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Objectives

Objectives. Learn about Electricity Pricing Electric systems. Electricity Billing. Electrical Use (energy) Peak Demand (power) Power factor Which is largest portion of residential bill? What about for commercial buildings?. Example: September cost of Electricity for ECJ.

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Objectives

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Presentation Transcript

  1. Objectives • Learn about • Electricity Pricing • Electric systems

  2. Electricity Billing • Electrical Use (energy) • Peak Demand (power) • Power factor • Which is largest portion of residential bill? • What about for commercial buildings?

  3. 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

  4. Solution

  5. 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

  6. Conductors • Material • Form • Composition • Voltage class • Insulation • Covering • Temperature rating AWG American Wire Gage

  7. Wiring method –Raceways • Electric tubes • Rigid conduits • Wire ways • Bus ducts • Underflow • Different variation www.hhrobertson.com/

  8. Design issues with conductors • Material (copper/aluminum) • Size of conductor (pg. 365) • Conduit requirements • Location • Residential or Commercial • With or without raceways • Compression fittings or set screws • Threaded connections • NEC and local codes

  9. Current-Carrying Capacity Ref: Tao and Janis (2001)

  10. Tubing size Ref: Tao and Janis (2001)

  11. Other Issues • In general, no more than 40% of raceway can be filled with wiring • Why? • To prevent extensive heat up • To prevent physical installation of wires

  12. Conductor Rules • Explain each of the following: • No more than 4 90 ° bends are allowed between pull boxes • In the same conduit: • No mixing of high- and low-voltage conductors • No mixing control and power conductors • No mixing phone and power conductors • Do place all three phases in the same conduit

  13. Receptacles (duplexes) Number Shape Voltage rating Current Rating Number of poles and wires Switches Type (NEC rating) Contact method Speed of operation Voltage rating Number of poles Method of operation Enclosure Duty Other (dimming) Receptacles and switches

  14. Protective Devices • What are we protecting from? • Overcurrent • Overvoltage • Circuit breakers • Switch that responds to thermal or short circuit loads • Can be bimetal, magnetic, or electronic • Reusable, remote control, compact, can be used as disconnect switch • Fuses • Melting metal • Self destructive, larger

  15. Why use fuses instead of circuit breakers? • Fuses can be used multiple times • Fuses are more aesthetically pleasing • Fuses are safer • Fuses cause less damage to equipment

  16. Ref: Tao and Janis (2001)

  17. Motor starters • ON-OFF switches are NOT for motors • Motor circuit-rated switches • Reduce the current during the start until the motor rich full speed • Protect the motor form overload • Emergency power systems Batteries Power generators

  18. Residential Systems • Very little variation between different houses • Many similarities to commercial buildings • Particularly as you get close to end uses • Need to be watchful for unusual circumstances

  19. Procedure • Analyze building needs • Determine electrical loads • Select electrical systems • Coordinate with other design decisions • Prepare plans and specifications

  20. List of needs • Appliances (incl. HVAC) • Receptacles • Ground fault protected (GFI/GFCI) • Switched • Lighting • Switches • Ceiling Fans

  21. Example House • Master Bedroom • Bathrooms • Entry and Outdoor (AC compressor) • Bedrooms • Dining and Mechanical Closet (resistance heat) • Kitchen (appliance circuits, range, oven) • Family • Garage/Laundry/Closet (resistance water heater, dryer)

  22. Outdoor Bathroom Closet Bedroom 2 Laundry Kitchen Bathroom Mechanical closet Family room Master Bedroom Entry Bedroom 3 Dining Garage

  23. NEC about receptacles No longer approve non-polarized and ungrounded receptacles in new installations. Each receptacle (duplex) is rated for 15 A. For 120 V: Each duplex 15×120 = 1800W

  24. Residential system sizing Typically 3 wire 1 phase system 120/240 V • Procedure defined by NEC article 220: • Identify characteristic electrical loads • Add lighting (3W/ft2) • Add two 20 Amps circuits for kitchen • Add one 20 Amps circuit for laundry • Electricity for HVAC equipment based on requirement for heating or cooling

  25. Summary of Power Sizing • Include enough capacity for heating and cooling • Work through kitchen and then other rooms • Include any items that are unusual • Take first 10 kVA and then 40% of remaining load

  26. Panel Sizing • Find panel power usage and neutral usage • Size panel conductors and associated conduit and switches

  27. Electric panel - 3 wire 1 phase 120/240

  28. Homework 5 - problem 2 • Sizing the residential electrical system • Defined by NEC article 220-30 • Similar to the example we worked out • You need to collect the data for several characteristic consumers • Includes conductor sizing

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