What HVAC Engineers Should Know About Electrical February 11, 2020
Course Outline ◼ Electric generation ◼ Measuring electric ◼ Electrical formulas ◼ Voltage selection ◼ Electrical devices ◼ Single and 3 phase motors ◼ Motor starters ◼ Electrical safety ◼ Quiz
Electricity and Electrical Systems ◼ Key Concepts ◼ Electricity is generated by a central utility, transported through conductors and transformed to a lower voltage for user at or near a building. ◼ Electricity is energy that is easy to move and easy to convert for useful work. The electromagnet is the basic electrical device that permits this use of electricity. ◼ The movement of electricity in wires is similar to the movement of water in a pipe. To flow, electrons need pressure which is called voltage and measured in volts. The amount of flow of electrons is called current and is measured in amperes (amps). The work performed by electricity is power measured in watts.
ELECTRIC GENERATION
ELECTRIC COMPARED TO WATER
MAGNETIC FIELD
GENREATING ELECTRIC
ELECTRIC SINE WAVE
SINGLE PHASE AC
THREE PHASE AC
MAGNETIC FIELD AROUND CONDUCTOR
ELECTROMAGNET
Measuring Electricity Volts (V)- Potential difference, similar to pressure Amperes (I)- Amps, amount of current, similar to quantity Watts(W or P)/Kilowatts(kW)-Measure of power used kW is a 1,000 watts P=VI (resistive loads) P=VI x power factor (all other loads) Kilowatt-hours (kWh)- Amount of energy used over a period of time Ohms( Ω )- The measure of resistance to flow of electrons. Ohms law- V=I X R
◼ Transformer- Increase or decrease voltage using electromagnetic energy for AC only ◼ Types of current ◼ DC direct current ◼ AC alternating current ◼ Has a frequency measured in Hz or cycles Phasing (AC only) ◼ ◼ Single phase ◼ Three phase ◼ Grounding ◼ Connects equipment case’s to earth ◼ Short circuit ◼ Short to ground
TRANSFORMER
TRANSFORMER
TRANSFORMER
Selection of voltage Based on planned load of building at time of design ◼ 120V 1φ - Typical outlet and incandescent light (1 ◼ hot & 1 neutral wire) 208- 230V 1φ - Residential (230V) and small ◼ commercial (208V)- Large appliances and office equipment and lights (2 hot wires) 208- 230V 3φ - Small commercial- motors ◼ 277V 1φ - Small to large commercial- lights and ◼ small motors (1 hot & 1 neutral wire) 480V1φ, 3φ - Large commercial- motors ◼ 2,300V 3φ - Large commercial and industrial ◼ 4,160V 3φ - Large industrial ◼ 13,200V 3φ - Large industrial ◼
Voltage Variations ◼ Utilities must supply and electrical equipment must work on +/- 10% of rated voltage ◼ Can equipment use both 208V and 230V? ◼ Yes for most motors ◼ Electric heaters, typically designed for 240V, will be derated to 75% wattage at 208V ◼ Control transformers can have problem
Electrical Devices ◼ Conductors ◼ Wire is a single conductor and may be solid or stranded ◼ Cable is a multiple conductor with each conductor separated by insulation ◼ Typical conductors are copper or aluminum ◼ Circuits ◼ Consist of a source of electric, control device, conductor and a load. ◼ Feeders- Heavy gauge conductors that carry electric to switchgear and distribution panels
◼ Branch circuits- Feeds equipment from panels ◼ Dedicated branch circuit- A circuit that supplies only one piece of equipment ◼ Switches ◼ Control flow of electricity ◼ SPST- single pole single throw ◼ SPDT- single pole double throw ◼ 3PST- three pole single throw ◼ 3PDT- three pole double throw ◼ Rotary ◼ Momentary- contact switch ◼ Mercury switch ◼ Relays
RELAY/CONTACTOR
Relay
◼ Fuses ◼ Limit current draw to protect equipment ◼ Selected based on voltage, current, time delay, AIC, non time delay and time delay ◼ Circuit breakers ◼ Thermal- Trips by excessive heat ◼ Magnetic- Trips by excessive magnetism ◼ GFIC ◼ Trips when a current to ground exceeds a certain limit ◼ Required by code in certain locations
Electrical outlets (receptacles) ◼ Common outlets are 120 vac 15 or 20 amps ◼ Different outlet configurations are used for different voltages ◼ and amp rating Electrical Equipment ◼ Transformers ◼ Consists of two coils called windings ◼ Power in is the primary, power out is the secondary ◼ Changes Voltage - step up (increase) or step down ◼ (decrease) Changes Current-voltage increases current decreases ◼ Formula: Watts=Volt X Amperes ◼ Power loss in transformers typically is 1% to 2%. This loss ◼ generates heat from transformer. Old transformers were filled with oils containing PCB’s ◼ Transformers are rated in Kilovolt-amperes or kVA ◼
