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第 17 卷 第 1 期2001 年 1 月农 业 工 程 学 报T ransactions of the CSA EV o l. 17 N o. 1Jan. 2001A rticle ID: 100226819 (2001) 0120016206M odern Greenhouses and The ir Performances in Ch inaZhou C ha ng ji, W a ng Yingkua n(Ch inese A cad em y of A g ricu ltu ral E ng ineering , B eij ing 100026, Ch ina)Abstract: A t p resent, Ch ina is being in a tim e of great developm ent of greenhouse facilities, and the annualincrease of large scale greenhouse is mo re than 100 hm 2. Since the greenhouse type is various, how to select thetype of greenhouse and its environm ental contro l equipm ent is the p rincipal p roblem to be so lved fo r everygreenhouse constructo r acco rding to local condition and p lanting crop s, because it is related to econom ic benefit.D uring the period of the N inth F ive2Year P lan (1995 2000) , on the basis of introducing structure; type; perfo rm ance; Ch inaCLC num ber: S625. 1 D ocum en t code: AReceived date: 2000210225B iograph ies: Zhou Changji ( 1964 - ) , m ale, Ph. D. , p rofesso r,Senio r m em ber of the CSA E, m ajo red in greenhouse research W ang Yingkuan (1971- ) , m ale, M. Sc. , engineer.1 Genera liza tionIn Ch ina m odern greenhou se started in the late1970s. D u ring 1978 1994, 21. 12 hm 2 large scalem odern greenhou ses w ere in troduced to Ch ina insuccession from ab road 1 . O n the basis of digest2ing the ven t2open ing m echan ism is rackand p in ion o r the 4 connecting bar system. Eachspan of greenhou se w as set up tw o row ven tsacro ss ridge on bo th sides, and each row of ven t isdriven w ith one electric m o to r con tro lledindependen tly. So, m o re electric m o to rs are u sedin th is k ind of ven t2open ing m echan ism.T herm al screen is no t in stalled on thegreenhou se in early stage; therefo re the in su lationof greenhou se is poo r. In o rder to im p rovein su lation perfo rm ance of greenhou se in co ldareas, doub le glass is u sed fo r glazing. Since th isis greenhou se structu ral type of early stage,greenhou se con tro l is conducted m ain ly by hand,basically w ithou t com pu ter con tro l system. T heco st of gate2type steel fram e greenhou se is h igherbecau se of m o re steel u sed ( around 15 kg m 2 ).A long w ith the in troduction and im p rovem en t ofthe V en lo greenhou se and w ide sp read of p lasticgreenhou se, the app lication of th is k ind ofglasshou se is few er and few er.2. 2 Ven lo GreenhouseV en lo greenhou se is a k ind of glasshou se w ithsm all roof, standard span is 6. 40 m , and bay is4. 00 m , every tw o sm all roofs are directlysu stained on tru ss. Sm all roof span is 3. 20 m ; theheigh t is 0. 80 m , as F ig. 2. O n the tru ss, m o reF ig. 2 V enlo greenhousethan tw o roofs of 3. 2 mcan be suppo rted andm ake up a b ig span, suchas 9. 60 m and 12. 80 m ,in w h ich m echan izedoperation is m o re conven ien t.T h is k ind of greenhou se is o riginated in D u tchand also su its the clim ate condition of N etherlandsvery m uch: w ind speed is h igh, so lar radiation isw eak, and tem peratu re is m oderate (- 5 30 ).Ch ina first in troduced th is k ind of greenhou se fromRom an ia in 1983. In the past 20 years, m o re than30 hm 2 of th is k ind of greenhou se w ere in troducedto Ch ina. T he b iggest characteristic of th is k ind ofgreenhou se is that ligh t tran sm ission is h igh. T heglass th ickness u sed in th is greenhou se is 4 mm.T he basic m easu re ach ieving h igh ligh ttran sm ission is the app lication of the specialgreenhou se glass w ith h igh ligh t tran sm ission (over92% ) , besides, reducing o r m in im izing greenhou seroofing com ponen t size is its m ajo r characteristics.O n the one hand, greenhou se roofing is m ade ofthe A lum inum alloy