Convection in mineral wool used as insulation for buildings.
Stankevicius, Vytautas ; Paukstys, Valdas ; Bliudzius, Raimondas 等
1. Introduction
The building sector consumes about 40% of the total energy consumed
in the European Union. Therefore, the directive issued by the European
Parliament and Council (Directive 2010/31/ES) introduces requirements
for low energy buildings and modernization of the existing ones. In
order to achieve this goal, heat loss from the building sector has to be
reduced by increasing the thermal resistance of enclosures. However,
with an increment in the thickness of a thermal insulation layer of
enclosures, convective heat transfer is formed in the air permeable
insulation material due to difference in temperature and wind pressure
through it.
Convective heat transfer does not occur in airtight insulating
materials, but can take place in air gaps located in the materials wider
than 5 mm (Sadauskiene et al. 2009). According to Roots (1997),
convection occurs exclusively in unqualitatively arranged walls, i.e.
those having big air cavity. Because of convection, general heat
transfer may increase up to 12-13%. As the scholar maintains, small
cavities and air gaps have no significant influence on the heat transfer
coefficient in walls. However, in the scientific accounts provided by
the Centre of Technical Research (VTT) in Finland, contradictory data
are presented. Kokko et al. (1997) claim that when mounting
thermal-insulating materials, especially solid slabs of mineral wool,
the absolute avoidance of small air gaps is impossible. Therefore, the
value of the heat transfer coefficient in the thermal-insulating layer
may increase up to 20-25% (Ojanen 1993).
Scientific research on the effect of convection on heat transfer
through enclosures has been recently carried out in different countries
(Abid 2012; Kokko et al. 1997; Ridouane et al. 2004; Cherif et al. 2009;
Tiwari et al. 2012; Ojanen, Kohonen 1995). The obtained results of these
studies allows forecasting external conditions for starting air movement
and an impact of it on the thermal characteristics of the enclosure. The
other scope of the conducted investigation focuses on heat exchange
between the outdoor air and the surface of enclosures and as well as on
natural convection in air space and fibrous thermal-insulating
materials, i.e. mineral wool that fills the entire volume of the
enclosure (Nield, Bejan 2006; Lakompte 1990). In addition, many cases of
the thermal insulating layer placed between two isothermal and airtight
surfaces have been also given attention (Bankvall 1992; Kohonen, Ojanen
1989; Samajauskas et al. 2003). Unfortunately, such conditions in many
cases are not fulfilled in real constructions of buildings. Thus, in
reality, the negative effect of natural and forced convection on the
thermal properties of building enclosures has to be much larger, and
therefore it has to be thoroughly researched (Abid 2012; Kohonen, Ojanen
1989).
The majority of authors carried out experimental research on the
fibrous thermal-insulating materials of a homogeneous structure. The
achieved results were amended employing the criteria of similarity
between heat transfer and hydrodynamic processes such as Nusselt,
Rayleigh, etc. (Altac, Kurtul 2007; Liu et al. 2011; Alam et al. 2012).
However, only concluding these works is not enough, because it
underestimates the factors having an influence on the thermal properties
of thermal insulating materials.
In real constructions, it is rather difficult to avoid the
formation of air gaps having various widths, the movement of air flows
caused by wind pressure, differences in temperature as well as the
continuity of the wind protecting layer. Hence, it has been decided to
analyse the laws on convection taking place in real building
constructions by estimating properties of thermal-insulating and wind
protecting materials, including environmental factors caused by the
climate of Lithuania, i.e. the influence of wind speed, its direction
and differences in temperature on air movement in the ventilated air
gaps of building enclosures.
2. Investigation methods
2.1. Investigation into walls insulated with air impermeable
thermal insulating slabs having small air gaps
To determine the influence of convection on heat transfer through
walls insulated with air impermeable thermal-insulating slabs having
small air gaps, computer simulation and experimental investigation into
the constructed wall model were carried out.
