Session: 15-01-01: ASME International Undergraduate Research and Design Exposition

Paper Number: 100407

100407 - Computational Fluid Dynamics Based Optimization Design of Naturally Ventilated Roofs 

Nowadays buildings energy efficiency is one of the prime objectives of energy policy at regional, national, and international levels. Among building services, the growth in HVAC systems energy consumption is particularly significant. A promising approach to reduce the energy consumption of the HVAC system is the reduction of heat fluxes through the building envelopes. In recent years, naturally ventilated roofs were widely studied due to their remarkable merits in reducing solar heat gain and improving indoor thermal comfort in summer. A naturally ventilated roof design is known as an effective way to reduce the building’s solar heat gain in summer. The objective of this paper is to use computational fluid dynamics as well as a machine-learning algorithm to investigate the problem and determine the optimal designs. First, I use a computational fluid dynamics tool to simulate the flow over the 50 two-dimensional roofs with varying angles and distances. Then, by using these computational fluid dynamics simulation results as a training database, I develop a machine learning-based algorithm to quickly determine the optimal design of the angle and the distances of the roofs. Usually, the computational fluid dynamics simulations take a long time to get the results, so here, I especially use machine learning to lever the results from the CFD simulation and further determine the optimal design with a greatly reduced simulation time. Finally, the conclusions show that the ventilation of roofs can reduce significantly the heat fluxes during summer and optimal configuration will help the building reduce energy consumption. In the paper, the numerical heat transfer models and relevant experimental validations are discussed. So most numerical simulations about naturally ventilated roofs are conducted in the 2-D case. A better understanding of the effect of cavity width can be obtained if we use 3-D modeling. So, in addition, the accuracies of 2-D and 3-D CFD simulations are compared and discussed.  Since most roofs have length and width much larger than spacing, a critical width-to-spacing ratio is proposed based on the discussion, beyond which the 2-D CFD simulation is accurate enough. Beyond, we further test the Winter Performance of Roofs with An Enclosed Air Cavity. During winter, the roof cavity is often enclosed at both ends to form a thermal insulation layer. The enclosed air layer contributes to increasing the roof thermal insulation and reducing the heat flux transferred from the building interior to an outdoor environment. Therefore, it is significant to study the winter performance of roofs equipped with enclosed cavities, as well as the convective heat transfer in the enclosed flat or inclined roof cavity.

Presenting Author: Weihan Zhang Winchester College

Presenting Author Biography: Weihan Zhang is a student at Winchester College. His research interests include applied mathematics and physics which are related to thermal fluid problems and general mechanical engineering problems. He would like to use his research to solve the scientific problems encountered in the real world. He is especially interested in designs that can reduce the energy consumption of buildings. He has received rewards in the British Mathematics Olympiad (top 50 in the UK) and British Physics Olympiad.

Authors:

Weihan Zhang Winchester College