This document summarizes an experiment investigating the effect of reducing a heat source on natural ventilation in an enclosed space using a small-scale hydraulic model. The model used a fresh water tank representing the outdoor environment within a box with openings immersed upside down in the tank to simulate an indoor space. A smaller tank with salty water provided a heat source via a pipe, placed on top of the enclosed space. Experiments examined the plume profile and flow characteristics under variations of opening geometry, density difference, and heat source flow rate. The results showed natural ventilation works best when combined with stratification. The findings aim to define design principles to advantage natural ventilation and reduce cooling energy requirements by understanding how opening position/size, density difference, and heat

1. LABORATORY SIMULATION OF NATURAL VENTILATION IN BUILDINGS WITH THE
PRESENCE OF THERMAL SOURCE
Natural ventilation is the process of supplying and removing air through an indoor space
without using mechanical systems. It refers to the flow of external air to an indoor space as a
result of pressure or temperature differences. There are two types of natural ventilation: wind
driven and buoyancy-driven ventilation. The second one occurs as a result of the directional
buoyancy force that results from temperature differences between the interior and exterior. Up
to now experiments have been carried out to study the process of natural ventilation in a small
scale using density difference in order to succeed the temperature difference which is required.
As far as the ventilation with a heat source is concerned, experiments and studies have
proven that the profile of the flow is defined by the area and the distance of the openings, the
density difference between the outside and inside fluid and the volume flux of the heat source.
There are two forms of ventilation: mixing ventilation, and displacement ventilation. The first
one refers to the process of the incoming air being mixed with the indoor because of the density
difference whereas in the second one, layers are displayed (the less dense fluid is located on the
upper zone).
The objective of this diploma thesis is to investigate experimentally the effect on reducing
the supply of the heat source to the natural ventilation of a closed space. A small scale hydraulic
model was used comprising a tank of fresh water that resembles the external environment
within a small box with various openings, immersed upside down to simulate the indoor space.
Furthermore, a smaller tank with free surface provided the heat source with colored salty water
via a plastic pipe. The heat source of this dense fluid was placed on the top of the enclosed
space. During the experiments the plume was examined in various combinations of the
geometric characteristics of the openings, the density difference and the source flow rate. This
examination focused on the profile and the main characteristics of the rate flow, in each case
separately.
Finally, the outcomes of this diploma thesis based on the quantitative and qualitative
analysis of the experiments are derived. According to the results, the natural ventilation is better
when it is combined with stratification. The aim of the findings is to set the main principles of the
building design in order to take advantage of the natural ventilation process and reduce the
required energy for cooling. An attempt was made to define which position and area of the
opening, density difference and flow rate of the heat source have the better impact on the
process of natural ventilation under the presence of an unsteady heat source.
Ifigeneia Papathanasiou,
Niki - Nikoletta Tsialkatoura,
Thessaloniki, April 2013.