Elisa Di Giuseppe

Thermal performance of an insulated roof with reflective insulation: Field tests under hot climatic conditions

The use of reflective insulation materials in buildings, for energy saving in summer, has been spreading in southern Europe. These products are not typical of the local building context. There is a lack of well-established measurement systems for reflective insulation thermal transmittance. The aim of this article is to understand whether a reflective insulation material could be effective in hot and temperate climate, also compared with other roof solutions. For this purpose, we compared the thermal performance of a roof with and without reflective insulation, both installed in a full-scale experimental building near Ancona (Italy) in the summer period. The results showed that the reflective insulation benefits are quite limited when using the insulation level imposed by actual laws, which consider insulation as the main strategy for energy saving in temperate and hot climates.

Assessment of the effectiveness of cool and green roofs for the mitigation of the Heat Island effect and for the improvement of thermal comfort in Nearly Zero Energy Building

The effectiveness of cool and green roofs to improve thermal comfort could be strongly dependent on the U-value of the roof itself and on the way it has been constructed (ventilated or unventilated, lightweight or massive, etc.). Recent strict limits on the U-values of building envelopes run the risk of reducing the effectiveness of cooling strategies in roofs which could be employed in warm and temperate climates to reduce surface temperatures and consequently to cool internal environment. In this paper, we experimentally analyse some roof systems (a high-albedo membrane and a green roof) compared to traditional ones in a Nearly Zero Energy Building, in order to provide new information concerning their effect on the internal comfort and the air temperatures of the surrounding environment. Experimental results confirm that, while the effectiveness of green and cool roofs for the mitigation of the Urban Heat Island effect is well established, the use of high-albedo materials on roofing systems with very low U-value is of little effectiveness for internal comfort. The green roof is distinguished by its passive cooling ability due to the evapotranspiration phenomena of the vegetation and the storage capacity of the substrate.

A field study of thermal inertia of roofs and its influence on indoor comfort

Many of the current European Member States regulations on energy saving in buildings seem to follow North European trends that call for high insulation of the envelope. However, this kind of set-up overlooks some specific elements that are necessary to build typical buildings in warmer climates. Thermal inertia on the internal surface of the envelope has traditionally been used in such contexts not only to contain solar gains but also to protect against cold winter because of its capacity to store and to slowly release energy. This research investigates how thermal inertia on roof slabs could positively affect the comfort indoors, also in buildings that tend towards being nearly zero-energy buildings, as suggested by last European Directive 2010/31/EU. With this aim, an experiment was conducted on a full-scale building with different roofs, on light and heavy slabs, under hot and moderate climatic conditions (Ancona, Italy). The thermal performance of roofs was monitored during summer and winter seasons. In winter, the building was also subjected to cyclical internal heat gains. The experiment demonstrated that a certain thermal inertia in the slab guarantees better indoor comfort in both summer and winter, and it can also reduce energy consumption from heating.

Remedial Actions and Future Trends

The aesthetic quality and durability of external building envelope could be seriously impaired by the development of microorganisms, which will colonise building materials whenever a suitable combination of dampness, light and “bioreceptivity” of the substrate occurs. The control of biodeterioration in buildings includes measures useful to eliminate the presence of microorganisms and, when possible, to delay their recurrence. The difficulty lies in applying methods that are effective against biodeteriogens but that do not have interaction with the materials of the substrates. This chapter outlines some of the consolidated or innovative approaches which aim to give a concrete answer to the biological problem in buildings, acting both on the microorganisms already disseminated and on the main causes of development. Several methods may be used, in function of the type of organism present, the materials of the substrate and its state of preservation, the construction methods of the building and the freedom and economy of the intervention. Among the traditional methods, mechanical, chemical and physical strategies for the removal of biodeteriogens have been mentioned, while a more detailed study will be done on the use of biocides and water repellents that directly act on the material to prevent it from becoming fertile ground for microorganism development. Among the innovative methods, the use of engineered nanoparticles as additives to envelope finishing materials is catching on. Strategies that include a set of practical design, construction and use of buildings, which allow acting on the environmental conditions that favour the proliferation of microorganisms will be finally reported as sustainable actions.

