1、How Solar Heating System Works?p A solar water heating system comprises solar collectors,a storage tank and interconnecting pipework.The solar collectors are usually mounted on roof of a building to capture solar radiation.Small tubes run through the solar collectors and carry liquid either water or
2、 heat transfer liquid with low boiling point.The heat pipe absorbs heat from the solar collectors and transfers heat to incoming water.Benefits of solar water heating Hot water throughout the year:the system works all year round,though youll need to heat the water further with a boiler or immersion
3、heater during the winter months.Cut your bills:sunlight is free,so once youve paid for the initial installation your hot water costs will be reduced.Cut your carbon footprint:solar hot water is a green,renewable heating system and can reduce your carbon dioxide emissionsIn general,solar water heatin
4、g systems falls into 2 types:Active and Passive.Common Types of Solar Water Heating SystemsAn active system uses an electric pump to circulate water or heat transfer fluid from storage tanks through the collector.Whereas a passive system relies on gravity and the tendency for water to naturally circ
5、ulate as it is heated,allowing water or heat transfer fluid to move through the system without the use of a circulating pump.Active solar water heating systems:Active solar water heating systems are characterized as either direct(also called“open loop”)or indirect(also called closed loop)depending o
6、n whether the incoming water is heated directly in the collectors or indirectly heated via a heat exchanger.Automatic solar controller Temperature sensor on collector Temperature sensor on storage tank Solar circulation pump Cold water inflow Hot water run-off Temperature sensor for additional heati
7、ngElements of a solar heating system for hot water:Direct solar heating systemPumps circulate household water through the collectors and into the home.They work well in climates where it rarely freezes.Active indirect water heaterAlso known as an active closed-loop system,a solar heater that circula
8、tes a fluid other than water(such as diluted antifreeze)through a collector.The collected heat is transferred to the household water supply using a heat exchanger.Indirect solar water heaters are popular in climates prone to freezing temperatures.Passive solar water heating systems:l Integral collec
9、tor-storage passive systeml Thermosyphon system A thermosyphon systemA thermosyphon system,also known as a passive system,does not require a pump to circulate the water but instead relies on density differentials where the warmer water rises to the highest point.For this system to function the tank
10、must be mounted above the collector,relative to the horizontal.Comparison between Active and Passive heating systemsAdvantage of Active over Passive(Thermosyphon）Advantage of Passive(Thermosyphon)over ActiveGreater control over systemSimple System setupSuperior efficiencyMore Cost EffectiveFlexibili
11、ty in positioning of storage tankOperates without powerEasier to overcome freezingCan be used with both low pressureand high pressure systems The Main Factors that govern the choice of types of system to be installed include the climatic condition,hot water demand,size of the system and space availa
12、bility for placing extra components,etc.For example,low maintenance direct system can be used in smaller facilities with low hot water demand whereas active indirect system is usually installed in larger facilities with higher hot water demand.Maintenance and Expected Life The maintenance requiremen
13、ts for solar water heating system vary depending on the system configuration.In general,solar thermal collectors have no moving parts and the maintenance requirements are very low.A well-made,properly maintained system should last 15 to 20 years or more.Issues to be considered when installing solar
14、water heating systemSolar Collectors Orientation Solar collectors needed to be located where plenty of sunshine strikes its surface.Solar collectors can be mounted from horizontal to an inclined angle.To maximize the amount of annual solar energy that solar collectors can receive,they should be idea
15、lly tilted at latitude(around 37 in Jinan)of the location on a south-facing roof.It is also necessary to avoid obstructions such as buildings or trees,etc that could prevent solar collectors from solar collectors getting adequate exposure to solar radiation.Types of Solar Collectors:Solar Collectors
