Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 1

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1 DAYLIGHT image by NASA use this powerful resource with skill and caution Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 1 Daylight and Design From the dawn of time until the widespread introduction of the fluorescent lamp during the post-world War II period, the sun was the predominant source of daytime light in buildings. It was far more available and effective than other sources, and it provided mankind with a continuing relationship with nature and the outdoors which were close to his origins. The introduction of daylight into buildings shaped structural concepts, stimulated product development, and, in general, influenced the form of architecture for some of our greatest buildings. Benjamin Evans: Daylight in Architecture Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 2 1

2 Solar and Terrestrial Radiation high temperature objects produce shortwave radiation; low temperature objects produce longwave radiation terrestrial radiation solar radiation includes: UV visible IR Lechner: Heating, Cooling, Lighting file this info away for upcoming greenhouse effect discussion Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 3 Solar Radiation Components direct = ray diffuse = spray reflected = more spray than ray Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 4 2

3 Blocking Solar Radiation direct radiation is more easily blocked than diffuse or reflected; file this idea away for upcoming shading device discussion Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 5 Solar Radiation vis-a-vis Daylight daylight daylight = visible solar at Earth s surface solar = visible + UV + IR solar radiation Lechner: Heating, Cooling, Lighting Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 6 3

4 Daylight vis-a-vis Glazing glazing for daylighting would ideally admit only the visible portion of the spectrum and block radiation in the grey shaded (IR and UV) regions of the graph through a process called selective transmission fades fabrics only this part of the solar spectrum allows us to see contributes heat Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 7 Daylighting versus Sunlighting energy-efficient, low-glare daylighting uses ONLY diffuse solar direct solar radiation is used for passive heating or sparkle (or to find truth in a forest) daylighting sunlighting Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 8 4

5 Some Defining Characteristics of Daylight Daylight is variable on a daily cycle availability (quantity) generally goes from 0 at midnight to some maximum around noon and then back to 0 in a 24-hour period Daylight is variable on an annual cycle maximum daily availability goes from a to z then back to a in 365 days Daylight is variable geographically is more readily available in some locales (primarily as a function of site latitude, but also due to climate) than in other locales Daylight is variable relative to surface position vertical, tilted, and horizontal surfaces receive different daylight illuminances under like sky conditions Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 9 Some Defining Characteristics of Daylight Daylight can vary with orientation depending upon sky type, N, S, E, W orientations receive different illuminances under like conditions Daylight is variable randomly and quickly as a result of weather The color of daylight is variable with sky type, orientation, and time of day Daylight is variable! Its magnitude at any time is statistically predictable but not absolutely definable Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 10 5

6 The Color of Daylight daylight varies in wavelength (light-source color) but is generally balanced (it has a broad spectrum) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 11 Predicting Daylight Availability Daylight is statistically predictable broadly speaking, daylight quantity can be fairly accurately predicted over long-term periods (say 5 to 10 years) such patterns are a function of climate historical-data-based predictions provide acceptable accuracy for energy analyses and simulations (similar to the accuracy of temperature, humidity, or rainfall projections) easily usable daylight data, however, are not readily available (even from Climate Consultant) Daylight is specifically unpredictable it is generally impossible to predict how much daylight will be available at noon next week such information is a function of the weather (and how accurate are weather forecasts?) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 12 6

7 it is quite variable and hard to predict So Why Use Daylight? It is a renewable energy resource It is a use-it-or-lose-it resource (it cannot be stored) People like it It requires an architectural design response It conserves non-renewable resources for potentially better uses (medicines, transportation, the future) It can contribute to an energy-efficient design solution It can contribute to a green design solution It can contribute to a net-zero-energy design solution It can contribute to a carbon-neutral design solution It can contribute to a sustainable design solution opinion: if this list sounds like a compelling argument for using daylighting that s good because it should Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 13 So Why Use Daylight? what s with the Watts for daylight? electric daylight Square One: a well-designed daylighting system without direct solar radiation (compare yellow arrows) can be VERY energy efficient Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 14 7

8 So Why is Daylight not Used More? It is variable It is not always well understood by designers Resource data are often not readily available (not a trivial concern) Analysis techniques (including simulations) can be daunting It requires an architectural design response Thus, its design cannot be farmed out to a consultant (as electric lighting often is) Thus, it may require more creative compromises Thus, blah, blah opinion: if this sounds more like a list of excuses than justifications that s good because it should Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 15 Daylight Sources The sky vault (sky dome or hemisphere) A viable source of daylight for building design Three primary types of skies are considered for design purposes Overcast (fully cloudy) Clear (no clouds) Partly cloudy (some percentage cloud coverage) Direct solar radiation Almost NEVER used as a light source in buildings due to unnecessary heat gain and glare potential Rethink what you may have thought about this!!! Good daylighting does not depend upon access to direct sun!!! Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 16 8

