Impact of air barriers application in LCA and LCC of naturally ventilated dwellings in mild climate regions

"Available online 17 November 2022"Assessing singular elements that constitute the air barrier of a building envelope is quite unfeasible in Life Cycle Assessment (LCA). The study of these solutions through this particular scope is often overlooked. Two major aspects contribute to it: the complexity of the relationships between elements and the reduced embodied impact of these materials in the overall construction or retrofitting works. This work uses LCA and Life Cycle Costing (LCC) to study the viability of applying two envelope air barrier solutions in dwellings with excessive air change rates and equipped with different heating systems. The application of air barrier solutions resulted in average energy consumption savings in urban terrain, almost half of those in rural terrain during the heating season. Environmental performance and life cycle costs revealed mechanically (MECH) fastened air barriers to outperform fluid (FLUID) applied ones. The median annualized cost of adopting a FLUID solution was almost four times that of a MECH solution. Dwellings equipped with electric radiators ranked first in the shortest average Energy Payback Period (EPP) and the highest average Reference Service Life (RSL) savings. With the current analysis, the adoption of MECH solutions is recommended, independently of the heating system the dwelling is equipped with.This work was financially supported by: Base Funding - UIDB/04708/2020 and Programmatic Funding - UIDP/04708/2020 of the CONSTRUCT - Instituto de I&D em Estruturas e Construções - funded by national funds through the FCT/MCTES (PIDDAC). The author would like to acknowledge the support of FCT - Fundação para a Ciência e a Tecnologia, the funding of the Doctoral Grant PD/BD/135162/2017, through the Doctoral Programme EcoCoRe. This work is supported by the European Social Fund (ESF), through the North Portugal Regional Operational Programme (Norte 2020) [Funding Reference: NORTE-06-3559-FSE-000176]

Reliability of quantitative and qualitative assessment of air leakage paths through reductive sealing

A full characterization of a building air leakage is labour intensive. As results of laboratory and mock-up experimentation rarely portray in situ conditions, the assessment of real case studies bring added value. Still, the results of experimentation of the latter face more challenges than the former. In this work a full quantitative and qualitative assessment of air leakage paths is performed, using a light steel framing (LSP) modular building with structural insulated panels (Sips) as case study. Blower-door measurements undergo for a sealing campaign of eleven steps, a technique often described as reductive sealing. Additionally, smoke tracer measurements were carried out to visually identify the air leakage locations. The application of three regression methods resulted in different uncertainty estimates. Less than 7% of the total air leakage was not attributed to one of the considered types of air leakage paths. Assessing less impacting leakage paths first and placing similar types of air leakage paths in a consecutive sealing order seems to be the most correct strategy when using the reductive sealing technique. On average, at a reference pressure difference of 4 Pa, the sealing step uncertainty averaged, 9.9%, 18.8%, and 27.5%, depending on the method used for regression of the blower door test results. Despite the highest calculated uncertainty, literature shows that the application of the method leading to it, Weighted Line of Organic Correlation (WLOC), provides the results in closer agreement with the observed uncertainty of measurements.- This work was financially supported by: Base Funding - UIDB/04708/2020 and Programmatic Funding - UIDP/04708/2020 of the CONSTRUCT-Instituto de 1&0 em Estruturas e Construcoes - funded by national funds through the FCT/MCTES (PIDDAC). The author would like to acknowledge the support of FCT - Fundacao para a Ciencia e a Tecnologia, the funding of the Doctoral Grant PD/BDIl35162/2017, through the Doctoral Programme EcoCoRe

