【正文】 五、太陽能中央。太陽能熱水器是目前太陽能產(chǎn)品中技術(shù)最成熟 、應(yīng)用最廣泛的一種，具有環(huán)保節(jié)能和安全方便的特點。在采取了適當(dāng)防凍措施并且結(jié)合適當(dāng)?shù)妮o助加熱設(shè)備以后太陽能中央熱水系統(tǒng)在全年365天都能正常供應(yīng)熱水，比單純的電加熱設(shè)備或燃油鍋爐或燃?xì)忮仩t更穩(wěn)定，并且可以節(jié)約更多能源耗費。目前由于許多單位擔(dān)心太陽能中央熱水系統(tǒng)不穩(wěn)定，影響了太陽能中央熱水系統(tǒng)大規(guī)模的使用，其實不然，由于太陽能中央熱水系統(tǒng)擁有獨立的輔助加熱設(shè)備，并且有儲熱水箱停水或停電時都能供應(yīng)一部分或全部的熱水，所以比單純的電加熱設(shè)備或燃油鍋爐或燃?xì)忮仩t穩(wěn)定得多，當(dāng)然我們也可以把原單位有電加熱設(shè)備或燃油鍋爐或燃?xì)忮仩t改造一下，作為太陽能中央熱水系統(tǒng)的輔助加熱設(shè)備節(jié)省一部分投資。電加熱設(shè)備或燃油鍋爐或燃?xì)忮仩t作為太陽能中央熱水系統(tǒng)時，輔助加熱設(shè)備由自動控制器控制，自動控制器由時間控制器、溫度控制器等組成。三、太陽能中央熱水系統(tǒng)及輔助加熱設(shè)備太陽能中央熱水系統(tǒng)不同于普通家用太陽能熱水器，專門用來解決學(xué)校醫(yī)院等企事業(yè)用水人數(shù)多、熱水用量大的問題，它包括太陽能主體工程和輔助加熱設(shè)備。在采取了適當(dāng)防凍措施以后太陽能熱水系統(tǒng)在嚴(yán)寒的冬季都能正常使用，可以充分利用太陽能從而節(jié)約更多能源耗費。這樣確保整個系統(tǒng)在最嚴(yán)寒的冬季夜晚（即使零下十幾度）也不會結(jié)冰，白天一到，只要有陽光，太陽能熱水器就能正常使用；③在冬季較長時間沒有陽光時且持續(xù)低溫時，采用排水法防凍既把水全部排掉，到陽光好時上水，但是上水必須在早晨或夜間以免產(chǎn)生的真空管爆管現(xiàn)象。另外還須采取適當(dāng)措施防止循環(huán)管道，熱水管及冷水管在冬季結(jié)冰影響整個系統(tǒng)正常使用，常用的防凍措施有以下幾種：①下循環(huán)管及冷水管道上安裝電熱帶，控制方式為：當(dāng)管道內(nèi)的水溫低于設(shè)定的下限溫度時如1℃，電熱帶通電加熱，當(dāng)管道內(nèi)的水溫達(dá)到設(shè)定的上限溫度時8℃時，電熱帶斷電，停止加熱。目前北京地區(qū)采用最多的太陽能熱水器為全玻璃真空管集熱器，全玻璃真空管集熱器本身類似暖水瓶結(jié)構(gòu)，有防凍功能，適應(yīng)在冬季溫度高于15℃的地區(qū)。日。冬季冷水水溫低，太陽能熱水器產(chǎn)水量約為夏季三分之一?？芍刻烀科椒教柲芗療崃繛?20（60－16）= 5280千卡,㎡據(jù)北京太陽能協(xié)會及北京氣象局提供資料統(tǒng)計太陽能資源相關(guān)參數(shù)如下：日照平均值：日照百分率：年平均63%，%，夏季55%日照輻射量年平均值：130千卡/cm2 即1512kw/㎡多年工程實踐給出，在北京地區(qū)若采用優(yōu)質(zhì)真空管太陽集熱器，每平方米集熱器從上午9點至下午3時運行，春秋季節(jié)可獲溫度為40～60℃的熱水60～80千克，夏季100～120千克，冬季25～35千克，年平均每平方米太陽集熱器日產(chǎn)水量75千克左右。Lesson62 After the fire 大火之后In future, astronauts will be required to descend from a spaceship while it is still in space and to return to it. The ability to do this will be necessary in future flights to distant planets. Scientists are now trying to discover if this is possible. The spaceship Astra which left the earth a short time ago, will be travelling three hundred miles into space. At a certain point, the Astra will stop for a short time and an astronaut will attempt to leave the stationary spaceship and then return to it. We shall not know whether the experiment has been successful until we have received a radio message. The first message is expected to arrive at 7 o39。 As she walked away, I followed her out of the fair. she asked impatiently. 39。 As soon as I went outside, I forgot all about Madam Bellinsky because my wife hurried towards me. 39。At a village fair, I decided to visit a fortuneteller called Madam Bellinsky. I went into her tent and she told me to sit down. After I had given her some money, she looked into a crystal ball and said: 39。Our dog, Rex, used to sit outside our front gate and bark. Every time he wanted to e into the garden he would bark until someone opened the gate. As the neighbours plained of the noise, my husband spent weeks training him to press his paw on the latch to let himself in. Rex soon became an expert at opening the gate. However, when I was going out shopping last week, I noticed him in the garden near the gate. This time he was barking so that someone would let him out ! Since then, he has developed another bad habit. As soon as he opens the gate from the outside, he es into