Methods for Day Lighting

8/9/2019 Methods for Day Lighting

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prof. Alessandro Rogora

Natural light and architectre:

tools, examples

POLITECNICO DI MILANODipartimento di Scienze e Tecnologie dellAmbiente Costruito

Science & Technology Building & Environment BEST

venerd 5 giugno 2009


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Detailed Site Obstruction SurveyThe sunpathdiagram can beused to plot aprofile of all siteobstructions. Thisprovides agraphicrepresentation ofobstructions at allsun angles andforms the basisfor latercalculation ofilluminance atwindow locations.

Application of the mwthod to the analysis of one site



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Obstruction MasksUsing the plan projectionformat, it is possible toconstruct a diagram that

defines that portion of thesky that is masked out bysurrounding obstructions(and, conversely, thatportion that can be"seen"). When usedtogether with theappropriate sun pathchart, the hours of directsun penetration andshading can bedetermined.

Imagine a series ofparallel, horizontal,overhead "bars" asviewed from a referencepoint on the ground. Ifthese bars were projectedas lines on the skydome,they would form an"orange-segment" pattern,with the lines convergingto a point on the horizonin the direction of thebars. This chart can beused to construct a maskshowing, for example theportion of the skydomeobscured by a longhorizontal overhang froma window.

Plan projection of horizontal bar projections (profiles): (a) on skydome; (b) inplan..



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Obstruction MasksA series of tallvertical "bars"

arranged in a circle.These bars wereprojected as lines onthe skydome, theywould also trace anorange-segmentpattern but the lineswould converge atthe top of the

skydome (i. e., atthe zenith). Thispattern wouldproject in plan as aseries of straightlines radiating outfrom the centre. Thischart can be used toconstruct a maskshowing the portionof the skydomeobscured by avertical side fin froma given referencelocation.

Plan projection of vertical bars traces on skydome.



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Dot ChartsSeveral authorshave described

charts for graphicallyestimating the skycomponent forovercast skyconditions. Thecharts consist of apattern of dotsdistributed as afunction of the sky

luminancedistribution and thecosine correction forthe angle ofincidence. FullerMoore (1982) hasdeveloped a skycomponent dot chartfor C. I. E. standardovercast skyconditions usingequidistantprojection that iscompatible with thesun path charts.

Sky component dot chart (C.I.E. standard overcast sky, equidistant projection).



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Dot ChartsTo use this overcastsky dot chart (or

charts for other skyconditions), anobstruction mask foran interior referencelocation is plottedshowing both sky andexterior obstructionsvisible through allopenings. This maskis overlaid on the dotchart (for overcast skyconditions orientationis not a factor, so therotation of the chart isimmaterial). The dotsare counted in thevisible sky area, and

divided by 10 todetermine the skycomponent (as apercentage of exteriorilluminance under anunobstructed sky).

Use of sky component dot chart for clear sky.



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Dot ChartsA different overlayallows the

estimation of theexternal reflectedcomponent forovercast skies.The dots withinthe area of themask for external

obstructions arecounted anddivided by 10 toequal the externalreflectedcomponent (%).This ERC is

based on anaverageobstructionreflectance of 0,2.

External Reflected Component dot chart



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Computer codesThe complexity ofcalculations

requested to modelthe effect of naturallighting in buildingsforced the planner touse computer toobtain significantand accurateresults. The currentavailable software

make possible tomodel notrectangular roomswith windowslocated on everysurface of theenvelope. Theoutputs of these kindof software areusually: the averageillumination levelsand the distributionof the light levels ona horizontal plane.

An example of results with the software RAFIS.



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RAFIS softwareThe images onthe side shows

how to use thesoftware tosimulate thedistribution ofnatural lighting ina rectangularroom with two

windows locatedone in the northfacing and one inthe south facingfacade

Start up screen



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Data about walls



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Inserting the cover



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Inserting windows (view is from the inside)



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RAFIS software

Viewing final results

The images onthe side shows




Documents

Methods for Day Lighting