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E nergy and Buildings 23 (1995) 1-8

H eat and mass transfer through large openings
by natural convection
M . Santamouris a, A. Argiriou b, D. Asimakopoulos a, N. Klitsikas a, A. Dounis c
• University of Athens, Department of Applied Physics, Laboratory of Meteorology, lppokratous 33, GR-106 80 Athens, Greece
b National Obsen)atory of Athens,Institute of Meteorology and Physics of the Atmospheric Environmen~ PO Box 20048,
GR-118 10 Athens, Greece
c Department of Computer Engineering, Hellenic Air Force Academy, Athens, Greece

Received 10 August 1994; accepted 2 September 1994

A bstract

C onvective heat and mass transfer through large openings play an important role in the thermal behaviour of buildings.
T hese phenomena becomeeven more determinant in the case of naturally ventilated buildings. This paper reviews the models
d escribing the involved phenomena due to gravitational and boundary layer pumping flows proposed up to 1992. A sensitivity
a nalysis is also presented, aimed at a comparison of these models and a determination of the points requiring further research.
Keywords: Heat transfer; Mass transfer;Natural convection

1. Introduction

N atural convection i's the main heat transfer mecha nism in many solar energy applications. Operation of
t hermosyphonic solar collectors is based on natural
c onvection; this is the cetse also in conventional buildings
a nd mainly in passive solar ones. Natural convection,
i f intelligently applied, can also significantly contribute
t o the natural coolingof buildings.
H eat flows convectively through the different zones
o f buildings since there are zones where heat is absorbed,
s uch as south rooms or sunspaces, and others that are
c ooler. Natural convection is also the main heat exchange
m echanism between a building and the environment.
W hen for instance during summer the windows of a
b uilding zone are opened, there is heat exchangewith
t he ambience, due to the temperature difference bet ween the inside and outside air, even if the wind
velocity outside is practically zero.
N atural convection between different building zones
is due to the air temperature difference between these
z ones. These differences in the air temperature are
d ue to the temperature differences between the various
s urfaces of the zonesinvolved or to the presence of
i nternal heating or cooling sources. Surfaces located
in south oriented zones are wanner during the day,
since they absorb solar radiation that enters the space.
A lso other surfaces can be heated up due to the contact
0378-7788/95/$09.50 © 1995 Elsevier Science S.A. All rights reserved
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w ith auxiliary heating equipment, or because theyare
p art of a heat storage medium. Cold surfaces are
windows (mainly during winter) and the surfaces of
d ischarged thermal storage media. This situation can
b e reversed during the night; south glazing can be the
c old surfaces and the thermal storage media the hot
o nes.
K nowledge of the physical laws describing natural
c onvection through the zones of a multi-zone building
isnecessary to accurately predict the temperature dist ribution inside the various zones. The contribution of
t hese considerations to the design of a building is that
k nowing these mechanisms, the dimensions and locat ions of the openings between the various zones can
b e designed in such a way to give a more homogeneous
t emperature distribution inside the building and theref ore avoid overheating.Also, in the case of passive
c ooling design, natural heat extraction mechanisms can
b e maximised by optimising the characteristics of these
o penings.
T his paper focuses on heat and mass transfer by
n atural convection through large openings between
a djacent zones in buildings. This is due to the following
t wo mechanisms:
• g ravitational flow, created by differences in the bulk
a...