MEANING & USE:
Fundamentally, electricity is the by product of another energy resources. It is produced from energy reserves. The conventional generation of electricity utilizes coal, oil, gas, or nuclear energy to heat water, producing high-temperature pressure steam. The steam flows through an electric turbine generator.
Generator is the machine used to convert mechanical energy into electrical energy. Generator is comprised of the essential elements of Faraday’s law to produce Electrical power. Faraday’s law says three things must be present in order to produce electrical current:
• Magnetic field
• Relative motion
Conductor cuts lines of magnetic flux; a voltage is induced in the conductor. Direction & speed is important in this activity.
Electricity is indispensable in the hotels. Electricity can be used for heat, light & power. Normal building electric energy cost is close to two third of the total energy budget for the building. The primary use of electricity is for production of mechanical energy through the electromechanical conversion in electric motors. Electric energy consumed by electric motors can account for up to 75 percent of the total electricity consumption for larger properties (motors for HVAC, elevators, laundry equipment, food chillers & freezers, water pumps, etc.). Electric energy for heat & lighting systems accounts for remainder of the uses of electric power. While electric –to-heat conversion is generally very efficient (approaching 95 percent or above), this can represent a costly heat resource. The use of electric energy for the generation of light is the most apparent use of electricity. Presently the electric light conversion process is not very efficient. There are a large number of electrical light sources, which produce all types of effects; especially interesting are the effects on surface colour (building surfaces, food & people).
Electricity will continue to be a primary energy resource in the future, as nuclear, solar, geothermal & other electric conversion processes will increase in the future, all resulting in abundant electric supply, which will eventually replace the dependence on natural gas & oil energy sources. Hence the hotel industry like other industries will become more & more dependent on electric energy.
ADVANTAGES AS A TYPE OF ENERGY:
The hospitality industry requires & uses large amounts of electric energy. The cost of electric energy remained at a relatively low unit cost level until the 1970’s. Since then electric energy costs have increased by factors of 5 to 10. Now, the average Hospitality industry manager spends two out of each three energy dollars for electricity.
This dependence on a single source of energy cannot be underestimated, & the value of electric energy in the hospitality industry is almost impossible to determine accurately. The industry is dependent on electricity for heat, light, & power. In addition, most building control systems operate electrically. Worker & customer activity areas are dependent on electricity as a lighting source. To appreciate the industry’s dependence on electricity for lighting, start to add up the number of electric lamps in guest room, guest bathrooms, halls, stairwells, meeting & conference rooms and employee work areas, as well as for exterior safety lighting & decorative lighting.
Electric motors are the largest consumers of electric energy in our buildings. The total air –conditioning system energy to drive fans, energy for cooling & heating air, energy for removing & adding moisture & energy for the control system. Management may also select electric energy as a heat source. While this can be an expensive form of heat, its convenience & ease of use make it desirable.
CONDUCTOR AND NON – CONDUCTOR:The material through which heat is transferred or offers little resistance to current flow is called conductor. E.g. Silver, copper, iron, etc. Different materials have different conductivities, which define the ability of the conduction of the material.
Non –conductors are also known as insulator, which have low conductivity, & or offers high resistance to electricity/current flow e.g. rubber, wood, paper, etc.
ELECTRICAL MEASUREMENTS:-Ampere (A) measures the flow of electric charges per unit or” flow rate” through a device or appliance. Electric motors are rated in amperes. Electric wires, fuses & most electric switching devices are rated in amperes. Generally if a device has a high ampere requirement, its initial cost will be higher than a similar device with a lower –ampere requirement.
Volt (v) is the unit of electrical potential difference or “electrical pressure”, which drives the flow of charges/current. If volts are not available, there are no amperes or watts. Many appliances & devices are rated in watts & volts, meaning that if the specified number of volts are supplied, the device consumes the indicated number of volts are available the rated number of amperes will flow through the device. Some appliances, especially electric motors have dual ratings. An electric motor may be rated as follows: volts 120/240=amperes 20/10. The correct interpretation of this rating is (1)If the motor is supplied with 120 volts, it requires 20 amperes (2) if supplied with 240 volts, It requires 10 amperes. Generally the initial cost of a device or appliance depends on its volt & ampere requirements. So if it is operated at a higher voltage, its ampere requirements are lower & its initial cost is less.
