Download Density of Thermal Insulating Materials Kg/m3 K

World Renewable Energy and Environment Conference
WREEC2006, Sebha University
Tripoli-Libya
Energy Conservation Through Thermally
Insulated Structures
Ayoub Abu-Dayyeh* •
*Engineer and Doctor of Philosophy •
President of the society of Energy Conservation and Environmental sustainability
P.O.Box: 830305 Amman 11183 Jordan •
E-mail: [email protected] •
Mobile no.: 00 962 79 5772533 •
•
1
Abstract: The purpose of this paper is to explicate its title through investigating the different
available thermal Insulating materials and the various techniques of application, as practiced in
Jordan, in particular, and as practiced in many parts of the world in general, which will satisfy
Jordanian standards in terms of heat transmittance and thermal comfort. A brief comparison
with international standards will shed some light on the stringent measures enforced in the
developed world and on our striving aspirations to keep pace.
The paper consists of four main parts, pseudoally divided. The first part will deal with the
mechanism of heat loss and heat gain in structures during summer and winter. It will also
explain the Time-Lag phenomenon which is vital for providing thermal comfort inside the
dwellings.
The second part will evaluate the damages induced by the temperature gradients on the
different elements of the structure, particularly next to exterior openings; The paper will also
demonstrate the damages induced by water condensation and fungus growth on the internal
surfaces of the structure and within its skeleton. A correlation between condensation and
thermal insulation will be established.
The third part of the paper will evaluate the different available thermal insulating materials and
the application techniques which will satisfy the needs for thermal insulation and thermal
comfort at the least cost possible. The criteria of an economical design shall be established.
As a conclusion, the paper infers answers to the following different criteria discussed
throughout the different parts of the paper. The main theme of questions can be summarized as
follows:
1) How energy conservation is possible due to thermal insulation?
2) The feasibility of investing in thermal Insulation?
3) Is Thermal Comfort and a healthy atmosphere possible inside the dwellings during all
seasons! What are the conditions necessary to sustain them?
4) What Environmental Impacts can exist due to thermally insulating buildings?
2
Introduction: The thermal properties of construction materials in buildings depend on
the thermal conductivity (k-value) of building materials as well as on its thicknesses. The
lower the K-value of a material is the better would be its resistance to heat movement in
all three modes of heat transfer: conduction, convection and radiation. Density of the
thermal material, its cell structure, the type of gas which is trapped within the cell
structure and the durability of the material's matrix are all important factors in controlling
its k-value.
Table1 illustrates different thermal insulating materials of different densities
with its equivalent k-value and its current prices in Jordan.
It must be stressed here that choosing the thermal insulating material is not pricecontrolled only, but depends on many other factors as well, such as: Fire resistance of
the thermal insulator, ability of material to work as a vapor barrier, moisture absorption
and adsorption, thickness, health hazards in handing the material, irritation caused
during handling, compressive strength, color, emissivity, effect of ultra violet light and
transportation on the structure of the cells and so forth.
Next illustration in figures 1 & 2 show the direction of heat flow through the
exterior members of the structure, both in summer conditions and in winter. The figures
also explicate the role of thermal insulation in resisting the heat flow and reducing the
intensity of heat losses in any directions, illustrating the differences in heat resistance
values when the direction of flow is opposite.
3
Concrete
Stone Cladding
Vertical
CrossSection
Through
exterior
walls
In
out
Thermal
Insulation
plastering
In
out
Section b
Section a
Heat Flow Direction in Summer
Figure 1
4
Vertical
CrossSection
Through
exterior
walls
Thermal Insulation
out
In out
In
Heat Flow Direction in Winter
Figure 2
5
‫ الجمعية العلمية الملكية‬- ‫ من دليل مواد العزل الحراري‬:Table (1)
Material
Density
K valve
W/m2.k
Cost US $/ m3
2005 (Author Judgment)
Aluminum
2800
200
Cast Iron
7000
40
Concrete
2300
1.75
Lime Stone
2200
1.53
Normal Glass
2500
1.05
Concrete Hollow Blocks
1200
0.77
Plastering
1570
0.53
Polystyrene (expanded)
15
0.040
90
Glass Wool
64
0.038
150
Polystyrene (expanded)
20
0.036
100
Polystyrene (extruded)
28-35
0.035
125
Rock Wool
50-100
0.035
90
Polystyrene (expanded)
25
0.034
110
Polyurethane (on site)
30
0.026
300
6
Design: The choice of type, thickness and density of the thermal insulating •
material is controlled by the designer's needs and by the criteria of design. The
Jordanian thermal insulation code published in 2002, specifies a minimum of
thermal transmittance value (U -value) of 1.8 W /m2.k for exterior walls
(Including exterior openings) and a value of 1 W/m2.k for roofs exposed to the
exterior atmosphere.
