Michele Zinzi ENEA Cool Roof Case Studies 09/03/2014 European Cool Roofs Council 1
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? The Mediterranean European heritage Santorini, Greece Ostuni, Italy Sidi Bou Said, Tunisia Alcalá de los Gazules, Spain 09/03/2014 European Cool Roofs Council 2
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. Commercial building, Italy Laboratory, Greece Detached house, Florida, US Dwellings, France 09/03/2014 European Cool Roofs Council 3
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. Case studies from the EU SAVE Cool Roofs Project 09/03/2014 European Cool Roofs Council 4
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 m 2 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. Office/school building in Trapani, Italy Surface temperatures 1-20/08 Measured not painted and painted - Predicted not painted 60 Ts- not painted measured Ts - painted measured T air 55 50 45 40 35 30 25 20 15 10 01/08 03/08 05/08 07/08 09/08 11/08 13/08 15/08 17/08 19/08 21/08 09/03/2014 European Cool Roofs Council 5
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. 16000 15000 14000 13000 12000 11000 10000 9000 8000 7000 6000 5000 4000 3000 2000 1000 Energy demand [kwh] and cooling savings [%] for the standard building and variations Net energy demand kwh 78 Cooling Savings (%) 61 61 54 44 39 22-28% 90 80 70 60 50 40 30 20 10 0 0 1 - standard 2 - cool roof 3 - roof insulation 4 - night ventilation 5 - external shading 6-3+2 7-4+2 8-5+2 9 - insulation (new building) 10-9+2 0 09/03/2014 European Cool Roofs Council 6
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. School building in Athens, Greece 09/03/2014 European Cool Roofs Council 7
Cooling Load (kwh/m 2 ) temperature ( o C) 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. 9.0 8.0 7.0 6.0 5.0 4.0 3.0 2.0 1.0 0.0-1.0 Reference Roof, uninsulated building Annual Cooling Loads (kwh/m 2 ) Cooling Load (kwh/m2) % -40% Cool Roof, uninsulated building Reference Roof, insulated building -35% Cool Roof, insulated building School building in Athens, Greece 28 26 24 22 20 18 16 14 12 10 8 6 4 2 0 Surface Temperature reduction 09/03/2014 European Cool Roofs Council 8 Roof 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)
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. Office building in London, United Kingdom 09/03/2014 European Cool Roofs Council 9
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 Office building in London, United Kingdom 09/03/2014 European Cool Roofs Council 10
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 Thanks for the attention! Michele Zinzi Tel: +39 06 3048 6256 / 4188 Email: michele.zinzi@enea.it 09/03/2014 European Cool Roofs Council 11