09/03/2014 European Cool Roofs Council 1

Michele Zinzi ENEA

Cool Roof Case Studies

The Mediterranean European heritage

• Solar reflecting materials for the building envelope were a widely used construction technology

• The Mediterranean region is still populated with exemplary demonstration sites

• Are Cool Roofs an energy efficient solution in modern buildings too?

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Santorini, Greece

Ostuni, Italy

Sidi Bou Said, Tunisia Alcalá de los Gazules, Spain

Demonstrating the impact of Cool Roofs in practice

• Many Cool Roofs case studies were carried out throughout the world in recent years: US and Canada, Brazil, Europe, Middle and Far East Countries, Australia.

• Monitored buildings include: dwellings, offices, schools, commercial buildings, sport infrastructures.

• Performance indicators for evaluation: energy use in cooled buildings, comfort analyses in not cooled buildings, roof thermal behaviour.

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Commercial building , Italy

Laboratory, Greece

Dwellings, France

Detached house, Florida, US

Case studies from the EU SAVE Cool Roofs Project

• 4 countries(France, Greece (2), Italy, UK).

• 4 typologies (dwellings, laboratory, office, school (2))

• Case study assessment procedures: – Due to the limited monitoring period allowed by the project

schedule, the case studies were implemented combining monitoring and calculation activities.

– The buildings were monitored in free floating conditions during the first phase.

– The buildings were modelled into TRNSYS. The model included: climatic data, envelope and structure characteristics, occupation profiles.

– The model was calibrated versus the monitoring data; target parameters were: air/operative temperature and roof surface temperature.

– The impact of the cool roof (and other alternative technologies and strategies) on the cooling performances was assessed by calculation.

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Office/school building in Trapani, Italy

• Trapani is located in western side of Sicily. The school consists of several blocks. Envelope not insulated.

• The test was carried out on the 800 m2 office/ laboratory block. It is used also in summer and suffers of severe overheating.

• Existing roofing material: mixed concrete tiles, estimated SR 25% and IE 0.90

• Product: milk and vinegar organic coating, SR 82%, IE 0.88. Two coats applied.

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Surface temperatures 1-20/08 Measured not painted and painted - Predicted not painted

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01/08 03/08 05/08 07/08 09/08 11/08 13/08 15/08 17/08 19/08 21/08

Ts- not painted measured

Ts - painted measured

T air

Office/school building in Trapani, Italy

• Monitoring from late May until early September.

• Before CR cool roof application the indoor temperature was 26.2°C with 24.4°C outdoor. After the application the indoor air was 27.1°C with 28.2°C outdoor temperature.

• Results of the calculation: reduction of the net cooling demand by 54%; reduction would be 24%, for an equivalent building thermally insulated

• The cool roof resulted to be the most efficient cooling measures, depending also on the favorable geometric configuration of the buildings.

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Energy demand [kWh] and cooling savings [%] for the standard building and variations

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54

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78

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1 - standard 2 - cool roof 3 - roof

insulation

4 - night

ventilation

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shading

6 - 3+2 7 - 4+2 8 - 5+2 9 - insulation

(new building)

10 - 9+2

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Net energy demand kWh

Cooling Savings (%)

-28%

School building in Athens, Greece

• Located in the large metropolitan area of Athens, with typical Mediterranean climate and affected by a significant urban heat island

• The school consists of two blocks, the application is on one building for410 m2 in total.

• The building has not insulation, not cooling system.

• Existing roofing material: cement and gravel screed, estimated SR 20% and IE 0.90

• Product: white elastomeric waterproof coating, SR 89%, IE 0.89.

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School building in Athens, Greece

• Infrared camera measurements show a 12°C reduction of surface temperature in not critical hours in summer

• Calculation estimates a 40% cooling demand, reduced to 35% for the insulated configuration

• The peak demand is reduced by 20% in both configurations.

• In free floating conditions the cool roof leads to an average reduction of the air temperature of 1.8°C in the reference room.

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Roof

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1/1 31/1 2/3 1/4 1/5 31/5 30/6 30/7 29/8 28/9 28/10 27/11 27/12

simulation time step (1h)

tem

pera

ture

(oC

)Surface Temperature reduction

Annual Cooling Loads (kWh/m2)

-1.0

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Reference Roof,

uninsulated building

Cool Roof, uninsulated

building

Reference Roof,

insulated building

Cool Roof, insulated

building

Co

olin

g L

oa

d (

kW

h/

m2)

Cooling Load (kWh/m2) %

-35%-40%

Office building in London, United Kingdom

• Portion of building in a heating dominated climate, with significant cooling demand in non residential buildings

• The total area is 137 m2, including an open office and small rooms.

• The building has insulated walls and roof. The office has central heating system and it naturally ventilated building. Some individual have small table fans.

• Existing asphalt roofing: estimated SR 10% and IE 0.90

• Product: pink elastomeric coating, SR 70%, IE 0.88.

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Office building in London, United Kingdom

• The observation of monitored data showed a 1.7°C reduction of the office temperature after the CR application

• Calculation results for not cooled building shows a significant thermal comfort improving, the maximum operative temperature is reduced by 2.2°C and the average operative temperature by 5.3°C.

• There is a reduction of heating and cooling demand by 3.5% for this case. Potential savings vary between less than 1 and 8.5% during the year, as a function of different albedo values

• Set points and ventilation rate strongly affect the impact of the cool roof and the performance of the building

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Conclusions

• Case studies are significant to better understand how cool roofs work in practice

• Case studies performed in EU demonstrated that the technology is relevant to reduce the cooling demand in cooled buildings and improve the comfort conditions in not cooled buildings

• Annual energy savings are always achieved for insulated buildings, whatever is the buildings. However, slightly negative results might be achieved in not insulated residential buildings, because of the high heating demand.

• Cool roof applications are particularly efficient if coupled to the thermal insulation of the roof in renovation works

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Thanks for the attention! Michele Zinzi Tel: +39 06 3048 6256 / 4188 Email: michele.zinzi@enea.it