Prediction of inside air and surface temperatures using a computer model sensitive to thermal mass distribution inside an unconditioned space.

Abstract

This research develops a method by which dynamic thermal effects are simulated for a room exposed to direct, time-varying insolation through a window onto appropriate areas of thermally-massive room surfaces. Most previous researches and standard architectural practices do not address this problem with sufficient temporal and spatial resolution to clearly reveal the effects and interactions which actually occur. However, this thermal situation continues to be a significant architectural design consideration in climates identified with strong solar impact and especially when passive solar energy strategies are attempted. Thus, the considerable efforts and complexities required to accomplish a closer examination of this seemingly common problem are justified. The approach is to write a computer simulation program based on a mathematical model using the heat balance method to provide a more precise computational tool than is currently available. First, each interior surface is subdivided, by means of a grid system, into smaller unit areas to which the Heat Balance Method is applied. Second, the specific algorithms incorporated in the heat balance are developed for the radiation-shape factors, the temperature (difference) dependent convection and conduction coefficients. The finite difference method--implicit technique--is used to solve for heat transfer through the room enclosure and glass window. A procedure is developed to instantly identify the area and the geometry of the sunlit internal surfaces, and to determine the specific quantities of direct and diffuse solar radiation impinging upon each interior surface. A validation of the simulation program is undertaken by evaluating the thermal behavior of internal mass using a Thermal Test Chamber located in the Building Technology Laboratory, College of Architecture and Urban Planning, University of Michigan. Selected experimental investigations provide confirmation that the computed results do correspond closely with thermal observations, both accomplished with fine temporal and spatial resolution. Thus, the theoretical considerations seem to adequately encompass the most important aspects of this complex and dynamic architectural thermal problem. Consequently, architecturally viable design features may be explored more completely to determine their thermal efficacy in the presence of direct insolation.