Why do we talk about thermal insulation?Why do we talk about thermal insulation?

Thermal insulation is the major factor inis the major factor in reducing the loss of heat from buildings.

Chapter 3 Thermal InsulationChapter 3 Thermal Insulation （建筑）隔热（建筑）隔热

Benefits of good thermal Benefits of good thermal insulation ?insulation ?

(1) to maintain a constant temperature within a building, we (1) to maintain a constant temperature within a building, we

need to reduce the heat exchange with the surroundingsneed to reduce the heat exchange with the surroundings

(2) to save energy needed to run the cooling plant(2) to save energy needed to run the cooling plant

(3) to save energy needed to run the heating plant(3) to save energy needed to run the heating plant

(4) One of the benefits of good thermal insulation is that the risk of surface condensation is reduced because of the warmer internal surfaces.

(5) Good insulation can also reduce the time taken for a room to heat up to a comfortable temperature.

The relatively small cost of extra insulating materials is quickly paid for by the reduction in the size of the heating plant required and by the annual savings in the amount of fuel needed.

It is useful to remember that good thermal insulation will also reduce the flow of heat into a building, when the temperature outside is greater than the temperature inside.

A well-insulated structure and a A well-insulated structure and a poorly-insulated structure, which one poorly-insulated structure, which one will stay cooler in summer?will stay cooler in summer?

《黄帝宅经》 治宅极宜壮实

3.1 Insulating materials 绝热材料3.2 U-values U- 值3.3 Thermal Bridging 热桥3.4 Structural temperature 结构温度

four topics are discussed in this chapter

3.1 Insulating materials 绝热材料

What is a thermal insulator What is a thermal insulator （隔热体）（隔热体） ?? A thermal insulator is a material which oppos

es （反对反对） the transfer of heat between areas at different temperatures.

what should a good insulator have?what should a good insulator have?

The best insulating materials have their atoms spaced well apart, so these materials will also tend to be porous （多孔多孔的的） and of low density.

Gas, which have the most widely-spaced atoms, are the best insulators against conduction.

Air, which is a mixture of gases, is the basis of insulators such as aerated lightweight concrete （轻型加气混凝土轻型加气混凝土） , expanded plastics （发泡塑料发泡塑料） , and cavities （空腔空腔） .

For air to act as an insulator it must be stationarystationary （静止（静止的）的） ,, otherwise moving air if allowed to move will transfer heat by convection.

3.1.1 Types of insulator3.1.1 Types of insulator

(1) Rigid preformed materials(1) Rigid preformed materials: aerated concrete blocks

预制刚性材料 预制刚性材料 : : 加气混凝土砖加气混凝土砖 以硅砂、水泥、石灰为主要原料，由经过防锈处理以硅砂、水泥、石灰为主要原料，由经过防锈处理

的钢筋增强，经过高温、高压、蒸汽养护而成的多的钢筋增强，经过高温、高压、蒸汽养护而成的多气孔混凝土制品。可锯可刨，加工便捷，其施工效气孔混凝土制品。可锯可刨，加工便捷，其施工效率是传统红砖的率是传统红砖的 4~54~5 倍，可广泛用于建筑的内墙、倍，可广泛用于建筑的内墙、外墙。 外墙。

(2) Flexible materials(2) Flexible materials: fibreglass quilts

柔性材料 玻璃纤维布柔性材料 玻璃纤维布

(3) Loose fill materials(3) Loose fill materials: expanded polystyrene granules

疏松填充材料 膨胀聚苯乙烯颗粒疏松填充材料 膨胀聚苯乙烯颗粒

(4) Materials formed on site(4) Materials formed on site : foamed polyurethane

现场加工材料 泡沫聚亚安脂现场加工材料 泡沫聚亚安脂

(5) Reflective materials(5) Reflective materials : aluminium foil 反射材料 铝箔反射材料 铝箔

When choosing materials for thermal insulation of buildings the physical properties of the material need to be considered.

Thermal insulation suitable for the purpose. Strength （强度强度） or rigidity （硬度硬度） suitable for the pur

pose. Moisture resistance. （防潮性能防潮性能） Fire resistance. （防火性能防火性能） Resistance to pests and fungi. （防虫和防霉防虫和防霉） Compatibility （兼容性（兼容性） with adjacent materials Harmless to humans and the environment.

