CWA 17890:2022

SLOVENSKI STANDARD
SIST CWA 17890:2022
01-november-2022
Navodilo za uporabo hladnih površin na ovoju stavb za ublažitev učinkov
mestnega toplotnega otoka
Guide to the implementation of cool surfaces for buildings’ envelope to mitigate the
Urban Heat Island effects
Leitfaden für die Implementierung kühler Oberflächen für die Gebäudehülle zur
Milderung des Urban Heat Island Effektes
Ta slovenski standard je istoveten z: CWA 17890:2022
ICS:
13.020.20 Okoljska ekonomija. Environmental economics.
Trajnostnost Sustainability
91.060.20 Strehe Roofs
SIST CWA 17890:2022 en,fr,de
2003-01.Slovenski inštitut za standardizacijo. Razmnoževanje celote ali delov tega standarda ni dovoljeno.

SIST CWA 17890:2022
SIST CWA 17890:2022
CEN
CWA 17890
WORKSHOP
September 2022
AGREEMENT
ICS 13.020.20; 91.060.20
English version
Guide to the implementation of cool surfaces for buildings'
envelope to mitigate the Urban Heat Island effects
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constitution of which is indicated in the foreword of this Workshop Agreement.

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Ref. No.:CWA 17890:2022 E
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Contents Page
European foreword . 3
Introduction . 6
1 Scope . 7
2 Normative references . 7
3 Terms and definitions . 8
4 EU strategic context and benefits to use cool materials . 11
4.1 Green deal . 11
4.2 Benefits and opportunities to use cool materials . 12
4.2.1 Conditions to integrate cool materials (when and for what kind of project) . 12
4.2.2 Benefits to use cool materials . 13
4.3 Limitations of the document . 18
5 Presentation of cool materials (specifics and potentials to mitigate the Urban Heat
Island effects) . 20
5.1 Identification of cool materials for a project . 20
5.1.1 Cool roof properties . 20
5.1.2 Residential buildings . 22
5.1.3 Non-Residential Buildings . 27
5.2 Cool roof materials . 36
5.3 Installation of cool material and implementation of cool roofs . 39
5.4 Ageing and durability of cool roofs properties . 40
5.5 Maintenance of cool roof materials . 42
5.6 Financial impacts along the value chain . 43
6 From building to district and district to territory implementation . 44
6.1 Performance at building level (inside and outside) of cool roofs . 44
6.2 Performance at the district level . 45
6.3 Performance at territory level . 45
Annex A (informative) Roadmap for standardization . 47

A.1 Status of CWA . 47
A.2 Benefits of standardization . 47
A.3 Check-list before moving toward standardization . 48
Bibliography . 50

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European foreword
This CEN Workshop Agreement (CWA 17890:2022) has been developed in accordance with the CEN-
CENELEC Guide 29 “CEN/CENELEC Workshop Agreements – A rapid prototyping to standardization” and
with the relevant provisions of CEN/CENELEC Internal Regulations - Part 2. It was approved by a
Workshop of representatives of interested parties on 2022-04-14, the constitution of which was
supported by CEN following the public call for participation made on 2021-07-06. However, this CEN
Workshop Agreement does not necessarily include all relevant stakeholders.
The final text of this CEN Workshop Agreement was provided to CEN for publication on 2022-06-29.
The following organizations and individuals developed and approved this CEN Workshop Agreement:
Bernard Gindroz - Chairperson
Giuliana BONVICINI Centro Ceramico
Jonathan BOUVIER LNE - Laboratoire national de métrologie et d'essais
Emmanuel BOZONNET Université de la Rochelle -
Nigel CHERRY BMI Group and CEN/TC 128
Massimo CUNEGATTI Soprema/ESWA
Mario CUNIAL Industrie Cotto Possagno S.p.A.
