Heat, air and moisture (HAM) models allow efficient simulation of the building components' hygrothermal behavior. However, specific model assumptions, simplifications and approximations, as well as users' preferences, biases and mistakes in the implementation of material properties, boundary conditions, etc., may yield divergences among results from different models. The lack of a standard framework for HAM model quality assessment results in inconsistent benchmark cases and assessment methods in previous studies. Thus, this stateof-the-art empirical round robin validation targets to test the robustness and the reliability of HAM models in predicting one-dimensional hygrothermal responses of building components under controlled boundary conditions. It ran from 2023 to 2024, was coordinated by KU Leuven, and achieved participation of 38 groups from 19 countries. A comprehensive experimental dataset serves as the "correct answer", and simulation results from other participants form "reference answers". Since the boundary conditions are simple and explicit, the material properties' implementation has the main impact on the simulated hygrothermal responses. Most models prove to be robust, particularly in the heat transfer prediction. The moisture transfer prediction, on the other hand, looks more challenging. Reliability is also achieved by most models, as the deviations between simulation and experimental results are reduced when actual measured material properties are implemented as inputs. However, inappropriate and/or incorrect implementations are also observed. More in-depth investigations are performed interpreting the hygrothermal behavior of building components.

Circular economy (CE) practices pave the way for the construction sector to become less material- and carbonintensive. However, for CE quantification by climate mitigation models, one must first identify the CE practices along a product (or material) value chain. In this review, CE practices are mapped for the value chain of 6 construction materials to understand how these practices influence and can be considered in climate mitigation modelling. The main sub-categories of steel, cement, glass, clay-brick, insulation materials, and wood were used to identify which Rs are currently addressed at the lab and industrial scales: refuse, reduce, rethink, repair, reuse, remanufacture, refurbish, repurpose, recycle, and recover. The CE practices were reviewed using scientific repositories and grey literature, validated by European-wide stakeholders, and mapped across the life-cycle stages of the six materials - extraction, manufacturing, use, and end-of-life (EoL). The mapping was limited to the manufacturing and EoL stages because materials could be identified at these stages (the extraction phase pertains to resources, and the use phase to a product, for example, buildings). All reviewed CE practices identified at the industrial scale were quantified at the European level. For example, EoL reinforcement steel is 1-11 % reused and 70-95 % recycled; manufacturing CEM I is up to 60 % reduced; remanufacturing flat glass is 26 % remanufactured while less than 5 % EoL flat glass is recycled. A major barrier to closed-loop recycling is the need for sorting and separation technologies. Open-loop recycling synergies are found at the industrial scale between, for example, flat glass and glass wool value chains. Climate mitigation models are proposed to be augmented to include these practices requiring an explicit link between building use and the other construction materials' value chain stages.

The present project investigated the hygrothermal performance and risk of mould growth in solid masonry walls retrofitted internally with three diffusion-open bio-based insulation materials (two loose-fill cellulose and one hemp fibre), installed in test containers with controlled indoor climate. Focus was on bio-based insulation materials, as these are upcoming due to necessary CO2 reductions and because the hygroscopic properties of bio-based materials are different from traditional insulation materials like mineral wool therefore, some manufacturers claim a vapour barrier is unnecessary, even in relatively cold climates. The project was a large experimental study in two reefer containers with reconfigured facades, in which solid masonry walls with embedded wooden elements were constructed. The study focused on the conditions in the masonry/insulation interface and in the embedded wooden elements. The effect of hydrophobization and different indoor moisture loads were also investigated. Moreover, the bio-based insulation systems were compared with a wall insulated with the traditional mineral wool and vapour barrier system. Relative humidity and temperature were measured at several locations in the test walls for 1 year and 9 months. Measurements show that exposed masonry walls retrofitted internally with diffusion-open bio-based insulation materials resulted in unacceptably high moisture levels (>80% RH over longer periods). Lower moisture levels were observed when the internal insulation was combined with hydrophobization against wind-driven rain, but unacceptably high moisture levels still occurred (60%–70% in summer and 95%–100% in winter in the interface). Hydrophobization reduced the moisture levels in the interface and embedded wooden elements only in walls facing southwest, which is the direction with the most wind-driven rain. Mould growth tests showed no growth in the interface in walls insulated with cellulose insulation (mycometer surface value <25). Meanwhile growth was found in all four walls insulated with hemp fibre matts (mycometer surface value >400).

