Beginning Question

1. How much wood would a woodchuck chuck if a woodchuck could chuck wood?

A. A lot

B. A little

C. None

D. Don’t know

Admin

• I sent a test message yesterday

• If you didn’t get it:• Send me an e-mail message with ARE346N in the

subject line• If you change your e-mail address over the course

of the semester you are responsible for forwarding me your new address

Admin

• Textbook• 3rd edition of Tao and Janis is on order at the co-op• Only 5 copies were ordered, so let them know if

more or you want them

Objectives

• Critically analyze conservation claims• Introduction to course themes

• List and define terms associated with electrical design in buildings

• Calculate electric quantities with Ohm’s Law and Kirchov’s Law (review)

• Calculate electricity costs for residential and commercial buildings

• Major emphasis – how do you begin designing an electrical system?

Critical Analysis

• Central objective of this course

• Myths website – myths aren’t always false• http://ficp.engr.utexas.edu/conservationMyths/• Goal is to evaluate them• Project I

2) Myth 1: How long would the average American have to leave the bathroom tap running to use as much

water as one shower

A. 60 minutes

B. 30 minutes

C. 15 minutes

D. 5 minutes

3) How long is your average shower?

A. 2 minutes

B. 5 minutes

C. 10 minutes

D. 20 minutes

E. 30 minutes

Myth 1: Tight With the Tap

min30gallon/min5.1

gallon/min5.4min10 sinkt

sink

showershowersink Q

Qtt

• Claim is unlikely to be true because very few people leave their taps running for ½ hour.

4) Myth 2: Using drapes reduces heat loss by ~1/3 for single glazed windows.

A. Untrue, heat loss is unaffected by drapes

B. Untrue, heat loss is only reduced by 10–15%

C. Approximately true

D. Untrue, a drape reduces heat loss by more than 40%

Conclusions

• Claims are often made without verification

• We have the tools to evaluate these claims

• Critical analysis is necessary/important for engineering

• Law of unintended consequences

Where are we going?

• Electrical systems

• Lighting technology and design

Applied Electrical Concepts

• Use terms to describe building electrical system• AC vs DC ch. 9• Ohm’s and Kirchov’s Laws ch. 8• Power vs. Energy ch. 9• Inductors and Capacitors• Power Factor ch. 9• Single-phase vs. Three-phase ch. 9• Grounding ch. 9

Electrical Codes

• National Electrical Code (NEC aka NFPA 70)• Library website

• Focus on safety

• Talk to the electrical inspector

AC DC• Direct Current (DC)

• Sign matters

• Alternating Current (AC)• Switching polarity

• Which are the following?• Photovoltaic solar cell

• Automobile alternator

• Household outlet

• Outlet in ECJ

• Battery

• High voltage lines

AC terms

• Frequency, f [Hz]• Wall outlet?• Fluorescent light?• Clock?• Electric resistance heater?

• Capacitor (plates separated by dielectric)

• Inductor (coil of wire)• Transformers

Why use AC?

• Easier to generate

• Able to use inductors and capacitors in meaningful way

• Voltage changes much easier• Lower distribution losses

Across a transformer

I1E1 = I2E2

Voltage and Current

•Voltage (potential difference)

•Units?

•Symbol V or E

•Current (electron flow)

•Units?

•Symbol I

Ref: Tao and Janis (2001)

Ohm’s and Kirchov’s Laws

• V = IR, E = IR (E = energy [V])

• P = EI = I2R

• ∑I = 0 for a node

• ∑E = 0 for a closed loop

• Are these for AC or DC or both?

Single-Phase vs. Three-Phase

Ref: Tao and Janis (2001)

For three phase:

P=√3 E I

5) Why do commercial buildings use 3 power?

a) Requires fewer wires

b) Higher motor efficiency

c) Requires bigger wires

d) Smaller space requirements

Why Three-Phase?

• Larger loads

• Smaller wire sizes (because higher voltages)• P = I2R• More efficient use of neutral wire

• 3 needed for efficient operation of equipment

Power Factor

• Difference between power supplied and power that does useful work “working power”

• P=E I cos θ• θ is the phase difference between current and

voltage

• For three phase• P=√3 E I cos θ

• Commercial buildings pay for power factor.

6) Are kWh units of energy or power?

A. Energy

B. Power

Electricity Billing (ch. 13)

• Electrical Use (energy)• Peak Demand (power)• Power factor

• Which is largest portion of residential bill?• What about for commercial buildings?

• http://www.austinenergy.com/About%20Us/Rates/Commercial/index.htm

Example: September cost of Electricity for ECJ

• Assume ECJ is 120,000 ft2 and that it needs, on average, 8 W/ft2 for 8 hours a day, 6 W/ W/ft2 for 4 hours a day, and 4 W/ft2 for 12 hours a day

• Use Austin Energy Large Primary summer service rate• 1.5¢/kWh, 12.60 $/peak kW/month

• Assume no power factor charges

7) What is peak demand?

A. 0.018 kW/ft2 × 120,000 ft2 = 2,160 kW

B. 0.008 kW/ft2 × 120,000 ft2 = 960 kW

C. 0.018 kW/ft2 × 120,000 ft2 × 8 hr = 17,280 kWh

D. 0.008 kW/ft2 × 120,000 ft2 × 30 days = 28,800 kW

Solution

large primary service

$/kW $/kWh

Daily $ 12.60 $ 0.015

hours kW kWh

8 960 7680 demand $12,096.00

4 720 2880 energy $ 7,344.00

12 480 5760

TOTAL 16320 Total $19,440.00

Other Pricing Strategies

• Time of use pricing• Becoming more common for residential and

commercial• Electricity cost related to actual cost• Requires meter

• Interruptible pricing• Utility can shut off electricity for periods of time

Summary

• Know where to find NEC• Compare DC and AC

• Calculate current/voltage across a transformer

• Describe 3-phase power and compare to 1-phase• List reasons for using 3-phase

• List and explain components of electrical billing• Calculate commercial electricity bill