Sami Al Sanea - State of the Art in the Use of Thermal Insulation in Building Walls and Roofs part 2

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

Copyright - Al-Sanea; KSU; Jan 2012 1

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.

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.

Introduction (1/6): Electric energy consumption
Estimate of electric energy consumption in KSA:
Residential

Commercial

Agricultural industrial

≈ 2/3 of electric energy generated in KSA is
used in buildings.

Introduction (2/6): Electric energy consumption
Estimate of electric energy consumption in KSA:
Generated Consumed in Consumed Consumed by
buildings by AC transmission
100% ≈ 2/3 ≈ 2/3 ≈ 2/3
of gen. of builds. 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.

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.

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.

Introduction (5/6): Increasing demand on
electricity

• Increasing population.
• Expansion / development plans.
• Increasing demand on thermal comfort.


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.


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.

Present Status (2/5): Requirements
Insulation Climatic Wall/Roof Numerical
Properties Conditions Configuration Input

Thermal Analysis

Thermal Characteristics & Yearly Transmission Loads

Economic
Economic Analysis Parameters

Optimum Insulation Thickness & Recommended R-Value

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.


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.


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.


Representative Insulation Materials (1/7)
Molded Polystyrene


Extruded Polystyrene


Polyurethane


Glass Fiber


Rock Wool


Perlite


Lightweight Concrete


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.


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.

Example:
Molded Polystyrene Extruded Polystyrene
Cheaper (per unit mass) More expensive
Larger k (for same ρ, temp., Smaller k
and moisture content)
Higher moisture absorptivity Lower moisture
(adversely affecting k) absorptivity
• Therefore, to select an insulation, a compromise
would often be made according to application.

Topic 2: Hordi (rib-slab) roofs (1/11)
Hordi roof versus solid-slab roof
Outside
20 Tiles
30 Mortar bed
Lins Insulation Membrane
5
75 Foam concrete

130
or Reinforced concrete
200

25 Cement plaster
Inside


Topic 2: Hordi roofs (2/11)


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.

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.

• 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.


Reinforced Reinforced
concrete concrete

Hordi unit Hordi unit

Air Air
space Rib space Rib

Inside plaster Inside plaster
“Not to scale”

Figure 1: Conventional Hordi unit. Figure 2: Improved Hordi unit.


Inside-surface temperature versus Transmission load versus time
roof width. of day.


Daily-total transmission load for Peak transmission load for
representative day of each month. representative day of each month.


• Recent
advances in
Hordi roof
design.
• Temperature
contours.


• Recent advances in Hordi roof design.
• Overall thermal characteristics.
Transmission load Roof R-value Time Decrement Peak load
(kWh/m2.yr) (m2.K/W) Lag factor (W/m2)
(tlag) (df)
Hordi unit
Cooling Heating Dynamic Nominal (h) (%) Cool Heat
(Qi,cool) (Qi,heat) (Rd) (Rn) (qpeak,c) (qpeak,h)

Conventional 17.08 6.46 2.04 1.79 13.7 0.35 5.07 3.70
Improved 11.09 4.12 3.16 2.92 13.0 0.15 3.23 2.30

Difference 35% 36% 35% 39% 57% 36% 38%


• Recent advances in Hordi roof design.
• Overall thermal bridging effects.

Transmission load (kWh/m2.yr) Qrib/tot Arearib/tot Ibr
(%) (%) (-)
Hordi unit Rib Hordi Total
(Qi,rib) (Qi,Hordi) (Qi,tot)
Conventional 9.83 13.71 23.54 41.8 20 5.5
Improved 3.44 11.77 15.21 22.6 20 1.3

Difference 65% 14% 35%


Topic 3: Thermal bridges in insulated walls (1/12)
Hmj
Mortar joint Overall vertical
Masonry section in wall
H
Hb showing whole
Insulation building-block units
and mortar joints
Masonry cutting across
with
air space insulation layer.

Outside Inside


Outside Inside

Mortar joint Hmj/2
Cement plaster

Cement plaster
Insulation

Air space
Hb/2
Concrete

Concrete

Concrete
H

y

x
25 45 75 30 25 25 25

L

Symmetric region showing various layers (dimensions in mm).

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.



Common and Serious Problem

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.


Topic 3: Thermal bridges in walls (5/12)

Transmission load variation with time during representative days
of August and January for different mortar joint heights.


(a) (b)
Cool. and heat. transmission loads for representative days of months
for different mortar joint heights; (a) daily loads and (b) peak loads.


(a) (b)
Cooling and heating transmission loads variation with mortar joint
height; (a) yearly loads and (b) peak loads.


Variation of dynamic and nominal thermal resistances with
mortar joint height.


