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A SIMPLIFIED APERTURE-SIZING
PROCEDURE FOR DAYLIGHTING DESIGN G. Arnold
INTRODUCTION
This papel~ describes the developMent of a SiMplified, site-spel:ific .:alculatille pl~l)cedur'e fo\" deter'Mining the apppo:<iMate size I)f a daylighting aper'tul"t? that is needed t.) pl",)vide a desil~ed level and dur'ati.)n of natur'al illuMination to an intel~il;:'l'" space.
In application, this pl"ocedul~e is siMilar to the "nIles of thUMb!! used to size passive solar' heating systeMS in the ear'ly stages I)f pr'oject developHent. It enables the designer- to pla,:e bounds ')l'I fundaMental design issues, and to C!1:I:eler'ate the daylighting design pr'Qcess, by liMiting the tiMe-consuMing iter'ative use of detailed cOMputational aids in the st?i:u'ch f(q~ an apPI"""::.pr'iate aper'tm'e ar-ea.
OBJECTIVES
Despite their' intel"est, and the gl~l)wing availability I::.f design t')ols, few building designers appear' to have adequate el·q:/!?l"ience f,)I" designing su.:,:essful daylit buildings by intuition aI"lle. Design for' daylight requir't?s the ,:ar'eful and systeMati.: cOl1sider'ation of a wide r'ange of inter'l"elated design issues (Figur'e 1). The designer' sele.:ts ':oMp,:.nents to satisfy both visual needs and econOMic cl~iteria; it is his Ol~ her' r'esp.)miibi1ity to enSUI"e the pel~forMance of all aspel:ts of the design.
Factol's liMiting the ,:ol'lsidel'at.,ion of daylight in COMI'1el".:::ia1 buildings are the tiMe and l~eSOUl".:es that May be I"'equiped to e:{aMine all (If the issues identified above, in adequate dJ!~tBil. Desil"'able l"e1ati('l1ships betweel~ spe.:ifi.: wind.)w (day1ighting apel"tur'e) COHp')nents and pel"'f.:q"ManCe cl"i ter'ia May not be l"eadily appc.went. The designer' May select ':!iO/"le key design features--aper'tul'e al"ea, glazing type, etc.--by intuition or' habit, and latel' use a detailed .:al.:ulati.jn pr'oceduPt? t.:, test the per'for'Haln.:e of this asseMbly against the ')1"igil1a1 design cl'iteria. When a design established in this Mannep fails to pel"fo\'M adequately, several Htl"i.al runs" May be needed t.o identify an al:':eptable s"lution. Delays May thus be en.:.)untel"ed that .:an jeapoj"dize the designel"s ability to COMplete his 01' hel' taskt~ in a tiMely and Co)st-eff'ective ManneI'.
The deSigner will Most .,ften star·t t.he design pl'o.:ess knowing the end r'esult that he 1)1" she needs to achieve: the level of intel'iol' d€*sign illUMination and the p€*l'cent I)f '::II:,:upied hour's that. need t.o be daylit t.o this l€*vel. The unkn,:twn el(~Ments al'e the physical cr'itel'ia that will satisf'y these I:onditions at a pal'ticulal" site. BecausJ:.~ they fOI .... :e the designer ·to wOI"k "backwal"ds," J"elativ€.' to his .)1' hel' fl'aMe of refel'en.:::e, by eMphasizing these Ullcel'tain aspel:ts, daylighting design tools intl"odUl::e what l'1ay be an intoler'able degl"ee I)f tr'ial and epr")I"' into an all"eady .:oMplel< pl"'ol:ess.
This "r'e-active" chal'a.:tel' .)f Most daylighting design tools is the pI"'in.:ipal barriel" to their' effe.:tille use in the conte:<t of the building deSign pl"o.:ess.
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They gener'ally I"'equir'e the designer' t.) Make e:<pli.:it decisi')ns about MajO}"' design val"'iables befol"'e an evaluation May be perf'oPMed. While these tools will evaluate (within liMits) whatevt?l"' configul"ation is input by the deSigner', they will I"'B}"'ely pl"'ovide pl"'iol"' guidan,:e as to the j""easl)nBbleness of the I:onditions described. Repeated ef'f('I"'t May be I"'equil"'ed if the designer"s judgeMent is faulty. It is as if the PI"(Il:o!?dul"'e is iMplicitly saying: IlGive Me anothel"' window ar'ea and I'll tell you how gl)od YOUl"' guess was. Maybe you 'I"'e getting wal"Mo!?l ... 1l
Ther'e is a ,:lear' need for' siMple Ilpr'oa.:tive H tools for daylighting design that will save the pl"al:titioner' tiMe by ,:onver'ting known design cI"itel"ia dir'ectly into an apPl"o:<it'lat€' physical solution that May be r'efined using M':'l"e detailed pl"o,:edul"es. A siMilal"' need gave iMpetus to the developMent of' IINll e ,)f thUMb!! appr'.)a.:hes for passive s.)lal"' design (Mazl"ia 1979; and Bab:')Mb 1980). By reducing the un.:er'tainty iMplicit in develo: ... ping a !!fil"st-.:ut" design s.;:olution, these pr":II:edul"es al ]..)w the designer to pay f10l"e attention tl:;' lar-gel" .:oncel~ns, such as integr'ating an ener'gy-col1ser-ving strategy into the design as a whole. If applied ear'ly in the design pl~a:,,:ess, a preal:tive tool May l"educe total design effol~t and allow M.))"e effil:ient use I:.f pl"'ofessio:.nal tiMe.
THE DEVELOPMENT OF PREACTIVE DAYLIGHTING DESIGN TOOLS
In Mc'lllY r'espeo:ts, design fo}" daylight i5 MOI"e cOMple:.: than the design of passive solar sp-s\I::e-heating systeMS. The daylight appiving in the inteol~i',,"' of a spal:e thl"'ough a window generally includes SIii~v€!I"al COMpOI1€'nts (Figul"e 2). besign ,:o:mditions will detel"'Mine whi.:h ':oMponent predOMinates. Daylighting cal.:uatiol1 pl"o':edul"es Hay be classified pl)ughly al:o:ording t.) the deg}"ee of accul"'acy with which they estiMate each ',f thE'S€' ':I)MpOnent pal~ts and by theil" for'Hats: MatheMati':al (fQ\"MLtla or tablt~) 0)" gr'aphic (protl"actol", gr'aph, 01" 91"id.) FOI"Mat May, ho:.wevel"', be of less signifi,:ance tl:' the designer' than the aSSUMptions built into the pl"o.:edtH'e. Although MatheMatical procedures al"e genel"ally MOI"'e al:,:ul"ate, n·) daylighting ,:al.:ulation pl"'ocedUl"e is entipely fundaMental in natupe. All includli.~ S')Me clegl"ee of eMpir'i.:al aSSUMption that involves tNIl.:ie-.)ffs between ac.:ur'a,:y and Ii.~ase I)f use.
Distinct fr";:OM MatheMatical pl"I).:edlll"es that o::alculat€, each ,:oMp.:.nent .;:.f daylight illUMination separ'ately, "single stage" pl"'o.:edur'es have been used extensively with ao:eptable ac,:ul".1:ICY as a COMPl""oMise between gl"'aphic pr'ocedur'es and detailed MatheMatical te.:hniques ( Hopkinson, et .al. 1966). NO\"Mally del"ived f'r'oM detailed pal"'aMetpiO: M€'BSUI"eMents ';,p .::al,:ulatiQns, these procedul"es estiMate the SUM of of all l:oMp')nents .;:of intel"i')I" daylight illUMination by Means of a single e:.:pr'ession. With SOMe 11)55 in fle:dbility, cOMple:< l"elati':.nships between sevel"al iMp,:q·'tant design val"iables can be '''educed to a Single tel~M. The aculI"acy of the l"esul ts de.:r'eases as the Meth.)d is applied tl) spa':es signifi.:antly differ'ent fl"':'/'1 the ':'l~iginal test ,:.ases. SiMilar- liMitations apply to the passive solar' pl~ocedUl~es (BalcoMb 1978; and Jones 1982).
