Energy performance assessment of historical buildings CFD simulations of Scirocco Room Relator Prof. Fabrizio Leonforte Author Lea Kazazi 878007 Mirko Vilei 900105 1 Index Introduction ............................................................................................................................................... 3 1. Numerical simulation to investigate the adequacy of historical buildings ............................................... 4 1.1 Natural ventilation and computational fluid dynamics ..................................................................... 4 1.2 Possibilities and limitations. CFD vs BES ............................................................................................ 5 2. Fluid simulations in heritage science ......................................................................................................... 8 2.1 Computational fluid dynamics in historical building: state of art ..................................................... 8 3. Ventilation and historical buildings: three case studies solved with CFD ............................................... 17 3.1 CASE STUDY I ................................................................................................................................... 18 3.2 CASE STUDY II .................................................................................................................................. 21 3.3 CASE STUDY III ................................................................................................................................. 24 4. Forerunner cooling systems: scirocco room ........................................................................................... 28 4.1 History and typology evolution ....................................................................................................... 28 4.2 Examples of scirocco rooms ............................................................................................................ 30 4.3 Defining the case study ................................................................................................................... 34 5. CFD modelling .......................................................................................................................................... 39 5.1 Setting simulations and control volume definition ......................................................................... 39 5.2 Setting Data ..................................................................................................................................... 40 6. Results and Discussion ............................................................................................................................. 43 6.1 Graphs ............................................................................................................................................. 43 6.2 Best Configuration and best Month ................................................................................................ 53 6.3 PMV e PPD ....................................................................................................................................... 60 7. Conclusions .............................................................................................................................................. 66 ▪ Appendix .................................................................................................................................................. 69 ▪ References ............................................................................................................................................... 76 2 Introduction Natural ventilation is the best system to be provided to historical buildings as a passive cooling. In this thesis the Scirocco Room of Villa Naselli-Ambleri has been analysed [1]. The system has been modelled and simulated through a pseudo-transient simulation on Ansys Fluent. CFD analysis is a very powerful tool to read and understand this kind of systems. The knowledge of such a construction and operating principles is particularly important to re-discover the forgotten “places of delight” that are a fundamental element in Palermo history and culture. Furthermore, preservation and reuse of surviving rooms represent a useful way to understand a simple passive cooling system whose principles could be reproduced in a contemporary way in modern buildings intended for a valid and functional energetic control. 3 1. Numerical simulation to investigate the adequacy of historical buildings Some architectural structures inside historical buildings are often interpreted as cooling systems. The problem is the knowledge about the real functioning of these systems during the past and at the present. Usually they have gone through a lot of changes. Full scale measurements can provide data on ventilation rate, airflow distribution, mean air velocity around and inside a building, but these experiments are expensive and time consuming. So how can we study these systems? Through CFD. CFD techniques allow to study large confined spaces, where it is difficult to predict the indoor air flows and thermo-hygrometric fields by means of simplified models or measurements. Thanks to their features, CFD software, originally used only for scientific research, have become, in recent years, a design support tool used by professional engineers when an in-depth knowledge of indoor air flow paths and pollutants distribution is required. Though, one of the hardest tasks of modelling is to obtain a reliable model but, once achieved, it can be a flexible tool that can be combined with experimental data to provide useful information on indoor airflow patterns. 1.1 Natural ventilation and computational fluid dynamics In these years, there has been extensive research dealing with CFD modelling of natural ventilation in buildings, probably because this ventilation is seen as a sustainable solution to reduce energy consumption and retain healthy conditions. However, there is the need of better addressing the effectiveness of natural ventilation in historical buildings and its implication in heritage preservation. Because of the monumental value of historical buildings, every intervention or refurbishment that can modify the indoors has to be carefully planned with the priority of conservation. This is because artworks have been adapted to a natural microclimate over centuries, gaining an equilibrium able to compensate cyclical seasonal variations in temperature and relative humidity. So, in these buildings, conservation should be a priority in the evaluation of indoor conditions. If adequate, a natural microclimate, to which artworks have been adapted over centuries, should be maintained to avoid sudden microclimatic changes and consider the main features of the site. This is why, at the stage of air-conditioning system design or retrofit, it is extremely important to carry out a series of preliminary analysis to evaluate and monitor the existing environmental conditions and to anticipatory simulate and predict the post-intervention conditions. In particular, the estimate, in “predictive” terms, of the microclimatic parameters and of their space distribution is becoming essential in order to define the compatibility of the environment with the maintenance of the desired conservation conditions. Consequently, natural ventilation is generally preferable for conservation reasons, and insulating the external walls might be avoided. In natural ventilated systems the airflow is driven through ventilation openings by the natural driving forces of wind and temperature, therefore a comprehensive understanding of complex airflow patterns linked to wind effects and buoyancy is essential. 4 1.2 Possibilities and limitations. CFD vs BES CFD simulation have the potential to predict the situation that is going to happen inside the volume analysed. As introduced before one of the hardest tasks of modelling is to obtain a reliable model but, once achieved, it can be a flexible tool that can be combined with experimental data to provide useful information on indoor airflow patterns. The main steps to follow in a CFD investigation procedure are here summarized: • definition of the geometrical model; • characterisation of the air flow opening/devices and of the internal gains (heat, pollutants, etc.); • definition of the boundary conditions and adoption of a turbulence model; • discretization of the calculation domain; • run of the numerical simulation and verification of the numerical convergence; • analysis of the results (air flow path, velocity fields, thermal fields, etc.). In general, In CFD models the equations of conservation for mass, momentum (expressed by the Navier– Stokes equations), energy and chemical species, together with the turbulence models, are written and solved. In particular, the partial differential equations ruling the system are discretized in terms of finite differences and solved in a given number of points of a grid overlapped to the geometrical domain. The discretization approach adopted for the air distribution analysis is typically that of the finite volume method. Alternatively, the finite element method is used. To define the volume in which the boundary conditions will be set, it’s always suggested to simplify the forms, so from a slightly trapezoidal plan, is preferred to take an equivalent rectangular shaped one. This will be carefully described in the Case Study of Palazzo Madama (Turin)[2]. Often The aim of CFD