Anna Laura Pisello

Local climate change and urban heat island mitigation techniques – the state of the art

AbstractIncrease of the ambient air temperature in cities caused by the urban heat island phenomenon has a seri- ous impact on the economic and social system of cities. to counterbalance the consequences of the increased urban temperatures important research has been carried out resulting in the development of efficient mitigation technologies. the present paper aims to present the state of the art in terms of local climate change and urban heat island mitigation techniques. In particular, developments in the field on highly reflective materials, cool and green roofs, cool pavements, urban green and of other mitigation technologies are presented in detail, while examples of implemented projects are given.

Active cool roof effect: impact of cool roofs on cooling system efficiency

Cool roofs represent an acknowledged, relatively simple, and low-cost strategy to reduce cooling energy demand of buildings and mitigate urban heat island phenomena. The purpose of this paper is to study the coupled passive–active effect produced by such a technology, where the active effect consists of the cool roof capability to decrease the suction air temperature of heat pump external units, when these units are located over the roof. This “cooling” benefit produces an extra increase of the energy performance of the heat pump in cooling mode, given that it produces the decrease of the temperature lift between the source and the output. In order to study this twofold effect, an industrial building with an office area located in Rome, Italy, was continuously monitored in summer 2012. The main results showed that the cool roof allows to decrease the roof overheating up to 20°C. The office indoor air temperature also decreased, even if the same set-point temperature was kept constant during the whole campaign. The energy requirement for cooling decreased by about 34%. In order to investigate the “active” contribution, suction air temperature was monitored and a new simple analytical model is proposed in order to estimate the cool roof active effect.

An energy-balanced analytic model for urban heat canyons: comparison with experimental data

The climate of high-density urban areas is often affected by the air temperature increase with respect to the neighbouring country-side. This phenomenon, known as the urban heat island (UHI) effect, is strongly influenced by the solar reflectance of building envelope and coating materials, and it is enhanced in the presence of built patterns that trap the solar and anthropogenic energy, usually referred to as urban heat canyons. An original method to quantify the urban heat canyon effect as a function of meteorological conditions, geometry, and surface properties is proposed. The goal is to provide a reliable tool to estimate the effect of the reflective properties of the canyon surfaces on the urban environment, in order to guide the choice of effective solution towards the UHI mitigation. An energy-balanced analytic model, specifically set-up to predict surface temperatures inside an urban canyon, is applied to a scale test facility located at the University of Perugia, Italy. The test facility is made of two twin arrays resembling urban canyons with different aspect ratios. Each canyon can be equipped with reflective films to quantify the radiative exchange variation. Preliminary results from the experimental facility monitoring and the analytic model validation are presented.

Natural Materials for Thermal Insulation and Passive Cooling Application

In this chapter a critical analysis about natural materials to enhance energy performance and thermal comfort in indoor and outdoor spaces is dealt with. In particular, thermal insulation and passive cooling application in buildings are analyzed. The physical properties permitting to achieve these benefits are presented, as well as the method and the international standards to measure them. Benefits deriving from these materials’ employment as insulation layers or buildings envelope in general of, or in the case of urban paving, are described and then the single materials are illustrated.Experimental and numerical data, as reported in the bibliography, support the dissertation with examples from the most recent research contributions.

Traditional and Innovative Materials for Energy Efficiency in Buildings

This chapter shows the most recent and innovative contributions and research trends arounbd the wide issue of energy efficiency in buildings by means of passive techniques, such as new effective materials for building envelope optimization. In particular, cool materials will be dealt with by considering their capability to keep a surface cooler than other solutions when exposed to solar radiation. Then multifunctional materials such as thermal and acoustic insulation panels will be analyzed. Finbally, natural and biobased solutions for energy saving will be investigated. Each one of these topics will be studied by elaborating a first general assessment of each technique and then by analyzing the most recent contributions and research trends in order to provide a wide perspective of the question that is going to be addressed in this chapter.

Simulating the Thermal-Energy Performance of Buildings at the Urban Scale: Evaluation of Inter-Building Effects in Different Urban Configurations

Abstract The reduction of the energy use of buildings at the urban scale represents a key research and design topic with the purpose of developing specific methods for saving energy in buildings. These methods are often focused on the analysis of building thermal-energy behavior by considering the building as a stand-alone object. In this perspective, the thermal-energy behavior of two buildings in New York City is evaluated in this paper with varying urban contexts, in order to evaluate the Inter-Building Effect (IBE). The IBE analysis shows that the inaccuracy in neglecting the urban context in building modeling varies from 9.6 percent, to 71.9 percent. These results confirm that, in order to make accurate predictions about building thermal-energy performance in real urban contexts through dynamic simulation, the interaction between the building and the urban surrounding should be taken into account, in particular in dense urban areas.

