Albedo:
Albedo, or solar reflectance, is a measure of a material's
ability to reflect sunlight (including the visible, infrared, and
ultraviolet wavelengths) on a scale of 0 to 1. An albedo value of
0.0 indicates that the surface absorbs all solar radiation, and
a 1.0 albedo value represents total reflectivity. EPA ENERGY STAR specifies an albedo of 0.65 or higher for low-slope roof applications
and 0.25 for sloped roofs.
American National Standards Institute (ANSI):
ANSI is a nonprofit organization that administers and coordinates
the U.S. voluntary standardization and conformity assessment system.
It is comprised of approximately 1,000 companies, not-for-profit
organizations, government agencies, and other members.
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.
Anthropogenic Heat:
Anthropogenic heat is man-made heat generated by buildings,
people, or machinery. Estimates of anthropogenic heat generation
can be made by totaling all the energy used for heating and cooling,
running appliances, transportation, and industrial processes. Anthropogenic
heat is small in rural areas, becoming larger in dense urban areas.
It is not usually large enough to be a significant factor in summertime
heat island formation, but has a more significant impact on wintertime
heat islands.
Asphalt Cement Concrete (ACC):
ACC, commonly known as "asphalt," makes up approximately
90% of all paved surfaces in the U.S. ACC is a hardened mixture
of asphalt cement binder (about 7% total weight) and aggregate (about
93% total weight).
Asphalt Chip Seals:
Asphalt Chip Sealing is a paving treatment in which a thin
layer of asphalt emulsion binder is applied and immediately covered
with a layer of light-colored aggregate. Afterwards, the aggregate
is pressed into the binder using a heavy roller resulting in an
exposed aggregate surface. Using light-colored aggregate increases
reflectance as the surface wears.
Asphalt Emulsion Sealcoats:
An asphalt emulsion sealcoat is a paving option consisting
of an aggregate of small rocks in an asphalt binder. Emulsion sealcoats
are brushed over existing pavement to seal small cracks and protect
the surface. Asphalt emulsion sealcoats are most commonly used in
low-traffic applications such as parking lots and driveways.
Biogenic Hydrocarbons:
Biogenic hydrocarbons are naturally occurring compounds,
including VOCs (volatile organic compounds) that are emitted from
trees and vegetation. High VOC-emitting tree species like eucalyptus
can contribute to smog formation. Species-specific biogenic emission
rates may be an important consideration in large-scale tree plantings,
especially in areas with high ozone concentrations.
Bioremediation & Phytoremediation:
These terms refer to the ability of trees and vegetation to remove
pollution from rain water. Green roofs and shade trees, for example,
mitigate urban runoff and nonpoint source nitrogen and phosphorus
pollution through these processes.
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.
Built-Up Roof (BUR):
Built-up roofs are a class of low-slope roof that consist
of layers of reinforcing felt between either asphalt or coal tar
bitumen. The reflectivity of BURs depends on the color of the surface
layer. Four BUR surfacing options are aggregate, smooth, mineral
cap, and protective coating.
Canopy:
Canopy refers to the tree cover in an urban setting. Canopy
size is an important determinant of a city's heat island reduction
potential. The "urban fabric" can be characterized both
above and below the canopy for a better understanding of the area's
surface cover.
Climate Change:
Climate change is sometimes used to refer to all forms of
climatic inconsistency. But because the Earth's climate is never
static, the term is properly used to imply a significant change
from one climatic condition to another. In some cases, climate
change has been used synonymously with global warming.
Scientists, however, tend to use climate change in the wider
sense to include both human-induced and natural changes in climate.
Consolidated Metropolitan Statistical Area
(CMSA):
A CMSA is an area with a population of one million or more
and meets other statistical criteria. The Office of Management and
Budget defines CMSAs for the purpose of collecting, tabulating,
and publishing federal data.
Continental Climate:
A continental climate is a climate lacking oceanic influence
and characterized by more extreme temperatures than marine climates.
Therefore, a continental climate has a high annual temperature range
for its latitude relative to a climate with marine influence.
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).
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.
