aesthetically pleasing. This phenomenon
is a significant issue under North American
moderate coastal climate condition, where
interior relative humidity is high in winter
and exterior temperature is moderately low.
Back-up Steel Stud Wall
In order to investigate the effects of heating
systems, it is important to understand each
of the heat transfer mechanisms involved,
i.e. conduction, convection and radiation.
While conduction and radiation can be
modelled accurately via the use of heat
transfer simulation software, it is not the
case for convection because convective heat
transfer is highly sensitive to buoyant and
mechanically induced air movements.
There are two available methods to
model convection coefficients in building
simulation: 1) empirical coefficients
obtained from laboratory experiments;
2) computational fluid dynamics (CFD)
simulation. In this project, these two
methods were explored and were used to
model the selected window-wall details.
Simulation software such as THERM and
Autodesk Simulation CFD were utilized to
simulate the condensation risk of typical
glazing units with different heating systems.
THERM was used to model the twodimensional (2D) heat transfer through
envelope details. THERM uses the
finite element method (FEM) based on
well-stirred (or well-mixed) room air
assumption: boundary conditions such
as convective and radiation heat transfer
coefficients are used to model heat transfer
between surfaces and the room air.
CFD was used to predict the air flow
patterns induced by the heating systems.
CFD uses the fluid (air flow) and heat
transfer finite control model based on
the room air flow model assumption:
simulation allows prediction of local heat
flow patterns, thermal stratification and
This project designed a methodology as
illustrated in Figure 1. Window-wall details
from the local industry were selected.
Boundary conditions data from past
research literatures were used for window
detail (THERM) and room air flow models
(CFD). 2D heat transfer models were
built in THERM and room air flow models
in CFD for the window details. These
steady state models were simulated with
representative boundary conditions for
each heating system under typical winter
conditions of Vancouver.
BCBEC ELEMENTS A BCBEC PUBLICATION
FIGURE 2: THERM MODELS ON BYPASS DETAIL AND EXTENDED SLAB EDGE DETAIL
Back-up Wall with insulation