Green roofs that can reduce air conditioning bills?
Wednesday, July 29, 2009 - 09:29
As promised, here is the data that I collected when doing experiments with my research team on green roofs. Our procedure for the experiments involved splitting up into two teams to go to a building with a green roof and a building without a green roof (to act as a control) to measure the temperatures of buildings on each floor. Using thermosensors, the two groups would simultaneously measure air and ceiling temperatures to determine if there was a greater cooling effect on high building floor levels because of the presence of a green roof. If, in fact our hypothesis was correct, green roofs can dramatically cool down buildings and save energy bills by reducing air conditioning usage.
The photo above shows the three buildings that were used for comparison. The results of the building to the north of the green roof building is shown with a yellow line on our graph and likewise the building to the East of the green roof building is designated with a yellow line. As shown in the graphs, our results were opposite from what we expected. The green roof building had similar air temperatures to buildings without green roofs, especially at higher floor levels. However, the green roof trend was relatively constant compared to the dramatic positive slope exhibited by the other building temperatures. This may be a point of interest because temperatures tend to rise significantly as one walks up a building. Therefore, the green roof may have contributed to cooling throughout the building.
Nevertheless, the primary factor that may have significantly affected our results was finding accurately controlled buildings to compare to green roof buildings. We tried our best to select control buildlings based on building orientation and height. However, other factors that were difficult to take into consideration include air conditioning already present in buildings, windows and time of day.
Photo: Columbia University
Graph: Brittany Hsu, Stuart Gaffin, Michael Ferrebee, Lawrence Brazin, Reid Jenkins, and NASA GISS/NYCRI