Download High Reflectance Hardscape Materials What are High Reflectance

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High Reflectance Hardscape Materials
What are High Reflectance Hardscape Materials?
High reflectance hardscape materials are paving materials
with high solar reflectance (albedo), such as concrete, that
absorb minimal heat, reducing the heat island effect. 1
Albedo, or solar reflectance, is the ratio of the amount of
light reflected from a surface to the amount of light shining
on that surface. Pavements with a lower albedo absorb more
Figure 1 - Concrete pavers
sunlight and increase in temperature, while pavements with
(Source: Queens Botanical Garden/
higher albedo absorb less sunlight, remaining cooler. 2 The
Patty Kleinberg)
heat island effect refers to the increase in temperature in
developed areas that results from heat-absorbing paved areas, the loss of naturally cooling
vegetation, and waste heat produced by buildings, motor vehicles and machinery. This increase
in temperature leads to increasing energy demands, air conditioning costs, greenhouse gas
(GHG) emissions, and pollution while increasing the risk of heat related illnesses. 3 Around 30%
to 45% of urban areas are covered by pavement. 4 Conventional pavements can reach
temperatures of up to 120 to 150 degrees Fahrenheit during the summer, with the excess heat
from the pavement being transmitted into the air. 5 The heat island effect is exacerbated by the
use of paving materials, particularly dark colored surfaces, which absorb more sunlight than light
colored surfaces and remit heat back into the environment. 6 Reducing the use of hardscape
materials and using high reflectance and light colored materials will reduce the absorption of
sunlight, thus reducing the heat island effect. 7
How to Incorporate High Reflectance Materials
When selecting hardscape materials, consider the albedo (solar reflectance) and solar reflectance
index (SRI) of the material. The SRI, which ranges from zero to 100, indicates the effect of a
1
Portland Cement Association. "Heat Island Reduction." http://www.concretethinker.com/solutions/Heat-IslandReduction.aspx (accessed October 10, 2010).
2
Lawrence Berkeley National Laboratory Heat Island Group. “Pavement Albedo.”
http://eetd.lbl.gov/heatisland/Pavements/Albedo/ (accessed October 11, 2010).
3
NJ DEP. “Urban Heat Island and Climate Change: An Assessment of Interacting and Possible Adaptations in the
Camden, New Jersey Region.” http://www.state.nj.us/dep/dsr/research/urbanheat.pdf (accessed July 29, 2010).
4
US EPA. “Heat Island Effect: Heat Island Mitigation: Cool Pavements.”
http://www.epa.gov/heatisld/mitigation/pavements.htm (accessed July 29, 2010).
5
US EPA. “Reducing Urban Heat Islands: Compendium of Strategies: Cool Pavements."
http://www.epa.gov/heatisld/resources/pdf/CoolPavesCompendium.pdf (accessed October 3, 2010).
6
NJ DEP. “Creating Sustainable Communities: A Guide for Developers and Communities.” (accessed July 29,
2010).
7
NJ DEP. “Urban Heat Island and Climate Change: An Assessment of Interacting and Possible Adaptations in the
Camden, New Jersey Region.” http://www.state.nj.us/dep/dsr/research/urbanheat.pdf (accessed July 29, 2010).
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surface's reflectance and emittance on its surface temperature. Materials with the highest SRI are
the coolest. New asphalt pavement has an SRI of 0, while new white Portland cement concrete
can have an SRI of between 86 and 100. Emitance, or emissivity, is a range between 0 and 1 that
indicates how much heat is emitted by a surface. Since most opaque materials used for paving
have an emittance of around .9, the SRI of a material is mostly determined by its albedo. 8
Pavers (concrete masonry units) can be used as an alternative to asphalt and other dark materials
in a variety of scenarios such as driveways, parking lots, plazas, and streets. Most pavers use
high reflectance materials and some pavers also help reduce stormwater runoff. 9 Check with the
manufacturer to find out each product’s specifications. Pavers are available in a wide array of
shapes, colors, and sizes.
Using the natural landscape to your advantage can help cool a building and the site (including
parking lots, streets, and entranceways into the building). For example, using trees and other
vegetation to shade paved areas can protect the area from unwanted solar energy. Incorporating
trees and plants for shade also decreases surface and air temperature, increases comfort, and
connects people to the natural environment. 10
Examples
New York State Energy and Research Development Authority’s Mitigating New York City's
Heat Island with Urban Forestry, Living Roofs, and Light Surfaces 11
This study uses a regional climate model in combination with observed meteorological, satellite,
and GIS data to determine the impact of urban forestry, living (green) roofs, and light-colored
surfaces on near-surface air temperature and the urban heat island in New York City. Among the
single-strategy scenarios, light surfaces, light roofs, and living roofs can potentially reduce the
summer peak electric load more than the other strategies.
http://www.nyserda.org/programs/Environment/EMEP/project/6681_25/0606%20Complete%20report-web.pdf
Urban Heat Island and Climate Change: An Assessment of Interacting and Possible Adaptations
in the Camden, New Jersey Region 12
8
Portland Cement Association. "Heat Island Reduction." http://www.concretethinker.com/solutions/Heat-IslandReduction.aspx (accessed October 10, 2010).
