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<br /> ��I , 280 CHAPTER 19 (��i;�..: . ,: . ,jHRAE Handboak of Fvndcmentuls
<br /> i ' prociJed:" 1'heir tot;i. uet nrea may be cukulated by tLe�a� burning,�fuel,tl�e attendnnt forced dratt tor eir for combue- �
<br /> formula: tion usunlly crentce small negntive preavurey within the build- �
<br /> � ! a � 2L d ingthutnccekrutesairezchnnge.Airexhnvstedbythetarnace �
<br /> 100 +300 �1�� unit, tun-driven ventilutore from kitchens, bativoomy, and �
<br /> whne Inundry dryers is repinced through leuks ¢round doors, wip- }
<br /> dows,nnd from such component�¢y firepinces.Thue there is e
<br /> L = tLe perimetr,r ot tl�o crnwl epnco,tinear feat. continunl interchnnge of air and the exhausted air cerries '
<br /> d m the uren of cho crnwl apuce,equuro feet. excess moisture with it to the outside. In fnet, it may be de- '
<br /> a � thetot¢Inecareno(nllvonta(urthegroeenrenHn4meah sir¢bleineomeofthoseinstnncevtoprovidendd'.tionnlhumidi_ �
<br /> � ecreen is used),equnre feet. ficntion. I ,
<br /> 1'his �entilntion is usually sufficient but cooLa the first ���ifterent eituntiom m�y caet in dwellings�ehere�he hen4
<br /> � floor so much thut insulntion is needed. A better tre¢tment 1°s�s produeecl by methods tLnt do not require(cel eombus- I
<br /> is u cover on the damp ground.Tliis cover mny Uc n wecrete tion.\ininly in thia category nre buildings heatecl from mmote {
<br /> �� slnb, or merely heury mll roo6ug or 0.004-O,C06 in. thicl• 5°urces (sepnmte hmUpower stations), electric hesting, end
<br /> �� polyethyleno plavtic &Im laid on a gradeu eudace with �}y heut pumps: Some positive ventilating or dehumidification
<br /> cdBes IaPP�d `E in. (but not neeeasr.dly cemented). �t'ith this must be dcs�gned into the building with enpacity t,�, remove
<br /> . barrier, the vent area i.�ay be reduced to 10 moisture in the amount that represents the d.iQerence b�tween
<br /> ,calculnted by Equetion IC. �10e°t of thst that generuted by the occupancy ¢ad the amounta loat
<br /> In buildiug walls, cavity ventilntio¢ can bo spplicd ]n 8 through such netural und iastnlled ventilstian ae kitehen
<br /> modernte climate ns tho sole vnpor contmi system.Horveveq ech¢ust fans and from o�ening outside doore +,o e¢kr and
<br /> nir pnssages in wnlls designed to remov..:::unrestricted v¢por ��°e premises.
<br /> � supply nre unduly inrge nnd may wnste considernble hect.On � similar, but much moro severe situ¢tion exieta in farm
<br /> the ott�er hand, ¢burrier ns the only control measure would, etrucb�res where hent o( the stock ilself is the priucipal heat
<br /> in eome cases,require so high n resietnnce ns to be impractical. a0urce.\fodern,tight fnrm etructure9 with the�mal iasulntiou
<br /> Ventilntion o( the structure in c:onjun^.tion with a vnpor and the necessnry vnpor barriers to mnintain the eBe�tiveness
<br /> bnrrieq is n prowdure with importnnt applications, but �� of tho insulntion by proven!inq insid�rhe-wall condeneation,
<br /> geneml utility hns not been fully investigated. Vm�tilation in virtuully contain all of tha moieture within the buildiag and
<br /> � most efTeetive u•lwn each elructural spnce hns n clenrly de- unless poyitive ventilntion is provid�d,moieture buiidup is eo
<br /> - fined air passuge with nn inlet and outlet. In wnll�� a small ��t th¢t surtaco wndensation,uaually on ceiGnge snd walle,
<br /> convective efiect muy be utilized by lowtiug one vent nt the �s s msjor problem.F�rther,in situutions lika ths,air temper-
<br /> bottom nnd one¢t the top of ench spaca 8tures r•e lower !han those in nortnally heated buildinge, so
<br /> 'fhe best time to vapor-proof a building is during its con- �e cap¢c,ty of the uir to hold moisture is reduced.