2.1.1. Numerical simulation of heat transfer by convection
PC-programs--AHCond and ANHond--invented by C. E. Hagentoft (1993)
were used for the numerical modelling of convection. The introduced
programs are used for estimating heat transfer in walls where heat is
transmitted by the air moving in small gaps and for establishing the
place where at the same time it expands by conduction through air
impermeable layers of thermal-insulating materials. The programs employ
a two-dimensional model based on the view that both environmental
temperature and pressure are stable and the air moves due to difference
in wind pressure and temperature.
[FIGURE 1 OMITTED]
The influence of convection on stationary heat transmission through
the wall having small ventilated and non-ventilated air gaps was
calculated using the above mentioned software (Fig. 1). The made
calculations used the heat conductivity coefficient of the
thermal-insulating layer is [lambda] =0.036 W/(m x K), thickness d =
0.15 m, height h = 2.2 m and the thickness of a small air gap b = 3; 5;
10 and 15 mm. The calculation results, regarding the effect of
convection in all cases indicated in Table 1, are presented in Fig. 2.
The achieved results have disclosed that the effect of natural
convection on heat transfer through the thermal-insulating layer mostly
depends on the thickness of a small air gap and difference in
temperature but rather insignificantly on the tightness of the gap. In
case of forced convection, the formation of any small gap increases
general heat transfer through the wall from two to thirteen times.
Therefore, heat transfer in the case of forced convection was not
further investigated. However, the dependence of heat transfer through
the construction on the thickness of the air gap and difference in
temperature was specified. The results are presented in Fig. 3.
The analysis of the results of numerical modelling (Fig. 3) shows
that the influence of natural convection on general heat transfer is
insignificant when a joining small air gap up to 3.0 mm thickness occurs
around the thermal-insulating layer. In larger (b >3.0 mm) air gaps,
the effect of natural convection on general heat transfer increases. It
may be explained by the interruption of natural air movement in narrow
air gaps caused by hydraulic friction. The data given in Fig. 3
demonstrate difference in the significant 35% Nu criterion value in the
cases of non-ventilated and ventilated constructions.
[FIGURE 2 OMITTED]
As mentioned above, the performed investigation determined rather
frequent cases when air gaps and cavities occurred between
thermal-insulating products mounted in the wall constructions of the
building as well as between those products and their limiting surfaces
in the exploited buildings.
The places of the above mentioned gaps in walls depend on numerous
factors: the properties of the wall material, mounting technology, etc.
Since, because of convection, heat transfer through the wall with small
air gaps is markedly greater than heat transfer through monolithic
walls, it must be estimated in the calculations of thermal resistance
and heat transfer coefficients. Furthermore, several calculation results
regarding the thermal properties of the thermal-insulating layer with
small air gaps ([lambda] = 0.036 W/(m x K); d = 0.15 m; h = 2.2 m; b
=5.0 mm) in various places of walls (Fig. 4) are presented in Fig. 5.
The achieved functional dependence of the values of Nusselt
criterion on difference in temperature is presented in Fig. 5. The
figure shows that, when the small air gap is on the cold part of thermal
insulation, the effect of natural convection is insignificant.
[FIGURE 3 OMITTED]
However, heat transfer through the construction increases markedly
when the air gap is situated between thermal insulation and the warm
side of the construction as well as when the construction is ventilated.
Because of convection, heat transmission through the above mentioned
construction increases 1.5 times when difference in temperature is
20[degrees]C, and 2 times when it reaches 40[degrees]C.
