bluuebunny/crossref_metadata_2025 huggingface dataset:
Conventional and deep learning methods in heart rate estimation from RGB face videos
Authors: Helwan Abdulkader , Azar Danielle , Ma’aitah Mohamad Khaleel Sallam
Published: December 2023

Contactless vital signs monitoring is a fast-advancing scientific field that aims to employ monitoring methods that do not necessitate the use of leads or physical attachments to the patient in order to overcome the shortcomings and limits of traditional monitoring systems. Several traditional methods have been applied to extract the heart rate (HR) signal from the face. Moreover, machine learning has recently contributed majorly to the development of such a field in which deep networks and other deep learning methods are employed to extract the HR signal from RGB face videos. In this paper, we evaluate the state-of-the-art conventional and deep learning methods for HR estimates, focusing on the limits of deep learning methods and the availability of less-controlled face video datasets. We aim to present an extensive review that helps the various approaches of remote photoplethysmography extraction and HR estimation to be understood, in addition to their drawbacks and benefits.
An electromagnetic vibration energy harvester with compact flexure guide for low frequency applications
Authors: Wang Lujie , Liu Tinghao , Hao Guangbo , Chitta Saha , Liu Lei , Ye TinCong , Zhang Zhengmin , Wang Ningning
Published: December 2023

This paper presents the design, modeling, fabrication, and characterization of a novel electromagnetic vibration energy harvester (EVEH) using a compact flexure guide structure and opposing permanent magnets. The flexure guide is a unique cylindrical structure, and can transfer force and motion by the deformation of elastic beams. It allows the single-degree-of-freedom motion characteristic, and eliminates the friction between the permanent magnets and the housing structure, which exists in mostly reported magnet-spring based vibration energy harvesters. The structure also greatly reduces the spacing between the coil and the permanent magnets, which considerably increases the magnetic flux linkage through the coil. Experimental results show that the EVEH prototype can generate an output voltage of 6.08 V and output power of 4.02 mW from 0.1 g acceleration at resonant (19.5 Hz), achieving a normalized power density of 3.28 mW cm
−

3g
−

2. In addition, the flexure guide can be directly fabricated by 3D printing, which greatly simplifies the harvester assembly compared to other EVEHs reported. In terms of the proposed EVEH, a self-powered sensor network is implemented to transfer the GPS data to some appointed terminals.
Superconducting TSV contact for cryoelectronic devices
Authors: Filippov Ivan , Anikanov Aleksandr , Rykov Aleksandr , Mumlyakov Alexander , Shibalov Maksim , Trofimov Igor , Porokhov Nikolay , Anufriev Yuriy , Tarkhov Michael
Published: December 2023

This work focuses on the fabrication of niobium through silicon vias (TSV) superconductors interconnects. The effect of supercycle of sequential oxidation and chemical etching process on the through-etch wall quality was investigated. It was experimentally shown that the use of supercycle in the fabrication process leads to significant improvement of the TSV wall quality and removal of the defect type—scallops. After 12 times repetitions of supercycles a dissipative bonding of superconducting strips on the front and back side of the sample is observed. The critical current density of such coupling is 5 × 104 A cm−2. The critical ratio of substrate thickness to hole diameter at which electrical coupling is formed is 3:1.
A protocol for mapping transport current density of REBCO-coated conductor by magneto-optical imaging
Authors: Mu Nana , Liu Cong , Zhang Xingyi
Published: December 2023

The measurement of transport current density is significant for investigations on improving the properties of REBa2Cu3O7−x
(REBCO, where RE refers to rare-earth elements)-coated conductors (CCs). In this work, a protocol for mapping the transport current density of CC by magneto-optical imaging (MOI) is presented. A calibration method is developed based on the non-linear physical governing function for the MOI indicator, in which only two parameters are determined, i.e. the anisotropic magnetic field BA
, and cMs
, which is the multiplication of the constant c related to the thickness of the MOI indicator and the spontaneous magnetization Ms
. The experimental results also showed that they were independent of the optical measure condition but dependent on temperature, making this calibration method comparative among different utilizers. The numerical results clearly manifested that the selected window size of the magnetic field around a long superconducting tape is closely related to the error of the reconstructed current density. A large window size of the magnetic field is needed to precisely reconstruct the transport current density. For actual MOI testing, a practical approach to extend the magnetic field data outside the MOI window was realized by fitting with a power function according to Ampere’s law, through which the false current density outside the sample is automatically suppressed to a large extent. On this basis, the mapping of the transport current density in the CC sample was achieved. It is believed that this work will improve MOI for a more precise measurement of the transport current density for long superconducting strips.
Thermoelectric power of overdoped Tl2201 crystals: charge density waves and T
1 and T
2 resistivities
Authors: Cooper J R , Baglo J C , Putzke C , Carrington A
Published: December 2023

