Classifying system for façades and anomalies

Façades play an important role in buildings’ energy demand, and their state of conservation obviously influences thermal performance. The energy performance gap in existing residential buildings due to façade conservation status has not been analyzed in depth. In order to facilitate the systematic analysis of this influence, a system for classifying façades and their corresponding anomalies was developed for the first time. The classification system includes 23 types of façades and eight types of anomalies. It was verified by a panel of experts, and a case study was carried out with a sample of 154 buildings. An analysis of the results showed that the classification system is useful for a future analysis of the energy performance gap in existing residential buildings.Peer ReviewedPostprint (author's final draft

Predicting fuel energy consumption during earthworks

This research contributes to the assessment of on-site fuel consumption and the resulting carbon dioxide emissions due to earthworks-related processes in residential building projects, prior to the start of the construction phase. Several studies have been carried out on this subject, and have demonstrated the considerable environmental impact of earthworks activities in terms of fuel consumption. However, no methods have been proposed to estimate on-site fuel consumption during the planning stage. This paper presents a quantitative method to predict fuel consumption before the construction phase. The calculations were based on information contained in construction project documents and the definition of equipment load factors. Load factors were characterized for the typical equipment that is used in earthworks in residential building projects (excavators, loaders and compactors), taking into considering the type of soil, the type of surface and the duration of use. We also analyzed transport fuel consumption, because of its high impact in terms of pollution. The proposed method was then applied to a case study that illustrated its practical use and benefits. The predictive method can be used as an assessment tool for residential construction projects, to measure the environmental impact in terms of on-site fuel consumption. Consequently, it provides a significant basis for future methods to compare construction projects.Peer ReviewedPostprint (author's final draft

Factors affecting rework costs in construction

Rework adversely impacts the performance of building projects. In this study, data were analyzed from 788 construction incidents in 40 Spanish building projects to determine the influence of project and managerial characteristics on rework costs. Finally, regression analysis was used to understand the relationship between the contributing factors, and to determine a model for rework prediction.Interestingly, the rework prediction model showed that only the original contract value (OCV) and the project location in relation to the company’s headquarters contribute to the regression model. The Project type, the Type of organization, the Type of contract and the original contract duration (OCD) which represents the magnitude and complexity of a project, were represented by the OCV. This model for rework prediction based on original project conditions enables strategies to be put in place prior to the start of construction, to minimize uncertainties and reduce the impact on project cost and schedule, and thus improve productivity.Peer ReviewedPostprint (author's final draft

Modelling indoor air carbon dioxide concentration using grey-box models

Predictive control is the strategy that has the greatest reported benefits when it is implemented in a building energy management system. Predictive control requires low-order models to assess different scenarios and determine which strategy should be implemented to achieve a good compromise between comfort, energy consumption and energy cost. Usually, a deterministic approach is used to create low-order models to estimate the indoor CO2 concentration using the differential equation of the tracer-gas mass balance. However, the use of stochastic differential equations based on the tracer-gas mass balance is not common. The objective of this paper is to assess the potential of creating predictive models for a specific room using for the first time a stochastic grey-box modelling approach to estimate future CO2 concentrations. First of all, a set of stochastic differential equations are defined. Then, the model parameters are estimated using a maximum likelihood method. Different models are defined, and tested using a set of statistical methods. The approach used combines physical knowledge and information embedded in the monitored data to identify a suitable parametrization for a simple model that is more accurate than commonly used deterministic approaches. As a consequence, predictive control can be easily implemented in energy management systems.Peer ReviewedPostprint (author's final draft

Data-driven model for predicting indoor air quality and thermal comfort levels in naturally ventilated educational buildings using easily accessible data for schools

