Conference Agenda

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Session Overview
Session 13: Hygrothermal assessment building components
Wednesday, 25/Aug/2021:
4:00pm - 5:30pm

Session Chair: Fitsum Tariku, British Colubia University of Technology
Location: Room 1 - Room 082, Building: 116

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4:00pm - 4:15pm

Hygrothermal Monitoring of Two Pilot Prefabricated Exterior Energy Retrofit Panel Designs

Brock Conley1, Mark Carver2, Sebastien Brideau2

1Mechanical and Aerospace Engineering, Carleton University, Ottawa, Canada; 2CanmetENERGY-Natural Resources Canada, Ottawa, Canada

The Canadian housing stock consists of 11 million low-rise detached, semi and row-attached dwellings. More than two-thirds of these units were built before energy efficiency standards. To enable net-zero emissions by mid-century, the heating demand of the stock needs to be significantly reduced. Natural Resources Canada’s (NRCan) Prefabricated Exterior Energy Retrofit (PEER) project seeks to develop, test, and validate innovative prefabricated building envelope technologies for retrofitting existing Canadian homes using a panelized approach. Reducing disruption and enabling industrialization are key aims, while minimizing risk of moisture related problems.

NRCan undertook a proof of concept pilot project in 2017 in Ottawa, Canada. The walls of the pilot building were retrofit using two different panelized designs: nailbase and woodframe. This enabled a side-by-side comparison of cost, constructability and performance under identical conditions. The nailbase panel used an expanded polystyrene (EPS) core with oriented strand board (OSB) sheathing bonded to the exterior and fibreglass batt adhered to the interior. The woodframe panel used a dimensional lumber frame and dense-packed, fibrous insulation with a 90 mm stand-off gap.

The building was instrumented to monitor the temperature, relative humidity and moisture content of sensitive layers within the wall assemblies. The data were used to evaluate the hygrothermal performance, moisture accumulation and risk of associated problems such as mold growth.

During construction, some of the fibrous insulation may have been wetted by wind-driven snow prior to drying-in. The monitored data showed that this initial moisture was able to dissipate without significant risk. The two wall assemblies followed similar trends over the three-year monitoring period but the sheathing of the woodframe panel had a higher peak moisture content during the dry-out period. Otherwise, both panel designs showed limited potential for mold growth on monitored surfaces over the monitored period, despite this elevated initial moisture content.

4:15pm - 4:30pm

Sensor specifications for in-situ measurement of the temperature distribution inside the wall material for evaluating thermal performance of residential buildings

Tatsuo Nagai, Jin Eto

Tokyo University of Science

Various in-situ measurement methods for evaluating the heat insulation performance of residential buildings have been proposed. Among those methods, we target "probe insertion method” in this research. Here, the “probe insertion method” is to inspect the presence or absence of heat insulating material visually with borescope or measure the temperature distribution in the depth direction with an inserted temperature sensor by providing a minute hole with a diameter of about 1 mm.

In the temperature distribution measurement by this method, when the temperature sensor is inserted from inside the room into the insulating material, the temperature sensor itself can be a thermal bridge, which causes a deviation from the original temperature distribution inside the insulation material. For this reason, it is necessary to define the sensor specifications that can be used for the measurement, but it is not fully understood what kind of physical parameters affect the deviation.

In this study, we examine firstly the relationship between the related parameters and the measured temperature deviation by measuring the temperature distribution of two kinds of insulating materials with different thickness and thermal conductivity using several temperature sensors with different diameters and thermal conductivity. Based on the measurement results, we introduce two dimensionless numbers that determine the degree of the deviation of the measured temperature distribution.

Next, we confirm by heat conduction simulation that the deviation is about the same if the assumed dimensionless numbers are the same even if each parameter is different.

Finally, we propose a procedure to determine the required specifications of a temperature sensor that can measure the temperature distribution accurately using the introduced dimensionless numbers.

4:30pm - 4:45pm

Determination of the anisotropic thermal conductivity of an aerogel-based plaster using transient plane source method

Ali Naman Karim, Bijan Adl-Zarrabi, Pär Johansson, Angela Sasic Kalagasidis

Chalmers University of Technology, Sweden

Aerogel-based plasters are composite materials with aerogel granules and plasters being the main constituents. Declared thermal conductivities of these materials are in the range of traditional insulating materials for building applications, i.e. 30-50 mW/(m K). Based on the results from reported field measurements, aerogel-based plasters can significantly reduce the thermal transmittance of uninsulated walls. However, the in-situ measured thermal conductivities have sometimes been higher than the declared values. While this deviation has often been explained by the differences in built-in moisture in the plaster, effects of the material's anisotropy have not been considered. The latter is common in composite materials and manifested as a difference between the heat flow when measured in different directions.

