towards a probabilistic approach in lca of building retrofit measures

Abstract This paper proposes an approach of sensitivity analysis for LCA of building retrofit measures aiming to establish the impact of input data uncertainties on the output variance. The approach includes the quantification of data input uncertainties in terms of their Probability Distribution Functions (PDFs), their sampling and the uncertainty propagation through Monte Carlo (MC) methods. A sensitivity analysis through Variance based decomposition (Sobol' method) techniques are used to point out the key parameters uncertainties that mostly affect the LCA results distributions. The paper presents a building case-study where the MC-based uncertainty and sensitivity analysis method is applied considering different design options (XPS and Cork internal insulation measures) and different scenarios for the assessment of the building energy need (use phase). Results obtained highlight that the differences on the Climate change environmental impact between the two design options is quite limited (about 12%) and this is mainly due to the use phase which is the more relevant input parameter on the overall result. Concerning the Sensitivity Analysis, when the building energy need is considered as a "deterministic" input in the LCA assessment, the unitary impacts of the design options materials uncertainties are the most influential parameters. On the other hands, when the building energy need is represented by a PDF, the quantity of energy carrier consumed and its unitary environmental impact are the most influential parameters on the output variance

Numerical assessment of the impact of roof reflectivity and building envelope thermal transmittance on the UHI effect

Abstract Cool materials benefits for the mitigation of the urban microclimate overheating caused by Urban Heat Island (UHI) effect are well-established at international level. Since the need for building energy efficiency is more and more pushing towards highly insulated envelope, there is a growing need for studies that address the correlation between the optical properties of building coatings and the thermal transmittance of the envelope where they are applied, also assessing their mutual impact on the UHI. The present paper reports a study, carried out through a fluid-dynamic microclimate simulation software in an Italian urban context, aiming at understanding the impact of the combination of several roof covering optical properties and building envelope U-value levels on the UHI, given the recent nation threshold values for both. The outcomes of the simulations, performed in urban contexts with a typical morphology of Italian town centres and under different climatic conditions, highlight how the increase of the environment air temperatures is influenced by the combinations of the following factors: lower urban canyons, roof surfaces with low solar reflectivity and highly insulated envelopes. In fact, the high insulation levels, in response to current regulatory standards for the reduction of winter energy consumption, inhibit the ingoing thermal fluxes (thermal decoupling phenomenon) leading to an increase of the external surface temperatures and consequently heating up the surrounding area. In this regard, the adoption of reflective materials can be beneficial in attenuating the overheating. Simulation results demonstrate that these materials are able to mitigate the outdoor air temperature until 2°C, depending on specific building envelope configurations and geographical locations

Performance assessment of different roof integrated photovoltaic modules under Mediterranean Climate

Abstract Many 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%

Moisture buffering "active" devices for indoor humidity control: preliminary experimental evaluations

Abstract In recent building practice, obligations of legislation relating to Nearly Zero Energy Buildings (NZEB) (European Directives 2002/91/EC and 2010/31/EU) are carried out mainly by high thermal resistance and total air tightness of the envelope, in order to minimize heat dispersions by conduction and infiltration as much as possible. These measures cause new ways of heat and moisture exchange in the building envelope and are likely to create high internal moisture load with consequences for durability of materials and inhabitants' comfort and health. Improvement in the thermal performance of the envelope can then lead to the paradoxical need for high energy consumption in order to handle the vapor peaks indoors by using mechanical ventilation equipments. Even if with HVAC devices it is possible to provide an acceptable indoor climate, there is still a need to develop more passive and less energy intensive methods to moderate the indoor environment in NZEB. In recent decades many authors have focused on a promising strategy related to the use of "moisture buffering" materials which dampen indoor humidity variations without additional energy costs. Nevertheless, many internal finishing materials commonly used at present are still not highly performant or lead to problems of hysteresis. In the present study, we propose an alternative solution, which is the design of a moisture buffering "active" device, to be integrated in a part of the building envelope, which is able to measure the relative humidity indoors and control its loads by a low-energy-consumption fan system. The humidity control performance of the device has been dynamically tested in a climate chamber and has been compared with traditional "passive" material samples in order to measure the Moisture Buffering Value (MBV) according to the DTU test method. Experimental results showed that "passive" samples have high moisture buffering values [MBV = 6.12 g/(m2% RH)] and do not lead to hysteresis phenomena. The MBV measured in the "active" devices increased up to 29%, which predicts promising future applications for low-energy-consumption indoor humidity control

Uncertainty impact on decisions related to historical buildings energy retrofit

Decisions concerning energy retrofit of historical buildings should be based on a complex set of parameters, ranging from not-tangible to tangible values, such as the historical and the cultural value, the expected costs and benefits, the environmental impacts. The tangible values, such as the monetary costs and benefits, are often prioritized considering their measurability, however neglecting that they are frequently affected by important uncertainties (related e.g. to the evolution of the macro-economic scenario, to the building components maintenance and replacement needs, etc.). This fact can lead to improper design choices and consequently to the risk of losing part of the building tangible or not-tangible value. For this reason, it is necessary to improve decision-making processes and tools, also considering uncertainty and sensitivity analysis as part of the design process related to the energy retrofit of historical buildings. In this paper we show the impact of different assumptions regarding future possible macro-economic scenarios on the monetary benefits of a historic building renovation intervention. A “probabilistic” Life Cycle Costing tool, developed through the software environment for statistical computing “R”, has been used to evaluate the parameters mostly influencing the global costs of the typical energy retrofit measures applied to a building case-study. Results demonstrate how the uncertainties related to the economic parameters are the most influencing the output variance. The uncertainties related to the building periodic maintenance and the energy costs are also prevailing on those related to the initial investment costs

