Solar energy use in buildings - Solar Energy Sciences and Engineering Applications - page 606

Figure 18.9.2 Amount of energy led into the component with a rise in temperature at the surface
of 10 K.

Figure 18.9.3 Relation of the surface temperature to the colder initial body temperatureT o during an
air temperature jump of + 10 K.

Usually, however, it is not the surface temperature but the air temperature which
is known. Between the air and the surface temperature change there is a phase shift
and a dampening of the amplitude.
With air temperature modifications, the potential for heat storage with a limited
duration of the temperature jump is clearly smaller than with direct impact of the
temperature jump on the surface. After 12 hours the surface has only taken up 60%
of the air temperature jump; i.e. the effective storage capacity sinks by 40%, as can be
seen in Figure 18.9.3.
The surface temperature changes during an air temperature jump essentially
depend on the relation of the heat transfer coefficient h i to the heat conductivity λ of
the component. Component surfaces of materials with low heat conductivity clearly
assume the air temperature faster (i.e. T ( x = 0, t ) /T c becomes zero) than components