From 1995 to 2023 moisture content has been measured on a south-faced 0,75 m thick outer wall of brickwork. The wall is whitewashed on the outside. On the inside, a whitewashed and a plastic painted area lay beside each other. Moisture measurements made with a capacitive instrument showed, as expected, that the whitewashed part dries out to equilibrium, whereas the plastic painted part is kept wet with a higher moisture content.

the determination of thermal resistances (R-values) for reflective insulation by considering multi-dimensional radiative exchange between all surfaces. Results are presented for varied aspect ratios (width/depth) to characterize the geometry and effective emittance (E) variation from 0 to 0.82. Additionally, the use of CFD to evaluate convective heat transport allows the evaluation of installation defects that impact the R -value. R -values calculated for single and double air spaces show the greatest variation with aspect ratio for E \ 0.05. Modeling of assemblies with non-parallel surfaces has also been evaluated. Double airspaces with gaps that permit air flow between regions show that installation with unin-tended gaps at one end of a cavity results in small reductions in R-value while gaps at both ends of a cavity have R -value reductions approaching 50% for E in the reflective range. These examples provide a glimpse of a new dimension in the evaluation of reflective assemblies to be used in buildings.

Abstract A recent Danish project has studied the possibilities of using bio-based materials for interior insulation of solid brick walls, without the use of a vapour barrier. The purpose was to give indications of the possibility to use hygroscopic insulation material in positions as interior insulation, where it is known to be potentially vulnerable to moisture accumulation. Three bio-based thermal insulation materials were investigated: loose-fill cellulose insulation (two variants) and hemp fibre insulation commercially available in Denmark. The hygrothermal performance of the three insulation materials for internal retrofitting purposes was investigated in a large-scale experiment comprising several solid masonry walls. The test walls were built in an outdoor test field north of Copenhagen, and exposed to a controlled indoor climate. The experiments were conducted over 1 year and 9 months where moisture measurements were done in several locations within the walls, including the interface between insulation and masonry, as well as in embedded wooden components such as a beam end and a wall plate. The paper illustrates the results from experiments with or without a hydrophobizing treatment on the exterior surface as causes of moisture content in potentially critical places in the walls. Finally, some results from mould growth determinations are reported. Generally, high levels of moisture content were found in the interior insulation, particularly for non-hydrophobized walls, but critical mould growth conditions were found only in the case of one of the tested materials.

The pace of building retrofit is expected to increase significantly in the coming decade if the European Union is to meet its ambitious climate targets. This study explores successes and challenges with current retrofit efforts, with focus on indoor environmental quality and occupants’ satisfaction with the technical installations. A survey, indoor environmental monitoring and semi-structured interviews were carried out in a Danish social housing area undergoing a deep energy retrofit. The retrofit considerably improved winter thermal comfort and indoor air quality, which was a great source of satisfaction for the occupants. Overheating was however identified as an important concern in summer. The mechanical ventilation units suffered from faults which caused discomfort, in particular dry air, noise and draft. Occupants lacked knowledge on ventilation and manual control over it, which led a share of them to mitigate discomfort in alternative ways, by obstructing diffusers or disconnecting the units. To avoid the risks linked to such behaviors, new retrofit efforts should pay particular attention to user-friendliness of technical installations, clear communication of technical information to the residents and a close monitoring of the installations’ performance and occupants’ satisfaction after move-in.

Operating district heating systems with low supply and return temperatures improves heat production and distribution efficiency, permitting greater integration of renewable heat sources. Low-temperature district heating is viable without compromising comfort, but faults in end-users’ heating systems constrain temperature reductions. Such faults include malfunctioning valves, improper hydronic balancing, and excessive supply temperature setpoints. Occupants lack the resources to detect and diagnose these faults, so there is a need for automated solutions without requiring additional hardware. This paper proposes a method for improving the operation of an apartment’s hydronic floor heating system using data from room thermostats, a heat meter and a circulation pump to identify a grey-box model of the system. The resulting model virtually senses each room loop’s heat flux, flow, return temperature, and flow coefficient. The authors tested the model on a low-energy apartment in Denmark, using it to diagnose causes of high return temperatures, including poor hydronic balancing and an excessive supply temperature setpoint and pump setting. The authors also used the model to predict the minimum permissible supply temperature maintaining comfort, yielding a reduction in the energy-weighted supply and return temperatures of 8.6 °C and 6.5 °C, respectively.

The overall objective of the IEA EBC Annex 68" Project, "Indoor Air Quality Design and Control in Low Energy Residential Buildings", has been to develop the fundamental basis for optimal design and control strategies for good Indoor Air Quality (IAQ) in highly energy efficient residential buildings, and to disseminate this information for use in practoce. The project was defined in 2015, the working phase lasted for the years 2016-19, and the project was concluded with publications on 2020. The project has engaged researchers from 21 companies and institutions from 15 countries. The work has gathered laboratory and field data and developed new knowledge on pollution sources in buildings and how the transport mechanisms for the pollutants interact with heat, air and moisture conditions in materials and indoor zones. Furthermore, the project has assembled a set of contemporary models to simulate the combined heat, air, moisture and pollution conditions of buildings and their assemblies. In addition, a set of so-called "common exercises" about the various subjects have been developed and tested. The purpose has been to identify and describe amenable ways to optimize the provision of ventilation and air-conditioning and to assess possibilities to bring this knowledge into practice. The paper will review the original intentions of the project against the final achievements with the purpose to focus on which elements have been successfully achieved, and to identify areas where the project has only opened research and applications that should be followed up.

