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1、4.3 Heat losses 失热量失热量4.3.1 Factors affecting heat loss影响建筑失热量的因素影响建筑失热量的因素Figure 3.1 Heat losses from a buildingFabric heat lossFabric heat loss 结构失热量结构失热量Ventilation loss Ventilation loss 通风失热量通风失热量Factors affecting heat losses影响建筑失热量的因素影响建筑失热量的因素1)insulation of shell 建筑外围护结构的保温Good insulation dec
2、reases the heat losses好的保温削减建筑失热量Poorly-insulated increase the heat losses 保温不好增加建筑的失热量2)area of the shell 建筑外围护结构的面积建筑外围护结构的面积A terraced house排房排房 and a detached house独立式住宅独立式住宅Which one loses less heat?Table 4.73）temperature difference between inside and outside 建筑内外的温差建筑内外的温差lLarge temperature di
3、fference increases the heat losses by conduction and ventilation.lMainly depend on the design temperature for the inside air.lRecommended comfort temperature for different types of buildings are given in table 4.54)Air change rate 换气次数换气次数lWarm air leaving a building carries heat and is replaced by
4、cold airlTable 4.5 gives typical rates of air infiltration 5)Exposure to climate 建筑的暴露状况 External surface resistance 外表面热阻Three types of exposure Sheltered:受遮挡 Buildings up to 3 storeys in city centres.Normal:正常 Most suburban and country buildingsSevere:严峻 Buildings on exposed hills or coastal sites
5、.山坡或海边的建筑 Floors above the fifth in suburban or country sites.市郊或农村的5层以上建筑 Floors above the ninth in city centres.市中心九层以上建筑6）efficiency of services 设备的效率设备的效率lFlue is positioned inside the building Flue is positioned inside the building lFlue is positioned on an external wall7)Patterns of use 建筑运用模式
6、lThe number of hours per day and the days per year that a building is used have a large effect on the energy consumption of a buildings lEach parts needs to be considered as a separated building for the heating calculations.4.3.2 Calculation of heat loss失热量计算失热量计算l lFabric heat lossFabric heat loss
7、结构失热量 walls,windows,roofs and floors.steady state conditions,稳态条件稳态条件 稳态计算法：不考虑建筑物以前时刻传热过程的影响，只稳态计算法：不考虑建筑物以前时刻传热过程的影响，只接受室内外瞬时或平均温差与围护结构的传热系数、传热接受室内外瞬时或平均温差与围护结构的传热系数、传热面积的积来求负荷面积的积来求负荷Applied in the following cases:l蓄热性能小的轻型、简易围护结构的传热过程，可用逐时蓄热性能小的轻型、简易围护结构的传热过程，可用逐时室内外温差乘以传热系数和传热面积近似计算室内外温差乘以传热系数和
8、传热面积近似计算l室内外温差的平均值远远大于室内外温度的波动值时，接室内外温差的平均值远远大于室内外温度的波动值时，接受平均温差的稳态计算带来的误差也比较小，在工程设计受平均温差的稳态计算带来的误差也比较小，在工程设计中是可以接受的。中是可以接受的。Ventilation loss 通风失热量通风失热量P73Pv=rate of ventilation heat loss (W)Cv=volumetric specific heat capacity of air(1300J/m3K)N=air infiltration rate for the room(air changes per ho
9、ur)V=volume of the room(m3)t=air temperature difference between the inside and outsideExternal temperature 室外温度室外温度l lIn winter:In winter:=outside air temperature for design purpose=outside air temperature for design purposelit is necessary to take account of solar radiation as well as air temperatu