2.1.2. Investigation into walls insulated with air permeable
thermal insulating slabs
Experimental analysis was carried out in order to determine the
reliability of numerical modelling. Theoretically calculated values of
the Nusselt criterion of constructions with natural convection in the
small air gaps of the wall were compared with the results of
experimental analysis. Special equipment was created for experimental
analysis according to the requirements of international standards ISO
8301 and ISO 8990. The height of constructions tested in this equipment
was 2100 mm, width--1100 mm and thickness--150 mm. The values of
temperature and heat flow density in the sample were measured under
stationary environmental conditions when the indoor temperature in
equipment was [[theta].sub.i] = +20[degrees]C, and the temperature of
climatic chamber [[theta].sub.e] = 0[degrees]C and [[theta].sub.e] =
-10[degrees]C. The measurement was carried out both in the horizontal
position of equipment with closed ventilated orifices (basic measuring)
and in the vertical position with closed and opened ventilation
orifices. The total area of fully opened ventilated orifices in bottom
and top parts covered 15000 [mm.sup.2]/m. For experimental analysis, the
thermal conductivity of polystyrene foam slabs of 50 mm thickness was
0.036 W/(m K). It should be emphasized that polystyrene foam slabs are,
in fact, air impermeable, and therefore the influence of small air gaps
between slabs and other layers determined that small air gaps up to 5 mm
thickness were formed between slabs that appeared practically impossible
to be avoided during mounting. That is why the wall model having 5 mm
air gaps between thermal-insulating slabs had been chosen. Fig. 6
presents a scheme of the construction mounted in equipment (3 layers of
slabs and 4 small air gaps).
[FIGURE 4 OMITTED]
[FIGURE 5 OMITTED]
Considering all types of measuring both cold and warm sides of
equipment, the vertical temperature gradient of approximately
0.1-0.2[degrees]C/m was formed. Thus, the temperatures of external
surfaces were different throughout the whole height. When calculating
the Nusselt criterion values of the whole construction, the unevenness
of the above mentioned temperature found in the places of heat flow
density measurement was estimated by the equation:
[MATHEMATICAL EXPRESSION NOT REPRODUCIBLE IN ASCII], (1)
where: n--the number of heat flow density measuring sensors;
[q.sub.cv]--density of heat flow rate transmitted by convection,
W/[m.sup.2]; [q.sub.cd]--density of heat flow transmitted by
conductivity, W/[m.sup.2].
Fig. 7 presents air temperature in the gaps where the construction
is vertical, ventilation orifices are closed and the construction is not
ventilated.
[FIGURE 6 OMITTED]
[FIGURE 7 OMITTED]
Natural convection in the climatic chamber started at the
temperature of [[theta].sub.e] = 0[degrees]C, and therefore temperature
curves were distorted in comparison with the basic measurement.
Temperature in the top part of the air gaps of the construction
increased by 3/5[degrees]C and in the bottom part decreased by 3/5
[degrees]C. Temperature in the construction where height varied from 0.6
m to 1.4 m remained unchanged.
When ventilation orifices were opened,, external air entered the
construction through its lower part and went out through its upper part
because of natural convection. In this case, temperature in the air gaps
of the lower part of the construction decreased by approximately
10[degrees]C, whereas in the upper part it remained unchanged as it was
in the closed construction.
Other experiments on the ventilated construction at difference in
temperature 30[degrees]C (Fig. 8) were also carried out. When ventilated
orifices were opened (A = 15000 [mm.sup.2]/m), different results were
achieved: the temperature of the air gap closest to the warm surface
decreased up to + 12[degrees]C and the temperature of other air gaps in
the lower part of the construction decreased below 0[degrees]C.
[FIGURE 8 OMITTED]
Both numerical modelling and experimental results revealed that
along with changes in the thickness of the non-ventilated air gap from 0
to 15 mm, heat transfer through the construction increased up to 8
times. A nearly analogous situation can be observed with regard to the
change of thermal resistance under the ventilated air gap. In the
opposite case, when the air in the wall cannot "wash" the
thermal-insulating layer, i.e. air gaps that are both in the cold and
warm sides of thermal insulation do not join, total convective heat
transfer will not increase.
2.2. Investigation into the effect of convection on heat transfer
through building walls insulated with air permeable thermal-insulating
slabs
The further development of the paper analyses the effect of natural
and forced convections on general heat transfer through ventilated
building walls and junctions of walls (wall--wall and wall--attic)
thermally insulated with air permeable mineral wool. The
thermal-technical properties of these materials are presented in Table
2.
