Facades and Summer Performance of Buildings - Low Energy Cooling for Sustainable Buildings - page 52

Figure 2.30 Measured air inlet and outlet temperatures together with calculated outlet air temperatures
using Nusselt correlations from Fux's work and from mixed and forced convection
Case PV0: To estimate the thermal buffer effect of the PV double fa¸ade the air
gap is ventilated by forced convection the whole year long but without thermal
coupling between the air gap and the building. Flow velocities in the fa¸ade are
varied between 0.4 and 1.5m s − 1 , and the ventilation rate of the building is constant
at 0.7 h − 1 .
Cases PV1 to PV3: In these cases, the air gap distance and the air speed rate within
the fa¸ade are changed. Facade air is led into the building if the zone temperature
falls below 21 ◦ C. Depending on the forced volume flow through the fa¸ade, the
air change rate of the building varies between 0.7 and 2.0 h − 1 . During the summer
period, or if the zone temperature exceeds 21 ◦ C, the fa¸ade air is exhausted to
Figure 2.31 Heat transfer coefficients on the warm PV side and the cold window side using different
Nusselt number correlations