Evaluation of the potential
use Natural of Ventilation in
a typical residential building in China
The first part of this study consisted in an
overall estimate of the available potential to use wind and buoyancy
driven ventilation in conjunction with night cooling strategies
as a mean of obtaining improved thermal comfort conditions in a
typical chinese apartment.
This estimate was done for three cities situated
in different climatic zones (Shanghai, Beijing and Canton). A typical residential building was
analyzed, taking into account its geometry, materials, average infiltration
caracteristics and typical occupancy (internal heat gains). Using
weather data generated by the Chinese software Medpha (see chart
below) and basic wind data from ASHRAE a simulation of the temperature
profiles obtainable using passive night cooling strategies was done
(supposing the use, if necessary, of simple forced ventilation during
the night and ceiling fans during the day). The ventilation rates
were obtained using a natural ventilation simulation tool (Vent).
These estimated ventilation rates were then inputted into a night
cooling analysis tool (Lesocool).
Night cooling strategies give better results
with a low night time temperature and a high variation during the
day so that more heat can be exchanged with the structure. The Beijing
climate has this characteristic, Shanghai has a lower temperature
spread as well as other urban characteristics (close building implantation)
that make the application of passive strategies less effective.
A night cooling procedure involves maximum
ventilation during the night in order to extract heat form the building
fabric, during the day minimum ventilation rates are maintained
and the building fabric is used an internal heat sink.
The results obtained are encouraging and show
that these passive strategies have the potential to improve living
conditions during the warm months of the year. Obtaining the same
internal conditions (for the case shown in the chart above) using
air conditioning would involve a monthly energy spending of (approximately)
6.2 GJ (5.88x106Btu). With this type of solution one
obtains not only savings for the users (depending on the cases they
might not be able to afford air conditoning at all) and also decreased
The next step in the project consists in the
development of a multi-zone (whole building) software tool for "passive"
architecture design. This tool uses tri-dimensional partition of
the interior of the building to be modeled. This modeling approach
will provide more precision and detail than currently available
whole building models while remaining fast enough to be used for
whole year real weather analysis.
The main strong points of this tool are: a numerical
procedure that starts from the heat gains and outside temperature
and predicts the internal temperatures of the rooms, the possibility
to deal with the spatial distribution of internal heat sources (which
in many cases are the main source of internal air movements) with
increased precision (gains in the walls and in the lower or middle
part of the space etc
) and improved coupling with the thermal
mass of the walls (taking into consideration the velocity of the
air currents adjacent to the walls).
This model will be used to study the natural
ventilation/night cooling system that will be part of the prototype
design to be developed next year, possibly in conjunction with an
optimization algorithm (currently being developed by L.Caldas).
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