Table 2 presents the values of the resultant air permeability of
mineral wool. These values are expressed by the following formula:
[l.sub.re] = 4 x [l.sub.[perpendicular to]] x [l.sub.II]/[([square
root of [l.sub.[perpendicular to]] + [square root of [l.sub.II]).sup.2],
(2)
where: [l.sub.[perpendicular to]], [l.sub.II]--air permeability of
the porous medium, perpendicular and parallel to heat transfer
direction, [m.sup.2].
Different materials were used as wind protecting layers the air
permeability and thermal resistance of which are presented in Table 3.
For conducting experiments, sheet materials were preferred, since they
were stiff and attached close to the thermal-insulating layer.
At the first stage of experimentation, when modelling heat transfer
regarding conductivity only, the values of heat flow density in the
construction as well as the temperatures of layers were calculated with
the help of numerical modelling software DAVID-32 (Table 4).
Calculations were made considering 34 thermal-insulating and wind
protecting layer combinations. The received values were used as the
initial data when calculating the values of the Nu criterion, i.e. an
increase in heat transfer because of the effect of convection and air
filtration.
Further, the values of wall heat flow density as well as the
temperatures of the layers were measured at natural and forced
convection. Ventilation orifices covering the area of A=40 000
[mm.sup.2]/m were opened both in the upper and lower parts of each wall
fragment. At this stage, the air in the wall moved only because of
natural convection. Later, applying a ventilator, the air pressure
gradient of 3.0 Pa/m was formed in the air gap.
Fig. 9 presents the most typical temperature and heat flow density
curves found when analysing a sample of non-wind-protected stone wool
(p=22.3 kg/[m.sup.3]) in both natural and forced convection.
The values of the Nusselt criterion were determined following
experiments on various thermal-insulating and wind protecting
combinations. The summary results of the made calculations are presented
in Figs 10 and 11.
The test results (Fig. 10) show that, because of natural
convection, when mineral wool thermal-insulating layers are not
protected against wind, heat transfer through the walls may increase up
to 15%.
[FIGURE 9 OMITTED]
The effect of convection on heat transfer increases under a lower
density (also at higher air permeability) of the thermal-insulating
material and higher thickness of the thermal-insulating layer. When the
air pressure gradient in the wall air gap reached 3.0 Pa, the opposite
results were achieved: heat transfer was more intensive in thinner (100
mm) layers and increased up to 25%. The test results presented in Fig.
10 show that, because of convection, heat transfer increased by
approximately 5-7% when the mineral wool slabs of higher density were
used for wall insulation. In the case of materials having low air
permeability, convection took place in the air gaps between slabs and
between slabs and the wall or carcass elements, which, actually,
increased heat transfer. The results achieved during the performed
experiments (Fig. 10) indicate that under natural convection, heat
transfer through the walls the thermal-insulating layer of which is made
of mineral wool slabs (l < 70.0 x [10.sup.-6] [m.sup.3]/(m x s x Pa))
without the wind-protecting layer will not be higher than 5-7%.
Therefore, in constructions with no forced air movement (i.e. when the
equivalent orifice area in the ventilated air gap does not exceed 3000
m[m.sup.2]/m), less permeable and denser materials with no wind
protecting should be used for thermal-insulating layers.
[FIGURE 10 OMITTED]
[FIGURE 11 OMITTED]
The results of investigation into heat transfer through the walls
of various constructional solutions (Fig. 11) show that heat transfer in
the walls does not significantly depend on the air permeability of wind
protection when the air permeability of sheet wind protection varies
from 23.2 x [10.sup.-6] to 1126 x [10.sup.-6] [m.sup.3]/ ([m.sup.2]x s x
Pa). Heat transfer through walls increases when rolling membrane
materials are used for wind protection. These materials unevenly
attaches to the layer of the thermal-insulating material, and thus
additional air gaps are formed thus increasing the heat transfer through
the wall.
