Two-Dimensional Analysis of
Natural Convection and Radiation in Utilidors
PAUL W. RICHMOND
INTRODUCTION
Many large building complexes, such as military facilities and university cam-
puses, are served by central heat distribution systems. Utilidors are often used to
contain the heat distribution lines and other utilities between utility stations and
the serviced buildings. These enclosures are generally constructed of concrete and
are usually installed below ground level. Other materials, such as wood and sheet
metal, are also used. Figure 1 shows cross sections of two utilidors constructed in
Arctic regions.
In the southern United States, utilidors are referred to as utility trenches and
often have their upper side (lid) at ground level. Because utilidors are used to dis-
tribute heat (steam or hot water), it is important to know what the heat loss from
the utilidor is in order to estimate losses in the heat distribution system and to
design for efficient use of insulation. Additionally, the presence of unheated lines
(e.g., domestic water, fire protection, or sewer lines) requires that the air tempera-
ture within the utilidor remain above freezing. Because of the complexity of the
geometry, the heat transfer analysis must be done using approximate or numeri-
cal procedures.
Recently, numerical methods (finite difference, finite element) have been used
to evaluate utilidor performance. Modeling of conductive heat transfer around
utilidors and building foundations has been done successfully (Zarling and Braley
1984, Phetteplace et al. 1986, Kennedy et al. 1988). Modeling of heat transfer within
utilidors is generally done using conductive approximations (Smith et al. 1979).
Convection and radiation can have a significant effect on the total heat transfer,
and accurate models are necessary. Once available, numerical models and corre-
lations of heat transfer within utilidors can be used in the design process of new
utilidors. A second application is in the thermal evaluation of existing utilidors
for rehabilitation or renovation, replacing current approximation methods.
Researchers of numerical methods have demonstrated that convection and radi-
ation can be modeled using finite element, finite difference, or other numerical
techniques (Gebhart et al. 1988, Arpaci and Bayazitoglu 1990). However, these
efforts have not been applied to utilidors, and in general have been limited to simple
geometries. Additionally, the two modes of heat transfer are not often evaluated
in tandem.
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