Single-stage calcuati,)n Methods al"e, how€'~yer, well suited to the initial appraisal .)f' daylighting design probleMs. They .:an be pl"epal"'ed in a way that does not pequire a pl"eMatul"e cOMMitHent to a det.ailed design ,:1\" t,;:o unl"ealistically e:<act specif'i':ations. Be,:ause ,)f the siHplifi,:ati,:ans that lowel"' their abs~lute BI:,:ur'a,:y, they May be applied qllickly at the eal"liest stages .)f proJect devel,:,pMent, when the designel"' is typi.:ally interested in evaluating
931
the feasibility of a I'ange of design sl)lutil)ns~
E:dsting €'l{ElMples of single--stage pl~ocedlll'..r~S in.:luL1e:
The Fr'uhling "Flll:{-tr'ansfel' F':'N1ulas" (Hopkinson, et~al. 1966)
This pl'(II:edur'e is siMilar' to ttH,! ,:oL~f"fi.:ient of utiliz.f.ltion tedH1iques used t.) evaluate elel:tr'ic lighting Syst€'MS. The pr'oceLil,.u'e developE-d by FI'uhling estiMates thE- average Daylight Facto)' on a hOl"izontal intel~il:II" w.:.d:; plane, due to daylight al'l'iving th)~.:.ugh vel~tiGtl glazing~
DFavg = F * U * (Ag/Af) * 100% (1)
DF .is the Daylight Factol', the d~\ylight illul'lination at a given point (In a given plane du,,~ t.;:. tht:~ light r'E'ceived dir'e.:tly 01' inLiil'ectly lUHinan':e distl"ibution, hOl'izontal plane due to an sky. Dir'e.:t sunlight is illUMination.
fl~()''1 a sky of assul'led .:>\' kn.:.wn to the illUMination on a
unl)bst\~ucl:.ed heMisphel'e of this excluded for both values of
F is the Window Fachn'r tr)e r\.::~til) of the "wE-rage vertical illUMination on the .)utside .)f Ul\~ glazing to th€, t.)tal illUMination on en unobstructed exterior vertical surface. An aver'age value of 0.5 is u-:;t~d fo)~ an un.)bstructed sit€'j
U is a coeffi.:ient of utilization, thE' 1~~ltio of the average illul'tinati')11 on the entil'E! w.:.\'k pUlne in thE! daylit zone to the vertical illUMination on the outside of the glazing. An averagE! value (If O.'t is used f(w ver'ti':al windows;
Ag is the wind.)w ar'ea; Af is the floor area of the daylit zone.
Fr'uhl.in~1 devel(.ped a sel'ies of coeffi.:ients .:.f utilization fOI' diffel'ent day lighting systeMS (Table 1). Al thouflh high IE-vels of aC':lll~acy al"e not p,:.ssible with this Method, it fa.:iliti:ltes the roapid estiMatil)l1 I:.f the appr'oN.ifvlate aperhll"e at'ea neE.'ded to /"H~.;:~t a p~:\r'ti'::ular' set of design cl"itel"ia. It .:annl:>t, howevt:'i', el<al'tine orientation ';:'I~ ~.jindow shaLiing, be.:ause these fa.:tors wel"e not considel'ed in thE.' ':;'l"igi.n.f.d dfJVelopMent .)f the procedure. Real'l'anged to solve for wind,)w al'ea r rat.hE!I" than Daylight Fact')I"', this Method has been used to devt::-lop rul12 .:,.f' thUMb t\~:{~H'f~·ssions that still appeal'" in publications (AlA Foundation 1982) as a 1'~::COM"'H~'nded sizing technique.
SiMilal' t.) Fr'uhlinfl's flLl:<·-tpansfel~ equ.stion~ Littlefail-"s Method utilizes tiM€'- and weat.hL:;<r'o-averaged vE!I'tical illut'1inancl:~ data t.:. ,:al.:ulate the aver'age dayli.ght illuMinat.i':'11 in a \'(101":
W * T * Ev Ein = ------------- (2 )
A*(!"'R)
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W is winda:,w ar'ea; T is glazing visible transMittance;
Ev is aver'age l,Iel~ti.cal e:<ter'i':l}~ illuMinance; A is the total interior surface area; R is the aver-age interior 5UI~fa(:e 1~~';?fleJ:t.ance.
Littlefair' has Modified earlier wor'k by ...J.A. L.ynes of the British Building Resear'd-, EstablishMent (BRE) te. in':('I"por'.atJi.~ hour-Iy (l1"ient{.~tion'~ and sitespe,:ific daylight availability data (Gr'eat Bl"ita,in, Office (11" the Ministep ,'; the Envil"(ll1Ment 1982). Littlefair' describes the u'!:)~:! I:.f this f('j"11ula in the early stages of the building desi.gn proce"!rI~5 to detel"Min€: eithl::r a \"equir'ed window ~wea, 0\" the h~vel of e:<ter'iol" illui'd.nati.::on requi.r'ed by.at par'ti.:ular' win(i.)w .:onfiguration to pl"ovide the inter'ior dE:sign level of intetiol" illUMination. A series .:;af illtIl1ination·'-,::w.c:''lilability .)vel",lays in equidistant forMat was developed to aid in the estil'l-i;d,i>:111 of the ~1\\~l~,::e\1tage (If the y~,~ar
when daylight can pr',:,vide adequate irl'~el~iQl" illw1ination. Only ver'tical windows Hay be consideredu
While MOl"e fle:dble, this pl~t).:edure is More dif-f'i,:ult t,) use due tl) the lal~gel"
nUMber' of te.:hni.:al and design assul"lptiol1s that Must be MB ... 1e prior to its use. The cal':ulatiQn of annual day lighting pel~fo::n~Mance is al.so cUI1bel~s':>Mer due t.:> the h,)ul"'-by-houp forMat. of the daylight avai.lability data~
DEVELOPMENT CR ITER Jr,
Based on E*NaMinatiol'l of design Methods (Hopkinson, central to the developMent
a range of thesl:: and .)'tht2l~ sil"lplified daylighting et.~Il. 1966) the foll,:lwing .::hal"actel"isti.cs appeal~
of a successful procedute:
1. ThE' fOI~I'I(:'\'t should lend itsl::-lf to use Wi.tI"l sirlple tools and the Most general of de'!:iigl'l i.nf')\"Mati.Ol1. All tel"l"li.nolo9Y sh.;:.uld be fai'lili~H' ,)\" l~eadily understl)od~ .and the effol~t r';':!fp.dl"ed t,) define input values should bE! Minil"1.:':'11, .in ,:onsicier'atil)l'I of the early stage of the design pl~l)':ess at whid-l the pl~(,,:::edUl~e is Most likely 1',.) be used, and will be M.)st benef:Lcial. Ideallyv a fOLlr'"'ful'\.:;-,tioil calculator should be the UpPI2l" liMi.t. of' cOl1puting powel~ ner:)(h:;:d;
2. Tht'? pr-oceclur'e sh.:oul d b~! intei"n~:lll y conmistl':I ... t,.. T echni.:al assllrlp~
tiOllS should be cOMpar'ablE: in all p.::n~ts .:If' tht\' pl"(Il:eduj~e, in.:luding tho'SI'? between the l:alo .. llative i,echnique and the daylight. availabil~' ity delta... Signifi':ant el~I~Ol"~i H':IY be pl"':u;lu.:::ed thl~OlJgh a lad:: of ':')l1sistel'lcy (T\"egenza t982),
3. Ac,:ul~a.:y should be roughly cOMparable to that of MOI"e detail€,d tools~ If a siMplified pl"ocedul"e i.s to bl\~ N~'?aningful, its results Must be C')Mpal~able t,) those pl",)dl\l:t~d by MOl~e detailed Meth.:u..1s, l"!?:ognizing SOM€' loss in a,:.:::uracy due to th12 process of siMplifying the PI~')I:edure;:
4. The pl"t)cedUI~\'" should bE! site-- <:lnd ol"'iE,'ntati')n spe.:::.ifil:~ The basic issues in the evaluation of a day lighting !:itl"i:ltegy inl:lude the ,:ollSiidel"ati.:on of spel:ifi,: site conditions of daylight availability, and the location ,:.f the apel"tul"e in the building env€olope;:
933
5. Results sh,)uld dl?scl~ibe annu<ill ':'l"' l,)ng-ter'M pl?l~for'Man,:e. This extended fr'aMe of refer'en.:e allows the designer' t.) MOI~e easily per'f')I"'M Meaningful ':')Mpar'isons between design al tel"'natives, notably life-I:ycle .:ost evaluations, e<in"'ly in thlr~ building design Pl"'l:u:ess. Single-event t.),)ls al"e inconvenient, in that Hul tiple analyses Must be per'fol"Med to establish these values;
6. The pl"'o.:edul"e sh"uld offer' a cer'tain MiniMal level J,)f fle~dbility t,) its user's. Designers sh.;)uld be able to ei-;:pli.:,itly evaluat.e the effects I)f ':OMM.)n design 'f'eatUl"es 1)1"\ per'fl)I"M.c'n1I:e, such as glazing tl"ansHissivity, fiNed i:md/or' 0T.H::.'I"'ablfJ shading device~, and known si te obstr·uctions, without having to change pr'.:II:edul"'es.
