This calculator compares the annual energy performance of a building with a green roof to the same building with either a conventional dark roof or a highly-reflective white roof. The results are based on simulations run for new construction (ASHRAE 90.1-2004) apartment or office buildings and use typical weather data for 100 major cities in the U.S. and Canada. Inputs include nearest major city, total roof area, percent green roof cover, growing media depth, and leaf area index of plants. With version 2.0, users can now specify whether construction is new or older and whether the green roof is irrigated or not. The calculator uses default utility rates for each city, or the user can enter his own. Results are the electrical, gas, and energy cost savings for a green roof compared to a dark roof and a white roof. Additional outputs with version 2.0 include heat exchange between the roof and the urban environment and an estimate of the annual roof water balance, including net runoff.
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