David DA SILVA ENGIE
Alexandre DHOTEL IKO SAS
Alfonsina DI FUSCO Confindustria ceremica
Elisa DI GIUSEPPE Università Politecnica delle Marche
Maxime DOYA TIPEE
Andréas DRECHSLER BMI Group
Marielle FASSIER CTMNC
Paris FOKAIDES Frederick University
Bernard GINDROZ Gindroz Bernard
Maria-José GONZALEZ Afnor
Louis GORINTIN ENGIE
Hans-Juergen HOFMANN Amberger Kaolinwerke Eduard Kick GmbH & Co.KG
Angela HULLIN Amberger Kaolinwerke Eduard Kick GmbH & Co.KG
Alain KOENEN LNE - Laboratoire national de métrologie et d'essais
Maria KOLOKOTRONI Brunel University London
Denia KOLOKOTSA ECRC/TUC
Evangelia KONTOU KALOMOIRI Thermacote Inc.
Martin LONDSCHIEN CEN/TC 254/SIKA
Yves MADEC BMI Group
Alberto MADELLA SITEB/Gruppo PRIMI and EWA
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Niklaus MARGADANT Eternit (Schweiz) AG
Milena MARTARELLI Università Politecnica delle Marche
Heinz MEIER SIKA Services AG/ECRC Certification Board
Stephan MERKLEIN BMI Group
Giovanni MURANO CTI
Christiana PANTELI Cleopa GMBH
Rémi PERRIN Soprema
Jonas PIGEON ENGIE
Gloria PIGNATTA University of New South Wales
Alkistis Plessis-MOUTAFIDOU CERIB
Sahar SAIAGH ENGIE
Agnese SALVATI Brunel University London
Lieven SANDERS Wienerberger
Mattheos SANTAMOURIS University of New South Wales
Hans – Peter SPRINGINSFELD WKO (Wirtschaftskammer Österreich)/ASI
Simona SCHRAMMEL Prospex Institute
Jouko VYORYKKA Dow Europe GmbH
Rupert WOLFFHARDT Holzforschung
Dimitrios XILAS ECRC/TUC
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Attention is drawn to the possibility that some elements of this document may be subject to patent rights.
CEN-CENELEC policy on patent rights is described in CEN-CENELEC Guide 8 “Guidelines for
Implementation of the Common IPR Policy on Patent”. CEN shall not be held responsible for identifying
any or all such patent rights.
Although the Workshop parties have made every effort to ensure the reliability and accuracy of technical
and non-technical descriptions, the Workshop is not able to guarantee, explicitly or implicitly, the
correctness of this document. Anyone who applies this CEN Workshop Agreement shall be aware that
neither the Workshop, nor CEN can be held liable for damages or losses of any kind whatsoever. The use
of this CEN Workshop Agreement does not relieve users of their responsibility for their own actions, and
they apply this document at their own risk. The CEN Workshop Agreement should not be construed as
legal advice authoritatively endorsed by CEN/CENELEC.
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Introduction
By 2050, according to UN projections, the world population is expected to reach ten billion people. Today
half of the population is living in cities and projections show more than 80 % by 2050. Cities are where
80 % of global GDP is produced, but they are also where 70 % of the energy is consumed and 75 % of
waste and Greenhouse Gas (GHG) emitted.
Abating GHG emissions and increasing energy efficiency are at the heart of our European strategy and
regulatory framework, with a focus on cities and built areas that offer a high potential for improvement
and for meeting the EU Green Deal objectives. Urban Heat Island effect is one important topic both to
mitigate climate change and to adapt. Minimizing these Urban Overheating effects contributes to
reducing energy consumption by lowering energy demand for cooling and ventilation during hot periods,
and thus the related GHG emissions , as well as to bringing better comfort to citizens.
This document presents guidelines about why, when, and how to consider mitigation of Urban Heat
Island effects with cool roofs and cool materials, as well as reference information about characteristic
parameters and how to select appropriate materials.
Cool materials are especially of high importance for new buildings and constructions but also for
retrofitting of existing built infrastructures. A cool material is characterised by higher solar reflectance
in comparison to conventional roof materials displaying the same colour and high infrared emittance
values. Cool roofing products can be applied to all types of roofs including those of residential buildings,
apartment blocks, industrial and commercial buildings, hospitals, and offices.
The benefits are direct and numerous, such as reducing the cooling energy consumption and even leading
to avoiding the installation of air conditioning, by keeping temperature indexes lower around Renewable
Energy Systems (i.e. Photovoltaic) and thus maintaining higher efficiency and longer life of these pieces
of equipment, by extending the life of the roofing materials, and of course by keeping the surrounding
temperature lower, which impacts the quality of life and health.
