Matheos Santamouris

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.

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.

Indoor air-quality control by a fuzzy-reasoning machine in naturally ventilated buildings

This paper investigates the performance of a fuzzy reasoning machine for the control of indoor air quality in naturally ventilated buildings. Simulations have been performed using a new airflow and pollutant transport model, which has been developed and validated for this purpose; CO2 concentration was used as the indoor-air quality (IAQ) index for these simulations. Results have shown that satisfactory IAQ levels can be maintained, while good stability of the control parameter (i.e. window opening area) was achieved. The impact of such a controller on indoor-air temperature was also studied. The performances were not as good as expected, but were not negligible when compared with the normal conditions of use of the building.

An Experimental Investigation of the Indoor Air Quality in Fifteen School Buildings in Athens, Greece

Abstract The present paper aims at investigating the indoor air quality in fifteen school buildings located in the greater Athens area. Experimental investigations were performed in fifteen different school classrooms and the concentration levels of various pollutants such as CO, CO, TVOC, HCHO, and radon, were measured. Moreover, the experimental investigation included measurements of several environmental parameters such as temperature, relative humidity and air velocity inside each classroom, while ventilation was examined by estimating the air changes using the tracer gas technique. From the above investigation, it was found that the indoor air quality inside the classrooms is strongly related to the number of occupants and their activities. The toxic pollutants such as CO, HCHO, TVOC and radon, measured inside the classrooms, present concentrations that are lower than their relative limit values and hence, they do not create any problem for the occupants. However, frequently, the CO concentration levels were found to be higher than the recommended limits. This can be attributed to insufficient natural ventilation as well as to the absence of mechanical ventilation.

Thermal remote sensing of Thom's discomfort index (DI): comparison with in-situ measurements

The bioclimatic index most commonly used in urban climate studies to describe the level of thermal sensation that a person experiences due to the modified climatic conditions of an urban area, is the discomfort index (DI) of Thom. DI reflects the proportionate contribution of air temperature (Ta) and relative humidity (RH) on the human thermal comfort. In this study, the discomfort index is estimated using thermal infrared data as acquired by the Advanced Very High Resolution Radiometer (AVHRR) sensor on board the National Oceanic and Atmospheric Administration (NOAA) satellite. For this purpose, a dataset of AVHRR-14 daytime images collected during the warm season from June to August 2000 covering the Greater Athens Area, in Greece, was used. Air temperature was related to a split-window estimate of land surface temperature (Ts), whereas relative humidity was assessed in terms of dew point temperature (Td) and of a split-window estimate of atmospheric precipitable water (PW). AVHRR-estimated DI values were compared with coincident DI values obtained from air temperature and relative humidity observations recorded at standard meteorological stations. Statistical analysis showed a good agreement (r2 = 0.79) between the AVHRR-estimated and the station-observed DI values, with a root mean square error (RMSE) of 1.2oC and a bias of 0.9oC. Results demonstrate the potential of using AVHRR data for defining the spatial variation of the DI index at a higher resolution (1.1 km) than is feasible from meteorological stations.

Active solar agricultural greenhouses. The state of the art

The stale of the art on the application of active solar systems for greenhouse heating is presented. Fifty three active solar agricultural greenhouses installed all over the world are reviewed. The identified systems are classified according to the used technology. The various used collecting systems as well as the coupled storage materials are investigated and their characteristics are analyzed. The performance of the various systems is presented. Problems related to technical and economical impact of the solar system are also discussed.

On the Typology, Costs, Energy Performance, Environmental Quality and Operational Characteristics of Double Skin Façades in European Buildings

Abstract The project BESTFAÇADE, sponsored by the Energy Intelligent Europe programme of the European Union, and led by MCE-Anlagenbau, Austria, accumulated the state of the art of double skin façades (DSFs) in seven European countries (Austria, Belgium, France, Germany, Greece, Portugal and Sweden). Twenty-eight façades of different buildings in all partner countries of BESTFAÇADE have been analysed for the aspects, types of façade in different countries, DSFs in different climatic regions of Europe, existing simulations and measurements, thermal behaviour, indoor air quality, comfort, user acceptance, energy demand and consumptions, control strategies, integrated building technology, cost (investment, maintenance and operation), resource conservation, environmental impact, comparison to conventional glass façades (CGFs), integration of renewable energy sources into DSFs, as well as non-energy related issues, such as, acoustics, aesthetics, fire protection, moisture, corrosion, durability, maintenance and repair. Most of the buildings are office buildings, followed by schools and service buildings. Nearly all of the buildings have mechanical ventilation systems, and both heating and cooling are performed mostly by air heating/cooling systems. The types of façades are mainly multi-storey and corridor types; in Belgium juxtaposed modules are frequently used. The façade gaps are mostly naturally ventilated (except for Belgium, where the indoor air is led by mechanical ventilation via the gap to the centralized air handling unit). The shading is performed mainly with Venetian blinds located in the gap. Unfortunately data on energy demand and temperatures are infrequently measured and rarely available. The cost of DSFs is significantly higher than conventional façades.

Computational modelling of airflow in urban street canyon and comparison with measurements

The main goal of this study was to predict the airflow in a street canyon surrounded by an urban area using CFD modelling. In the street geometry described in the main part, the actual airflow directly influences air infiltration into buildings. Different models of turbulence were tested as well as specific wind boundary conditions. A correct assignment of boundary conditions (i.e., mainly wind conditions) is a very important step to obtain results that are comparable with measurements. Results of 3D airflow in the street canyon were obtained for different velocities and directions of an undisturbed wind above the roof level. Wind conditions were prescribed in two different ways, as a velocity profile on the incoming side of the solution domain, in the other as a fixed velocity in the layer where the wind velocity was measured. Results of calculations are compared with measurements done in the studied street canyon. Individual models of turbulence were tested to obtain the best agreement between predictions and measurements.

FUTURE RESEARCH ACTIONS IN PASSIVE COOLING

The PASCOOL program was the most important European project on passive cooling of buildings. The project addressed topics included solar control, the combined effect of ventilation and thermal mass, thermal comfort during summer and the potential of natural cooling techniques. PASCOOL put in evidence also the axes towards which future research on passive cooling should be oriented. This research, giving the continuously increasing trend of energy consumption for cooling purposes, is absolutely necessary in order to take advantage of the complete potential that passive cooling can offer to buildings while maintaining the living standards, health and comfort of the occupants. This paper presents these future issues that comprise (a) research on the microclimatic scale in order to address the impact of outdoor environment on the cooling load of buildings, (b) investigation of comfort requirements under transient conditions during summer, (c) research on natural ventilation in urban environments and the impac...

Assessing the Interlinks between Urbanization, the built Environment and the Thermal Environment in view of Smart and Sustainable Urban Development: A Demonstration Application for Athens

In this paper, the interlinks between urbanization, the built environment and the thermal environment are recognized and assessed in view of smart and sustainable urban development. In particular Earth Observation data, in conjunction with census data and geographic information systems, are used in order to address the urban thermal environment, with emphasis to the state of the built environment and the presence and spatial distribution of thermal hot spots (small size areas with considerable and steadily higher temperatures within the urban web) at the district level. The analysis refers to the overall urban agglomeration of Athens (with emphasis to the City of Athens) and shows a thermal environment in pressure as a direct, among others, consequence of the high urban population density, the ageing of the building stock and the limited presence of green areas. In terms of Earth Observation, the analysis is based on satellite data of high and medium spatial resolutions, with the latter being improved through the application of a downscaling technique.