A traditional wall in Jordan is made out of an over whole thickness of 30
cm consisting primarily of plain concrete and stone cladding (3-5 cm thick)
with cement-sand plastering from the inside, almost 2 cm thick. We shall name
this traditional wall: Wall 1.
•
Recently, the construction industry has been using a similar sort of •
construction by introducing hollow blocks made of concrete, 10 cm thick, 40
cm in length and 20 cm in height. They are used as a replacement to formwork
from the inside, keeping the total thickness of the wall in the range of 30 cm.
The section consists of an extra 2 cm of cement-sand plastering from the inside
as. So, here we have assembled our second traditional wall which we will
name: Wall 2.
These two types may be called traditional walls in modern and contemporary •
Jordanian building industry of middle class upwards dwellings. Neither wall
satisfies the Jordanian code for thermal insulation as we shall see in the
coming detailed calculations.
7
• Definitions of symbols:
• K (Thermal Conductivity); R (Thermal Resistance) = d / k ; U (Thermal
Transmittance); e ( Emissivity ) ; d ( Thickness )
•
•
•
•
•
•
•
•
•
•
•
•
•
U – value calculations:
U = 1 ÷ R ; R = d ( Thickness ) ÷ K ( Thermal Conductivity )
Ri = 0.13 ; Ro = 0.04m2.k/W
For Wall 1
U1 = 1 ÷ (Ri + Ro + (0.05 ÷ 1.53) + (0.25 ÷ 1.72) + (0.02 ÷ 0.53)
= 1 ÷ 0.383
= 2.6 W/m2.k
For Wall 2
U2 = 1 ÷ (Ri + Ro + (0.05 ÷ 1.53) + (0.15 ÷ 1.75) + (0.10 ÷ 0.77) + (0.02 ÷ 0.53)
= 1 ÷ 0.46
= 2.19 W/m2.k
For Wall 3
U3 = 1 ÷ (Ri + Ro + (0.05 ÷ 1.53) + (0.15 ÷ 1.75) + (0.03 ÷ 0.035) + (0.10 ÷ 0.77)
+(0.02 ÷ 0.53)
•
= 1 ÷ 1.32
•
= 0.76 W/m2.k
8
• Energy Saving: If we add exterior opening effects on the over whole U-value
of the walls (Doors and Windows), which we assume they constitute 20 % of
the total exterior peripheral area, we can then calculate the saving attained in
energy and fuel consumption due to thermally insulating the exterior walls
only. The calculations follow:
• Assume that the average U-Value for exterior openings U-value (Windows &
Doors) = 4 W/m2.k
• The average U-value becomes:• 0.76 × 0.8 + 4 (0.2)
• = 1. 4 < 1.8
•
• This is okay for the existing Jordanian thermal Insulation code, but we are
striving to reduce this value by 50% which will still be dramatically higher
than the values recommended by many European standards.
• The average U-value for the traditional wall:
• 2.6 x 0.8 + 4 x 0.2
• = 2.88 W/m2.k
• Percentage saving = 2.88-1.4/2.88 = 51.3%
9
•
•
•
•
•
•
•
•
•
•
•
•
•
•
Fuel Saving: Assuming that the air exchange stays the same before and after applying the
new insulated section, and also assuming that the flat is loosing heat from four directions
only.
Where the roof is occupied by neighbors and heated. The area of the flat is 15 × 10 =150m2.
Where U1 & U3 represent Walls 1 & 3
Q saved = (U1-U3) x A x T (Ti-To)
Where U1=2.88, U3 = 0.76, A= 125m2, T = 20 K (Average temperature change)
The flat in question has a wall surface area of 125 m2.
Q = (2.88 – 1.4) × (125 m2) (20)
= 3700W = 3.7 Kj/second
= 3.7x3600 Kj/ hour
One liter of diesel = 7000 K.calory = 7000x4.2 Kj ( 1calory=4.2 joules)
Saving in diesel/hour = 3.7x3600/7000x4.2
= 0.45 lt./ hour
If we Assume that Amman needs 1300 Heating Hour Day and 700 cooling hour day, then
the total consumption is:
0.45x2000 = 900 lt. yearly
This means nearly 200 US$ Saving on fuel only by thermally insulating walls only, if we
add reduction in maintenance and spare parts and increasing the time life of the electromechanical system, this number is easily doubled. Therefore saving is up to 400$ yearly.
