1 Copyright - Al-Sanea; KSU; Jan 2012 1 PRESENTATION State of the Art in the Use of Thermal Insulation in Building Walls and Roofs – Part II By Prof. Sami Ali Al-Sanea Department of Mechanical Engineering, King Saud University, Riyadh, KSA
Jun 12, 2015
1 Copyright - Al-Sanea; KSU; Jan 2012 1
PRESENTATION
State of the Art in the Use of Thermal Insulation in Building Walls and Roofs –
Part II
By
Prof. Sami Ali Al-Sanea
Department of Mechanical Engineering, King Saud University, Riyadh, KSA
2
Objectives
• Outline importance of thermal insulation.
• Highlight proper use of thermal insulation.
• Warning against presence of thermal
bridges.
• Introducing concept of smart walls.
• Introducing concept of critical mass.
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3
Contents
• Introduction; electric energy consumption.
• Present status.
• Is there a “best” insulation material to use?
• Insulated Hordi (rib-slab) roofs.
• Thermal bridges in insulated walls.
• Insulation and “smart walls”.
• Insulation and “critical” thermal mass.
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4 Copyright - Al-Sanea; KSU; Jan 2012 4
Introduction (1/6): Electric energy consumption
Estimate of electric energy consumption in KSA:
industrial
Commercial
Agricultural
Residential
≈ 2/3 of electric energy generated in KSA is used in buildings.
5 Copyright - Al-Sanea; KSU; Jan 2012 5
Introduction (2/6): Electric energy consumption
Estimate of electric energy consumption in KSA:
Generated Consumed in
buildings
Consumed
by AC
Consumed by
transmission
100% ≈ 2/3
of gen.
≈ 2/3
of builds.
≈ 2/3
of AC
• 2/3 × 2/3 × 2/3 ≈ 30%.
• Hence, ≈ 30% of total electric energy generated is consumed by transmission loads in walls/roofs.
• Insulation is effective means of energy savings.
6 Copyright - Al-Sanea; KSU; Jan 2012 6
Introduction (3/6): How much electric
energy can be saved by using insulation?
Compared to un-insulated wall (R ≈ 0.4 m2.K/W),
insulated wall (R ≈ 2.0 m2.K/W) saves:
Transmission AC Building Generated
≈ 80% ≈ 55% ≈ 35% ≈ 25%
• Applying insulation is, therefore, a must.
• More savings achieved under opt. condts.
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Introduction (4/6): AC consumption
constitutes big portion of total electric
energy use in GCC region
• Extreme temperature in summer.
• Buildings not designed to conserve energy.
• Improper settings of thermostat.
• Thermal bridging effects.
• Subsidized electric energy cost.
• Awareness and habit of consumers.
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Introduction (5/6): Increasing demand on
electricity
• Increasing population.
• Expansion / development plans.
• Increasing demand on thermal comfort.
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Introduction (6/6): Present and future problems
• Cost of energy is increasing worldwide.
• Insufficient supply of electricity, especially
at peak hours.
• Adverse impact on environment by energy
production plants.
• Increasing demand on electricity.
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Present Status (1/5): General
• Increasing use of insulation without proper
scientific guidance.
• Building Codes are based on Int. Standards.
• Recommended R-values need to be
established rigorously under local condts.
• Scientific research must be encouraged and
be generously funded.
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Present Status (2/5): Requirements
Insulation
Properties
Climatic
Conditions
Wall/Roof
Configuration
Numerical
Input
Thermal Analysis
Thermal Characteristics & Yearly Transmission Loads
Economic Analysis Economic
Parameters
Optimum Insulation Thickness & Recommended R-Value
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Present Status (3/5): Active research areas (I)
• Proper location of insulation and thermal
mass layers in building envelope. Effect of
AC operation mode (continuous/intermit.).
• Splitting insulation into two/three layers.
• Optimization of insulation layer thickness.
• Use of critical amount of thermal mass.
