs, resulting in the release of electricity.
R value: A measure of insulation. The higher the R-value, the better walls and roofs will resist the transfer of heat. For more information visit the Department of Energy's Web site.
Renewable Energy Certificates (RECs): Also known as green tags, green energy certificates, or tradable renewable certificates, RECs represent the technology and environmental attributes of electricity generated from renewable sources. Renewable energy certificates are usually sold in 1 megawatt-hour (MWh) units. A certificate can be sold separately from the MWh of generic electricity it is associated with. This flexibility enables customers to offset a percentage of their annual electricity use with certificates generated elsewhere. For more information, view Green Tags vs. Delivered Product (PDF) (3 pp, 233K, About PDF).
Renewable Energy Credits: See renewable energy certificates.
Reverse Osmosis (RO): A membrane separation process designed to treat wastewater containing a variety of contaminants including organic compounds.
Reverse Osmosis Reject Water: Waste water released from the reverse osmosis process.
Sanitary Water Use: Domestic water uses, such as faucets, toilets, and showers.
Single-Pass Cooling: During this process, water is circulated once through a piece of equipment and then disposed down the drain. To remove the same heat load, single-pass systems use 40 times more water than a cooling tower operated at 5 cycles of concentration.
Sulfur dioxide (SO2): A gas that causes acid rain. Burning fossil fuels, such as coal, releases SO2 into the atmosphere. For more information, visit EPA's Air and Radiation Web site.
Tradable Renewable Credits: See renewable energy certificates.
Variable Air Volume (VAV): An HVAC system strategy through which the volume of air delivered to conditioned spaces is varied as a function of ventilating needs, energy needs, or both.
Variable Frequency Drive (VFD): A specific type of adjustable-speed drive that controls the rotational speed of an alternating current (AC) electric motor by controlling the frequency of the electrical power supplied to the motor. VFDs are also known as adjustable-frequency drives (AFD), variable-speed drives (VSD), AC drives, or inverter drives.
Volatile Organic Compounds (VOCs): Emitted as gases from certain solids or liquids, VOCs include substances—some of which may have short- and long-term adverse health effects—such as benzene, toluene, methylene chloride, and methyl chloroform.
Water Side Economizer: A water side economizer reduces energy consumption in cooling mode by allowing the chiller to be turned off when the cooling tower alone can produce water at the desired chilled water set point. The cooling tower system, rather than the chiller, provides the cold water for cooling.
Wet Laboratory: Laboratory where chemicals, drugs, or other material or biological matter is tested and analyzed, and which requires water, direct ventilation, and specialized piped utilities.
Xeriscaping: Landscaping based on native, water-efficient plants to minimize the need for irrigation.