Uudet vaipparakenteet. Energian säästö ja kosteustekniikka

This report summarizes the results of the project "Development of Innovative Building Envelope Structures" which is part of the Finnish Energy Technology Programme RAKET and concentrates on the results that deal with reducing heating energy loss through building envelopes, improving hygric (moisture) behavior of structures and utilizing solar energy. The objective was to produce new innovative structures and principles of applications for low-energy houses. The applications with the purpose of reducing heating energy consumption are based on conventional mineral wool and cellular plastic insulation materials, low-emissivity foils and coatings that reduce long-wave thermal radiation and building papers with desired properties. Utilization of solar energy was investigated with a solar energy collector system consisting of transparent insulation and glass layers, air circulation with natural convection and thermal mass. Thick light-weight mineral wool insulation layers in the exterior walls are in practice always somewhat non-ideal which increases convection air flows in or through the walls when compared to ideal structures. Increasing the thickness of the insulation layer makes it more non-ideal and thus susceptible to drawbacks of convection flows. For example, the thermal resistance of a 300 mm thick insulation layer, may correspond to that of only 250 mm thick layer of ideal insulation without convection. Furthermore the internal moisture in the structure is distributed unevenly increasing the risk for mold growth and rotting. The convection effects in thick walls can be eliminated by isolating the insulation layers with air tight but vapor permeable vertical convection barriers. Significant portion of the total heat transfer in light-weight mineral wool insulation is caused by long-wave radiation (Infrared Radiation - IR). A low-emissivity foil attached directly to a surface of a mineral wool insulation has only a small effect on the thermal resistance of the whole insulation layer. The foil reduces the radiation heat transfer only in a thin layer of insulation material close to the foil. Farther off from the foil the radiation heat transfer happens mainly between the fibers regardless of the foil. Radiation inside thick insulation layers can be reduced significantly only by making use of fibers with low-emissivity surfaces or fibers transparent to IR-radiation and using low-emissivity foils on the sides of the layers. Thermal insulation structures based on only low-emissivity foils and air cavities were analyzed both with calculation tools and experimentally. The foils had two functions: to prevent thermal radiation and to cut convection air flows. In vertical structures in which the thickness of the cavity is 20...30 mm and one of the surfaces of the cavity has low emissivity (ε < 0,05) the apparent 'thermal conductivity' is in the order of 0,03 W/(m-K). In horizontal insulation layers with the direction of heat flow being downwards the same was achieved when the thickness of the cavity was 50 mm. The thermal transmittance coefficients of various horizontal and vertical experimental structures were measured to be around 0,14...0,17 W/(m²K). A 'real life' structure consisting of a thick light-weight mineral wool insulated wall with a 30 mm air cavity between the drywall and vapor retarder was analyzed. An aluminum foil laminated on paper and attached to the interior surface of the mineral wool insulation bright side facing the air cavity acted as a vapor retarder. The gained benefits were: 30 mm air cavity provides additional thermal resistance and installation space, vapor retarder is maintained undamaged functioning as an effective air barrier and vapor tight layer. Another application investigated was the use of low-emissivity foil installed 50 mm under the floor in the crawl space. The objective was to raise the temperature of the floor surface facing the crawl space and improve moisture conditions and the thermal resistance of the base floor. Both the simulations and the experiments showed that the surface temperature raised several degrees because of the foil which lowered the relative humidity under the floor surface from 90% to 65%. Due to the foil the steady-state temperature difference and the heat flux through the floor decreased approximately 40%. Drying of an invented flat roof insulated with a thick layer of expanded polystyrene (EPS) was investigated in laboratory conditions. The drying of the roof was based on a capillary drainage layer. A continuous, thin layer of capillary conducting cellulose fiber material transferred water from its injection point 6 m away from the gutter all the way till the eaves where the water left the roof first by dripping and later by evaporating at the edge of the capillary layer. Drying of the roof due to capillary flow started approximately one day after the water injection and most of the water had dried out in 21 days. The residue of moisture in the roof was 0,5...0,7 kg/m² in the end of the experiment. A solar energy collector system having air circulation based on natural convection was studied using simulations and experimental studies. This system, integrated to building structures, proved promising. In the system the collector and accumulator structures were separate from each other but connected through an air duct. The solar collector consists of glazing or transparent insulation layers. The air warmed up in the collector is transported by natural convection to the thermal storage wall inside the building. The benefits of this system compared to a passive one are that the U-value of the collector wall can be low and the heat loss from the accumulator gets released inside the building warming up the rooms. According to the-measurements the system could transfer over 40% of the solar energy available to the collector to the inner sections of the building. Another version of the collector with open air circulation into the room resulted in a higher efficiency, but dirt build-up and high instantaneous heat gains may prove to be problematic. Only 25 - 30 % of the total energy transported by convection was charged into the thermal storage wall made of light-weight concrete, while the rest was transferred mainly to the duct system. In the future research will be focused on developing a compact system that is integrated into a single wall.