(a) (b)
Variation of thermal characteristics with mortar joint heights; (a)
yearly-averaged time lag and (b) yearly-averaged decrement factor.


(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.


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.


Possible solution: Tongue-and-groove arrangement.


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.


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.


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.

Representation of time lag and decrement factor:
Ai Ts ,i ,max  Ts ,i ,min
tlag = tTs,o,max - tTs,i,max df  
Ao Ts ,o,max  Ts ,o,min
tlag
Wall
Ts,o,max
Ts,i,max
Ts,o(t)
Ao Ai t
Ts,i(t)
Ts,i,min
Inside Outside Ts,o,min
x=0 x=L
tTs,i,max tTs,o,max


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.



Monthly settings of indoor air temperature, Tf,i (oC).
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

Values of parameters used in economic model.
ci cad ce pc pf m rd ri
($/m3) ($/m2) ($/kWh) (years) (%) (%)
42.67 * 0.0317 3 4 30 5 3



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.



Time lag for representative days of months for various walls.


Decrement factor for representative days of months for various walls.


Peak cool. Transm. loads for representative days of months for walls.


Transm. load versus time during represent. day of Aug. for walls.


Temperature distribution across wall thickness at different times
during representative day of August for wall W3.

Yearly transmission loads, yearly-averaged time lag and decrement factor, and
peak transmission loads for different walls with optimized insulation thickness.
Transmission load Time lag Decrement Peak loads*
(kWh/m2.yr) (tlag) factor (W/m2)
Wall Cooling Heating (h) (df) Cool Heat
(Qi,cool) (Qi,heat) (%) (qp,cool) (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.

Topic 5: Insulation and critical mass (1/12)

Inside Outside

Cement plaster (1.5 cm) Cement plaster (1.5 cm)

Thermal mass; Thermal Insulation (9 cm)
varying thickness

Wall configurations with varying thermal mass thickness but
same and constant Rn-value; wall W1 with outside insulation
and wall W2 with inside insulation.


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?


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.


2
W1, cool. W2, cool.
W1, heat. W2, heat.

1

Qi (kWh/m2.day) × 100 0 0

-1

-2

-3
0 0.1 0.2 0.3 0.4 0.5
Lmas (m)

Daily cooling and heating transmission loads variation with
masonry thickness in November for walls W1 and W2.

10
W1, cool. W2, cool.

9

Qi,c (kWh/m2.day) × 1000 8

7

6

5
0 0.1 0.2 0.3 0.4 0.5
Lmas (m)

Daily cooling transmission load variation with masonry
thickness in August for walls W1 and W2.

15
W1, cool. W2, cool.

14.5

Qi,c (kWh/m2.yr) d 14

13.5

13

12.5

12
0 0.1 0.2 0.3 0.4 0.5
Lmas (m)

Yearly cool. Transm. loads variation with masonry thickness for
walls W1 and W2; asymptotes and Lmas,cr by using 5% criterion.

10
W1, cool. W2, cool.

8 W1, heat. W2, heat.

6

4
qpeak (W/m2)

2

0

-2

-4

-6
0 0.1 0.2 0.3 0.4 0.5
Lmas (m)

Yearly peak cooling and heating transmission loads variation
with masonry thickness for walls W1 and W2.

W1 W2
14

12

tlag (h) 10

8

6

4

2

0
0 0.1 0.2 0.3 0.4 0.5
Lmas (m)

Yearly-averaged time lag variation with
masonry thickness for walls W1 and W2.

4
W1 W2

3

df ×100

2

1

0
0 0.1 0.2 0.3 0.4 0.5
Lmas (m)

Yearly-averaged decrement factor variation

3.5

R (m2.K/W) 3

2.5
W1, dyn. R W1, nom. R
W2, dyn. R W2, nom. R

2
0 0.1 0.2 0.3 0.4 0.5
Lmas (m)

Yearly-averaged dynamic and nominal R-values variation

35
W1, cool. W1, heat.
W2, cool. W2, heat.
30

25
Lmas,cr (cm)
20

15

10

5

0
70 75 80 85 90 95 100
Energy savings potential, Δ (%)

Critical thermal mass thickness variation with cooling and
heating energy-savings potentials for walls W1 and W2.

45
Aug.
Jan.
40 Nov.

35

T (oC) 30

25

20

15

10

5
0 6 12 18 24
Time (h)

Outdoor air temp. variation with time of day in Aug., Jan.,
and Nov. showing thermostat settings of indoor air temp.

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.

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.


THANK YOU


Sami Al Sanea - State of the Art in the Use of Thermal Insulation in Building Walls and Roofs part 2

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