We report measurements of the in-plane thermoelectric power (TEP) for an overdoped (OD) crystal of the single layer cuprate superconductor Tl2Ba2CuO

6
+
x

(Tl2201) at several hole concentrations (p), from 300 or 400 K to below the superconducting transition temperature (Tc
). For p = 0.192 and 0.220, small upturns in the TEP below 150 K are attributed to the presence of charge density waves (CDW) detected by resonant inelastic x-ray scattering studies. This suggests that measurement of the TEP could provide a simple and effective guide to the presence of a CDW. Over a certain temperature range, often strongly restricted by the CDW, the TEP is consistent with the Nordheim-Gorter rule and the T
1 and T
2 terms in the in-plane resistivity of similar crystals observed below 160 K. Two scenarios in which the T
1 scattering term is uniform or non-uniform around the Fermi surface are discussed. As found previously by others, for uniform scattering the T
1 terms give scattering rates (τ
−1) at lower p that are somewhat larger than the Planckian value

k
B

T

/

ℏ

and fall to zero for heavily OD crystals. Near 160 K, τ
−1 from the T
2 terms corresponds to the Planckian value.
Quantum space-time marginal problem: global causal structure from local causal information
Authors: Jia Zhian , Song Minjeong , Kaszlikowski Dagomir
Published: December 2023

Spatial and temporal quantum correlations can be unified in the framework of the pseudo-density operators (PDOs), and quantum causality between the involved events in an experiment is encoded in the corresponding PDO. We study the relationship between local causal information and global causal structure. A space-time marginal problem is proposed to infer global causal structures from given marginal causal structures where causal structures are represented by the reduced PDOs; we show that there almost always exists a solution in this case. By imposing the corresponding constraints on this solution set, we could obtain the required solutions for special classes of marginal problems, like a positive semidefinite marginal problem, separable marginal problem, etc. We introduce a space-time entropy and propose a method to determine the global causal structure based on the maximum entropy principle. The notion of quantum pseudo-channel (QPC) is also introduced and we demonstrate that the QPC marginal problem can be solved by transforming it into a PDO marginal problem via the channel-state duality.
Renovation of 20th century modern buildings: Some common challenging architectural details analysed to find optimal insulating solutions
Authors: Csaszar Bernadett , Kinnane Oliver , O’Hegarty Richard
Published: December 2023

Reusing existing buildings is a valid response to the architectural challenge associated with climate change. However, these buildings must be adapted for better performance to ensure low carbon impact in the future. That demands retrofitting strategies which enable thermal comfort, indoor environmental quality, and energy efficiency. In addition, energy retrofit solutions that abide by conservation ethos are needed to ensure higher performance while protecting cultural heritage, architectural features, and identity. Energy retrofits of post-war modern-age buildings pose particular challenges. There is a paucity of general guidance, particularly academic literature, focusing on optimum retrofit strategies for awkward architectural details. These optimum strategies mainly consider the balance between the retrofit cost and the energy-saving potential. Environmental concerns related to the insulation materials are often not mentioned. As the results of this study show, the “optimum” solution might shift once we add this third aspect. In certain instances, no or minimal insulation is often more optimal when considering the environmental effects associated with the insulation and additional materials involved in retrofits.
Effect of abnormal weather on the microenvironment of Mogao Cave 285, Dunhuang
Authors: Jiang X Y , Xie H R , Zhang R H , Luo Z H , Zhang Z M , Li Y H
Published: December 2023

Cultural heritage is directly affected by the conservation environment, and climate change is already having an impact on the conservation of cultural heritage. The Mogao Caves murals, one of China’s most prestigious cultural heritages, have been affected by extreme rainfall. The aim of this study was therefore to assess the impact of abnormal weather on the microenvironment within the caves and on the preservation of the murals. First, the 30-year meteorological data of the Dunhuang area and the one-year cycle of Cave 285’s monitoring data are collated. The results show that for Cave 285, summer is the most noteworthy period. Then, a heat and moisture transfer model is established, and the accuracy of the model is verified. Finally, the model is used to evaluate the effect of different abnormal weather factors on the hygrothermal environment in the cave. The simulation results indicate that for Cave 285, abnormally high temperatures in summer do not make the situation worse, but both abnormally low temperatures and abnormally high humidity can cause the relative humidity in the cave to exceed safety critical value. In particular, when high humidity persists for a week, the relative humidity inside the cave can exceed 80% and take about 4 days to fall back to a safe value. In such cases, dehumidification measures are recommended.
Accuracy of using Moisture Reference Years for assessing the Long-Term Moisture Performance of Wall Assemblies
Authors: Xiao Zhe , Defo Maurice , Wang Lin , Lacasse Michael A.
Published: December 2023

