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THEORY AND CASE STUDIES
Cool roofs impact into building’s thermal
conditions:
Workshop: “National Energy Security – Future prospect” 13 December 2012 KSIR Kuwait
Prokopis Perdikis U.G.I CYPRUS/ABOLIN CO GREECE
Communication Committee: European Cool Roofs Council
Kuwait: Energy Consumption #1
Residential buildings consume about 60% of national power.
(DC Consortium Report 2009)
Kuwait District Cooling Summit - 2011
Prof. A. Ben-Nakhi
Workshop: “National Energy Security – Future prospect” 13 December 2012 KSIR Kuwait
Kuwait: Energy Consumption #2
Building sectors are the major consumers of electrical energy with a
share of over 75%; 0ver 65% goes for air- conditioning.
27840 GWh
9744 GWh
7424 GWh
Residential
Sector 60%
Commercial
sectors 16%
Other
sectors 21%
Industrial
sector 3%
Annual electrical consumption in GWh per sector*
1392 GWh
*MEW (2007)
Total: 46400 GWh
Saad Al Jandal, PhD. KISR / EUD- BET
October, 2010 GBC Forum, Doha
Workshop: “National Energy Security – Future prospect” 13 December 2012 KSIR Kuwait
Kuwait: Energy Consumption #3
Demand of peak power increases @ 5.6% and annual electricity
increases @ 5.3%
6160
6450
6750
7250
7480
7750
8400
8900
31.6 32.3
34.3
36.4
38.6
41.3
43.7
46.4
30
35
40
45
50
5500
6500
7500
8500
9500
1999 2000 2001 2002 2003 2004 2005 2006
Pe
ak P
ow
er
De
man
d (
MW
) Peak power
Yearly Electricity Consumption
Ye
arly Ele
ctricity Co
nsu
mp
tion
(MW
h/y)*
10
Saad Al Jandal, PhD.
KISR / EUD- BET
October, 2010 GBC
Forum, Doha
Workshop: “National Energy Security – Future prospect” 13 December 2012 KSIR Kuwait
Kuwait: Energy Consumption #4
Ali Ebraheem Hajiah
Building Energy
Technologies Dept. October 2010 Manama
Workshop: “National Energy Security – Future prospect” 13 December 2012 KSIR Kuwait
Kuwait: Energy Code 2010 2nd Edition*
*MINISTRY OF ELECTRICITY AND WATER
Energy Conservation Program
CODE OF PRACTICE
MEW/R-6/2010
Second Edition 2010
7.2 Building envelope construction
7.2.1 Walls and roofs
Minimum requirements for wall and roof insulation: Table 7 provides a list of the
maximum allowable overall heat transfer coefficients (U) for variety of wall and
roof constructions and their external color.
Table 7. Maximum Allowable U-values for Different Types of Walls and Roofs.
Description Wall Roof
Heavy construction, medium-light external color 0.568 (0.100) 0.397 (0.070)
Heavy construction, dark external color 0.426 (0.075) 0.256 (0.045)
Medium construction, medium-light external color 0.483 (0.085) 0.341 (0.060)
Medium construction, dark external color 0.426 (0.075) 0.199 (0.035)
Light construction, medium-light external color 0.426 (0.075) 0.284 (0.050)
Light construction, dark external color 0.369 (0.065) 0.170 (0.030)
What About
Cool Roofs ? Workshop: “National Energy Security – Future prospect” 13 December 2012 KSIR Kuwait
What about Cool Roofs ?
The creation of surfaces of high reflectivity and emissivity in the urban
environment constitutes an easily applicable and economic passive
cooling method that contributes in the reduction of urban temperatures.
The creation of such surfaces can be achieved with the use of “cool
materials” which are characterized from :
High solar reflectance
High infrared emittance
Workshop: “National Energy Security – Future prospect” 13 December 2012 KSIR Kuwait
How Cool Roofs Work?
Sourc
e:h
ttp:/
/heatisla
nd.lbl.gov/
incident
sunlight
reflected
sunlight
net emitted
thermal
radiation
opaque surface at temperature T
convection
conduction
• High solar reflectance (Rsol) lowers solar heat gain (0.3 - 2.5 µm)
• High thermal emittance (E) enhances thermal radiative cooling (4 - 80 µm)
high solar reflectance + high thermal emittance = low surface temperature
Workshop: “National Energy Security – Future prospect” 13 December 2012 KSIR Kuwait
Five case studies were implemented, within the framework of the Intelligent
Energy Europe (IEE) program SAVE 2007 "Promotion of Cool Roofs in EU" to
demonstrate cool roof capabilities in real buildings, in terms of improving the
thermal conditions in non-air conditioned buildings and reducing the energy
consumption in air-conditioned buildings.