POWER FACTOR:A power factor relationship applies to all phases of alternating current. It refers to the difference in time at which volts & amperes reach their peak or maximum values. If volts & amperes both peak at the same time, the power factor is 1 or unity.
The power factor can actually vary from 0to 1. It normally varies from less than 0.60 to above 0.85. Electric supplier will usually impose a power factor surcharge on the electric bill whenever the power factor drops below a present value, frequently 0.85.
Watt (W) is the electric term used to measure the use of electrical energy. A high –wattage appliance has greater energy requirements 7 consumption than low wattage appliance.
The cost of electric energy depends on kilowatt-hours. The kilowatt hour is the rate of electric consumption. A kilowatt is 1000 watts. The kilowatt hour is 1000 watt- hours or 1 kilowatt being used For 1 hour. Watts depend on three factors ampere; volt & power factor.
Ohms (R) is the resistance, an electrical circuit’s opposition to current flow. Wires conducting electric energy have a resistance to flow of energy, conductors offer little resistance to flow of the current & insulators offer high resistance to the flow of current. Electric energy flowing through a resistance wire is converted to heat, causing the wire to get hot. For example, copper wires are good conductors which offer little resistance than iron, also since thick wire offers low resistance thick copper wires are used in wiring than a bunch of very thin copper wires as thin wires will offer more resistance. Similarly for protective devices like fuse, thin copper wires are used, because the moment electric flow will be raised it will get heated & melt down, thus safeguarding the appliances & other devices from high voltage.
Ohm’s law:- Ohm’s law says that current in a circuit is directly proportional to the applied voltage & inversely proportional to the circuit resistance.
V = I x R
Alternating Current (AC) Power: Hotel buildings are supplied with alternating current or AC, from the local electric supply board. The magnitude & direction of current flow in an AC circuit will change periodically (called a cycle). The frequency (Hz) of an AC circuit is the number of cycles per second. Current is constantly changing in magnitude & direction at regular intervals. Current is a function of time & usually varies as a sine function.
Direct current (DC) Power: Direct current or DC has limited applications in the hotel industry. Direct current provides a constant flow of amperes, when a constant flow of amperes, when a constant voltage is impressed on the amperes. Direct current is unidirectional & of constant magnitude. Amperes change only if the electrical load changes or if the impressed voltage changes. Direct current is used in some security systems & for limited emergency energy use for selective devices, such as exit lighting, & sometimes for power back up by using inverters with the DC source.
For these uses, a battery or a series of batteries probably provides DC. Many data- processing systems have back up DC sources. It is important to keep these systems in operation even when electric energy from the local electric supply is interrupted. These back up devices are frequently long-life batteries that are automatically charged when electric energy is being supplied to the unit.
AC vs. Dc: -
• AC power is easier to generate & requires less complex equipment (smaller machines).
• AC energy can be used in transformers to step up or step down voltages where DC energy cannot.
• DC can be ‘stored” for reserve use.
CAUSES AND DANGERS OF ELECTRICITY:-
INDIRECT DANGERS:The storage & use of electricity is often associated with sparks-electrical or electrostatic discharges. Plugging in an appliance which is already turned on cause a small spark connecting a battery to a device which is turned on will also cause a small spark. And finally there is the common discharge of static electricity that occurs when a charged body comes into contact or near contact with a body at a different potential. In most circumstances, such sparks are not a problem. However, if the atmosphere in which the spark occurs is laden with fine particulates, or a flammable gas, one spark can set off an explosion & /or a fire.
Spark plugs are probably the most common example of an explosion ignited by an electric discharge. In this case, the explosion is intended & occurs under carefully controlled conditions. However, electric or electrostatic discharges can be very dangerous in many less-controlled environments. These environments include grain elevators, paint-spraying booths, explosives & firework facilities fuel storage facilities coal mines & many others. If there are fine airborne particulates of combustible material or vapours of volatile compounds, the conditions are ripe for ignition & subsequent explosion. Another indirect danger associated with electricity & directly connected with above danger of explosions, is the danger of fire. Not all explosions ignited by an electric spark result in a subsequent fire, but many do. So, even if a person survives the initial blast, unless they are removed from the area, they could be injured or killed by a subsequent fire.
