Chapter 5.3 - Guidelines for Limiting Environmental Stress Factors in Glazed, Ventilated Solar Collectors

Abstract

This chapter provides design guidelines for optimizing the humidity in the microclimate inside a solar collector to improve the service lifetime. Humidity inside a collector is the major factor that must be minimized to provide the most favorable microclimatic condition for preventing the corrosion of the internal materials of the collector. This microclimate inside the collector is important for determining the service lifetime of an absorber coating. During the design of the collector, the location and size of ventilation holes, properties of the insulation materials, and dimension of the solar collector box are parameters that have to be taken into account for the optimization to achieve the most favorable microclimate to prevent corrosion. Simulation of the microclimate in solar thermal collectors can be a valuable tool for optimization of the ventilation rate for the collector. Manufacturers of collectors can be advised if their solar collectors need to be tighter, if fewer or more ventilation openings are needed, and what influence the insulation material has on the microclimate inside the collector. Guidelines for collector designers are proposed that are suggestions to be considered during the design of solar collectors. Simulation data for the influence of ventilation rate on the annual hours that areal condensation exceeds, certain amounts are presented for a traditional International Energy Agency (lEA) collector, for collectors with a vapor barrier, and for collectors with 10 mm of insulation instead of 50 mm. Based on calculations, the optimum ventilation rate is 601/h at a pressure difference of 1 Pa.