Hygrothermal simulation is commonly used to understand the effects of climate loads on wall assemblies. This helps determine the risk of deterioration of wall components due to factors such as mould, wood rot, corrosion, and other modes of degradation. Owing to the lengthy computing time and high cost of undertaking simulations over extended periods of time in excess of 30 years, common practice is to select representative years, generally referred to as moisture reference years (MRYs), amongst the climate data series with the assumption that they would provide results similar to that obtained using the entire climate data series. In this study, simulations were performed for a wood-frame wall having brick veneer and fibreboard as cladding and located in 4 Canadian cities using both a 31-year climate data series and MRYs. The mould growth index on the outer layer of the sheathing panel was used as the performance indicator to permit comparing the moisture performance obtained using the long-term climate series to that obtained using MRYs. It was determined that different strategies should be implemented to analyse the MRY simulation results for different types of wall assemblies to obtain a similar conclusion as that of 31-year simulations.
Proposed flood risk classification of buildings - A case study with a heavy rain event
Authors: Lidén Peter , Stenvall Brita , Thidevall Niklas
Published: December 2023

Climate change and associated risks create high costs and must be considered in both city planning and construction. The increasing recognition of threats influences how investments are made both in future projects and in the valuations of existing assets. A feasibility study was performed on how a climate resilience certificate (CRC) can create a tool for better valuation for contractors, and property owners to increase efforts regarding climate change adaptation, easy-to-understand benchmarks for climate resilience of properties for comparability, and to reduce uncertainty if insurance coverage can be guaranteed. This study focuses on a risk classification, tested, and evaluated in a Swedish case study on a property level, with emphasis on heavy rain, as a base for a potential CRC. The study discusses the benefits and drawbacks of on-site assessments versus what is digitally available. Furthermore, this study also highlights vulnerabilities of the evaluated buildings, and where the focus should be placed concerning climate adaptive measures.
Numerical investigation of mould growth risk in a timber-based facade system under current and future climate scenarios
Authors: Coelho Guilherme B. A. , Kraniotis Dimitrios
Published: December 2023

Due to today’s sustainability concerns, we must find ways to decrease, the CO2 footprint of the products and systems that are used in buildings. The StaticusCare project, funded by EEA/Norway Grants, emerged from this need, since it aims to decrease the greenhouse gas emissions associated to the construction industry by developing a hybrid timber and aluminium based facade system that will integrate IoT sensors. A decrease of the facade’s embodied CO2 footprint of 70-75 % and of the non-renewable energy consumption to 53-56 % is expected. However, it must be ensured that this system has the necessary quality to be installed in the Nordic climates, even for future conditions. Computational models, both at the assembly level as well as at the building level, will be developed. The first level model will allow to perform thorough hygrothermal analysis of the facade system, whilst the second level model will allow to analyse the effect of the system at the building level, i.e. in terms of energy and indoor environment. In addition, this second level model will also be used to obtain the indoor conditions – i.e. temperature and relative humidity – that the first level model needs as an input to run. In order to make this study more comprehensive and, at the same time, determine how differently the facade system will perform under different climates, several representative Nordic outdoor climates will be used in the simulations. Climate change, by means of outdoor weather files, was considered, as well as the effect of moisture penetrating in the tested facade system due to air infiltration or even using timber with a high moisture content due to unprotected storage. It is determined that the tested system is able to properly dry the excess of moisture under current and future conditions. However, if the timber is not properly protected from moisture, then the situation is completely different.
Climate Change Effect on Freeze-thaw Load in Finland
Authors: Pakkala Toni A.
Published: December 2023

Freeze-thaw damage is one of the major degradation mechanisms of climate exposed porous rock-based building materials in existing Finnish building stock. In recent studies, it has been shown that not only the amount of freeze-thaw cycles but especially the amount of wind-driven rain (WDR) before freeze-thaw cycles has a major effect on the rate of freeze-thaw damage in concrete structures. In this study, freeze-thaw cycles after a rain event, the average annual amount of WDR before freeze-thaw cycles and the average amount of WDR before each cycle is calculated in different locations in Finland. The calculations are made for present and projected 2050 and 2080 climates with three greenhouse gas scenarios: RCP2.6, RCP4,5 and RCP8.5. Based on the results, the freeze-thaw load is decreasing in coastal and southern areas and staying at current level or increasing in northern parts of Finland. In addition, the level of freeze-thaw load is getting less direction or geographically dependent. The results strongly indicate that the exposure level might be decreasing in coastal area and southern parts of Finland because both the freeze-thaw cycles and the annual amount of WDR before cycles are decreasing. However, an average amount of WDR before a freeze-thaw cycle is actually increasing and so, the intensity of freeze-thaw attack is not decreasing. Thus, for the future climates freeze-thaw durability of porous rock-based structures should be still emphasised.
Moisture buffer value for hygroscopic materials with different thickness
Authors: Rasmussen Oliver Søndergaard , Qin Menghao
Published: December 2023