10、re.l lIn summer:In summer:=sol-air temperature t=sol-air temperature teoeol Sol-air temperature（室外空气综合温度）（室外空气综合温度）1 1 围护结构外表面的热平衡图围护结构外表面的热平衡图 1 1）对流换热量）对流换热量2 2）太阳辐射）太阳辐射 太阳直射辐射太阳直射辐射 天空散射辐射天空散射辐射 地面反射辐射地面反射辐射3 3）长波辐射换热量）长波辐射换热量与大气之间的长波辐射与大气之间的长波辐射与环境表面之间的长波辐射与环境表面之间的长波辐射与地面的长波辐射与地面的长波辐射太阳太阳太阳太阳直射
11、直射直射直射辐辐辐辐射射射射大气大气大气大气长长长长波波波波辐辐辐辐射射射射太空太空太空太空散射散射散射散射辐辐辐辐射射射射对对对对流流流流换换换换热热热热地面反射地面反射地面反射地面反射辐辐辐辐射射射射环环环环境境境境长长长长波波波波辐辐辐辐射射射射地面地面地面地面长长长长波波波波辐辐辐辐射射射射壁体得壁体得壁体得壁体得热热热热式中式中 建筑物外表面单位面积上得到的热量，建筑物外表面单位面积上得到的热量，W/m2W/m2 围护结构外表面的对流换热系数，围护结构外表面的对流换热系数，W/m2W/m2 室外空气温度，室外空气温度，围护结构外表面温度，围护结构外表面温度，围护结构外表面对太阳辐射的
12、吸取率围护结构外表面对太阳辐射的吸取率 太阳辐射照度，太阳辐射照度，W/m2W/m2 围护结构外表面与环境表面的长波辐射换热量，围护结构外表面与环境表面的长波辐射换热量，W/m2W/m2太阳太阳太阳太阳直射直射直射直射辐辐辐辐射射射射大气大气大气大气长长长长波波波波辐辐辐辐射射射射太空太空太空太空散射散射散射散射辐辐辐辐射射射射对对对对流流流流换换换换热热热热地面反射地面反射地面反射地面反射辐辐辐辐射射射射环环环环境境境境长长长长波波波波辐辐辐辐射射射射地面地面地面地面长长长长波波波波辐辐辐辐射射射射壁体得壁体得壁体得壁体得热热热热2 2 建筑物外表面单位建筑物外表面单位面积上得到的热量：面积
13、上得到的热量：白天：太阳辐射强度长波辐射，可忽视长波辐射作用白天：太阳辐射强度长波辐射，可忽视长波辐射作用夜间：没有太阳辐射的作用，天空的背景温度夜间：没有太阳辐射的作用，天空的背景温度 空气温度，不空气温度，不 可忽视建筑物向天空的长波辐射可忽视建筑物向天空的长波辐射 特殊是冬季夜里忽视天空辐射可能导致对热负荷的估计特殊是冬季夜里忽视天空辐射可能导致对热负荷的估计 过低过低 Qlw Qlw 也被称为夜间辐射或有效辐射也被称为夜间辐射或有效辐射人环奖试题：人环奖试题：室外空气温度升降的缘由是（室外空气温度升降的缘由是（）A、空气在白天接受太阳辐射而升温，夜间向天、空气在白天接受太阳辐射而升温，
14、夜间向天空进行长波辐射而降温空进行长波辐射而降温B、空气因与地面传热而白天升温、夜间减温、空气因与地面传热而白天升温、夜间减温C、空气在白天接受太阳辐射而升温，夜间则由、空气在白天接受太阳辐射而升温，夜间则由于海陆风导致降温于海陆风导致降温D、由于日、夜风的流向不同而导致空气温度变、由于日、夜风的流向不同而导致空气温度变更更 Worked example 4.1 A window measuring 2 m by 1.25 m has an average U-value,including the frame,of 6.2 W/m2K.Calculate the rate of fabric
15、 heat loss through this window when the inside comfort temperature is 20 and the out side air temperature is 4.know U=6.2 W/m2K A=2X1.25=2.5m2t=20-4=16 using So fabric loss=248WWorked example 4.2 A simple building is 4 m long by 3 m wide by 2.5 m high.In the walls there are two windows,each 1 m by 0
16、.6 m,and there is one large door 1.75 m by o.8 m.The construction has the following U-values in W/m2K:windows 5.6,door 2.0,roof 3.0,floor 1.5.The inside environmental or comfort temperature is maintained at 18 while the outside air temperature is 6.The volumetric specific heat capacity of the air is
17、 taken to be 1300J/m3.There are 1.5 air change per hour.Calculate the total rate of heat loss for the building under the above conditions.Step1:sketch the building with its dimensions,as in figure 3.2.calculate the areas and the temperature difference.Step 2:tabulate the information and calculate th
18、e rate of fabric heat losses usingStep3:calculate the ventilation heat loss.CV=1300J/m3,N=1.5/h V=4X3X2.5=30m3,t=18-6=12 using So rate of ventilation heat loss=195WStep4:total rate of heat loss=fabric heat loss+ventilation heat loss=1734.24+195=1929.24Wl围护结构的稳态传热是指（）总传热量不变热流强度不变总热阻不变平均传热系数不变4.3.3 No