Direct and Indirect Energy Savings:
Air conditioning energy savings from installing a cool roof or
planting shade trees to reduce heat transfer into homes and buildings
are direct energy savings. Indirect energy savings
are savings accrued from lower ambient temperatures (presuming a
decrease in air conditioning under cooler outdoor temperatures).
DOE-2 Model:
The DOE-2 Model is a computer program that simulates hourly
building energy use. It is an international benchmark used as the
basis for building standards in the U.S. and other countries.
Elastomeric Roof Coatings:
Elastomeric coatings have elastic properties, and can stretch
in the summertime heat and then return to their original shape without
damage. Elastomeric coatings include acrylic, silicone and urethane
materials.
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%).
Energy Balance:
An energy balance is a detailed accounting of all energy
flowing into and out of a volume or surface. Examples of energy
flows include convection, evaporation, heat stored or conducted,
and heat generated in a volume (such as anthropogenic heat in a
city). Energy balances of urban and rural areas can illustrate the
cooling effects of trees and vegetation on evaporation and heat
storage rates.
Evaporative Emissions:
Evaporative emissions are from fuel evaporating from vehicle carburetors or fuel systems. Evaporative emissions can occur while vehicles are refueling, operating, or even when vehicles are parked.
Evapotranspiration:
Evapotranspiration is the process through which plants release
water to the surrounding air, dissipating ambient heat. According
to the Department of Energy's Lawrence Berkeley National Laboratory,
a single mature and properly watered tree with a crown of 30 feet
can "evapotranspire" up to 40 gallons of water in a day.
Tree planting on a large scale can reduce surrounding air temperatures.
Field Campaign:
A field campaign, or field study, is an intensive monitoring
effort in a small area that lasts for a few weeks or months. This
on-the-ground research technique is used to monitor temperature
differences within cities, and between urban and rural areas.
Global Warming:
Global warming is the gradual rise of the Earth's surface
temperature. Global warming is believed to be caused by the greenhouse
effect and is responsible for changes in global climate patterns
and an increase in the near-surface temperature of the Earth. Global
warming has occurred in the distant past as the result of natural
influences, but the term is most often used to refer to the warming
predicted to occur as a result of increased emissions of greenhouse
gases.
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).
Green Roofs:
Green roofs are rooftops planted with vegetation. Intensive
green roofs have thick layers of soil (6 to 12 inches, or more)
that can support a broad variety of plant or even tree species.
Extensive roofs are simpler green roofs with a soil layer of 6 inches
or less to support turf, grass, or other ground cover.
Heat Exhaustion:
Heat exhaustion is a phenomenon caused by fluid loss, which
in turn causes decreased blood flow to vital organs. Reduced blood
flow from heat exhaustion can result in a form of shock. Victims
of heat exhaustion often complain of flu-like symptoms hours after
exposure.
Heat-Health Watch Warning Systems:
Heat-health watch warning systems correlate weather conditions
with human comfort and health risks. When harmful weather conditions
are predicted, a warning is given to the public to guard against
the effects of heat stroke and heat exhaustion. The alert system
can also be used in conjunction with social service programs to
check on at-risk populations and provide them with cooling services.
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).
Heating Penalty:
Cool roofs reflect solar energy year-round. In the winter, cool
roofs reflect solar energy that could have been used to warm the
building, and more heating energy may be required. This heating
penalty is small in most U.S. climates because there is less
sunlight available during the winter. In addition, it is usually
offset by cooling energy savings during the summer. Cool roofs typically
result in net annual energy savings.
Heat Stroke:
Heat stroke occurs when the body's heat regulating mechanisms including
convection, sweating, and respiration fail. The likelihood of heat
stroke increases when air temperatures are higher than skin temperature,
and when individuals are low on fluids. Body temperatures can be
raised to the point at which brain damage and death can result unless
cooling measures are quickly taken.
Homology Mapping:
Homology mapping is an analytic technique in which similarities
in the geographical, land-use, and meteorological characteristics
of a monitoring site are used to identify a homologue, or best match
, for that site or area. This technique was developed to estimate
ozone concentrations in unmonitored areas using data from actual
monitoring sites. Homology mapping can therefore provide the basis
for impact calculations in unmonitored areas.
