Development of smart control system for leakage warning in compact roofs

Smart Sensor technologies to monitor temperature and moisture conditions in building components, can be used to give automatic warnings for abnormal high levels of moisture. Flat compact roofs are of particular interest, especially due to their vulnerability to rain leakages through the roofing membrane. Installing moisture sensors in such a roof measuring relative humidity (RH) or free water may give an early warning of rain leakages or condensation due to air leakages from indoors – before they start to get problematic. One challenge is, however, that normal moisture redistribution in the insulation layer over the season or day may give very high levels of RH in the top or bottom part of the insulation. The sensor system must be able to distinguish between these normal levels and leakage events. Together with a sensor technology and control system producer we have previously developed a semi-quantitative system that defines typical or normal RH levels in the insulation layer during the year. This system was based on hygrothermal simulations for various conditions, such as different exterior climate and levels of built-in moisture. This paper presents the preliminary findings from the further development of the system using real measurements from two pilot buildings located in Norway.publishedVersio

Fuktsikre løsninger for yttervegger av massivtre

Nye beregninger og laboratoriemålinger gir grunnlag for råd om sperresjikt mellom massivtre-elementer og utenpåliggende isolasjon.publishedVersio

Hygrothermal Simulation of Interior Insulated Brick Wall - Perspectives on Uncertainty and Sensitivity

Energy retrofit of existing masonry buildings has become attractive to meet demands for reduction in energy consumption. Retrofit may, however, introduce moisture risk that needs to be assessed. Hygrothermal simulation analysis is often conducted in this respect. Nevertheless, hygrothermal simulation of interior insulated bare brick masonry exposed to driving rain can be challenging due to the many aspects involved that determine heat- and moisture-transport behavior, and which should be addressed by an applied model. The present study highlights uncertainty encountered when establishing a hygrothermal simulation model. Furthermore, different modeling choices or simplifications are studied to determine impact on results. As a check of realism, results of 2D simulations are compared to results of a previous laboratory experiment of masonry wall segments subjected to severe rain wetting and subsequent drying. Rain absorption is modeled conservatively, attempting simulation results to envelope experiment results. Conservative results were not achieved for a relative humidity sensor placed on the masonry interior without inclusion of a “leaky” mortar joint. Simultaneously, the conservative approach underestimated drying experienced by the relative humidity sensor in two of three experiment wall segments. Regarding beam-end moisture content, the modeling approach conservatively enveloped experiment results in 3D but not in 2D.publishedVersio

Thermo-fluid dynamic performance of a ventilated pitched roof: Numerical modelling and experimental validation

Wooden ventilated pitched roofs represent a widely spread construction solution in Nordic countries. They have several benefits, including the drainage of excessive moisture from the construction and the reduction of the surface temperature to prevent snow melting and thus icing at the eaves and gutters. Modelling ventilated components is complex and requires a thorough understanding of the phenomena occurring in the air cavity, where convection plays a central role in the heat transfer process. The approach and the assumptions adopted for the roof model are therefore crucial to investigate the thermo-fluid dynamics in the air cavity. A literature review showed the need for comprehensive numerical and experimental research focusing on ventilated roof constructions, especially for Nordic climates. This article presents the thermo-fluid dynamic modelling of a ventilated pitched roof, which belongs to a full-scale experimental building located in Trondheim (Norway), the ZEB Test Cell Laboratory. A model of the roof was created using the finite element method-based software COMSOL Multiphysics. Transient simulations were performed in different climate conditions and the results of temperature and air flow speed along the cross section of the roof were compared with measurement data for validation. The simulation results show a good agreement with measurement data for both air speed and temperature in the air cavity, particularly in the summer day. The deviations in the numerical results will be object of study in future research, where the modelling approach will be further explored by testing different inputs, including boundary conditions and turbulence models.publishedVersio

Montana Kaimin, March 5, 1993

Student newspaper of the University of Montana, Missoula.https://scholarworks.umt.edu/studentnewspaper/9619/thumbnail.jp