3.1.2 Properties of insulators3.1.2 Properties of insulators

thermal conductivity Is a measure of the rate at which heat is conduction through a particular material under specified conditions

Unit: W/m K ( W/m )℃Referring to figure3.1 the general formula is: P39

d

)(kA

t

H 21

3.1.3 Thermal conductivity , lamda-value3.1.3 Thermal conductivity , lamda-value 导热率 导热率 lamda-lamda- 值值

Resistivity 热阻

Resistivity （ r ） is an alternative index of conductio

n in materials and is the reciprocal of （成反比） the

rmal conductivity, so that r = 1/lamda

The thermal conductivities of some building

materials are given in table 3.1.

The thermal conductivity of practical building

materials Varies with moisture content as the

presence of water increases conduction.

Variations in density have significant effects on the

k-values of brickwork, concrete and stone and more

comprehensive tables of thermal conductivities

should be used to obtain specific values.

3.1.4 Emissivity and absorptivity 3.1.4 Emissivity and absorptivity 发射率 吸收率发射率 吸收率

the ability of a material to absorb or give off radiant he

at is a property of the surface of the material.

Rough black surfaces absorb most heat and emit most

heat.

Conversely, shiny slivered surfaces absorb least heat

and emit least heat.

black bodyblack body

黑体：是指能吸收投入到其面上的所有热辐射能的物体，是一种科学假想的物体，现实生活中是不存在的。但却可以人工制造出近似的人工黑体。

黑体模型

Emissivity Emissivity is the fraction ofis the fraction of energy radiated by a body compared toto that radiated by a black body at the same temperatureAbsorptivity Absorptivity is the fraction ofis the fraction of ( ) by a body compared toto that ( ) by a black body

3.1.5 Clear sky radiation 3.1.5 Clear sky radiation 晴空辐射晴空辐射 At night time a building emits radiant heat to its surroundings an

d the rate of this heat loss from the roof will be increased if the night sky is clear and cloudless.

This radiant “suck”( 允吸允吸）occurs because a clear dark sky iscloser in form to a black body

The same radiant mechanism

causes dew( 露 )or ground frost (( 霜）霜）to occur during a clear

starry ( 布满星星的 ) night.

Now the next topic

3.2 U-values

3.2.1 Thermal transmittance ,U-value3.2.1 Thermal transmittance ,U-value

传热系数，传热系数， U-U- 值值 Heat is transferred through an element of a building , such

as a wall , by a number of mechanisms. Layers of different materials conduct heat at different rate

s a U-value is a measure of the overall rate of heat transfer ,

by all mechanisms under standard conditions, through a particular section of construction

Thermal transmittance Thermal transmittance 传热系数传热系数

Unit : W/m2K (W/m2 )℃ The rate of heat flow in watts through 1m2 of a

structure when there is a temperature difference

across the structure of 1 ℃ Lower U-values provide better thermal insulation.

For example, a wall with a U-value of 0.4 W/m2K

loses heat at half the rate of a wall with a U-value of

0.8 W/m2K

3.2.2 Elemental U-value3.2.2 Elemental U-value （围护结构）各部分的（围护结构）各部分的 U-U- 值值

Standard U-values are calculated by making certain assumption

s about moisture contents of materials and about rates of heat t

ransfer at surfaces and in cavities.

not always agree exactly with U-values measured on site.

they are needed as a common basis for comparing the thermal

insulation of different types of structure and for predicting the he

at loss from buildings.

they are also used to specify the amount of thermal insulation r

equired by clients 客户 or by regulations.

the values for （ some common types of construction ） are giv

en in table 3.3

Figure 3.1 Maximum U-values for new dwellings

McMullan

3.2.3 Thermal resistance , R-value3.2.3 Thermal resistance , R-value 热阻 热阻 R-R- 值值 Is a measure of the opposition to heat transfer offered by a

particular component in a building element. Unit : m2K/w Higher thermal resistance gives better thermal insulation There are there general types of thermal resistance which

need to be determined , either by calculation or by seeking published standard values.

（ 1 ） Material resistances 材料热阻（ 2 ） Surface resistances 表面热阻（ 3 ） Airspace resistances 空气间层热阻

（ 1 ） Material resistances 材料热阻

The thermal resistance of each layer of material in a

structure depends on the rate at which the material

conducts heat and the thickness of the material.