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Present Status (4/5): Active research areas (II)
• Thermostat settings for maximum energy
savings while maintaining thermal comfort.
• Effects of thermal bridges on transmission
loads and opt. insulation thickness (Lopt).
• Effects of economic parameters on Lopt.
• Effect of wall orientation on Lopt.
14 Copyright - Al-Sanea; KSU; Jan 2012 14
Present Status (5/5): Active research areas (III)
• Develop new building and insulation
materials.
• Use of phase change materials (pcm) in
building envelope.
• Use of roof garden and roof pond cooling.
• Etc.
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Representative Insulation Materials (1/7)
Molded Polystyrene
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Extruded Polystyrene
Representative Insulation Materials (2/7)
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Polyurethane
Representative Insulation Materials (3/7)
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Glass Fiber
Representative Insulation Materials (4/7)
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Rock Wool
Representative Insulation Materials (5/7)
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Perlite
Representative Insulation Materials (6/7)
21
Lightweight Concrete
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Representative Insulation Materials (7/7)
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Topic 1: “Best” insulation to use (1/3)
• Insulation materials differ with respect to
properties and cost.
• Properties include thermal, mechanical, etc.
characteristics of materials.
• Cost constantly changes with time.
• Insulation should be looked upon as system.
• Insulation is used according to application.
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Topic 1: “Best” insulation to use (2/3)
Therefore:
• There is no such material as the best
insulation material.
• Type of application, climate, cost, thermal
properties and other properties determine
what insulation material to use.
• This explains presence of various types of
insulations in market.
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Topic 1: “Best” insulation to use (3/3)
Example:
Molded Polystyrene Extruded Polystyrene
Cheaper (per unit mass) More expensive
Larger k (for same ρ, temp.,
and moisture content)
Smaller k
Higher moisture absorptivity
(adversely affecting k)
Lower moisture
absorptivity
• Therefore, to select an insulation, a compromise
would often be made according to application.
25 Copyright - Al-Sanea; KSU; Jan 2012 25
Topic 2: Hordi (rib-slab) roofs (1/11)
Hordi roof versus solid-slab roof
Lins
Mortar bed
Outside
Insulation Membrane
Foam concrete
Reinforced concrete
Cement plaster
Inside
30
75
25
5
Tiles
130
or
200
20
26 Copyright - Al-Sanea; KSU; Jan 2012 26
Topic 2: Hordi roofs (2/11)
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Topic 2: Hordi roofs (3/11)
Hordi roof versus solid-slab roof
• Increasing use of Hordi roofs due to
advantages over solid-slab roofs.
• R-values of Hordi roofs are often larger
than R-values of solid-slab roofs.
• When Hordi units are made of insulating
materials, the roofs become lighter and offer
further increase in R-value and sound proof.
28 Copyright - Al-Sanea; KSU; Jan 2012 28
Topic 2: Hordi roofs (4/11)
Recent advances in Hordi roof design
• Hordi roofs, with insulating Hordi units, suffer from effects of thermal bridges.
• Novel and practical Hordi roof design that eliminates thermal bridges was sought.
With the new design, substantial energy savings can be achieved.
Hot and cold spots are eliminated resulting into better thermal comfort.
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Topic 2: Hordi roofs (5/11)
Recent advances in Hordi roof design
• The following results are extracted from the
reference below, in which the improved Hordi
unit design is the idea of the authors and should
not be used without their consent.
Al-Sanea S.A. and Zedan M.F., "Preventing Thermal
Bridging Effects in Hordi Roofs by Using a Novel
Design for the Hordi Unit", Proceedings of the Seventh
Saudi Engineering Conference, Volume I, pp. 237-257,
KSU, Riyadh, 2-5 Dec. 2007.
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Topic 2: Hordi roofs (6/11)
Recent advances in Hordi roof design
Reinforced
concrete
Rib
Inside plaster
Hordi unit
Air
space
Reinforced
concrete
Hordi unit
Air
space Rib
“Not to scale”
Figure 1: Conventional Hordi unit.
