Simulating home cooling load reductions for a novel opaque roof solar chimney configuration

The roof solar chimney (RSC) is a low cost passive ventilation technique for reducing the energy consumption for cooling buildings. This study examines the performance and level of energy savings by simulating a detached home in four climates with RSC, cross-ventilation, and standard ventilation strategies. Each case was simulated in ESP-r for baseline and high efficiency construction, detached homes with a single story, three bedrooms, a 189m2 floor plan and high thermal mass constructions. Photovoltaic panels were integrated into the surface of the solar chimney on the South-facing roof to improve the RSC performance with their absorptive properties, and provide cooling to the reverse of the panels with the ventilation airflow. To form the RSC, a gap under the external layer of the roof allowed airflow from the interior of the house to a plenum in the peak of the attic with vents to the outside. Cross ventilation was aided with openings in the interior walls allowing flow between rooms. The ventilation gap was modeled by discretizing the RSC into 12 sections and calibrating the air-flow and convection coefficients with corresponding computational fluid dynamics models. The results indicate that the ventilated roof provides free cooling and natural ventilation in all climates and seasons tested. Flow was caused more by the stack effect rather than through natural convection and the solar chimney effect. Cross ventilation reduced cooling load by approximately 50% percent over the baseline, and the ventilated roof by up to another 80%. Either advanced natural ventilation approach reduced cooling load by more than the green envelope and efficiency practices in three of the four climates. The natural ventilation techniques were proportionally as effective in reducing load in a high efficiency home as in the base case home.