The interior natural convective heat transfer coefficient
is
computed for each interior surface as
where
is the
characteristic length of the surface,
is the
indoor air temperature and
are
correlation coefficients. These parameters {
,
,
} are
identical to {1.823,-0.121,0.293} for vertical surfaces [Awbi
1999], {2.175,-0.076,0.308} for horizontal surfaces wherefore the
heat flux is in the same direction as the buoyancy force [Khalifa 2001], and
{2.72,-,0.13} for horizontal surfaces wherefore the heat flux is in
the opposite direction as the buoyancy force [Awbi 1999]. The
interior natural convective heat transfer coefficient is only
described as function of the temperature difference. Similar to the
thermal model for heat transfer through a wall, a thermal circuit
formulation for the direct radiant exchange between surfaces can be
derived [ Buchberg
1955, Oppenheim 1956].
[Awbi 1999]: H.B. Awbi, A. Hatton, Natural convection from heated room surfaces, Energy and Buildings 30 (1999) 233–244.