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Radiation
is a major mode of heat transfer between the human body and the
environment and thus plays an important role in modeling human
comfort. It has been shown the Mean Radiant Temperature (MRT)
is one of the six critical parameters in human thermal comfort
analysis. Since human comfort is both a physiological and
psychological phenomena, the predicted mean vote (PMV) remains
the most effective parameter to correlate the two and quantify the
comfort sensation in terms of percentage of comfortable floor space
area. The presence of fenestration (viz. doors, windows or skylights
comprised of a frame and glazing system) in a room, which has thermal
and optical properties quite different from the walls, impacts the MRT
considerably and thereby affects the comfortable floor space area.
Apart from radiation, the energy exchange in a room also occurs due to
conduction through the walls along with convection past it. To
simulate the impact of fenestration, the biggest challenge is to
develop a suitable three-dimensional mathematical model incorporating
all the modes of the heat transfer, which will accurately calculate
the MRT and a suitable PMV model will quantify comfort.
The Building Comfort Analysis Program (BCAP) does this by numerically
solving the general energy equation. A numerical method, the Discrete
Ordinate model, is employed to first solve the non-linear radiative
transfer equation (RTE) and obtain the localized and directional
radiation intensity and the radiative flux. The general energy
equation is then solved to balance the radiative energy with the
conductive and convective energy in the room using a finite volume
numerical scheme. The work reported in this project uses a fundamental
approach to determine the radiation intensity throughout the room, and
then uses the intensity to directly calculate the localized MRT
rather than using empirical relationships. The calculated MRT
is then used to calculate the PMV using
Fanger’s model at each point in the room and obtain the comfort
distribution as a percentage of floor space that is thermally
comfortable. The results obtained show how and where the fenestration
system significantly impacts the localized thermal comfort within the
room.
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