Modeling indoor air quality and thermal conditions in educational buildings is significant for protecting students' health, well-being, and productivity. The predictive models in existing studies were mainly built and applied in controlled environments with HVAC systems. These models did not involve occupant-related factors, had limited scope in a single building or space, and required indoor environmental monitoring data for the model input. This limits the applicability and generalization ability of the model in a large number of schools relying on natural ventilation, where indoor air quality and thermal conditions are significantly affected by occupants’ activities and ventilation practices. Hence, this paper proposes a methodology to develop a data-driven model for predicting the level of indoor air quality and thermal comfort in naturally ventilated educational buildings, and identifies the key influential factors. The model was developed using the class-weighted random forest algorithm with data collected from a large measurement campaign. The developed model demonstrated good accuracy, generalization ability, and robustness. The analysis concluded that occupancy, windows and doors operation, and outdoor environmental parameters are key factors must be involved, whereas building characteristics have no practical contribution to the prediction. The model inputs are easily accessible data for schools. Once the model is developed with data collected from an initial measurement campaign in representative educational buildings, it can be used in all local schools without requiring monitoring sensor networks, thereby rendering a “cost-effective” way of assessing indoor air quality and thermal comfort to help relevant stakeholders improve building management practices in schools.This research is part of the R&D project IAQ4EDU, reference no. PID2020-117366RB-I00, funded by MCIN/AEI/10.13039/501100011033. This work was supported by the Catalan Agency AGAUR under their research group support program (2021 SGR 00341). The author Sen Miao is funded by the China Scholarship Council (CSC) as a full-time PhD student, reference no. 202208390065.Peer ReviewedObjectius de Desenvolupament Sostenible::4 - Educació de QualitatObjectius de Desenvolupament Sostenible::11 - Ciutats i Comunitats SosteniblesObjectius de Desenvolupament Sostenible::3 - Salut i BenestarPostprint (published version

Assessing the influence of operating conditions and thermophysical properties on the accuracy of in-situ measured U-values using quantitative internal infrared thermography

Within the European context, most of the current residential building stock does not fulfil minimum thermal requirements and needs to be refurbished urgently. Quantitative internal infrared thermography can provide valuable information about the in-situ thermal transmittance of existing buildings for their future refurbishment. This paper aims to establish how operating conditions and thermophysical properties might affect the accuracy of the measured U-value using this technique. To assess the most influential operating conditions, one experimental room with a heavy single leaf-wall was chosen to develop the research in quasi steady-state conditions, with a wide temperature difference range (3.8<¿T<21°C). A statistical analysis demonstrated that the variance in thermal transmittance could mainly be predicted by changes in the outer air temperature. To analyze the impact of the thermophysical properties, specifically the heat capacity per unit of area, four unoccupied residential buildings with heavy multi-leaf walls were tested (6<¿T<10°C). The results mainly showed that the quantitative internal infrared thermography method is more accurate in heavy multi-leaf walls with high kappa values, reaching maximum deviations of 0.20%.Peer ReviewedPostprint (author's final draft

A comprehensive assessment of indoor air quality and thermal comfort in educational buildings in the Mediterranean climate

Maintaining good indoor air quality and thermal comfort is a challenge for naturally ventilated educational buildings, as it can be difficult to achieve both aspects simultaneously. Nonetheless, most of the existing studies only focus on one aspect. To explore the potential of balancing indoor air quality and thermal comfort, both topics must be investigated concurrently. This study assessed indoor air quality and thermal comfort in 32 naturally ventilated classrooms of 16 primary and secondary schools in the Mediterranean climate, based on a large on-site measurement campaign lasting one year that gathered over 460 hours of data. The research investigated occupants’ adaptive behaviors, analyzed the actual thermal comfort of around 600 students, and characterized the representative scenarios leading to good and poor indoor air quality and thermal comfort by clustering analysis. The results showed that poor indoor air quality was mainly due to closing windows and doors in winter, while thermal discomfort mainly occurred in summer because of the high indoor temperature. The findings suggested that a proper ventilation protocol is the key to balancing indoor air quality and thermal comfort.This research is part of the R&D project IAQ4EDU (reference no. PID2020-117366RB-I00), funded by the MCIN/AEI/10.13039/501100011033. This work was supported by the Catalan Agency AGAUR under their research group support program (2021 SGR 00341). The author Sen Miao is funded by the China Scholarship Council (CSC) as a full-time PhD student (reference no. 202208390065).Peer ReviewedObjectius de Desenvolupament Sostenible::3 - Salut i BenestarObjectius de Desenvolupament Sostenible::4 - Educació de QualitatObjectius de Desenvolupament Sostenible::11 - Ciutats i Comunitats SosteniblesPostprint (published version