Remember that if improvement on the thermal properties of the roof is also administered,
the savings are far greater.
10
•
It must be noted here that air gaps do not have the ability to resist heat more
than 0.18 W /m. k, no matter how thick the gap is (provided the gap is
bounded by traditional construction materials, such as concrete). Actually the
wider the gap is the worse would be its resistance to heat transfer as
convection currents become more effective in wasting energy in winter (see
figure 3 for details).
• If we calculate U3, for wall 3 once again using an air gap 2cm wide, then the
U-value becomes as follows:
• U3 = 1 ÷ (Ri + Ro + (0.05 ÷ 1.53) + (0.15 ÷ 1.75) + (0.03 ÷ 0.035) + (0.10 ÷
0.77)+ 0.18 ( see figure 3, the value 0.18 is illustrated by arrows) +
(0.02/0.53)
• U3 = 1/1.46
•
= 0.67 W/m2.k
• It is clear now that not much change has been achieved through adding the
effect of the air gap, that is from 0.76 to 0.67W/m2.k. Whatever width the air
gap is, no more resistance to heat flow is attained. Actually the opposite
happens as the wider the gap becomes the lesser the resistance to heat flow
the air gap sustains.
11
7
0.6
R- value
Air gap trapped between
two layers of Aluminum foil
0.4
Air gap trapped between
two layers of construction
material (Concrete and Blocks)
0.2
0
0
R-value
=
0.18
2
4
6
8
Thickness of Air Gap
Figure 3
12
• One way the resistance of air gaps can be improved is by
introducing a reflective surface on at least one surface inside the
cavity. This is illustrated in more details in Figure 4.
•
In that case, R is increased from 0.22 (for roofs) to a value
reaching up to 1.00. This happens in summer where the heat flow
is from the upward direction towards downwards. This
improvement in thermal resistance is due to a trapped air cavity
up to 60 mm in width. This value is achieved by using a single
aluminum foil as a reflective membrane, provided that it is
exposed to the air gap in order to function effectively in reflecting
heat by radiation.
• This characteristic can also be achieved by introducing reflective
surfaces inside the cavity. The more polished the surface is the
better, the lower emissivity value means the lesser heat is emitted
from its surfaces.
• Where as in winter, while heat is moving from inside the dwelling
to the outside cooler temperature due to the high temperature and
high pressure, in most cases. The R value for a cavity is increased
from 0.15 to 0.30 only, regardless of the thickness of the cavity
(see figure 4)
13
BS 6993:PART1-1989
Thermal resistance -R-value (m 2. K / W)
1.2
Heat Flow Direction in Summer
Aluminum Foil
Cavity
1
Heat Flow Direction in Winter
0.8
Cavity with
with one
one
Cavity
aluminum surface
surface
aluminum
0.6
Cavity uncoated
0.4
0.2
0
0
10
20
30
40
Cavity thickness (mm)
Figure 4
50
60
14
•
•
•
•
Time lag and thermal comfort phenomena: we saw in figures 1 &2 the heat flow
direction, now we see in figure 5 how the heat wave enters through the exterior wall in
summer and how it is reduced according to the type of construction, building materials
used and the thicknesses applied. The lesser the decrement factor is the lesser the
variations in temperatures would be on the inside surfaces between night and day. The
smaller the decrement factor the more comfortable living inside the house will be. See
figure 5 a for details about thermal comfort and its relationship with the ambient internal
temperature and the average temperature of the internal surfaces.
It must be noted that a difference of more than 3ْ c between the Mean Radiant
Temperature of the surface of the wall or roof and the temperature of the ambient air
inside the house will make a human being uncomfortable. Other factors get into the
formula as well, such as the relative humidity, clothing, wind speed and human nature.
These differences will be illustrated further in Iso-thermal analysis of Walls 1 & 3.
It must be noted that the internal ambient temperature inside the house is recommended
to be 20 degrees in winter, for energy saving and thermal comfort purposes, meanwhile,
in summer, it is allowed to keep rising up to 26degrees and the atmosphere will still be
comfortable.
The other problem that might arise from bigger differences between the ambient
temperature and the mean radiant temperature of the surface of walls and roofs is water
vapor condensation in winter, invoking the growth of Fungus and creating an unhealthy
atmosphere inside the house.