Moisture buffering is the capacity of hygroscopic building materials or adsorbents to mitigate the humidity fluctuations in the indoor environment through the adsorption/desorption phenomenon. NORDTEST proposed the moisture buffer value to quantitively characterize the moisture buffering capacity of porous materials. Materials with high moisture buffer values have a higher ability to passively control indoor humidity conditions and thus reduce building energy consumption and improve indoor thermal comfort. However, the ideal moisture buffer value theory is based on the assumption that the thickness of the studied materials should exceed the penetration depth of that material. This assumption significantly limits the application of moisture buffer value theory to thin-layer materials, such as textiles, desiccant coating, wallpaper, wood wall panels, etc, which represent a large proportion of moisture buffering in the built environment. In this study, we developed a new numerical model to calculate moisture buffer values for hygroscopic materials with different thicknesses. Experimental measurements were also carried out to validate the solutions. The moisture buffer value of a new kind of desiccant (metal-organic frameworks) under different thicknesses were measured by climatic chamber tests. Simulated results showed agreement with both the measurements and theory. The results indicate that the new moisture buffer value model can be used to find the optimal thickness of desiccant coating or hygroscopic materials for autonomous indoor humidity control.
Development of a fast moisture prediction model based on the moisture buffer value theory
Authors: Zu Kan , Qin Menghao
Published: December 2023

Moisture transfer in buildings significantly affects indoor thermal comfort, energy consumption, and durability of construction materials. It is crucial to predict the moisture storage and transfer in building simulations accurately. However, moisture transfer was neglected in many simulation tools for building performance analysis. In those calculation tools, including a moisture model, moisture transfer has been either estimated by simple approximations or calculated by complex combined heat, air, and moisture transfer (HAMT) models that require orders of magnitude more computing time than simple calculations. In this study, a new moisture prediction model with fast solution time and reasonable accuracy was developed based on the moisture buffer value (MBV) theory. The moisture buffer value was initially designed to quantify the moisture buffering ability of porous building materials. Very little research has been conducted to use MBV for calculating building energy performance directly. This paper first studied the MBVs under different boundary conditions (i.e., square wave and harmonic wave variation of vapour content), and then a time-average MBV was proposed. Experiments were carried out to get the parameters for the new FMBM model. Finally, simulation tests were conducted to compare the FMBM model with other moisture prediction models (e.g. EC, EMPD and HAMT models). The results indicate that the FMBM can provide a fast and reasonably accurate solution for indoor moisture prediction.
A three-dimensional steady-state heat and vapour transport model to assess the risk for interstitial condensation in building enclosures
Authors: Langmans Jelle , Houthuys Piet , Roels Staf
Published: December 2023

The article presents a practical 3D heat and vapour model to estimate the risk for interstitial condensation in building enclosures. The model is in fact a three-dimensional implementation of the Glaser method. In the first part of this article the modelling assumptions and solution technique are outlined. Next, the model is validated against an example from the literature. The third part of the article zooms in on the applicability of the proposed model in comparison to more complex hygrothermal models. Both the weaknesses and the strengths of the methodology are discussed. This section reviews the circumstances in which the model can be used safely and when a more detailed analysis is preferable. Finally, the article presents an actual case whereby the applicability of the model is demonstrated by making design decisions for the energetic retrofit of a curtain wall system.
Measurement and modelling of the moisture distribution in early-age concrete in the joint of composite beam and hollow core slab
Authors: Sekki P , Raunima T , Vinha J
Published: December 2023

The building moisture in concrete can damage the surface material if applied too early before the excess moisture has dried out. The composite beam forms an abnormal structure at the joint of the hollow-core slab, in which the thickness of the structural concrete is almost the thickness of the entire slab. For this reason, the joint of the beam and hollow core slab must be taken into account when assessing the adequate drying of concrete structures. The considered composite beams are steel casing beams, which are casted full of concrete. To achieve a composite structure, there are holes in the sides of the casing, through which moisture from the concrete transfers to the surrounding structure. However, the drying of the concrete inside the beam is significantly limited. The level of relative humidity of the concrete inside the beam remains moderately high for a long time, depending on the quality of the concrete and, consequently, the self-desiccation of the concrete. When using concrete with a low water binder ratio, drying occurs at a level of about 85%RH as a result of self-desiccation. In the study, relative humidity in the joint was measured continuously and with instantaneous measurements. The relative humidity in the joint concrete was also monitored after the surface structure layers were installed. In addition, humidity was measured from below the surface material and continued until equilibrium was reached. The structure was simulated as a 3D model and studied using a concrete material model which takes into account the self-desiccation and the thermal dependence of the sorption. A good agreement was found to describe the effect of temperature changes on the relative humidity of concrete that can be observed in continuous measurement. In addition, a suitable prediction of relative humidity below the surface material can be achieved based on modelled relative humidity distribution before the installation of the surface structure.
Towards automated stochastic Grey-Box Model Calibration for Heat Transfer Coefficient Inference
Authors: Faure Gaëlle , Juricic Sarah , Rabouille Mickaël , Rouchier Simon , Challansonnex Arnaud , Jay Arnaud
Published: December 2023

