Mechanical and Electrical Systems

[CIV 311] Comprehensive coverage of mechanical systems, electric al systems, plumbing, fire protection, security, vertical transportation, lighting, acoustics and communications. The course includes analysis techniques and design principles for each system. A comprehensive design project is required for a major building project.. Psychrometry and process of air. Cooling load estimation. Refrigeration cycles. Water chiller systems. Air handling system. Cooling towers. Equipment selection. Installation, operation and maintenance of air conditioning systems.

Basic knowledge of data communication: data transmission technology, transmission media, signal interference, etc. Network topology: logical aspect and physical aspect. Local area network technology. Networking equipment: repeaters, signal transceivers converters, switches/hubs, connectors/interfacing equipment, etc.

Principles of lighting, lighting design for buildings which includes artificial lighting, point, line and area light sources, types and properties of luminaries, polar curves, design methods and calculations, glare index, lighting design standard, luminaire heat recovery system and lighting energy management, hybrid lighting, daylighting of buildings, effect of climate on lighting

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PART ONE ELECTRICAL

Chapter 1Electrical

fundamental T0-2

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Electricity

• Development can be measured by a nation’s electricity consumption

• Electricity usage is divided into:a) Industrial

b) Commercial and residential

c) Agriculture and irrigation

• Electricity important input for industry

General Electricity

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Electricity

• How can electricity supply shortage be solved?a) Renovation and modernization of plants, transmission and

distribution systems

b) Demand side management with the utilization of energy efficiency technologies

c) Awareness raising among energy users

General Electricity

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Electricity

Generation & Distribution

Generator

10.6 KV

GT 220 KV

Step down transformer

Distribution

Power plant Transmission system

Distribution system

380/220 V

22 or 11 KV

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Electricity

• AC generators (“alternators”) generate electricity

• Electricity generated at 9-13 KV

• Power generated from 67.5 to 1000 MW• Power stations: generating transformers (GTs) to increase voltage

to 132-400 KV

• Substations: step-down transformers to reduce voltage before distribution

Generation & Distribution

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Electricity

Benefits of high voltage transmission

• Less voltage drop: good voltage regulation

• Less power loss: high transmission efficiency

• Smaller conductor: lower costs

Generation & Distribution

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Electricity

Single phase AC circuit:• Two wires connected

to electricity source• Direction of current

changes many times per second

Phase of Electricity

3-phases of an electric system(Wikipedia contributors, 2005)Three phase systems:

• 3 lines with electricity from 3 circuits• One neutral line• 3 waveforms offset in time: 50-60 cycles/second

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Electricity

Star connection

Phase of Electricity

Delta connection

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Electricity

• Active power (kW): real power used

• Reactive power (kVAR): virtual power that determines load/demand

• Utility pays for total power (kVA)

Active and Reactive Power

Source: OIT

kVA = (KW)2 + (KVAR)2kVA = (KW)2 + (KVAR)2

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Electricity

Power Factor Correlation

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Electricity

• kVAR demand should be as low as possible for the same kW output

PF Correction: Capacitors

Figure: Capacitor as kVAR generator

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Electricity

• Act as reactive power generators

• Reduce reactive power

• Reduce total power generated by the utilities

PF Correction:CapacitorsE

l ect ri cal Syst em

s/E

l ect ri c it y

Figure: Fixed capacitor banks Source: Ecatalog

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Electricity

Advantages for company:

• One off investment for capacitor

• Reduced electricity costs:

• Total demand reduced

• No penalty charges

• Reduced distribution losses

• Increased voltage level at load end, improved motor performance

PF Correction: Capacitors

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Electricity

Advantages for utility:

• Reduced reactive component of network

• Reduced total current in the system from the source end

• Reduced I2R power losses

• Reduced need to install additional distribution network capacity

PF Correction: Capacitors

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Electricity

• Goal: reduce maximum electricity demand to lower the electricity costs

• Load curve predicts patterns in demand

Electrical Load Management

Daily load curve of an engineering industry (National Productivity Council, India)

KV

A

Hours

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Electricity

Strategies to manage peak load demand:

• Shift non-critical / non-continuous process loads to off-peak time

• Shed non-essential loads during peak time

• Operate in-house generation or diesel generator (dg) sets during peak time

• Operate AC units during off-peak times and utilize cool thermal storage

• Install power factor correction equipment

Electrical Load Management

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Electricity

• Energy charges

• Actual charges based on active power

• Charge based on apparent power

• Maximum demand charges

• Based on maximum demand registered

• Penalty for peak load

Electricity Billing Mechanism

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Electricity

• Power factor penalty or bonus

• Fuel costs

• Electricity duty charges

• Meter rentals

• Lighting & fan power consumption

• Time of Day (TOD) rates

Electricity Billing Mechanism

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Electricity

Electricity Billing Mechanism

Utility uses trivector meter for measurement during billing cycle (usually month):

• Maximum demand

• Active energy in kWh

• Reactive energy in kVArh

• Apparent energy in kVAh

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Electricity

Electricity Billing Mechanism• Demand

measured in time intervals

• Maximum demand is highest reading

• Customer charged on highest maximum demand value!