The adoption of urban digital twins

The urban management industry has recently shown interest in implementing digital twins in cities to improve urban planning, optimize asset management and create secure, sustainable cities. Built on the knowledge gained with the development of smart cities and the implementation of digital twins in other industries, urban digital twins have experienced a significant expansion in just a few years. However, this rapid growth has led to a fragmented situation where the definition of the concept of urban digital twin is not clear and implementations share few similarities. For this reason, the main objective of this paper was to contribute to the conceptualization of the digital twin in urban management. To do so, existing initiatives were mapped in terms of applications, inputs, processing and outputs. Requirements were elicited and the basic structure of a city digital twin was defined. Benefits, open issues and key challenges were also identified. This paper will be useful for stakeholders within the urban management area as it establishes the basis for the future design, development and widespread adoption of urban digital twins.This work was supported by the Spanish Ministry of Science, Innovation and Universities via a doctoral grant to the first author (FPU19/ 04118), the Catalan authority AGAUR (2017SGR00227) and the University Service of the Terrassa City Council.Peer ReviewedObjectius de Desenvolupament Sostenible::7 - Energia Assequible i No Contaminant::7.3 - Per a 2030, duplicar la taxa mundial de millora de l’eficiència energèticaObjectius de Desenvolupament Sostenible::7 - Energia Assequible i No Contaminant::7.b - Per a 2030, ampliar la infraestructura i millorar la tecnologia per tal d’oferir serveis d’energia moderns i sos­tenibles per a tots els països en desenvolupament, en particular els països menys avançats, els petits estats insulars en desenvolupament i els països en desenvolupament sense litoral, d’acord amb els programes de suport respectiusObjectius de Desenvolupament Sostenible::7 - Energia Assequible i No ContaminantObjectius de Desenvolupament Sostenible::9 - Indústria, Innovació i InfraestructuraObjectius de Desenvolupament Sostenible::9 - Indústria, Innovació i Infraestructura::9.1 - Desenvolupar infraestructures fiables, sostenibles, resilients i de qualitat, incloent infraestructures regionals i transfrontereres, per tal de donar suport al desenvolupament econòmic i al benestar humà, amb especial atenció a l’accés assequible i equitatiu per a totes les personesObjectius de Desenvolupament Sostenible::9 - Indústria, Innovació i Infraestructura::9.4 - Per a 2030, modernitzar les infraestructures i reconvertir les indústries perquè siguin sostenibles, usant els recursos amb més eficàcia i promovent l’adopció de tecnologies i processos industrials nets i racionals ambiental­ment, i aconseguint que tots els països adoptin mesures d’acord amb les capacitats respectivesObjectius de Desenvolupament Sostenible::11 - Ciutats i Comunitats Sostenibles::11.6 - Per a 2030, reduir l’impacte ambiental negatiu per capita de les ciutats, amb especial atenció a la qualitat de l’aire, així com a la gestió dels residus municipals i d’altre tipusObjectius de Desenvolupament Sostenible::11 - Ciutats i Comunitats SosteniblesObjectius de Desenvolupament Sostenible::11 - Ciutats i Comunitats Sostenibles::11.2 - Per a 2030, proporcionar accés a sistemes de transport segurs, assequibles, accessi­bles i sostenibles per a totes les persones, i millorar la seguretat viària, en particular mitjan­çant l’ampliació del transport públic, amb especial atenció a les necessitats de les persones en situació vulnerable, dones, nenes, nens, persones amb discapacitat i persones gransObjectius de Desenvolupament Sostenible::11 - Ciutats i Comunitats Sostenibles::11.3 - Per a 2030, augmentar la urbanització inclusiva i sostenible, així com la capacitat de planificar i gestionar de manera participativa, integrada i sostenible els assentaments humans a tots els païsosObjectius de Desenvolupament Sostenible::11 - Ciutats i Comunitats Sostenibles::11.4 - Redoblar els esforços per a protegir i salvaguardar el patrimoni cultural i natural del mónObjectius de Desenvolupament Sostenible::11 - Ciutats i Comunitats Sostenibles::11.5 - Per a 2030, reduir de forma significativa el nombre de morts causades per desastres, inclosos els relacio­nats amb l’aigua, i de persones afectades per aquests, i reduir substancialment les pèrdues econòmiques directes causades per desastres relacionades amb el producte interior brut mundial, fent un èmfasi especial en la protecció de les persones pobres i de les persones en situacions de vulnerabilitatObjectius de Desenvolupament Sostenible::11 - Ciutats i Comunitats Sostenibles::11.7 - Per a 2030, proporcionar accés universal a zones verdes i espais públics segurs, inclusius i accessibles, en particular per a les dones i els infants, les persones grans i les persones amb discapacitatObjectius de Desenvolupament Sostenible::11 - Ciutats i Comunitats Sostenibles::11.a - Donar suport als vincles econòmics, socials i ambientals positius entre les zones urbanes, periurbanes i rurals enfortint la planificació del desenvolupament nacional i regionalObjectius de Desenvolupament Sostenible::11 - Ciutats i Comunitats Sostenibles::11.b - Per a 2020, augmentar substancialment el nombre de ciutats i assentaments humans que adopten i posen en marxa polítiques i plans integrats per promoure la inclusió, l’ús eficient dels recursos, la mitigació del canvi climàtic i l’adaptació a aquest, així com la resiliència davant dels desastres, i desenvolupar i posar en pràctica una gestió integral dels riscos de desastre a tots els nivells, d’acord amb el Marc de Sendai per a la reducció del risc de desastres 2015.2030Postprint (published version