Inside plaster
Figure 2: Improved Hordi unit.
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Topic 2: Hordi roofs (7/11) Recent advances in Hordi roof design
Inside-surface temperature versus roof width.
Transmission load versus time of day.
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Topic 2: Hordi roofs (8/11) Recent advances in Hordi roof design
Daily-total transmission load for representative day of each month.
Peak transmission load for representative day of each month.
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Topic 2: Hordi roofs (9/11)
• Recent advances in Hordi roof design.
• Temperature contours.
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Topic 2: Hordi roofs (10/11)
• Recent advances in Hordi roof design.
• Overall thermal characteristics.
Hordi unit
Transmission load
(kWh/m2.yr)
Roof R-value
(m2.K/W)
Time
Lag
(tlag)
(h)
Decrement
factor
(df)
(%)
Peak load
(W/m2)
Cooling
(Qi,cool)
Heating
(Qi,heat)
Dynamic
(Rd)
Nominal
(Rn)
Cool (qpeak,c)
Heat (qpeak,h)
Conventional 17.08 6.46 2.04 1.79 13.7 0.35 5.07 3.70
Improved
Difference
11.09
35%
4.12
36%
3.16
35%
2.92
39%
13.0 0.15
57%
3.23
36%
2.30
38%
35 Copyright - Al-Sanea; KSU; Jan 2012 35
Topic 2: Hordi roofs (11/11)
• Recent advances in Hordi roof design.
• Overall thermal bridging effects.
Hordi unit
Transmission load (kWh/m2.yr) Qrib/tot
(%)
Arearib/tot
(%)
Ibr
(-)
Rib
(Qi,rib)
Hordi
(Qi,Hordi)
Total
(Qi,tot)
Conventional 9.83 13.71 23.54 41.8 20 5.5
Improved
Difference
3.44
65%
11.77
14%
15.21
35%
22.6 20 1.3
36 Copyright - Al-Sanea; KSU; Jan 2012 36
Overall vertical
section in wall
showing whole
building-block units
and mortar joints
cutting across
insulation layer.
Topic 3: Thermal bridges in insulated walls (1/12)
Mortar joint
Masonry
Insulation
Masonry
with
air space
Hb
Hmj
Outside Inside
H
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Symmetric region showing various layers (dimensions in mm).
x
y
25 45 75 30 25 25 25
Air
spac
e
Mortar joint
Hb/2
Hmj/2
Insu
lati
on
Concr
ete
Cem
ent
pla
ster
Cem
ent
pla
ster
Concr
ete
Concr
ete
Inside
H
Outside
L
Topic 3: Thermal bridges in insulated walls (2/12)
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Topic 3: Thermal bridges in insulated walls (3/12)
Common and Serious Problem
• Almost all insulated building blocks suffer
from thermal bridges (as manufactured
and/or due to adding mortar joints at
construction site).
• Such walls have R-values that are rather
low (less than 1 m2.K/W) which are well
below “recommended” R-values.
39 Copyright - Al-Sanea; KSU; Jan 2012 39
Topic 3: Thermal bridges in insulated walls (4/12)
Common and Serious Problem
• The following results are extracted from the
reference below, which is presently submitted for
publication.
Sami A. Al-Sanea and M. F. Zedan, “Effect of Thermal
Bridges on Transmission Loads and Thermal Resistance of
Building Walls under Dynamic Conditions”, paper
submitted for publication, 2012.
40 Copyright - Al-Sanea; KSU; Jan 2012 40
Transmission load variation with time during representative days
of August and January for different mortar joint heights.
Topic 3: Thermal bridges in walls (5/12)
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(a) (b)
Cool. and heat. transmission loads for representative days of months
for different mortar joint heights; (a) daily loads and (b) peak loads.
Topic 3: Thermal bridges in walls (6/12)
42 Copyright - Al-Sanea; KSU; Jan 2012 42
(a) (b)
Cooling and heating transmission loads variation with mortar joint
height; (a) yearly loads and (b) peak loads.