This study aims at obtaining feedback from occupants of low-energy retrofitted houses concerning the indoor environmental quality (IEQ) and the building systems in their homes. A questionnaire study was carried out in a social housing complex consisting of 2007 single-family houses, of which 1305 were retrofitted between 2014 and 2019. The different retrofitted houses were equipped with two types of heating systems, as well as balanced mechanical ventilation with two inlet locations. The questionnaire was sent to both retrofitted and non-retrofitted houses, and focused on four aspects: (1) thermal comfort and indoor air quality, (2) perception of the usability of the heating and ventilation systems, (3) adaptive actions in case of discomfort, and (4) interest in obtaining information about IEQ and building systems. The results show a large improvement in satisfaction with IEQ in the retrofitted houses compared to the non-retrofitted houses, apart from overheating in summer and drier air. The type of heating and mechanical ventilation does not show a significant influence on the occupants' adaptive actions in case of thermal discomfort, but occupants of retrofitted houses air out less frequently in winter. Occupants express a lack of sufficient knowledge about heating and ventilation systems in retrofitted houses. Floor heating is seen as more difficult to control than radiators. Mechanical ventilation with inlets placed on the top part of the walls generates more noise and draft issues than when the inlets are placed on the floor under the radiators. Finally, occupants of retrofitted houses are largely interested in receiving information on IEQ, energy use and systems' status. This study highlights the need for more communication and guidance regarding the operation of technical installations in private homes. The usability and transparency of these systems should be major attention points in future residential retrofit projects.

Heat and Moisture Transfer (HMT) simulations are used to evaluate moisture related damage risks in building envelopes. HMT simulations are commonly performed accepting the hypothesis of not considering the moisture hysteresis of materials. The results of HMT simulation of a timber wall with hysteresis are presented, and compared to the results of three simplified models, showing the effects of hysteresis on the simulation results and on the assessment of the risk of decay. Moisture content is the most influenced variable, while temperature and relative humidity are slightly affected. The wood decay risk analysis is performed using the simplified 20% moisture content rule. Similar temperature values and relative humidity values are calculated as simplified models, while the moisture content annual average values have differences up to 2.3%. The wood decay risk obtained with the simplified models could be overestimated if the simulation is performed using the desorption curve, while it could be underestimated with the adsorption curve. The best approximation is obtained with the mean sorption curve, while the desorption curve and the adsorption curve could be used to calculate the upper and lower boundary of the moisture contents respectively.

This project investigated fungal growth conditions in artificially contaminated interfaces between solid masonry and adhesive mortar for internal insulation. The project comprised several laboratory experiments: test of three fungal decontamination methods; investigation of development of fungal growth in solid masonry walls fitted with five internal insulation systems; and investigation of volatile organic compounds (VOC) diffusion through materials and whole insulation systems. One aim was to examine whether the alkaline environment (pH > 9) in the adhesive mortars could prevent fungal growth despite the water activity (aw ) in the interface exceeds the level (aw  > 0.75) commonly considered critical for fungal growth. The findings indicate that do-it-yourself decontamination solutions were inadequate for removal of fungal growth, while professional solutions were successful. However, the choice of decontamination method was of minor importance in the case of application of internal insulation with high pH adhesive mortar, as the high pH adhesive mortars were found to inactivate existing growth and prevented spore germination during the experimental period. The three tested VOCs were capable of diffusing through most of the examined products and could potentially affect the indoor air quality.

The study investigated the hygrothermal performance and risk of fungal growth in a phenolic foam system with a closed cell structure and a diffusion-open and capillary active lime-cork based insulating plaster, for internal retrofitting purposes. The setup comprised two 40-feet (12.2 m) insulated reefer container with controlled indoor climate, reconfigured with 24 holes (1 × 2 m each) containing solid masonry walls with embedded wooden elements on the interior side. Focus was on the conditions in the masonry/insulation interface and embedded wooden elements, and the performance of the two systems were compared to three diffusion-open insulation systems and one diffusion-tight. The effect of exterior hydrophobisation was also investigated. Relative humidity and temperature were measured in several locations in the test walls over 2½ years, and the risk of fungal growth was evaluated by on-site measurements and the VTT mould-growth model. The findings indicate that internally insulated walls with bare brick exterior surfaces performed poorly with high risk of fungal growth. The effect of exterior hydrophobisation was found to vary with the orientation and the installed insulation system, with a generally positive effect on walls facing south-west but limited effect for north-east. Furthermore, the more diffusion-tight insulation systems were found to perform better in combination with exterior hydrophobisation than the highly diffusion-open systems. The lime-cork insulating plaster showed high relative humidity and risk of moisture-induced problems. The on-site fungal tests showed no growth in the masonry/insulation interface inside the two insulation systems, probably due to high initial pH-value.