3. Conclusions
The results of investigation into air pressure put in the air gaps
of building walls show big differences in air pressure formed
exclusively in the air gaps of intensively ventilated walls (area of
ventilated orifices A >40 000 [mm.sup.2]/m). The influence of wind
velocity on air movement in the air gaps of enclosures is insignificant
when the area of ventilated orifices is smaller than 3000 [mm.sup.2]/m.
The pressure gradient in the ventilated air gaps of small buildings with
the area of ventilated orifices from 3000 to 40 000 [mm.sup.2]/m does
not depend on wind speed and makes 2-3 Pa/m.
The results of numerical modelling show that the influence of
natural convection on general heat transfer is insignificant when air
gaps around the thermal-insulating layer are up to 3.0 mm thickness.
The results of investigation into heat transfer through the walls
of various constructional solutions disclose that heat transfer in the
walls does not significantly depend on the air permeability of wind
protective slabs when air permeance varies from 23.2 x [10.sup.-6] to
1126 x [10.sup.-6][m.sup.3]/([m.sup.2] x s x Pa).
Wind protective slabs to be applied to the mineral wool insulation
of intensively ventilated (A > 40 000 [mm.sup.2]/m) walls must have
the air permeance value lower than 50.0 x [10.sup.-6]
[m.sup.3]/([m.sup.2]-s -Pa). Air impermeable layers should be arranged
in thermal-insulating layers in order to stop internal air filtration.
doi: 10.3846/13923730.2013.775182
References
Abid, A. F. 2012. Natural convection heat transfer enhancement in
air filled rectangular enclosures with portirions, Al-Qadisiya Journal
for Engineering Sciences 5(2): 191-208.
Alam, P.; Kumar, A.; Kapoor, S.; Ansari, S. R. 2012. Numerical
investigation of natural convection in a rectangular enclosure due to
partial heating and cooling at vertical walls, Communications in
Nonlinear Science and Numerical Simulation 17(6): 2403-2414.
http://dx.doi.org/10.1016/j.cnsns.2011.09.004
Altac, Z.; Kurtul, O. 2007. Natural convection in tilted
rectangular enclosures with a vertically situated hot plate inside,
Applied Thermal Engineering 27(11-12): 1832-1840.
http://dx.doi.org/10.1016Zj.appltherma leng.2007.01.006
Bankvall, C. G. 1992. Thermal insulation and research in heat
transfer, in A. Elmorth, L. E. Nevander (Eds.). Research and development
in building physics during the last 25 years: symposium to celebrate
Professor Lars
Erik Nevander's, 70 years birthday, Stockholm: Swedish Council
for Building Research, 29-35. Directive 2010I31IEC of the European
Parliament and of the Council of19 May 2010 on the energy performance of
buildings (recast), Brussels [cited 26 June 2012]. Available from
Internet: http://eur-lex.europa.eu/ LexUriServ/ LexUriServ.do?uri =
OJ:L:2010:153:0013: 0035:EN:PDF.
Cherif, Y.; Joulin, A.; Zalewski, L.; Lassue, S. 2009. Superficial
heat transfer by forced convection and radiation in a horizontal
channel, International Journal of Thermal Sciences 48(9): 1696-1706.
http://dx.doi.org/10.1016/j.ijthermalsci.2009.01.017
Hagentoft, C. E. 1993. Thermal effects due to air flows in cracks,
in Building Physics in the Nordic Countries (Building Physics
'93),13-15 September, 1993, Copenhagen, Denmark, 1: 153-160.
Kohonen, R.; Ojanen, T. 1989. Coupled diffusion and convection heat
and mass transfer in building structures, in Research Reports. Technical
research centre of Finland, 247-251.
Kokko, E.; Ojanen, T.; Salonvaara, M. 1997. New building envelope
structures. Espoo: Research reports No. 1869. Technical research centre
of Finland. 90 p.
Lakompte, J. 1990. The influence of natural convection on the
thermal quality of insulated cavity construction, Building Research and
Practice 6: 345-354.