Topic 3: Thermal bridges in walls (7/12)
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Variation of dynamic and nominal thermal resistances with
mortar joint height.
Topic 3: Thermal bridges in walls (8/12)
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(a) (b)
Variation of thermal characteristics with mortar joint heights; (a)
yearly-averaged time lag and (b) yearly-averaged decrement factor.
Topic 3: Thermal bridges in walls (9/12)
45 Copyright - Al-Sanea; KSU; Jan 2012 45
(a) (b)
Percentage change versus percentage mortar joint area to total wall
area; (a) increase in yearly cooling transmission loads and (b)
decrease in yearly-averaged dynamic thermal resistance.
Topic 3: Thermal bridges in walls (10/12)
46 Copyright - Al-Sanea; KSU; Jan 2012 46
Possible solutions
• Using “insulating” mortar joint material.
This can help but does not necessarily
eliminate problem. Also, possible weakness
regarding structural strength.
• Using tongue-and-groove type of insulation.
However, problems can arise with regard to
stacking and storage and structural strength.
Topic 3: Thermal bridges in walls (11/12)
47 Copyright - Al-Sanea; KSU; Jan 2012 47
Possible solution: Tongue-and-groove arrangement.
Topic 3: Thermal bridges in walls (12/12)
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Topic 4:
Insulation and
smart walls
(1/13)
All insulated
walls have same
optimal R-value of
2.75 m2.K/W and
same thermal
mass.
49 Copyright - Al-Sanea; KSU; Jan 2012 49
Topic 4: Insulation and smart walls (2/13)
• How can thermal insulation and thermal
mass complement each other in building
envelope?
• Introducing concept of smart wall.
• Novel and practical wall design that
achieves best overall dynamic thermal
characteristics was sought.
50 Copyright - Al-Sanea; KSU; Jan 2012 50
Topic 4: Insulation and smart walls (3/13)
Recent advances in wall design
• Novel and practical wall design achieves:
substantial reduction in total and peak transmission loads,
substantial increase in time lag (shift in peak load) and hence makes electric-grid load profile more evenly distributed, and
substantial decrease in decrement factor.
51 Copyright - Al-Sanea; KSU; Jan 2012 51
Topic 4: Insulation and smart walls (4/13)
Representation of time lag and decrement factor:
Wall tlag
tTs,i,max
x=0 x=L
Ai
Ts,i,max
Ts,i,min
Ts,o,max
Ts,o,min
t
Ts,o(t)
tTs,o,max
Ao
Ts,i(t)
Outside Inside
tlag = tTs,o,max - tTs,i,max min,,max,,
min,,max,,
osos
isis
o
if
TT
TT
A
Ad
52 Copyright - Al-Sanea; KSU; Jan 2012 52
Topic 4: Insulation and smart walls (5/13)
• The following results are extracted from the
reference below, which has been published
recently in Applied Energy.
Al-Sanea, S.A., Zedan, M.F., Improving thermal
performance of building walls by optimizing insulation
layer distribution and thickness for same thermal mass,
Applied Energy 88 (2011) 3113-3124.
53 Copyright - Al-Sanea; KSU; Jan 2012 53
Topic 4: Insulation and smart walls (6/13)
Monthly settings of indoor air temperature, Tf,i (oC).
Values of parameters used in economic model.
Month Jan Feb Mar Apr May Jun Jul Aug Sep Oct Nov Dec
Tf,i 21 21 21 24 26 26 26 26 26 24 21 21
ci
($/m3)
cad
($/m2)
ce
($/kWh)
pc pf m
(years)
rd
(%)
ri
(%)
42.67 * 0.0317 3 4 30 5 3
54 Copyright - Al-Sanea; KSU; Jan 2012 54
Topic 4: Insulation and smart walls (7/13)
Material properties.