An accurate on-site measurement of the intrinsic thermal performance of the building envelope is a strong leverage to promote quality management and energy performance contracting. The building sector expects on-site measurements of the Heat Transfer Coefficient to be as short as possible and highly accurate. Perturbation measurement methods analysed by RC models have been shown to be promising with accurate results within 2 days. However, stochastic RC model calibration is highly dependent on expert knowledge. In particular, model initialisation jeopardises the calibration success if not carefully chosen a priori and all the more so with second or higher order models. This paper proposes and assesses a novel automated initialisation procedure for RC models. After having brought to light that the capacitance initialisation is critical to the calibration success, the paper shows how first-order models are almost always highly identifiable. The first-order model estimated parameters then serve as initial values for all second and higher order models. This novel procedure is in 78 % of the 156 cases tested better than or similar to expert knowledge initialisation. The results are very encouraging and suggest a successful integration in a global RC model calibration and selection workflow for a fully automated process.
Assessment of wind-driven rain (WDR) on buildings in an urban area: comparison of different CFD frameworks
Authors: Gholamalipour P , Ge H , Stathopoulos T
Published: December 2023

The study of Wind-Driven Rain (WDR) loading on building facades is essential to design more sustainable and climate-resilient buildings, as well as to prevent further damage to old and historical buildings. Both WDR loading on buildings and façade responses to impinging raindrops have been studied previously but results for such a multi-parameter problem are not generally conclusive. Thus, the relevant provisions of ISO semi-empirical model cannot be applied with confidence for complex building configurations, such as those in urban areas since the WDR prediction can be more than twice that of the experimental data. In this paper, the Eulerian Multiphase (ME) technique is coupled with the RANS model to simulate the WDR loading on a six-story building under steady rainfall event conditions. Wind and WDR results are compared with the available wind-tunnel and on-site field measurement results, respectively. The field measurements were carried out on a six-story mid-rise residential building, located in Vancouver, Canada. The results show that the Euler-Euler framework (RANS-EM) predicts wind and WDR in such an urban area configuration more rapidly and accurately compared to the more traditional Euler-Lagrange framework (RANS-LPT) for both stand-alone and urban area configurations.
Occupant behaviour and the potential of automating lighting control in terms of energy consumption – is there a link for residential buildings?
Authors: Thillo L Van , Verbeke S , Audenaert A
Published: December 2023

The implementation of occupancy-controlled and daylighting-dimmed lighting systems has an impact on the energy consumption of residential buildings. The BAC factor method of EN ISO 52120-1 estimates that 8% of the lighting energy can be saved compared to conventional manual control. However, it is assumed that their ability to potentially lower the lighting energy consumption is strongly related to external factors, such as the extent of daylight entrance and the behaviour of the inhabitants. By means of simulations in EnergyPlus, the performances of automated and manual lighting control are compared for an apartment and semi-detached building located in Brussels (Belgium) with variation in the occupant behaviour and orientation.

It appears that an automated lighting control including 0-100% dimmer reduces the lighting energy demand for all investigated cases with savings up to 38.4%, whereas a similar control without dimmer does not necessarily reduce the lighting electricity demand. However, the results show a considerable variation, making prediction methods as the BAC factor method highly inaccurate. The actual relative energy performance depends on the automation system, type of building, orientation and occupant behaviour (i.e. number of inhabitants and occupancy rate). Hereby, the number of inhabitants has the most considerable impact on the relative energy performances with differences up to 50%, while the occupancy rate shows a significant correlation, especially for low numbers of inhabitants.
Impact of Positioning Phase Change Materials on Thermal Performance of Buildings in Cold Climates
Authors: Norouziasas Alireza , Yin Hang , Hamdy Mohamed
Published: December 2023

The building envelope, an essential component of any building, plays a critical role in meeting energy efficiency and thermal comfort requirements. Incorporating phase change materials (PCM) into the building envelope can offer an opportunity to minimize energy usage and enhance thermal comfort by offsetting daily temperature fluctuations. However, the optimal performance of PCM is contingent on the material’s placement and thickness within the building envelope. Therefore, this study investigated the effects of positioning and thickness of PCM on thermal comfort and heating loads in a lightweight timber building in Trondheim, Norway. Four scenarios were considered based on the positioning of the PCM layer in the exterior wall and roof. Using IDA ICE, parametric simulations were conducted for various PCM wallboard positions and thicknesses in the exterior wall and roof. In Nordic climates, adding PCM reduces the risk of annual overheating. The findings of this study showed that installing 75mm of PCM wallboard in the exterior wall’s inner layer reduced the annual heating load by 2.3%. Compared to the base case scenario, increasing PCM thickness reduced zonal maximum indoor air temperatures by up to 6.2°C. This study underscored the importance of carefully considering the placement and thickness of PCM in building envelopes for optimal performance.
Lime-hemp as Wall Insulation - Hygrothermal Performance Analysis by Validated Simulations
Authors: De Mets Timo , Prignon Martin , Knapen Elke
Published: December 2023

