• Energy Research

Abstract An experimental study was carried out on buildings constructed in the 1980s adopting vertical envelopes with a glass wool insulation layer in the cavity. The aims of this study are to evaluate the insulation conservation state after 25 years, to assess the actual indoor thermal comfort and to compare different retrofit interventions. The research included the following phases: laboratory tests on insulation samples to quantify any changes of morphological, chemical, physical and thermal proprieties of the material; detailed on-site monitoring in order to analyze the thermal comfort conditions; dynamic thermal simulations to assess the impact of different retrofit scenarios to satisfy the limits imposed by the current energy saving standard. The results show that the glass fibers and the binder were affected by a degradation process thus increasing both water absorption and thermal conductivity; thermal comfort and consumptions were not influenced by the insulation aging; the most effective retrofit is the introduction of an external insulation layer.

Abstract The research deals with the experimental assessment of the yearly thermal performance of a green roof compared to other passive cooling technologies under temperate climate. All roofs are installed on highly insulated slabs (U-value

While the EU Directive 2002/91/CE on the Energy Performance of Buildings (EPBD) clearly establishes regulations for the thermal insulation of buildings for saving energy in winter, the summer strategy is described by a little more than qualitative provisions. As a consequence, in the national requirements, the high insulation of the building envelope is considered as the principal strategy to control energy consumption even in summer, regardless of the different climates. This approach leads to a homologation of the building trade, and imposes construction technology and materials which do not adhere to the traditional way of making buildings, like in Southern Europe. Here, the “over insulation” of buildings runs the risk of reducing the effectiveness of traditional passive cooling strategies (thermal mass, air permeability of the roof covering, roof ventilation) and could have adverse effects on internal comfort. In this paper, we focus on the effects of over insulation on the thermal performance of roofs in summer, by analyzing experimental data from monitoring a full-scale mock-up in Italy. Results show how an increase in insulation thickness reduces the effectiveness of traditional passive cooling strategies, as an effect of the thermal decoupling between the interior and the upper layers of the roofs.

Abstract The exterior envelope of some social housing scheme buildings constructed at the beginning of the 1970s without thermal insulation has proved to be the cause of great thermal loss and condensation. At the start of the 1980s, in order to resolve these problems, our research group carried out a study which led to the introduction of external thermal insulation (on the basis of previously developed performance specifications) and verification of the thermal performance achieved. With the aim of verifying the efficacy of the intervention after 20 years and in order to assess the thermal–hygrometric performance and the state of conservation of the exterior envelope we carried out a two stage study: 1. Performance analysis carried out through monitoring and laboratory tests. 2. Formulation of hypotheses for retrofitting, assessed through simulations and parametric analysis. The results showed the efficacy and durability from the thermal–hygrometric and mechanical point of view of the external insulation applied in the 1980s. It was also possible to verify energy saving for the different types of retrofit scenarios and to identify the correct positioning of the thermal insulation on the brickwork and on the floors so as to increase the surface temperatures in winter phase.

Abstract The aim of the study is to verify the actual performance of a super-insulated wooden envelope in a residential building located in a hot dry summer temperate climate and to optimize its thermal behavior favoring a dynamic interaction with the indoor environment. The method involved an integrated strategy between monitoring and calibrated simulations on experimental data and the simultaneous analysis of several aspects such as energy performance ( EnergyPlus software), comfort (dynamic analysis with Fanger’s PMV comfort model) and environmental-economic sustainability (LCA analysis with SimaPro software). Parametric analyses were carried out to generalize the results to various usage patterns of plants and passive cooling techniques and to several climate zones. The study highlighted the presence of overheating phenomena and demonstrated that this problem can be solved or reduced through the adoption of appropriate passive strategies, such as massive inner linings combined with natural or hybrid ventilation. Appropriate values of internal areal heat capacity and decrement factor will configure comfortable and energy efficient solutions. In temperate climates the optimal solution, namely the adoption of a 12 cm thick solid brick (or double dry clay panel) and natural ventilation, reduces the discomfort levels of 30–50%. In hottest periods of extreme climates the best solution, namely CMV + free-cooling combined with internal lightweight plaster, only slightly reduces the overheating with a 6% reduction of discomfort.