Liu, D.; Zhao, F.-Y.; Wang, H.-Q. 2011. Passive heat and moisture
removal from a natural vented enclosure with a massive wall, Energy
36(5): 2867-2882. http://dx.doi.org/10.1016/j.energy.2011.02.029
Nield, D. A.; Bejan, A. 2006. Convection in porous media. 3rd ed.
Berlin: Springer. 640 p.
Ojanen, T.; Kohonen, R. 1995. Hygrothermal performance analysis of
wind barrier structures, in ASHRAE/DOE/ BTECC Conference on Thermal
Performance of the Exterior Envelopes of Buildings IVJ4-7 December,
1989, Orlando, Florida, 234-249.
Ojanen, T. 1993. Criteria for hygrothermal performance of wind
barriers structures, in Building Physics in the Nordic Countries
(Building Physics'93),13-15 September, 1993, Copenhagen, Denmark,
2: 643-652.
Ridouane, E. H.; Hasnaoui, M.; Amahmid, A.; Raji, A. 2004.
Interaction between natural convection and surface radiation in a square
cavity heated from below, Numerical Heat Transfer, Part A: Applications:
An International Journal of Computation and Methodology 45(3): 289-311.
Roots, P. 1997. Heat transfer though a well insulated external
wooden frame wall. PhD thesis. Lund University, Lund, Sweden. 173 p.
Samajauskas, R.; Stankevicius, V.; Bliudzius, R. 2003. The effect
of convection on heat transfer through the ventilated building
partitions. Monograph. Kaunas: Technologija. 166 p.
Sadauskiene, J.; Buska, A.; Burlingis, A.; Bliudzius, R.; Gailius,
A. 2009. The effect of vertical air gaps to thermal transmittance
ofhorizontal thermal insulating layer, Journal of Civil Engineering and
Management 15(3): 309-315.
http://dx.doi.org/10.3846/1392-3730.2009.15.309-315
Tiwari, A. K.; Singh, A. K.; Chandran, P.; Sacheti, N. C. 2012.
Natural convection in a cavity with a sloping upper surface filled with
an anisotropic porous material, Acta Mechanica 223(1): 95-108.
http://dx.doi.org/10.1007/s00707-011-0544-5
Vytautas Stankevicius (1), Valdas Paukstys (2), Raimondas Bliudzius
(3), Jolanta Sadauskiene (4), Zenonas Turskis (5), Rolandas Samajauskas
(6)
(1,2,3,4) Building Physics Laboratory Institute of Architecture and
Construction of Kaunas University of Technology, Tunelio g. 60, LT-3035,
Kaunas, Lithuania
(5) Faculty of Civil Engineering, Vilnius Gediminas Technical
University, Sauletekio al. 11, LT-10223 Vilnius, Lithuania
(6) IE "PSB", Europos av. 121, LT-46339, Kaunas,
Lithuania
E-mails: (1)
[email protected]; (2)
[email protected]
(corresponding author); (3)
[email protected]; (4)
[email protected]; (5)
[email protected]; (6)
[email protected]
Received 26 Nov. 2012; accepted 15 Jan. 2013
Vytautas STANKEVICIUS. Prof. Dr Habil, the author of more than 230
papers and 4 patents. Research interests: physical properties of
building materials, physical-technical processes in building envelopes,
energy saving in buildings, weather durability of the external finish of
building walls.
Valdas PAUKSTYS. Assoc. Prof. Dr, researcher at the Laboratory of
Thermal Building Physics at the Institute of Architecture and
Construction, Kaunas University of Technology (KTU). Research interests:
the moisture state of building constructions, physical-technical
processes in building envelopes, heat loss in buildings.
Raimondas BLIUDZIUS. Prof. Dr, chief researcher at the Laboratory
of Thermal Building Physics at the Institute of Architecture and
Construction, KTU. Research interests: heat transfer, technical
properties of thermal insulations products.
