Design and zonal building energy modeling of a roof integrated solar chimney

Roof integrated solar chimneys use solar radiation to heat air and induce natural ventilation through a house. They can improve the performance of roof integrated photovoltaic arrays by removing heat absorbed by the panels, and enhance buoyant free cooling at night. This paper studies an unobtrusive, integrated solar chimney design in a detached single family home. A method for modeling it in the zonal building energy modeling program ESP-r is proposed, to assist in evaluating the design and predicting the thermal dynamics in changing ambient conditions. The model discretizes the solar chimney by dividing it into several zones to better resolve the airflow and heat transfer. Computational fluid dynamics is used to calibrate key model inputs. The results show that with the proposed rooftop design, the chimney airflow is induced mainly by buoyancy forces whenever the temperature difference from interior to ambient differs by more than a few degrees, so there is the potential to provide effective free cooling. A sensitivity analysis evaluates the model's sensitivity to several inputs and assumptions. It confirms that the inside to ambient temperature difference is the most important predictor of ventilation airflow. Solar insolation levels are less important, being significant for less than one third of the time-steps sampled. Sensitivity of modeling results to uncertainty in the calculation of the convection coefficient is explored, showing there is high sensitivity in the prediction of the heat transfer normal to the surface of the roof, but low sensitivity in the prediction of the rate of ventilation airflow through the house and the temperature of the roof surface. The amount of pressure loss in the flow through the vent at the entrance to the chimney is a significant factor for the ventilation flow rate.