Switchgear ◼ Large Fuses and Circuit Breakers ◼ Function ◼ 1.To start and stop the flow of current ◼ 2. To protect against overloads and overheating. ◼ 3. To protect against short circuits. ◼ Arcing-Flow of electricity across a small gap. Causes ◼ burning and rapid wear of equipment. Device usually spring loaded , oil filed, gas filled or in a vacuum Rating- Switchgear must be rated to handle available fault ◼ current. Distribution panel boards- Large metal cabinets containing ◼ circuit breakers or fused switches Branch circuit panel boards- Small metal cabinets ◼ containing up to 42 circuit breakers
ELECTRIC MOTORS ◼ Function- Converts electric energy into mechanical energy. ◼ Opposite of generators ◼ Size rated in horse power (HP) ◼ Available in 1 or 3 phase and with different voltages ◼ Enemies are high heat, low voltage, high voltage and moisture ◼ Has a safety factor (SF) ◼ Typically consume 60% of electrical energy in office building ◼ Energy savings available ◼ 1. Energy efficient motors ◼ 2. Variable frequency drives (VFD)
SINGLE PHASE ELECTRIC MOTORS ◼ Have internal motor protection so a motor starter is not required for motor protection ◼ Have low starting torque so typically need some help such as a capacitor or start winding ◼ Do not use standard VFD’s for speed control ◼ Do to the various types of single phase motor consult manufacturer for speed control ◼ Different types of single phase motors: ◼ Split-phase motor ◼ Capacitor start motor ◼ Permanent capacitor run motor ◼ Capacitor start capacitor run motor ◼ Shaded pole motor
THREE PHASE ELECTRIC MOTORS ◼ Doesn't have motor protection so it requires a starter ◼ Has high starting torque ◼ Usually can operate on 208-230/460 VAC ◼ Changes speed by varying voltage and frequency in direct proportions ◼ Changes rotation by switching two of the three wires
Electronically Commutated Motor (ECM) ◼ Brushless DC motor ◼ Has two components ◼ The motor ◼ The motor control module ◼ More efficient then single phase motor ◼ Can provide constant CFM ◼ Verify the correct electronics are specified for what you want to achieve
TYPICAL MOTOR EFFICIENCIES
MOTOR STARTERS ◼ Function- Starts/stops motor and provides motor protection ◼ Not required if motor has VFD!!! ◼ Five different types of starters ◼ 1. Across the line (also used in VFD’s with bypass) ◼ Don’t use with large belt driven fans. ◼ 2. Reduced Voltage (Part winding) ◼ 3. Reversing ◼ 4. Two speed ◼ 5. Soft starter ◼ HOA- Hand/Off/Auto ◼ Phase loss- When one fuse in a 3Ø circuit is blown it shuts off motor
OVERLOAD HEATER
HOA
HOA
ADJUSTABLE MOTOR OVERLOAD
MOTOR NAMEPLATE
MOTOR NAMEPLATE
MOTOR NAMEPLATE
Table 1 VFD % Speed % Flow % HP Required 100 100 100 90 90 73 80 80 51 70 70 34 60 60 22 50 50 13 40 40 6 30 30 3
VFD
WATER SOURCE HEAT PUMP
Three categories of power Emergency required by code ◼ Emergency lighting ◼ Fire alarm systems ◼ Fire pumps ◼ Elevators ◼ ◼ Legally required standby systems ◼ Communication systems ◼ Smoke control systems ◼ Sewage disposal ◼ Optional standby ◼ Computer equipment ◼ Heating ◼ Cooling ◼ Security
Power Distribution Systems ◼ Bus duct is a factory manufactured assembly of copper or aluminum bars enclosed in a metal case ◼ Conduit and cable ◼ Heavy wall conduit- Exposed ◼ Thin wall conduit (EMT)- Typically protected from physical damage ◼ Flexible metal conduit- Interlocking armored cable consist of insulated cables enclosed in a flexible metal casing ◼ Plastic conduit- Corrosive environments ◼ Under floor systems
Safety ◼ Regulations ◼ Designed by PE ◼ Installed by licensed electrician ◼ State code ◼ NEC ◼ OSHA ◼ Permits ◼ Safety practices ◼ Lock out tag out ◼ Emergency Actions
LOCKOUT TAGOUT
Electrical Drawings ◼ E-1 Symbols, Abbreviations and specifications ◼ E-2 Lighting Plan ◼ E-3 Power and Signal Plan ◼ E-4 Riser Diagrams or Single line Diagrams ◼ E-5 Schedules ◼ E-6 Details
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