Colour degradation of facade coatings - the effect of nanopigments incorporation

The increasing interest in the use of a wide range of colours in buildings, especially dark colours, may lead to the early degradation of the facades, compromising their aesthetic and thermal performance. On the other hand, the incorporation of nanopigments with high reflectance properties can contribute to reducing the absorption of solar radiation. The nanoparticles contribute to increasing the solar reflectance of coatings, decreasing the surface temperature and improving the coating performance. This work evaluates the natural degradation of the colour of finishing coat with nanopigments in ETICS. The colour parameters were evaluated in different ETICS specimens, considering the colour black and red with and without incorporated nanopigments, under natural ageing. The colour measurement was performed according to ISO 1164-4, using a portable spectrophotometer. The results confirmed that the use of nanopigments improved the colour durability, promoting the maintenance of the colours parameters. The total colour difference was lower than the perceptible by the human eyes, even as the lower variation on chroma and hue parameters of the colours with nanopigments. In summary, the incorporation of nanoparticles in finishing coat of ETICS can contribute to increasing their durability and improve their thermal performance without compromising the aesthetic characteristics

Solar reflectance of ETICS finishing coatings - a comparison of experimental techniques

The solar reflectance has a significant role in the thermal behaviour and surface temperature of ETICS finishing coats. Incomplete information of solar reflectance of ETICS with nanopigments can sometimes difficult their adequate selection. In this work, the solar reflectance of different ETICS finishing coats was measured using two distinct methodologies, and the importance of the adopted procedure was discussed. The experimental methodologies used were: i) the adapted conventional pyranometer technique (non-ASTM E 1918A), which measures the global solar reflectance; and ii) the use of the spectrophotometry, to measure the spectral reflectance. It was verified that the El 918A methodology is more sensitive to environmental conditions than the spectrophotometry procedure. Also, the calculation of solar reflectance with spectrophotometer can be carried out by the 50 or 100 ordinates. However, the surface characteristics, as the concentration of pigments and roughness, affect more the solar reflectance measured with the spectrophotometer than with the pyranometer. It was verified that the nanopigments could improve solar reflectance and change the spectral reflectance. The results showed that, if the procedure is well applied, both methodologies could be used to evaluate the advantages of incorporating nanopigments in facade finishing coatings and also to assess the durability of these materials

Impact of atmospherical stability and intra-hour variation of meteorological data in the variability of building air change rates

In contrast with structural engineering, where the focus for design is on extreme values, for the proper assessment and modelling of air change rates in natural ventilation and infiltration, one must use the full range of input variables. Most of the modelling in infiltration research relies on hourly datasets for air infiltration balance. This consideration overlooks the intra-hour variability on meteorological variables. Additionally, it is customary to assume unchanging neutral atmospheric conditions when modelling, which affects the calculated airflows. This work intends to detail and quantify these effects in a case study representative of an average single-family dwelling in a Southern European climate setup. By comparing four setups with an increasing degree of complexity, a median of 0.04 h(-1) of the hourly standard deviations in air change rates (ACH) is attributed to the time step effect. Approximately 43% of the occurrences experienced non-neutral atmospheric stability, skewing for stable conditions. This effect contributed to differences in the ACHs ranging from-0.202 to 0.131 h(-1) at the 5% and 95% quantiles. Overall, by using hourly uniform distributions and smart sampling of meteorological variables, one ensures that the values in between and others potentially occurring around the boundaries are being considered for air change rates calculation, and therefore providing a more detailed picture of actual conditions.This work was financially supported by: Base Funding -UIDB/04708/2020 and Programmatic Funding - UIDP/04708/2020 of the CONSTRUCT -Instituto de I&D em Estruturas e Construcoes - funded by national funds through the FCT/MCTES (PIDDAC). The author would like to acknowledge the support of FCT - Fundacao para a Ciencia e a Tecnologia, the funding of the Doctoral Grant PD/BD/135162/2017, through the Doctoral Programme EcoCoRe.The authors also acknowledge Dr. Ricardo Deus and the Portuguese Institute for Sea and Atmosphere, I. P. (IPMA, IP) for providing the meteorological dataset for this work

Evaluating the freeze–thaw phenomenon in sandwich-structured composites via numerical simulations and infrared thermography

