Simulations of Airflow in the Roof Space of a Gothic Sanctuary Using CFD Models

Radoslav Ponechal,Peter Pisca,Peter Kysela,Peter Krušinský

doi:10.3390/en14123694

Abstract

For a deep understanding of the airflow in an environment of historic wooden trusses, it is necessary to analyze the object using simulation methods. To calculate the amount of air passing through the structural openings (components) using dynamic simulation, multi-zone network models based on the simplicity of modeling the individual zones are suitable. For a more detailed analysis of airflow and temperature distribution within one space, a computational fluid dynamics (CFD) simulation model was performed. The air volume through openings and surface temperatures was adopted from the multi-zone airflow network model. By using this simulation technique during a sunny summer day four characteristic states of air movement were simulated in the attic: more intense flow at noon and at midnight caused by a large temperature difference between air and surrounding surfaces and, subsequently, less intense flow when the air was mixed up effectively. The temperature distribution in the cross-sections did not only indicate an increase in temperature with increasing height (up to 50 °C at noon) but also a temperature increase near the southern roof. The surface temperature of the masonry walls was stable (19–33 °C), while the air temperature fluctuated. The image of the flow was completed by ventilation through the tower, which acted as a solar chimney. The airflow through the door to the tower was almost 0.5 m3 s−1 at summer midnight.

Highlights

The analysis of historic trusses, in addition to craftsmanship, geometry and stability, examines the microclimate
Stationary simulation, adopting boundary conditions from building performance simulation (BPS). These states changed at approximately 6-h intervals as in the analysis of coupled building energy and computational fluid dynamics (CFD)
Two states feature more intense flow, which occurs at noon and at night and is caused by a large difference between air temperature and surface temperature

Summary

Introduction

The analysis of historic trusses, in addition to craftsmanship, geometry and stability, examines the microclimate. Suitable climatic conditions in the attic space can have a positive effect on the service life of the structure These conditions are mainly influenced by the attic ventilation and external weather conditions [1,2,3,4,5]. In recent years Richter et al have been dealing with the unheated attic spaces (so-called ”cold attics”) as one of the most moisture-problematic spaces in the building [10]. They stated that that the colder the climate is, the more advantageous the use of a ventilated attic becomes. While in the past the builders relied on empirical experience to a greater extent than at present, they can use computer simulation models to analyze how the construction behaves and how it works in principle [14,15,16,17,18,19,20,21]

Methods

Results

Conclusion