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Improving thermal insulation of timber frame walls by retrofitting with vacuum insulation panels – experimental and theoretical investigations:

Many of the Norwegian buildings from the 1960s–1980s with timber frame walls are ready for retrofitting. Retrofitting of these buildings with vacuum insulation panels (VIPs) may be performed without significant changes to the buildings, e.g., extension of the roof protruding and fitting of windows. Effectively, U-values low enough to fulfill passive house or zero energy requirements may be achieved; thus, contributing to a reduction of the energy use and CO2 emissions within the building sector. Retrofitting with VIPs on the exterior side is normally considered as a better solution; however, it may cause condensation in the wall. To investigate this and the interior option, four different wall fields were tested. One of them was a reference wall field built according to Norwegian building regulations from the 1970s, and three other fields represent different ways of increasing the thermal insulation level. In addition to the experiments, numerical simulations were performed where temperature, relative humidity, and surface wetness were measured. In total, the results from the experiments, simulations, and condensation controls conclude that timber frame buildings insulated with 100 mm mineral wool, might be retrofitted at the outside by adding 30 mm VIPs. However, this method for retrofitting provides limits to outdoor temperature, indoor moisture excess, and indoor temperature.

Hot box investigations and theoretical assessments of miscellaneous vacuum insulation panel configurations in building envelopes

Vacuum insulation panels (VIPs) are regarded as one of the most promising existing high performance thermal insulation solutions on the market today as their thermal performance typically range 5—10 times better than traditional insulation materials. However, the VIPs have several disadvantages such as risk of puncturing by penetration of nails and that they cannot be cut or fitted at the construction site. Furthermore, thermal bridging due to the panel envelope and load-bearing elements may have a large effect on the overall thermal performance. Finally, degradation of thermal performance due to moisture and air diffusion through the panel envelope is also a crucial issue for VIPs. In this work, laboratory investigations have been carried out by hot box measurements. These experimental results have been compared with numerical simulations of several wall structure arrangements of vacuum insulation panels. Various VIP edge and overlap effects have been studied. Measured U-values from hot box VIP large-scale experiments correspond well with numerical calculated U-values when actual values of the various parameters are used as input values in the numerical simulations.

The Importance of Wind Barriers for Insulated Timber Frame Constructions

The goal of this research project was to get more information about the influence of wind pressure on the heat transmission through timber frame con structions and to establish a recommended limit for air permeance of wind barriers.* The project was divided into three parts: wind pressure measurements on a rotatable test house, hot-box measurements on a wall, and calculations. The theoretical studies as well as the experimental investigations in the hot-box, have been restricted to one specific type of forced convection in the thermal insulation, the interchange of air be tween the insulation and the air gap between the wind barrier and the outer cladding. The results of the project show the importance of protecting the insulation layer with a wind barrier to achieve full effect of the insulation in wind exposed constructions. The measurements indicate that heat loss caused by this type of forced convection can be three to ten times higher than calculated for ideal constructions. Based on the measurements carried out in this project, Norwegian Building Research Institute, NBI, is recommending an upper limit for the air permeance of wind barriers, includ ing joints, of 0.05 m3/m2 h Pa (1.4E-5 m3/m 2 s Pa).

Moisture Robustness During Retrofitting of Timber Frame Walls with Vacuum Insulation Panels: Experimental and Theoretical Studies