Assuming that a material is homogeneous, this type

of resistance can be calculated by the following can be calculated by the following

formulaformula.

kd /R

（ 2 ） Surface resistances 表面热阻 The thermal resistance of an open surface depends upon t

he conduction, convection and radiation at that surface.

Some useful values are given in table 3.5**are given in table 3.5**

Factors which affect surface resistance are given beloware given below

Direction of heat flow: upward or downward

Climatic effects: sheltered or exposed

Surface properties: normal building materials with high emi

ssivity or polished metal with low emissivity.

（ 3 ） Airspace resistances 空气间层热阻

The thermal resistance of an airspace

or empty cavity depends on the nature

of any conduction, convection and

radiation within the cavity. useful airspace resistances are given in table 3.5 P47 Factors affecting airspace resistance are given below Thickness of the airspace Flow of air in airspace ； ventilated or unventilated Lining （衬里 , 内层） of airspace ； normal surfaces

or reflective surfaces of low emissivity.

Total thermal resistances The thermal resistances of the consecutive （连续的） la

yers in a structural element, such as a wall or roof, can be likened to electrical resistances connected in seriesin series. （串联）

Thus the total thermal resistance is the sum of the thermal resistance of all components in a structural element.

3.2.4 Calculation of U-values3.2.4 Calculation of U-values

The thermal transmittance , or U-values, is the is the

reciprocal ofreciprocal of the total thermal resistance and can can

be calculated using the following formulabe calculated using the following formula

TR

1U

soa21si RR...RR

1U

R

Worked example 3.1

Calculate the U-value of a cavity wall （空心墙体空心墙体） with a 105mm(millimetre millimetre ) thick brick out leaf （外外砖墙砖墙） , a 75mm unventilated cavity containing 50mm of fibreglass quilt, then a 100mm lightweight concrete block inner leaf （内砖墙内砖墙） with a 15mm layer of lightweight plaster （轻质石膏板轻质石膏板） . The thermal conductivities in W/m K are: brickwork 0.84, lightweight concrete block 0.19, lightweight plaster 0.16, fibreglass 0.04. standard thermal resistances in m2K / W are: internal surface 0.123, external surface 0.055, cavity 0.18

Step 1:Step 1: sketch a figure indicating all parts of sketch a figure indicating all parts of the construction with surface layersthe construction with surface layers

kd /R

soa21si RR...RR

1U

R

Step 2:Step 2: tabulate all information and ,where tabulate all information and ,where necessary ,calculate thermal resistance using necessary ,calculate thermal resistance using

注意作图，分母是热阻， 不要带入导热率注意作图，分母是热阻， 不要带入导热率Work to a final accuracy of 2 decimal places结果精确到小数点后两位Lay the calculation out in a table

Step 3:Step 3: using using

3.2.5 U-values of floors3.2.5 U-values of floors

Heat losses through the floor are highest near the exposed edges of the floor,

Heat losses are lowest near the centre of the floor.

The calculation of the actual U-values for ground floors is complex and it is useful to use table or graphs to find the minimum thickness of insulation needed to meet a particular average standard required by regulations.

For some large buildings the standard may be achieved without the use of insulation because the ratio of exposed floors edges to total area is proportionally small.

3.2.6 Adjustments to U-values3.2.6 Adjustments to U-values

It is sometimes necessary to calculate the effect that

additional insulating material has upon a U-value,

or to calculate the thickness of material that is required

to produce a specified U-value.

Use the following guidelines to make adjustments

U-values can can not not be added together or subtracted be added together or subtracted

from one anotherfrom one another

Thermal resistances can be added and subtractedcan be added and subtracted.

Worked example 3.2 illustrates the technique.

A certain uninsulated cavity wall has a U-value of 0.91

W/m2K. If expanded polyurethane( 聚亚安酯 )board is i

ncluded in the construction what minimum thickness of

this materials is required to reduce the U-value to 0.45

W/m2K? Given that the thermal conductivity of the exp

anded polyurethane = 0.025W/mK.