Abstract The paper presents an analytical and experimental study on external solar shadings. The purpose is to compare the behaviour of different typologies in various seasons in a Mediterranean climate from the point of view of thermo-physical behaviour, energy consumptions, thermal comfort, day lighting and environmental impact. The study included two phases: i. Simultaneous summer monitoring of different devices typical of a perimeter office building: sliding perforated panels, ventilated double-glazed window, aluminium horizontal louvers; ii. In-depth study of the louver shading devices through the analysis of the impact of adopting different materials, length of slats and vertical distance between slats. Configurations mainly adopted on residential buildings were also considered. The following activities were carried out: simultaneous winter monitoring of different louver shading devices, aluminium horizontal louvers, aluminium persiana, traditional wooden persiana; dynamic thermal simulations (Energy Plus software) to analyse energy consumptions, indoor thermal comfort and daylighting for different seasons and louvers configurations; assessment of the environmental impact with LCA analysis (SimaPro software). The study made it possible to highlight different behaviours of the shadings depending on their specific characteristics. The shade permeability influences the presence and efficacy of the stack effect in the air channel behind it while its geometries and materials (with relative optical and thermal properties) have an impact on the temperature trends of the adjacent layers, on yearly consumptions, on indoor thermal comfort and on uniformity level of the natural light. The results demonstrate that the wooden solution could to be a good compromise between the different aspects and that adopting an aluminium louver screen it is important to choice configurations characterized by wide and movable slats.

AbstractMany countries, for aesthetic purposes, offer economic advantages (tax deductions, incentives, etc..) for the installation of building integrated photovoltaic modules (BIPV), with water-tightness capability and adequate mechanical resistance in order to substitute tile covering or part of it. Nevertheless, poor or absent ventilation under BIPV panels could cause them to overheat and reduce their efficiency.It is well established that the presence of an air gap between a photovoltaic (PV) module and roof covering facilitates ventilation cooling under the device and consequently reduces cell temperature and improves its performance.In this study, we investigated the thermal performance of PV modules installed in a real scale experimental building over a traditional clay tile pitched roof in Italy for almost one year (from August 2009 to June 2010). One PV module was rack-mounted over the roof covering with a 0.2 m air gap; the others were fully integrated and installed at the same level of the roof covering (one with an air gap of 0.04 m, the other mounted directly in contact with the insulation). Temperature and heat flux measurements for each panel, and environmental parameters were recorded.Experimental results demonstrate that even though the rack-mounted PV module constantly maintains cell temperature below that of the other full-building integrated modules, due to the presence of a higher air gap, the difference in the energy produced by the PV modules estimated for the entire monitoring period is less than 4%.

Abstract The aim of this study was to assess the influence of thermal mass placed on the inner side of the building envelope, described as the dynamic internal areal heat capacity (International Standard ISO 13786), on the summertime thermal comfort in buildings characterised by high internal heat loads. To that aim, simultaneous monitoring was carried out on rooms with high internal heat loads (school classrooms), varying the internal inertia of the envelope through the introduction of an insulating panel on the interior side. Analytical assessment was performed in order to include different inertia values and combinations of both external and internal heat loads. The study allowed the threshold values of internal areal heat capacity to be determined with respect to the different periodic transmittance values of the walls, assessed according to the adaptive thermal comfort model described in Standard EN15251. These values could be adopted in energy saving regulations which, being based on semi-stationary calculation models, tend to consider the performance of building envelopes as analogous even if there is different thermal inertia.

Abstract The aim of this research is to verify the dynamic performance of 3 envelopes characterised by different traditional wall constructions adopted in temperate climates. In each case the optimal retrofit solution from the point of view of comfort and energy savings is identified. To that end contemporary experimental comparisons were made between 3 buildings which are characteristic of the existing building heritage. They were all constructed between the 1940s and the 1980s adopting envelopes which use different wall constructions to deal with the outdoor climate conditions: capacity (high thermal mass), stratification (different layers and a cavity), and resistance (the use of an insulation layer). Dynamic parametric analyses (EnergyPlus, CFD Fluent) were carried out in order to verify the impact of different retrofit solutions on the buildings studied. The results show that the behaviour of the 3 envelopes differs greatly because they interact in different ways according to climate changes. The use of considerable thicknesses of thermal insulation causes problems of overheating when coupled with high thermal mass, while it is an improvement in the stratified envelopes. The problem of summer discomfort can be resolved by adopting mixed insulation strategies such as a ventilated external insulation layer, which allows the existing envelopes to maintain their dynamic behaviour.