A final indirect danger associated with electricity is associated with one of the physiological responses of the human body to electric shock & is the hazard of being involuntarily moved by the electric shock. The body’s muscles contract when they receive a small electric signal from the brain through the nerve system. External electrical signals, such as those resulting from an electric shock, can also cause muscle contractions are involuntary, & in many cases can be violent.
Direct Dangers:The direct dangers associated with electricity are primarily divided into burns & cardiac effects. The former danger can readily be modelled when considering the body as a conductor of electricity. The latter danger is much more complex, & involves an understanding of the normal operation of the heart & the interfering action electricity can have on it.
Burns: The primary resistive material of the human body is the epidermis, the layer of dead skin cells that lie on top of the dermis. Normally this layer of skin is relatively dry, & the cells themselves are also dry, having died & released their moisture. Thus, this layer of skin provides a reasonable amount of resistance to the flow of electricity generally from about 1kΩ up to about 100 kΩ. The wide variation is a function of the ambient humidity, the individual’s production of body oils & exterior emollients that may have been added to the skin, such as lotion. It also depends on the degree to which the skin is compressed, greater compression forces the dead skin cells into contact with each other & reduces the resistance of the skin.
Once electricity enters the body through the skin, it encounters very little resistance due to the electrolytes (conductive fluids) contained within the body. Most of the fluids within the body are electrolytes & vary in resistance from milli-ohms to only a few ohms.
Due to the large difference between the resistance of the skin compared to that of the inner body withal its electrolytes, the major limitation to the flow of current is the skin. This would also be where the greatest heating occurs, since the heat is proportional to the resistance.
Cardiac Effects; - The effects of electricity on the human heart are generally the most serious considerations when dealing with electricity, because this is how most victims of accidental electrocution die.
Physiological Effects Of Various current intensities:- The danger is that these electrical currents will interrupt the normal electrical signals of the body that cause the rhythmic contractions of the heart muscle. When this happens, the heart enters a state of fibrillation, which is essentially the ineffective random quivering contractions of the heart, rather than the rhythmic full contractions that pump blood. If fibrillation is not overcome within a matter of 3-5 minutes, the victim will die.
PRECAUTIONS WHILE HANDLING ELECTRIC APPLIANCES:
We must take the following precautions while dealing electrical appliances:
1. Never handle an electric appliance barefoot.
2. We should never look into the fault of the appliance when it is connected to mains.
3. We should not switch on or switch off the mains switch wet hands.
4. In case of fire, we should immediately close the main switch.
5. Sparking in an electric circuit should be avoided. Sparking is generally caused by loose wiring or damp wiring.
6. Before fitting electric fixtures, bulb in wiring should switch off the electric supply.
7. Don’t touch the electric poles or fittings carrying the main supply, especially during the mains.
8. Use rubber gloves & a tester while finding fault in circuit or the appliance.
Importance Of Earthing:-Potential difference of earth is zero. A secondary wire is attached to a device for human life, devices & appliances, circuit & electric network protection. The wire is physically attached to the ground water table & will conduct accidental energy flow from a defective circuit to the ground. The ground serves as a potential path for unwanted, excessive or dangerous energy flow. Fluctuation in current comes to an end when a circuit is connected to the earth or earthened. Each device must be connected with the ground wire. Generally the earth wire is green in colour.
Earthing is necessary:
1. To save human life in case of leakage.
2. To maintain voltage constant.
3. To protect building & appliances from lightning,
4. Earth electrode is embedded in the earth to offer resistance to the faulty circuit to blow off quickly.
ELECTRICAL DISTRIBUTION COMPONENTS
- Enclosures that house various electrical instruments, indicating devices, protective devices, and regulating apparatus required for the control of the generators and for the distribution of electricity.
- Contains busbars and distributes electrical power to various circuits.
- An electrical protective device consisting of a fusible (easily melted) metal alloy strip of wire encased in a cartridge.
- If current exceeds a predetermined value, sufficient heat is generated to melt the fuse causing an open circuit.
- Protects the circuit/equipment from possible damage due to excessive current.
- An electrical device that opens due to various trip set points (over-current, under-voltage, under frequency) to protect generators and loads.
- Circuit breakers trip open, and may be reset when the operators close the circuit breakers.
- Circuit breakers may be operated manually or electrically and can be used as switches in some circuits.
Automatic Bus Transfer (ABT)
- A device that senses a loss of power from a normal source and will automatically disconnect the load from the source and connect it to an alternate source.