<br /> etniction. After a building is com leted, ventilntion of the nfoisture is introducecl by tespiration ot the atock snd a!eo
<br /> occupie!1 spnce is tho most easily Rpplied of the three basic bY evaporntion (rom manure and wet feerls Gke silege.
<br /> control mens�res. Paint thnt is:hosen for its low vnpor per- ���ountsnreuppreciable asdiscuesed in Reference 24.
<br /> mennce cnn Ge npplicd av a bnrrier on the interior with good �Ioisture control nnd ventilatio¢ in theso situntione r�
<br /> resclts, enre being fuken thnt nll nreas, including parts of 4ui:es idtilly both a pluce (or air to enter nud o positive
<br /> partitions and ccilings which olTer an indirect vapor pnth to methal (or ejecting. Positive mover.ment o( sir to eGmivate
<br /> the cold waf1, nre covered. Ventilstio¢ of the wnll cnvity is d�epols .nust be considered i�design.Exi�aust fsne should
<br /> etlective iu cerfnin enses especially to eupplement ihe tore- � controlle9 by hygrostnfe eo thnt they will function auto-
<br /> going meesures, }yhen such ventin is re uired each cnvit matically b} turning on when relative humidity exceede the
<br /> apace �solqted Uy Iraming ahould be sepnrntely venteci witl desired nmount, nnd so t6ey will ehut oEf when the reletive
<br /> nn inleE nnd outlet judiciou�ly placed, to eccompiish proper humidi:y drops below the eet amount. Ductwork should be
<br /> air chnnge. coasidered in special eituations where air may etagnaW unlese
<br /> pwiti�•e ventilation is provided. �
<br /> There is not geneml agreement ee to tho limita of relative
<br /> VENTILATION OR DEHUMIDIFICATION TO PRE- humidit�thut shauld be maintained iu buildings with human
<br /> VENT MOISTURE BUILDUP IN ELECfRICALLY occupuncy.Medicaipmplenndt6osewithprimaryinkrestsin
<br /> OR QTHER ..iPECIALLY HEATED BUILDII�G� humidi(ying equipment advocnw high relntive huriiditiee.
<br /> Chnn�es in resenWn , Those concerned with the practiesl problems of sudace con-
<br /> , 6 p y prar.tice of providing tig:ter con- densation acound windowa and mold growth on bne!cs ot up-
<br /> etruction when coupled wrth some of the more advnnced kinds holstered turnituro recommeud lower amounfa. A practica!
<br /> ot henting can provide a situation where t6o moisture content compromise betweeu 35 and 50 percent relative humidity
<br /> in an occupied structure mill continue to build up until seenyy•P,as�����E except in amay of extreme cold where aurfeco
<br /> amounLv exceed that either aatisfactory trom the standpoint conden.satio¢ on B7II(IONB a¢d other places ,e:�uires lower
<br /> of the occupnncy or tho contents of the atructure or the struc- vafues. Por Gve�tock,higher telative humidities uiay be per-
<br /> tare itseV. The dumpueys may become oppresvive und un- mitted 6ecnuse of lower indoor temperatures,but ma�mume
<br /> healthy,and mold may pourish in rome srens.Sudaco couden- ehould not a�ceed thoso which will permit moisture contente W .
<br /> eatio¢mny become s problem,where�viEh notma!humidities become high enough tor decay or W ba dnngeroue fmm the �, .;� :.
<br /> this would not occur at¢II, atandpoint oF rrapiratoiy in(ections o[theateck.�, � i �`
<br /> During normal occupancy in drvellings, the coneideruble • '+•` '
<br /> amounts of moisture genernted by accupauts� must be die- CONDENSATfON IN COOLEG STRUCTURES . , . t
<br /> aipnted or objectionable moieture buildup will occuc Nith `
<br /> modern,tight construction(low air in6ltroticn)and adequate Nater vapor is soms4mee an even grenter problem in';�i .. e
<br /> vapor barriero, ventilation nnd mechanical �ehumidification caaled than in heated etr�ctures, buE tha beeia fscte of iW 'j t
<br /> sre tha eole m�ane of maintnining moieture in the eir et se- migration end condeasation on rold eudaces aro the eama : B
<br /> ceptab;y low limits. �Vith normal heating eyetems employing Re(r.geratore, cold pipee, aud cold veseele sll requiro imuls. r,
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