Absorption: Process by which a particle or substance is drawn into the structure of another.
Acid Rain: The precipitation of dilute solutions of strong mineral acids, formed by the mixing in the atmosphere of various industrial pollutants (primarily sulfur dioxide and nitrogen oxides) with naturally occurring oxygen and water vapor.
Adaptive Reuse: Renovation of a building or site to include elements that allows a particular use or uses to occupy a space that originally was intended for a different purpose.
Adsorbent: Material that is capable of the collection and binding of substances or particles on its surface without chemically altering them.
Air Changes Per Hour (ACH): Number of times per hour a volume of air, equivalent to the volume of space, enters that space.
Air Exchange Rate: The rate at which indoor air is replaced by outside air in a given space.
Air Handling Unit: Equipment that includes a fan or blower, regulator controls, condensate drain pans, heating and/or cooling coils, and air filters.
Air Plenum: Any space used to convey air in a building, furnace or structure. The space above a suspended ceiling is often used as an air plenum.
Alternative Energy: Energy from a source other than the conventional fossil-fuel sources of oil, natural gas and coal (i.e., wind, running water, the sun). Also referred to as "alternative fuel."
Ambient Air: Surrounding air.
American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE): ASHRAE is an international organization that establishes standards for the uniform testing and rating of heating, ventilation, air conditioning, and refrigeration equipment. It also conducts related research, disseminates publications, and provides continuing education to its members.
American Society for Testing and Materials (ASTM): ASTM is a member-based organization that develops a wide range of voluntary standards. It promulgates standard test methods, specifications, practices, classifications, and terminology in over 130 industrial segments. Two ASTM standards used in defining the performance of cool roofs are ASTM E 903-88, for testing solar absorptance, and ASTM E 408-71 (1990), for testing the solar emittance of materials.
BACT -Best Available Control Technology: An emission limitation based on the maximum degree of emission reduction (considering energy, environmental and economic impacts) achievable through application of production processes and available methods, systems and techniques. BACT does not permit emissions in excess of those allowed under any applicable Clean Air Act provisions. Use of the BACT concept is allowable on a case-by-case basis for major new or modified emissions sources in attainment areas and applies to each regulated pollutant.
Bake-out: Process by which a building is heated in an attempt to accelerate VOC emissions from furniture and materials.
British thermal unit (Btu): A Btu is the quantity of heat required to raise the temperature of one pound of water one degree Fahrenheit at a specified temperature.
Building Envelope: Also referred to as "building shell." Exterior surface of a building's construction includes the walls, windows, roof and floor.
By-product: Material, other than the principal product, generated as a consequence of an industrial process or as a breakdown product in a living system.
Commissioning: Process by which the operating systems of a building are tested and adjusted prior to occupancy.
Cool Roofs: The term cool roof is used to describe roofing material that has high solar reflectance. This characteristic can reduce heat transfer to the indoors and enhance roof durability. Cool roofs may also be highly emissive, releasing a large percentage of the solar energy they absorb.
Cooling Degree Day (CDD): Cooling degree days are used to estimate how hot the climate is and how much energy may be needed to keep buildings cool. CDDs are calculated by subtracting a balance temperature from the mean daily temperature, and summing only positive values over an entire year. The balance temperature used can vary, but is usually set at 65°F (18°C), 68°F (20°C), or 70°F (21°F).
Cubic ft./min. (CFM):Cubic feet per minute, a common measure of airflow.
Daylighting: Daylighting includes strategies for increasing the percentage of illumination provided by natural light in your building such as toplighting, optimized building orientation and room layout, light shelves, clerestory windows, and shading among others. By incorporating daylighting into a building, first cost, operating cost, and additional cost that is added to the monthly operating cost due to the heat given off from the lighting itself, which increases the heat load on the HVAC system, can all be reduced. Daylighting is free, it is a more enjoyable light to in which to work, play and live.
Dose-response: Relationship between exposure levels and adverse effects.
Dynamic Environmental Chamber: Well-controlled system (including temperature, relative humidity (RH) and air quality/purity) that utilizes realistic air flows for the assessment of chemical emissions from products and materials
Embodied Energy: The amount of energy used in the production, construction, and transportation of materials.
Emission Controls: Any measure that reduces emissions into air, water or soil. The most effective emission controls involve the redesign of the process so less waste is produced at the source. Common emission controls are wastewater treatment plants, stack scrubbers and in-plant, solid waste reduction programs.
Emission Factor: Quantity of a substance or substances released from a given area or mass of a material at a set point in time; i.e., milligrams per square meter per hour.
Emissions: The release of gases, liquids and/or solids from any process or industry. Liquid emissions are commonly referred to as effluents.
Emittance: The emittance of a material refers to its ability to release absorbed heat. Scientists use a number between 0 and 1, or 0% and 100%, to express emittance. With the exception of metals, most construction materials have emittances above 0.85 (85%).
