SOLAR SHADING. Shading Devices

Transcription

1 SOLAR SHADING Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 1 Shading Devices The term shading device describes a design element intended to reduce the amount of solar radiation falling on, or making its way into, a building; there are several broad categories of such devices External devices Are the most thermally-effective approach; these block radiation before it can engage glazing or opaque wall/roof surfaces; many types of external device are available Integral devices Next most effective approach; these engage radiation within the plane of the building envelope; various glazings or window inserts are available; heat absorbing glass is an integral device Internal devices The least thermally-effective approach; these engage radiation only after it is within the building; many popular examples (such as drapes or blinds) are available Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 2 1

2 External Shading Devices overhang blocked generally admitted external overhang; can be very effective with direct radiation Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 3 External Shading Devices vegetation external tree; can be very effective (and, if deciduous, can act as a switch) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 4 2

3 External Shading Devices an overhang is an altitude-responsive device a fin is an azimuth-responsive device overhang vs. fin external overhang (in section) and fin (in plan) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 5 Integral Shading Devices tinted glass increased heat convection MRT? reduced solar radiation transmission integral radiation-absorbing glass, increases glass surface temperature Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 6 3

4 Internal Shading Devices draperies complex thermal interactions internal draperies; radiation is only blocked once it is within the envelope; solar energy (heat) is allowed to enter the building Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 7 Shading Devices California State Office Buildings: San Jose Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 8 4

5 Shading Devices Dallas City Hall, TX shading by inherent building form Georgia Power offices, Atlanta Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 9 Shading Devices blinds placed between two sheets of glazing (integral) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 10 5

6 Shading Devices 1 = vegetation; 2 = overhang; 3 = blinds reverse shading (oops) layered shading Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 11 Shading Devices are Not Modern? New Capitol Old Capitol North >>> Florida State Capitol, Tallahassee, FL Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 12 6

7 Shading Device Design Establish design intent (part of OPR) For example block sun in summer (the overheated period) Establish design criteria (part of OPR) For example full shade, all day from May through September For example no shade from November through January For example no blockage of views Decide upon design method Design can evolve rationally through the use of various tools; or design can be based upon trial and error using precedents Verify success of design in meeting criteria Numerous tools are available: physical models and heliodons, hand calculations and sketches, computer simulations Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 13 Shading Device Design Tools shading pattern provided by device type; projected onto sunpath diagram shading masks, these provide a pattern language for shading devices: from Solar Control and Shading Devices (Olgyay and Olgyay) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 14 7

8 Shading Device Design Tools lighter area indicates times of the year when device does NOT shade window shading mask for a south-facing overhang plotted on a vertical projection sunpath diagram Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 15 Shading Device Design Tools shaded shaded no shade a shading mask for a specific overhang, showing period of sun penetration Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 16 8

9 Shading Device Design Tools not shaded shaded fisheye photo of sky vault from a site, and similar image with sunpath superimposed: Design with Climate, Olgyay Solar Pathfinder tool Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 17 Shading Device Design Tools overhang length L is set to provide full shade (from direct sun) during times of the year when the solar altitude angle is β (or greater) L H overhang design using trigonometry (or, even easier, using a scale drawing) Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 18 9

10 Shading Device Design Tools series of images courtesy of Alison Kwok, Univ. of Oregon shading device design analysis using a scale model and sunpeg diagram; what you see is what you ll get Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 19 Shading Device Design Tools shading device design analysis using a scale model and sunpeg diagram Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 20 10

11 Shading Device Design Tools shading device design analysis using a scale model and sunpeg diagram Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 21 Shading Device Design Tools shading device design analysis using a scale model and sunpeg diagram Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 22 11

12 Shading Device Design Tools devices and inquisitive designers Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 23 Shading Device Design Tools three types of heliodons (solar position simulators) fixed-table, moving sun fixed table, selectable suns fixed sun, moving table Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 24 12

13 Shading Device Design Tools photos from the Pacific Energy Center a heliodon provides information on shading performance and direct sun patterns; it provides no information on daylight factors Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 25 Expressing Shading Performance An historic (and still conceptually useful) performance metric for shading systems is: SC = Shading Coefficient (SC) solar heat gained through glazing x solar heat gained through reference glazing Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 26 13

14 Shading Coefficient (SC) The reference glazing is single-pane, clear glass As a ratio, SC is dimensionless (it is stated as a percent or more commonly as a decimal value) SC values may be found in manufacturers literature, in handbooks (such as from ASHRAE), or may be derived from calculations SC, as generally used, applies only to glazing (not to opaque frames or mullions) An overall SC may be assembled from parts SC overall = (SC 1 )(SC 2 )(SC 3 ) where, SC 1 may be for an overhang, SC 2 for glazing, Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 27 Expressing Shading Performance A newer (and necessary-to-know for code compliance) shading performance metric is: Solar Heat Gain Coefficient (SHGC) SHGC = the fraction of incident solar radiation that is admitted through a window or skylight (including the frame) including that directly transmitted, and that which is absorbed and subsequently released inward Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 28 14

15 Solar Heat Gain Coefficient (SHGC) SHGC is a dimensionless value (it is stated as a percent or most commonly as a decimal value) SHGC applies to glazing and frame/mullions SHGC is a simulated value backed by laboratory testing (the National Fenestration Rating Council NFRC tests and certifies products) Determining (figuring) an overall SHGC (considering site additions to shading) is a problematic issue SHGC SC SHGC (SC)(0.87) SHGC is self-referential; while SC references a base product for comparison Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 29 NFRC Window Label full solar spectrum if product is residential if product is non-residential visible spectrum label is removed from window after code inspection Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 30 15

16 Window Performance Indicators Florida Solar Energy Center SC glazing only a selective transmission product SHGC entire unit Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 31 movable shading device (sail); Alpine House, Kew Gardens, UK Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 32 16

17 52 N latitude Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 33 Ball State Architecture ENVIRONMENTAL SYSTEMS 1 Grondzik 34 17