This document will also contribute to setting common elements of language (terms and definitions) and
raising awareness among decision-makers, urban planners and constructors, both private and public, and
among investment institutions and investors, about the benefit of cool materials, as well as guiding them
towards the selection of appropriate solutions against Urban Heat Island effect with immediate and long-
term multi-benefits.
Whilst the guide focuses on cool materials for roofs it is also relevant to other parts of the building
envelope, other construction and built infrastructures, including roads and pavements, by aligning terms
and definitions as well as considerations about characteristics of cool materials.

This document is not intended to address consideration about carbon footprint of materials.
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1 Scope
The document provides the terminology relating to cool materials and a guide to the implementation of
cool surfaces for building envelopes to mitigate the urban overheating effects. It concentrates on the
application to roofs.
The document will focus on urban areas for local authorities and building/construction owners.
The users of CWA 17890:2022 will be local authorities, urban planners for cities including construction,
infrastructures and landscape architects.
In addition, the terminology and characteristics of cool materials will serve as a reference for other
applications where the use of cool materials will have a significant contribution to adaptation to climate
change as well as quality of life, such as for roads and pavements.
Whilst reflective surfaces can be very beneficial, they are not appropriate or effective in all climates for
all buildings or building constructions and some guidance is provided.
2 Normative references
The following documents are referred to in the text in such a way that some or all of their content
constitutes requirements of this document. For dated references, only the edition cited applies. For
undated references, the latest edition of the referenced document (including any amendments) applies.
EN 490, Concrete roofing tiles and fittings for roof covering and wall cladding
EN 492, Fibre cement slates and their fittings for roofing
EN 494, Fibre-cement profiled sheets and fittings — Product specification and test methods
EN 501, Roofing products from metal sheet — Specification for fully supported roofing products of zinc sheet
EN 502, Roofing products from metal sheet — Specification for fully supported roofing products of stainless
steel
EN 504, Roofing products from metal sheet — Specification for fully supported roofing products of copper
sheet
EN 505, Roofing products from metal sheet —Specification for fully supported roofing products of steel sheet
EN 506, Roofing products of metal sheet — Specification for self-supporting products of copper or zinc sheet
EN 507, Roofing products from metal sheet — Specification for fully supported roofing products of
aluminium sheet
EN 508, Roofing and cladding products of metal sheet — Specification for self-supporting products of steel,
aluminium or stainless steel sheet
EN 534, Corrugated bitumen sheets — Product specification and test methods
EN 544, Bitumen shingles with mineral and/or synthetic reinforcements
EN 1013, Light transmitting single skin profiled plastic sheets for internal and external roofs, walls and
ceilings — Requirements and test methods
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EN 14509, Self-supporting double skin metal faced insulating panels — Factory made products —
Specifications
EN 12326-1, Slate and stone for discontinuous roofing and external cladding
EN 1304, Clay roofing tiles and fittings
EN 13956, Flexible sheet for waterproofing — Plastic and rubber sheets for roof waterproofing —
Definitions and characteristics
EN 13707, Flexible sheets for waterproofing — Reinforced bitumen sheets for roof waterproofing —
Definitions and characteristics
EN 15976:2019, Flexible sheets for waterproofing — Determination of emissivity
EN 17190, Flexible sheets for waterproofing — Solar Reflectance Index
ISO 9346, Hygrothermal performance of buildings and building materials — Physical quantities for mass
transfer — Vocabulary
ISO 9050, Glass in building — Determination of light transmittance, solar direct transmittance, total solar
energy transmittance, ultraviolet transmittance and related glazing factors
ASTM E903, Standard Test Method for Solar Absorptance, Reflectance, and Transmittance of Materials
Using Integrating Spheres
ASTM D7897-18, Standard Practice for Laboratory Soiling and Weathering of Roofing Materials to
Simulate Effects of Natural Exposure on Solar Reflectance and Thermal Emittance
ASTM E1980-11, Standard Practice for Calculating Solar Reflectance Index of Horizontal and Low-Sloped
Opaque Surfaces
ISO 14082, Radiative Forcing Management— Guidance for the quantification and reporting of radiative
forcing-based climate footprints and mitigation efforts
ISO 6707-3:2017, Buildings and civil engineering works — Vocabulary — Part 3: Sustainability terms
ISO 16474-3:2021, Paints and varnishes — Methods of exposure to laboratory light sources — Part 3:
Fluorescent UV lamps
ISO 16378:2013, Space systems — Measurements of thermo-optical properties of thermal control materials
ISO 22969:2019, Peintures et vernis — Détermination du facteur de réflexion solaire
ISO 9488:1999, Solar energy — Vocabulary
ISO 9229, Thermal insulation — Vocabulary
3 Terms and definitions
For the purposes of this document, the following terms and definitions apply.