16、Flat-plate solar collectorsEvacuated tubesolar collectors Flat-plate Solar CollectorsFlat-plate collectors are the most common solar collectors for use in solar water-heating systems in homes and in solar space heating.A flat-plate collector consists basically of an insulated metal box with a glass
17、or plastic cover(the glazing)and a dark-colored absorbing plate.Solar radiation is absorbed by the absorbing plate and transferred to a fluid that circulates through the collector in tubes.Sketch of flat-plate collector Direct flow evacuated tube collectors These consist of a group of glass tubes in
18、side each of which is a flat or curved aluminum fin attached to a metal(usually copper)or glass absorber pipe.The fin is covered with a selective coating that absorbs solar radiation well but inhibits heat loss.The heat transfer fluid is water and circulates through the pipes,one for inlet fluid and
19、 the other for outlet fluid Heat pipe evacuated tube Collectors.The Vacuum Solar Tube absorbs the solar energy and transfer into the heat energy,then pass it to the heat pipe,which transfer the heat to the working media.There is no water in the vacuum tube,so the tube will not break in water,it is s
20、teady and credible and can be combined with the architecture perfectly.It can be combined with existing pipeline and even operate in the event of occasional tube breakages.Flat plate collectors VS Evacuated tube collectors Cheaper More efficient Longer service life No freeze Easy installation Better
21、 performance in cloudy days Climate limitation More reliableFlat plate collectors are Good,Evacuated tube collectors are Better!Vacuum Solar Tube:What Is Solar Collector TubeThe vacuum solar collector tube is a simple and effective energy converter,which absorbs the solar energy and converts it into
22、 heat for use via the selective absorbing coating.?Each evacuated tube consists of two glass tubes made from extremely strong borosilicate glass.The outer tube is transparent allowing light rays to pass through with minimal reflection.The inner tube is coated with a special selective coating which f
23、eatures excellent solar radiation absorption and minimal reflection properties.The top of the two tubes are fused together and the air contained in the space between the two layers of glass is pumped out while exposing the tube to high temperatures.This evacuation of the gasses forms a vacuum,which
24、is an important factor in the performance of the evacuated tubes.In order to maintain the vacuum between the two glass layers,a barium getter is used.During manufacture of the evacuated tube this getter is exposed to high temperature which causes the bottom of the evacuated tube to be coated with a
25、pure layer of barium.This barium layer actively absorbs any CO,CO2,N2,O2,H2O from the tube,thus helping to maintaining the vacuum.The silver colored barium layer will turn white if the vacuum is ever lost.Basic Specifications of Evacuated tube Length(nominal)1500/1800 mm Outer tube diameter58 mm Inn
26、er tube diameter47 mm Tube thickness1.6 mm MaterialBorosilicate Glass 3.3 Absorbing coatingGraded Al-N/Al Absorption92%(AM1.5)Emission8%(80 )Vacuum P230 Heat loss 0.8W/(m2 )Maximum strength0.6MPaAll-glass evacuated solar collector tubesProduction:pull-seal（拉封）拉封）inner tube&outer tube rinsing（清洗）（清洗）
27、:deionized water drying（烘干）（烘干）:140,30 minutes coating（镀膜）（镀膜）:one target&three target sealing（封口）（封口）:fuse annealing（退火）（退火）:eliminate stress evacuating（排气）（排气）:1 hour,P3.0 x10-3 Pa firing（烤消）（烤消）:getter,extra air packing（包装）（包装）:carton with foam inspection（质检）（质检）Coating（镀膜）（镀膜）:p Coating method:磁
28、控溅射镀膜磁控溅射镀膜 One-target coating（单靶镀膜）（单靶镀膜）blue，red,black Three-target coating（三靶镀膜）（三靶镀膜）blue,black,redp Coating types:Double-target（双靶镀膜）（双靶镀膜）Ti-tube,purplep Coating layers：absorption layer(SS-ALN)reflection layer(copper)anti-reflection layer(ALN)Indictors of evacuated collector tubes performancep
29、 Absorption ratep Emission ratep Coefficient of average heat lossp Vacuum qualityp Water temperaturep Stagnation temperatureCommon quality Defects:u Scratches:appearanceu Shattered coating film:thermal performanceu Uneven coating color:appearanceu Black mirror surface:thermal performanceHeat pipes:A
30、 heat pipe is a two-phase heat transfer device with an extremely high effective thermal conductivity.The heat pipe is evacuated and backfilled with a small quantity of a working fluid such as water,acetone,nitrogen,methanol,ammonia,or sodium.Heat pipes:A heat pipe usually comprises two copper components:the shaft and the condenser.Prior to evacuation,the condenser is brazed to the shaft.p Boiling point:30oC(86oF)pFreezing point:0oC(32oF).Heat Pipes Productioncondenserheat pipepipe rinsingweldingvacuum extraction fluid injectionpipe sealingThank youJuly 02,2011