The application of lime-hemp as a thermal insulation material is promising: besides its ecological benefits, lime-hemp has a reasonably low thermal conductivity, combined with a good moisture buffering capacity and high thermal inertia. However, adequate design and accurate execution on-site are required, as severe long-lasting moisture accumulation could cause the hemp shives to degrade. In this study, a numerical simulation model is validated using long-term measurements. Then, it is further used to evaluate the hygrothermal performance of lime-hemp as both external and internal wall insulation. The simulations show that high humidity levels are found in lime-hemp as external insulation if an external render with inadequate rain protection is used. If the lime-hemp is used as internal insulation, its high vapour permeability allows the masonry to dry towards the inside, resulting in a drier wall compared to vapour tight materials such as cellular glass.
An influence of temperature on thermal conductivity of loose fill insulations of natural origin
Authors: Kosiński Piotr , Wójcik Robert , Rosiński Arkadiusz
Published: December 2023

Basing the calculations of heat losses of buildings on the constant thermal conductivity calculated for the average temperature of 10°C may be a source of calculation inaccuracies. It may lead to oversizing heating systems or the inability to achieve high efficiency of devices, e.g. heat pumps or ventilation heat exchangers. At the same time, in the summer it may turn out that the rapidly increasing thermal conductivity of thermal insulation will not protect the building against overheating. In the paper, the authors described the influence of temperature on thermal conductivity of loose fill insulations, mineral wool, cellulose, hemp fibers and flax shives. Authors measured the properties of materials under 15 and 20°C temperature differences. The highest effect of temperature was observed for hemp fibers, with up to 18% rise of conductivity in the range from 10 to 40°C with 20°C temperature difference. While 14% rise of thermal conductivity in the range 2.5 to 37.5°C with 15°C temperature difference. The lowest increase was observed in the case of flax shives, 11% and 9% rise, respectively. The measurements were supplemented by thermal simulation performed in the Delphin software. The authors are currently researching the influence of moisture on heat transport and thermal diffusion through the described materials.
Experimental study on the capillary water absorptivity of an aerogel-based coating mortar under subsequent drying and wetting cycles
Authors: Karim A N , Kalagasidis A Sasic , Johansson P
Published: December 2023

Aerogel-based coating mortars with thermal conductivities ranging from 30 to 50 mW/(m·K) are an emerging type of thermal insulation coating mortar. They are intended for retrofitting uninsulated building envelopes due to their thermal performance which is comparable to conventional thermal insulation materials such as mineral wool. Meanwhile, their long-term hygrothermal performance and the reliability of the material properties are not fully demonstrated since these normally are declared based on single-cycle laboratory measurements. This paper presents laboratory measurements to determine the capillary water absorptivity of a commercial aerogel-based coating mortar after three consecutive wetting and drying cycles. The effect of the chosen drying (elevated versus room temperature) and sealing condition (sealed versus unsealed samples) on the measurement results were also assessed. The results show that the capillary water absorptivity of the samples increased after each repeated wetting and drying cycle regardless of the drying and sealing conditions. After three cycles, the measured capillary water absorption was more than five times higher than the initial measurement. Future research should investigate the causes of the observation and whether it applies to other aerogel-based coating mortars.
Evaluating the indoor radon concentrations in the Swedish building stock using statistical and machine learning
Authors: Wu Pei-Yu , Johansson Tim , Mangold Mikael , Sandels Claes , Mjörnell Kristina
Published: December 2023

Exposure to excessive indoor radon causes around 500 lung cancer deaths in Sweden annually. However, until 2020, indoor radon measurements were only conducted in around 16% of Swedish single-family houses and 17% of multifamily houses. It is estimated that approximately 16% of single-family houses exceed the indoor radon reference level of 200 Bq/m3, and the corresponding situation in multifamily houses is unknown. Measuring indoor radon on an urban scale is complicated and costly. Statistical and machine learning, exploiting historical data for pattern identification, provides alternative approaches for assessing indoor radon risk in existing dwellings. By training MARS (Multivariate Adaptive Regression Splines) and Random Forest (RF) regression models with the data labels from the radon measurement records in the Swedish Energy Performance Certification registers, property registers, soil maps, and the radiometric grids, the correlations between response and predictive variables can be untangled. The interplay of the key features, including uranium and thorium concentrations, ventilation systems, construction year, basements, and the number of floors, and their impact magnitudes on indoor radon concentrations, are investigated in the study. The regression models tailored for different building classes were developed and evaluated. Despite the data complexity, the RF models can explain 28% of the variance in multifamily houses, 24% in all buildings, and 21% in single-family houses. To improve model fitting, more intricate supervised learning algorithms should be explored in the future. The study outcomes can contribute to prioritizing remediation measures for building stocks suspected of high indoor radon risk.
Local control of near-field diffusion of infected respiratory cloud in a room by air-blades
Authors: Rasam Hamed , Gentile Vincenzo , Simonetti Marco , Tronville Paolo
Published: December 2023

