Overview of a Research Project of Novel and Rapid In-Situ U-Value Measurements

A Finnish-German collaborative project was carried out in 2018–2020 with the objective to investigate the accuracy and reliability of a novel metering device for in-situ determination of U-values of envelope structures. A rapid and reliable in-situ measurement method would clearly be a desirable tool for surveying the actual energy performance of existing buildings. Series of experimental and computational studies around a novel measurement device were carried out in Rapid U project. Rapidness of the measurement is sought by scheduling the moment of measurement so that the outdoor temperature has been sufficiently stable and cold before the measurement. Several test building measurements were carried out for certain structures in real weather conditions. Numerical modelling was also used to estimate the total number of hours in a year when the conditions are theoretically possible for similar structures to be measured rapidly. Repeated test building measurements showed unfortunately significant variation in the results. However, on average the results were promising and according to the simulations there should be plenty of suitable hours per year for rapid U-value measurement in cold countries if certain error tolerance is allowed.Peer reviewe

Dynamic water vapor sorption in wood-based fibrous materials and material parameter estimation

Building physical simulation software rely on assumptions regarding the local equilibria in materials’ pore systems, which may be unjustified for certain materials. While local hygrothermal non-equilibrium has still been in focus in some previous studies, it has been unclear how significant factor it may be when modeling real structures. In case of wood, the non-equilibrium is related to the slowness of intrusion of water molecules into the hygroscopic cell walls. Including local non-equilibrium in macroscopic model requires separate variables for pore air vapor and adsorbed moisture, and modeling the local mass transfer between pore air and adsorbed moisture requires effective material parameters, whose experimental determination is not straightforward. Commercially available sorption balances can be used to record data, which can be used in the parameter estimation. In this type of problem of parameter estimation from time-dependent data the mathematical challenge is to find global optimum from different solutions, which yield similar values for objective function. This difficulty can be overcome by using statistical inversion approach, which we applied in studying low-density woodfibre material (LDF). Dynamic sorption parameters were finally applied in numerical analysis of a laboratory test assembly. Based on the results, our conclusion is that the slowness of sorption is obvious in small LDF sample, which is exposed to changing humidity, but with the studied material the sorption seem to happen fast enough so that local non-equilibrium may have only slight effects in modeling of real structures.publishedVersionPeer reviewe

Ruggedness test made with mortars by free water intake test

Capillary movement in porous building materials is modelled by unsaturated flow. Material property needed for the calculations is liquid water diffusivity which is usually estimated by water absorption coefficient and capillary saturation moisture content. While determining of water absorption coefficient can be done according to EN-ISO 15148:2002 there is still lack of knowledge about sources of uncertainty in the experiment. In this paper author presents results of ruggedness tests done with mortar. The sources of errors investigated here was the shape and water inflow area of the specimen. Some specimens were also deprived of side sealing and sealing of upper surface as it was known to have impact on results. Results shows there is no considerable impact on measured capillary properties if the specimen sides are sealed or not. Nor does affect the immersed surface area of the specimen. The shape of the immersed surface instead has significant impact on values of both water absorption coefficient and capillary saturation of the specimen.Peer reviewe

Temperature-dependency of hysteretic sorption in hygrothermal modelling of wood fibreboard sheathing : analysis of exterior wall laboratory experiments

Wood is known for its temperature-dependent and hysteretic sorption behaviour. Several hysteresis models can be found from the literature, but the temperature-dependency of sorption especially in cold temperatures has received less attention. In this paper, we show experimental results for low-density fibreboard, which can be obtained with relatively inexpensive equipment and used for constructing temperature-dependent EMC function. The results were applied in the numerical analyses of a previous laboratory experiment involving an exterior wall with an LDF layer as sheathing. The optimal parameters for hysteresis models were determined by the least-squares data fitting approach. Our conclusion is that both the temperature-dependency and hysteresis in sorption behaviour must be included and with proper model parameters in the hygrothermal model in order to obtain satisfactory results when modelling LDF sheathing in a cold climate. Existing literature related to these aspects in hygrothermal modelling is scarce, and more experimental and computational research is needed.Peer reviewe

Puurunkoisten tuuletettujen yläpohjien kosteustekninen toiminta

Tämä artikkeli esittelee Tampereen teknillisessä yliopistossa keväällä 2015 valmistuneen pientalojen puurakenteisten tuulettuvien yläpohjien lämpö- ja kosteusteknistä toimintaa käsittelevän diplomityön tuloksia. Diplomityö on osa Honkarakenne Oyj:n hirsitalojen tutkimus- ja kehitysprojektia. Tutkimuksen tavoitteena oli selvittää puurunkoisten tuuletettujen yläpohjien kosteusteknistä toimintaa laskennallisesti tietokonemallinnuksen avulla. Tavoitteena oli tarvittaessa tehdä rakenteisiin niiden rakennusfysikaalista toimintaa parantavia muutoksia. Tutkimuksessa tarkasteltiin ideaalisesti toimivien rakenteiden lisäksi tilanteita, joissa rakenteisiin kohdistui ylimääräistä kosteuskuormitusta sade- ja ilmavuotojen seurauksena.publishedVersionNon peer reviewe

Temperature dependence of concrete drying and a method for estimating the effect of temperature on the relative humidity in concrete pores

In northern climates, the drying temperature of concrete floors under construction can range from 5 °C to 60 °C, covering average outdoor temperatures and potential increases to enhance drying. Given that the internal relative humidity (RH) of concrete is temperature-dependent, its effect on RH should be considered to eliminate the risk of moisture damage. The hygrothermic coefficient κ, which characterizes the effect of temperature, is determined and used to define temperature-dependent sorption (TDS) with the introduction of a novel method. Modeling methods for moisture transfer in early-age concrete are examined and models developed to take temperature effects into account within the studied temperature range. Model results are then compared with those of drying experiments performed at various temperatures. The conventional model, which lacks TDS, fails to describe the effect of temperature on RH; however, it can account for the impact on drying. Conversely, the TDS model can depict the temperature effect on RH, which was found to be substantial, especially at larger temperature deviations. The developed models improved the prediction of drying at low temperatures. In addition, κ results are applicable to the temperature correction of measurements. A novel method is presented that takes into consideration the direction of the correction and thus provides additional certainty from a moisture safety perspective.Peer reviewe

Timber-framed exterior walls insulated with wood shavings: A field study in a nordic climate

Wood processing residues provide a possibility to produce thermal insulation material with low environmental impact. This paper deals with the hygrothermal performance of timber-framed exterior walls with wood shavings as insulation material. The presented study onsisted of field measurements of five exterior wall structures with two different types of wood havings insulation and three reference walls. The study was performed in cold Nordic climate, where hygrothermal conditions at outer parts of a wall structure are critical. ntreated wood shavings and wood shavings coated with pulverized clay were compared as insulation materials. Different wind barriers as well as a water vapour barrier and sheathing acting as vapour retarder were also used. Results indicated no suitable conditions for mould growth inside any wall. The thermal resistance of wind barriers as well as the clay-coating of wood shavings had positive effect on the hygrothermal performance of the test walls. Wood shavings proved to be suitable insulation materials for well-insulated structures from the hygrothermal point of view, when the overall design, construction and maintenance are carried out in a proper way.Peer reviewe

Lämpimän ryömintätilaisen alapohjan lämpö- ja kosteustekninen toiminta

publishedVersionNon peer reviewe