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3.1
cool property
property of a material or product of reflecting solar heat by high solar reflectivity (SR) and by high
infrared emittance (IE) and thus limiting temperature increase
3.2
cool materials
cool materials are exposed products with specific properties concerning solar and infrared reflectivity
and emittance
Note 1 to entry: Only passive cool materials are considered in this document.
3.3
cool roofs
roofing assemblies where the exterior surface has high solar reflectance and high thermal emittance
3.4
heat island effect
tendency of an urban area to be warmer than its non-urban surroundings
Note 1 to entry: For further details see ISO 6707-3:2017.
3.5
infrared emittance
emittance in the infrared range at least from 4 μm to 40 μm (with the full thermal range comprised
between 4 and 80 μm)
Note 1 to entry: For further details see ISO 16378:2013.
3.6
solar radiation
wavelength range, typical values, and power should be specified (to explain that between 2 500 nm and
2 800 nm there’s not much solar power so the measurements with UV-Vis-NIR spectrophotometers are
OK
3.7
infrared (or thermal) radiation
wavelength range and power should be specified
3.8
solar reflectance (SR), also known as albedo
ratio of the reflected global radiant flux to the global solar radiation flux incident on surface in the solar
wavelength range (250 – 2 800 nm)
Note 1 to entry: For further details see ISO 22969:2019.
3.9
solar reflectivity
ratio of the reflected solar irradiation from the surface to the solar irradiation incident on that surface
Note 1 to entry: For further details see: EN 17190.
The terms solar reflectivity and solar reflectance have similar definitions and are commonly used by the
construction sector. For ease of reading, the term solar reflectivity will be preferred in this document.
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3.10
thermal emittance
the thermal emittance of a material (usually written ε) is the ratio (proportion) of the heat energy
radiated by a surface relative to the heat energy radiated by a blackbody at the same temperature; it is a
measure of a material's ability to radiate heat
Note 1 to entry: Further details see EN 15976:2019.
3.11
bituminous roofing sheet
factory made bitumen sheet including any reinforcements, carriers, facings, surface texture and/or
backing
Note 1 to entry: The sheet is part of the roof waterproofing system, which ensures the watertightness. Within the
roofing industry it is also called a membrane. An exposed sheet is the roof covering which can be a single sheet
(single ply system) or a build-up of several sheets. These sheets can be mechanically fixed or adhered e.g. torched.
The sheet is built up with inner layers (e.g. reinforcements .). Both sides of the sheets typically consist of
waterproofing modified bitumen and with additional backing/adhesive or lacquers/surface finish etc. Further
details see EN 13707.
3.12
synthetic roofing sheet
factory made plastic and rubber waterproofing sheet, which can be rolled up or folded for easy transport
to the site
Note 1 to entry: The sheet is part of the roof waterproofing system, which ensures the watertightness. Within the
roofing industry it is also called a membrane. An exposed sheet is the roof covering. This is typically a single sheet
(single ply system). These sheets can be mechanically fixed or adhered e.g. glued, self-adhesive etc. The sheet can
be built-up with or without inner layers (e.g. reinforcements, carriers…). Both sides of the sheets consist of
waterproofing polymer/elastomer and with additional backing/adhesive or lacquers/surface finish etc.
Note 2 to entry: Further details see EN 13956.
3.13
liquid-applied roof waterproofing kits (LARWK)
the Liquid Applied Roof Waterproofing Kits (LARWK) consist of a material or a combination of materials,
where at least the main component is liquid form, applied on roofs, terraces or balconies.
In addition to providing a waterproofing layer kit with cool properties act as a reflective layer
Note 1 to entry: Within the roofing industry these systems are also referred to as LAM. For further details see
harmonized EAD 030350-00-0402.