Determining the Vapour Resistance of Breather Membrane Adhesive Joints

Due to increasingly stringent requirements, tapes and adhesive joints are a commonly used method to ensure tightness and energy efficiency in modern building envelopes. Previous studies have researched and tested properties such as the strength and tightness of adhesive joints. So far, water vapour resistance has been neglected. This article aims to determine the vapour resistance and shed light on possible consequences of vapour-tight adhesive joints in breather membranes used in roof assemblies. Laboratory measurements of vapour resistance were conducted according to NS-EN ISO 12572:2016, known as the cup method. Eleven products of breather membranes were tested. Results from the laboratory measurements were used to evaluate the impact of vapour-resistant adhesive joints related to the drying of built-in moisture. The simulation programs WUFI 2D and WUFI Mould Index VTT were used to model scenarios for moisture transport and risk for mould growth. Laboratory results show that the vapour resistance of breather membrane adhesive joints varies from 1.1 to 32 m in sd-value. Three of the tested products have a vapour resistance larger than 10 m, while four products have an sd-value less than 2.0 m. The sd-values of the membranes themselves range between 0.027 and 0.20 m. All tested adhesive joints are considerably more vapour tight than the Norwegian recommended value for breather membranes (<0.5 m). However, the mould growth analysis shows that the risk of mould growth is low in most practical cases, except when using adhesive joints with the highest vapour resistance in roofs assembled during autumn.publishedVersio

Moisture safety strategy for construction of CLT structures in a coastal Nordic climate

To reduce the carbon impact of new buildings, wood is seeing increased use as a structural material. Cross-laminated timber (CLT) and glue-laminated wood (glulam) elements allow the construction of multi-storey buildings. However, wood is vulnerable to moisture, especially when naked wood is exposed to weather during the construction process. This paper presents the moisture strategy employed during the construction of a four-storey CLT/glulam building in Trondheim, Norway. The building was constructed without the use of a weather-protective tent, requiring alternative protective measures. The construction of the main structure was scheduled to be as short as possible. Local protective measures were employed to protect the structure from rain and free water was removed after rain events. The project was closely supervised by the client, with particular care for moisture control. Moisture was regularly measured at 50 points throughout the building. No wooden surfaces were encapsulated until a wood moisture content below 15 weight-% was measured. The performance of the moisture strategy was evaluated using measurements of wood moisture, indoor climate, airtightness, and visual inspections. The wood moisture content quickly decreased as the building envelope was assembled, indicating that drying was well facilitated. In the first year after construction, gaps between the flooring and baseboards were observed, suggesting that the wooden elements have experienced some shrinkage. The moisture safety strategy is deemed to have been generally successful. The overall experiences were important in the development of new recommendations in the SINTEF Building Research Design Guides for CLT structures.publishedVersio

Moisture-resilient performance of concrete basement walls – Numerical simulations of the effect of outward drying

The moisture safety designs of basements used for habitation have become a topic of concern. Basements are prone to high moisture strain and have a limited outward drying ability compared with above-grade structures. The risk of interior moisture-related damage can be reduced if the basement walls are allowed to dry outward below grade. The use of vapour-permeable thermal insulation and the effect of air gaps behind dimpled membranes on the outward drying of concrete basement walls were investigated in this study. One- and two-dimensional hygrothermal simulations were conducted using WUFI®Pro and COMSOL Multiphysics®. First, the outward drying of concrete wall segments, previously investigated in a laboratory experiment, was simulated. Two EPS types and two dimpled membrane positions were compared, with an emphasis on the airflow through the air gap behind the membrane. Second, the long-term moisture performance of concrete basement walls was simulated. It was observed that when the dimpled membrane was placed between the concrete and exterior EPS, the bottom of the concrete segments dried faster than the top. When the dimpled membrane was placed on the exterior side, the concrete dried more uniformly along the height. Thus, the results indicated that the latter ensured outward drying of the concrete basement walls. However, the overall effect on the interior RH depended on the characteristics of concrete and the amount of interior and exterior insulation. Optimum drying was achieved when the thickness of interior insulation was reduced. The variability of the concrete properties used in basement walls requires further investigation.publishedVersio