"The paper presents the results of a monitoring campaign, performed in the course of the last summer, on a building retrofitted with a “cool roof” material.. The building is a one-storey construction, located on a plot belonging to Roma Tre University, with a total floor area of 275 m2, built in the ‘50s and partially restored in the ‘90s. The building hosts a Cultural and Recreational Center for Senior Citizens, managed by the City of Rome. Users have frequently complained with the management about the uncomfortable thermal conditions during hot periods, despite the presence of air conditioning units.. In fact, a visit to the roof showed that it was flat, not insulated, and that it was covered with a very dark weatherproofing (tar) layer, totally unshaded, which would heat up considerably when struck by strong solar radiation. As a consequence, the internal surface temperature of the ceiling was very high, leading to high Mean Radiant Temperatures, inadequately compensated by the air conditioning, which would cause the uncomfortable conditions.. A research group of Roma Tre University, in cooperation with ENEA, the Italian Agency for Energy and Environment, decided to experiment the use of “cool roof” strategies to improve the situation.. ENEA had already studied and tested several materials, to be used as coatings for roofs and walls. Such materials need to present very high reflectances in the visible-near infrared spectrum (solar radiation), while having high emissivities in the far-infrared range. An Italian company manufactures materials of this kind, which come in rolls and can be easily glued to existing flat surfaces.. First of all, the building has been provided with eleven temperature sensors, five of which to measure outdoor and indoor air temperatures, and the remaining ones to measure surface temperatures, both external (roof) and internal (ceiling). In addition to that, a pyranometer has been installed to measure solar radiation.. All sensors were linked to a data acquisition system, which collected and stored all data. Measures were taken before and after installing the cool roof material. The data acquisition period ran from June 17th to august 31st. The new material was installed on July 19th., covering approximately 120 m2 of roof.. Particularly interesting appear the data collected from July 2nd to 6th and from August 9th to 29th. In fact, during those periods we were able to have the Center closed, without users and with the air conditioning units shut off. That allowed us to analyse surface and indoor air temperatures with and without the cool roof material, thus enabling us to compare the two situations.. We were also lucky because the two periods were very similar in terms of weather and outdoor temperatures.. Finally, the building was simulated using TRNSYS in both situations, first without air conditioning, to check the correspondence between measures and simulation, then assuming continuous air conditioning operation. The first exercise showed the degree of thermal comfort improvement, the last exercise provided an valuation of the energy savings, associated with the adoption of cool roof strategies.. The paper presents the main results of the study, which show a significant improvement in both aspects.. "
Fanchiotti, A., Carnielo, E., Zinzi, M. (2011). Cool Roofs: Monitoring A Retrofit Project In Rome, Italy. In 40th ASES National Solar Conference 2011, SOLAR 2011. Boulder, CO : American Solar Energy Society.