建筑環(huán)境學(xué)chapter41-2 thermal comfortable (9)

1、lThermal insulation reducing the loss of heat from buildings. lIt 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. l黃帝宅經(jīng)黃帝宅經(jīng) l治宅極宜壯實治宅極宜壯實 意大利羅馬萬神廟 3.1 Insulating materials 絕熱材料絕

2、熱材料 3.2 U-values U-值值 3.3 Thermal Bridging 熱橋熱橋 3.4 Structural temperature 結(jié)構(gòu)溫度結(jié)構(gòu)溫度 four topics are discussed in this chapter 3.1 Insulating materials 保溫材料（熱絕緣材料）保溫材料（熱絕緣材料） lA thermal insulator is a material which opposes（） the transfer of heat between areas at different temperatures. l室溫條件下，導(dǎo)熱系數(shù)小于

3、0.12w/mk的材料 lThe best insulating materials tend to be porous（ ） and of low density. lGas, are the best insulators against conduction. lAir, which is a mixture of gases, is the basis of insulators such as aerated lightweight concrete（ ）, expanded plastics（）, and cavities（）. lFor air to act as an insu

4、lator it must be otherwise moving air if allowed to move will transfer heat by convection. : aerated concrete blocks : fibreglass quilts : expanded polystyrene granules : foamed polyurethane : aluminium foil When choosing materials for thermal insulation of buildings the physical properties of the m

5、aterial need to be considered. uThermal insulation suitable for the purpose. uStrength （）or rigidity（） suitable for the purpose. uMoisture resistance. （） uFire resistance. （） uResistance to pests and fungi.（） uCompatibility） with adjacent materials uHarmless to humans and the environment. thermal co

6、nductivity Unit: W/m K ( W/m) Referring to figure3.1 the general formula is: P39 d )(kA t H 21 Resistivity 熱阻熱阻 lResistivity （r）is an alternative index of conduction is the reciprocal of（成反比）（成反比） thermal conductivity, so that r = 1/lamda lThe thermal conductivities of some building materials are gi

7、ven in table 3.1. lThe thermal conductivity of practical building materials Varies with moisture content as the presence of water increases conduction. lVariations in density have significant effects on the k-values of brickwork, concrete and stone and more comprehensive tables of thermal conductivi

8、ties should be used to obtain specific values. the ability of a material to absorb or give off radiant heat is a property of the surface of the material. lRough black surfaces absorb most heat and emit most heat. lConversely, shiny slivered surfaces absorb least heat and emit least heat. 黑體：黑體：是指能吸收

9、投入到其面上是指能吸收投入到其面上 的所有熱輻射能的物體，是一種的所有熱輻射能的物體，是一種 科學(xué)假想的物體，現(xiàn)實生活中是科學(xué)假想的物體，現(xiàn)實生活中是 不存在的。但卻可以人工制造出不存在的。但卻可以人工制造出 近似的人工黑體。近似的人工黑體。 黑體模型黑體模型 energy radiated by a body compared that radiated by a black body at the same temperature ( ) by a body compared that ( ) by a black body lAt night time a building emits

10、radiant heat to its surroundings and the rate of this heat loss from the roof will be increased if the night sky is clear and cloudless. lThis radiant “suck”(） occurs because a clear dark sky is closer in form to a black body The same radiant mechanism causes dew(露露)or ground frost to occur during a

11、 clear starry (布滿星星的布滿星星的) night. 人環(huán)獎試題：人環(huán)獎試題： 晴天清晨樹葉最容易結(jié)霜，原因是（ ） A、空氣的溫度下降低于露點溫度 B、空氣的溫度下降達到露點溫度 C、樹葉表面的溫度下降低于濕球溫度 D、樹葉表面的溫度下降低于露點溫度 Now the next topic 3.2 U-values lUnit : W/m2K (W/m2) lThe rate of heat flow in watts through 1m2 of a structure when there is a temperature difference across the stru

