IMPORTANCE OF ENERGY EFFICIENCY: FROM THE PERSPECTIVE OF ELECTRICAL EQUIPMENTS

Transcription

1 1B International Conference on Science & Technology: Applications in Industry & Education (2008) IMPORTANCE OF ENERGY EFFICIENCY: FROM THE PERSPECTIVE OF ELECTRICAL EQUIPMENTS Anwar Al-Mofleh, Soib Taib, Wael Salah, Mokhzaini Azizan School of Electrical & Electronic Engineering, Universiti Sains Malaysia, Pulau Pinang Soib Taib, CETREE USM, Pulau Pinang Malaysia 0BAbstract. Electrical energy which forms vital energy input in any industrial activities is demanding increased attention in recent times due to the escalating power costs and crippling power shortages. Much energy is needlessly wasted in buildings through the negligence of electrical services. Combination of low power factor, bad management in motor speeds, as well as poor lighting selections further highlight the possible disturbances to effective energy efficient practices. This paper investigates the energy saving measures which can be applied specifically to electrical services in buildings and also in street lightning including tunnels. It also provides substantial knowledge upon the activities that can increase the energy efficiency. In particular low energy lighting and use of variable speed motor derives are discussed. By observing the related tables, reduction in motor speed, changing the types of lights, and usage of more efficient heat pumps and better ventilation system, are the examples of energy efficient practices that are possible to be applied. A thorough research and modernization of several related systems have proved to be reliable and extremely helpful in order to maximize the saving of energy of today. Index term. Energy efficiency, power factor, electric motor I. INTRODUCTION Energy is a primary component in our lives and energy is needed to provide heating, lighting, mobility, consumer goods and comfort appliances. The consumption of particular fuel sources are critical issues in a country s development and it forms the driving force in sustaining many industrial, commercial and domestic sectors. Studies have shown that industry and public sectors in developing nations, including Malaysia are more energy intensive than their competitors in developed countries like Japan, Denmark and Germany, partly because of lack of awareness of the real costs of energy consumption [1].Much energy is needlessly wasted in building through poor design and maintenance of electrical services. The energy that is wasted is of the warts kind namely expensive electrical energy, which can be up to five times as expensive as the unit cost of heat. Unfortunately excessive electrical energy consumption is all too often overlooked by misguided building designers. Thus resulted in energy waste and inefficient usage of energy. Another significant consequence is that the usage will is too uneconomic for such amount of usage [2]. II. POWER FACTOR Electric induction motors and fluorescent lamp fitting are classic examples of reactive electrical loads. Reactive electrical loads are important because unlike resistive loads such as incandescent light, they because the current to become out of phase with the voltage.this in simple term means that item of equipment which is inductive in nature draw a large current than would be anticipated by their useful power rating. Ultimately it is the consumer who has to pay for this additional current. The electrical power consumed by a resistive load can be determined by: 144

2 W = V I where; v, = i = voltage, current, w = power (1) Equation 1 defines the useful power consumed and applies to all types of resistive load where the current is in phase with voltage. However equation 1 does not hold true for reactive loads, where the current lags behind the voltage since reactive loads consume more power than consume be usefully used. A reactive load such as an induction motor will therefore draw a larger current than would be anticipated by its useful power rating. The reactive components of the load consume what is termed reactive power. [3] Figure1. Relation ship between KW, KVA and KVAr In order to determine the apparent power consumed by a reactive load the true power must be add vectorally to the reactive power as shown in Figure 1.it should be noted from figure 1 that the reactive power is drawn at right angles to the true power. The apparent power is therefore a function of the true power consumed and the reactive power and can be expressed as: True Power Apparent Power = COS ϕ where : cos ϕ the power factor, (2) From Figure 1 and Equation 2 it is evident that when the current and voltage are in phase with each other, the apparent power is the same as the true power. When the two are out of phase the apparent power consumed is always going to be greater than the true power in order to differentiate between true and apparent power, true power is measured in watts (W) or kilowatts (KW), and apparent power is measured in volt amps (VA) or kilovolt amps (KVA) similarly reactive power is measured in volts amps reactive (VAR) or kilovolt amps reactive (KVAR).The ratio of true power to apparent power is known as the power factor. Power Factor = True Power Apparent Power, (3) 145