The buildings were selected to achieve maximum geographical and building
typology coverage aiming to promote the benefits coming from this technique with
reference to cooling energy demand and peak savings all around the EU.
The corresponding activities were performed at two levels:
• experimental monitoring in real buildings treated with Cool Roof
techniques (hardware task)
• numerical analysis of the same buildings with a number of variants
(software analysis)
The findings of the case studies show 10-40% energy savings depending on the
climatic conditions. More info about the case studies : www.coolroofs-eu.eu.
Here we present 3 of them implemented in France, Greece and UK.
Carrefour Italy
Cool Roofs – European Case Studies
Workshop: “National Energy Security – Future prospect” 13 December 2012 KSIR Kuwait
Cool Roofs –Case Study FRANCE #1
Le Parvis: Collective Dwellings, Poitiers -Non A/C Building
Fig 2. Duplex flat chosen for the case study Fig1 Collective dwellings in Poitiers
The roof slope (11.5%) faces east and is not shaded by adjacent dwellings. The roof was
constructed with steel cladding, insulated with a 100mm mineral wool and sealed with
asphalt. This Cool Roof case study focuses on the dwellings under the roof which are all
duplex apartments of approximately 100m2 each (Fig.2). The walls are insulated with
100mm polystyrene and the windows are made of PVC with double glazing. The attic above
each duplex apartment is also insulated with 200mm mineral wool. The studied building
has no cooling system for summertime. So the impact of the Cool Roof’s technology
application is evaluated in terms of indoor temperature difference for the studied duplex flat
compared to the adjacent duplex flats.
Cool Roofs Project
Workshop: “National Energy Security – Future prospect” 13 December 2012 KSIR Kuwait
Cool Roofs –Case Study FRANCE #2
Le Parvis: Collective Dwellings, Poitiers -Non A/C Building
Cool Roof technology
The roof was coated with a white cool paint at the end of July 2009. The cool paint’s
solar reflectance was 0.88 and the infrared emittance 0.90.
The temperatures evolved with the same daily variation, with high maximum temperatures
differences. During the night, the minimum temperatures were very similar. The predicted
mean surface temperature for the cool painted surface is 21.6°C compared to 34.1°C for
the default roof surface for the summer period. The difference in the indoor operative
temperature is less visible due to the good insulation of the attic: the mean operative
temperature in the room decreased from 24.9°C to 24.2°C. In this case, with a very well
insulated roof, there is a predicted gain of approximately 1°C on the maximum operative
temperature, from 30.2°C to 29.3°C.
Cool Roofs Project
Workshop: “National Energy Security – Future prospect” 13 December 2012 KSIR Kuwait
Cool Roofs –Case Study GREECE #1
School building in Kaisariani, Athens, Greece Non Insulated No A/C
Figure . School building in Kaisariani, Athens, Greece
Figure . The spectral reflectance of the roof surface before (grey concrete, SR=0.2)
and after the Cool Roof application (ABOLIN Cool Roof barrier, SR=0.89)
This case study involves a 410m2 flat roof school building located at the Municipality of
Kaisariani, a densely built urban area near the centre of Athens (Fig.5). It is a rectangular,
two floor building with a school courtyard and was constructed in 1980. The load bearing
structure of the building is made of reinforced concrete and an overall concrete masonry
construction which is not insulated. The school building is occupied by 120 children and 15
adults (the school staff) and is non-cooled and naturally ventilated. There is an installed
heating system using natural gas. Walls: U value = 2.846 W/m2K , Roof: U value = 1.971
W/m2K , Windows : U value = 2.95 W/m2K .
Cool Roofs Project
Workshop: “National Energy Security – Future prospect” 13 December 2012 KSIR Kuwait
Cool Roofs –Case Study GREECE #2
School building in Kaisariani, Athens, Greece Non Insulated No A/C
Cool Roof technology
The initial roof surface was covered by cement and gravel having a solar reflectance of 0.2.
The cool material used is a white elastomeric coating (Cool Roof Barrier by ABOLIN) with a
solar reflectance of 0.89, infrared emittance 0.89 and SRI 113.
Impact on air temperature
Additionally, a variant of the model has been studied considering the building with
increased insulation. External insulation of 5cm has been added to the walls resulting in a
U-value of 0.417 W/m2K and 7cm on the roof resulting in a U-value of 0.302 W/m2K.
The maximum, minimum and average air temperatures in both cases (non insulated and
insulated) and for the cooling and the heating period are presented.
