pls 2016: exploring daylight metrics

Exploring Daylight MetricsLongyu GuanJemima Unwin

Part 1: A look at current daylight metricsPart 2: The potential of volumetric lighting metricsPart 3: Challenges and ongoing research of new metrics

Exploring Daylight Metrics

Daylight Factor approach: x 100%

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𝐸𝑜𝑢𝑡Overcast Sky

A look at current daylight metrics

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Direct Component

External Reflected ComponentInternal Reflected Component

Overcast Sky



Overcast Sky



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Direct Component

External Reflected ComponentInternal Reflected Component

Overcast Sky

In real life practice…Climate-based Daylight Modelling• Daylight autonomy • Useful daylight illuminance• Annual sunlight exposure

Climate Data

Similar process & the same “working plane”


Working environment in the 1970s

Working environment nowadays

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Working Plane“Visual Performance”

Perceived Daylight Adequacy

Whole Space“Volumetric”

Cylindrical illuminance:

2DISinEcyl

EN 12464-1 (2002)‒“Working plane” removed‒Recommended illuminance on major room surfaces‒Mean cylindrical illuminance (2011)

The potential of volumetric lighting metrics


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1.2 m




2DISinEcyl

1.6 m



Cubic Illuminance


Can we make volumetric lighting metrics simpler?

Cubic Illuminance


Exitance

Incident flux

Exitance


Incident flux

Exitance

Average exitance of all Room surfaces

Exitance


MRSE =

MRSE

Mean Room Surface Exitance (MRSE)

Exitance


Why MRSE has good potential as a daylight metric

1. A new term, but established concept

Overcast Sky

MRSEIRC


2. Simplicity

• One single number




• One single number• Can be easily calculated (to a first approximation)

Total flux entering the room()

Room surface area & reflectance ( & R)

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2. Simplicity




3. Correlates well with electrical lighting guidance

EN12464-1(Lighting of indoor work places)

Recommendsilluminance on

major room surfaces

Reflectance of room surfaces

Effectively forced a minimum MRSE value

2. Simplicity




So far we only considered daylighting in a “box”…

However in real life…

So far we only considered daylighting in a “box”…

However in real life…However in real life…

Problems with MRSE approach:

Challenges and ongoing research of new metrics

MRSE starts to break down when the building is open-planned and geometrically more complicated

Essence of MRSE:

MRSE

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Cubic Illuminance


Cubic Illuminance

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Essence of MRSE:

Direct Illuminance

Indirect Illuminance

Cubic IlluminanceIndirect Illuminance


Essence of MRSE:

Cubic Illuminance Indirect Illuminance


Essence of MRSE:



Essence of MRSE:

Average Indirect Illuminance (of the space)



Essence of MRSE:

Average Indirect Illuminance (of the space)


Essence of MRSE:

A pilot study on the new metrics: • The Heelis building (HQ of national trust)


Scale 1 to 7:

•How is the lighting overall?•How is the natural lighting overall?• Is there any glare from natural lighting?

Plus respondents’ comments Respondents’ working desk can be traced back.

A pilot study on the new metrics: • The Heelis building • BUS datasets


- Daylight Factors (DF) & Average Indirect Illuminance (AIE)- Overcast Sky with external illuminance of 10,000 lx

A pilot study on the new metrics: • The Heelis building • BUS datasets• Computer simulation (Radiance)


DF: 7.2%AIE: 164 (1.6%)

DF: 2.1%AIE: 75 (0.7%)

DF: 5.2%AIE: 213 (2.1%)

Heelis Building-Data source: Roderic Bunn BSRIA/UCL

1 2 3 4 5 6 7-10%

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1 2 3 4 5 6 70%

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1 2 3 4 5 6 7-10%0%

10%20%30%40%50%60%

ratings

ppl %


• AIE encourages shading + large window

• AIE encourages high room surface reflectance

• AIE represents daylight in the whole space

• Reasons to believe AIE better reflects people’s perception of daylight adequacy


Difficulties of testing new metrics:

- Data selection

Further research:- More real life case studies- Compare the performance of different daylight metrics- Explore the CBDM potential of new metrics

Metrics can only be reliably tested in many real buildings

- Validity- Comparing different metrics What should I

have for lunch?Pfffff… just tick the middle score


Thank you & Questions?

[email protected]@ucl.ac.uk

pls 2016: exploring daylight metrics

Environment