Optical properties of traditional clay tiles for ventilated roofs and implication on roof thermal performance

A remarkable advantage of clay tiles roof coverings in hot climates is the realization of a ventilated air layer between them and the roofing underlay that allows a natural and forced convection through the tiles joints and the channel from eaves to ridge, thus cooling the roof materials. However recently, in many countries, regulatory developments on buildings energy efficiency or buildings sustainability certification protocols are increasingly encouraging the use of alternative strategies, with the aim of reducing the urban heat island (UHI) effect and the buildings’ cooling consumptions. Among them, the use of ‘cool’ materials for roof covering. These mandatory or voluntary measures de facto push the construction products market towards specific directions, risking penalizing traditional components such as clay tiles. This article reports the results of experimental and numerical activities carried out in order to extensively characterize the optical properties of clay tile materials and investigate their impact, also coupled with above sheathing ventilation, on the thermal performance of a ventilated roof under warm-temperate climate. In the first phase of the research, the main optical properties of over 30 different clay products have been experimentally characterized in order to get a clear and extensive picture of such properties for the materials spread in the market. In a second phase, starting from the thermal data collected on an experimental real-scale building, a dynamic energy analysis tool was calibrated and used to perform simulations by varying the optical properties of the roof covering thus assessing the impact on the roof temperatures, also in comparison to a clay tiles roof. The results underline that the use of the above sheathing ventilation obtained through clay tiles is an effective strategy to reduce roof temperatures, even if covering materials are not qualified as ‘cool’, thus impacting on both UHI and indoor comfort.

Development of Mould in Indoor Environments

Mould spores are widely disseminated in the environment. Even inside the buildings, we can find hundreds of species of fungi, proliferating with a favourable combination of conditions (oxygen, appropriate temperature, moisture, nourishment from the substrate) in which to germinate, grow, and sporulate. The presence of mould in buildings is not welcome for two main reasons: they are responsible for several types of illnesses and pathologies experienced by building occupants, grouped under the name of “Sick Building Syndrome”, and their presence contributes to the defacement of paint and finishes. In recent years, since buildings are always more airtight and highly insulated, internal moisture load risks to become always greater if not managed by an adequate strategy. Consequently, the presence of moulds has considerably increased, despite the fact that living spaces should have better quality. Attention should be paid to the correct application of all that leads to minimisation of mould risk in buildings.

Nearly Zero Energy Buildings and Proliferation of Microorganisms

In recent building practice, obligations to legislation on energy saving are carried out mainly by a high thermal resistance and a global airtightness of the envelope, aiming to minimise heat dispersions by conduction and infiltration as much as possible. These measures determine new ways of heat and moisture exchange in the building envelope and are likely to exacerbate the growth of microorganisms. New poorly permeable buildings are in fact more subject to high internal moisture load, in combination with an unsuitable ventilation strategy. Modern exterior insulation finish systems do not have much thermal inertia and are more subject to undercooling phenomena, condensation and a consequent higher biological growth risk. Renovation techniques, such as the replacement of single glazed windows by new very tight double or triple glazed windows or the addition of interior insulation, induce condensation phenomena on the unavoidable thermal bridges (frames, subframes, structure). The NZEB of the future must be able to give a concrete answer to these problems, since, although no changes occur in the thermal performance of the buildings, biological defacement has an enormous aesthetic, health and economic impact, which gathers the disapproval of building’s dwellers. This chapter will explore these topics, by describing the major consequences of the ‘sealing action’ and ‘overinsulation’ on the proliferation of microorganisms in NZEB.

Analytical and Experimental Methods for the Assessment of the Biological Proliferation in Buildings

In order to preserve buildings from the colonisation of microorganisms and to act efficiently against biodeterioration, it is necessary to have a better understanding of biodeterioration mechanisms and their effects on materials properties. Consequently, there is a growing demand for calculation methods in building engineering to assess the moisture behaviour of building components and microorganism risk prediction in order to ensure a healthy environment and to avoid defacement of materials and other social and economic consequences. Many building hygrothermal analysis methods are able to simulate the coupled transport processes of heat and moisture for one or multidimensional cases, aiming to predict biological risk. Additional measurements in laboratory and in situ conditions have been used for the validation of these models. In the first part of this chapter, we review some of the major biological risk predictive models, both inside and outside the buildings. Then, in the second part, we will describe some methods of accelerated experimental testing for the evaluation of biological defacement of building materials. A more in-depth study of microorganism growth under transient conditions is still necessary in order to define the most reliable prediction model. To do so, additional measurements in laboratory and in situ conditions on new Nearly Zero Energy Buildings and components would be desirable.

Algal Growth on External Building Envelope

Algae are very ancient living organisms. Their presence on earth came about some 3.5 billion years ago. They are considered “pioneer organisms” of outdoor environment, and it is actually possible to find different varieties of algae on the ground, in the air, in ice and even in anthropogenic elements such as the facades of buildings since they are able to survive through frequent freeze–thaw and dehydration cycles. The aesthetic quality and durability of an external building envelope could be seriously impaired by the development of algae which will colonise building materials whenever a suitable combination of humidity, warmth and light occurs. The fundamental role of water for algal growth is clear which, for several reasons, is found in large quantities on building facades. External sources of water here include rain, snow, ground moisture, airborne humidity and condensation of vapour from outdoor air. In addition to environmental conditions, the rate of stain development largely depends on the “bioreceptivity” of the material, that is, its aptitude to be biologically colonised which is related to the material properties that contribute to the anchorage and development of microorganisms. The facades of the buildings are then fertile substrates for the growth of algae.