Facades and Summer Performance of Buildings - Low Energy Cooling for Sustainable Buildings - page 60

typically higher than the delivered electrical energy from the fa¸ade. For the Spanish
case study building, a ventilation rate of 0.7 h − 1 gave winter thermal gains between 80
and 150 kWhm − 2 a − 1 , increasing with flow velocity. The summer gains, which can
be used to drive a thermal cooling machine (see section 5.2), are of the same order
of magnitude. In total, the thermal gains are 2.5 to 5 times higher than the electrical
energy produced. If higher ventilation rates can be used in the building, increasing
volume flows improve the heat transfer and thus the collector efficiency, which can
reach 15-35 % as an annual mean value. However, as the pressure drop increases
with the square of flow velocity, care has to be taken to minimize ventilation power.
The best COPs were obtained for larger gap sizes, where flow velocities were below
0.5ms − 1 and COPs over 10 can be obtained.