12、cture of 1 lLower U-values provide better thermal insulation. l圍護結(jié)構(gòu)的傳熱系數(shù)表示圍護結(jié)構(gòu)兩側(cè)空氣溫度差為圍護結(jié)構(gòu)的傳熱系數(shù)表示圍護結(jié)構(gòu)兩側(cè)空氣溫度差為1 1，單位時，單位時 間通過間通過1m1m2面積傳遞的熱量。面積傳遞的熱量。 l數(shù)值上，它等于圍護結(jié)構(gòu)傳熱阻的倒數(shù)。數(shù)值上，它等于圍護結(jié)構(gòu)傳熱阻的倒數(shù)。 lStandard U-values are calculated by making certain assumptions about moisture contents of materials and about ra

13、tes of heat transfer at surfaces and in cavities. lnot always agree exactly with U-values measured on site. lthe values for （some common types of construction）are given in table 3.3 Figure 3.1 Maximum U-values for new dwellings McMullan Rooflight _采光天窗 lUnit : m2K/w lHigher thermal resistance gives

14、better thermal insulation lThere are there general types of thermal resistance which need to be determined , either by calculation or by seeking published standard values. （1）Material resistances 材料熱阻材料熱阻 （2）Surface resistances 表面熱阻表面熱阻 （3）Airspace resistances 空氣間層熱阻空氣間層熱阻 （1）Material resistances材料熱

15、阻材料熱阻 lAssuming that a material is homogeneous均勻的均勻的, this type of resistance . kd /R （2）Surface resistances表面熱阻表面熱阻 lThe thermal resistance of an open surface depends upon the conduction, convection and radiation at that surface. lSome useful values Factors which affect surface resistance Direction

16、 of heat flow: upward or downward Climatic effects: sheltered or exposed Surface properties: normal building materials with high emissivity or polished metal with low emissivity. 表面?zhèn)鳠嵯禂?shù)？H？ note lInside surface 0.12 lOutside surface 0.06 （3）Airspace resistances 空氣間層熱阻空氣間層熱阻 lThe thermal resistance of

17、 an airspace or empty cavity depends on the nature of any conduction, convection and radiation within the cavity. luseful airspace resistances are given in table 3.5 P47 lFactors affecting airspace resistance are given below Thickness of the airspace Flow of air in airspace ； ventilated or unventila

18、ted Lining（襯里襯里, 內(nèi)層內(nèi)層）of airspace； normal surfaces or reflective surfaces of low emissivity. 封閉的空氣間層用處多（補充） l不僅具有良好的絕熱作用，而且具有很好的防潮性能。不僅具有良好的絕熱作用，而且具有很好的防潮性能。 l因為在空氣層中，只要兩側(cè)有溫差存在，由于溫差驅(qū)使，因為在空氣層中，只要兩側(cè)有溫差存在，由于溫差驅(qū)使， 產(chǎn)生產(chǎn)生convectionconvection，高溫側(cè)空氣始終保持較低的，高溫側(cè)空氣始終保持較低的RHRH，低溫側(cè)，低溫側(cè) 空氣始終保持較高的空氣始終保持較高的RHRH，只要兩側(cè)

19、有，只要兩側(cè)有temperature temperature difference, difference, 則高溫側(cè)則高溫側(cè)RHRH100%100%，由此可保證與空氣層高溫，由此可保證與空氣層高溫 側(cè)接觸的材料用不受潮。側(cè)接觸的材料用不受潮。 l如何提高封閉空氣間層的熱阻？如何提高封閉空氣間層的熱阻？ l用于保溫作用的空氣層通常設(shè)在圍護結(jié)構(gòu)的冷側(cè)，熱側(cè)？用于保溫作用的空氣層通常設(shè)在圍護結(jié)構(gòu)的冷側(cè)，熱側(cè)？ 為什么？為什么？ 11、為了改善夏季熱環(huán)境，雙層玻璃窗溫度會升 高，影響室內(nèi)熱舒適（ ） A、應(yīng)該通風(fēng)，否則內(nèi)層玻璃溫度會升高，影響 室內(nèi)熱舒適 B、應(yīng)該通風(fēng)，這樣可以有效帶走太陽輻射的熱