3.14
roof coatings
liquid coatings applied on roofs
Note 1 to entry: These coatings do not provide a waterproofing function. For further details see harmonized
EAD 030350-00-0402.
3.15
tiles and slates
tiles and slates are usually rectangular, flat or profiled elements, which are discontinuously laid as part
of a system to form a weather-tight, air permeable covering on pitched roofs and walls. They are made
from durable, hardwearing material such as ceramic (fired clay), concrete, stone, slate, fibre cement,
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durable timber, metal, or even glass and are available in a variety of colours and finishes. They may be
coated or uncoated.
Note 1 to entry: For further details see EN 1304, EN 490, EN 12326-1 and EN 492.
3.16
shingles
shingles made of bitumen or wood and are fixed in a discontinuous overlapping manner onto a roof
substrate, to ensure weather-tightness. Bitumen shingles are factory made and may be multi-layered,
with or without reinforcement and surface layers. Wood shingles are factory cut, commonly from red
Cedar wood
Note 1 to entry: For further details see EN 544.
3.17
fully supported metal sheet
fully supported metal sheets are typically of zinc, steel, stainless steel or aluminium. The sheets may be
coated and available in a variety of colours and finishes and they form a substantially airtight roof
covering. Included are prefabricated or semi-formed products (for example metal tiles) and strip or coil
sheeting (for example standing seam construction)
Note 1 to entry: For further details see: EN 501, EN 502, EN 504, EN 505 and EN 507.
3.18
self-supporting profiled sheeting
self-supporting profiled sheets, typically of copper, zinc, aluminium, steel, fibre cement, bitumen or rigid
plastic. Available in a range of profiles, including sinusoidal, trapezoidal and pressed tile arrays, giving a
substantially airtight roof covering, available in a range of colours and finishes.
Note 1 to entry: For further details see: EN 506, EN 508, EN 494, EN 534 and EN 1013.
3.19
double skin metal faced insulating panels
factory made, self-supporting, double skin metal faced insulating sandwich panels, for discontinuous
laying of roofs and walls, giving essentially an airtight finish. They are available in a variety of colours and
finishes.
Note 1 to entry: The insulating material forming the core is generally of rigid polyurethane, expanded polystyrene,
extruded polystyrene foam, phenolic foam, cellular glass or mineral wool. For further details see: EN 14509.
3.20
radiative forcing
difference between the energy from the sun absorbed by the earth and the energy radiated back into
space. When incoming energy exceeds energy outgoing, the earth’s atmosphere will warm, and global
temperatures rise (from ISO 14082)
4 EU strategic context and benefits to use cool materials
4.1 Green deal
The European Green Deal sets out one of the most ambitious road maps for an entire continent, outlining
a series of key initiatives to bring greenhouse gas emissions to net zero by 2050.
The European Green Deal supports and promotes a climate-neutral context, with a sustainable economy
by deeply transforming sectors like transport, buildings and construction, manufacturing and energy, as
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well as through policy and legislative proposals – a key part of the Green Deal -, as a major driver to
decarbonize our cities and buildings – ensuring it benefits citizens across the EU while keeping housing
affordable.
Cities are, indeed, centres of innovation and growth, and the engines of European economic development.
They host around 75 % of the population and use about 80 % of the energy produced in Europe, with an
expected increasing trend. But cities are also major contributors to climate change, with significant
greenhouse gas emissions. In addition, cities are especially vulnerable to the impacts of climate change:
extreme heat waves, flooding, water scarcity and droughts can impact health, infrastructure, local
economies, and quality of life of city habitants. Over the past decades, Europe has seen a 60% increase in
extreme weather patterns [1].
Climate change mitigation and adaptation is among the top priorities of the Green Deal, and Cities and
built areas are at the heart of this priority with a high potential in meeting the EU Green Deal objectives.
The European Union Climate Adaptation Strategy [2], adopted on 24 February 2021, sets out how the
European Union can adapt to the unavoidable impacts of climate change and become climate resilient
by 2050.
The capacity to prepare for and respond to climate impacts at the local level is crucial. Urban authorities
have a catalyst role in getting together all actors to co-develop policies and strategies for territorial
development. Urban authorities should play a leadership role to create policies responding to all these
needs.