DEVELOPMENT OF THE SIMPLIFIED PROCEDURE
The prinl:iples outlined above wel"'e applied in the developMent .)f a Pl"ototypi':al, single-'stage daylight.ing (:al.:ulat.ion pl~(II:edul"'e (Ar'nold 1984). Thl",)ugh.)ut the fl)llowing des':f'ipti.)tl, the pOl"'tion of the pr'o':edul"1? applying tl) vertical winct.)ws is us~.:'d t.) illustr'ate its developMent., featul"es, and use.
lDesired : IlluMinance: :Level
Daylit : * :Zone Area: * Fa
Window Al"ea :::: -~ .. ---------------.---,--.. --.-.---------- (3 )
wher'l:? Desir'ed IllUMinance Level
Fs
1000
1000
is det,81"Mined fr'I)M th€:> IES Illu"linance 8e1el:tio1"1 prol)cedur'e, 01" fr't:>M proj€:>ct design crit~~I"ia;
is detel~Mined by Multiplying the length along the window wall, by the product I)f the glass height above the finish fll)Ol" level and 1.5. The latter' factor establishes the effective depth of the daylit zone in a space ill.uMinclted by vertical windl)ws. It is iii. siMplifying aSSUMption based on eMpir·i.:al dat-Cl, descr-ibed in liopkins')l1 (1966)jl is the apertur'e sizing I:oefficient, selel:ted fl"('M tabul..-:d:.ed values (Table 2) ac,:or'ding to Ql"ientation and pe\"centi1e level I)f illUMination availability; is a scaling fa.:t.)r that allows tabulated values of F-::i to be elq.H"e-ssed in a MQ\"'e legible forMat (e.g., 7.51 VB. 0.00751).
The developMent of this prol:edul"'e ilw.)lved a sel"ies of detailed tel:hni,:al tasks, in,:luding:
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1. Definition of tedll1ical basis~ Th~? SiMplified sizing equation is der'ived froM an hour'ly ,:::al':Lllation pr'(II:edure developed by Law\,'en.:e Ber'keley National Lnb.:q"'atol"'y (Selkowitz 1.981) to suppo!"'t the BEPS Pr'og!"'aM. This Methodol(')gy, her'eafter .:alled the IlSEPS PI"(II:edur'e, It has sever'al desipable attl~ibLltes trlat Makes it suitable for' the developMel1t of siMpler .:alculating t(.015:
a. It uses a ':')l1stant tel"'H, the ROOM Cal.:ulation Fa.:t!))'" (ReF) to estiMat.e the l"'esponse I)f a space t.:. e;del"'iol"' daylight illuMinati.)n. Analogous to a .:oeff'il:ient of utilizati.)n, it is the average l"'atio between h.)l"'izonial illUMination at a ppedef'ined intel"'iol" r'efer'eIKe pOint, and e:<te I"' i.))"' illUMination on a ver-til:al sur'face.
The RCF desl:l"'iI"Jes the rel<ilti.)l1ship between inter'ior' and eNter'ior illUMination in t.EH'MS .::.r glass and wall heights, I"ather' than cll"'eas. It effe.:tively aSSUI'1es a one-f.:.ot-wide "slice" ttwough a space, independent of its length. The iMpO\"'tant geI)Hetl~i': r'elati.:onships ape shown in Figul~e 3. The level 1)1 illUMination at the r'eff.'l~el-ICt!' point is used tl) desl:r'ibe conditions thl"'ougr/l)ut the day lit zonE', and t.) estiMate the per'f'~\rl"!ance 1)1 photo:u:€.'ll I::ontrols~ Since thl? aSSUMed effective depth of tl·ll~ daylit z.)ne is ':I:onser'vatively fi:<ed at (Jne-and--·one-half til'1eS the height of the window wall, its ar'ea var'ies as the l:eilin9 height .:hmnges.
The ReF was del"'ived fr'('M detailed COl"lputer studies I)r typi,:al daylit spal:es (Selk,:.witz 1981)~ Analys\~!s wel~e per'fO)"'Med to estiMat,e illul"linance 1)11 task with gl.r.izing in the b,:.ttoH, Middle, and top thipds I)f the wadI ar'ea ab.)v.;:.' the woddng plane undel"' cll?ar' and over'l:ast condi.tions~ The season, r'1)I)H or'ientation, and pl"'esl:.:.-nce and size of an e)<tel·-i.ol~ ovel"'hang wel"'e also varied. Evaluati')l1s wet-e p~:_'r'for'Med ')l-Ily for' ol~ientatil)ns 1)1" sky .:onditions wher'E! dif'l:tct sun dit::1 not entel"' the l-'OOM.
The r'esul ts of trii~5 st.udy fOl"' d_E-ar and over'cast sky ,:,)nditiol1s, e:--;p\"'essed as dt:l:it'lal pel"'centages of unl)bstl~ul:ted vel.,til:al illuHinanl:e an"'iving on task, wer~' then weighted to obtain an annual average value of 0.233 fl)\"'.a totally-glazed e:del"'iol"' wall. This valuf~ May be <.~d~jl.lst,ed to .:onsider' pr'ojel:tspe,:ific I:onditions of glazing al-'ea~ visible tr'ansMissivity, fi:<ed and optH'able shading, and Mail1t,~:nan.:e, through SiMple Mul ti p 1 il:ative r't!-~ 1 ationshi ps:
RCF • RCO * T * W • 0 * M (4 )
ReF is the Roof'1 Calcuati(n1 Fa,:to,"'; ReO is the base ReF f'1)1"' a to:1t.ally-glazed eH
ter'iol"' wall, T is the visiblE' tranSMittance of the
glazing, in,:luding the influenl:e .:.f opt:.H'able shades;
W is the patio of the net glass a\~ea t.) net total wall area, il1l:luding Mullions;
o is the r'ati.) between the al"'ea of glazing
935
2.
with a view of tht:! ~iky fl"')1'l the stati')11 point unob-::itr'ucted by a fi:<ed e:<ter'ior ovephang, and the total glazed area above task height (30" abOVE! finish floor' level),;
M is the Maintenance factor, 0.80_
Inter'iol~ illul"lination May b~,~ found by Multiplying eNter'ior illuMination by the ReF:
INIiAY = EXDAY * ReF ( 5 )
INDAY is the level of interior illuMination at the stat.i':I\'l point, lUf'lens pel~ Squa\"e FO(lt;
EXDAY .is t>:.tal availablE.' e:.:;ter'ior illul"linal'\l:e on a vel"ti.:al sUl~f'ace, lUMens per' SquaN? Fl)ot r
ReF is the R')OH CaJ..:ulation Fa.::to)"'.
b. The ReF is bi:lsed 011 standar'd cal.:ul,mting pr'o'::(tdu\~es defined by the C')MMissi';:'l1 Inter'nationale de L 'E.:::lail~age (elE), using ~',')ul"ly illul"linati')n data for' both clear' zmd ovel"cast, skies. Tht-::- illul'lil1<;Il1':e Model (Dogniau:< 1978) is sensitive tQ ol"ientation, and can be e:<t."::tnded t'~1 any lo.::;,;,:~t..i()n fOl~ whid. key MEd:.eol"olog.i.:al pal"'aMet,el~s, such as at,Mosphel"ic tUl"bidity, aroe known. SiI1l:~~ the cal,:ulating Pl"'OO:E,'dur'e~~ originally used to del~ive the ReF wel"e able to c')l1sider' tt'n',~ eff\::o.:t of fil<ed and oper'.::~ble window ':.)ntN)ls, this capalbility is ':ar'l"ied ovel~ intI) the SiMplified pl"'ocei.'lul"'e.
c. The techni.:al dl::-rivation of the !IfF'S Pt(II:edul"e also ensure~~ a degroee .)f cOMpatibility with othel"' Haml':11 and ':oMputel"ized pr'oc~~dU\"f:'S b,~~sed on 5il1i1ar· eIE as'!',H,IMptiol1'!-:i- cun'"'ent.ly avail alb Ie to designer-os (Wilde 1.985).
Pl"'epal"atiol1 ,:.f t.he daylight. ava.ilability datab<.~se. T,) pl"ovide the desiJ~ed annual ped'Oi"Manc:e data, the corr'elatiol1 between intel"i,;:,I" leVti,~ls of illUMination and window design used in thl? SiMplified pr")':edur'e is based on a stat.i;:jtical de~"::l~iption of daylight avail<:~bility data. Wh,ilE' the BEPS F'r.::II:edur'e was or'iginally intended fop use with hl)Ul~ly illuMinan,:e data~ it I"lay also be used with data e:<pl"essed in terMS of pl"'obability, i.e. r the e:del"i.ol" illul'1inan.:e available at a given per'cE.'ntile of Ol::cltl"l"enceo.
