Note: Descriptions are shown in the official language in which they were submitted.
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HEAT-INSULATED COMPOSITE PROFILED SECTION
The invention relates to a heat-insulated composite profiled
section especially intended for windows, doors, façade walls
etc , consisting of outer and inner metal profiles connected
and spaced apart from each other via at least one insulating
web with connector profiles. The connector profiles engage in
grooves in the metal profiles and the insulating web has two
essentially parallel boundary walls forming a cavity between
them, and permitting transverse webs to be positioned between
lo them, thus dividing the cavity within the insulating web into
several hollow chambers positioned successively between the
metal profiles
Heat-insulated composite profiled sections of thi,s type are
known, for example, from DE 42 38 750, in which the insulating
web or webs ensure the thermal separation of the outer and
inner metal profiles.
Care must be taken when deciding on the dimensions of the
insulating webs to ensure that heat can be transferred from
the warmer to the colder metal profile in three different
ways, i.e. conduction, radiation or convection. All of these
three transfer mechanisms usually operate at the same time.
In the case of conduction thermal energy is conveyed directly
between immediately neighbouring portions of stable bodies or
immobile liquids or gases. The quantity of heat conducted in
the present case is determined by the proportion of heat
flowing both over the boundary walls and over the still air
inside the cavity or the hollow chambers and inside the
airspace adjoining the insulating web on the outside. The
proportion of heat flowing over the insulating web is
influenced essentially by the thickness and the width of the
boundary walls and the thermal conductivity of the material.
However, the mechanical magnitudes (stability, thickness,
thickness of the walls, width) also determine the mechanical
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properties of the insulating web which forms a statically
load-bearing spacer. Consequently, there are as a rule for
static reasons limits (wall thickness, width) to further
reduction of conductivity.
In the case of radiation no transfer medium is required and
therefore the dimensions of the insulating web do not matter
unless allowance has to be made for shadow, reflections or
similar influences on the radiation through the insulating
web.
In the case of convection thermal energy is conveyed to flows
of liquids, gases or vapours by conduction or in some cases by
radiation and convected by the flow. Since the heat conductor
loses thickness when it receives thermal energy and becomes
buoyant in consequence the heat transfer itself causes a flow
of heat which is termed free convection.
It has been shown that the shape of the insulating web has
considerable influence on the proportion of heat convected,
and therefore the purpose of the present invention is to
improve the design of the insulating web in composite profiled
sections of the type referred to above in such a way that the
convection, and therefore the proportion of heat convected, is
restricted to such a value that the heat transfer which it
determines is of the same magnitude as simple thermal
conduction in still air while at the same time and in parallel
the radiation exchange (heat transfer by long-wave infrared
radiation) is reduced. This should achieve a heat loss
reduction of about 30~ as compared with the existing state of
the technology.
The purpose of the invention is achieved as follows:
- starting from a wall thickness s=0.5 mm and a thermal
conductivity lambda = 0.35 W/mK in the boundary walls - the
width (D) of the insulating web measured along the space
between the metal profiles is set at 20 mm to provide a
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thermal insulance in the insulating web of 0.15 m[2]K/W to
0.30 m[2]K/W, at 30 mm to provide a thermal insulance of
0.25 m[2]K/W to 0.50 m[2]K/W, at 40 mm to provide a thermal
insulance of 0.35 m[2]K/W to 0 65 m[2]K/W, and at 50 mm to
5 provide a thermal insulance of 0.40 m[2]K/W to 0.80 m[2]K/W,
the width (d) of the cavity or the hollow chambers similarly
measured along the distance between the metal profiles being
less than or equal to the width (D) of the insulating web and
greater than or equal to one third of the width (D) of the
insulating web provided that the height of the cavity or the
hollow chambers is smaller than or equal to 5 mm. If the
height of the cavity or khe hollow chamber is more than 5 mm
and does not exceed 20 mm and at least one transverse web is
present the proportion of height (h) to width (d) of the
hollow chamber is greater than or equal to 0.2 and less than
or equal to 5, and the wall thickness (s) is between 0.25 mm
and 1.0 mm, where the dependence of the thermal insulance on
the wall thickness (s) is given by the equation
R(s)=R(s=0, 25 mm) + (s - 0.25)/0.25 * delta R
with values for delta R ranging from 0.025 to 0.05, and where
a 10~ increase in the thermal conductivity of the boundary
walls ranging from 0.15 W/mK to 0.40 W/mK produces a 2~ to 4
reduction in thermal insulance. Intermediate values in the
equation between the interval of the thermal insulance and the
width (D) of the insulation web can be interpolated linearly.
