Solar energy use in buildings - Solar Energy Sciences and Engineering Applications - page 603

Figure 18.8.1 Amount of heat flowing into a component and the effective storage mass thickness d eff .

transfer coefficients and high heat conductivities, which in practice is not the case. To
what extent the storage capacity can be used depends, apart from the materials values,
primarily on the duration of a rise in temperature.
Figure 18.8.1 illustrates the heat flow in a building element. If the amount of heat
Q per surface A that flows in a given period into the wall is determined by dynamic
calculation methods or by measurement, then an effective thickness d eff wherein full
storage capability is utilized can be calculated for the wall.

Q
AcρT

d eff = (18.8.2)

1m 2 surface) can,
largely irrespective of its thickness, take up approximately 33 Wh for each Kelvin of
temperature rise (with heat take-up on both sides). This corresponds to an effective
thickness of approximately 5 cm. With a six-hour rise in temperature this value is
approximately 9 cm.
If the heating up of a room is to be calculated, then rough estimates of the amount
of heat Q flowing into the component can be calculated by using the heat transfer
coefficient h i and the temperature difference between the component surface T s ,1 (at
the beginning of a time step t) and the room air T i .

=

During a three-hour rise in temperature, a concrete wall (with A

Q = h i At ( T i − T s ,1 ) (18.8.3)

After the time step, the new temperature of the component T s ,2 results from the stored
amount of heat Q s = Q :

Q s
Acρd eff

= +

T s ,2 T s ,1 (18.8.4)