Material k (W/m.K) (kg/m3) c (J/kg.K)
HWHCB* (100 mm) 0.81 1618 840
Cement plaster 0.72 1860 840
Molded polystyrene 0.034 23 1280
* Values of properties quoted correspond to block thickness of 100 mm.
Properties of hollow masonry blocks can depend on block thickness due to
different void configurations.
55 Copyright - Al-Sanea; KSU; Jan 2012 55
Topic 4: Insulation and smart walls (8/13)
Time lag for representative days of months for various walls.
56 Copyright - Al-Sanea; KSU; Jan 2012 56
Topic 4: Insulation and smart walls (9/13)
Decrement factor for representative days of months for various walls.
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Topic 4: Insulation and smart walls (10/13)
Peak cool. Transm. loads for representative days of months for walls.
58 Copyright - Al-Sanea; KSU; Jan 2012 58
Topic 4: Insulation and smart walls (11/13)
Transm. load versus time during represent. day of Aug. for walls.
59 Copyright - Al-Sanea; KSU; Jan 2012 59
Topic 4: Insulation and smart walls (12/13)
Temperature distribution across wall thickness at different times
during representative day of August for wall W3.
60 Copyright - Al-Sanea; KSU; Jan 2012 60
Topic 4: Insulation and smart walls (13/13)
Yearly transmission loads, yearly-averaged time lag and decrement factor, and
peak transmission loads for different walls with optimized insulation thickness.
Wall
Transmission load
(kWh/m2.yr)
Time lag
(tlag)
(h)
Decrement
factor
(df)
(%)
Peak loads*
(W/m2)
Cooling
(Qi,cool)
Heating
(Qi,heat)
Cool
(qp,cool)
Heat
(qp,heat)
W1a 13.18 5.041 6.13 1.35 4.77 3.36
W1b 13.19 5.061 7.33 1.34 4.79 3.42
W1c 13.03 4.957 6.71 0.74 4.41 3.15
W2a 13.00 4.870 9.33 0.42 4.02 2.86
W2b 12.97 4.889 8.19 0.24 3.91 2.78
W2c 12.96 4.889 10.44 0.26 3.92 2.80
W3 12.97 4.887 12.13 0.13 3.80 2.69 * Peak cooling and heating transmission loads occur in August and January for all walls.
61 Copyright - Al-Sanea; KSU; Jan 2012 61
Topic 5: Insulation and critical mass (1/12)
Wall configurations with varying thermal mass thickness but same and constant Rn-value; wall W1 with outside insulation and wall W2 with inside insulation.
Thermal mass;
varying thickness
Thermal Insulation (9 cm)
Cement plaster (1.5 cm) Cement plaster (1.5 cm)
Inside Outside
62 Copyright - Al-Sanea; KSU; Jan 2012 62
Motivation
• Can transmission load be reduced, and hence
energy be saved, by thermal mass alone, while
keeping wall R-value constant?
• Walls in „moderate‟ climates are built massive!
• What is the „critical‟ thickness of thermal mass
and how much energy, if any, can be saved?
• We do have „moderate‟ months in GCC region,
can we utilize thermal mass for energy savings?
Topic 5: Insulation and critical mass (2/12)
63 Copyright - Al-Sanea; KSU; Jan 2012 63
• The following results are extracted from the
reference below, which has been published very
recently in Applied Energy.
Al-Sanea, S.A., Zedan, M.F., and Al-Hussain, S.N.,
Effect of thermal mass on performance of insulated
building walls and the concept of energy savings
potential, Applied Energy 89 (2012) 430-442.
Topic 5: Insulation and critical mass (3/12)
64 Copyright - Al-Sanea; KSU; Jan 2012 64
Daily cooling and heating transmission loads variation with
masonry thickness in November for walls W1 and W2.
-3
-2
-1
0
1
2
0 0.1 0.2 0.3 0.4 0.5
Lmas (m)
Qi (k
Wh
/m2.d
ay)
× 1
00
0
W1, cool. W2, cool.
