Thermal properties of contemporary lightweight cavi ty bricks: a semi-scale experimental study
Z. Pavlík, J. Fo řt, M. Jerman, R. Černý
■■■ CTU Prague, Faculty of Civil Engineering
Department of Materials Engineering and Chemistry
THERMAL PROPERTIES OF CONTEMPORARY LIGHTWEIGHT CAVI TY BRICKS: A SEMI-SCALE EXPERIMENTAL STUDYcontact: [email protected]
Outline:
• Introduction – motivation of the work – design of new advanced types of
cavity bricks
• Semi-scale experiment and its evaluation
• Studied cavity bricks – basic properties of the brick body, materials • Studied cavity bricks – basic properties of the brick body, materials
producer, cavities arrangement and filling
• Results and discussion – thermal conductivity, thermal transmittance,
valuation of cavity fillers effect
• Conclusions
Introduction – work motivation
• Thermal comfort of buildings occupants and indoor air quality are important
factors to be considered during building design and operation.
• With reference to the sustainable development principles, especially the
passive and low energy buildings should be constructed - the key features
THERMAL PROPERTIES OF CONTEMPORARY LIGHTWEIGHT CAVI TY BRICKS: A SEMI-SCALE EXPERIMENTAL STUDYcontact: [email protected]
of passive and low energy buildings design: building location and
orientation on the site, window design, building layout, shading and
ventilation, insulation and thermal mass (heat storage capacity) of building
envelopes.
• In order to meet requirements on thermophysical properties of materials for
envelopes of passive and low energy buildings, new advanced materials
are being developed.
Introduction – work motivation II
• In Central European countries, there is paid specific attention to the design
and manufacturing of single-layer building envelope systems based on
lightweight cavity bricks, whereas the cavities are filled either by air or
thermal insulation materials as polystyrene balls, mineral wool, crushed
polyurethane foam, etc.
THERMAL PROPERTIES OF CONTEMPORARY LIGHTWEIGHT CAVI TY BRICKS: A SEMI-SCALE EXPERIMENTAL STUDYcontact: [email protected]
polyurethane foam, etc.
• Filling the cavities by thermal insulation materials reduces the heat transfer
by radiation and contributes to the higher thermal resistance of brick block
compared to materials with air cavities only.
• In this contribution we refer about determination of thermophysical
properties of new types of cavity bricks produced in Czech Republic.
Determination of thermal conductivity λλλλ (W/mK)
• Main material parameter describing the heat transport in materials.
• From the engineering point of view this parameter includes heat
conduction, convection, and radiation.
• For determination of thermal conductivity, steady state methods can be
used - as for the practical experimental setups, the guarded hot plate
THERMAL PROPERTIES OF CONTEMPORARY LIGHTWEIGHT CAVI TY BRICKS: A SEMI-SCALE EXPERIMENTAL STUDYcontact: [email protected]
used - as for the practical experimental setups, the guarded hot plate
arrangement is the most frequently applied method.
• Application of the transient methods of thermal conductivity measurement
- hot wire method, heat flow impulse method, laser flash, etc.
• Most of the laboratory methods allow determination of thermal conductivity
on small samples or for a plate sample configuration with small specimen
thickness. This makes possible measurement of homogeneous materials
with no large-scale discontinuities only – new steady state technique is
designed and applied for entire brick blocks testing.
SEMI-SCALE EXPERIMENT
Within the semi-scale experiment, the climatic chamber system originally
developed for investigation of hygrothermal performance of building materials
and structures was used.
THERMAL PROPERTIES OF CONTEMPORARY LIGHTWEIGHT CAVI TY BRICKS: A SEMI-SCALE EXPERIMENTAL STUDYcontact: [email protected]
• The measured brick block was provided with necessary temperature and
heat flux sensors and thermally insulated in the tunnel between the climatic
chambers.
THERMAL PROPERTIES OF CONTEMPORARY LIGHTWEIGHT CAVI TY BRICKS: A SEMI-SCALE EXPERIMENTAL STUDYcontact: [email protected]
THERMAL PROPERTIES OF CONTEMPORARY LIGHTWEIGHT CAVI TY BRICKS: A SEMI-SCALE EXPERIMENTAL STUDYcontact: [email protected]
• In the climatic chambers, specific different temperatures were set,
nominally temperature difference 15/30°C and 30% re lative humidity were
used. In this way, the 1-D heat transport through the studied brick block
was simulated until the steady state heat flux was obtained.
• Sensors form Ahlborn Germany - the capacitive relative humidity sensors
are applicable in the 5-98% relative humidity range with accuracy ± 2%,
THERMAL PROPERTIES OF CONTEMPORARY LIGHTWEIGHT CAVI TY BRICKS: A SEMI-SCALE EXPERIMENTAL STUDYcontact: [email protected]
are applicable in the 5-98% relative humidity range with accuracy ± 2%,
the thermometers have an accuracy ± 0.1°C in the temp erature range from
0°C to 70°C.
