Utilisation of Passive Solar Energy - Renewable Energy: Technology, Economics and Environment - page 115

energy amounts to 0.076 kWh/(m 2 d) under the side conditions assumed for this
wall within the given period. The temperature only varies significantly up to a
wall thickness of approximately 15 cm. An increased wall thickness does thus not
enhance the heat storage capacity.
In most indirect gain systems only the outer wall is used for heat storage, which
is thus of solid design, whereas the outer wall surface serves as absorber. For this
purpose the surface is either painted in black or covered with black absorber foil.
Only within decoupled systems, absorber and accumulator are separate compo-
nents, whereas black or selectively coated sheet metal serves as absorber medium.
The heat carrier is transferred to the accumulator by means of a channel or a more
sophisticated medium. The accumulator itself may also be part of the building
structure, for instance, if it is designed as hollow ceiling or double wall masonry.
Rock storage, however, are not of double use, as they are not part of the building
structure.
Dynamic building simulations permit the determination of energy requirements
for heating Q H (see Equation 3.8) by means of the building heat losses Q L reduced
by usable energy from solar radiation Q S and internal heat Q i (i.e. heat created by
people and household appliances) as well as utilisation factor η .

( )

Q = Q − η Q + Q

(3.8) H L S i

In simplified terms, this is attributable to the determination of the utilisation
factor η for the available solar energy Q S , and internal heat gains Q i . Equation
(3.9) shows the approximate calculation of utilisation factor η for a ratio of heat
gain to heat loss γ below 1.6, and common thermal inertia of Equation (3.10)
/3-6/.

η = 1− 0 . γ

(3.9)

γ ( Q + Q ) / Q

(3.10)

S i L

3.2.3 Functional systems

Depending on their form and arrangement, four different functional systems (i.e.
direct gain systems, indirect gain systems, decoupled systems, sunspaces) are
distinguished; however, the borderline between the systems remains fluid.

Direct gain systems. Solar radiation penetrates into the living space through
transparent external surfaces and is converted into heat at the internal room sur-
faces. Room temperature and room surface temperature change almost simultane-