Abstract:
In recent years natural ventilation is widely recognised as excellent contributing
towards in design low energy buildings. The main challenge in natural ventilation is
identified as lack of knowledge in providing acceptable thermal comfort in an
occupied space to meet the internal requirements against the prevailing climatic
conditions variations. Numerical investigations of the indoor thermal comfort
condition in a simple office space governed by the solar chimney stack effect have
been undertaken using CFD techniques. A mathematical model was developed based
on the relevant analytical framework governing the phenomena to simulate the
velocity flow field and temperature distribution on the designated plane within the
indoor space. Boussinesq approximation was incorporated to numerical scheme with
realistic boundary conditions for flow simulation. The model was enriched by
incorporating a sufficient fluid volume to represent environment surrounding the
space and thereby eliminating the entry effect to the flow. Hexahedral cells were
used in a non-uniform grid distribution to minimise numerical diffusion. A fine mesh
is used near the walls to enhance the resolution and accuracy resolving the problems
under the turbulent flow conditions. Grid independence analysis was carried out to
ensure the accuracy of the numerical results. Under-relaxation factors 0.3, 1, 2, 0.8,
0.8, 1, 0.9 for pressure, density, momentum, turbulence kinetic energy, turbulence
dissipation rate, turbulent viscosity, energy respectively were used. The model
outputs were compared with the available experimental measurements taken under
the same condition to calibrate the numerical scheme. A parametric study was carried
out using the calibrated model to assess the distribution of thermal comfort index
against the changes in geometrical and solar radiation parameters. The values of
activity, metabolic rate for seated activity and clothing insulation were selected as 0,
60 W/m2 and 0.5 Clo respectively for thermal performance analysis. The effect of
each input parameter was investigated in terms of mean value and standard deviation
corresponding to the flow velocity and the PPDNV value. It can be concluded that the
present model is capable of predicting the indoor thermal performance of a building
under stack effect.