15
External surface
Internal surface
Maximum temperature
Reached during the day
Maximum surface temperature
Minimum surface temperature
Minimum temperature
Reached during the night
Structural member
Time Lag
24 Hours
Figure 5
Decrement Factor
16
Average Temperature of Ambient Air
35
30
Very Hot Zone
20
Comfort Zone
10
Very Cold Zone
0
55
10
10
15
15
20
20
25
25
Average surface temperature of internal walls
Figure 5 a
17
Table 2
Averages of weight of water vapor produced by a family in Jordan
consisting of an average of 5 persons
1
Breathing and Sweating
4 – 7 kg
2
Using petrol based fuel in heaters
of no exhausts
10 – 15 Kg
3
Cooking
2 – 6 kg
4
Bathing (Twice weekly)
1 – 3 kg
5
Washing activities
1 – 2 kg
6
Laundry
2 – 4 kg
7
Drying clothes
4 – 8 kg
8
Washing and drying dishes
0.5 – 1 kg
9
Other activities, plants, .. etc
0.5 – 1 kg
Total
25 – 47kg
18
• In table 2, it is shown that a typical family in Jordan produces nearly 25-47 kg of
water daily, this exists as water vapor inside the dwelling. By looking at any
psychometric chart available, it can be seen that water vapor will be condensating on
the internal surfaces of walls in winter, nearly all the time, particularly on traditional
wall types Wall 1 & Wall 2 . This will happen at about 60 % relative humidity.
Although the ambient air temperature is 20 degrees, but the exterior wall's
surface temperature from the inside will be around 13 degrees as seen in figure 6b,
6d and 7b, exactly at the corners where two walls meet. This value of relative
humidity ( 60%) is easily reached daily in winter with a family of an average of 5-6
persons, which is very common and considered as an average in Jordan. On the
other hand, a wall type Wall 3, will be subjected to water vapor condensation at
corners only if the relative humidity reaches 90 %, which is a value rarely
approached in dwellings in Jordan due to natural air exchanges. Note that the
temperature of the surface of the meeting walls does not go below 18.2 degrees ( see
figure 8b and 8d).
•
Condensation due to the lack of thermal Insulation in buildings does not only
trigger the growth and multiplication of Fungus, but causes surface cracks due to the
continuous shrinkage and drying of the surface on which condensation takes place
and due to the thermal movement induced by the temperature gradient.
•
Different modes of cracks also appear in areas where a temperature gradient
sharply persists. In plates 1 & 2, the temperature gradient due to placing the window
far on the outside or far on the inside will definitely encourage cracks in that area.
Cracks follow the area where the temperature gradient exists. These cracks can also
be seen in plate 3.
19
Plate 1
Outside
0k
Window Frame
Area of a Sharp
Temperature
Gradient
Plate 1
Winter Condition
Inside
20 k
20
Plate 2
outside
Area of extremely sharp
temperature gradient
T
e
Plate 2
m
p
e
r
a
t
u
r
e
21
Plate 3
Cracks elongated
on the interface of
two areas of
different temperature
gradient similar to
the damage seen
In the cases
displayed in
plates 1 & 2
Cold
Joint
Temperature
Gradient Cracks
22
• Cold Joints:
Heat is lost in winter as the ambient outside
temperature decreases to 0ْ c or less. We need to keep the ambient
temperature inside the house near 20ْ c in order to allow the residents
in the dwellings to feel comfortable. This requires a thermal design
capable of maintaining the mean radiant temperature of the inside
surface at around 17ْ c in winter. That is to reduce the fluctuations to
a maximum of 3 degrees.
• Notice in figure 6 that wall 3, even at 18.2 degrees at corners (see
Figure 8b & 8d) where exterior walls meet, falls in the comfortable
region. While wall 1 and wall 2 being at a surface temperature of 13
degrees fall in the uncomfortable region (The very cold zone).
•
Now, the heat lost from inside to outside cold air is moderate in
thermally insulated areas, whereas in areas were the surface
temperature is quite low, it means there is a greater loss of energy.
This usually happens at corners and at places we call them cold-joints.
One cold joint area we have seen earlier at the sides of a window
where some sections of the cavity had no insulation due to bad
workmanship. A problem which most under developed countries in
general suffer from. In the following slides some examples of cold23
Joints are demonstrated:
picture 1-1.