20、量，減少向室內(nèi)傳熱量 C、不應(yīng)該通風(fēng)，因為這樣會增加空調(diào)濕負荷 D、不應(yīng)該通風(fēng)，因為這樣會降低玻璃窗的熱阻 15、在北方地區(qū)用玻璃封閉了南向陽臺會使房間 （ ） A、冬天變暖，夏天變涼 B、冬天變涼，夏天變暖 C、冬、夏均變暖 D、冬、夏均變涼 Total thermal resistances lThus the total thermal resistance is the sum of the thermal resistance of all components in a structural element. Rock wool 巖棉 圍護結(jié)構(gòu)最小總熱阻（補充）圍護結(jié)構(gòu)最小總熱阻（

21、補充） l民用建筑熱工設(shè)計規(guī)范中，從控制圍護結(jié)構(gòu)內(nèi)表面溫度不 低于室內(nèi)露點溫度，保證內(nèi)表面不致 結(jié)露的起碼要求出 發(fā)，為滿足使用者的最基本衛(wèi)生要求，提出圍護結(jié)構(gòu)熱阻 不能小于某個最低限度值 l圍護結(jié)構(gòu)的最小傳熱阻 l圍護結(jié)構(gòu)的實際熱阻可以高于它，但不能低于它 The thermal transmittance , or U-values, the total thermal resistance and T R 1 U soa21si RR.RR 1 U R Worked example 3.1 lCalculate the U-value of a cavity wall（） with a

22、105mm() thick brick out leaf（ ）, a 75mm unventilated cavity containing 50mm of fibreglass quilt, then a 100mm lightweight concrete block inner leaf （）with a 15mm layer of lightweight plaster（）. The thermal conductivities in W/m K are: brickwork 0.84, lightweight concrete block 0.19, lightweight plas

23、ter 0.16, fibreglass 0.04. standard thermal resistances in m2K / W are: internal surface 0.123, external surface 0.055, cavity 0.18 kd /R soa21si RR.RR 1 U R Work to a final accuracy of 2 decimal places 結(jié)果精確到小數(shù)點后兩位結(jié)果精確到小數(shù)點后兩位 Lay the calculation out in a table The calculation of the actual U-values

24、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. lFor some large buildings the standard may be achieved without the use of insulation because the ratio of exposed flo

25、ors edges to total area is proportionally small. 1）calculate the effect that additional insulating material has upon a U-value, 2） calculate the thickness of material that is required to produce a specified U-value. lUse the following guidelines to make adjustments lU-values lThermal resistances . W

26、orked example 3.2 illustrates the technique. lA certain uninsulated cavity wall has a U-value of 0.91W/m2K. If expanded polyurethane(聚亞安酯聚亞安酯)board is included 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 conduc

27、tivity of the expanded 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 （所需的額外熱阻所需的額外熱阻） R2-R1=2.222-1.099=1.123 the k-value of proposed insulating material

28、k=0.025 Thickness of material d=RXk=1.123X0.025=0.028metres=28mm So minimum thickness of insulating board needed to give 0.45U-value=28mm Exercises in class 1 The thermal resistance of an open surface depends upon the ( ) at that surface. A conduction B convection C radiation D Thickness of the airs

29、pace 2 There are there general types of thermal resistance which need to be determined , either by calculation or by seeking published standard values. A Material resistances B Surface resistances C structure resistances D Airspace resistances 3 This picture is related to ( ) A stack effect B greenh

30、ouse effect C clear sky radiation D altitude 4 The thermal conductivity of practical building materials Varies with ( ) lA moisture content lB mass lC volume lD density 3.1 Insulating materials 絕熱材料絕熱材料 3.2 U-values U-值值 3.3 Thermal Bridging 熱橋熱橋 3.4 Structural temperature 結(jié)構(gòu)溫度結(jié)構(gòu)溫度 日期：日期：2005-6-10 8