Conditions will be still more favourable if, with the height
of the cavity or hollow chamber measuring over 5 mm and not
more than 20 mm and with at least one transverse web present,
the ratio of the height (h) to the width (d) is greater than
or equal to 0.5 and is l,ess than or equal to 2.
The basic purpose of the invention can be achieved in a
comparable manner if, given that the insulating web has a
height (H) and a width (D) measured along the space between
the metal profiles which determined by static or
constructional considerations and that the wall thickness is
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(s) and that the thermal conductivity of the boundary walls is
lambda, the aspect ratio o~ the height (h) to the width (d) in
the cavity or hollow chamber measured along the space between
the metal profiles is selected so that the thermal insulance R
calculated by the equation
R=2.08*(D/100)[1.43]-O.l+P*f(lambda)*f(s)*f(h/d) and
P=a]O[+a]l[*H+a]2[*H[2]+a]3[*H[3]+a]4*[*H~4]
lies within the range o~ a maximum, the coefficients being
a]0[=-0.06898+5.19*10[4]*D[-4.171],
a]1[=+0.2005-21.86*D[-1.531],
a]2[=+0.0425-0.00174*D for D<30 and a]2[=~0.0292-0.0013*D
for D>=30,
a]3[=-1.384*10[-3]+8.125*10[-7]*D[2.268],
a]4[=+4.632*10[-5]-3.528*10[-7]*D[1.47] and the correcting
functions being f(lambda)=1.27-0.807*1ambda[1.04],
~(s)=1.324-0.458*s[0.5] and f(h/d)=(1-0.015*((h/d)-2.5)[2].
In particular, the aspect ratio of the vertical height (h) to
the horizontal width (d) o~ the cavity or the hollow chambers
can be such that, allowing for the expected temperatures on
the outer and inner metal profiles, the square of this aspect
ratio multiplied by the Rayleigh number (Rah) is less than the
numerical value 72.
The dimensionless Rayleigh number (Rah) is the product of the
Grashof number and the Prandtl number which characterizes
solely the properties o~ the ~luid in the enclosed cavity;
for air it can be assumed that this number is Pr=0.71.
The magnitude of the Grashof number is a measure o~ the heat
trans~erred by convection from the warm to the cold side of
the cavity or hollow chambers. If the geometry of the
insulating web, that is to say, the aspect ratio h/d o~ the
cavity or the hollow chambers is so selected with allowance
for the expected temperatures that the product of the square
of the aspect ratio and the Rayleigh number remains less than
the numerical value 72 this will ensure that the convection in
the cavity or the hollow chambers is sufficiently limited for
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the heat transfer to be of the same magnitude as in the case
o~ pure heat conduction ~in still air.
In a preferred embodiment of the invention the number of
hollow chambers can be determined by the width and height o~
the insulating web and the specified aspect ratio.
It has in addition been ~ound advantageous for the thickness
of each of the two boundary walls to be in the range 0.4 mm to
1.0 mm.
A preferred embodiment of the invention is characterized by
the ~act that the insulating web has three hollow chambers and
the geometric ratio for the external contour of the insulating
strip (width D and height H) lies within the interval
1.3*D - 0.022*D2 < H < 4.14*D -0.088*D2.
For the purposes of this invention it has also been found
bene~icial i~ the heat conductivity L of the boundary walls is
between 0.17 and 0.35 W/(mK). It is also recommended that the
selected width of the boundary walls which determines the
spacing between the metal pro~iles should be made dependent on
the wall thickness in such a way that the specific heat flow
qO, that is the heat ~low through a strip 1 meter long with
delta T = 1 K, which ~lows over the boundary walls, is always
less than 0.02 W.
The advantages thus obtained are essentially as follows: an
insulating web designed in accordance with the indicated
criteria will permit both optimum thermal insulation and a
satisfactory adjustment of the achievable stability of the
insulating webs. These dimensions are also based on the
finding that the materials to be used for the insulating webs,
especially PVC, polypropylene and polyamide, have in that
order an increasing thermal conductivity. In order to
increase the mechanical stability o~ these materials
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aggregates are frequently incorporated into them which do
increase stability but also increase conductivity.
If the width selected for the boundary walls is small the load
on the insulating web will be small but at the same time the
thermal conduction will increase because o~ the short distance
between the two metal profiles. On the other hand the smaller
load makes it possible to work with smaller quantities of
aggregate and this will in turn reduce the thermal
conductivity.