The water ingress phenomenon in sandwich-structured composites used in the aerospace/aeronautical sector is a current issue. This type of defect can cause in the course of time several other defects at the boundary, such as corrosions, deformations, detachments. In fact, water may change its state of physical matter going towards the freeze–thaw cycle caused by the atmosphere re-entry of, e.g. space probes. In this work, the alveoli of a composite laminate have been filled with water, which was initially transformed into ice. By taking into account, the known quantity of water, the freeze–thaw cycle was simulated by Comsol Multiphysics® software, reproducing exactly the shape of the sandwich as well as the real conditions in which it was subsequently subjected in a climatic chamber. The experimental part consisted of monitoring the front side of the specimen by means of a thermal camera operating into the long-wave infrared spectrum, and by setting both the temperature and the relative humidity of the test chamber according to the values imposed during the numerical simulation step. It was found that the numerical and experimental temperature trends are in good agreement with each other since the model was built by following a physico-chemical point-of-view. It was also seen that the application of the independent component thermography (ICT) technique was able both to retrieve the positions of the defects (i.e. the water inclusions) and to characterize the defects in which a detachment (fabricated between the fibres and the resin) is present; the latter was realized above an inclusion caused by the water ingress. To the best of our knowledge, this is the first time that ICT is applied to satisfy this purpose.Postprint (author's final draft

Impact of Incorporating NIR Reflective Pigments in Finishing Coatings of ETICS

Near-infrared (NIR) reflective materials are being developed for mitigating building cooling needs. Their use contributes to broadening the range of colours, responding to the urban aesthetic demand without compromising the building performance. Despite the increase in NIR reflective pigments investigation, there is still a knowledge gap in their applicability, impact, and durability in multilayer finishing coatings of External Thermal Insulation Composite Systems (ETICS). Hence, the main goal of this work consists of evaluating the impact of incorporating NIR reflective pigments (NRP) in the solar reflectance of the surface layer of ETICS, without affecting the colour perception, as well as their influence on the colour durability and surface temperature. As such, colour, solar reflectance, and surface temperature were monitored for 2 years in dark-coloured specimens of ETICS, with and without NRP and a primer layer. It was confirmed that the main contribution of NRP is the increase of solar reflectance and, consequently, the decrease in surface temperature, especially for high exterior temperatures (around 30 degrees C). Moreover, these pigments highly increase the NIR reflectance without affecting the visible colour. In addition, they contribute to maintaining the colour characteristics. The application of primer increased the surface temperature, especially for higher exterior temperatures. However, it contributes to a lower colour difference and solar reflectance variation, which is an important achievement for durability purposes

An insulation thickness optimization methodology for school buildings rehabilitation combining artificial neural networks and life cycle cost

The energy efficiency of buildings, including public buildings, is a major concern for all European governments, since they are responsible for a large share of the total energy bill of the states. School buildings play an important role in these costs. The best strategy for reversing this scenario includes efforts on buildings retrofit, seeking to optimize their energy efficiency and indoor environmental quality. However, in the unfavourable economic climate we are experiencing, which requires great prudence when it comes to public investment, special attention should be given to this multi-objective optimization process. In this research, a methodology to optimize the insulation thickness of the external walls and roof on school buildings retrofit is proposed. The procedure includes the optimization of the building performance considering the following objectives: the minimization of the annual heating load; the minimization of the discomfort in the classrooms due to overheating; and the minimization of the life cycle cost of retrofitting external walls and roof. This methodology was applied to two Portuguese school buildings

A labelling strategy to define airtightness performance ranges of naturally ventilated dwellings: An application in southern Europe