31、:48:27 來源來源: 每到冬天，住在天天家園的崔女士就會為臥室墻角滴水的事犯每到冬天，住在天天家園的崔女士就會為臥室墻角滴水的事犯 愁。昨天，天天家園開發(fā)商代表汪先生已答應(yīng)盡快幫崔女士解決臥愁。昨天，天天家園開發(fā)商代表汪先生已答應(yīng)盡快幫崔女士解決臥 室墻角結(jié)露的問題。室墻角結(jié)露的問題。 結(jié)露現(xiàn)象已有三年結(jié)露現(xiàn)象已有三年 記者在崔女士家的臥室內(nèi)看到，屋頂墻角上布滿了黃豆大小的記者在崔女士家的臥室內(nèi)看到，屋頂墻角上布滿了黃豆大小的 水滴，側(cè)面墻壁上也出現(xiàn)了淡黃色的水痕，有的地方甚至發(fā)霉了。水滴，側(cè)面墻壁上也出現(xiàn)了淡黃色的水痕，有的地方甚至發(fā)霉了。 崔女士說，她搬到這兒已經(jīng)三年了，每年崔女士說，

32、她搬到這兒已經(jīng)三年了，每年11月初到次年的月初到次年的2月都會月都會 出現(xiàn)這種情況。出現(xiàn)這種情況。 “我家現(xiàn)在不但不敢裝修，就連柜子里的棉被都發(fā)霉了。我家現(xiàn)在不但不敢裝修，就連柜子里的棉被都發(fā)霉了?！贝夼夼?士告訴記者，自從前年冬天發(fā)現(xiàn)臥室墻角有結(jié)露現(xiàn)象后，她一直用士告訴記者，自從前年冬天發(fā)現(xiàn)臥室墻角有結(jié)露現(xiàn)象后，她一直用 毛巾進行擦拭，毛巾進行擦拭，“最嚴(yán)重的時候，柜子后邊的墻壁都是濕的，跟澡最嚴(yán)重的時候，柜子后邊的墻壁都是濕的，跟澡 堂子似的。堂子似的?！贝夼繎岩墒鞘覂?nèi)空氣遇冷后在墻角凝結(jié)成水滴，崔女士懷疑是室內(nèi)空氣遇冷后在墻角凝結(jié)成水滴， “周圍的鄰居都沒有出現(xiàn)過這種情況。周圍的鄰居

33、都沒有出現(xiàn)過這種情況?！?lA is a portion of a structure whose high thermal conductivity lowers the overall thermal insulation of the structure. lThere is increased heat flow across the thermal bridge and the surfaces on the interior side of the bridge therefore become cooler, giving rise to the informal term of

34、 “”. lThere is an increased risk of condensation and mould growth （發(fā)霉發(fā)霉）on these internal surfaces around cold bridges. lThermal bridges Thermal bridges 熱量容易通過的地方，內(nèi)表面溫度往往低于主體熱量容易通過的地方，內(nèi)表面溫度往往低于主體 部分。部分。 房子房子冒汗冒汗-冷橋冷橋現(xiàn)象的處理與維護現(xiàn)象的處理與維護 l熱橋以往又稱冷橋，現(xiàn)統(tǒng)一定名為熱橋。熱橋以往又稱冷橋，現(xiàn)統(tǒng)一定名為熱橋。 l熱橋是指處在外墻和屋面等圍護結(jié)構(gòu)中的熱橋是指處在外墻和屋

35、面等圍護結(jié)構(gòu)中的鋼筋混凝土或金屬梁、鋼筋混凝土或金屬梁、 柱、肋等部位柱、肋等部位。因這些部位傳熱能力強，熱流較密集，內(nèi)表面溫。因這些部位傳熱能力強，熱流較密集，內(nèi)表面溫 度較低，故稱為熱橋。度較低，故稱為熱橋。 l常見的熱橋有常見的熱橋有: 1 1 圈梁是連續(xù)圍合的梁所以叫做圈梁圈梁是連續(xù)圍合的梁所以叫做圈梁 lFigure 3.5 Thermal bridges lCantilevered concrete floor 懸臂混凝土地板 lBoot lintel over window 窗戶過梁 Pattern staining on a ceiling is the formation o