19、n-steady condition 非稳定条件非稳定条件lFor situations where the steady state assumption is invalid it is necessary to consider the effects of daily variations in the outside temperature Variations in solar radiation Changes in the internal heat inputl lThermal admittanceThermal admittance（蓄热系数）（蓄热系数）（蓄热系数）（蓄
20、热系数）or Y-valueor Y-value l lUnitUnit：W/m2KThermal transmittance Thermal transmittance 传热系数传热系数传热系数传热系数For very thin units,such as glass,the admittance For very thin units,such as glass,the admittance becomes the same as the U-value.becomes the same as the U-value.传热系数和蓄热系数是相反的概念。传热系数表示热传热系数和蓄热系数是相反的
21、概念。传热系数表示热传热系数和蓄热系数是相反的概念。传热系数表示热传热系数和蓄热系数是相反的概念。传热系数表示热传导的实力，蓄热系数表示储存热量的实力。传导的实力，蓄热系数表示储存热量的实力。传导的实力，蓄热系数表示储存热量的实力。传导的实力，蓄热系数表示储存热量的实力。Complement（补充）：（补充）：l对于一个有确定厚度的均质材料来说，假如一侧对于一个有确定厚度的均质材料来说，假如一侧的空气温度作周期性波动，那么材料层表面的温的空气温度作周期性波动，那么材料层表面的温度和热流也都要随着作同样周期的波动，此时用度和热流也都要随着作同样周期的波动，此时用表面上的热流波幅与表面温度波幅之比
22、表示材料表面上的热流波幅与表面温度波幅之比表示材料蓄热实力的大小，称为材料的蓄热系数。蓄热实力的大小，称为材料的蓄热系数。l蓄热系数大，材料的热稳定性好，材料表面的温蓄热系数大，材料的热稳定性好，材料表面的温度波幅就小度波幅就小l反之，。反之，。l它是建筑围护结构热稳定性设计不行缺少的一个它是建筑围护结构热稳定性设计不行缺少的一个重要参数重要参数Figure 4.3 Thermal responseMcMullanHeavyweight structures have smaller temperature swings(温度温度温度温度波动波动波动波动)than lightweight st
23、ructures.damping,衰减About thermal response,Lightweight structure has()A short lagB long lagC high swing D low swing E less dampingF loss damping 人环奖试题：人环奖试题：地下室的温度是（）A、春天最低B、冬天最低C、冬天比夏天低D、夏天最高It is too difficult to solve空气调整Important terms：lThermal conductivity 导热系数lThermal resistivity 比热阻lThermal re
24、sistance 热阻lThermal transmittance 传热系数lThermal admittance 蓄热系数4.4 Heat gains 建筑得热量建筑得热量Figure 4.4 Typical heat gains in a buildingMcMullantypical heat gains in a building1 1）Solar heat gains from the sunSolar heat gains from the sun 太阳辐射得热量太阳辐射得热量2 2）Casual heat gains from occupants and equipment in
25、 the Casual heat gains from occupants and equipment in the building building 室内人员和设备形成的一般得热量室内人员和设备形成的一般得热量1）Solar heat gains from the sun太阳辐射得热量太阳辐射得热量Depends on many factorsTable 4.9 seasonal solar gain through windowsSun controls to Prevent excessive heat gain and glare（眩光）caused by direct sunshi
26、ne.External controls （外遮阳）Internal controls （内遮阳）Special glasses （特殊玻璃）Complement:shading coefficient of external controls外遮阳系数：外遮阳系数：l遮阳对削减太阳辐射作用特别显著遮阳对削减太阳辐射作用特别显著l通常用外遮阳系数作为衡量遮阳效果的指标通常用外遮阳系数作为衡量遮阳效果的指标l外遮阳系数：在直射阳光照射的时间内，透进有外遮阳系数：在直射阳光照射的时间内，透进有外遮阳窗口的太阳辐射量与透进没有外遮阳窗口外遮阳窗口的太阳辐射量与透进没有外遮阳窗口的太阳辐射量之比的太阳
27、辐射量之比l系数愈小，通过窗户进入室内的太阳辐射量愈小，系数愈小，通过窗户进入室内的太阳辐射量愈小，防热效果愈好防热效果愈好遮阳的基本形式遮阳的基本形式西南朝向的外窗当需设置遮阳板时最好接受（西南朝向的外窗当需设置遮阳板时最好接受（）A A 水平式水平式B B 垂直式垂直式C C 挡板式挡板式D D 综合式综合式朝西的外窗当需设置遮阳板时宜接受（朝西的外窗当需设置遮阳板时宜接受（）A A 水平式水平式B B 垂直式垂直式C C 挡板式挡板式D D 综合式综合式公共建筑可调整的金属材质遮阳装置公共建筑可调整的金属材质遮阳装置 External controlsSpecial glasses （特