Jolanta SADAUSKIENE. Assoc. Prof. Dr, researcher at the Laboratory
of Thermal Building Physics at the Institute of Architecture and
Construction, KTU. Research interests: the moisture state of building
constructions, physicaltechnical processes in building envelopes, heat
loss in buildings.
Zenonas TURSKIS. Prof. Dr of Technical Sciences, a senior research
fellow at the Laboratory of Construction Technology and Management,
Vilnius Gediminas Technical University. Research interests: building
technology and
management, decision-making theory, computer-aided automation in
design, expert systems.
Rolandas SAMAJAUSKAS. Dr of Technical Sciences, Expert, IE
'PSB'. Research interests: heat transfer, technical properties
of thermal insulations products.
Table 1. Data for modelling the influence of convection on
heat transmission
Air gap Closed Open
Convection Natural Natural Natural and forced
(grad P = 3 Pa/m)
Thickness b, mm 3; 5; 10; 15
[DELTA][[theta], [degrees]C 10; 20; 30; 40
Table 2. Thermal-technical properties of thermal-insulating materials
Thermal conductivity
[[lambda].sub.10], W/(m x K)
Mineral Mark Density [rho], [[lambda].sub. [[lambda].sub.
wool kg/[m.sup.3] [perpendicular to]] [parallel]]
Rock wool MV-4 22.3 0.0375 0.0430
Glass wool MV-5 19.2 0.0358 0.0379
Rock wool MV-6 32.7 0.0345 0.0380
Rock wool MV-7 38.1 0.0344 0.0378
Rock wool MV-8 57.6 0.0337 0.0376
Air permeability l,
Mineral wool [m.sup.3]/(m x s x Pa)
[l.sub.re]
Rock wool 251.0 x [10.sup.-6]
Glass wool 152.0 x [10.sup.-6]
Rock wool 125.0 x [10.sup.-6]
Rock wool 110.0 x [10.sup.-6]
Rock wool 70.9 x [10.sup.-6]
Table 3. Thermal-technical properties of wind protecting products
Product Mark d, mm Air permeance Thermal
K, [m.sup.3]/ resistance
([m.sup.2] R, ([m.sup.2]
x s x Pa) x K)/W
Glass fibre VI-1 0.6 17024 x [10.sup.-6] --
LDPE ** VI-2 0.2 -- --
HDPE * VI-3 0.15 2.45 x [10.sup.-6] --
Wood fibre board VI-4 12.0 23.2 x [10.sup.-6] 0.075
Glass wool board VI-5 13.0 46.4 x [10.sup.-6] 0.406
Rock wool board VI-6 30.0 633 x [10.sup.-6] 0.938
Rock wool board VI-7 30.0 1126 x [10.sup.-6] 0.882
* Water vapour permeable polyethylene pellicle of light density;
** The low density of the polyethylene pellicle impermeable to air and
water vapour. This product cannot be used for protecting mineral wool
layers against the impact of the wind. However, it was included in the
experiment as a rolling product absolutely non-conductive to the air.
Table 4. The calculated average heat flow density values of the non-
ventilated wall under air temperatures [[theta].sub.e] =
-10.0[degrees]C, [[theta].sub.1] = +22.0[degrees]C and [DELTA][theta]
= 32.0[degrees]C
Calculated average heat flow density values q, W/
[m.sup.2], when a cold surface of mineral wool is
covered with wind protection product:
Sample d, mm VI-1; VI-2; VI-3 VI-4 VI-5 VI-6 VI-7
MV-4 100 10.24 10.00 9.06 -- --
150 7.18 7.06 6.58 -- --
MV-5 100 9.84 9.62 8.75 -- --
150 6.88 6.78 6.33 -- --
MV-6 100 9.53 9.32 8.50 7.45 7.55
150 6.66 6.56 6.14 5.57 5.63
MV-7 100 9.51 9.30 8.49 7.44 7.53
150 6.64 6.54 6.12 5.56 5.61
V-8 100 9.34 9.14 8.35 -- --
150 6.52 6.42 6.02 -- --