Impact on energy loads
In order to estimate the impact of the cool roof on energy loads it has been assumed
that the building is cooled during the summer and heated during the winter. Set point for
cooling is set to 26C and for heating is set to 20C. The building is considered to be in use
all year round. Figure 5 displays the absolute and percentage variation of the annual
heating and cooling loads for all the simulation scenarios that have been carried out.
Cool Roofs Project
Workshop: “National Energy Security – Future prospect” 13 December 2012 KSIR Kuwait
Cool Roofs –Case Study GREECE #3
School building in Kaisariani, Athens, Greece Non Insulated No A/C
Air Temperature, Cooling and Heating Loads before and after the cool roof application for the
zone adjacent to the roof
Min [oC] Max [oC] Average [oC]
Cooling period (May – September)
Uninsulated building 0.8 2.8 1.8
Insulated building 0.3 0.7 0.5
Heating period (October – April)
Uninsulated building 0.9 1.2 0.9
Insulated building 0.2 2 0.4
Annual Cooling Loads (kWh/m2) Annual Heating Loads (kWh/m2)
Uninsulated building -40% +10%
Insulated building -35% + 4%
Cool Roofs Project
Workshop: “National Energy Security – Future prospect” 13 December 2012 KSIR Kuwait
Cool Roofs –Case Study UK #1
Office at Brunel University, Uxbridge, West London, UK, Colored Cool Roof
Cool Roof Light Red Brown CB 012
The office is located (moderate climate of South East England) on the top floor (flat roof) of a
four storey building of which the top floor was constructed in 1995. The total floor area is
137m2 of which the open office area accounts for 97.6m2. The floor to ceiling height is
approximately 2.65m. The open office area has 6 window openings while each room has one
opening. Each of these openings is approximately 0.9m x 1.5m. The roof is made of 0.15 m
thick concrete slab with a 0.04 m insulation layer on top of the slab and is covered with a layer
of water proofing material (asphalt). Roof: U Value 0.6 (W/m2 K). The external wall structure
is made of 0.125 m thick concrete block work and is protected with 0.18 m insulation layer
and ZnAl cladding.. Wall: U Value 0.184. (W/m2 K) Glazing Argon filled double glazing: U value
1.4 (W/m2 K). The office has a central heating system with perimeter radiators and is naturally
ventilated through open-able windows.
Cool Roofs Project
Workshop: “National Energy Security – Future prospect” 13 December 2012 KSIR Kuwait
Cool Roofs –Case Study UK #2
Office at Brunel University, Uxbridge, West London, UK, Colored Cool Roof
Cool Roof technology
“Cool Barrier 012 (CB012)” was applied on the roof with an SR of 0.6 The reflectivity of the
original roof was 0.1. The building was monitored from April 2009 until October 2009
Evaluation results:
There is reduction on maximum and average internal air and operative temperatures
during the summer months. For the month of July, maximum internal air temperature is
reduced by 1.3 ◦C and average air temperature by 2.1 ◦C. In terms of thermal comfort,
max operative temperature is reduced by 2.2 ◦C and average operative temperature by
2.5 ◦C improving significantly thermal comfort.
Increasing insulation levels would decrease the potential energy benefits in heating
and cooling demand.
Thermal comfort can be improved by as much as 2.5 ◦C (operative temperature
difference for a change of 0.5 in albedo) but heating demand could be increased by
10%.
Cooling load is decreased, although there is a heating penalty, the overall contribution
is positive.
Cool Roofs Project
Workshop: “National Energy Security – Future prospect” 13 December 2012 KSIR Kuwait
Cool Roofs –Case Study UK #3
Office at Brunel University, Uxbridge, West London, UK, Colored Cool Roof
Simulated heating and cooling energy demand for the case-study building before and after
the application of the cool roof.
Albedo Heating demand Cooling demand Total energy demand (kWh/year)
Winter, set-point 21◦C Summer, set point 25 ◦C
2 ACH * 2 ACH * 2 ACH *
BEFORE 0.1 1769 2443 4211
COOL ROOF 0,6 2015 2017 4031
*2 air exchanges per hour
Optimum surface albedo is estimated between 0.6 and 0.7 with air exchange rate of 2 air
exchanges per hour. This combination creates an overall heating and cooling load reduction
of 3-6% depending on the set-point temperature for winter and summer.