Infrared Radiation:
Infrared radiation is the heat energy emitted from a material.
The term infrared refers to energy in the region of the electromagnetic
radiation spectrum at wavelengths longer than those of visible light,
but shorter than those of radio waves.
Joule (J):
A joule is a metric unit of energy equal to the work done
by a force of one newton acting through a distance of one meter.
Kilowatt hour (kWh):
A kilowatt hour is a metric unit of energy most often used
to measure electricity use.
Landsat 7 Satellite:
Landsat 7 is a U.S. satellite used to acquire remotely sensed
images of the Earth's land surface and surrounding coastal regions.
The goal of the satellite program is to improve our understanding
of the Earth as an integrated system, including how it responds
to natural and human-induced disturbances.
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%.
Mesoscale Model (MM5):
The MM5 model was developed by the National Center for Atmospheric
Research and Penn State University. It is used in a range of applications,
including evaluations of how heat island mitigation strategies affect
weather in different regions of the country.
Microclimate:
A microclimate is a climate in a small area that varies
significantly from the overall climate of a region. Microclimates
are formed by natural or man-made geography and topography, such
as hills, buildings, and the presence or absence of trees and vegetation.
Mixing Layer:
The atmosphere's mixing layer is the near-surface area where
air is well mixed from turbulence caused by the interaction of the
Earth's surface and atmosphere. The mixing layer is usually located
at the base of a temperature inversion.
National Ambient Air Quality Standards (NAAQS):
In 1971, EPA promulgated NAAQS for six classes of air pollutants.
According to the Clean Air Act, the purpose of the NAAQS is to protect
the public from air pollutants "with an adequate margin of
safety" (primary NAAQS) and to promote the public welfare (secondary
NAAQS). Under the Clean Air Act, individual states are required
to develop plans for implementing, enforcing, and maintaining the
standards. Several states have considered including heat island
mitigation in their air quality plans for ozone, a "criteria"
air pollutant. (A "criteria air pollutant" is one of the
six classes of air pollutants for which EPA has established a NAAQS.)
Nitrogen Oxides (NOx):
NOx is the collective term for nitrogen compounds such as
NO and NO2. These two nitrogen oxides are an environmental and public
health concern because human activity has increased their concentration
in the atmosphere. NO and NO2 are interconvertible and are precursor
molecules for the production of ground-level ozone.
Nonattainment Area:
A nonattainment area is a region in which the level of a
criteria air pollutant is higher than allowed by the federal NAAQS.
For ground-level ozone, the one-hour standard is 120 parts per billion.
EPA puts a city or metropolitan area on its "nonattainment"
list when ozone exceeds, or violates, the standard more than once
a year averaged over a three-year period.
Ozone:
Ozone is a colorless gas with a pungent odor that has the
molecular form, O3. It is found in two layers of the
atmosphere, the stratosphere and the troposphere. In the stratosphere,
ozone provides a protective layer shielding the Earth from ultraviolet
radiation's potentially harmful health effects. At ground level
(the troposphere), ozone is a pollutant that affects human health
and the environment, and contributes to the formation of smog.
Photochemical Modeling:
Photochemical modeling is computer modeling of reactions
in the atmosphere that produce ozone from nitrogen oxides and volatile
organic compounds. Photochemical modeling can be used to evaluate
the air quality impacts of heat island reduction strategies.
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.
Polyurethane Spray Foam (SPF):
Polyurethane spray foam is an insulating foam material often
used on rooftops. Two liquid components are combined and sprayed
onto a surface to form SPF. The components react and harden to form
a rigid, waterproof insulating layer.
Porous Block Pavement Systems:
Porous block pavement systems are prefabricated lattice
structures made of concrete or plastic that are designed to support
light traffic from cars and pedestrians, while allowing water to
drain through. The blocks are filled with aggregate, or with soil
planted with vegetation.
Portland Cement Concrete (PCC or Concrete):
Concrete is a hardened mixture of portland cement, sand, and coarse
aggregate. Waste materials like fly ash, slag and plastic fibers
can also be used in the concrete mixture. These materials are mixed
with water, installed between specially constructed forms, then
allowed to dry and cure for as long as several days. The addition
of various polymers and other additives to the pavement mix can
increase pavement strength and decrease the curing time to 12 hours.