The combination of parameters proposed in accordance with the
invention marks out the limits within which both optimum
thermal insulation and the required stability of the
insulation web are achieved. Even if the width of the
boundary walls is increased the resultant lessening of the
heat flow will because of the gain achieved be more than
compensated by the dimensions required for the hollow chambers
enclosing the air.
It is also proposed in connection with this invention that in
selecting the thickness of the boundary walls and/or the
thermal conductivity of the boundary walls these magnitudes be
small enough within the specified interval for the width of
the boundary walls to lie within the range 20-50 mm.
In addition, it has been ~ound advantageous in connection with
the invention for the clearance of the boundary walls to lie
within the range 1-15 mm. It is however especially beneficial
for the clearance of the boundary walls to lie within the
range 5-10 mm.
It is useful to align the transverse insulating web or webs at
right angles to the boundary walls and to secure them firmly
to the latter. It is however also possible in principle for
the angle between the transverse web and the boundary walls to
lie within the range 75-105 degrees.
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In addition, ~or the purpose of optimizing- the parameters it
has been found advantageous for the thickness of the two
boundary walls to lie within the range 0 5-0.8 mm.
Lastly, a design of the invention with an additional advantage
is characterized by the fact that the connector profiles are
positioned symmetrically (axially) with respect to the
insulation web.
The invention is explained in detail below with reference to
the examples of embodiments shown in the drawings, as follows:
~0 Fig. 1 a single insulation web showing schematically how it
is used to find the basic dimensions,
Fig. 2 a composite profiled section shown in cross-section,
Fig. 3 another embodiment shown as in Fig. 2.
Fig. 1 shows in outline, for the heat-insulated composite
pro~iled section intended especially ~or windows, doors,
façade walls etc., the outer and inner metal profile 3, 4 and
the insulation web 6 with a connector profile 5 Oll each of its
two sides, connecting and spacing apart the two metal
profiles 3, 4.
The insulation web 6 has two essentially parallel boundary
walls 6.1, 6.2 forming a cavity between them, with transverse
webs 10 positioned transversely to the boundary walls 6.1, 6.2
and dividing the cavity within the insulation web 6 into
several hollow chambers positioned successively along the
length of the insulation web 6.
The heat transfer is calculated by appropriate procedures
which take account of the transfer mechanisms referred to in
the introduction. If the aspect ratio of the vertical height
(h) to the horizontal width (b) of the cavity or the hollow
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chambers is varied it will be found that the proportion of the
passage of heat from the warmer to the colder metal profile,
attributable to convection in the hollow chambers 11, can be
reduced by an appropriate choice of aspect ratio to the point
where its proportion is insignificant in relation to the heat
conduction and heat radiation.
If the thermal insulance;for different widths of the
insulating web 6 is plotted against the height of the
insulating web a range appears in which the thermal insulance
has a maximum. This shows that if allowance is made ~or the
expected temperatures on the outer and inner metal profiles 3,
4 and a suitable aspect ratio is selected for the hollow
chambers the thermal insulation can be improved.
Moreover, by plotting the dependence of the thermal insulance
on the height of the insulation web ~or di~erent wall
thicknesses a maximum will be found for a given range of
values. Because of the changes in thermal conduction the
variation in the wall thickness will result as expected in a
change in total heat resistance; here too, however, the
influence of the proportion of convection can be detected.
This can be used to determine the dimensiGns of the insulating
web in the following manner:
starting from a wall thickness s=0.5 mm and a conductivity
lambda = 0.35 W/mK in the boundary walls 6.1, 6.2 the width
(D) of the insulating web is set at 20 mm to provide a thermal
insulance in the insulating web of 0.15 m2K/W to 0.30 m2K/W, at
30 mm to provide a thermal insulance of 0.25 m2K/W to 0.50
m2K/W, at 40 mm to provide a thermal insulance of 0.35 m2K/W to
0.65 m2K/W, and at 50 mm to provide a thermal insulance of 0.40
m2K/W to 0.80 m2K/W. The selected width (d) of the cavity or
the hollow chambers then becomes less than or equal to the
width (D) of the insulating web and greater than or equal to
one third o~ the width (D) of the insulating web provided that
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the height of the cavity or the hollow chambers 11 is smaller
than or equal to 5 mm. If the height of the cavity or the
hollow chambers is more than 5 mm and does not exceed 20 mm
and at least one transverse web 10 is present the selected
ratio of height (h) to width (d) is greater than or equal'to
0.2 and less than or equal to 5. If the wall thickness (s) is
varied,between 0.25 mm and 1.0 mm, allowan,ce must be made for
a dependence o~ the thermal insulance on the wall thickness
(s) as given by the equation
R(s)=R(s=0, 25 mm) + (s - 0.25)/0.25 * delta R
with values ~or delta R ranging ~rom 0.025 to 0.05. A 10~
increase in the thermal ,conductivity of the boundary walls
(6.1, 6.2) ranging from 0.15 W/mK to 0.40 W/mK produces a 2
to 4~ reduction in thermal insulance, which must be allowed
for given the selected initial magnitudes referred to in the
introduction.