Cool Roofs Project
Workshop: “National Energy Security – Future prospect” 13 December 2012 KSIR Kuwait
Cool Roofs –Carrefour Italy
Hypermarket Carrefour Assago Milan Italy
Date: 14/07/2011
Place: Assago Milan Italy
Total Roof Surface: 17.000 Sqm
Concrete Flat Roof Top Covered with Gray PVC
Application: Cool Barrier Roof Waterbased
Space 1: Non Treated Area – Surface Temperature 50.4 °C
Space 2: Treated Area - Surface Temperature 32.2 °C
“We are about 25% reduction in electricity
consumption for air conditioning “
“Around 65.000€ savings per year”
“Payback period: 2.5 Years”
Energy Manager: Mr. Giovanni Piano
ENERGY CONSUMPTION DATA AND SAVINGS
Consumption (weekly) measured on multimeters
(Week average for the period July-August)
Without Cool Barrier Roof System
2007: 44.573 kWh, 2008: 46.783 kWh, 2009: 46.627
kWh 2010: 45.259 kWh Average: 45.810 kWh
With Cool Barrier Roof System 2011: 33.500 kWh
Workshop: “National Energy Security – Future prospect” 13 December 2012 KSIR Kuwait
Energy savings from installing a Cool Roofing Product depends on the local
climate, existing insulation levels, the type of roof replaced, the type of roof
installed, and maintenance. In the best applications, cool roofs have no
incremental cost and deliver a nearly instant payback.
Winter Penalty:
Also known as heating 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. (US Environmental Protection Agency –EPA)
The Absolute Benefits of Cool Roofs in a climate hot and sunny, at least in summer
can summarised as follows:
Cool Roofs and Energy Savings
Workshop: “National Energy Security – Future prospect” 13 December 2012 KSIR Kuwait
Cooling load reduction - Less heat penetrates into building
Energy Savings - Minimize the need for cooling
Money savings
Improved thermal comfort conditions
Improved public health conditions
Enhanced building’s durability - Less thermal stress
Improved microclimatic conditions - Urban Heat Island Mitigation
Cool Roofs Consequences in Buildings
Workshop: “National Energy Security – Future prospect” 13 December 2012 KSIR Kuwait
Urban Heat Island mitigation – Temperature and Smog reduction
Lower surface temperature increase thermal comfort conditions of the
land users.
Lower air temperatures penetrate into the surrounding buildings –
thermal comfort in buildings –energy savings
Downtown Dallas Surface
Temperatures
Cool Roofs Consequences in City Level
Workshop: “National Energy Security – Future prospect” 13 December 2012 KSIR Kuwait
Cool Roofs - Peak Demand Reduction
High peak electricity loads oblige utilities to build additional plants in order to
satisfy the demand, but as these plants are used for short periods, the average
cost of electricity increases considerably. Southern European countries face a
very steep increase of their peak electricity load mainly because of the very rapid
penetration of air conditioning. “Kuwait’s peak power demand is set to almost
double by 2020”, according to Suhaila Marafi, director of the Electricity
Ministry’s department of studies, MEED’s Arabian Power & Water Summit in Abu
Dhabi on 6 March 2012
“Cool Roofing products can help reduce the amount of air conditioning needed
in buildings, and can reduce peak cooling demand by 10-15 percent”.
(www.epa.gov)
Workshop: “National Energy Security – Future prospect” 13 December 2012 KSIR Kuwait
Cool Roofs – CO2 Emissions
“Cool roofs are one of the quickest and lowest cost ways we can reduce our
global carbon emissions and begin the hard work of slowing climate change,”
U.S. Secretary of Energy Steven Chu “By demonstrating the benefits of cool roofs
on our facilities, the federal government can lead the nation toward more
sustainable building practices, while reducing the federal carbon footprint and
saving money for taxpayers.”
http://iopscience.iop.org/1748-9326/5/1/014005/fulltext/
“We estimate that increasing the albedo of urban roofs and paved surfaces by 0,1 will induce a negative radiative forcing on the earth surface equivalent to removing 44Gt CO2 from atmosphere. “ Hashem Akbari and Surabi Menon Lawrence Berkeley National Laboratory, USA H_Akbari@LBL.gov Arthur Rosenfeld California Energy Commission, USA ARosenfe@energy.state.ca.us 2006
Workshop: “National Energy Security – Future prospect” 13 December 2012 KSIR Kuwait
Cool Roofs – Policies and Initiatives
Workshop: “National Energy Security – Future prospect” 13 December 2012 KSIR Kuwait
Cool and Photocatalytic Construction Materials
Manufacturer, Athens Greece
www.abolinco.com
Urbanus Green Innovations Cyprus Ltd (U.G.I
Cyprus) operates as a sustainable management
consultant and as a raw materials supplier. U.G.I
focuses on the promotion of specifications and
standards into national and local construction codes
and on the supply of high performance raw materials
for the industrial and construction sector.
Prokopis Perdikis U.G.I CYPRUS/ABOLIN CO GREECE
Email: abolin@otenet.gr, ugi.cyprus@gmail.com
Thank you for your attention !