Indeed, vulnerability to the impact of climate change is often a result of inadequate planning or building
design. For example, the covering of soil for housing, roads and car parks (soil sealing) increases the
absorption of energy from the sun and leads to higher urban temperatures - the so-called “urban heat
island effect”. At the same time, natural drainage is decreased, which, particularly during heavy rains, can
lead to urban floods.
Through appropriate and resilient urban design, the impacts of climate change can be reduced, for
instance using green infrastructures such as forests, parks, wetlands, cool materials for walls, roofs and
pavement. Such approaches also lead to significant co-benefits, including improved air quality, energy
savings, reduce radiative forcing, support for biodiversity and enhanced quality of life, as well as
employment opportunities.
Urban Heat Island effect is thus a major topic, where an appropriate urban design/planning with
consideration of cool materials contributes in a significant manner to meeting climate change and energy
objectives while enhancing the quality of life of all citizens.
Cities have also the opportunity to reduce climate change. Indeed, increasing the albedo of urban and
human settlement areas can in turn decrease atmospheric temperature and could potentially offset some
of the anticipated temperature increase caused by global warming.
As such, this may be an effective strategy to complement climate mitigation efforts as a way of further
slowing the rate of global temperature increase in response to continued greenhouse gas emissions.
If cities in Europe are starting to develop and implement adaptation strategies or action plans, mainly
motivated by experiences of extreme weather disruptions, there is still a lack of consideration of the
importance of preparing for climate change, a lack of communication about good practices and
experiences, as well as of support and guidance documents. Awareness-raising campaign and
communication about the maturity and benefits of cool materials on the Urban Heat Island effect need to
be intensified and guidance documents to be developed.
4.2 Benefits and opportunities to use cool materials
4.2.1 Conditions to integrate cool materials (when and for what kind of project)
Based on the improvement or the renovation a surface needs, there are several different cool materials
that can be used. Cool materials are known for their wide variety and versatility.
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On existing surfaces for instance, for retrofitting applications all types of cool material could be applied,
provided that they are compatible with the existing materials, meaning that there shouldn’t be any risk
of unexpected degradation of their main functionalities over time, and neither of the cool material in
contact with (e.g. staining or soiling). Moreover, the existing surfaces should have received proper
preparation by cleaning, application of a primer or a physical barrier preserving from any interaction.
On horizontal or with low slope roofs, which need revamping, the application of any liquid-type
membrane cool material would be ideal. Also, such a roof can be retrofitted by the installation of
single-ply or bitumen membranes. In case there is a pre-existing applied cool material, that has lost some
of its radiative properties from weathering, or a simple waterproofing material (approx. 5 to 10 years of
initial application), but they maintain their mechanical properties, the roof can be recovered with liquid
materials to renew or add cool properties.
On the other hand, pitched roof elements can be coated with liquid membranes or coatings of a
corresponding colour to add cool properties to the existing structure or be replaced at the end of their
life circle by tiles or shingles with cool properties.
Newly constructed buildings, depending on the design and the requirements, can be protected from solar
radiation by the application of any type of cool material, besides the common insulation usually
integrated into the design.
4.2.2 Benefits to use cool materials
4.2.2.1 Environmental benefits
4.2.2.1.1 Reduce the energy consumption
European Union targets the protection and preservation of the environment by developing short-term
and long-term strategies. Cool materials make a great contribution to achieving these targets.
The application of cool materials on a structure can reduce the roof/surface temperature by up to 27 %.
This percentage is translated to lower indoor temperatures on the last floor of the building and
consequently less energy demand for maintaining the interior comfort conditions.
4.2.2.1.2 Mitigate the Urban Heat Island effect
Building surfaces tend to absorb a significant proportion of the incident solar radiation due to their low
solar reflectance. Many materials have albedo in the range 0,1 to 0,3. This is one of the contributing factors
to the Urban Heat Island effect; it is important and has been documented. Indeed, the more is the
absorbed quote of thermal energy the higher is the increase of i) the material’s surface temperature, ii)
the corresponding near-surface air temperature, iii) the thermal energy released in the environment as
heat.