The respiratory cloud of an infective subject contains droplets of mucosalivary fluid carrying pathogens. As this cloud spreads at a certain distance from the emission point, the droplets accumulate and their volume concentration increases in the room unless dilution, adequate ventilation, or filtration reduce it. A susceptible subject, standing a short distance away can be exposed more easily to the infected respiratory cloud, thus inhaling a higher dose of pathogens than someone breathing the mixed air in the room. A local airflow pattern can be employed to reduce this short-distance risk of inhalation and potential contagion. We present experimental and numerical investigations of a novel device acting as a barrier to airborne pathogen diffusion at a short distance. This portable device generates V-shaped air blades in front of the subjects, shifting the respiratory clouds. The air blades are generated by 12 small fans, three on each side of the cube. The air is sucked into the small plenum inside the device body through the bases. By being positioned obliquely on a meeting table, the device acts as a direct barrier to virus-laden aerosols without any filtration. The experimental tests show that the system can reduce the local concentration of aerosol by 63 to 84% at the respiratory position of a subject sitting at a table in front of an infective person. CFD simulation outputs using the Multiphase Eulerian-Lagrangian model show a good agreement with the experimental results. The validated model will be used to extend the range of investigation to different settings and to perform a parametrical analysis of the main design conditions.
Openings in ventilated Attics
Authors: Møller E B , Morelli M , Hansen T
Published: December 2023

How big should ventilation openings be in ventilated attics? In Denmark, guidelines describe what is sufficient to remove excess moisture penetrating through the ceiling. These guidelines are based on many years of experience. An important parameter is the tightness of the ceiling. With current regulations for the airtightness of buildings, convection through the ceiling is reduced compared to older buildings. Therefore, it is relevant to review these old rules of thumb and maybe revise them. In this two-year study, tests with different sizes of ventilation openings were conducted in a test house with 18 separate ventilated attics and airtight ceilings. One third of the attics were ventilated according to the guidelines, one third’s ventilation was reduced by one third and the last third had 50 % ventilation of the recommendations. Hourly measurements of temperature and relative humidity in the attics were conducted. Rafters in the attics were tested for mould growth. Six different types of insulation systems were used in the attics (with and without a vapour barrier, different insulation materials, and insulation thickness), therefore, the study also includes these differences. Earlier investigations, with full ventilation in all attics, showed no significant hygrothermal differences between them; consequently, it was assumed that the amount of ventilation would be decisive for the hygrothermal performance. This study follows up on this assumption. Results show little differences between the attics, mainly that having a vapour barrier becomes more important with reduced ventilation, and the insulation thickness and thereby U-value is of less importance. Reducing the requirements for ventilation of attics could be relevant, provided that the ceiling is airtight.
Thermal performance of two different PV-ETICS integration solutions in a real environment
Authors: Heim Dariusz , Knera Dominika , Krempski-Smejda Michał , Wieprzkowicz Anna , Kalamees Targo
Published: December 2023

The main aim of the paper was to experimentally investigate the thermal performance of the newly developed concept of building integrated photovoltaics. The first experimental results were obtained for the two proposed techniques of direct integration of photovoltaic panels (PV) with an external thermal insulation composite system (ETICS). Both systems were developed, described in detail, and constructed on a south-oriented building wall, and the main novelty was the introduction of an additional layer with increased heat capacity in one of the variants. Components were equipped with temperature and heat flux sensors connected to the datalogger system. The measurement period was from July to December, while the temperature of the PV panels was measured and analysed. The results were statistically analysed, and the main differences were emphasized. Moreover, the advantages of the case with a higher mass were listed and recommendations were formulated. The obtained results of the possible temperature of exploitation allow one to determine the risk of damage or loss of performance.
Innovative Integration of Phase Change Materials and Conceptional Design of Test Cases – New Products for the Building Envelope
Authors: Ali Asmaa , Kieseritzky Esther , Bogacz Anna , Tsiokou Vaia , Susana P.B. Sousa
Published: December 2023