Environmental Footprint: For an industrial setting, this is a company's environmental impact determined by the amount of depletable raw materials and nonrenewable resources it consumes to make its products, and the quantity of wastes and emissions that are generated in the process. Traditionally, for a company to grow, the footprint had to get larger. Today, finding ways to reduce the environmental footprint is a priority for leading companies.
Environmental Impact: Any change to the environment, whether adverse or beneficial, wholly or partially resulting from human activity, industry or natural disasters.
Fossil Fuel: A fuel, such as coal, crude oil and natural gas, produced by the decomposition of ancient (fossilized) plants and animals;
Green Design: A design, usually architectural, conforming to environmentally sound principles of building, material and energy use. A green building, for example, might make use of solar panels, skylights and recycled building materials.
Green Roof: A roofing system that utilizes vegetation to absorb rainwater and reduce heat reflection. Green roofs have many advantages over traditional roof systems. Not only do they provide benefits for the residents themselves by reducing the heat load on the building and monthly utility costs and by providing additional outdoor space, but they also provide benefits for the surrounding community by controlling the rate of storm runoff during heavy rains and reducing the heat-island effect. Roof gardens can be installed with a wide variety of plants, which must be chosen depending on the available soil depth as well as the climate. The desired type of roof garden has to be taken into consideration in the earliest design phases to accommodate the structural implications of the additional weight.
Greenhouse Effect: The warming of earth's surface and lower atmosphere as a result of carbon dioxide and water vapor in the atmosphere, which absorb and reradiate infrared radiation.
Greenhouse Gas: A greenhouse gas is any gas that absorbs infrared radiation in the atmosphere. Greenhouse gases include water vapor, carbon dioxide (CO2), methane (CH4), nitrous oxide (N2O), halogenated fluorocarbons (HCFCs), ozone (O3), perfluorinated carbons (PFCs), and hydrofluorocarbons (HFCs).
Greenwash: Disinformation disseminated by an organization so as to present an environmentally responsible public image.
Heating Degree Day (HDD): Heating degree days are used to estimate how cold the climate is and how much energy may be needed to keep buildings warm. HDDs are calculated by subtracting the mean daily temperature from a balance temperature, and summing up only positive values over an entire year. The balance temperature used can vary, but is usually set at 65°F (18°C), 68°F (20°C), or 70°F (21°F).
Indoor Air Quality (IAQ): ASHRAE defines acceptable indoor air quality as air in which there are no known contaminants at harmful concentrations as determined by cognizant authorities and with which 80% or more people exposed do not express dissatisfaction
Life Cycle of a Product: All stages of a product's development, from extraction of fuel for power to production, marketing, use and disposal.
Life Cycle Analysis (LCA): The assessment of a product's full environmental costs, from raw material to final disposal, in terms of consumption of resources, energy and waste.
Life Cycle Inventory (LCI): An accounting of the energy and waste associated with the creation of a new product through use and disposal.
Low-Slope Roof: A low-slope roof is a roof surface with a maximum slope of 2 inches "rise" for 12 inches "run" as defined in American Society for Testing and Materials Standard E 1918-97. ENERGY STAR low-slope products have a minimum reflectance of 0.25, or 25%.
Nonrenewable Energy: Energy derived from depletable fuels (oil, gas, coal) created through lengthy geological processes and existing in limited quantities on the earth.
Nonrenewable Resource: A resource that cannot be replaced in the environment (i.e., fossil fuels) because it forms at a rate far slower than its consumption.
Odor Threshold: The minimum odor of a water or air sample that can just be detected after successive dilutions with odorless water. Also referred to as "threshold odor."
Open-loop Recycling: A recycling system in which a product made from one type of material is recycled into a different type of product (e.g., used newspapers into toilet paper). The product receiving recycled material itself may or may not be recycled.
Organic Compound: Vast array of substances typically characterized as principally carbon and hydrogen, but that may also contain oxygen, nitrogen and a variety of other elements as structural building blocks.
OSHA: Occupational Safety and Health Administration
Passive Heating and Cooling: Mechanical heating and cooling systems are not the only ways to achieve indoor comfort. Passive heating strategies most often rely on the collection of heat from the sun during the day, while passive cooling strategies rely on heat gain avoidance and the use of cross ventilation, evaporation, and thermal mass which stores heat during the day to release it at night. Passive heating and cooling cannot only reduce the first costs of your HVAC system, but they can drastically reduce your operating costs. Since these strategies make use of free solar energy and local breezes, they do not cost anything themselves. Include them in your schematic design discussions of building orientation, skin construction, and plan layout to get the greatest benefit.
Photovoltaic Cells: Photovoltaic cells are designed and engineered to convert solar radiation into usable energy. They are considered a "renewable" form of energy and can be installed on rooftops in conjunction with cool roof materials.