Review of criteria for determining HFM minimum test duration

The actual thermal behaviour of façades is important to identify suitable energy-saving measures and in- crease the energy performance of existing buildings. However, the accuracy of in situ measurements of façades’ U-values varies widely, mostly due to inadequate test durations. The aim of this paper was to evaluate the minimum duration of in situ experimental campaigns to measure the thermal transmittance of existing buildings’ façades using the heat flow meter method, and to analyse the thermal performance of the façade during the test. Minimum test duration was determined according to data quality criteria, variability of results criteria, and standardized criteria for different ranges of theoretical thermal trans- mittance and for the same range of average temperature difference. Then, the minimum test duration results were compared. The findings show that ISO criteria are more sensitive and provide more accurate results, requiring a longer test duration. However, when certification is not required, the duration of the test could be reduced by applying data quality and variability of results criteria. The minimum duration of experimental campaigns depends on the theoretical thermal transmittance and the stability of climatic conditions. Moreover, results are more accurate when the dynamic method is used.Peer ReviewedPostprint (author's final draft

A comparison of standardized calculation methods for in situ measurements of facades U-value

In recent years, a growing concern has been how to determine the actual thermal behaviour of façades in their operational stage, in order to establish appropriate energy-saving measures. This paper aims at comparing standardized methods for obtaining the actual thermal transmittance of existing buildings’ façades, specifically the average method and the dynamic method defined by ISO 9869-1:2014, to verify which best fits theoretical values. The paper also aims to promote the use of the dynamic method, and facilitate its implementation. Differences between the theoretical U-value and the measured U-value obtained using the average and dynamic methods were calculated in three case studies, and then compared. The results showed that differences between the theoretical and the measured U-value were lower when the dynamic method was used. Particularly, when testing conditions were not optimal, the use of the dynamic method significantly improved the fit with the theoretical value. Moreover, measurements of the U-value using the dynamic method with a sufficiently large dataset showed a better fit to the theoretical U-value than the results of other dynamic methods proposed by authors. Further research should consider the optimum size of the dataset to obtain a measured U-value that is correctly adjusted to the theoretical U-value.Peer ReviewedPreprin