air temperature is set at the same value as the
mean temperature of the sample, i.e. usually
+10 °C. Measured values are collected by a
computer-controlled data logger, collecting
values of heat flow and temperatures and calculating the thermal conductivity (λ) from
λ=
q⋅d
ΔT
W/(m·K)
where q = the thermal flux density (W/m²)
d = the sample thickness (m)
ΔT = the temperature difference
across the sample (K)
Measurement of thermal conductivity
Thermal conductivity is measured by a flat
plate apparatus, with heat flow meters fitted to
the upper and lower plates.
Measurements are made by placing the material sample (which, in the case of loose-fill
insulation, is contained in a box) between a
hot and a cold plate, each 600 x 600 mm in
size. The plates can be set at a distance
apart as needed to suit the sample. Temperatures and heat flows are measured in the
centre of the sample over an area of
250 x 250 mm.
The temperatures of the
upper and lower plates are controlled by
circulating a liquid at the appropriate temperatures through ducts in the plates. Generally, the upper plate is at a temperature of
about 20 °C, and the lower at about 0 °C,
giving an mean temperature of +10 °C.
The equipment is installed in a climatecontrolled chamber, in which the air temperature and humidity can be controlled, so that no
condensation occurs on the cold plate. The
SP Technical Research Institute of Sweden
Energy Technology
Box 857, SE-501 15 BORÅS, SWEDEN
Telephone: +46 10 516 50 00, Telefax: +46 33 13 55 02
E-mail: [email protected], Internet: www.sp.se
Upper plate (hot)
Sample (600 x 600 mm)
Lower plate (cold)
Heat flow meters with
temperature sensors
Sample preparation
When preparing loose-fill insulation for measurement of its thermal conductivity, the material must be blow-delivered in the same way
as is used in practical application. Samples
are therefore prepared either by the customer,
using his normal equipment, or by SP, using
SP's equipment. SP's equipment is as follows:
Volumatic III, from Unisul Inc.:
• 45-60 m polyurethane hose, 100 mm
internal diameter
• electrically powered.
SP INFO 2000:16 E
2008-04-16
SP Technical Research Institute of Sweden
Thermal conductivity - loose-fill insulation
Shelter Shield 400:
• about 20 m of hose, 65 mm internal
diameter
• electrically powered
• this machine is intended primarily for
cellulose materials.
To produce a sample of suitable format for the
hot plate equipment, the material is blown into
a 150 mm high test frame, as shown below.
20
600
150
600
Bottom of plastic film
The quantity (weight) of material needed to fill
the frame is calculated from the density of the
material and the volume of the frame, as
follows:
Weight = density x volume
The material is blown such that it falls almost
vertically into the frame. In order to ensure
uniform density in all parts of the frame, it is
important that the material is distributed as
uniformly as possible over all parts of the
frame. About half of the material is therefore
blown into the frame, after which the frame is
rotated through 180° and the remainder of the
material is blown.
In order to ensure that the frame is completely
filled for measurement of the thermal conductivity, the material is blown until its depth is
about 5-20 % greater than that of the frame,
depending on how much it tends to settle.
Final, careful adjustment of the sample is carried out by hand, in order to ensure the correct
weight and smooth upper surface. In the test
equipment, the material is compressed to the
depth of the frame, giving it the required density.
Hygroscopic materials are usually measured
in the form of dried samples, which means
that allowance must be made for moisture
content (decided in advance) when calculating
the weight. The material is dried by placing
the test frame in a drying chamber at +70 °C
until the weight ceases to fall, which usually
takes about 4-5 days.
Declared thermal conductivity (λD)
Rules for determining the declared value of
thermal conductivity are set out in the VIM
Certification Rules for Declared Thermal Conductivity.
The declared thermal conductivity (λD) must
be higher than the calculated value of λ90/90.
This value is determined by adding the mean
value from the thermal conductivity measurements, with corrections for uncertainty and
hygroscopic moisture.
Contact persons
Bertil Jonsson
[email protected], tel. +46 10 516 51 60
Eva-Lotta Kurkinen
[email protected], tel. +46 10 516 51 77