9 (Fully) Overcast Sky spring; San Antonio, Texas Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 17 Overcast Sky Luminance Pattern highest luminance (L) at zenith orientation is not relevant aperture aperture = daylight opening aperture horizontal skylights work very well under overcast skies: they provide more light per square foot of opening than a vertical window Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 18 9

10 Clear Sky spring; Australian outback Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 19 Clear Sky Luminance Pattern highest luminance (> L) is toward sun, but that brings problems luminance at horizon (L) is greater than at zenith orientation is relevant windows work well under clear skies: they provide more light per square foot of opening than a horizontal skylight and are easier to shade Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 20 10

11 Partly Cloudy Sky spring; central Wyoming can range from almost clear to almost fully overcast; variability and uncertainty make this a difficult design sky (even if a common occurrence) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 21 Which Design Sky? A designer must decide which sky condition to use for building design and system analysis: In an arid climate (Phoenix), it is logical to design for a clear sky condition and live with overcast conditions now and then In a maritime climate (Seattle), it is logical to design for an overcast sky and live with clear conditions now and then In a temperate climate (Muncie), it is logical to design with both skies in mind and try to optimize performance using computer simulations Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 22 11

12 A Cautionary Note Much of the information written and published about daylighting comes from the UK (or similar dreary climates). An often unstated assumption is that an overcast sky condition predominates. Consider this when using daylighting design recommendations and tools. Sky type makes a difference to design decisions. Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 23 Daylight Illuminance Data Overcast vs. Clear Sky Evans: Daylight in Architecture, note vertical scale change on graphs and lack of orientation info on overcast graph Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 24 12

13 Daylight Illuminance Data Clear Sky Summer vs. Winter Evans: Daylight in Architecture note vertical scales are identical and winter curves are depressed versus summer curves Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 25 Daylight Illuminance Data Clear Sky vs. Direct Sun Evans: Daylight in Architecture note vertical scale change on graphs and patterns of illuminance values Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 26 13

14 Handling Daylight Variability If the only way to present information on daylighting system performance was via illuminance values, the discussion might go like this The illuminance is 250 lux, no wait it s 265, no make that 240, no wait it has changed again. And if you ll wait 8-10 hours the illuminance will be 0. Daylight factor (DF) provides a means of handling variable daylight illuminance One can say: the DF at point x is 1.5% (without hedging or the need for detailed footnotes). Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 27 Daylight Factor (DF) DF is the ratio of interior daylight illuminance (E) on a defined point to exterior daylight illuminance (on a horizontal reference point) DF = E interior (daylight, at point x ) E exterior (daylight, reference) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 28 14

15 Daylight Factor (DF) DF normalizes for variances in external daylight illuminances (as the numerator in the ratio increases, the denominator also increases) DF is reasonably constant across time, for a given daylighting approach/sky; thus DF provides a more consistent performance indicator than illuminance The exterior reference daylight illuminance is normally an ambient, unshaded, horizontal-surface daylight illuminance that excludes direct solar radiation The concept of DF was developed for overcast sky conditions; it must be used with caution if applied to clear sky conditions DF can be conceptually viewed as the efficiency of a building design in delivering daylight to a desired location in the building (a 2% DF is a 2% efficiency) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 29 Daylight Factor (DF) DF is a point phenomenon There is no such thing as the daylight factor of a room Daylight illuminance distribution across a room is usually highly variable (there are many values of DF within a room) Minimum daylight illuminance is usually more important to design than maximum (minimum should be used to determine whether design criteria have been met; maximum may be of concern relative to glare) DF is often used as a design criterion, usually as a threshold to be met For example, LEED (NC-2.1 an older version) required a minimum 2% DF (excluding direct sun) in approximately 75% of building spaces to obtain a daylighting credit As a side note: direct exterior views in 90% of spaces could earn another credit, an expression of the anticipated effect of visual accommodation on comfort Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 30 15

16 Daylight Factor (DF) Conceptually, daylight factor (DF) is a measure of the effectiveness of a building design in admitting and distributing a site s daylight resource to a specific point within a building. Many design decisions (aperture size and location, glazing materials, surface reflectances, shading devices, etc.) will affect DF. A 2% DF literally means that only 2 of every 100 lumens of exterior light reaches a given interior point yet this is often more than enough to make a difference. Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 31 Daylight Factor (DF) Contours DF in % (note the low values) ^^ Ecotect analysis << hand-plotted iso-df contours are often used to represent measured or predicted daylight distribution in a space (note the many DF values for both spaces) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 32 16