Three-dimensional modelling of heat transfer from slab floors
Bahnfleth, William Parry
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https://hdl.handle.net/2142/23689
Description
Title
Three-dimensional modelling of heat transfer from slab floors
Author(s)
Bahnfleth, William Parry
Issue Date
1989
Department of Study
Engineering, Mechanical
Discipline
Engineering, Mechanical
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
Engineering, Mechanical
Language
eng
Abstract
Earth-coupled heat transfer processes have been recognized in recent years as a potential source of significant energy savings in both conventional and earth-sheltered designs. Because of the complexity of the building/soil/atmosphere interaction, however, important aspects of earth-coupled heat transfer are not well understood. There is a particular lack of three-dimensional foundation heat loss data. In this study, a detailed three-dimensional finite difference model of a slab floor was used to generate 93 annual simulations in parametric groups focusing on effects of size and shape, soil properties, boundary conditions, climate, insulation, and building shadow. These results indicate that soil thermal conductivity, ground surface conditions, foundation design, and floor shape/size are essential elements of a general model. Each of these parameters could be responsible for a 50% change in heat transfer rate. Effects of thermal diffusivity, and lower boundary condition variation were small (on the order of 10%) for the range of conditions considered. The building shadow produced an effect that was generally small, but much more significant in a warm sunny climate than in a cool, cloudy one. Diurnal variation in total floor heat loss also was small, indicating that a daily time step is sufficient for energy analysis purposes. Design heat loss methods based on perimeter loss coefficients were shown to be unreliable because of a significant total area effect. Heat loss per unit area was found proportional to (A/P)$\sp{\rm d}$ where A, P, and d are floor area, perimeter length, and an empirically determined exponent. A model employing this scaling and separating heat loss into mean and periodic parts may be useful as a design equation.
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