Correlation between Microclimate and Macroclimate

This chapter presents two models, which can be used for optimizing the microclimate inside a solar thermal collector, and the results of calculations for several types of collectors. Damage of materials inside a solar collector depends on the corrosivity of the climate inside the collector, the so-called microclimate.

The microclimate depends on the ambient weather and the construction of the collector. Two models were developed, which can be used to optimize the construction of collectors with the most favorable microclimate, and are based on an analytical heat and moisture balance and on computational fluid dynamics, respectively.

The models, which take into account the condensation of water vapor on the inside of collector surfaces and for the sorption of water vapor in the insulation material, have been demonstrated to predict these phenomena reliably in realistic situations. Calculated results are presented for the annual average humidity hours and the amount of condensate exceeds areal concentrations of 1 to 10g/m2 for air permeabilities up to 1001/h.

Results are also presented for ventilation rates at normal operating and stagnation conditions. The measured and calculated absolute humidity in a collector during a typical 24-h period are comparable..