W1, heat. W2, heat.
Topic 5: Insulation and critical mass (4/12)
65 Copyright - Al-Sanea; KSU; Jan 2012 65
Daily cooling transmission load variation with masonry
thickness in August for walls W1 and W2.
5
6
7
8
9
10
0 0.1 0.2 0.3 0.4 0.5
Lmas (m)
Qi,
c (k
Wh
/m2.d
ay)
× 1
00
0
W1, cool. W2, cool.
Topic 5: Insulation and critical mass (5/12)
66 Copyright - Al-Sanea; KSU; Jan 2012 66
Yearly cool. Transm. loads variation with masonry thickness for
walls W1 and W2; asymptotes and Lmas,cr by using 5% criterion.
12
12.5
13
13.5
14
14.5
15
0 0.1 0.2 0.3 0.4 0.5
Lmas (m)
Qi,
c (k
Wh
/m2.y
r) d
W1, cool. W2, cool.
Topic 5: Insulation and critical mass (6/12)
67 Copyright - Al-Sanea; KSU; Jan 2012 67
Yearly peak cooling and heating transmission loads variation
with masonry thickness for walls W1 and W2.
-6
-4
-2
0
2
4
6
8
10
0 0.1 0.2 0.3 0.4 0.5
Lmas (m)
qpea
k (
W/m
2)
W1, cool. W2, cool.
W1, heat. W2, heat.
Topic 5: Insulation and critical mass (7/12)
68 Copyright - Al-Sanea; KSU; Jan 2012 68
Yearly-averaged time lag variation with
masonry thickness for walls W1 and W2.
0
2
4
6
8
10
12
14
0 0.1 0.2 0.3 0.4 0.5
Lmas (m)
t lag
(h
)
W1 W2
Topic 5: Insulation and critical mass (8/12)
69 Copyright - Al-Sanea; KSU; Jan 2012 69
Yearly-averaged decrement factor variation
with masonry thickness for walls W1 and W2.
0
1
2
3
4
0 0.1 0.2 0.3 0.4 0.5
Lmas (m)
df ×
10
0
W1 W2
Topic 5: Insulation and critical mass (9/12)
70 Copyright - Al-Sanea; KSU; Jan 2012 70
Yearly-averaged dynamic and nominal R-values variation
with masonry thickness for walls W1 and W2.
2
2.5
3
3.5
0 0.1 0.2 0.3 0.4 0.5
Lmas (m)
R (
m2.K
/W)
W1, dyn. R W1, nom. R
W2, dyn. R W2, nom. R
Topic 5: Insulation and critical mass (10/12)
71 Copyright - Al-Sanea; KSU; Jan 2012 71
Critical thermal mass thickness variation with cooling and
heating energy-savings potentials for walls W1 and W2.
0
5
10
15
20
25
30
35
70 75 80 85 90 95 100
Energy savings potential, Δ (%)
Lm
as,c
r (
cm)
W1, cool. W1, heat.
W2, cool. W2, heat.
Topic 5: Insulation and critical mass (11/12)
72 Copyright - Al-Sanea; KSU; Jan 2012 72
Outdoor air temp. variation with time of day in Aug., Jan.,
and Nov. showing thermostat settings of indoor air temp.
5
10
15
20
25
30
35
40
45
0 6 12 18 24
Time (h)
T (
o C)
Aug.
Jan.
Nov.
Topic 5: Insulation and critical mass (12/12)
73
Conclusions (1/2)
• “Best” insulation to use depends on many
factors including type of application.
• Thermal bridges in Hordi (rib-slab) roofs
should be eliminated.
• Thermal bridges in insulated walls should
be eliminated.
• Concept of “smart walls” should be utilized.
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74
Conclusions (2/2)
• Concept of “critical” thermal mass should
be utilized.
• Recommended R-values for building walls
and roofs must be determined and/or be
revised based on local conditions.
• Scientific research in thermal insulation use
must be encouraged.
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75
THANK YOU
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