A novel transient testing method for heat/energy wheel components

Abstract

Heat wheels and energy wheels are widely used in ventilation systems to recovery sensible and latent energy, and consequently, reduce the energy required to condition outdoor ventilation air for buildings. This Ph.D. thesis proposes a novel transient testing facility and method to predict the effectiveness of heat/energy wheels by testing a small component of the wheels. The component required for this test is a few coated sheets (for energy wheels) or non-coated sheets (for heat wheels). The effectiveness values predicted for small-scale testing and determined from correlations in the literature agreed within ±3% and within the experimental uncertainty bounds (at wheel angular speed, ω, of 20 rpm when NTU < 13.1 and 2 < NTUm < 10). The transient component testing was also used to investigate the effects of physical and sorption properties of mesoporous silica gel on moisture transfer. It was found that the smaller the pore width and the larger the specific surface area, the higher the sorption capacity of the desiccant. However, the smaller pore width increases the vapour diffusion resistance and reduces the sorption rate. It was observed that the energy exchanger coated with silica gel that has an average pore width of 63 Å and an average particle size of 150 μm (63 Å-150 μm) performed better than the two other silica gel coated exchangers (77 Å-55 μm and 115 Å-160 μm), especially when ω < 5 rpm. The latent effectiveness of all the exchangers were nearly the same at higher angular speeds, ω > 10 rpm. Finally, the performance of an exchanger coated with biopolymer starch particles was compared with the silica gel coated exchangers through transient testing. It was found that the starch particles increased the latent effectiveness by 13% at ω = 0.5 rpm compared to the silica gel particles while the latent effectiveness values were nearly equal at ω = 20 rpm. Considering that starch typically costs less than silica gel, bio-desiccants such as starch have great potential to be used in desiccant coated exchangers.