3 Power Factor Correction Power factor is the key figure in electrical energy conservation. Not only would be paying penalties to electricity supply authorities for low P.F., we also have to cope up with oversize cabling and equipment entailing further increase in capital cost. We have also se the inherent P.F. characteristics of induction motors on no load or light load. All these factors have to be taken in to stock and a detailed study made by taking readings of incoming voltage, load current, power factor (if a P.F. meter is fitted), frequency and M.D. values and plotting them accordingly. With the aid of prepared Made monographs, ascertain KVA ratings of capacitors to suit the conditions. The aim is to establish and maintain a P.F. around 0.95 to P.F. correction capacitors can be connected across lare motors to be switched in and out along with them. Power factor in large establishment can be improved by employing a synchronous motor with over-excited field (synchronous condenser) which will act as a capacitor [4].The main advantage of good P.F. is to control M.D. when the letter is contracted on KVA basis. More KVA can be drawn from a source like a transformer. Table 1. Impact of poor power factor Power =0.7 factor Power factor=1 Total current 417.4A 292.2A Apparent power (KVA) 300KVA 210KVA Switchgear rating 450A 350A Transformer rating 400KVA 300KVA Cable size 240mm 2 150mm 2 The overall current, as read by ammeter, drops; undue heating cables and equipment reduced, resulting in improvement in supply voltage. Though not translatable in terms of cash saving (unless penalized for low P.F.) P.F. correction and improvement enhances the efficiency of electrical equipment. Or medium size industries utilizing electric power, it is advantageous to employ automatic P.F. demand controllers (which will be switching in capacitors as per requirement to maintain a steady predominant P.F.) as shown in table 1. This system works well in fluctuating loads of general engineering workshops and batch production units [5]. III. ELECTRICAL MOTORS The motor consumption may be anticipated to equal 50% of the total electrical energy. Most of the designs oversize the motor with respect to the load by safety factors of 10-15%, resulting in 27-49% more power consumption during the life cycle. The speed of recent motors can be controlled smoothly by electronic devices, resulting in good savings in energy consumption [6]. Figure 2 represents the effect of speed variation on the energy consumed. In case the speed of the fan motor is reduced by 33% during night ventilation, the energy consumed is decreased by 70%. Rewinding of a motor will increase its energy consumption. Therefore the motor must be replaced if the repair cost is greater than 60% of the cost of a new energy efficient motor. Efficient motors, on average, are 4% more efficient than standard motors and 6-8% more efficient than a rewound failed motor. Proper preventive maintenances will result in longer life time, less energy consumption and high reliability service [6, 7]. It is very useful to record information and measurements of the motor for performance evaluation to help make decisions at the proper time for preventive maintenance [7]. The use of DC motors, whenever it is possible, will provide up to 40% reduction in energy consumption as compared to conventional AC motors of similar rating capacity. 146

4 Figure 2. Relation between power and speed for electric motors The efficiency of old and new types of electrical motors is shown in Figure. 3. It is found that an average of 1.5% efficiency is achieved throughout the operation and this mean a lot of energy saving for kwh Figure 3. Efficiency of asynchronous motors for old and new ranges. III. LIGHTING The percentage of electrical energy used for lighting in industrial facilities represents 10-20% of their total energy and in buildings about 30-35% of total energy is consumed by lighting and other appliances, except air conditioning [6]. Savings can be achieved by many advanced lighting fixture and control methods. Table 2 shows a comparison between various lighting fixtures. It is clear from Table 2 that some lighting fixture can not be used in all applications, mainly in places where immediate lighting is required whenever the fixture is switched on (no delay). Energy conservation in lighting for new advanced houses is designed on 100 lumens/watt as compared to 15 lumens/watt in classical houses. The optimum electrical lighting design aims to reduce the amount of power capacity, i.e. W/m2. In advanced houses, it was limited to an average of 8W/m2 [8] as compared to more than 35W/m2 in typical classical residential houses. In this condition about 77% saving is possible in the residential sector. The new available compact fluorescent fixtures are equipped with electronic ballast which has a good power factor and lower power consumption [9]. For example, the recommended lighting level for offices, classrooms, stores and supermarkets is 500, 300, 500 lux (1 lx= lumen/m2) respectively. 147