Wood decay risk assessment of building envelopes is commonly performed by engineers, architects and practitioners using results of Heat and Moisture Transfer (HMT) simulations and damage models. The commonly accepted HMT models use bijective sorption functions, accepting that materials reach hygrothermal equilibrium with the humidity contained in the air of the material’s pores and of the environment at a single MC. On the other hand, due to moisture hysteresis, equilibrium can be reached at different MCs for the same air condition, depending on previous equilibrium states. The aim of this work is to quantify the effect of considering hysteresis in HMT simulations and to evaluate its propagation in the risk assessment procedure for the case of wood decay. The software MATCH is used, implementation of an HMT model with hysteresis. Three timber walls are simulated in seven locations (Bolzano, Copenhagen, Hong Kong, Ottawa, Shanghai, Udine, and Vienna), first with hysteresis and then with simplified bijective sorption functions (adsorption, desorption, and mean sorption curve). MC and temperature time series are used to perform wood decay risk assessment with two damage models. The results show that the influence of hysteresis can be relevant, and that the choice of the sorption curve used in the simulations should be discussed. For the case of a CLT wall in Shanghai, simulated using the adsorption curve, a mean difference of 1.6% MC is found from the hysteresis case. This resulted in a difference of 0.7 decay rating in 10 years and 6% mass loss in 30 years.

In this extended abstract, we introduce the new IEA EBC Annex on 'Energy Efficient IAQ Management in residential buildings'. In this Annex, we address a number of challenges in implementing smart IAQ management strategies. Annex 68 provided us with a general framework for integrated simulation and assessment of Energy Efficiency (EE) and chemical indoor air pollution. This framework can now be further extended to develop and assess a series of smart Indoor Air Quality (IAQ) management strategies. By mapping the existing work on the pollution sources in residential context, we develop a consistent set of metrics for assessing the performance of the various technologies in terms of energy efficiency, comfort and health for the occupants. This includes extending the framework developed in Annex 68 with specific metrics for energy efficiency and particulate matter, explicitly including moisture control and HVAC component modeling as well as creating a common methodology for IAQ data sharing among smart devices. By pooling and analyzing the data, the range of conditions in dwellings can be better understood and the most appropriate energy efficient IAQ management strategies can be identified. The application of the metrics over time also allows continuous commissioning and conveying the achieved performance to the occupants. In this Annex, we therefore optimize the energy efficiency of IAQ management by addressing these issues. For the IAQ management we mainly focus on the use of smart materials (materials that have an ability to actively influence IAQ situation in the space) and smart ventilation (as defined by AIVC VIP paper nr. 38), since these are the strategies that have a high EE potential (air cleaning is already studied in a separate Annex 78).

The objective of the IEA EBC Annex 68 Project, “Indoor Air Quality Design and Control in Low Energy Residential Buildings”, has been to develop the fundamental basis for optimal design and control strategies for good Indoor Air Quality (IAQ) in highly energy efficient residential buildings. Focus has been on emission of chemical pollutants from building products and use of ventilation to alleviate IAQ effects. The question has been whether new paradigms for demand control should be developed based on knowledge from this project. The paper gives an overview of the project’s activities with regards to: - Gathering of laboratory and field data on pollution sources in buildings. - Formulation of a so-called “similarity approach” to predict emissions of volatile organic compounds based on knowledge from moisture transfer properties. - Gathering of a set of contemporary models to simulate the combined heat, air, moisture and pollution conditions of buildings and their assemblies. Based on this background, the project has identified and described an extended set of amenable ways to optimize the provision of ventilation and air-conditioning and to assess possibilities to bring this knowledge into practice. The paper gives an overview of the suggested solutions and their conditions.

Cement is the second most consumed substance by weight in the world, after water. The growing demand for reduced emissions of CO2 urges the cement industry to find materials with a low CO2 footprint, which calls for cement substitution. An assumption of the study has been that sewage sludge ash (SSA), an industrial by-product, can be applied as a potential cement substitute in cement-based materials without compromising material performance. The study investigated the effect of partial replacement of cement by SSA in mortar on hygrothermal properties of mortar. Two sewage sludge ashes originated from wastewater treatment plants located in the Greater Copenhagen area, Denmark. SSAs consisted of larger particles compared to cement particles; thus cement-ash-based mortar resulted in more porous structures compared to cement-based mortar. The higher porosity was responsible for a decrease of the thermal conductivity of the mortar. Significant differences were recognized in sorption isotherms of individual components, i.e. cement and ashes. However, their effect on the sorption isotherms of the mortars was minor.