28、殊玻璃）（特殊玻璃）人环奖试题：人环奖试题：Low-eLow-e玻璃能够改善夏季室内热环境的缘由是玻璃能够改善夏季室内热环境的缘由是（）A A、对长波辐射的低放射率和高反射率、对长波辐射的低放射率和高反射率B B、对近红外线的低透过率、对近红外线的低透过率C C、对可见光的高透过率、对可见光的高透过率D D、有较低的综合传热系数、有较低的综合传热系数一般来说，燃料燃烧、电一般来说，燃料燃烧、电热器具热源等放出的红外热器具热源等放出的红外线多属于近红外线，由于线多属于近红外线，由于波长较短，因此产生大量波长较短，因此产生大量的热效应，长期照射人体的热效应，长期照射人体后会产生灼伤皮肤及眼睛后会产
29、生灼伤皮肤及眼睛水晶体等损害水晶体等损害人环奖试题：人环奖试题：Low-eLow-e玻璃能够改善夏季室内热环境的缘由是玻璃能够改善夏季室内热环境的缘由是（）A A、对长波辐射的低放射率和高反射率、对长波辐射的低放射率和高反射率B B、对近红外线的低透过率、对近红外线的低透过率C C、对可见光的高透过率、对可见光的高透过率D D、有较低的综合传热系数、有较低的综合传热系数2 2）Casual heat gains from occupants and Casual heat gains from occupants and equipment in the buildingequipment i
30、n the building室内人员和设备形成的一般得热量室内人员和设备形成的一般得热量Heat from people Heat from lighting Heat from cooking and water heatingHeat from machinery,refrigerators,electrical appliancesTable 4.11 domestic seasonal heat gainsTable 4.11 domestic seasonal heat gains 4.5 Heat balanceFabric Heat Losses ventilationHeat
31、Losses solarHeat gains casualHeat gainsEnergy for heating or cooling+=+This is a general expression of balance which is true for summer and winter conditions.?Seasonal energy requirements季节性能耗季节性能耗lTemperature:average temperature l lare valid forare valid for calculating total energy consumption and
32、 can be used to predict the quantity of fuel required in a season and how much it will cost.l lcan not be used to predictcan not be used to predict the size of the heating or cooling plant required;lsuch a prediction needs consideration of the coldest and hottest days.Worked example 4.3 Over a heati
33、ng season of 33 weeks the average rate of heat loss from a certain semi-detached housesemi-detached house（半独立式住宅半独立式住宅半独立式住宅半独立式住宅）is 2500W for the fabric loss and 1300W for the ventilation loss.The windows have areas:6m2 south-facing,5m2 east-facing,6m2 north-facing.The house is occupied by three p
34、eople and cooking is by gas.Use the values for seasonal heat gains given in table 3.7 and 3.9 and calculate:(a)The seasonal heat losses(b)The seasonal heat gains;and(c)The seasonal heat requirements.(a)total rate of heat loss=fabric loss+ventilation loss =2500W+1300W=3800W heat energy lost=rate of h
35、eat loss time taken =3800W (337 24 60 60)s =75.842GJ(giga joules)千兆焦千兆焦千兆焦千兆焦 so seasonal heat loss=75.842GJ =75842MJ(mega joules)兆焦兆焦兆焦兆焦(b)Heat gains solar window gain(table 3.7)solar window gain(table 3.7)south(680MJ/m26)4080 east(410MJ/m25)2050 north(250MJ/m26)1500 casual gains(table 3.9)casual
36、gains(table 3.9)body heat(1000MJ3)3000 cooking(gas)6500 water heating 2000 electrical 3000 total 22130MJtotal 22130MJSo seasonal heat gain=22130MJ(c)Seasonal heat requirement=heat loss-heat gainheat loss-heat gain =75842-22130 =53712MJ(mega(mega joulesjoules兆焦兆焦兆焦兆焦)=53.712GJ(giga joules(giga joules
