Characterizing leaf area index of rooftop farm to assess thermal-energy performance by simulation

Abstract

This paper presents an exploratory research about the possibilities to simulate the thermal performance of buildings with green roofs, or in this case rooftop farming. Different from the green roofs, a rooftop farming has a leaf area index (LAI) variable during all the year because the vegetable crops growing cycle repeats sometimes along the year. The contribution of this paper is to bring this discussion to the art state. The method uses computer simulation as a research strategy using the software Energy Plus. The research method was developed in 3 steps. In the first one, a literature review was performed in order to search data from 18 vegetable crops and 3 substrates. One of these data was the LAI, which in the second research step was simulated considering 5 different possibilities (LAI constant all the year; LAI observing monthly the growing cycle; Average LAI considering the growing cycle; crop rotation with average monthly LAI; and LAI defined each ten days considering the crop growing cycle). The results demonstrated that: a) the simplified LAI found in the literature considering the rooftop farming simulations are defined as constant; b) using LAI constant all the year can overestimate until 7% the energy use intensity (EUI) in buildings for the climate in the South of Brazil. c) Thus, in order to simulate the performance of buildings with rooftop farming it is important to develop a data base of the vegetable crop considering the LAI variation along the cycles, and also the number of cycles during the year.