Page 37 - ZEB AnnualReport 2015

THERMAL INSULATION PERFORMANCE OF REFLECTIVE MATERIAL

LAYERS IN WALL AND FLOOR CONSTRUCTIONS
VARMEISOLERENDE EFFEKT AV REFLEKTERENDE BELEGG I VEGG- OG

GULVKONSTRUKSJONER

Silje Kathrin Asphaug and Sivert Uvsløkk (SINTEF)

Heat transfer through cavities can be reduced F = λ · DT / d [W/m²] stagnant air will also be small, because the
air
min
by good air tightness, by illing the cavity with thermal conductivity of the air is low, about
thermal insulation material or by relective λ thermal conductivity of air, 0.025 W/(mK) 0.025 W/(mK). Heat transfer will be dominated
air
layers to reduce heat transfer by radiation. Air DT temperature difference across the cavity, K by radiation from the underside of the loor
leakages can be reduced and even eliminated d thickness of the cavity, m structure to the ground, but the radiation can
by air tight material layers like vapour- and be reduced using one or more relective foils
wind barriers. ZEB focuses on reducing the carbon footprint mounted horizontally in the cavity, parallel to
from construction materials. The idea behind the loor area.
The traditional solution, to ill some type utilizing air cavities in building envelope
of thermal insulation in the entire cavity, components is to reduce the amount of The maximum theoretical heat resistance that
will reduce or eliminate both radiation and thermal insulation materials while keeping the can be obtained in crawl space are about 3.5
convection. Still air has higher thermal thermal resistance of the envelope. m²K/W and about 4.1 m²K/W, respectively.
resistance than mineral wool. For air illed This corresponds to a continuous layer of
cavities the thermal properties can be By using relective foils in loors cavities (such normal insulation (thermal conductivity 0.035
improved by relective surfaces to reduce as crawl space), one can achieve a signiicant W/(mK)) with a thickness of around 120 mm
radiation. Convection is kept low by reducing reduction of heat loss. The air in the cavity will and around 140 mm. In theory, this will reduce
the thickness of the cavity. Conduction cannot be relatively stable as long as the temperature the heat loss through the loor with about 20%.
be reduced in air illed cavities since the in the cavity is higher than the temperature in
thermal conductivity of air sets a lower limit for the ground under the building. This is because In addition to the reduction in heat loss,
heat transfer: the heat transfer by convection becomes the temperature on the underside of the
small. The heat transfer by conduction in the loor joists is raised a few degrees during

ZEB annual report 2015 37