Three-dimensional modelling of heat transfer from slab floors

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.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Engineering, Mechanical

Grantor

University of Illinois at Urbana-Champaign

Year dc:date

2011

Author dc:creator

• Bahnfleth, William Parry

• Engineering, Mechanical

Statement dc:rights

• Copyright 1989 Bahnfleth, William Parry

Language dc:language

eng

Identifier

AAI8924763
(UMI)AAI8924763

OAI identifier oai:identifier

oai:www.ideals.illinois.edu:2142/23689