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.
Radiation:
Radiation is energy emitted in the form of electromagnetic
waves. Radiation has differing characteristics depending upon the
wavelength. Because the radiation from the sun is relatively energetic,
solar radiation has a short wavelength (ultra-violet, visible, and
near infrared). Energy radiated away from the Earth's surface and
the atmosphere has a longer wavelength (e.g., infrared radiation)
because the Earth is cooler than the sun.
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.
Remote Sensing:
Remote sensing is a method of visualizing the radiative
properties of the Earth's surface using instrumentation mounted
in satellites or aircraft. Remote sensing instrumentation measures
the radiation reflected and emitted from the earth at different
wavelengths, primarily at those wavelengths not absorbed by the
atmosphere. Remotely sensed data can be converted to maps showing
the visible or thermal properties of an area.
Resin Modified Emulsion Pavement:
Resin modified emulsion pavement contains a binder made
primarily from tree resins. Construction processes using resin-modified
emulsion are similar to those for asphalt pavements. The resin binder
is translucent so that the pavement keeps the color of the aggregate.
R-Value:
R-value or "thermal resistance value" is a measure
of the resistance of a material to heat flow. The term is typically
used to describe the resistance properties of insulation. The higher
the R-value, the greater the insulation's resistance to heat flow.
Sedum:
Sedum is a plant genus containing several species suited
for use in green roof construction. Sedum species are a common choice
for rooftop applications because they have high water-retention
capability, an ability to filter pollution, and are hearty.
Single-Ply Roof:
Single-ply roofing is a flexible or semi-flexible pre-manufactured
membrane typically made of rubber or plastic materials. Single-ply
roofing comes in large rolls and must be glued or mechanically fastened
to a roof, and sealed at all seams.
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%).
State Implementation Plan (SIP):
A SIP is a detailed description of the programs a state
will use to carry out its responsibilities under the Clean Air Act.
SIPs are collections of regulations used by a state to reduce air
pollution. The Clean Air Act requires that EPA approve each state's
SIP. Members of the public have an opportunity to participate in
review and approval of these plans.
Steep-Slope Roofs or Sloped 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%.
Surface Roughness:
Surface roughness is used in the context of heat island
mitigation to refer to the presence of buildings, trees, and other
irregular land topography in an urban area.
Therm:
A therm is a unit used to measure the quantity of heat equal
to 100,000 British thermal units.
Transect Study:
For heat island monitoring purposes, a transect study measures
temperature changes across a transect, or sample area, often using
hand-held devices or measurement equipment mounted on cars or aircraft.
When conducting transect studies to measure the heat island effect,
researchers should select a transect that samples a range of land-uses
and land-cover. Timing and weather conditions are also important
factors, as the magnitude of heat islands is often greatest in the
early evening.
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.
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 Fabric Analysis:
An Urban Fabric Analysis is a method for determining the
proportions of vegetative, roofed, and paved surface cover relative
to the total urban surface in the city. To analyze the effect of
surface cover modifications and simulate realistic estimates of
temperature and ozone reductions resulting from such modifications,
the baseline urban fabric must be quantified.
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.
Volatile Organic Compounds (VOCs):
VOCs are molecules containing carbon and varying proportions
of other elements such as hydrogen, oxygen, fluorine, and chlorine.
They are the "precursors" that react in sunlight and heat
to form ground-level ozone.
Watt:
A watt is the absolute unit of power equal to the work done
at the rate of one joule per second.
Whitetopping:
Whitetopping is a cool paving technique in which an existing
pavement is covered by a layer of light-colored concrete. Usually,
whitetopping involves adding a four to eight inch thick layer over
the asphalt base. However, a new method called ultra-thin whitetopping
requires only two to four inches of concrete.
Winter Penalty:
Just as cool roofs reflect solar radiation throughout the summer,
they also reflect wintertime sunlight. Thus, the winter penalty
is the potential for increased heating demand in winter due to reflected
solar radiation by light colored roofs. Over an entire year, decreases
in summer energy use typically exceed any wintertime increases.
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