5 Table 2.Technical specification of lighting fixtures Type Lumen/Watt Life time (h) Relight time (min) Tungsten Energy saved% Mercury Fluorescent, conventional Fluorescent new compact Metal halide High pressure sodium < A typical saving for lightning in tunnel as shown in Figure 4 where conventional fluorescent is used can be achieved if a saving CFL is used. The amounts of lamps depend on the tunnel s length. In average 4 lamps per meter. Table 3 shows the saving if a CFL tubes are implemented. The cost for Malaysia unit per kwh is 23 cents. Figure 4. Lightning in tunnel using fluorescent tubes. Table 3. Saving of cost using cfl. Length (m) Fluorescent CFL Lamp 9W Bill per Saving per Lamps bill per months month month x30= x30= x30= x30= x30=

6 V. HVAC & HEAT PUMP Much equipment is used for heating, ventilation, and air conditioning (HVAC) in various types of buildings. The air conditioning unit consists of mainly a compressor, evaporator and condenser. Recent energy efficient designs of the main components of air conditioning systems have contributed in reducing their energy consumption. For instance, the use of a variable speed motor will reduce the energy consumed in each of the air conditioning unit. The recent centrifugal chiller has lower electrical consumption, 0.6 to 0.65 kw/ton refrigeration, as compared to the old chiller values of 1.2 to 1.5 kw/ton refrigeration, which represents an energy saving of 43 to 50% (1 ton refrigeration = Btu/hour). [10] Also, the frequent operation of a limited number of chillers at full rated load is more efficient because a chiller operating at partial load will consume higher energy. The design specification of the air conditioning system must be based on the real conditions of the plant, therefore any over sizing and additional safety design factor may be cancelled. Many available industrial air conditioning units have a built in heat pump. Heat pumps are also used in many industrial countries. Heat pumps are manufactured with various capacities suitable for various applications, both for heating and cooling purposes. But for Malaysian environment the need for the heat pump can be cancelled. VI. QUALITY OF ELECTRIC SUPPLY Quality plays a vital role in utility. The parameters like voltage and frequency; must be maintained by the suppliers to the best possible values, which may ultimately contribute to the efficient running of electrical equipment and to keep losses to minimum. Let us take one parameter viz., the voltage, and its influence on an Induction Motor. Table 4 gives the fact that low voltages entail in energy loss, because of low torque, less speed, more current, and finally low-efficiency Table 4. Supply voltage as percentage of normal voltage Induction motor 90% 100% 110% performance Starting torque 81% 100% 121% Total current 111% 100% 93% speed 98.5% 100% 101% Efficiency Decrease 100% Increase According to statutory regulations, the supply authorities (electricity boards) should maintain a declared voltage at the consumer s premises up to a variation of 5% and frequency up to 3%. Far flung consumers in rural sectors, depending only on electricity to run their pump sets for irrigation, incur heavy losses due to low-voltage supply for the above reason VII. CONCLUSION Engineering managers should update their knowledge on the energy efficient equipments available to them in the market. Of late, there has been a technological jump in designing and manufacture of energy efficient motors, softstart and variable speed starting systems in induction motors already install, better luminaries and lighting systems. These improvements can be incorporated progressively for the most economic use of electricity, with national capital expenditure. VIII. REFRENCES [1]I. K. a. G. Dunn, "measured energy consumption and carbon emissions of air conditioning in UK office building," in building service engineering research technology, 2005, pp [2]B. Bose, K, modern power electronics evaluation technology and applications, in ISBN, [3] International Energy Agency, World Energy Outlook

7 [4] E. Richard, P.C.H. Frederick and K.P. Jayanta, Optimal reactive power control for industrial power networks, IEEE Trans Ind Appl 35 (1999) (3), pp H[5]H Gutierrez J, Montano JC, Castilla M, Lopez A. Power-quality improvement in reactive power control using FC-TCR circuits. In: IECON 02 industrial electronics society, IEEE th annual conference, vol. 2; p [6] US Department of Energy (US DOE). Fact Sheet: Determining Motor Load and Efficiency.2003 [7] IEEE, Industry Applications Conference (IAS), 28th Annual Meeting Proceedings, Canada, Part 3, [8] International Energy Agency (IEA), Energy Conservation News, 1994, pp19. [8] Lighting Hand Book: reference and application, 7 th Edition. Illuminating Engineering Society of North America, New York,1998 [9] Thomas, Bellarmine G. and Turner, M. K., Energy Conservation and Management, 1997, 35(4), pp [10] C.R. Nave, Department of Physics and Astronomy, Georgia State University. How does an electric motor work In: Hyperphysics, Electricity and Magnetism