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Transcript
LIGHTING DESIGN & APPLICATION E nergy savings claims made for electronic ballasts should be understood in context. If their efficacy is taken into account, in the proper application, magnetic ballasts will outperform their electronic counterparts. Energy efficiency of fluorescent lamp and ballast systems The efficiencies of technical devices and processes are normally rated as percentages. Only in the case of light does this not really apply, since in its perception of brightness the human eye is different in sensitivity to different colours. The sensitivity of a standardised average eye has already been integrated into the unit for assessing the brightness of light sources. This unit is called lumen (the Latin word for light). Hence, the efficiencies of lamps and luminaires need to be given in lumens per watt (lm/W). This is the appropriate quantity to be used in a comparative study of lighting devices when investigating quantities of light generated as a function of electrical energy consumed. T h e o r e t i c a l l y, a n e f f i c i e n c y o f 683 lumens per watt (lm/W) can be achieved. This, however, is only valid for mono-chromatic green light with a wavelength of 555 nm at which the human eye has its greatest sensitivity. It remains more than questionable whether we really want to illuminate streets, squares, halls, offices, supermarkets or even living rooms in this way. White light, or what we consider white when mixing all colours from 380 nm to 780 nm wavelengths, yields a theoretical maximum efficacy of 199 lm/W. Setting this efficacy equal to 100% brings fluorescent lamps already considerably closer to the desired 100% ideal than a modern diesel engine is. Speaking in these terms, an incandescent lamp could be compared to an ancient steam locomotive. The European Commission set out to support trends towards efficient lighting by Stefan Fassbinder, German Copper Institute, and Johan Rens, North-West University, Potchefstroom techniques. It released in June 1999 the first draft of a directive with the objective “to accelerate the transition of the Community (EU) industry towards the production of electronic ballasts and the overall aim to move gradually away from the less efficient magnetic ballasts and towards the more efficient electronic ballasts which may also offer extensive energy-saving features, such as dimming”. South Africa is experiencing similar trends. Energy conservation programmes, more often than not, Fig. 1: Behaviour of a dimmable electronic ballast opted for electronic ballasts to be according to manufacturer’s documents. used in new installations and in the retrofitting of existing installations. Although not stated explicitly, these This phenomenon is expected to escalate approaches sound as if an electronic even more in the next few months as the ballast is: significance and detail of new tariff l always the more energy efficient systems are better understood. Eskom choice, is considering various self-regulating l always dimmable. tariff schemes which could include Is this in fact always the case? And how heavy penalties as a measure to achieve much more is “more efficient”? energy savings targets. Lamp power rating 50 Hz (magnetic) 15 W 18 W 30 W 36 W 38 W 58 W 70 W Maximum input power of ballast and lamp circuits (ratings according to 2000/55/EU) HF Class D Class Class Class Class Class (electronic) C B2 B1 A3 A2 14 W > 25 W 25 W 23 W 21 W 18 W 16 W 16 W > 28 W 28 W 26 W 24 W 21 W 19 W 24 W > 40 W 40 W 38 W 36 W 33 W 31 W 32 W > 45 W 35 W 43 W 41 W 38 W 36 W 32 W > 47 W 47 W 45 W 43 W 40 W 38 W 50 W > 70 W 70 W 67 W 64 W 59 W 55 W 60 W > 83 W 83 W 80 W 77 W 72 W 68 W Table 1: Classes and ratings of linear fluorescent lamps with ballasts. September 2008 - Vector - Page 28 Don’t replace losses with losses Care must be taken not to replace the energy saved by lighting with energy dissipated in the standby mode of electronic control gear. In poorly designed apparatus, especially automatic office lighting, all dimmable electronic ballasts remain in a standby mode of operation while not in use, in order to be always on the alert, ready to receive signals. From an engineering viewpoint, the power consumption required for this state could be minimized to a negligible amount, but the customer never knows how much power is being consumed. An office may be used for 3000 hours/ annum