The Discrete Transfer Equations

In a general case, the surfaces participating in the heat radiation (hereinafter radiative surfaces) can emit, absorb, and reflect a heat radiation (both the solar and thermal).

The heat radiation leaving a radiative surface or radiation source is defined as:

for thermal radiation:

(1)

where: ε is the surface emissivity, σ is the Stefan-Boltzmann constant, T is the temperature of the surface ( is the heat flux radiated by this surface in accordance with the Stefan-Boltzmann law), A is the radiative surface area, QTin is the incident thermal radiation arriving at this surface;
for solar radiation:

(2)

where: Qsin is the incident solar radiation arriving at this surface, Qssource is the radiation arriving at this surface from solar sources.

	(1)

	(2)

The net radiation Qnet being the difference between the heat radiation Qout leaving this surface and the incident heat radiation Qin arriving at it:

	(3)

are calculated for each of the surfaces participating in the radiation heat transfer.