A SIMPLIFIED APERTURE-SIZING PROCEDURE FOR DAYLIGHTING...

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.

930

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)

932

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:

934

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