Manual Bus Transfer (MBT)
- Can connect a load to either a normal or alternate source, but unlike ABT’s must be shifted manually.
Lamps and Luminaries
A lamp is a source of light. A lighted candle is a lamp because it is a source of light. A flashlight is a lamp. The common electric lamps are incandescent and fluorescent. Lamps are available in different shapes and sizes.
A lamp is inserted into a lighting fixture. The combined lamp and lighting fixture is a luminaire. If an incandescent lighting fixture is capable of holding a 25, 40, 60, or 75 watt incandescent lamp, the single lighting fixture becomes one of four luminaries. The general light output characteristics of the lighting fixture change with each size of lamp, resulting in different types of luminaries.
Lumens and Foot-candles (Lux)
Lamp light output is given in lumens. A lumen is a quantity of light. One very good efficiency rating for lamps is the number of lumens produced per watt of energy input. This technique allows the manager to compare different lamps and the cost of lighting.
The lumen is the amount of light energy that strikes an area at a specific distance from a standard candle. If 1 lumen falls on- a 1-square-foot area at a distance of 1 foot from a standard candle, it is called 1 foot-candle of light intensity; or if 1 lumen strikes 1 square meter of surface at a distance of 1 meter from a standard candle, it is called 1 lux. Foot-candles and lux refer to the intensity of light.
Room lighting design is based on foot-candles (lux) and lumens. As you move farther away from the lamp, the lumens are spread over a larger surface area, so lighting intensity decreases. If correct lighting is not provided in an area, poorly lit objects can become hazards for guests, patients, or employees.
Resistance Type Lamps
One very common source of light is the incandescent lamp, which has a high-electric-resistance filament wire. As energy flows through the filament wire, it will incandesce, or glow. The emitted energy is visible light and heat.
Incandescent lamps are rated in volts, watts, hours (life expectancy in average operating hours), and lumens. Through lamp purchasing specifications and with knowledge of your building's voltage, you can take advantage of the operating characteristics of these lamps.
The incandescent lamp radiates visible light that is rich in such warm colors as red, orange, and yellow. Hence, the lamps have a tendency to bring out the warm reddish color of food products, especially cooked meat and red and blush-color wines. Many foodservice operation interior color combinations are based on warm colors, which complement cooked meat items on the menu. Then, too, people look better in incandescent lighting, which highlights warm or pink flesh tones. The major disadvantage of incandescent lamps is their low light efficiency: They are only about 5 to 15 percent light efficient.
Another form of resistance lamp is the tungsten-halogen lamp, frequently called a halogen lamp. The life of a halogen lamp is generally greater than a normal-life incandescent lamp; its life varies from 2000 to 3000 hours. Its efficiency equals that of the most efficient incandescent lamp (12 to 15 per¬cent light efficient), and its lumen output does not greatly decrease with its age; however, its initial cost is higher in comparison to an incandescent lamp.
Electric Discharge LampsFluorescent Lamps
The fluorescent lamp is an electric-discharge lamp, which operates on alternating current, or simulated alternating current. The operation of the lamp is complex compared to an incandescent lamp. Like the incandescent lamp, the fluorescent lamp has a small filament, but its purpose is to heat an electric device called a cathode. The cathode has voltage impressed on it, so that it becomes heated and "charged up" at the same time. The electric energy now actually flows through space as an electron discharge, and the electrons are attracted to another cathode-type device (called an anode) at the opposite end of the lamp. Electrons are constituents of atoms that are on the cathode. The high voltage at the cathode forces the electrons toward the anode. As the alternating current reverses, electron flow also changes between cathode and anode.
The space between the ends (within the glass tube) is filled with low-pressure mercury gas. The electrons flowing from one end to the other are absorbed by the mercury gas, and energy is emitted-for every action there is a reaction. Now, as this different energy passes through the glass tube with its chemically coated interior, visible light energy is produced along with low-temperature heat.
High-Intensity Discharge Lamps
High-intensity discharge (HID) lamps are somewhat similar to fluorescent lamps. These lamps have a glass bulb with an internal glass, ceramic, or quartz tube filled with a gas that determines the type of high-intensity discharge lamp. There are electrodes (cathodes) at both ends of the tube. Electric energy arcs between the electrodes. Voltage is regulated by ballast that serves the same function as in a fluorescent lamp.