w ith little section p rofile asbearing pu rlin and glass2in stalling stripcom p letely. Glass is in stalled from the gu tter toroof ridge; pu rlin is no t u sed betw een the gu tterand ridge, w h ich reduced the shading of roofingbearing com ponen t. O n the o ther hand, oncondition of satisfying drain and structu ral bearingrequ irem en t, m in im izing gu tter section size hasalso m ade huge con tribu tion fo r raising greenhou seligh t tran sm ission.Excep t the h igh ligh t tran sm ission, low er u seof steel m aterial is ano ther characteristic of theV en lo greenhou se. T he to tal steel u sed in standardV en lo greenhou se w ith the span of 6. 4 m and bayof 4. 0m is less than 5 kg m 2, bu t in o ther type ofglasshou se, it is around 12 15 kg m 2. T he rackand p in ion roof ven t2open ing m echan ism is also an71 第 1 期 周长吉等 : 中国现代温室结构的主要型式及其性能 1995-2005 Tsinghua Tongfang Optical Disc Co., Ltd. All rights reserved.ou tstanding characteristic of the V en logreenhou se. In the standard V en lo greenhou se,the roof ven ts are arranged at in terval of differen topen ing direction s. In every bay (4 m ) , there aretw o ven ts of 1. 5 m in length in differen t direction sand left 1. 0 m is fixed, as F ig. 3. T he ratio of roofven t area to the greenhou se ground area( abb reviated as ven t ratio ) is 18. 75%. R ecen tlysom e com pan ies increase the ven t w idth from thetraditional 0. 80 m to 1. 00 m , thu s, the ven t ratioincreases to 23. 43%. How ever, becau se of therestriction of the open ing angle of ven t, the actualF ig. 3 V ents ofV enlo greenhouseven t heigh t is on ly 0. 36 0. 45 m , nam ely theratio of actual ven tilationnet area to ground area(abb reviated as ven tilat2ion ratio ) is on ly 8. 5% 10. 5% 2 .T he coo ling of the V en lo greenhou se inN etherlands m ain ly relies on natu ral ven tilationand in side therm al screen. T here is no ven t onw alls in large2scale greenhou se. T h is k ind ofgreenhou se is su itab le under D u tch clim atecondition, bu t under the m o st of clim ate condition sin Ch ina, the in troduction and p ractice of V en logreenhou se from D u tch show ed that the roofven tilation is no t enough, and the coo ling insumm er is difficu lt. T he ou tdoo r sun shade systemand fan2pad coo ling system m u st be u tilized inp roduction in summ er.Besides, h igh heat con sum p tion is also asign ifican t baffling p rob lem runn ing th isgreenhou se in N o rth Ch ina in w in ter. In general,the heating co st in w in ter takes 30% 40% ofp roduction co st. A lthough som e greenhou ses u sedoub le glass fo r w all covering, fo r large aream u lti2span greenhou se, the p ropo rtion of w all areatakes on ly 10% 12% of the to tal heat tran sferarea, the effect of th is k ind of in su lation m easu reis really sm all.3 Pla stic Greenhouse3. 1 Arch Roof Greenhouse3. 1. 1 Structu reA rch roof greenhou ses are a k ind of p lasticgreenhou ses w ith m o st comm on structu ral type,w h ich are w idely app lied in Ch ina. In general, thespan is 8. 0 m o r 9. 0 m , bay is 3. 0 4. 0 m , eavesheigh t is 3. 0 4. 5 m , the heigh t of roof arch isam ong 1. 5 2. 0 m , and roof structu re types arevariou s, as F ig. 4. Since p lastichou se is ligh t inw eigh t, the roof structu re is in stalled no rm allyw ith a m ain arch and several aux iliary arches inone bay. T he m ain arch is the m ajo r load bearingstructu re directly jo ined w ith greenhou se co lum n,w h ich tran sm its roof load to foundation th roughco lum n. T he aux iliary arch is connected w ith thegu tter, w h ich, in function, takes m ain ly the ro lein suppo rting p lastic film and bears less load.T here are tw o w ays to in stall the aux iliary arch instructu re design: m ain and aux iliary arches arein stalled in tervally o r 2 3 aux iliary arches arein stalled betw een every tw o m ain arches. T hefo rm er is no rm ally u sed in the greenhou se w ithou tp ressing film line on roofs, and the latter sets upone p ressing film line betw een each arch, w h ich isu sed to com p ress tigh tly p lastic film.F ig. 4 Structure of arch roof p lastichouse3. 