The building sector contributes to a great part of energy consumption and has a major impact on climate in Europe. Development of climate-friendly and energy-efficient products is required to reach low and net-zero energy buildings and to facilitate the energy transition. The building envelope is critical in defining the demand for space heating and cooling as well as ensuring thermal comfort and indoor environmental quality through proper ventilation. This paper presents the conceptual test cases integrating phase change materials (PCMs) in the building envelope. PCM absorbs, stores, and releases the heat energy in a controlled manner taking advantage of the temperature difference between night and day. Hence PCM can support the thermal management of the building by minimizing unwanted heat gains and losses while integrated into walls or support the energy efficiency of ventilation while supplying fresh air. Smart ventilated heat harvesting windows and multifunctional sandwich panels are developed within the EU-funded iclimabuilt project. Additionally, commercial air-guided PCM storages are presented as ready-to-install products for decentralized ventilation and heat recovery systems.
Impact of indoor humidification on hygrothermal performance of building envelope in Northern Finland
Authors: Schroderus S , Kuurola P , Haverinen-Shaughnessy U , Fedorik F
Published: December 2023

Dry indoor air is known to increase the risk for respiratory infections, viability, transport of influenza virus and intensifies sensitivity of nasal systems. The aim of this study was to investigate the effect of humidification on the hygrothermal performance of the common timber wall structure of a day care building located in Northern Finland. Hygrothermal performance of structures under different indoor moisture loads was analysed. Numerical simulation and the Finnish mould growth model were used to evaluate the impact of humidification on moisture safety of the envelope. Largest impact of indoor air humidification is observed in the low humidity ranges on inner side of water vapour barrier. At the outer side of the water vapor barrier the indoor humidification has no effect on the hygrothermal conditions or mould growth risk. The most favourable conditions for mould growth are obtained at the corner of the building envelope, at the interface of load bearing timber and windshield where hygrothermal conditions are almost 60% of the time over 80% of relative humidity. However, the Finnish mould index does not indicate any mould growth risk. The study demonstrates that the indoor air can be humidified to RH of 35% during the cold dry period.
Moisture Performance Requirements for Insulation in Exterior Wood-Frame Walls without a Vapour Barrier
Authors: Leszmann Anna E. , Morelli Martin , Rasmussen Torben Valdbjørn
Published: December 2023

An increased interest has been observed, especially among architects, in constructing the building envelope without using a vapour barrier membrane of polyethene (PE) foil. An increasing interest in biogenic building materials has also been expressed, as their use, besides storing embedded carbon, can reduce greenhouse gas emissions, replacing nonrenewable building components. Further, building envelope construction without a vapour barrier reduces expenses and the difficulty of the work process, especially around joints and penetrations. This study aims to determine the most important material properties of biogenic thermal insulation materials that influence the moisture-robustness of exterior wood-frame walls constructed without a vapour barrier. A literature study was performed to examine which material parameters have the most influence on the moisture conditions in an exterior wall without a vapour barrier. Hygrothermal simulations of lightweight exterior walls were performed to investigate the significance of variations in material properties (e.g., equilibrium moisture content and vapour diffusion resistance) and determine their necessary characteristics when used as thermal insulation material in an exterior wall without a vapour barrier in internal humidity class 3 (defined in EN ISO 13788). The moisture-robustness of the construction is assessed based on the risk of mould growth in the layer between the thermal insulation and wind barrier. The study suggests that the moisture capacity of the available common biogenic thermal insulation materials does not significantly affect the overall moisture performance of the wall. Simulations demonstrate that, for the thermal insulation layer in internal humidity class 3, at least one of the following requirements must be met to ensure moisture-robustness in exterior walls without a vapour barrier: (I) high diffusion resistance of the thermal insulation and (II) high moisture capacity of the thermal insulation material at relative humidity between 60% and 90%. Commercial biogenic thermal insulation materials on the market do not meet the latter requirement.
Numerical and experimental estimation of building wall heat flux in presence of moisture transfer
Authors: Assaad M El , Colinart T , Lecompte T
Published: December 2023

Insulating building envelope is an efficient way to increase building energy efficiency and minimize greenhouse gas emissions related to heating. After building refurbishment, on-site measurements are suitable for verifying the actual thermal transmission properties of plane building components. For instance, the standard ISO 9869-1 describes a HFM method based on the measurement of surface heat flux with heat flow sensor (HFS). This method has been extensively investigated in the literature and successfully applied on vapor tight building walls. Nevertheless, hygroscopic building insulation materials (like biobased materials) are increasingly used, and heat transfer are coupled to moisture transfer within the wall. In this case, the HFS acts as a vapor barrier: it modifies the local moisture transfer and the associated latent heat flux. In this view, this study aims to clarify what it is measured with HFS in presence of moisture transfer. The question is first treated by numerical simulation of heat and moisture transfer within hygroscopic building wall. Then, experiments are carried out on hygroscopic building insulation where the moisture effects are exaggerated.