Thermal simulation of ventilated PV-facades
The application of double glazed facades, especially in administration buildings is becoming more and more popular. Aside from the architectural aspects, the energetic consequences with respect to the building into which it is integrated have been discussed much over the past few years. In order to quantify the energy balance of such facades, the heat transfer rate between the inner facade layers and the gap temperature are important factors and constitute the core of this thesis. In contrast to experimental estimations of heat transfer rates, which are measured using heat flux sensors, in this study the energy balance within the facade was determined primarily by means of computational fluid dynamics (CFD). For the purpose of verifying the CFD results, simulation results were assessed through comparison with experimental flow data obtained using particle image velocimetry (PIV). Comparison of CFD simulations and PIV measurements showed good agreement for different symmetric and asymmetric plate temperatures as well as for different forced flow rates. A new Nusselt correlation was developed, which was derived from a CFD parameter study. The suggested correlation includes plate distances which vary from 0.05 to 0.5m, surface temperatures from -10 to 60 degrees C, inlet temperatures from -10 to 30 degrees C and Reynolds numbers (Red) between 500 and 6500. In order to estimate the thermal behaviour of a ventilated facade at an early stage of building planning, a transient simulation program was developed which is able to calculate the dynamic energy balance that occurs in a double facade. To facilitate integration of the calculation method into the commercial building simulation program TRNSYS 15, a new Type (Type 111) was written. This Type 111 can be used to connect an arbitrary facade construction to the existed building model Type56. Comparisons between calculated results from the developed model and measurements on real facades(a hybrid, mechanically-ventilated PV fagade and a naturally-ventilated, double glazed facade) provided sufficiently good agreement. The total energy rate through a window (g-value), estimated by the special g-value test rig at the Stuttgart University of Applied Sciences could also be reproduced accurately using the developed program.