1. 2 T he ven tilation and coo ling systemA cco rding to the ven t location, the ven tilationcan be divided in to gu tter ven t ven tilation, ridgeven t ven tilation and half2roof2ven t ven tilation, asF ig. 5. R idge ven t has very good ven tilation effect,w hereas, the ven t in stalled on near the gu tter,ow ing to little ven t2open ing area, ven tilation effectis often w o rse, and ven t2open ing m echan ism oftenaffects indoo r operating space and co st is h igher.T he ven tilation ratio of half2roof2ven t is abou t50%. Its ven tilation effect shou ld be seem inglybest, bu t becau se of the influence of the ven topen ing angle, gu tter ven t and ridge ven t can open45 , half2roof2ven t can on ly open w ith in 30. So81 农业工程学报 2001 年 1995-2005 Tsinghua Tongfang Optical Disc Co., Ltd. All rights reserved.the actual ven tilation ratio of half2roof2ven t is on ly16% , bu t the ven tilation ratio of ridge ven t canreach 20% , and the co st of ven t2open ingm echan ism of half2roof2ven t is at least 30% h igherthan that of the o ther tw o ven tilation system s. Sow hen choo sing and design ing greenhou se, theactual ven tilation effects of variou s ven t2open ingsystem m u st be co rrectly analyzed, no t con tro lledby the im p ractical p ropaganda and tho se superficialdata. In fact, acco rding to the research of V.W oodruff 3 , the ven tilation effect is the best w henridge ven t is in stalled in the location of 1 4 1 2 ofthe roof. U nder th is condition, the ven tilationtim es keep s 1 h as standard fo r natu ralven tilation, the ven tilation ratio of 15% can satisfythe needs. Bu t fo r the ven t of the sam e area, ifu sing gu tter ven t, the ven tilation is 0. 65 h; ifridge ven t, it is 0. 95 h. R educing ven t ratio canno t on ly save the investm en t of ven t2open ingm echan ism , it can also im p rove the in su lation ofgreenhou se.F ig. 5 D ifferent roof vents of p lastic greenhouses3. 2 Sawtooth Structure GreenhouseSaw too th structu re greenhou se can be dividedin to 3 k inds acco rding to the roof shape, as F ig. 6.Becau se of b ig ven t, the natu ral ven tilation effectF ig. 6 Saw too thgreenhouseof saw too th structu re gre2enhou se is generally bett2er than that of arch roofgreenhou se. It is m easu r2ed that w hen th is k ind ofgreenhou se is equ ipedw ith ou tside sun shadescreen, the effect ofnatu ral ven tilation canreach the difference of 1 3 in tem peratu rebetw een in side and ou tside of the greenhou se. Bu tit is hard to seal the ven t in w in ter, so thein su lation of th is k ind of greenhou se is ofteninferio r com paratively. U sing th is greenhou se hasbetter econom ic benefits in sou th Ch ina w heretem peratu re is h igher in w in ter and is no t very ho tin summ er, bu t it is no t su itab le in no rth Ch inaw here in summ er it is ho t and dry and in w in ter itis severely co ld. Special atten tion shou ld be paid tothe local p revailling w ind direction w hencon structing saw too th greenhou se. T he ven tilationo rien tation of greenhou se shou ld locate in leew arddirection so as to fo rm the greater ven tilation ofnegative p ressu re and to avo id that co ld air flow sbackw ard in to greenhou se.3. 