Impact of surface division and zone characteristics on outdoor surface temperature modeling with EnergyPlus

Abstract

Several graphical user interface (GUI) tools used by energy modelers are powered by EnergyPlus, a widely recognized building energy modeling engine. Recent advancements in these tools have improved the creation of building geometries for energy modeling. Ladybug Tools, a Grasshopper plug-in, uses EnergyPlus for energy simulations and leverages Grasshopper's capability to subdivide surfaces into smaller grids for more precise shadow and surface temperature modeling. This method enables a realistic representation of walls and ground surfaces and enhances simulation accuracy. The study evaluates this approach to estimate outdoor ground surface temperature by comparing simulated and measured surface temperatures in two case studies: one involving exposed pavement and the other involving shading from trees and buildings. The novelty of this study lies in its role as the comprehensive investigation to perform an hourly validation to EnergyPlus to estimate outdoor surface temperatures using hourly observations over multiple days. EnergyPlus accurately predicted surface temperatures, with R 2 values of 98% and 90%, and root mean square error of 2.35°C and 3.15°C, respectively. Subdividing surfaces significantly improved shading representation, increasing R 2 from 73% to 90% in shaded areas. The study also conducts a parametric simulation to determine optimized zone characteristics, such as zone depth, soil depth, and thermal condition of the zone space, to maximize the model accuracy. These findings support EnergyPlus as a reliable tool for modeling complex urban environments.