A large amount of the buildings in Norway is from the 1960s–1980s. Many of these buildings have timber frame walls and are now ready for retrofitting. Application of vacuum insulation panels (VIPs) may make it easier to improve the thermal insulation in timber frame walls with a minimal additional thickness. Retrofitting of timber frame walls using VIPs may therefore be performed without large changes to the building, e.g. extension of the roof protruding and fitting of windows. Additionally, U-values low enough to fulfil passive house standards or zero energy building requirements may be achieved, thus contributing to a reduction of the energy use and CO2 emissions within the building sector. This work investigates different ways of retrofitting timber frame walls with VIPs on the exterior or the interior side. Timber frame walls retrofitted with VIPs on the exterior side is interesting because it allows for a continuous layer of VIPs over the building envelope, and it is also considered as a more robust solution than VIPs at the interior side (less risk of puncture). However, application of VIPs on the exterior side may cause condensation in the wall. To investigate this, a wall module containing four different wall fields was built between two climate rooms with indoor and outdoor climate, respectively. One field represents a reference wall built according to Norwegian building regulations from the 1970s. The three other fields represent different ways of improving the thermal insulation of the reference field, with VIPs at the interior or the exterior side. To minimize the size of the thermal bridge caused by traditional methods of fastening VIPs, a tailor-made VIP fastening bracket was applied in the build-up of the fields. Temperature, relative humidity (RH), and surface wetness was measured during the experiment. The surface wetness was measured on the wind barrier with a tailor-made surface wetness sensor consisting of double-sided tape, metal electrodes and paper sheets. In addition to the experimental investigations, numerical simulations and condensation control calculations were performed for the same wall fields with hygrothermal robustness performance as the main objective. In overall, the results from the experiments, simulations, and condensation controls conclude that timber frame buildings insulated with 100 mm mineral wool, might be retrofitted at the outside by adding 30 mm VIPs. However, this method for retrofitting provide limits to outdoor temperature, indoor moisture excess and indoor temperature.

Thermal performance of in-between shading systems in multilayer glazing units: Hot-box measurements and numerical simulations

Shading systems are widely used, also in Nordic climates, in conjunction with glazed facade in office buildings. The primary functions of the solar shading devices are to control solar gains leading to cooling needs during operational hours and reduction of discomfort caused by glare. A secondary property of shading devices incorporated in glazing units is that they can be utilized as an additional layer in the glazing unit when the shading device is deployed. This can improve the thermal transmittance value (U-value) of the windows. It can be deployed during night-time or in periods when a blocked view does not have any consequences for the users of the building. This article presents hot-box measurements of thermal transmittance values (U-values) performed for three insulated glazing units with integrated in-between pane shading systems. The shading devices are venetian-type blinds with horizontal aluminum slats. The windows with double- and triple-pane glazing units have motorized blinds. The window with a 4-pane glazing has a manually operated blind placed in an external coupled cavity. The measurements are compared to numerical simulations using the WINDOW and THERM simulation tools. The results showed that only minor reductions of U-values of the glazing units were obtained as function of shading system operation. It was, however, found that the introduction of shading devices in the window cavities will increase the total U-value of the window due to thermal bridging effects caused by shading device motor and the aluminium slats of the blinds. coupled cavity.

Hot-Box measurements of highly insulated wall, roof and floor structures

The purpose of this study was to investigate how natural convection in air-permeable glass wool insulation affects the thermal transmittance in walls, roofs and floor structures. The results can be used to evaluate the need for a convection barrier in thick mineral wool layers. Natural convection is affected by several parameters. In this study, the angle of inclination, the heat flow direction and the temperature difference across the test section have been studied. Thermal transmittance and temperature distribution measured using thermocouples placed inside the insulation cavity clearly showed convection in the insulation when the test section was in pitched roof and wall positions. An efficient measure to reduce the natural convection is to divide the insulation layer into two thinner layers using a diffusion open convection barrier. A convection barrier is recommended by the authors both in wall and pitched roof structures if the insulation thickness exceeds 200 mm.

Local loss coefficients inside air cavity of ventilated pitched roofs

Pitched roofs with a ventilated air cavity to avoid snow melt and ensure dry conditions beneath the roofing are a widely used construction in northern parts of Europe and America. The purpose of this study has been to determine pressure losses at the inlet (eaves) and inside the air cavity consisting of friction losses and passing of tile battens. These results are necessary to increase the accuracy of ventilation calculations of pitched roofs. Laboratory measurements, numerical analysis as well as calculations by use of empirical expressions have been used in the study. A large difference in the local loss coefficients depending on the edge design and height of the tile batten was found. The local loss coefficients of the round-edged tile battens were approximately 40% lower than the local loss coefficients of the sharp-edged tile battens. Furthermore, the local loss factor increased by increasing height of the tile batten. The numerical analysis was found to reliably reproduce the results from the measurements.