Effect of Screening Solar Chimneys on Induced Air Flow Rate

Abstract

This paper reports on a field investigation of the effect of screening on the induced flow rate in solar chimneys. The solar chimney considered here was a roof solar collector (RSC). It is composed of CPAC monier concrete tiles, an air gap and gypsum board. Two RSC units were integrated into the south-facing roof of a centre single room house of 25 m3 volume. Different types of screening were considered, namely: mosquito net, square net, metal grille and nylon filter. Different arrangements of one or more screens were installed at the top of one RSC unit while the other unit was not screened and served as a reference.It can be concluded that the addition of screens decreased the induced air ventilation depending on the remaining free surface area of the opening. The smaller the remaining free surface area of the opening, the higher the percentage decrease of air flow rate. However, the induced air flow rate is still relatively important to ensure sufficient space ventilation and indoor air motion. Based on experimental data, a simple linear relationship between the percentage of remaining opening area and the percentage decrease or drop of air flow rate was derived. The use of a nylon filter yields the highest rate of decrease (about 8%). When mosquito net, grille and nylon filter were used together, the decrease of air flow rate was about 18 %. However, when the wind speed is important, the drop of air flow rate is less significant.Finally, since screening (particularly the nylon filter) decreases the rate of dust admitted into the house with the incoming ambient air, it will play an important role in promoting the concept of the solar chimney ventilated house (SCVH)