Palme, Massimo

The urban heat island (UHI) effect is constantly increasing the energy consumption of buildings, especially in summer periods. The energy gap between the estimated energy performance - often simulated without considering UHI - and the real operational consumption is especially relevant for institutional buildings, where the cooling needs are in general higher than in other kind of buildings, due to more internal gains (people, appliances) and different architectural design (more transparent façades and light walls). This paper presents a calculation of the energy penalty due to UHI in two institutional buildings in Rome. Urban Weather Generator (UWG) is used to generate a modified weather file, taking into account the UHI phenomenon. Then, two building performance simulations are done for each case: the first simulation uses a standard weather file and the second uses the modified one. Results shows how is it necessary to re-develop mitigation strategies and a new energy retrofit approach, in order to include urbanization ad UHI effect, especially in this kind of buildings, characterized by very poor conditions of comfort during summer, taking into account users and occupant-driven demand.

Global warming affects the built environment by changing the environmental conditions under which buildings operate. This change probably means a shift in thermal demand, from a predominant demand for heating to a higher demand for cooling in many climates. For instance, in cold climates global warming seems to be a self-decreasing phenomenon because of lower energy demand in warmer environments. In warmer climates, like the Mediterranean, and in the hottest climates (both humid and arid), global warming must be regarded as one of the main factors (the others are the change in comfort standards and the heat-island effect) in increasing the energy demand to cool buildings. This chapter analyses the environment of various cities, characterised by mild average temperatures and small thermal oscillations, that can be regarded as Mediterranean climate emplacements. Today these cities have more heating than cooling demand but in the future will probably have higher cooling requirements. Results show that by 2050, in most of the considered emplacements, cooling demand will be higher than heating demand and emissions will rise proportionally. Solutions to this problem must be sought in the flexible operation of buildings, and policies should focus on summer-related issues: good natural ventilation, protection from the sun, and internal gain reduction, rather than insulation, air infiltration reduction and solar access.

Although Urban Heat Island (UHI) is a fundamental effect modifying the urban climate, being widely studied, the relative weight of the parameters involved in its generation is still not clear. This paper investigates the hierarchy of importance of eight parameters responsible for UHI intensity in the Mediterranean context. Sensitivity analyses have been carried out using the Urban Weather Generator model, considering the range of variability of: 1) city radius, 2) urban morphology, 3) tree coverage, 4) anthropogenic heat from vehicles, 5) building’s cooling set point, 6) heat released to canyon from HVAC systems, 7) wall construction properties and 8) albedo of vertical and horizontal surfaces. Results show a clear hierarchy of significance among the considered parameters; the urban morphology is the most important variable, causing a relative change up to 120% of the annual average UHI intensity in the Mediterranean context. The impact of anthropogenic sources of heat such as cooling systems and vehicles is also significant. These results suggest that urban morphology parameters can be used as descriptors of the climatic performance of different urban areas, easing the work of urban planners and designers in understanding a complex physical phenomenon, such as the UHI.

Urban heat island effect often produces an increase of overheating sensation inside of buildings. To evacuate this heat, the current use of air conditioning increases the energy consumption of buildings. As a good alternative, natural ventilation is one of the best strategies to obtain indoor comfort conditions, even in summer season, if buildings and urban designs are appropriated. In this work, the overheating risk of a small house is evaluated in four South American cities: Guayaquil, Lima, Antofagasta and Valparaíso, with and without considering the UHI effect. Then, natural ventilation is assessed in order to understand the capability of this passive strategy to assure comfort inside the house. Results show that an important portion of the indoor heat can be evacuated, however the temperature rising (especially during the night) due to UHI can generate a saturation effect if appropriate technical solutions, like the increase in the air speed that can be obtained with good urban design, are not considered.

Ecuador is starting to consider climate change as a priority for the country development. Recently, was founded the Sub-secretariat for climate change, and many Ministry started to insert related topic in the political agenda. Particularly, Urban Development and Housing Ministry, MIDUVI, launched in 2011 the competition “Dwellings for climate change” in order to improve the basic social house that is still constructing in all the climates of the country. For instance, Ecuador, even small, has a unique climatic diversity: in the Andes the climate is tropical mountain, in the Amazons is tropical wet and in the Coast is hot, both arid and humid, depending on the specific position. One of the competition goals was to put in evidence the need of different design for each climate, even for social dwellings, that have to be very cheap. The National Institute of Energy Efficiency and Renewable Energy (INER) is also developing some prototypes for the different climates of Ecuador [1]. In this paper, a simulation study has been conducted in order to estimate the discomfort hours (both undercooling and overheating) that inhabitants could feel in the base case (the actual MIDUVI social house) and in the three competition winner prototypes. Simulations have been conducted for the climate of nowadays (Typical Meteorological Year –TMY) and for the future (2050 and 2080) taking into account the global warming effect under the Intergovernmental Panel for Climate Change (IPCC) A2 scenario. Because of in Ecuador heating and air-conditioning systems are used only by a small part of the population (the richer one), the analysis was conducted thinking in naturally ventilated buildings, searching for the total discomfort hours during the year.

The aim of this research is to simulate the performance of a solar chimney located in different macro-zones in Ecuador. The proposed solar chimney model was simulated using a python script in order to predict the temperature distribution and the mass flow over time. The results obtained were firstly compared with experimental data for dry-warm climate. Then, the model was evaluated and tested in real weather conditions: dry-warm, moist-warm and rainycold. In addition, the assumed chimney dimensions were chosen according to the literature for the studied conditions. In spite of evaluating the best nightly ventilation, different chimney wall materials were tested: solid brick, common brick and reinforced concrete. The results showed that concrete in a dry-warm climate, a metallic layer on the gap with solid brick in a moist–warm climate and reinforced concrete in a rainy cold climate used for the absorbent wall improve the thermal inertia of the social housing.