M. Ciampi, F. Leccese and G. Tuoni

Department of Energetica “Lorenzo Poggi” — University of Pisa

Faculty of Engineering — Via Diotisalvi, 2 — 56126 Pisa (Italy)

e-mail: m. ciampi@ing. unipi. it; f. leccese@ing. unipi. it; g. tuoni@ing. unpi. it

The energy performance of peculiar ventilated structures, such as walls with advanced screen, is investigated. In these structures the duct thickness is small and the air flow inside is laminar.

The obtained results show that an energy saving, even exceeding the 20%, can be achieved by using these structures in summer, compared to the same non — ventilated structure; in winter, the increase in heat losses, due to ventilation, can result to be remarkable and such as to make advisable closing the air duct or reducing the ventilation.

Introduction

The European Directive 2002/91/CE on the energy performance of buildings [1] devotes its attention to the necessity of more carefulness in the building design, with particular respect to its envelope, in order to reduce the energy consumption as well as the impact on the outdoor environment. The Directive also focuses its attention on the fact that the air­conditioning plants have become, in the last few years, widespread systems; this causes a remarkable electricity demand growth in summer, e. g. during the last August, in Italy, several black-outs occurred due to an excessive demand from the users. For this reason the Directive suggests adopting priority strategies which could enhance the thermal performance of buildings especially in summer. For instance, passive cooling techniques could be developed in order to improve the indoor climatic conditions as well as the microclimate around buildings. The Member States of the European Union have to bring into force the laws, regulations and administrative provisions necessary to comply with the Directive at latest on 4th January 2006.

The ventilated walls (VW) are fully included in the passive cooling techniques, explicitly provided for by the Directive. In the last few years they have been widely investigated by several authors [2-10]. In [4, 8, 10] the same authors have proposed a calculation method, suitable for design applications, in order to evaluate the reduction in summer thermal loads achievable by using VW. They have also studied, in [5], the influence of the variation of several thermal and fluid dynamic parameters on the energy performance of a VW.

In this paper, referring to several remarks synthetically reported by the same Authors in [9], the energy performance achievable, with particular reference to the summer case, by using VW characterized by small thicknesses of the air duct and by laminar flow, is investigated. These building components are generally indicated, in technical literature, as walls with advanced screen (ASW) which are frequently used in contemporary architecture. The obtained results show that an energy saving, even exceeding the 20 %, can be reached by using these structures in summer, compared to the same non — ventilated structure.