Because data in this fOl"11at a!"'!? not ,:urrently avail.:~ble fi)l~ ,:ities on this ':ol'ltinent, illuHin.r.ltion datt1 e:,:;pl"essed in statisti,:al fOl"Mat WEH'e developed fo\" sever'al typical .:::liMates in North AMer'ica fr'oM hourly daylight availability data sets f.)\" d. t:!a 1" Clnd .;:,vel"l:ast conditions published with the DEPS procedure (Selkowitz 1981.}. These data l"epl"esent average I:ondi tions in urban ar'eas at pal"ti,:ular latitudes, and EI.1"e not ass')ciatl'2d with specifi.: locat.ions. The REPS d~ta sets contain seasonal houl"ly dil"ect, diffuse, and total illuMinan.::e on the- foul" CaNtinal ver'tical 5\'1l~fi:KeS, and h')l"izl)ntal.
936
The value for total lU,Min')llS fluN is used with the RCF to der'ive interior illuMination.
Per',:ent of Possibl€* Sunshine was uSt::,d to deterl1ine weighted avepage seas.)nal hourly values of total lUMinous flln< frol"1 the published data f(ll~ d,t:.oar and over-cast .:onditions. Standar'd statistical-analysis pr'ocedul~es wer'e used to gr'oup the h,)ul"ly daylight availability data, and deterMine the p~'r-centile levE.,ls of occul''I''enc€'. Figure 4 sh.:.ws the r'esulting d.aita base for' one cliMatic zone, developed using weather par-aMeter's for Nashville, Tennessee.
3. Descr'iption of th€~ I~elationship b€\,tween e)der'iol~ daylight availability and intel"ior' illUMination level!:i. F.:l\~ this key stE.-P, the nOI~Mal
use of the BEF'S F'1~(I!:edur'ef sl-'t(.wn in Equati.)n 4 y was invel~ted. The interior and extel~iol~ illuMim:{tion levels were treated as knl)wn var'iablE's, and a M(.dified ver'siol1 of Equation (4) was solved fOl~ the requi\~E.od value .)f the ReF at diffepent. p~~r-(:el'\t:i.le It.:'vels of e)<teti,)r daylight availability:
INDAY I:-':CF - ---,----- ( 6 )
EXDAYi
INDAY EXDAYi
.i s th~:.' .i nt~,~\~ .lor' design i 11 t.1I-dnation leve 1; is the level of e)<tel~iol~ daylight at the i trl p0~r'c~~mtile (.f Ol:(:ul~r'ence;
ReF is the I"equiped ReF.
F'al"aMet.\~i.:: studies wel~e pe\~fO\~Med fOj" ve\~til:al sur'faces fa.:ing eadi J:.au"dinal ol"ientation, witt', INDAY equal to 30, 50, and 70 footJ:andles; EXDAYi was v'::ir"ied fl~OM the 10th to 90th pel~cent.ile of (,,:.:ur·\"en.: ... ~~ by tens" Di-I"fering d~.'gl"ees 1)1 '~·,hClL1ing by a fi:<ed eJd,eriJ)r ')VedH:\ng-'·'n.)nt?, 507., .:H1d :lOOi,;··--wer'Ic;, als() CI)nsider'ed. The \"\'?sulting v21lues I)f RCF indi.::.at,e the pel"centage .)f e)<tel~iol"
illUMination equalling INDAY.
Fl"')11 these data, the gl~lz.>?d al"ea .:J)l~responding to RCF was dt'?t.~:H·11il'l(:",d, {:ll1d fl~('1"1 this r rel~ltionships w~'?r\;; dfi!veloped I':.etwt:.=:en glmss -::H'ea and e;del~iol~ wall 2ti~e.:" and b~.'twt"'I\:,·n glass cll~ea and the 1'1')0\"' -i:we':l (If th>2 daylit. ~:(lne. Figw">2 5 shows one set of calculations f(Jl~ a west-facing spac~,' without .oln E.';del"i.)r' ollt:'phang, in a tel"lper'ate clil1ate, with ,:1.1'1 inted,or de-::iign illuMin.1:1ti')11 level of 50 footcandles.
DevelopMent of cOr'relations between interior' and exterio)" 'li.on ancl window design paraMetEq"S~ A l:i.ne.o\I~ l"egl~ession
pel"for'11ed to define the ,"elati('llship betWE'Em inter-i.»)" illuMinati.)l'l If..'..,,els~ and £~lwelope de~iign conditi.ons:
Y = MX + b or:
RCF = INDAY * (Line Slope) + Intercept
illuM.Lllawas then
design
( 7)
Since the Magnitude of the constant terMS I"egression ana 1 yses wel"e all less than 0 M 001 ~
( intercepts) in the they wel"e discatded.
937
E~<.:ellent .:')I~I~elati(.n between these var'iables was ,)btained using the linear' M.)t.iel. This lineapity also enables a single set of ':oeff'icients to be used with any desir'ed level of inter'ior illUMination.
Tht.~ regr'ession coef'fi':ients we!"'€' then ,:oMbined with e:<pl"'essions r'elating glass al~ea to floor ape-a at ea,:tl pepce-ntile level of illuMinan,:e to genel~ate ttle sizing coe.-ffi.:ients used with the siMplified l"'elationship describ€.'d in Equ':lti':.n 3:
Daylit : INDAY * : Z')nli.~ Ar'ea: * Fs
Window Al~ea - ----------- .... ----.. --.. ,--".---- (8 ) 1000
Daylit 1
: Zone Ar'ea I * Fs Fi:CF Window Apea ::: --------""--.--.- ... -.--. * ( 9)
1000 Slope
Wind,)w AI~ea Slope Fs ::: ------------- * * 1000 ( 10 )
Floof Area ReF
The sizing co€:d-'fi,:if~nts shown in Table 2 Wf.~r'8 thus cal.:ulated using data pr'evi':;iusly gener'ated by the l"'e~Jl"'ession analysis (Equati':;in 7), and the analyses pel~fl)\"Med in St.ep 3, abov€'.
5. DevelopMe.-nt of awdliar'y r'outines for' i:\djusting initial r'esults. The l~esults of Equatiol"t 3 11ay be Modified to ;,.:t':':':;'tmt f,)r variations in glazing visible transMittal1':e, and the use of .:,pet~abl€' int€'\~iol"' shading devi.:€<$:
For glazing transMissivity~
Adjusted 0.82 Window -= A,) * ----".,--- ( 11) AI"'ea
whet"'e Ao
Tv new
Tv new
is the unM.;;.dified winliow al~e.-a ,:.al,:ulated using Equation 3; is the visible tr'ansHittance of the glazing ~;ysteM;
0.82 is the baseline visible tr'ansMittal1,:e, used il1 the .:al,:ulation of the sizing .:oefficients.
rot"' oper'able.- shading:
Adjusted Window At"'ea
0.82 = Ao * -----------------------------
{(Ta * Is) + (Tg * (I-Is»))
938
( 12)
A"
Ts
is the unModified window apE-a ,:al,:ulated using Equation 3; is the visible tpansMittan.:e of the glazing systeM and t.he orJl.~rable shading devi,:I?';
Xs is the pepcentage of o.:,:upied hom's that the shading dL~vi,:Ii.\' is in use;
T9 is the visible tN1nsMittan,:e of the 91.azin9 Syst'ii.'M alone.
A statistical approach was Llsed to dt~st:d.be the effel:t of the oper'able shading device, due to thE' diffi,:ulty of stating with pl"el:ision the e)<B,:t hours that the shad~.' Wt)uld be depl,)yed. Publ.ished studies (Paul 1950) ~5u99"'~st. the extensive use ,:11"' ':'per'able shading, wher'e pl'ovided, in a Mannel' sh,)wing n.) ,:on'elation t,) either' season, hOU1~" 01' orientl:ltion.
6. Validation I)f j"'esul ts again~it dc·tailed pr'I)J:edttr'es~ A liMited validation ':')Mpared the per'{")l"'Man,::l":' ')r -iii window area Lierined I'.)Y the SiMplified Sizing Equati,:1\1, to tht~ r'esul ts of the QUICKLITE pr'ogr'aMMable ,:alculatO:I\~ pPOgNIM (Br'yan et.aI. 1981). Significant effl)\~t is r'equir'ed to develop a M€'aninghl1 cl)Mpal~ison between the resul ts of a sing1e-"event calculating to~)lr SIKh as OUICKLITE, and a statistil:i-\l pl~lxedllr'e. aUICKLITE was stde,:ted because: it is l"'eaf:lily availabile; it. has been valid-1!ited against a series of detailed calculation tCII)ls;; and it is based on the saMe standarLi CIE assuMptions as the BEF'S pl~,).;::edure ,:oncer'ning trn= lUl"linanl:e distl"'ibuti.)n of the sky and thE' call:ulation of intel"'iol"' illUMination levels based on this distributil)n~
A test I~OOI'l was developed, and the siMplified prIKI'.~dul"'e used t(.) size a west-f'a.:ing window t,:. pr'ovide all 8Ve\~age of .sIt least 50 fOl)t,:andles (If inter'io\~ illuMinat.i.)n in the daylit zone, dur-ing 70 pel"'cent of the (Il:,:upied hJ)lll~s of t.he yeat. The saMe space and window al~ea wer'e then descl~ibe(1 f,n' QUICI"LITE r and a ser'ies of analyses was ~le\~fl)r'Med to develop an lIIllwnnaU"on Calendal"'" (Wats(ln and Gh,vel'" 1981), a per'fOr'Manl:e Map showing annual perfol~ManJ:e. (See Figur'e 6). Twenty caiJ:ulati':H1s wel"'l~ per'f'(ll~l"'led using QUICKLITE tl) genel"'ate this diagl~aM, r'~:.'quil~i.ng appro:dM3.tely fifteen hl)UI"'S of \~un
tiMe on t.he ,:al':lllat.or. The illul·lination availability data and oper'ating instrw:t.i')l1s published with the pl"'ogl'"aM listing Wt::<\"'e used faithfully.
