Objectives

• Finish commercial electrical systems

• Learn about lighting system in buildings• Terminology• Lamp types

Electrical Systems for Commercial

• Example:

• Duplexes (receptacles)

• Phase total 60 kVA, 14kVA (neutral)

• 30 poles

Panel D

• Duplexes (receptacles)• 3 Phase total 60 kVA, 14kVA (neutral)• 30 poles• 60 kVA / (208V √3 ) = 167A• Select: 200 A panel and same size conductors for all three phases • Neutral same like a phase 200 A

• Hot wires should be 250 MCM, Neutral #2/0 aluminum

• 2½ inch conduit

Panel D

Transformer capacity

• P = I V ∙√3 =200∙208∙√3 = 72 kVA ~ 75 kVA

SD switch selection: • For transformer: I1E1=I2E2 • I2 = I1E1/E2 = 200∙208 / 480 = 86 A

• Select switch rated for 100 A

• For 100 A rated switch select: Three #1 (aluminum)

and one #1 for neutral (aluminum)• 90A fuse for phases

Lighting Panel

• 100A - 20 poles

• Hot: 65kVA/(480V∙√3) = 78 A - #2 Aluminum

• Neutral: 22 kVA /277V = 79 A - #2 Aluminum

• Select 100 A three pole fused switch

• 1½ inch conduit

Power Panel

• No neutral? – all three phase circuits• 33 poles required – chose 42 standard size and allows

for expansion

• 165kVA/(480 √3) = 198 A

• Choose 225A switch (could use 200 A, but you count on expansion)

• 3 300 MCM aluminum wires – 2 inch conduit(in the book table you don’t have MCM 300, however it exist)

Wireway

• 198A + 86 A + 78 A = 362A

• 400A would allow for some expansion, some would probably go to 600A

• 400A three-pole switch

• Six 250 MCM (unlikely to find conductors big enough to just have 3) and one #2/0 aluminum

• Neutral current: maximum = 117 A, you can expand neutral too (130 A)

Summary Panel Sizing

• Find panel power usage and neutral usage

• Size panel conductors and associated conduit and switches

Summary of Electrical Systems

• Power generation transport and voltage transformation

• AC/DC Fundamentals

• Equipment

• Residential Buildings

• Commercial Buildings

• NEC code

Source: DOE

Lighting

Motivation

• Lighting represents a third of commercial building energy use

• Lighting has been measured to influence:• Worker productivity• Retail sales• Mood/emotion/comfort• Accident avoidance/safety

Vision and light

• Brightness, pattern, motion, and color

• Which is more sensitive – eye or camera?

• Which is more important, brightness or contrast?

Color

• Does color change the apparent size of rooms?

• Does color change perception of temperature, noise, elapsed time?

Want is light ?

• Light – electromagnetic radiation

• Radiation wavelength • Visible light 0.4 – 0.7 μm

Solar radiation spectrum Major part of solar radiation is visible light

Photometrics

• Luminous intensity [candela, cd] • Define the ability of light source to generate light (illumination) in

given direction

• Power – luminous flux [lumen, lm] • Quantity of light

• Illuminance – light power density [foot-candela, fc] [lux, lx] SI units

• Density of light (illumination) incident on a surface

• Luminance - surface brightness [foot-lambert, lm/ft2] • directional emission of visible light

Relation

between:

1) Luminous

intensity [cd]

and

2) Illuminance [fc]

fc = cd / distance2

Units and conversion• 1 cd = Area of unit sphere = 4·π = 12.57 lumens

Luminous flux [lumen]= Luminous intensity [cd] · (4·π)

• Illuminance [foot-candle, lux] = Luminous flux [lumen]/Area [ft2,m2]

• Luminance [Foot-lambert] = lumen/ft2 from surface in the direction of view

– define the brightness of surface – important for contrast

r=1

1cd

Ref: Tao and Janis (2001)

1

Important quantities

Chapter 14.2 (Tao and Janis)

• Sections: 14.2.3, 14.2.4, 14.2.5, 14.2.6

Major design parameters

• Lighting systems (lamps):• Define Luminous flux [lumen]

• Required level of light at design spot (table spot on the wall etc.) • Defined by Illuminance level (E)

Illuminance (E) depends on angle

Example:• Spot light with luminous

intensity I= 5000cd is aimed at painting at the wall 5 ft from the light and the angle φ=45°.

• What is the illuminance level (E) at the center of the painting?

Solution• Distance:

• Illuminance orthogonal to the beam

E=I/L2=5000/

Ebeam= 100 fc

• Illuminance orthogonal to the painting

Epainting= Ebeam/

Epainting=71 fc

25' L

2' )25(

25' L

2

Color of light• Color temperature is used to express the color

of the light

Surface color rendering

Depending on the light type the surface colors can be different

Depends on spectral energy distribution

Color rendering

lamp source can cause a color shift

Terms for Lamps

• What is luminous efficacy?

• What does a lifetime of 1000 hours mean?• What affects lifetime?

• Does color rendering index (CRI) indicate if a lamp source will cause a color shift?

Luminous efficacy

• Define the light output per unit of electric power input

Efficacy = Lumens/Watt

Ref: Tao and Janis (2001)

Incandescent

• Thomas Edison first incandescent lamp• Efficacy of 1.4 lumens/watt

• Life – 750 to 1000 hours

• 10 – 20 % decay in output

Specialty Incandescent Lamps

• Halogen

• Low voltage

• Long-life

• Infrared

• Interference filters

Is Dimming Bad For Incandescent Lamps?

- 10% lower Voltage

- 25% lower light

- life of lam double

Fluorescent Lamps

• Electrodes arc through mercury vapor

• Phosphors fluoresce in visible range

• Efficacy of 60 to 100 lumens/watt (after burn-in)

Reading Assignment

Tao and Janis

Sections: 14.1

14.2.3, 14.2.4, 14.2.5, 14.2.6, 14.2.8

14.4

15.1, 15,2, 15.3, 15.4