9
Portland Cement Association. “Hardscape & Pavers - Permeable Pavement and Surfaces.” (accessed July 29,
2010).
10
US EPA. “Heat Island Effect: Trees and Vegetation.” http://www.epa.gov/hiri/mitigation/trees.htm (accessed July
29, 2010).
11
NYSERDA. http://www.nyserda.org/programs/Environment/EMEP/project/6681_25/0606%20Complete%20report-web.pdf (accessed April 6, 2011).
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A research project focusing on the analysis of the urban heat island effect in the greater Camden
region and on mitigation strategies for the urban heat island in the city of Camden and adjoining
communities. Mitigation strategies for the urban heat island effect included increased urban
vegetation and lighter-colored surfacing.
http://www.state.nj.us/dep/dsr/research/urbanheat.pdf
Benefits
o Reduces energy demand, thus cutting down utility costs
o Improves water quality, as high pavement temperatures heat stormwater runoff, which
can be harmful to aquatic life 13
o Improves air quality, as decreased energy demand results in decreased air pollution and
greenhouse gas emissions
o Improves aesthetics with an increase of trees and vegetation along with a reduction of
large paved spaces
o Improves health and comfort by reducing the heat island effect 14
Costs
The cost of any pavement application varies by region, the contractor, the time of year, materials,
accessibility of the site, local availability of materials, underlying soils, size of the project,
expected traffic, and the desired life of the pavement. Although the cost of these materials will
also vary based on the factors listed above, an estimated cost range for concrete at installation is
$0.30–$4.50/square foot, while asphalt costs $0.10–$1.50/square foot. However, concrete has an
estimated service of 15-35 years, while conventional asphalt's service life is about 7-20 years.15
High reflectance concrete pavers are comparable in price to darker colored concrete pavers.
Refer to the Tree Protection Placement strategy for cost information for shading.
There are also cost savings associated with mitigating the urban heat island effect. For every 1 °F
increase in air temperature, electricity demand for cooling grows by 1.5-2%.16 A 1.75% increase
in cooling demand over the American Society of Heating, Refrigerating and Air-Conditioning
Engineers (ASHRAE) base of 11.85 kwh/sf/yr equates to an additional .21 kwh/sf/yr. For every
1°F reduction in temperature achieved through heat island mitigation strategies, a building’s
12
NJ DEP. http://www.state.nj.us/dep/dsr/research/urbanheat.pdf (accessed April 6. 2011).
US EPA. “Heat Island Impacts.” http://www.epa.gov/heatisland/impacts/index.htm (accessed October 3, 2010).
14
NJ DEP. "1000 people in the United States die each year due to extreme heat,” September 2007.
http://www.state.nj.us/dep/opsc/docs/Heat_Island.pdf, pg. 1 (accessed August 2, 2010).
15
Reducing Urban Heat Islands: Compendium of Strategies: Cool Pavements," US EPA, accessed October 3, 2010,
http://www.epa.gov/heatisld/resources/pdf/CoolPavesCompendium.pdf.
16
US EPA. “Heat Island Impacts.” http://www.epa.gov/heatisland/impacts/index.htm (accessed August 2, 2010).
13
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cooling demands are decreased by .21 kwh/sf/yr. Densely populated urban areas are often 2 to 9
degrees Fahrenheit higher than surrounding suburban and undeveloped areas; this translates to an
increase in cooling demand ranging between 3.5-15.75%. 17 Project teams that want to use high
reflectance pavements as part of a heat island mitigation program may find it hard to estimate the
net costs or benefits based on temperature reduction alone. The greatest overall value may result
when multiple benefits, such as improved stormwater management and water quality, are
factored into the evaluation of a paving approach. For more in-depth cost-benefit analysis of
various urban heat island mitigation scenarios using high reflectance hardscape materials and
shading see Section 6 of the New York State Energy and Research Development Authority’s
Mitigating New York City's Heat Island with Urban Forestry, Living Roofs, and Light Surfaces.
Resources
US EPA Information on the Heat Island Effect
http://www.epa.gov/hiri/index.htm
US EPA Cool Pavements Strategy Guide
http://www.epa.gov/heatisld/resources/pdf/CoolPavesCompendium.pdf
NJ DEP Urban Heat Island and Climate Change: An Assessment of Interacting and Possible
Adaptations in the Camden, New Jersey Region
http://www.state.nj.us/dep/dsr/research/urbanheat.pdf
New York State Energy and Research Development Authority’s Mitigating New York City's
Heat Island with Urban Forestry, Living Roofs, and Light Surfaces
http://www.nyserda.org/programs/Environment/EMEP/project/6681_25/0606%20Complete%20report-web.pdf
Material Surface Specifications
http://www.concretethinker.org/solutions/Heat-Island-Reduction.aspx
17
Rutgers Center For Green Building. "CAP Project." http://rcgb.rutgers.edu/ (accessed August 9, 2010).