Mercury Lamps: The most common high-intensity discharge lamp is the mercury lamp, frequently called the mercury-vapor lamp. High-pressure mercury gas is used in the arcing tube
There are three types of mercury-vapor lamps; each produces different color effects. The clear mercury lamp makes people look greenish. Its use may make it difficult to find red and orange objects. These lamps are frequently used for very large-area lighting (in parking lots and warehouses), where color characteristics are not critical.
The metal-halide lamp is very similar in construction and operation to the mercury-vapor lamp. Metal particles are added to the mercury gas in the arcing tube. This generally improves the color response to objects, and light output is almost double the mercury-vapor efficiency, varying between 56 and 125 lumens per watt.
High and Low Pressure Sodium Lamps:
Sodium lamps have a ceramic arc tube. Sodium is the arcing gas, and it provides a white-yellowish light. The high-pressure sodium (HPS) lamp, which is almost 35 percent light efficient, is currently one of the most efficient lamps available (61 to 140 lumens per watt).
BILL CALCULATION OF POWER CONSUMPTION
Calculate the electric bill for a month of 30 days for the following load if the cost of electricity energy is Rs. 4.75 per unit.
18W Electric lamp 18 nos. used for 8 hrs./day
60W Electric lamp 20 nos. used for 7 hrs./day
100W Electric fan 10 nos. used for 18 hrs./day
750W Electric iron 2 nos. used for 6 hrs./day
1.5kW A.C. 6 nos. used for 8 hrs./day
6kW Electric motor 1 no. used for 3 hrs./day
1 kW Electric mixer 1 no. used for 15 min/day
128.4 x 30 = 3847.2 kWH
Therefore, for the month the electric bill @ Rs. 4.75 will be,
3847.2 x 4.75 = Rs. 18274
Other charges for the billing will include service and deferred energy charges and taxes.
ENERGY MANAGEMENT CONTROL SYSTEMS
There are four common energy–management control systems: time clock, load, cycling, electric demand, & computer control.
TIME CLOCK SYSTEMS:
Time clock systems are the simplest & least costly energy –management control systems. They have been available for years. They turn devices on & off at predetermined or programmed time intervals. A common application is outside lighting. The timer is set for sunrise & sunset. Timers can be manually reset every 45 to 60 days. In the case of outside lighting, time clocks have now been replaced by light sensors. Most hospitality buildings have some type of time clock energy control system.
Photoelectric cells are also used as sunset & sunrise timers. They do not have to be reset for changing sunrise/sunset times. They are also activated if it becomes very dark during normal daylight hours because of a storm.
LOAD CYCLING SYSTEMS:
Some control systems are load cycling. These control several large energy consuming devices so that they do not all operate at the same time. They can also be programmed to allow only certain devices to operate within specified time periods. In this manner, they limit the length of time an electromechanical device is in operation, thereby controlling energy consumption. For example, dining room air conditioning could be cycled to operate only when the room is in use (much like a time clock system). At the same time load cycling may shut down another major energy consumption system, such as electric hot –water hearers, while the dining room air conditioner is in operation.
These systems ensure that the energy delivery system will not be over extended during any time period. Thus, they are similar to a combined demand control & time clock system.
ELECTRIC DEMAND CONTROLLERS:
Electric demand controllers are very similar to load cycling in that a maximum electric demand, or energy requirement, is set. Initially, every electromechanical device that is turned on operates until a preset demand is reached. Now, no additional device can operate until another is shut off. During peak demand periods many devices will not operate at the same time, so both demand charges & energy consumption are reduced.
COMPUTER ENERGY CONTROL:
The complete computer energy control system will cycle loads, control demand, and reduce total energy consumption. The cost of the system is usually large, but fire, security control, and occupancy sensor subsystems can be added to the basic system with little additional cost. Some of these complex systems can control air temperatures within definite set points in separate rooms of a building, so that the system can reduce the excess temperature rise that occurred with the older system. When the system is properly programmed and maintained, substantial energy savings can result. Computer systems can also be expanded to include maintenance scheduling that is dependent on operating hours, since these systems can accumulate operating times of such electromechanical devices as air conditioners. The high system cost results from connecting, or interfacing, each controlled device with a computer. Telephone lines or electric lines most frequently used for this interfacing. Several computer software programs are available for energy-management systems. Some can be operated with a PC for smaller properties, while others require a mainframe computer.