Paper 3: Volume 3 No.4 March 2005 Edition
Derivation of a Theoretical Model to Explain the Functioning
of a Window as a Pre-Heat Ventilation Device and its Verification using Physical
Models
M
E McEvoy and R Southall
Department
of Architecture, University of Cambridge, The Martin Centre, 6 Chaucer Road,
Cambridge, UK, CB2 2EB
Abstract
‘Supply air’ windows are designed with an air gap
between the inner panes of glass that is used as the incoming air path for room
ventilation; air is pre-warmed within the window and thereby avoids the
sensation of draughts. A series of
tests, verified by model simulations, were carried out to determine those
aspects of the window’s specification that govern the extent to which air is
pre-warmed by the windows before entering rooms.
The first was a laboratory experiment investigating the influence that
the width of gap between the glass panes had on the pre-heating of the airflow,
the results from which were simulated using an algebraic model based on fluid
dynamics principles. The following
experiments were carried out in test cells analysing the influence of the
location of a low emissivity coating within alternative glazing assemblies, the
relationship between pre-heat temperature and ambient temperature, and its
variation with ventilation rate. The
later stages were modelled by the use of the Computational Fluid Dynamics
program FLOvent. The outputs of
these experiments and simulations has enabled a clearer understanding of the
physical processes at work, and the development of simulations that accurately
predict the window’s performance as a pre-heat device.
Key words: ventilation
pre-heat, windows, sustainability, indoor air quality, measurements, CFD.
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