A Typical Demand Curve (National Productivity Council)

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Electricity

• Static electrical device that transforms electrical energy from one voltage level to another

• Two or more coils linked magnetically but electrically insulated

Transformer

• Turns Ratio: turns on 2nd coil (connected to load)

turns on 1st coil (connected to power source)

Figure 12: A view of a transformer(Indiamart.com)

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Electricity

Transformers are classified based on:

• Input voltage

• Operation

• Location

• Connection

Transformer types

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Electricity

• Electricity is the flow of electrons in a conductor.

• The electrons must have a path to and from its source.

• This path is called a circuit.

Normal, Open and Short Circuits

Normal Circuit◦ When normal current is flowing through the

circuitOpen Circuit

◦ When the current flow is interrupted by switch or fuse

◦ Circuit break presents an extremely high resistance.

Short Circuit◦ When the current flowing through the circuit is

following a “shorter” low resistance path between the power source terminals.

◦ Allows high current to flow in the circuitT0-25

ElectricityVarious electrical devices are

used as a part of the circuit.

These devices are used for a variety of activities, such as turning the electricity off and on, providing electricity to various lights or appliances, etc.

Types of Electrical Currents

Electrical current comes in two forms:

◦Direct current (DC)Flows in only one direction .

It is usually generated by battery-base electrical systems and used in the electrical systems of internal combustion engines or flashlight batteries.

◦Alternating current (AC)Reverses the direction of flow of current many

times each second .AC is the type used in homes, factories, etc.

Electrical ServiceService is provided to homes,

businesses and other small users of electricity by three wires from a utility pole.

Two of the wires are “hot,” each carrying 220 volts.

The other wire is “neutral,” and provides the return path for electricity.

Electrical Service (cont.)These wires are connected to a

service entrance, which is where the electricity enters a building.

A meter is used in the service entrance to measure the amount of electricity being used.

Electrical Service (cont.)The service entrance is grounded

with a wire connected to a ground rod driven several feet into the ground.

It is needed to provide a return path to the ground and to carry away stray electrical current out of the system.

Service Panel

Follows the meter .

It houses the circuit breakers for the system and is used to distribute

the power to individual circuits

throughout the system.

OvercurrentWhen a circuit uses too much electricity, an

overcurrent causes a circuit breaker to trip, shutting down the power to that circuit.

The excessive heat caused by an overcurrent condition may burn or damage a conductor’s insulation and cause a fire.

A circuit breaker is a heat-sensitive switch, which automatically trips when electricity demand is too great which causes the temperature in the conductor to get too hot.

Amps Volts WattsThe following relationship exists between Amps, Volts and Watts.

Amperes are a measure of the rate of flow of electricity in a conductor.

Volts are a measure of electrical

pressure.

Watts are a measure of the amount of energy or work that can be done by amperes and volts.

Amps Volts Watts (cont.)

Thus, the following relationship exists.

Work = Pressure x FlowOr

Watts = Volts x Amperes

Amps Volts Watts (cont.)This formula is commonly

referred to as the West Virginia Formula

W=VA

When we know any two variables of the formula, we can calculate the other.

Amps Volts Watts (cont.)

Formulas

Watts = Volts x Amps

Volts = Watts / Amps

Amps = Watts / Volts

Calculating Amperage

If we have a 100 watt lamp plugged into a 120 volt receptacle, we can determine the rate of flow or the

amperes for that circuit.

Amps = 100 Watts / 220 Volts

100 / 220 =.4545 Amps

Calculating Watts

If a water heater operates at 20 amps on a 240 volt circuit, what is the wattage of the appliance?

Watts = 220 Volts x 20 Amps

4800 Watts =220V x 20A

Watts=4400

Calculating Volts

If an electric motor operates at 2880 watts and 12 amps, what would be the voltage requirement for

that motor?

Volts = 2640 Watts / 12 Amps

2640 / 12 = 240 Volts

Maximum Minimum Average

Find the max and min load of the following domestics daily curve

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Hour 6 8 9 12 14 16 18 20 24 2 4 6

Kw 2 10 12 14 4 6 8 20 6 4 4 2

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Transformer Rating

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Example Design

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  Number

power Power factor

Dishwasher 1 2.5 KW 0.7Air condition 3 5 hp 0.6Water heater 1 4 KW 1

Washer 1 6 KW 0.8Light total 7 KW 1

1.High rising building consists of 12 level

Each level 4 flats (4 bed room, reception and two bath room)If each flat has the following equipmentThe main building has the following 3 lefts 15 hp 0.8 pf3 water pump 12hp 0.7 pfOutdoor light 10kw 1 pfCalculate•Total power design the electrical installation of the building •Main cable and branch cable cross section•Switchboard main and sub switchboard flat switchboard•No of transformer

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