The final resul t, Becor'ding to QUICI"LITE and the IllUMination Calendar" p\"'(,,:edUJ~e, indicated that the wind(.w ar'ea derived f'\~OM the SiMplified pl"'ocedure would pl"'ovide the desiN":·d 50 footcandles dUl"'ing apPl"'ciNiMately 78i.: of oecupi~2d hour"s1 a diffel"eno"," of rl)ughly 1ii;: fr'I)M the 01"'i9inal estiMat,e.
A Majol"' liMitation of this Mf.:'th.:.d of evaluation is the dif'fil:ulty of developing a dil"'el:t J:oNpar"is(.n of the u!:"e (,f ')pe\"'able shading devices between the two pr"OCedul"'es. A Nor'e e:densive study is c.u\"t'ently under'way, cOrlpa\"'ing the ~1I~el.iil:til)ns I)f the siMplified pro,:edul"'e t,) the I~esul ts of DOE-2. HI (WinkelMBl1I1 1985).
939
7. Definition of the pl"'esentation fOI"'l'1at. Equal in iMportan.:e t.) l"'elative ac.:uracy is the devt'!lopl"lt.~nt (.f a presentation f')j"'Mat for- a SiMplified pl"'(II:edUl"e that enhanCE'S its U~ie.' and clal"'ifies the relationship between its results and other issues relCiting to pe-l~forl'1anCe and design.
This infol"MEltiol1 May be as-::.ie11blecl in <.~ "pEtter'n" fOl~Mat (Ale;{ander 1976; and Hastings and Cl~enshaw 1978). (SeE.' Figul~e 7).. IMpor'tant issues hK~lude~
a.. Selection of data to I"'efh:'c:t both design-related and analytical C(fn(~ei"ns;
boo IILayel"'ing" J~f infJ))~Mation to fac:ilitatt~ study by the desi.gner at. thl,:\> appr'opl"iate level of detElil;
J:.. DevelJ)pMent of an inde)·(ing systeM 'l'el.alting dipectly to specific (h~sign <:1nd evalu.8t.iorl pr·oc€'(!ures r
ct.. DevelopMent J)f a consistent. fOr'I"I':;lt that J:an .8CCI)MModate a variety of systeM types and cOMponents;
e.. Use of gr'ap!"IlJ:s whepe aPP1"'opI"iate; f. Use J::d:' a "vJ)'::abular'y" .r.lppropr'iate to the audili.~nce, g.. Inclusi.)n J)f PI"'.:.totypical data telating to enel"'gy and .:ost
per'fOl"'ManCe and to dt'.'sign issues such as thl? quality of the inter-,lJ))"' envir'onMental y th':lt 11ay not be e~{ClMined in det.ail until latE't- in the de~;ign proJ::ess"
Thi.s patt~.H"11 could ilKlud€' a gr'aphi,: pr'€'5entation I)f the sizing coefficients, as in Figur'i!! 8.. Stich a nOMogr'mph would l"educe t.he ef·f',:Jrt inv.)!ved in b:,,:ating spt~cific cl)effi,:ients and in intel~PJ~l
ating bE,tween d.itf\:~r·\:!n1·. or-ientations and degr'et~s .)t obstruction by J)verhCll1gs ,.
APPLlC(,TlON OF THE SIMPLIFIED f'RDCEDUf,E
The SiMplified Siz.ing F'1~(,,:e(ll~l~e descr'ibJi:'!d i;lt,'IOVI? wa~t d\C:!!:iigned to fi.t into the str'uJ:tLu"'E.' of the cll?sign de.:isiJ)n-MC'lking pl"')I:e~js shown in Figure 9. Note the following pl~ogressiQn (If C01Kel~ns:
1. IDENTIFY DESIGN CONCEPTS, 8>.g .. ~ "Dayl.ight th6'! building, II s8>l~t:t€;>d
bas€;>d on the requireMents of the building'S architectural prograM; 2. DEVELOP DESIGN STRATEGIES, e.g .. , "Pr-ovide 50 f,)(.tJ:andles of daylight
f.)r 70% (If the year', using skylights, II developed 'fr'ol"! space design l"'equil"'~11ents and the per-fOl"Marll:e attr'ibutes (.f spe(:ific stl~ategies;:
3. H1PLEMENT MEASURES, e~ rJ., II Install eighty of Manufactur(~\" X I s pl"'oduct, 8c:o:>l"ding to these dl~,:;I,wings <.~ncl speJ:ifi.:ati.)nsy II de .... eloped aftel"' the basic: feasibility of the con.:ept has be8>n J2stablished.
As sh.)wn in FiguI"'e 9, thJ;.~ SiMplified Sizing F'r'o.:edul"'~.' fa.:ilitatE's the tl"'ansitiJ;)l1 fp(JN lI,::onc:epVI to " s tl"'ategy" by l"edu,:ing the nUMt;par (If iter-ations potentially r-equin?d to establish an .:lc:J:eptable claylighting systeM using conventi.)nal d>i.~sign tell)l s. Its l"'esul ts ate conc8>ptu.f~ll y lo(.t:;e E.·nough en.)ug~!
to encour'agJ!'~ fle:dbility and e){pePi_Mentation by the designel~.
940
The followinq e:<aMpl~ illustl~.ates the us"' .. of the SiMpli.-fied Sizing F'l~(II:edur"e:
1. IDENTIFY DESIGN CONDITIONS
a. Or'ient.ation; W\i.:.'st-f acing; b~ ROOM Size: Appr(f:dnat€!l.y 30 fet= .. t deep and 40 feet along the
window wall; .:. Cei.ling Height: Appr'o;dMatE'1.y to feet;: d. Design IlluMination Level: 70 footcandles; e. Daylighting Goal: SLdy rH'.'l~Cent (If' of::cupied j"I')UI"S (8 A~M. - 5
P.M.) should Meet or eKceed the design goal in the daylit zone~ f. Glazing Type: DoubJ.\:.~-glazed aS5121'1bly, o)utE!I~ lite is blue-gl~een
heat-absorbing glass. V.i.siblE! tr'ansMitt,2,IKB ~" 80:'C g.. Window C':mtl"ols: Nf) ol,lel"hangn Light'"'colol"ed venetian blind is
used 50~~ of th\i.\' tiMe (vi-5ible tl"al'ist'littanc8 .:.f window asseMbly :::; ft1~~, when blind is in USE'. )
2. DETERMINE SIZE OF DAYLlT ZONE
For' v\i.H,ti.:aJ. windQws~ this e:d:.ends the entir't":< length of the winck.w wall, t.o a dept.h equal to 1~5 tiMI!i.'S thtl\, space h~~.i9htn In th:i..s c.i±\Se:
Ar'ea L~ngth * Depth = 40 * (10 * 1,5) _. 600 Square Feet~
3. SEL.ECT (,F'PROF'RIATE SIZING COEFFICIENT
F01" a w!\~st-fal::ing vertic.al wi.ndow with no (,vE'l"hang r a design i11uHination level (If 70 f(H:d:,c.:~ndle$ ~\11d a goal (.f 60% of the yeap daylit (f,Oth p~:!i~centile (If ~\vailmbil:.Lt.y); Figu\"e 8 indi':atE':' that thE' value of Fs should be appro:d.M.at\i.:,.].Y 2n6 «(fl~ 2.62 fl~OM Table 2.)
4. DETER~HNE BASE AF'Erm.lf'[ AREA, A(o
Using the SiMplified Sizing £quation~
70 fc * 600 SF * 2.62 Ao - 110 Square Feet.