Cool materials can be employed in the building envelope as a cost-effective and passive strategy to
counteract the Urban Heat Island phenomena thanks to their high thermal emittance and high solar
reflectance, particularly, within the visible and IR light spectrum. These two optical characteristics allow
the material to reflect the solar radiation by a great percentage, limiting the portion that is absorbed by
the building elements and then released into the urban environment as heat.
4.2.2.1.3 Reduce power plant emissions, including carbon dioxide, sulphur dioxide, nitrous
oxides, and mercury, by reducing cooling energy use in buildings
While there are lower environmental and indoor temperatures, the needs for air conditioning will be
reduced. This reduction, eventually, will lead to lower energy productions from power plants and as a
result, the levels of hazardous emitted gases will progressively be reduced (and the greenhouse effect
development will be delayed) [3].
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4.2.2.1.4 Reduce Radiative forcing and Global warming impact
Urban Heat Island effect contributes to global warming. However, albedo control strategies and cool roof
implementation could mitigate this trend in a significant manner. Studies and meta-studies proposed to
value between 1,6 to 8 kgCO eq/m [4] for an increase of 1 % of the surface albedo.
With the acceleration of urbanisation, the use of cool materials could significantly reduce the Urban Heat
Island effect at a reasonable cost. This requires consideration from city planners and policy makers for
the large-scale deployment of cooling materials.
A recommendation is to allocate a 5 kgCO eq/m for each % of the albedo or reflective index increase.
4.2.2.2 Social benefits
4.2.2.2.1 Primary benefits
Urban Overheating has a serious impact on the cooling energy consumption of buildings and cities,
increases the peak electricity demand, and worsens the levels of indoor and outdoor thermal comfort
while increases the concentration of harmful pollutants like the ground level ozone. In parallel, it affects
the vulnerability and survivability levels of the low-income population, rises the levels of heat-related
mortality and morbidity and increases the ecological footprint of cities [5]. Research has shown that
urban overheating causes an additional cooling energy penalty close to 0,7 kWh per square meter of city
and degree of temperature increase, while on average the additional peak electricity demand is estimated
close to 21 (± 10,4) W per degree of temperature increase and per person [6] [7].
Exposure to high ambient urban temperatures is a serious health hazard. As the human thermoregulatory
system cannot offset extreme heat, heat-related morbidity and mortality increase significantly [8]. It is
well proven that because of the serious overheating and the increased urban deprivation and
vulnerability levels the health risk in cities is considerably higher than in rural environments [9].
Systematic meta-analysis research on the impact of higher urban temperatures on heat-related mortality
showed that the population living in warmer urban precincts present almost 6 % higher mortality risk
compared to the population living in cooler neighbourhoods [10].
Urban overheating increases considerably the concentration of harmful pollutants like the ground level
ozone and particulate matter [11]. The association between Urban Heat Island and the concentration of
the ground level ozone is well documented and urban overheating seems to be the main cause of ozone
concentrations increase above the accepted thresholds. The forecasted concentration of the ground level
ozone under future climate change conditions are is quite alarming and may be a serious threat for human
life.
Urban Heat Island has a serious impact on the vulnerable and low-income population [12]. As vulnerable
population usually lives in deprived urban zones presenting a significant overheating and in low-quality
houses [13], households are seriously exposed to higher indoor and outdoor ambient temperatures and
pollution levels, while they have to consume more energy than the average to satisfy their energy
needs [14].
Improving indoor comfort for spaces that are not air conditioned.
Cool materials can improve indoor comfort thanks to indoor temperature decrease. By reducing the
temperature, the use of cool materials can reduce the effect of heat on health. Facing severe and long heat
peaks as a consequence of climate change, cool materials can thus contribute to adapt to climate change,
by reducing direct negative impacts from such extreme heat patterns on the comfort of people.
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The application of cool materials can improve the occupants’ thermal comfort. In retrofit actions or new
building designs, the implementation of cool roof materials can be seen as a passive cooling solution to
avoid the installation of a cooling system (depending on the geographical area) by maintaining a correct
comfort level .
Lower peak electricity demand, which can help prevent power outages.
Cool materials, because of their nature, prevent the envelope of a building from becoming overheated.