37、千兆焦千兆焦千兆焦千兆焦)Efficiency 效率效率Efficiency is a measure of the effectiveness of a system which converts energy from one form to anotherDomestic heating efficiency table 4.12Delivered energy（供应能量）（供应能量）Useful energy（有用能）（有用能）Worked example 4.4 The seasonal heat requirement of a house is 54GJ,which is to
38、be supplied by a heating system with an overall house efficiency of 67%.The solid fuel used has a calorific value of 31MJ/kg.calculate the mass of fuel required for one heating season.Efficiency=67/100,output=54MJ,input energy=?Using Input energy=80597MJMass of fuel needed=4.6 Energy regulations 能源规
39、范能源规范Why do we need energy regulations?Can help to minimise energy use in buildingsRegulation about thermal insulation control heat loss from buildingsMinimise the heat load for heating in winter Minmise the cold load for air conditioning in summer there are many regulations4.6.1 Building regulation
40、s 建筑规范建筑规范 How to realize energy efficiency in buildings by regulations?(1)Heat loss by transmission through the fabric(2)Heat loss by air leakage around openings and through the fabric(3)Control system for space heating and hot water(4)Heat loss from vessels 容器 and pipes used for water(5)Heat loss
41、from hot water pipes and hot air ducts used for space heating(6)energy-efficient lighting sources and switching for the lighting4.6 Energy regulations 能源规范能源规范4.6.1 Building regulations 建筑规范建筑规范4.6.2 Energy rating,SAP 建筑能耗评级建筑能耗评级4.6.3 Carbon Index，CI 碳指数碳指数4.6.4 Insulation of the building fabric 围护
42、结构保温围护结构保温4.6.5 Other measurements for energy conservation 其他节能措施其他节能措施lControlling the insulation of the building fabricl 限制建筑围护结构的保温lThermal bridging around openingsl 开孔处的热桥lInfiltrationl 空气渗透lSpace heating controll 分区供暖限制lHot water controls and insulation of storagel 热水限制和储罐的保温llightingl 采光Import
43、ant words in chapter 4metabolic rateStack effectNon-renewable energyRenewable energyPrimary energySecondary energyCalorific valuesDry resultant temperaturesol-air temperaturelAir change ratelThermal admittance1 SAP Energy Ratings are expressed on a scale of()A 0 to 1.0B 0 to 10C 0 to 100D 0 to 100%2
44、 Carbon Index energy ratings are calculated using the information for a SAP rating and expressed on a scale of()A 0 to 1.0B 0 to 10C 0 to 100D 0 to 100%3()may contribute to energy efficiency A Controlling the insulation of the building fabricB avoid Thermal bridging around openingsC mimise Infiltrat
45、ionD Space heating controlE Hot water controls and insulation of storageF energy-efficient lighting source and control4 Casual heat gains in a building include()A heat from peopleB heat from lightingC heat from sun D heat from cooking and water heatingE heat from machinery,refrigeratorsF heat from electrical appliances建筑的互遮挡状况64