Transcript 346N_092804_designIII_daylighting

1) Which time would be best for an
exam review session?
A)
B)
C)
D)
E)
Thursday 4 pm
Friday 5 pm
Monday 5 pm
Monday 6 pm
Can’t make any of these times
Homework questions?
• Practice midterm on website now
• Treat it like a real exam
• Review in class on Thursday (also Quiz #5)
• HW solutions posted Thursday evening
• Office hours on Monday October 4th after 4pm
if I know in advance that you will be there
• Fieldtrip postponed
• October 7th – regular class, no quiz
Objective
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Use room geometry to calculate coefficient
of utilization (CU)
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What is CU?
Parameters
1. Cavity ratio (from geometry)
2. Surface reflectances (from paint/surface color)
• Combine these to get effective reflectances
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Use table for specific fixture to get CU
Figure 16-1
Ref: Tao and Janis (2001)
2) What is the cavity ratio for a room
with a right-angle triangular footprint?
A.
B.
C.
D.
5 × (A+ B)/(A × B) × h
1.25 × (A+ B + C)/(A × B) × h
2.5 × (A+ B)/(A × B) × h
5 × (A+ B + C)/(A × B) × h
C
B
A
Thought experiment
• Consider an open box with a white floor and
black walls
• Is this box going to reflect more or less light
than a box with a black floor and black walls?
• The effective reflectance establishes a surface
at the lid of the box and determines the
reflectance from this imaginary surface.
• Invert box for ceiling cavity
Notation
• Base reflectances: ρw = ρr , ρc, ρf (also OK to use R)
• Experience
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White ceiling, ρc = 70 – 80 %
White walls, ρw = 60 - 70 %
Medium to light colored walls, ρw = 50 %
Dark wood paneling, ρw = 25 %
Floor, ρf = 10-30 %
• Effective reflectances, ρcc, ρwc = ρrc , ρfc
• Table 16-8
• Special modifier for floor Table 16-9
Standard assumptions
• Floor effective reflectance is equal to floor
base reflectance
• ρf = ρfc = 20 %
• Need to use Table 16-9 otherwise
• Wall base reflectance is equal to wall effective
reflectance
• ρr = ρrc = ρwc
• When CCR = 0
• ρc = ρcc
Distribution
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Direct 90 – 100 % downward
Semi-direct 60-90% down, rest upward
Direct-indirect/General Diffuse
Semi-indirect
Indirect
Illumination calculation
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Iws = N × LPL × LOF × CU / A
N = number of fixtures
LPL = rated lamp lumens per fixture
LOF = lamp operating factor
• Ballast, voltage, temperature, position (HID)
• CU = coefficient of utilization
• Fraction of light that meets the work surface
• N = Iws × A / (LPL × LOF × CU)
Ref: Tao and Janis (2001)
Ref: Tao and Janis (2001)
3) A fixture has a S/MH of 0.5
The space is 20 ft. × 10 ft.
9 ft ceiling height, 3 ft work surface
A. With 2 fixtures, there will
be dark areas
B. With 6 fixtures, there will
be dark areas
C. With 10 fixtures, there
will be dark areas
D. With 14 fixtures, there
will be dark areas
Fixtures spaced evenly along these lines
4) A fixture has a S/MH of 1.0
The space is 20 ft. × 10 ft.
9 ft ceiling height, 3 ft work surface
A. With 2 fixtures, there will
be dark areas
B. With 4 fixtures, there will
be dark areas
C. With 6 fixtures, there will
be dark areas
D. With 8 fixtures, there will
be dark areas
Fixtures spaced evenly along dotted lines
Summary
• Calculate number of fixtures need for a
specific space
• Calculate CU
• Do not ignore S/MH
What about lighting quality?
• Zonal cavity calculations focus on light
quantity
• Quality can not be ignored
• CRI, evenness of illumination, transition between
light and dark, flicker, glare, color temperature
• Quality is more important
• Daylighting is one strategy to reduce lighting
energy use and increase lighting quality
• Use the sun for illumination
Commercial Building Costs
Energy
Operating
Cost
Capital Cost
Human Cost
Daylighting
• Scientific and psychological studies have
found:
• People prefer buildings where changes in sunlight
exterior affect interior lighting
• Properly lit spaces are preferred to underlit or
overlit spaces
• Diffuse lighting is preferred to direct lighting
• North sky lighting is ~universally preferred
What are problems with daylighting?
• Can require extensive controls
• Requires extra hardware to avoid direct
lighting
• Can require expensive glazing
• Can damage works of art
• Need to limit the amount of heat associated
with solar gains
Strategies for Daylighting
• Orient your building on an East-West axis
• Limit direct sunlight with exterior shades, light
shelves, clerestory windows, translucent
glazing
• Control glazing and conventional lighting with
controls
• Occupancy sensors
• Automatic blinds
• Light-level sensors
5) Why do we use daylighting?
A.
B.
C.
D.
To protect works of art
To save energy
To reduce peak demand
To increase lighting quality
Other stuff (not responsible)
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Accent lighting
More sophisticated lighting design
Lighting controls
Daylighting calculations
Summary
• Determine required lighting levels
• Calculate work surface illumination
• Integrate daylight