Low-Power Wearable ECG Monitoring System for Multiple-Patient Remote Monitoring

Many devices and solutions for remote electrocardiogram (ECG) monitoring have been proposed in the literature. These solutions typically have a large marginal cost per added sensor and are not seamlessly integrated with other smart home solutions. Here, we propose an ECG remote monitoring system that is dedicated to non-technical users in need of long-term health monitoring in residential environments and is integrated in a broader Internet-of-Things (IoT) infrastructure. Our prototype consists of a complete vertical solution with a series of advantages with respect to the state of the art, considering both the prototypes with integrated front end and prototypes realized with off-the-shelf components: 1) ECG prototype sensors with record-low energy per effective number of quantized levels; 2) an architecture providing low marginal cost per added sensor/user; and 3) the possibility of seamless integration with other smart home systems through a single IoT infrastructure

COVID-19 impact on end-user's maintenance requests. A text mining approach

COVID-19 pandemic changed our way of working, limiting the usual physical attendance of working spaces. Despite the drastic reduction in the number of daily users due to the pandemic restrictions, working buildings were often kept open to provide services to internal and external users. Pandemic obliged to change operation and maintenance (O&M) plans, due to the increase of ventilation requirements and the reduction of other types of services, with a strong impact on cost and management. Now the pandemic is reducing its effects and is time to question the future asset of buildings’ O&M plans, based on the pandemic lesson. Data collected by Computerized Maintenance Management Systems (CMMS) during COVID-19 then become an important source of understanding the future management of working places. End-users’ maintenance requests are usually expressed by natural language, then a text mining approach can be a useful tool to discover hidden knowledge from unstructured data stored in CMMS. This study applies text mining methods, including sentiment analysis, to the field of building maintenance, with the scope to evaluate how COVID-19 changed some aspects of the facility management process, including users’ perception

design and performance assessment of building counter walls integrating moisture buffering active devices

Abstract The use of building materials with high moisture buffering capacity is a well-recognized strategy to moderate the variation of indoor moisture loads. Many researchers investigated the ability and potential of finishing materials and furniture for the reduction of the amplitudes of indoor relative humidity by characterising their Moisture Buffering Value. Nevertheless, the recent and widespread building practice, which is increasingly trying to reduce the air permeability and thermal transmittance of the envelope, is likely to even worsening indoor humidity conditions, with consequences for durability of materials and inhabitants' comfort and health. Very performing materials are then needed to act as buffering and quickly dampen high moisture loads. This paper proposes the design of a building internal counter wall equipped with an "active" moisture buffering device. This is able to measure the indoor relative humidity and consequently increase the adsorbing capacity of a porous material through an air-flow. Experimental activities were carried out on different prototypes with the combination of granular Sepiolite with two different pore structures and nonwoven fabrics. The devices effectiveness in terms of MBV has been dynamically tested in a climate chamber according to the DTU Nordtest method. Different "activation" times against several humidity levels were set in order to assess the best solution in different scenarios

On the evolution of elastic properties during laboratory stick-slip experiments spanning the transition from slow slip to dynamic rupture

The physical mechanisms governing slow earthquakes remain unknown, as does the relationship between slow and regular earthquakes. To investigate the mechanism(s) of slow earthquakes and related quasi-dynamic modes of fault slip we performed laboratory experiments on simulated fault gouge in the double direct shear configuration. We reproduced the full spectrum of slip behavior, from slow to fast stick slip, by altering the elastic stiffness of the loading apparatus (k) to match the critical rheologic stiffness of fault gouge (kc). Our experiments show an evolution from stable sliding, when k>kc, to quasi-dynamic transients when k ~ kc, to dynamic instabilities when k<kc. To evaluate the microphysical processes of fault weakening we monitored variations of elastic properties. We find systematic changes in P wave velocity (Vp) for laboratory seismic cycles. During the coseismic stress drop, seismic velocity drops abruptly, consistent with observations on natural faults. In the preparatory phase preceding failure, we find that accelerated fault creep causes a Vp reduction for the complete spectrum of slip behaviors. Our results suggest that the mechanics of slow and fast ruptures share key features and that they can occur on same faults, depending on frictional properties. In agreement with seismic surveys on tectonic faults our data show that their state of stress can be monitored by Vp changes during the seismic cycle. The observed reduction in Vp during the earthquake preparatory phase suggests that if similar mechanisms are confirmed in nature high-resolution monitoring of fault zone properties may be a promising avenue for reliable detection of earthquake precursors