Post-industrial Material: Industrial manufacturing scrap or waste; also called pre-consumer material
Post-industrial Recycle Content: product composition that contains some percentage of manufacturing waste material that has been reclaimed from a process generating the same or a similar product. Also called pre-consumer recycle content.
ppb: parts per billion.
ppm: Parts per million.
Pyranometer: A pyranometer is an instrument for measuring the solar reflectance, or albedo, of materials. The American Society for Testing and Materials Standard E 903-88 provides guidance on performing these measurements.
Pyrolysis: Decomposition of a chemical by extreme heat.
Radiometer: A radiometer is an instrument for detecting and measuring the intensity of the sun's energy in the electromagnetic spectrum. Measured radiation is characterized by its frequency of oscillation of ultraviolet, visible, and infrared frequencies.
Recycling: Process by which materials that would otherwise become solid waste are collected, separated or processed and returned to the economic mainstream to be reused in the form of raw materials or finished goods.
Recycled Content Materials:  One way to reduce the environmental impact of construction is to specify recycled content materials. Many types of construction materials can be purchased with some degree of recycled content. As you are designing your building and specifying building materials, not only should you try to use as many recycled content building materials as you can – but you should also consider how the building you are constructing can be dismantled and recycled as it reaches the end of its useful life.
Renewable Resources: A resource that can be replenished at a rate equal to or greater than its rate of depletion; i.e., solar, wind, geothermal and biomass resources.
Solar Radiation: Solar radiation is heat energy from the sun, including the infrared, visible, and ultraviolet wavelengths. For heat island mitigation purposes, solar radiation is measured by American Society for Testing and Materials Standard E 1918, which provides for in-field use of a pyrometer to measure incoming and outgoing radiation.
Solar Reflectance: Solar reflectance is a measure of the ability of a surface material to reflect sunlight – including the visible, infrared, and ultraviolet wavelengths – on a scale of 0 to 1. Solar reflectance is also called "albedo."
Solar Reflectance Index (SRI): SRI is a value that incorporates both solar reflectance and emittance in a single value to represent a material's temperature in the sun. SRI quantifies how hot a surface would get relative to standard black and standard white surfaces. It is calculated using equations based on previously measured values of solar reflectance and emittance as laid out in the American Society for Testing and Materials Standard E 1980. It is expressed as a fraction (0.0 to 1.0) or percentage (0% to 100%).
Sick Building Syndrome: A building whose occupants experience acute health and/or comfort affects that appear to be linked to time spent therein, but where no specific illness or cause can be identified. Complaints may be localized in a particular room or zone, or may spread throughout the building and may abate on leaving the building.
Stack Effect: Flow of air resulting from warm air rising, creating a positive pressure area at the top of a building and negative pressure area at the bottom. This effect can overpower the mechanical system and disrupt building ventilation and air circulation.
Steep Slope Roofs: Steep-slope roofs, or sloped roofs, are roof surfaces with a slope greater than 2 inches "rise" for 12 inches "run." ENERGY STAR steep-slope products have a minimum reflectance of 0.65, or 65%.
Superinsulation: Superinsulation of the building envelope minimizes heat gain during the summer and heat loss during the winter. Superinsulation involves substantially increased R-values combined with proper detailing for minimized thermal bridging and thorough air sealing for minimized infiltration. This strategy must be paired with controlled ventilation in order to maintain a healthy indoor environment.
Sustainability: Practices that would ensure the continued viability of a product or practice well into the future.
Sustainable Development: An approach to progress that meets the needs of the present without compromising the ability of future generations to meet their needs.
Transmittance: Transmittance is the fraction of radiant energy that, having entered a layer of absorbing material, reaches its further boundary. For example, when sunlight reaches a tree's canopy, some amount of light is absorbed by the leaves and used for photosynthesis, some amount is reflected back into the atmosphere, and some amount is transmitted to the grass or ground below. The latter quantity determines the tree's transmittance, which is typically 10% to 30% in the summertime.
Transpired Solar Collector: Developed in the 1980's, Transpired Solar Collectors, precision perforated metal wall panels, are a renewable energy technology that uses solar energy to preheat outdoor air as it is drawn into a building. 
Typical Meteorological Year (TMY): A TMY is a data set of hourly values of solar radiation and meteorological elements for a one-year period. This concept is used in computer simulations of solar energy conversion systems and building systems to conduct performance comparisons of different systems, configurations, and locations. Because TMYs represent average rather than extreme conditions, they are not suited for designing systems to meet the worst-case conditions at a location.
Urban Heat Island Effect: The urban heat island effect is a measurable increase in ambient urban air temperatures resulting primarily from the replacement of vegetation with buildings, roads, and other heat-absorbing infrastructure. The heat island effect can result in significant temperature differences between rural and urban areas.
Ventilation: Process by which outside air is conveyed to an indoor space.

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