High-albedo roof coatings for reducing building cooling needs

Abstract This chapter gives a critical analysis of high-albedo coatings for building applications, i.e., cool roofing systems. After a brief introduction concerning the threefold benefits of such applications, i.e., at building, urban, and global climate scale, specific characteristics of these coatings are discussed. The physical properties determining their cooling potential, i.e., solar reflectance, thermal emittance, and the final overall solar reflectance index, are presented. In Section 9.3 , the thermal-energy behavior of a roof is assessed. Section 9.4 details the methodology for measuring solar reflectance and infrared emittance and references technical standards. In Section 9.5 , the benefits of high-albedo coatings for roofs are presented. Section 9.6 concerns new scientific trends in high-albedo materials. Finally, aging and weathering phenomena are discussed. The analysis of these aspects is supported by experimental, analytic, and numerical data reported in the reference section.

ON THE IMPACT OF COOL ROOFS IN ITALIAN RESIDENTIAL BUILDINGS: EXPERIMENTAL ASSESSMENT OF SUMMER AND WINTER PERFORMANCE

The purpose of the work is to evaluate the impact of roof surface properties, i.e. reflectance, on building thermal performance in summer and winter conditions. In particular these properties have been analyzed on traditional roof brick tiles through indoor and outdoor two-years long continuous monitoring for investigating “cool roof” benefits and penalties. The experimental campaign has been set up in a residential single family building in the central Italy, where a meteorological station and a microclimate station have been installed. The monitoring campaign consisted of the evaluation of the base case configuration and the high reflecting roof configuration, after the optimization of the reflectance properties through in-lab measurements of traditional brick tiles. Thanks to the overall analysis and to the cooperation with industrial companies producing brick tiles and reflective coatings, a new tile with notable “cool roof” properties has been produced following the traditional industrial path of the tiles already commercialized in Italy and all over the world. The final purpose of this experimental activity was to evaluate the effect, in terms of indoor thermal free-running behavior of the attic, of high reflecting tiles, previously optimized with respect to Solar Reflection Index, and to assess summer benefits and potential winter penalties in the typical temperate climate of central Italy. First important results show that during summer the high reflective tiles are able to put down the average external roof surface temperature by more than 10°C and the indoor operative temperature by more than 3°C. During winter the average external surface temperature is lower with high reflective tiles by about 1°C. Also, comparing December-January results of both these scenarios, the indoor operative temperature basically does not register any notable reduction given by the new tiles setting.

Network of buildings’ impact on indoor thermal performance

Purpose – The development of strategies for energy efficiency optimization in buildings has become a fundamental way to reduce buildings’ environmental impact because the amount of energy consumed by buildings is responsible for one‐third of total global energy consumption. The purpose of this research is to evaluate the performance of buildings in terms of their indoor operative temperature dynamics considering the impact of other neighbouring buildings. The goal of the paper is to verify whether close spatial relationships of buildings and urban morphology within a local network of buildings could cause a considerable effect on indoor thermal behaviour.Design/methodology/approach – The authors simulated buildings in an existing city block in Albany, New York, USA. The block consisted of six single‐family houses.Findings – The results demonstrate that buildings mutually impact the indoor thermal behaviour of other buildings in the network with indoor operative temperature differences of over 20 percent i...

Self-sensing and thermal energy experimental characterization of multifunctional cement-matrix composites with carbon nano-inclusions

The recent progress of Nanotechnology allowed the development of new smart materials in several fields of engineering. In particular, innovative construction materials with multifunctional enhanced properties can be produced. The paper presents an experimental characterization on cement-matrix pastes doped with Carbon Nanotubes, Carbon Nano-fibers, Carbon Black and Graphene Nano-platelets. Both electro-mechanical and thermo-physical investigations have been carried out. The conductive nano-inclusions provide the cementitious matrix with piezo-resistive properties allowing the detection of external strain and stress changes. Thereby, traditional building materials, such as concrete and cementitious materials in general, would be capable of self-monitoring the state of deformation they are subject to, giving rise to diffuse sensing systems of structural integrity. Besides supplying self-sensing abilities, carbon nano-fillers may change mechanical, physical and thermal properties of cementitious composites. The experimental tests of the research have been mainly concentrated on the thermal conductivity and the optical properties of the different nano-modified materials, in order to make a critical comparison between them. The aim of the work is the characterization of an innovative multifunctional composite capable of combining self-monitoring properties with proper mechanical and thermal-energy efficiency characteristics. The potential applications of these nano-modified materials cover a wide range of possibilities, such as structural elements, floors, geothermal piles, radiant systems and more.