THE IMPACT OF REFLECTIVITY AND EMISSIVITY OF ROOFS ON BUILDING COOLING AND HEATING ENERGY USE (original) (raw)
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E3S Web of Conferences
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Energy, 2003
Energy use and environmental parameters were monitored in two small (14.9 m 2 ) non-residential buildings during the summer of 2000. The buildings were initially monitored for about 1 1/2 months to establish a base condition. The roofs of the buildings were then painted with a white coating and the monitoring was continued. The original solar reflectivities of the roofs were about 26%; after the application of roof coatings the reflectivities increased to about 72%. The monitored electricity savings were about 0.5kWh per day (33 Wh/m 2 per day). The estimated annual savings are about 125kWh per year (8.4 kWh/m 2 ); at a cost of 0.1/kWh,savingsareabout0.1/kWh, savings are about 0.1/kWh,savingsareabout0.86/m 2 per year. Obviously, it costs significantly more than this amount to coat the roofs with reflective coating, particularly because of the remote locations of these buildings. However, since the prefabricated roofs are already painted green at the factory, painting them a white (reflective) color would bring no additional cost. Hence, a reflective roof saves energy at no incremental cost.
Proceedings of the EuroSun 2014 Conference, 2015
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Lawrence Berkeley National Laboratory, 2003
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IOP Conference Series: Materials Science and Engineering
In cities vegetated roofs are becoming more popular because they can mitigate Urban Heat Island phenomena by decreasing the outdoor air temperature in summer. This decrease reduces the electric energy demand for climatization of buildings, which, in front of a milder climate, will recur less to mechanical tools for guaranteeing thermal comfort conditions to occupants. Cities can registered another indirect positive effect: the reduced cooling energy demand, limits the heat released by the climatization systems' external unities toward the urban open spaces, thus lowering the outdoor air temperature. Therefore, the outdoor surface temperature of green, as well as cool roofs, can be assumed as an important design parameter for guaranteeing the sustainability of buildings and their approach toward an nZEB path. Obviously, designers and city planners must have at their disposal simple and effective tools for evaluating the economic feasibility of these two choices. This paper proposes a simple method to assess the economic effectiveness of green or cool roofs. It relies on the appraisal of the number of hours during which a building requires a cooling mechanical support for maintaining the indoor comfort conditions. This duty period of the cooling system is then simply converted into the cost of the needed electric energy.