3 A ir- Inf la ted Pla stic GreenhouseT here is no difference betw een air2inflatedp lastichou se and traditional single2layer of p lasticfilm greenhou se excep t that the fo rm er is coveredw ith tw o layers of film betw een w h ich the air iscon tinuou sly fanned in to. A s the air2inflated filmis covered, the in su lation of greenhou se w illincrease by over 30% , bu t at the sam e tim e theligh t tran sm ission of greenhou se w ill decrease by10%. T he app lication of th is type of greenhou sehas better econom ic benefits in no rth areas ofCh ina, w here so lar radiation is adequate andtem peratu re is low er in w in ter. Bu t in the sou thareas of the Yangze R iver, as in w in ter theradiation is inadequate and tem peratu re is h igher,the energy saved by air2inflated greenhou se can behard to balance the in sufficien t lo ss ligh t. T hu s,the air2inflated greenhou se is no rm ally unfit fo rbeing app lied in sou th Ch ina 4 .W hen air2inflated greenhou se is in u se, w em u st pay m o re atten tion to the conden sationbetw een tw o layers of film. If the air filled in to theinflated space from in side of the greenhou se, w h ichis h igh in m o istu re especially su itab le fo r the sou th areas of Ch inaw here radiation is in sufficien t. Bu t doub le2deckstructu re greenhou se increases the co st ofgreenhou se becau se of a layer of additionalstructu re, and the shadow rate of greenhou sefram e also increases. F rom view po in t of operationeffect, its energy2saving is 5% 10% h igher thanthat of air2inflated p lastichou se. T h is typegreenhou se in Beijing, com b in ing w ith therm alscreen, can realize the difference of 10 intem peratu re 5 betw een indoo r and ou tside inw in ter w ithou t heating. Bu t the tw o layers of filmof doub le2deck structu re greenhou se can be bo thacted as ou ter2layer (w hen ou ter film is ro lled up ,the film of in ternal layer acts as ou ter film ). W henu sed in heavy du st2con tained air in no rth areas ofCh ina, the po llu tion of the p lastic film is greater,w h ich cau ses low er overall ligh t tran sm ission ofgreenhou se. T herefo re w hen u sing doub le2deckstructu re greenhou se, the ligh t tran sm ission ofp lastic film m u st be h igher.In design ing doub le2deck structu re greenhou2se, the therm al resistance fo r in su lation ofgreenhou se shou ld be con sidered fu lly in snow loadcalcu lation. Since the roof therm al resistance ofgreenhou se increases, the tim e of snow load delayw ill p ro long relatively, fo r heavy snow areas,snow 2clean ing load especially roof uneven loadshou ld still be con sidered. T h is also increases them aterial con sum p tion of greenhou se structu re.4 PC-Greenhouse4. 1 Ven lo Type of PC-houseA long w ith the p len ty app lication of PC sheet,the structu re of the standard V en lo glasshou seagain has go t new im p rovem en t, u sing PC sheet tosub stitu te glass as cover m aterial. F irst,greenhou se span increased 9. 60 m and 10. 8 m ,sm all roofs in each span still m ain tain 2, and theco rresponding roof heigh t also increased from theo riginal 0. 80 m to 1. 20 m and 1. 35 m. Since theroof area increased, the roof load also increased. Ifalum inum alloy is still u sed to p lay doub le ro les ofin stalling cover m aterial and bearing load, thesection of the p rofile m u st be increased, w h ich w illraise the overall co st of such greenhou sesub stan tially. T herefo re, on the basis of retain ingthe greenhou se tru ss structu re of V en lo m odel, thesm all section ligh t steel structu re is u sed to bearload on the roof, and the alum inum p rofilesm oun ting PC sheet reduce fu rther to m ake theoverall co st of greenhou se increase less. Second,fo r increasing roof ven t of greenhou se, ven ts w eredesigned along the ridge on bo th sides, and thew idth of the ven ts is 1. 0 1. 2 m , so the ven t ratiow ill rise to m o re than 40%. T he b iggest can reachhalf roof as
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