Energy efficiency and indoor air quality are frequently-two conflicting objectives when establishing the air change rate (ACH) of a dwelling. In Europe, the northern countries have a clear focus on energy conservation, leading to an obvious awareness of the importance of airtightness, which translates into a high level of regulation and implementation. Meanwhile, the southern counterparts experience a more com-plex challenge by having predominantly passive ventilation strategies and milder climates, which often results in a more permissive approach. This work proposes an innovative labelling methodology to classify the performance of naturally ventilated dwellings. A representative sample of a southern European national built stock is used in a stochastic process to create a pool of 43,200 unique dwellings. The simulation period refers to a month of the typical heating season in the southern European mild conditions. The results test the labelling methodology. With feature selection, ACH limits, and a labelling strategy, dwellings classify according to their ability to provide adequate ACHs. The terrain was the best splitter of the dataset from the applied categorical variables. Regarding continuous variables, the airtightness was the one explaining most of the variability of the outputted ACHs, followed by the floor area. From the best performing dwellings labelled as compliant (Com), the average airtightness level was 5.3 h(-1), with 4.9 h(-1) and 5.8 h(-1) in rural and urban locations. (C) 2022 Elsevier B.V. All rights reserved.This work was financially supported by: Base Funding - UIDB/04708/2020 and Programmatic Funding - UIDP/04708/2020 of the CONSTRUCT - Instituto de I&D em Estruturas e Construcoes - funded by national funds through the FCT/MCTES (PIDDAC). The author would like to acknowledge the support of FCT - Fundacao para a Ciencia e a Tecnologia, the funding of the Doctoral Grant PD/BD/135162/2017, through the Doctoral Programme EcoCoRe. This work is supported by the European Social Fund (ESF), through the North Portugal Regional Operational Programme (Norte 2020) [Funding Reference: NORTE-06-3559-FSE-000176]. The authors also acknowledge Dr. Ricardo Deus and the Portuguese Institute for Sea and Atmosphere, I.P. (IPMA, IP) for providing the meteorological dataset for this work

Towards an airtightness compliance tool based on machine learning models for naturally ventilated dwellings

Physical models and probabilistic applications often guide the study and characterization of natural phenomena in engineering. Such is the case of the study of air change rates (ACHs) in buildings for their complex mechanisms and high variability. It is not uncommon for the referred applications to be costly and impractical in both time and computation, resulting in the use of simplified methodologies and setups. The incorporation of airtightness limits to quantify adequate ACHs in national transpositions of the Energy Performance Building Directive (EPBD) exemplifies the issue. This research presents a roadmap for developing an alternative instrument, a compliance tool built with a Machine Learning (ML) framework, that overcomes some simplification issues regarding policy implementation while fulfilling practitioners' needs and general societal use. It relies on dwellings' terrain, geometric and airtightness characteristics, and meteorological data. Results from previous work on a region with a mild heating season in southern Europe apply in training and testing the proposed tool. The tool outputs numerical information on the air change rates performance of the building envelope, and a label, accordingly. On the test set, the best regressor showed mean absolute errors (MAE) below 1.02% for all the response variables, while the best classifier presented an average accuracy of 97.32%. These results are promising for the generalization of this methodology, with potential for application at regional, national, and European Union levels. The developed tool could be a complementary asset to energy certification programmes of either public or private initiatives. (c) 2023 The Author(s). Published by Elsevier B.V. This is an open access article under the CC BY-NC-ND license (http://creativecommons.org/licenses/by-nc-nd/4.0/).This work was financially supported by: Base Funding - UIDB/04708/2020 and Programmatic Funding - UIDP/04708/2020 of the CONSTRUCT - Instituto de I & D em Estruturas e Construcoes - funded by national funds through the FCT/MCTES (PIDDAC). The author would like to acknowledge the support of FCT - Fundacao para a Ciencia e a Tecnologia, the funding of the Doctoral Grant PD/BD/135162/2017, through the Doctoral Programme EcoCoRe. This work is supported by the European Social Fund (ESF), through the North Portugal Regional Operational Programme (Norte 2020) [Funding Reference: NORTE-06-3559-FSE-000176]