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

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.

Copyright - Al-Sanea; KSU; Jan 2012

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.



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.


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.


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

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


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


21

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.,

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.


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


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

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.


Topic 2: Hordi roofs (7/11) Recent advances in Hordi roof design

Inside-surface temperature versus roof width.

Transmission load versus time of day.


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.



• Recent advances in Hordi roof design.

• Temperature contours.




• 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%




• 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


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


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




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.


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)


(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:

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




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).

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



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.

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.


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


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.



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.



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.



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.



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.



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



Yearly-averaged decrement factor variation


0

1

2

3

4

0 0.1 0.2 0.3 0.4 0.5

Lmas (m)

df ×

10

0

W1 W2



Yearly-averaged dynamic and nominal R-values variation


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



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.



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.


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.


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.


75

THANK YOU


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

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