Modeling and Design of Net ZEBs as Integrated Energy Systems - Modeling, Design, and Optimization of Net-Zero Energy Buildings - page 36

1. Combined radiative-convective coefficients (so-called film coefficients)
are often assumed, leading to a star-network as shown in Figure 2.6 .
This type of model is acceptable if the temperature differences between
the room air and the surfaces are low (generally 1-3 °C). In rooms with
high passive solar gains and radiant heating this can result in significant
simulation errors.
Fig. 2.6 Schematic of one-zone (heated by convective heating) with a
star thermal network and equivalent networks for the walls without
discretization (Norton equivalents) (Figure courtesy of Ali Saberi
Derakhtenjani)
2. Separate modeling of convective and radiative exchanges in room
interiors as depicted in Figure 2.7 (see also Athienitis, Stylianou, and
Shou (1990)). The thermally massive walls are modelled by a two-port
distributed element (as in the previous case), while the room air and
light-weight room contents can be modeled by a lumped thermal
capacitance. Although this capacitance has no effect on load
calculations because of the relatively low frequencies involved, it is
important to include it for short-term (high-frequency) control studies.
Each two-port element represents the equivalent two-port for each wall,