The objective of this study is thus to evaluate the anisotropic thermal conductivity of an aerogel-based plaster. This is done in a set of laboratory measurements using the transient plane source method. Six identical and cubic samples with the dimensions of 10x10x10 cm3 were prepared. These six samples were paired two and two, creating three identical sample sets. In total, 360 measurements of thermal conductivity and thermal diffusivity, and 130 measurements for specific heat capacity were conducted. The results indicate a weak anisotropy of less than 6.5 % between the three directions (x, y, z). The accuracy of the transient plane source method for measuring the thermal conductivity is better than 5 % which means the anisotropic thermal conductivity of the studied aerogel-based plaster does not fully explain the deviation between the declared and measured in-situ thermal conductivity.

4:45pm - 5:00pm

Hygrothermal performance assessment of split insulated cork wall assemblies under various moisture load conditions

Tigran Ghazaryan, Fitsum Tariku

British Columbia Institute of Technology, Canada

Every year along with the implementation of energy saving, energy conservation and other green energy initiatives the demand for effective, but sustainable, renewable insulation materials in the construction industry increases. It is worth mentioning that the selection of insulation materials nowadays is not limited to its cost and technical characteristics only, but health-related aspects and carbon footprint are also taken into consideration. However, there are not many insulation materials that have competitive technical characteristics, are sustainable, renewable and do not pose risk for health.

Cork and cork-based materials like insulation cork boards (ICB) are of these types of materials which have unusual combination of material properties, have low to negative carbon foot print and have low to almost zero negative impact on the ecology and human health during the whole life cycle and later on. That is why with the increasing demand for sustainable, renewable and ecological materials the interest toward the cork in North America is expected to increase. However, there are not so many researches performed on lightweight wall assemblies common in North America with cork insulation applications.

In this paper, the hygrothermal performance of natural cork insulation used in split wall assemblies is compared against similar, commonly used mineral wool and EPS wall assemblies for three different Canadian climates, using WUFI hygrothermal analysis computer simulation tool. The relative performance of seven wall assemblies, with various combinations of insulation type and vapour control strategies, exposed to different moisture loads including elevated indoor humidity, air leakage and rain penetration are presented. The simulation results suggest that, in general, assemblies with cork have a slight advantage in performance against the EPS assemblies, especially when the amount of moisture affecting the assemblies are high. In most cases assemblies with mineral wool performs better than that of with cork and EPS insulations.

5:00pm - 5:15pm

Probabilistic assessment of timber frame wall compositions using a convolutional neural network

Astrid Tijskens, Staf Roels, Hans Janssen

University of Leuven, Belgium

In recent years, there is a growing market share of timber frame constructions across Europe, due to its suitability for low-energy buildings. A major disadvantage of timber frame construction, however, is its susceptibility to moisture damage. A correct design of a timbre frame wall’s composition is vital to avoid moisture damage. In Europe, timber frame walls typically consist of a wind barrier at the cold exterior side and a vapour barrier/retarder at the warm interior side, while the vapour permeability of consecutive layers increases from inside to outside. Currently, no general guidelines exist to determine which wall compositions prevent moisture damage in a specific context. To develop such general guidelines, a comprehensive study is required, taking into account the uncertainty in boundary conditions. Such a probabilistic assessment is typically carried out through a Monte-Carlo approach, which easily becomes computationally inhibitive. This paper thus makes use of a metamodel, which mimics the complex hygrothermal model while being considerably faster. The authors previously developed a metamodel using a convolutional neural network and demonstrated its’ capacity to accurately predict the highly non-linear hygrothermal response of a timber frame walls. In this paper, this metamodel is used to predict the hygrothermal response of multiple timber frame wall compositions, taking into account variability in climate as well as other influencing uncertainties. Based on these results, general guidelines on timber frame wall compositions are formulated, adapted to the specific climate and cladding type. Preliminary results show that a lower limit for the -ratio can be a good criterion to avoid mould growth. To avoid condensation run-off, one should ensure either the insulation or the wind barrier can buffer the excess moisture.

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