Conference Agenda

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Session Overview
Session 20: Building envelope
Wednesday, 25/Aug/2021:
10:30am - 11:15am

Session Chair: Prof. Staf Roels, KU Leuven
Location: Room 3 - Room 013, Building: 116

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10:30am - 10:45am

Requirements to Building Envelope Characteristics in Cold Climates

Lyle Axelarris1, Aaron Cooke2, Craig Fredeen3, Robbin Garber-Slaght2, Emmett Leffel4, Lorne Ricketts5, William Rose6, John Zarling7, Alexander Zhivov8

1Design Alaska, United States of America; 2Cold Climate Housing Research Center, United States of America; 3Cold Climate Engineering, United States of America; 4Alaska Thermal Imaging, United States of America; 5RDH Building Science, Canada; 6William B. Rose & Associates, United States of America; 7Zarling Aero and Engineering, United States of America; 8US Army Engineer Research and Development Center, United States of America

Prescriptive guidelines for thermal insulation in the design of buildings in cold climates have traditionally been derived by a holistic consideration of climatic factors, energy policy, environmental policy, and economics. The differences in thermal barrier requirements in buildings across the Arctic and Subarctic regions of the world are as influenced by the differing priorities of the governing bodies that set these requirements as they are on actual physical demands and conditions. Usually national requirements for building envelope characteristics such as thermal insulation values, building envelope airtightness, vapor permeability, building mass, and detailing are based on economics, durability, and environmental considerations. Consideration of thermal energy system resilience provides a new paradigm through which to view the optimization of these parameters.

The paper summarizes best practice requirements to the building envelope characteristics for buildings located in cold and Arctic climate of the United States, Canada, and Scandinavian countries and compares the effect of different levels of building envelope efficiency and mass on indoor air temperature decay when heat supply is interrupted.

The paper results from research conducted under the IEA EBC Annex 73, the Environmental Security Technology Certification Program (ESTCP) Project “Technologies Integration to Achieve Resilient, Low-Energy Military Installations” and U.S. Army Program project 633734T1500 under Military Engineering Technology Demonstration

10:45am - 11:00am

Hygrothermal performance of internally insulated masonry walls with embedded wooden beam heads: a field study on the impact of hydrophobisation

Evy Vereecken, Staf Roels

KU Leuven, Belgium

To reach the 2030 energy targets, a thermal upgrade of our cultural heritage is necessary. When dealing with existing buildings, three post-insulation techniques could be applied to thermally upgrade the walls, i.e. cavity wall insulation, external insulation or internal insulation. From a building physics point of view, internal insulation is the most risky, as this technique can lead to a higher moisture level and a colder temperature in the wall. For massive walls in an urban context or with a valuable exterior facade, however, internal insulation remains as the only option. Hence, potential measures to diminish or to avoid the risk on frost damage, wood rot of embedded wooden beams and other damage patterns have been put forward in recent years. One of these measures is the application of a hydrophobic treatment. A clear understanding of the moisture behaviour of hydrophobised walls is however lacking. Therefore, this paper shows the results of a field study on the hygrothermal performance of internally insulated hydrophobised masonry walls with embedded wooden beam heads. Special attention is given to the impact of wind-driven rain and solar-driven inward vapour transport. Both walls with a vapour tight as well as a vapour open capillary active insulation have been studied. Additionally, non-insulated and non-hydrophobised walls are analysed as a reference. To study the hygric performance, traditional relative humidity sensors are supplemented with in-house made moisture pins making measurements in the high-moisture range possible. Just after applying the hydrophobic treatment, the wall’s moisture level is found to be high. A drying period is needed to again lower the wall’s moisture content. After this drying period, a hydrophobic treatment is shown to lower the relative humidity. At the wooden beam heads, this decrease in relative humidity is especially found during Spring and Summer.

11:00am - 11:15am

Investigation of phase change materials (PCMs) on the heat transfer performance of building systems

Hongxia Zhou, Åke Fransson, Thomas Olofsson

Umeå University, Sweden

Energy use of building systems contribute to a large percentage of total energy consumption, which requires consideration. Solutions of improvement to save energy are crucial. Phase change materials have been proved to be good candidates to be used in building envelopes, where they act as a thermal storage tank. If the temperatures of the surrounding become higher than the phase transition temperature of the PCM, a melting process starts and excess temperatures in the surrounding are held back due to the heat absorption. The opposite happens when surrounding temperature falls below the transition temperature, and temperature fluctuations are reduced in this way. As a temporary heat storage, PCMs can therefore reduce the energy consumption of a system.

In this paper, we have improved and used a, previous introduced, extended Explicit Finite Element Method (ex-FEM), for simulation of temperatures and heat transfer in simplified multilayer wall constructions, consisting of PCM and insulation. The method simulates the heat transfer processes that take place at and in such a wall construction, exposed to temperature increases and decreases, and the results have been validated against experimental data measured in a so called Hot-Box. Temperature data are measured at different positions in a number of simplified multilayer walls.

Our results show a good agreement between the simulations and the experiments, at both heating and at cooling when we consider the temperature hysteresis effect in the PCM. The temperature stabilization ability of the PCM is clear, in both the simulations and the experiments, and particularly in the data when the transition range of the PCM is fully activated and matching the temperature variation in the wall at that particular PCM position. Our ex-FEM tool has here been proved to be able to predict the thermal performance of simplified wall constructions of multiple layers with PCMs incorporated.

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