1000
5. ADJUST APERTURE AREA FOr, GLAZING TYPE AND SHADE TRANS~iISSIVITY
Using Equation 9:
0.82
Aa :::; ----------------------- = 149 Square Feet. ( 0 ~ 42 * 0.5) + (0.8 * 0.5)
6. DEVELOP WINDOW SYSTEM
As~;uMil1g that the window -systeM will nm thE.' entire length of the 40-Foot wind.:;.w wall and that appr-o:<iMately 10% of t.ht:! apel~tul"e Br'ea will be taken by Muntin!:
941
149 SF Glass Height = - ,·.1 Feet.
40 FT * 0.9
7. LOCATE WINDOW SYSTEM IN BUILDING ENVELOPE
Based 011 the above inf'JI"Mation, t.he designl;£'j" Might. seleJ:t a window height of 4 Feet (48 Inches, ) as the cl,)sest standapd Module, or' selel:t a sMallel' Module (e.g. 36 Inches) and al:cept the pel'fl)l'Han':e penalty that this iMplies, depending UPQI1 C(lHpOnent availability and .:.)st. TWI) p')ssible ap~'l .. tu\"e ,:onf'iguN'Itit)llS Qf'fer'ing ':')Mpar'able per-forMan,:€, ar'e sh,:,w\1 in FigUl"t? 11. N.:,te that sUppoI'ting infol"Mati.)n, del'ived frOM MOI'Ii£' detailed studies, is ne,:essar'y to ensur'e that trlt? final gla;d.ng configur'ation offel's adequate pel'foI"Man.:e in all r·egal"ds.
CDNCLUSIOUS ANn FURIHER "'(SEARCH
The studies (lut.lined in thi5 paper show the pot.ential th,mt SiMplified, sin91e-' stage daylighting-cal,:ulati,:an pr',:,cedures ,:affliH' the d>i!.'signer' 1:.:a\1.:epnel1 with cOMpleting the initial stages .:af pr'oje.::t deveb:a{:l11t'?nt as quickly and painlessly as p,)ssible. These pr-ocedur'E.'s allow the j~apid estiMati.)n of ape\~tur-e ar'eas with MiniMal inf(~rMation exp\~essed in t~~\~/"IS faMiliar' t,) the Majo\~ity of design pr',)f'l!ossionals.
As noted ab(IVe, however r E~){pli.:it and iMpli.::it liMitations restr'ict the issues that it I:an aLi(.kess, including;
1. G\"~':\dients I)f i1luMinat.i.:al'\ in .i,ntel"ior spa.:::eSj 2. Daily 01" h")ul~ly variati.)ns in intel~i(tr daylight levels; 3. Reasonableness (If day lighting goals - strl:ltegies Hay still be
iMppoper'l y sized, due to the designel"'s ':.ieh\'(~tion I:aT inappr,::,pl~iate
design object.ives. Sud'l er'rQPS in judgeMf~nt May, twwever', be identified MOI~e quid::ly thl~ough us~' of a siMplified pr"':acedul~e;
4. Changes to key val~iables, in.:luding length .~f oo::upied ptH~iod, and the size l:of the daylit zone relatiVE.' tQ thE.' diMensions of the spa.:e;
5. F'el"f':OI"MarJl:e of a l1aylighting str'atl~gy in terliS (If visual. ,:oMfl)\~t.
Sever'al liMitations ar-e inher'ent in stati~itil:al Pl~o,~~edul~es. Although the SiMplified p\~(,,:edur'e descr'ibed in this paper satisfies t.he initial developMl;':!nt cpiter'ia, its I~esults should always be c')nfil~Med by Mo)""e detailed tools.
Additil)nal effor't to devel.)p 1:'~Mpanion pr'I)':e(!ures that More closely \"elate the selel:tion of design goal~ ,to physical design pa\"aMeters (liMitation 1:13) is cUI"j"ently in pr'og\~ess. One b:1I)1 ch:~vel(,pt7.'d fl"OM the I"elati.»)')ships between window and wall al"ea and between window and fh:t1)I~ ar'ea in the daylit zone is the Window and Wall Design Pa)"aHetel~ NOMogNlph (Figute 12). This n')Mogl~aph relates possible design obj\?:tives < pel~cent of ye.c:H' daylit to 70 f')l)tcandles, ) to readily-available infol"Mation about the building envel.)pe, Ol~ to data on solar' heating per'fol~Mance taken fr'I)t1 othel" pules of t.huMb.
While a ':oMplete discussion of its use i.s tlt?y,)nd the scope of this papel~, the following e){aMple illustpates sevepal useful attr'ibutes Made possible by the
942
1. Wind"w-to-Wall-Al~ea Rati,:o. This n':OMograph r'e-Iates percentile levels of daylight availability to the per'cent of the E.*nvelope at a given ol"ientation that Must be glazed to pr'"du':e a desir'ed intel~il)l~
illUMination level. A building designer' ,:an use it to l~elate a goal (e.g. 807. "f hl:,ul~s daylit) to what hI!!' or' shl!!' May all~eady know about a building (e.g. Ma:<iMuM 407. of e:ded_or envelope glazed, without a special ol"dep for' the window asseMbly.)
IMpor'tant questions that it May help to answer- in,:lude:
What daylighting ,:.)ntr'ibution is possible with a standa)~d
window systet'l? Is the per'fol~Man.:e 9.:oa1 COMpatible with design .:on$tl~aints? What per":entage of the envelope Must be glazed to Meet daylighting design goals? CCim this be d.)ne within the ,::onstNdnts of the stl~UI:tural and glazing systeMS?
Use of' this por,ti,)n ,:of the nI)M')gr-aph is with sele,:tion ,:of the krwwn vahle on l,:u:atil)n I)f the l~elated val~iable .)n the
s tl~aightfo)~wanl, the appr'opr'iate othe)~ a:<is, with
beginning a:ds, an'd
pef'el'ence
2. Equivalent-Floor-Area Ratio. This pOJ"t.ion of the n>:OMI)graph relates the percentage of wall aNi'a glazed to the equivalent pel~,:entage I)f fl,).»)-' .=1I'ea glazed in the daylit 2:':Ol1e. When e:<pl"essed in terMS ,)f the fob).)I" al'ea of t.he entire (ther'Mal) zone, this allows the desigl1el~ to J"elate daylight-ing .:::r'ite)'ia diretly to infol~Mation
on passive-sol'=Il'--heat.ing per'fOr'Mf.llKe f)~')M ':':'MMon )'ules of thUMb fOl~
dire.:t-gain systeMS. (A liMitation is the typical liMitati,)n ,:of solap per'foPMance data to S,:;.uth--facing glazing.) The optiMizati')rI of these r'elated issues in I~esidences "r sl"Ia11 O)MMer,:ial buidings can take a signifi.:ant. po)~ti':'11 of design tiMe.
FI)I" e:<.=mple, a pl~eliMinar'Y passive-5.:.1a)~ evaluath'l1 indicates that a south""fa,:ing window al~e.El equal to C;;' per'cent of the floor' i:H'ea will pl",)vide aPP1"',:o:dMately 20 per,:ent of the annual heating l'equir'eMent in a given cliMate:
What is the cOl~l~esponding daylighting ,:ontl~ibutil;:.n? Is this adequate, .:onsider'ing the potential savings in lighting enel~gy?
If the window ai~ea is incl"'eased to benefit. daylight..ing, what is the effect ')n heating per'fol'Man':e? Could the space ovel~heat?
Use of this nOMgl~aph is Mope involved than the Wind,)w-t,)-Wall-Ar'ea Ratio p')r'tion, depending on whether' daylighting potential Ol~ passive heating 1:l)ntl~ibution has been evaluated f'il"'st ••
If the sl)lar' analysis has been done f'ir'st, the flo»l~ al'ea in the thel'Mal zl)ne Must be e:<pl~essed in tel"MS of the al'ea of the daylit zone. Knowing this value, the ':ol"r'esponding daylighting ,:ontl~.ibutil)n May be f'.)und, with r'efel'ence to the appl~opr'iate
943
REFERENCES
(south) elU"'v€' fc.)" ol"'ientati')\'h The ,:')l"l"eSp,)nding per"cent of wall ar'ea glazed Hay then be found, using t.he other' side of the nOMogl"aph.
If the day lighting analysis has been done fir'st, thE< d<ilylighting contl"'ibution May b\\~ l>::,,:ated on th€:< h,:,j"iz.)ntal a:<is, and the equivalent percent of floor area i~ the daylit zone found with l"'eferen.:e to the appI"'opriat~! (S,)uth) curve f')I~ ol"'ient.ation. The floor' arl!~a in thE' ctaylit zone May then be e:<pr-essed in tel"'MS of the are.a\ of the thel"'Mal z')ne, and this value .:.)Mpal'ed to the r'esul t5 of thE.> cOlw>!~ntional passive '..'iolal" l"ule of thUMb, t.:. E.>valuate the ,:ol"l'~sponding heating pel"fol"'Mance.