Target U-value U2=0.45

Target total resistance(1/U) R2=1/0.45=2.222

Existing U-value U1=0.91

Existing total resistance(1/U) R1=1/0.91=1.099

Extra resistance required （所需的额外热阻） R2-R1=2.222-1.099=1.123

the k-value of proposed insulating material k=0.025

So using formula R=d/kSo using formula R=d/k

Thickness of material d=RXk=1.123X0.025=0.028metres=28mm

So minimum thickness of insulating board needed to give 0.45U-value=28mm

日期： 2005-6-10 8:48:27 来源 : 每到冬天，住在天天家园的崔女士就会为卧室墙角滴水的事犯愁。昨天，天天家园开发商代表汪先生已答应尽快帮崔女士解决卧室墙角结露的问题。 结露现象已有三年 记者在崔女士家的卧室内看到，屋顶墙角上布满了黄豆大小的水滴，侧面墙壁上也出现了淡黄色的水痕，有的地方甚至发霉了。崔女士说，她搬到这儿已经三年了，每年 11月初到次年的 2月都会出现这种情况。 “我家现在不但不敢装修，就连柜子里的棉被都发霉了。”崔女士告诉记者，自从前年冬天发现卧室墙角有结露现象后，她一直用毛巾进行擦拭，“最严重的时候，柜子后边的墙壁都是湿的，跟澡堂子似的。”崔女士怀疑是室内空气遇冷后在墙角凝结成水滴，“周围的邻居都没有出现过这种情况。”

实例：墙角结露卧室像澡堂 设计方施工方各有说法实例：墙角结露卧室像澡堂 设计方施工方各有说法

3.3 Thermal bridges, cold bridges3.3 Thermal bridges, cold bridges 热桥、冷桥热桥、冷桥 A thermal bridgethermal bridge is a portion of a structure whose hig

h thermal conductivity lowers the overall thermal insul

ation of the structure.

There is increased heat flow across the thermal bridge

and the surfaces on the interior side of the bridge ther

efore become cooler, giving rise to the informal term of

“cold bridgecold bridge”.

There is an increased risk of condensation and mould

growth （发霉） on these internal surfaces around col

d bridges.

房子 "冒汗 "-"冷桥 " 现象的处理与维护 热桥以往又称冷桥，现统一定名为热桥。热桥是指处在外墙

和屋面等围护结构中的钢筋混凝土或金属梁、柱、肋等部位。因这些部位传热能力强，热流较密集，内表面温度较低，故称为热桥。

由于热桥部位内表面温度较低，寒冬期间，该处温度低于露点温度时，水蒸气就会凝结在其表面上，形成结露。此后，空气中的灰尘容易沾上，逐渐变黑，从而长菌发霉。热桥严重的部位，在寒冬时甚至会淌水，对生活和健康影响很大。

通风 \ 加热 \保温 \赔偿

石材内部产生的冷凝水积聚 石材内部产生的冷凝水积聚

Pattern staining Pattern staining 暗斑暗斑

Pattern staining on a ceiling is the formation of a pattern , in dirt or dust, which outlines the hidden structure of the ceiling.

It is aIt is a particular result ofresult of thermal bridging and also depends upon the frequency of redecoration（再次装修） .

Pattern 模范 , 式样 , 图案 Staining 着色

Average U-valuesAverage U-values

If a wall, or other element , is composed of different constructions with different U-values then the overall insulation of the wall depends upon the relative areas of the different constructions.

The general formula is as follows

...AA

.....UAUAU(average)

21

2211

Worked example

A wall has a total area of 8 m2 of which 2m2 are windows. The U-values are 0.35 W/m2K for the cladding(覆层 )and 2.8W/m2K for the glazing. Calculate the average U-value for the wall.

...AA

.....UAUAU(average)

21

2211

96.08

8.2235.06U

3.4 Structural temperature 结构温度

The thermal insulation installed in a building affects

the rate at which the building loses heat energy

which is measured by the U-value.

The thermal performance of the building also

depends upon the thermal capacity of the insulating

material, which affects the times taken to heat or

cool the structure,

and the position of the insulation, which affects the

temperatures in the structural elements

3.4.1 Response times 响应时间

.

In general, lightweight structures respond more quickly to surrounding temperature changes than do heavyweight structure .This is because heavyweight materials have a higher thermal capacity and require more heat energy to produce given temperature changes

Figure 3.6

thermal response

A structure made up of different materials,

will have varying temperature gradients between the inside and

outside

The boundary temperatures between layers in a structural elem

ent can be determined from the thermal resistances which mak

e up the U-value of that element

The ratio of the temperature changes inside a structure is p

roportional to the ratio of the thermal resistance.