36、f a pattern , in dirt or dust, which outlines the hidden structure of the ceiling. particular thermal bridging and also depends upon the frequency of redecoration（再次裝修再次裝修）. lPattern 模范, 式樣,圖案 lStaining 著色 房子房子 冒汗冒汗-冷橋冷橋 現(xiàn)象的處理與維護現(xiàn)象的處理與維護 l通風(fēng)通風(fēng)加熱加熱保溫保溫賠償賠償 l保溫結(jié)構(gòu)按保溫層所處的位置可分為：保溫結(jié)構(gòu)按保溫層所處的位置可分為： 內(nèi)保溫內(nèi)保溫保溫

37、層在室內(nèi)一側(cè)保溫層在室內(nèi)一側(cè) 外保溫外保溫保溫層在室外一側(cè)保溫層在室外一側(cè) 中間保溫中間保溫保溫層在中間夾心保溫層在中間夾心 從保溫節(jié)能的角度看，外保溫的優(yōu)點較多，更利于從保溫節(jié)能的角度看，外保溫的優(yōu)點較多，更利于 防止熱橋防止熱橋 國內(nèi)外都極力主張發(fā)展外保溫圍護結(jié)構(gòu)國內(nèi)外都極力主張發(fā)展外保溫圍護結(jié)構(gòu) 但內(nèi)保溫往往施工方便但內(nèi)保溫往往施工方便 中間保溫則有利于松散填充材料作保溫層中間保溫則有利于松散填充材料作保溫層 Thermal insulation: how to improve thermal insulation ? 如何提高圍護結(jié)構(gòu)保溫性能如何提高圍護結(jié)構(gòu)保溫性能? lControl

38、 thermal transmittance 控制傳熱系數(shù)值 lThermal bridge insulation 熱橋保溫 l在民用建筑節(jié)能設(shè)計標(biāo)準(zhǔn)和夏熱冬冷地 區(qū)居住建筑節(jié)能標(biāo)準(zhǔn)中對不同地區(qū)采暖居住 建筑各部分圍護結(jié)構(gòu)傳熱系數(shù)作了限定。 l 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 diffe

39、rent constructions. The general formula is as follows .AA .UAUA U(average) 21 2211 Worked example lA wall has a total area of 8 m2 of which 2m2 are windows. The U-values are 0.35 W/m2K for the cladding(覆層覆層)and 2.8W/m2K for the glazing. Calculate the average U-value for the wall. .AA .UAUA U(average

40、) 21 2211 96. 0 8 8 . 2235. 06 U 3.4 Structural temperature 結(jié)構(gòu)溫度結(jié)構(gòu)溫度 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 熱容of the insul

41、ating 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 響應(yīng)時間響應(yīng)時間 l. In general, lightweight structures respond more quickly to surrounding temperature changes than

42、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 lA structure made up of different materials, lwill have varying temperature gradients between the inside and o

43、utside lThe boundary temperatures between layers in a structural element can be determined from the thermal resistances which make up the U-value of that element lThe ratio of the temperature changes inside a structure is proportional to the ratio of the thermal resistance. TT R R Worked example 3.5

44、 lA 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. l inside temperature= 20 outside temperature= 5 resistance of tha

45、t layer R= 0.123K/W total resistance of the structure RT=1/U=1/1.5=0.667 Using l=2.77 lSo temperature on the inside surface=20-2.77=17.23 TT R R TT R R Exercises in class The thermal performance of the building also depends upon( ) lA thermal transmittance lB thermal capacity lC thermal bridge lD the position of the insulation 設(shè)備師考題設(shè)備師考題 l冬季在同一室內(nèi)溫度條件下，A墻體總熱阻比B墻體大， 則（ ） A A 墻體外表面溫度高 B B墻體外表面溫度高 C A墻體內(nèi)表面溫