The procedure for determining the shape of the insulating web
can be continued in such a manner that the number of hollow
chambers 11 depends on the width and height o~ the insulating
web and the specified aspect ratio.
If the insulating web has three hollow chambers 11 the
calculation of the aspect ratio is simpli~ied: The geometric
ratio ~or the outer contour of the insulating strip
(width D and height H) will then lie within the interval
1.3*D - 0.022*D2 < H c 4.14*D - 0.088*D2. For a different
number of hollow chambers 11 appropriate intervals can be
plotted.
In the examples of embodiments shown in Fi,gures 2 and 3 the
composite profiled section is used with a window of which,
however, only the lower cross-section of the wing profile and
the screen frame profile are shown.
Both the screen ~rame profile 1 and the wi,ng pro~ile 2 are
designed as heat-insulated composite profile sections and
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likewise consist of outer 3 and inner 4 metal profiles each
connected together via and spaced apart by insulating webs 6
provided with connector profiles 5. The connector pro~iles 5
are essentially dovetailed and engage precisely in grooves in
the metal profiles 3, 4.
The glass pane 7 itself is retained on the wing profile 2 over
glazed seals 8 by means of a glass strip 9.
The insulating webs 6 have two essentially parallel boundary
walls 6.1, 6.2 ~orming a cavity between them. The boundary
walls 6.1, 6.2 are connected together via a number of
transverse webs 10, the number of transverse webs 10 being
dependent on the limiting conditions explained above.
In the examples of embodiments shown in Figures 2 and 3 the
transverse web 10 is aligned at right angles to the boundary
walls 6.1, 6.2 and firmly attached to them. It is however
also possible to align such transverse webs 10 at an angle of
75-105 degrees to the boundary walls 6.1, 6.2, or even, i~
need be, at a still larger angle to them provided that this
does not significantly reduce the heat insulation.
The thickness of the boundary walls 6.1, 6.2 can lie in the
range 0.4-1 mm, the thicknesses o~ the two boundary walls 6.1,
6.2 being equal to each other. It has been found especially
advantageous ~or the thickness of the boundary walls 6.1, 6.2
to lie in the range 0.5-0.8 mm.
In selecting materials for the boundary walls 6.1, 6.2 it is
necessary to ensure a thermal conductivity L in the range
0.1-0.35 W/(mK). Care must be taken to see that the amount of
aggregates added to the material both increases its stability
and also its heat conductivity, and therefore a compromise
must be found within the interval proposed in accordance with
the invention and the thickness of the boundary walls 6.1, 6.2
which will however make it possible, given an appropriate
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width and thickness of the boundary walls 6.1, 6.2, for the
specific heat flow qO, i.e. the heat flow through a 1 m long
strip for which delta T = 1 K, flowing over the boundary walls
6.1, 6.2, remains less than 0.02 watts. As excessive width in
the boundary walls 6.1, 6.2 produces an increased load the
thickness selected for the boundary walls 6.1, 6.2 and/or the
selected thermal conductivity selected for them in the within
the specified interval must be small enough for the width of
the boundary walls 6.1, 6.2 to lie in the range 20-50 mm.
In the example of an embodiment shown in E'igure 2 the
connector profiles 5 are positioned symmetrically, i.e.
axially, to the insulating web 6. It is however possible to
position the connector pro~iles 5 asymmetrically to the
insulating web 6, especially when using insulating webs 6 with
boundary walls 6.1, 6.2 spaced comparatively far apart. An
example of this is shown in Figure 3, in which the two
insulating webs 6 in the screen frame profile 1 and the upper
insulating web in the wing profile 2 are designed in the
manner just described. It is also possibl.e in this case to
increase still further the distance o~ the boundary walls 6.2
of the insulating webs 6 in the screen fra.me profile 1 from
the boundary walls 6.1.
