ExteriorWall represents heat conduction and heat
storage within walls. It links a variable number n of
thermal resistances and capacities to a series connection.
n thus defines the spatial discretization of thermal
effects within the wall. All effects are considered as
one-dimensional normal to the wall's surface. This model is thought
for exterior wall elements that contribute to heat transfer to the
outdoor. The RC-chain is defined via a vector of capacities
CExt[n] and a vector of resistances
RExt[n]. Resistances and capacities are connected
alternately, starting with the first resistance
RExt[1], from heat port_a to heat
port_b. RExtRem is the resistance between
the last capacity CExt[end] and the heat
port_b.