Alexander, C, et.al. 1976. A pattern language: Towns, buildings, construction. O:<fol"'d University F'r"ess M
AlA 1982. The a1"'"chi tel:t f s handb.:.ok .,.f ent:'I"'gy pI'act.!.ce ~ Dayl.l.ght.l.ng design. The AMer"ican Institute of Ar.:hitect.5, Resear'dl Foundatl.:,n.
Anl.:;.ld, G.W. 1984. HDevelopMEint of a siMplified window-s.iz,ing TH'c,,:edu\"e for' daylightin9 design. JI Master"s thesis, Al~i;,~on.a\ Stat.~! Univel"'sity.
BalcoMb, ... J.D., et.al. 1978. The passivE' f:~olal~ de!'sign handbook, Vol II. U.S. DepartMent of' Energy.
BalcoMb, J.D., and McFal~laru:.i, R" 1978" "A siMple eMpiriGd Methocl for' for' estil"1ating the pel~t"")t"'11aIKE! .:,.f' a passiVE' sl)l~n" building of the thel'Mal storage wall type. II f'r.:,,:el':,dinf.)s (.f Un':! Second National f'assive Solar'. Confet"'ence, AMeri,:an Sol.aH' Energy S.:,,:iety~ f'hiladt:l phia, fA.
BI'yan, H.J., >i.~t"al~ 1981. "QUICKLITE I~ New p1"ocedur'e for' day lighting design." Solar' Age M<ilgazine"
DogniauN, R. 1978. "Disponibilite de L"'Ecl-i:1i\~eMent LUMirH!!u:~ Natlll~el." Institut Royal Meteorologique de Belgique, Br'u:<elJ.es.
H.)pkinson, R. G.; F'etrl\~l~b\~idge, P.; and L()ngM(ll"'e r J. t 966" Daylighting" Will iaM HeineM.alnn Ltel., London.
Littlefair', P. 1982" "Designing t.»)", daylight using the BRE average sky." GI"'eat Britain, Office .)f the Minist~\" of the Envil"OnME!nt, Building Re5eal"'ch EstablishH~H\t.f Ll)nd.)n.
Jones, R.W., et~aJ.. 1982. Th€' passive solal~ design handbook, Vol. III. U.S. nepal~tHent of Energy ~
Paul, H. 1950. IIDaylight in $.:ho01 .:1a55)"'00M5." Univer'sity of Mid'ligan, Ann
Ar-bo\" •
944
TABLE 2
Sample Sizing Coefficients for Vertical Windows, All Orientations
PERCEHTIL£ DEGREE Of OBSTROCTION BY FIXED O'JERHAHCS Of DAYLlQIT
CIIloo ATlOM AUAILAlILlTY - SO PERC£HT 100 PERC£HT ---IOITH 10 I.!' 11.41 19.24
20 5." 1.:17 14.03 30 4.67 6.~ I..,. 40 3.'4 5.38 9.02 SO l.lI 4.75 7.95
" J.Ol 4.25 7.13 70 2.75 3.15 6.~
10 2.58 3.62 6.07 90 2.41 3.38 S.S3
---EAST 10 6.87 '.64 16.16
20 4.67 6.55 10.91 30 3.S2 4.95 1.29 40 2.15 4.01 6.71 SO 2.58 3.62 6.07
" 2.16 3.04 5." 70 1.55 2.17 3.64 10 1.11 1.56 2.61 90 .15 1.2 2.01
-- --SOUTH 10 2.12 3.'4 '.64
20 2.25 l.16 5.29 30 1.63 2.29 3.84 40 1.38 1.94 3.26 SO 1.24 1.74 2.92
" 1.07 1.51 2.51 70 .95 1.34 2.24 10 .15 1.18 1.99 90 .78 1.09 1.14
--- ---IlEST 10 5.23 7.35 12.32
20 3.84 5.38 t.02 30 2.94 4.13 '.'3 40 2.62 3.67 6.16 SO 2.38 3.34 5.6
" 1.5' 2.24 3.76 70 1.11 1.55 2.61 10 .19 1.25 2.1 90 .75 1.04 1.75
946
MYlICtfi J AVAIlULI SITE IUUHlWollON ILlUMlN411DN of fEATURES IUSPI£f
• LOCATION ·LATITUDE 'lIME OF DAY .ORIENTATION .SEASOII 'L~NDS(APING
• CLOUD COVER 'OBSTRU(TIONS ·TURBIDlTV • MICROCLIMATE
J ANNUAL MYlIGtfi
~f! LIGHTING IllUHlIl'lION INIRGV 'M t.SPI££ SAVINGS DAV
Figure 1
\ \ \
\
, '0""" \ 00 \
PATHS FOR DAYLIGHT ILLUMINATION FROM SUN AND SKY TO TASK
----DIRECT
__ --0- FROM INTERIOR SURFACES - -- __ 0- FROM EXTERIOR SURFACES
-------FROM THE GROUND
HOUR ZONE
APERTIIRE
~ DESIGH + DE5~"
.SYSTEM TYPE ·GfOMEIRV 'LOCATION ,SURfACI 'SIZE RlfUx:TANCI 'SUN CONTROL .IISK LOCATIO" 'fRAMING 'fURNITURI .GLAZIHG TYPE • MAl Nil NINtI 'NAINTEHAN(E
LIGHTinG
• Ca.1ROl
SYSlEM
'SENSOR LOCATIO" .TIM[ RESPONS[ ·CONTAlllDGIC • LIGHT IPDWER RATIO .lIGHTING S't'ST[N lVPE ·AUTDNATIC/MilNUAl
.USER RESPONSf
Figure 2. Sources of daylight illumination at a point in a room
947
Figure 3.
- ~ - .-.-- -.~ --~~---.- ~..- ......... ---" --.-.~-'-~ ---"--~~~-......---..--........... ---~~~ .... --...---- -.--.,." .. ~ -~ -' ~. '
,. WIOE "SLICE- THROUGH SeoACE ASSUMED BY THE BEeoS PROCEDURE
BY OVERHANG
OlSTANCE=SPACE HEIGHT
Spatial relationships used in the BEPS procedure
e 0 a.'" ~ 0
I ::l EO • x .,'" "' .... a:'" ,,> ~~ "-5 ~~ ZZ '" -0" ffi 3 a. =1
100
90
80
70
60
50
40
30
20
10
I\..~ . ...•.• \\\ \ ....
'.
\'\ \ •.•.•.•.
\ '\ . .••... \\ \ ••... . \"-.m \ ....
". HORIZONTAL '.
\ ~ 1\ ". .... NORTH ~ ~ \ SOUTH VERTICAL ••••••
o o .,
\ \
g N
~~ \.. ~
g o M
o o o .. o
o o ~
o o o ~
...... '.
'. ".