In order to perform EN ISO 9869 (Greece-Mediterranean Climate conditions, performed by CRES) and
compare the heat flux between a conventional roof (TR2) and an identical one (TR1), with cool colour
applied on the roof, temperature sensors were placed on the roof and the ceiling and the fluctuation of
temperature was recorded. The indoor temperature was set on 26 °C and was controlled by A/C units.
The measurements showed that for the room with the conventional roof, it was harder for the A/C unit
to maintain a constant temperature range and the A/C units worked for longer periods. On the contrary,
the room with the cool-coloured roof, kept a stable temperature range indoors. Moreover, the ceiling
temperature of the conventional roof showed more fluctuations than the cool-coloured one, which also
explains the difference in the behaviour of the A/C of the two test rooms (see Figure 1).
This implies that with the application of cool materials, the building has lower peak electricity demands,
which can help to prevent power outages.
4.2.2.2.2 Secondary benefits
Photovoltaic panel performance
Photovoltaic (PV) panels can convert up to 20 % of the solar radiation to electricity, this value is called
the PV module efficiency. The remaining percentage is converted to internal heat, which results in lower
electricity production [15]. Moreover, the photovoltaic panels’ temperature rises because of the heat
transferred from the roof they are placed on and the Urban Heat Island effect. Applied cool material can
reduce the roof temperature and decrease the Urban Heat Island effect, which could be really beneficial
for the PV performance.
Several standards cover the indoor temperature conditions:
— EN 16798-1, Indoor environmental input parameters for design and assessment of energy performance of buildings
addressing indoor air quality, thermal environment, lighting and acoustics
— ISO 15265, Risk assessment strategy for the prevention of stress or discomfort in thermal working conditions
— ISO 7730, Ergonomics of the thermal environment — Analytical determination and interpretation of thermal
comfort using calculation of the PMV and PPD indices and local thermal comfort criteria
— ISO 7243, Assessment of heat stress using the WBGT (wet bulb globe temperature) index
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Key
X Time (date / hour)
Y Temperature (C°)
Ceiling TR1
Ceiling TR2
Tair-TR1
Tair-TR2
Figure 1 — In-situ temperature measurements for evaluation of the results of EN ISO 9869
“Thermal insulation — Building elements — In-situ measurement of thermal resistance and
thermal transmittance”, Location: Greece Date July 2015
The background of the last quote is the dependence of PV panel efficiency on temperature. In terms of
temperature, when all other parameters are constant, the higher the temperature, the lower the voltage.
This manifests in a loss of power. On the other hand, if the temperature decreases compared to the
original conditions, the power of the PV panel will show an increase in voltage and power. Therefore, a
cool roof under a PV panel can contribute to a slightly higher PV panel efficiency.
A practical example: the temperature coefficient of an average crystalline PV panel is -0,4 % (negative
value). If it were possible to lower the operating temperature of the PV module by e.g. 3 °C using a cool
roof, this would result in a 1,2% higher relative PV panel efficiency than the temperature without a cool
roof.
Lower intake temperature will decrease consumption for ventilation and A/C
Any reduction in air conditioning energy consumption or efficient energy utilization will offer significant
savings in total building energy consumption and carbon emissions. In addition, it contributes to
maintaining an ideal comfort inside the building and guaranteeing the maximum goals of health and
productivity of the occupants.
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Increase the value of the asset
European Union enforced the categorization of building energy performance in order to distinguish the
buildings based on their energy demands. This classification guides future owners to consider buying
buildings with lower energy consumption, as they are willing to spend on a property at a higher initial
price, with lower maintenance fees (energy bills).
Implementing cool materials on buildings and construction infrastructures, both new ones and
retrofitted ones, will be of benefit in terms of:
— energy savings, thanks to a mitigated local temperature that will positively impact intake air
temperature of building ventilation and air conditioning energy consumption;
— extension of life duration of materials (due to a reduced range of temperatures) and thus with
positive resource efficiency and circular economy-related impacts;
— ensuring better environmental temperature conditions for the operating condition of solar
equipment and thus higher efficiency.
Cool roof materials can be thus considered a real benefit in the real estate market.
In addition to benefit at the building/construction infrastructure level and especially in reducing energy
consumption, contributing to mitigation of climate change and resources efficiency, generalizing the
implementation of cool materials at the district level and even more at the city level, will lower the local
felt temperature which will directly impact the quality of life and health critical situations, especially
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