the garden and waits until the gate shuts. Then he sits and barks until someone lets him out. After this he immediately lets himself in and begins barking again. Yesterday my husband removed the gate and Rex got so annoyed we have not seen him since. if he picks a leaf, he will die. Many villagers believe that the tree has already claimed a number of victims. The vicar has been asked to have the tree cut down, but so far he has refused. He has pointed out that the tree is a useful source of ine as tourists have been ing from all parts of the country to see it. In spite of all that has been said, the touristshave been picking leaves and cutting their names on the treetrunk. So far, not one of them has been struck down by sudden death!cursed tree39。Lesson58 A blessing in disguise? 是因禍得福嗎？The Revealer39。Lesson55 Not a gold mine 并非金礦Lesson54 Sticky fingers 粘糊的手指Lesson53 Hot snake 觸電的蛇t need bookcases at all. You can sit here in your spare time and read the carpet!39。 she said. She gazed at it for some time then added, 39。We have just moved into a new house and I have been working hard all morning. I have been trying to get my new room in order. This has not been easy because I own over a thousand books. To make matters worse, the room is rather small, so I have temporarily put my books on the floor. At the moment, they cover every inch of floor space and I actually have to walk on them to get in or out of the room. A short while ago, my sister helped me to carry one of my old bookcases up the stairs. She went into my room and got a big surprise when she saw all those books on the floor. 39。My friend, Herbert, has always been fat, but things got so bad recently that he decided to go on a diet. He began his diet a week ago. First of all, he wrote out a long list of all the foods which were forbidden. The list included most of the things Herbert loves: butter, potatoes, rice, beer, milk, chocolate, and sweets. Yesterday I paid him a visit. I rang the bell and was not surprised to see that Herbert was still as fat as ever. He led me into his room and hurriedly hid a large parcel under his desk. It was obvious that he was very embarrassed. When I asked him what he was doing, he smiled guiltily and then put the parcel on the desk. He explained that his diet was so strict that he had to reward himself occasionally. Then he showed me the contents of the parcel. It contained five large bars of chocolate and three bags of sweets! I answered. said the conductor. 39。 39。I39。t matter,39。 39。 said the conductor suddenly.39。 I asked. 39。 39。 the conductor said. 39。 You39。 answered the conductor. I39。t know where it is.39。 I said to the conductor as I got on the bus,39。 I39。t like losing my way. I went on an excursion recently, but my trip took me longer than I expected. Lesson50 Taken for a ride 乘車兜風(fēng)Tired of sleeping on the floor, a young man in Teheran saved up for years to buy a real bed. For the first time in his life, he became the proud owner of a bed which had springs and a mattress. Because the weather was very hot, he carried the bed on to the roof of his house. He slept very well for the first two nights, but on the third night, a storm blew up. A gust of wi