24
See picture 1-2
25
Picture 1 - 3
26
Figure 6
o
16.5 C
o
33 C
o
o
o
15 16
o
13
14
o
33 C
o
32
o
31. C
o
33.5 C
o
20 C
Wall 1 (Vertical
section-Winter)
6(a)
o
50 C
inside
o
o
32
o
20 C
o
31. C
out side
o
16.5 C
16 o
o
0 C
o
15
o
14 o
o
0 C
o
26 C
inside
16.5 C
Wall 1 - plan- Winter
6(b)
Wall 1 - plan - Summer
6(c)
27
Figure 6d
28
Figure 7
o
17.2
o
o
0 C
o
20 C
out side
Wall 2 (Vertical cross-section)
7(a)
o
o
17.2 C 17
o
17.2 C
16
o
14.5 C
o
o
32
17.2 C
o
20 C
o
50 C
inside
Wall 2 - plan , Winter
7(b)
32.5 C
o
16 o
32. C o
15 o
15
o
o
0 C
33.5
o
26 C
inside
Wall 2 - plan , Summer
7(c)
29
Figure 8
Wall 3 (Vertical cross-section)
8(a)
o
19.2 C
o
20 C
19.2 Co
o
0 C
o
20 C
19 Co
o
18.2 C
o
50 C
27.2 Co
19.2 oC
19 Co
o
0 C
27.2o
o
28.2 C
o
Ambient temp. = 26 C
Wall 3 - plan , Winter
8(b)
Wall 3 - plan , Summer
8(c)
30
Iso-thermal
Lines
No 18
19.2K
Figure 8 d
18.2K
31
Economical Design
• When choosing foam concrete for thermal insulating walls and roofs, we have
to choose the most suitable density in order to satisfy the criteria required:
strength, cost, durability, thickness and the K-value. We need a minimum of
600 kg/m3 density for strength to allow the concrete to withstand walking loads
and mechanical impacts.
• Choosing a higher density concrete will give a lower K-value and then a thicker
mass is required. For an economical design, thickness, density and price must
be balanced (see figure 12 ).
• The same argument applies for perlite concrete as using perlite is an advantage
in sloped roofs compared to foam concrete which cannot withstand steep
slopes. (see figure 10).
• When using other thermal insulating materials such as polystyrene, rock wool..
etc.. (see figure11 ). There comes a stage when increasing the density will not
affect the K-value much, thus to have an economical thermal design the most
efficient density must be chosen. Note that for expanded polystyrene and rock
wool, as shown in figure 11, the K-value hardly increases when the density is
above 25 kg/m3, so it is a waste of money to apply high density thermal
material of this sort.
32
0.25
K-value
0.20
0.15
0.10
0.05
0.00
1000
800
600
400
200
Density of Perlite Concrete Kg/m3
Figure 10
33
0.06
0.05
Rock Wool
K- value (W/m. C )
o
0.04
Expanded Polystyrene
0.03
Figure
11
Polyurethane
0.02
0.01
0
10
20
30
40
50
60
70
80
90
100
Density of Thermal Insulating Materials Kg/m3
34
0.25
o
THERMAL CONDUCTITY (W/ C)
0.20
Figure
12
0.15
0.10
0.05
0.00
1000
800
600
400
200
Density of Light Perlite Concrete ( Kg/m3)
35
• Conclusion: To be efficient designers, we must choose the best price-efficient
product most suitable for our method of construction and our budget. For low cost
housing we must be knowledgeable too of an important fact that the cost of thermal
insulating a structure is not a costly procedure at all. It is actually a profitable
procedure to the investor; as from the very beginning, that is as early as the design
stage, the following reductions in cost occur during construction due to thermally
insulating the structure. The reason is manifested in the dramatic reduction in the
initial cost of installing mechanical works, central heating and air conditioning
systems. In Jordan, we have proved that using, only, a wall 3 solution at an extra
cost of 1000 US $ per 150 m2 flat is immediately refunded from the reduction in
boiler capacity, quantity of radiators, diameter of pipes and capacity of pumps.
• The profitable investment in thermal insulation persists and multiplies by time ever
since the moment of occupying the building, as less fuel and electricity is spent on
heating and cooling, and very little maintenance thereafter is needed. We have also
proved in this paper that a saving of 400 $ per flat per year is achieved, only via heat
losses through walls. This means that even if we did not consider the initial profit,
the pay back period will be two and a half years, if fuel prices stay the same.
• A more comfortable environment is also prevailing inside the house, whence
thermal insulation is used. Less cracks on the internal surfaces, and less thermal
movement within the insulated zone. No water condensation is actually possible and
no fungus growth. And above all less fumes are emitted to the atmosphere. That
means less pollution for the environment.
• ----------------------- The End-----------------------------
36