• The heat flux through the studied brick was monitored by the heat flux plate
sensors Ahlborn FQA020C of a cylindrical shape having diameter 33 mm,
which were fixed on both front sides of the brick block. The accuracy of
these sensors was ± 5% of the measured value.
Evaluation of Semi-Scale Experiment
• Calculation of thermal conductivity λ (W/m/K) was done using the
measured data of heat fluxes according to the equation
THERMAL PROPERTIES OF CONTEMPORARY LIGHTWEIGHT CAVI TY BRICKS: A SEMI-SCALE EXPERIMENTAL STUDYcontact: [email protected]
,gradTq ⋅−= λ
where q (W/m2) is the heat flux and T (K) temperature.
• The heat flux data were averaged over a time interval of several days and
then used for calculations.
Studied cavity bricks
• Three types of brick blocks with internal cavities produced by company
Heluz Brick Industry, Czech Republic, were analyzed.
• Two types of bricks had the cavities filled by mineral wool or polystyrene
balls, whereas the third brick had air cavities only, without additional
thermal insulation filling. The bricks were designed for application in
THERMAL PROPERTIES OF CONTEMPORARY LIGHTWEIGHT CAVI TY BRICKS: A SEMI-SCALE EXPERIMENTAL STUDYcontact: [email protected]
thermal insulation filling. The bricks were designed for application in
thermal insulation masonry having
a width of 500 mm.
Bulk density(kg/m 3)
Matrix density(kg/m 3)
Total open porosity
(-)
1 389 2 830 0.51
THERMAL PROPERTIES OF CONTEMPORARY LIGHTWEIGHT CAVI TY BRICKS: A SEMI-SCALE EXPERIMENTAL STUDYcontact: [email protected]
Results and discussion
THERMAL PROPERTIES OF CONTEMPORARY LIGHTWEIGHT CAVI TY BRICKS: A SEMI-SCALE EXPERIMENTAL STUDYcontact: [email protected]
Typical heat flux measured at air-cavities
brick surface.
THERMAL PROPERTIES OF CONTEMPORARY LIGHTWEIGHT CAVI TY BRICKS: A SEMI-SCALE EXPERIMENTAL STUDYcontact: [email protected]
Typical heat flux measured at polystyrene-
balls filled cavities brick surface.
Typical heat flux measured at mineral-wool filled cavities brick surface.
Thermal conductivity of brick blocks (W/mK)
• One can see improvement of bricks thermal resistance by application of
THERMAL PROPERTIES OF CONTEMPORARY LIGHTWEIGHT CAVI TY BRICKS: A SEMI-SCALE EXPERIMENTAL STUDYcontact: [email protected]
Air cavities
Polystyrene balls filled cavities
Mineral wool filled cavities
0.123 0.091 0.075
thermal insulation materials as cavity fillers.
• From the quantitative point of view, the best thermal insulation performance
exhibited brick block with mineral-wool filled cavities. Its thermal
conductivity was about 40% lower compared to brick block with air cavities.
• Also the application of polystyrene filler led to the significant improvement
of thermal insulation properties.
Thermal transmittances of brick blocks (W/m2K)
THERMAL PROPERTIES OF CONTEMPORARY LIGHTWEIGHT CAVI TY BRICKS: A SEMI-SCALE EXPERIMENTAL STUDYcontact: [email protected]
Air cavities
Polystyrene balls filled cavities
Mineral wool filled cavities
0.246 0.182 0.150
• According to the Czech standard ČSN 730540-3, all the measured
materials are up to this standard that specifies required value of thermal
transmittance for external wall equal to 0.3 W/m2K and recommended
value equal to 0.25 W/m2K.
Conclusions
• A steady-state experiment in semi-scale conditions was applied for the
determination of the effective thermal conductivity of a brick blocks with
internal cavities.
• The result of the experiment presents valuable information for the building
practice, where the measured thermal conductivities can find use at the
THERMAL PROPERTIES OF CONTEMPORARY LIGHTWEIGHT CAVI TY BRICKS: A SEMI-SCALE EXPERIMENTAL STUDYcontact: [email protected]
practice, where the measured thermal conductivities can find use at the
thermal design of brick based structures.
• The obtained data pointed to the effectiveness of tested cavity fillers for
improvement of thermal resistance of single-layer brick building envelopes.
• In future work, the real climatic data for the Prague test reference year will
be applied on the exterior surface of the brick block in order to simulate real
climatic loading and hygrothermal performance of the brick blocks.
THERMAL PROPERTIES OF CONTEMPORARY LIGHTWEIGHT CAVI TY BRICKS: A SEMI-SCALE EXPERIMENTAL STUDYcontact: [email protected]
THANK YOU FOR YOUR ATTENTION!
This research has been supported by the Ministry of Industry and Trade of the Czech Republic, under project No FR-TI2/007.