o o ~
o o g
AVERAGE EXTERIOR ILLUMINANCE - LUMENS PER SQUARE FOOT
Figure 4. Daylight availability ogive
~
~
~;:fCAlC - ~OO/1 CALC~H·TlON fACTOR WORKSHEET
SI~F'L!qfn DAYlIG~TING SIZING ROUTINES
'J£RTICA/.. WIHacWS
ORWHiiTIOH: IlEST
[HIGN ILLUMINATION LEVEL (Fe J:
GEORCE ~RNOl~ 1/8~
SO r'~r::CC:IIT 1J~I"I~ST~'l.:C7H GLtii:ltlG (/100):
CAS [ CAS E
FtRCOITlLE DAYLIGHT LEVEL: 10 m:CElfTlLE DAYLIGHT lE1JtU /lVAJU8lE BAYLICHT He ): 625 AVAILABlE DAYLIGHT (Fe):
ClAZINC TRAHSltISSIVITY: .82 GlAZING TRANSIIISSIVITY: SHADE TRANSIHSSIVIH: 1 SIiAD[ TRilNSl1lSSIVlTYl SflAC£ HEICHT 1FT): 10 $PACE HEIGHT 1fT):
REQUIR£D 'SERVICE' 1tCf: .08 REOUIRU 'SEINJC£' Rtf:
REQUIRED FT: .523 R[DUIR£II rr: ClASS HUGHT: 3.9225 ClASS HEICHT:
Q.ASS/FlOOR AA£A RATIO: .2615 GLASS/fLOOR AREA RATIO: WIHDOW/ItALL AREA RAllO: .39225 WINDOW/iiALL AREA k,;lIO:
CAS [ CAS E
PERCENTILE DAYlIGlfT LEVEl: .0 PERCENTILE DAYlICHT LEVEL: A'JAILA&LE DAYLICHT (fe): 1250 AVAILA81[ DAYlIGHT «(e):
ClAZIHG TRA,IISltISSIVITY: .82 "-AZINC TRAlfSHISSIVITY: SHADE TAAHSltISSIVITY: 1 SI\A[)E TRANSIIISSIVITYl $Pia HEIGHT In); 10 SPACE HEIGHT (FT):
REOUIRED 'SERVICE' ReF: .0' REQUIRED ~S(jNICE' ReF:
R£IlUifi.ED Fr: .262 REQUlRED IT: "'ASS HE lCIIT : I~S cuss HEIGHT:
ClASS/FLOOR AREA RATIO: .131 CLiiSS/FLOOR AREA R.mo: WINDOW/WALL AREA RATIO: .)9115 WIWDOW/IAALL AREA RATIO:
CAS E CAS E H
f1:RCEHTILE DMLIGHT LMU 70 f'[fiCEHTILE {lAYLIGHT LEVEL: AVAILA8LE DAYLICHT (k): 2.25 AVAILABLE DAYLIGHT I fe I: CLAZINC TRANSI1ISS!VITY: .82 GLAZING TRANSI1ISSIVITY: SHADE TRAHSI1ISSIVITH 1 5HA/.J£ TfI:{jIISIUSSIVITY: Sf'AC[ HUCHT (fT): 10 SPACE H£ICHT (FT):
REGUIRED 'SERVICE' RCF: .017 REIlUIii'U 'SERVICE' "Cf:
REQUIRED Fr: .111 R£DUIRED rF: CLASS HEICHT: .8325 'LASS HEICHT:
GlASS/FLOOR AAEA RATIO: .0555 ClASS/flOOR AREA RATIO: WINDOW/WI\lL AREA RATIO: .08325 WIHOOW/WAlL AREA RATIO:
P£RCEHT Il£: ReF: fF: AqIA.: Aq/Afl ----10 .08 .S23 .39~2S .~615 20 .059 .386 .2895 .19J JO .045 .294 .2~05 .147 .,
.0' .262 .1965 .Ill SO .036 .236 .177 .118
'" .024 .157 .11775 .0785 70 .017 .111 .08325 .0:555 80 .OU .092 .069 .046 90 .011 .072 .054 .036
AVERAC(S .036 .237 .178 .119
CAS E
20 PERCENTILE DAYlIrJH LEvrU 850 AVAILABLE DAYLIGHT (fo.:):
.82 Cl"ZIHG TRAHSI1ISSIVITn 1 SHAlJ£ TRAHSI1ISSIVITr:
10 Sf'ACE HEIGHT (fT):
.05~ REIlUIII£D 'SERVICE' Ref:
.386 REQUIRED fF: 2.895 CLASS HEIGHT:
.193 ClASStrLOOR AREA RATIO: .2895 WINDOW/IIALL AREA RAllO:
CAS [
SO PERCENTILE DAYLIGHT LEt.tU 1375 AVAILABlE DAYLIGHT (fe):
.92 CLAZIHG YRAHSI11S5IVITY: 1 SHADE TkAHSIIISSJVITH
10 SPACE HEIGHT (n);
.036 REQUIRED 'SERVICE' RtF:
.2JII "EDUIREIl rr: 1.77 ClASS HEIGHT:
.118 CLASS/FLOOR AREA RATIO:
.177 WlliDOlitWALL ARH IIATIO:
CAS E
80 PERCEHTILE DAYLIGHT LEVEll 35'10 AVAILASLE DAYLIGHT I Fe):
.82 CL..;ZINt: TIi'AIISltISSIVITn 1 SHAM T!lANS~ISSIVIIY:
10 SPACE HEICHT (FT):
.OU REDUJI1ED 'SEl1vIC£' IICf:
.O9~ REOOIRED FF: . ., CLASS HE IGHT:
.046 CliiSS/FLOOli: AR[A RiliIO: ,Oli9 WINDOII/WALL AREA !lilllO:
Figure 5. The RCFCALC spreadsheet
949
30 1110 .82
1 10
.045
.294 2.205
.147 .2205
.0 2059
.82 1
10
.0~4
.157 J.lns
.Oi85 .11775
" H7S .8~
I 10
.011
.072 .5'
.036 .Os.
.. ~---.-'------ ----.............. ....,.......... ..- .... ' ...... ~r .,...--,-. "I '.UF
WEST -F ACING SURF A.cF
IllUMINATION CALENDAR: Cleer Sky Conditions IllUMINATION CALENDAR: OvercestCondihons
6:00
6:00
10:00
NOON
2:00
4:00
6:00
JFMAMJJASOND -.-
90 96 90 , 84
121
97
70 FOOTCANOlE INTERIOR IllUMINATION lEVEl AVAilABLE APPROXIMATELY 76% OF HOURS
8 AM TO 5 PM
JFMAMJJASOND
6:00
6:00
10:00
NOON
2:00
4:00
6:00
Figure 6. Illumination calendar for clear sky conditions (left) and overcast conditions (right)
o ~ ~
TITLE C.~.,,~ ",.ug_ n •••.
DESCRIPTION M,"" ","" •• 1 .... \0 of .II-U·n·
IMAGE c ••••• " •• 1 ,,'''.0<. ~r ,h"'.9 ...... 1 ..... bl.
''''''''.' .f .. """.
PERfORMANCl! D£SCRIPTION c •••• d .... ) ........... r c.""." ., ........ l.,... :~ •• ';:!:~:'. <".1 •• 1, ....
~ I f-Z !!! U u: u. w 0 U
Cl z ~ '"
14
13
12
11
10
9
8
7
6
5
4
3
2
FRONT
111101 DIAGRAM £NERGY/COST MATRIX ,~ ••• i'"or'~ '"0<''' ("00' ., < •• c .. ' •••••••• co.",. 0. ' •• '9 .... 'ft c .... ,Mw. f ... dll' ...... b ... coo. b.Il~I.i' •• d .... ,
~:~d ' II , ,
BACK
IELECTOR Kt:y , ••• ,... ,.1<" ••••• ~ to I.co," .,,1.1 ....... t ....
Figure 7. Example presentation format
J
\ WESTr
\ \ 100 % OBSTRUCTION
\ . \. ...... I'-...
'. ............ •• 50 %
"'- ".
" ". . "-.. '" "-....... . NO OBSTRUCTION -.......
t--.. •••• "-r--".
-......:.::: ....... .......
10 20 30 40 50 60 70 80 90
PERCENTILE LEVEL OF DAYLIGHT AVAILABILITY
90 80 70 60 50 40 30 20 10
PERCENT OF HOURS DAYLIT - Sam TO Spm
EHERGY/COST TEXT ~ .. <"..... Qf E~."."'<O ~ ..... ", oUh c ........ . b ....... "~ ... ""9."'"
PERfORMANce GRAPHICS A", .. " .. d." ...... "" V .... ,. ''''''''.''co ,«1> •••
Figure 8. Nomograph of sizing coefficient vs. illumination percentile
951
- ARCHITECTURAL PROGRAM
\
DESIGN CONCEPT
J,
DE:SIGN CRITE:RIA I
SIMPLIFIED SIZING ROUTINE
STRATEGY CONFIGURATION
~
PERFORMANCE ANALYSIS
It PERFORMANCE
INDICES ,
I ,
EVALUATION ACCEI
Figure 9. The role of the simplified sizing procedure in daylighting evaluation
- ...... - ""I"""" " ,...,..... ~. __ .., .... -,. __ • _______ ..,.... -~ ............... -r-~""",--- ...- _--- ____ -------v--- -,- .....
A. STRIP WINDOW WITHOUT OVERHANG
CLERESTORY WINOO'w' YIEW'r(1NDO'n' 2'-0·' "* 4 '-0" _______ 5'-0~ "* 4 '-0"
B. ClERESTORV AND VIEW WINDOWS
Figure 10. Possible glazing configurations
" r..,..~_~·~
1'-6"
4'-6"
5'-0"
N :s;
1'-6"
2'-6"
5'-0"
2'-0"
ClERESTORV UNIT
2'-0" "* 4 '-0"
EQUIVAlENT PERCENT ~ DAYLIT ZON£ AREA GLAZED
PERCENT OF \'( ALL GLAZED
100
90
80
70
60
50
40
30
20
10
I)
100
90
80
70
60
50
40
30
20
10
0
VERTICAl WINDO .... S
70 rOOTCANDlES AlL ORIENTATIONS - UNOBSTRUCTED
..
1'"'---0_ i I!I---~::::::::::~~.--•... ' "''''''''j ............ t'''=:1'~~=?=?~9~¥~'~'''''''''''!
···········T···········'t'··········'{'··········T· .......... ,1' .............. ,: .............. ,: ······ .. ····,r········'···,i· ...... ' .... ~., 1 : : 1
0 10 20 30 40 50 60 70 80 90 100
PERCENTILE LEVEL OF DAYLIGHT AVAILABILITY
Figure 1,. Window and wall design parameter nomograph
953
+- NORTH
0- EAST
8- ~IEST
0- SOUTH