TT R

R

Worked example 3.5

A room has an external wall with a U-value of 1.5 W/m2K and contains air at 20 when the outside temperature is ℃5 . The internal surface resistance is 0.123 ℃ ㎡ K/W. calculate the boundary temperature on the internal surface of the wall.

inside temperature= 20 ℃ outside temperature= 5 ℃ resistance of that layer R= 0.123 ㎡ K/W

total resistance of the structure RT=1/U=1/1.5=0.667Using ⊿=2.77 So temperature on the inside surface=20-2.77=17.23 ℃

TT R

R

Chapter 3 Thermal InsulationChapter 3 Thermal Insulation

3.1 Insulating materials 3.1 Insulating materials 绝热材料绝热材料3.1.1 Types of insulator3.1.1 Types of insulator3.1.2 Properties of insulators3.1.2 Properties of insulators3.1.3 Thermal conductivity , k-value 3.1.3 Thermal conductivity , k-value 3.1.4 Emissivity and absorptivity 3.1.4 Emissivity and absorptivity 3.1.5 Clear sky radiation 3.1.5 Clear sky radiation 晴空辐射晴空辐射3.2 U-values3.2 U-values 3.2.1 Thermal transmittance ,U-value3.2.1 Thermal transmittance ,U-value3.2.2 Elemental U-values 3.2.2 Elemental U-values 3.2.3 Thermal resistances3.2.3 Thermal resistances3.2.4 Calculation of U-values3.2.4 Calculation of U-values3.2.5 U-values for floors3.2.5 U-values for floors3.2.6 Adjustments to U-values3.2.6 Adjustments to U-values

3.3 Thermal Bridging3.3 Thermal Bridging3.3.1 Thermal bridge3.3.1 Thermal bridge3.3.2 cold bridges3.3.2 cold bridges3.3.3 pattern staining3.3.3 pattern staining3.3.4 average U-values3.3.4 average U-values

3.4 Structural Temperature3.4 Structural Temperature3.4.1 response time3.4.1 response time3.4.2 temperature gradients3.4.2 temperature gradients

That’s all for chapter 3 Since there’s time, please read the text

carefully and try to find the main points in chapter 3.

If you have questions, you can ask me.

some useful sentence patterns

影响 xxx 的因素如下：Factors which affect xxx are given below影响表面热阻的因素如下影响空气层热阻的因素如下

表 3.5给出了一些常用的 xxx 值Some useful xxx are given in table 2.5 表 3.5给出了一些有用的空气热阻值 表 3.5给出了一些常用结构的 U 值

xxx 是 yyy 的倒数xxx is the reciprocal of yyy 传热系数是总热阻的倒数

xxx 可用下式计算 xxx can be calculated using the following for

mula 传热系数可用下式计算

最终结果精确到小数点后 xx 位 Work to a final accuracy of xx decimal places最终结果精确到小数点后 2 位最终结果精确到小数点后 3 位列表计算 Lay the calculation out in a table

Exercises in class

1 Benefits of good thermal insulation ?( )1 Benefits of good thermal insulation ?( )A to maintain a constant temperature within a buildingA to maintain a constant temperature within a buildingB to reduce the heat exchange with the surroundingsB to reduce the heat exchange with the surroundingsC to save energy needed to run the cooling plantC to save energy needed to run the cooling plantD to save energy needed to run the heating plantD to save energy needed to run the heating plantE to reduce the risk of surface condensationE to reduce the risk of surface condensationF to reduce the time taken for a room to heat up to a F to reduce the time taken for a room to heat up to a

comfortable temperaturecomfortable temperatureG energy conversationG energy conversation

2 Rough black surfaces( )2 Rough black surfaces( )

A absorb most heat

B emit most heat.

C absorb least heat

D emit least heat

3 Shiny silvered surfaces ( )3 Shiny silvered surfaces ( )

A absorb most heat

B emit most heat.

C absorb least heat

D emit least heat

4 ( ) is a measure of the overall rate of heat 4 ( ) is a measure of the overall rate of heat transfer ,by all mechanisms under standard condtransfer ,by all mechanisms under standard conditions, through a particular section of constructioitions, through a particular section of constructionn

A a U-value

B a r-value

C a R-value

D a lamda-value

5 ( ) gives better thermal insulation5 ( ) gives better thermal insulation

A higher thermal resistance

B higher U-value

C lower thermal resistance

D lower U-value

6 ( ) be added together or subtracted fr6 ( ) be added together or subtracted fr

om one anotherom one another

A U-values

B R-values

C r-values

D lamda-values