and a conventional office lighting be kept in operation manually for about two thirds of this time, say 2000 hours/ annum. As a cautious estimate, during half of these two-thirds, say 1000 hours/ annum, one half of the power could be saved if automatic daylight-dependent continuous control had been installed, so this would result in 500 full-load hours saved annually, while the standby power intake of the automatic control gear remains busy for 8760 hours/annum. It is not the sense of such automatic control and therefore unrealistic to expect anyone to look after it and completely shut it down manually for weekends, holidays and so on. So if the standby power intake is not substantially lower than some 5% of the power rating controlled by the equipment, the energy saving equals zero, while the documentation of a renowned and famous manufacturer with a very good reputation rates 13% (see Fig.1). So you may very well end up with zero or even “negative savings” under the bottom line! Mind that with above assumptions the standby input for each controlled 58 W lamp (in an office environment) needs to lie below 3 W to save any energy at all, while this already assumes that a conventional lighting system wastes 25% of the “full load lighting hours”, i.e. of the nett light generated. This could be saved if the saving is not used up for monitoring the daylight level, the presence of room users, what time of day it is, what weekday it is and the like. The savings potential – of gross energy input in such measures may often be greater by a simple luminaire replacement. Care mst be taken when proposing dimmability as a means of energy saving, all the more since dimmed operation requires permanent filament heating. Dimming may very well be justified as a necessity of the application or for the luxury to have variable light. As a means Type (device under test) T8 lamp 58W with magnetic ballast EEI=D T8 lamp 58W with standard magnetic ballast EEI=C T8 lamp 58W with low-loss magnetic ballast EEI=B2 T8 lamp 58W with low-loss magnetic ballast EEI=B1 Metering conditions T lamp 51W with low-loss magnetic ballast EEI=B1 T8 lam 51W with electronic ballast EEI=A3 Calculated values Ptot W PBall W PLamp W I mA ø lm hLamp lm/W htot lm/W PLoss Ptot Ptot P(UN) R20=19.73Ω 190,0 49,13 6,18 43,10 447 4039 93,71 82,21 12,6% 61,4% m= 1,60 kg 200,0 58,99 8,97 49,92 544 4624 92,62 78,38 15,2% 73,7% 210,0 67,10 11,80 54,87 624 5010 91,31 74,67 17,6% 83,9% 90,1% Rated power 218,0 72,10 14,20 58,00 679 5311 91,56 73,66 19,7% Rated voltage 220,0 73,90 14,80 58,97 695 4301 89,89 71,73 20,0% 81,4% 230,0 80,00 18,10 62,60 765 5543 88,55 69,29 22,6% 100,0% 240,0 88,00 21,90 65,93 839 5756 87,30 65,41 24,9% 110,0% 250,0 96,30 26,50 69,62 918 5954 85,53 61,81 27,5% 120,4% R20=23,30Ω 190,0 39,02 4,28 33,71 328 3197 94,83 84,08 11,3% 55,1% m= 1,02 kg 200,0 47,61 6,56 41,04 415 3895 94,90 81,81 13,8% 69,0% 210,0 55,46 9,00 46,41 490 4365 94,06 78,71 16,2% 80,4% 220,0 62,36 11,55 50,89 555 4722 92,80 75,78 18,5% 90,3% Rated voltage 230,0 68,98 14,36 54,67 622 5033 92,06 72,96 20,8% 100,1% Rated power 240,0 75,40 17,30 58,00 686 5301 91,40 70,31 22,9% 109,3% 250,0 82,28 20,88 61,30 753 5504 89,79 66,90 25,4% 119,3% R20=17,90Ω 190,0 36,71 2,90 33,85 325 3233 95,51 88,07 7,9% 57,9% m= 1,10 kg 200,0 45,41 4,54 40,84 410 3894 95,36 85,76 10,0% 71,6% 210,0 51,92 6,15 45,93 478 4349 94,68 83,76 11,8% 81,9% 220,0 57,92 7,73 50,07 541 4692 93,71 81,01 13,3% 91,3% Rated voltage 230,0 63,41 9,66 75,73 602 4979 92,66 78,52 15,2% 100,0% 240,0 68,690 11,40 57,07 656 5228 91,60 76,20 16,6% 108,2% Rated power 243,5 70,50 12,40 58,00 681 5306 91,48 75,26 17,6% 111,2% 250,0 73,80 13,80 59,94 718 5417 90,38 73,41 18,7% 116,4% R20=13,80Ω 190,0 35,42 2,44 32,94 314 3157 95,85 89,14 6,9% 57,7% m= 1,32 kg 200,0 43,78 3,82 40,03 397 3813 95,25 87,09 8,7% 71,3% 210,0 50,57 5,14 45,38 470 4295 94,65 84,94 10,2% 82,3% 220,0 56,24 6,57 49,70 537 4662 93,80 82,89 11,7% 91,6% Rated voltage 230,0 61,42 8,01 53,36 596 4952 92,80 80,62 13,0% 100,0% 240,0 66,40 9,60 56,72 659 5198 91,64 78,28 14,5% 108,1% Rated power 244,0 68,53 10,31 58,00 683 5306 91,48 77,42 15,0% 111,6% 250,0 71,60 11,50 59,91 724 5420 90,47 75,70 16,1% 116,6% 190,0 54,92 297 4722 85,98 200,0 54,72 285 4723 86,27 99,9% 210,0 54,90 275 4724 86,06 100,2% m= 0,22 kg T8 lamp 58W with electronic ballast EEI=A3 Measurement DIAL U V Rated voltage Rated voltage ø mag=ø elec Rated voltage 100,2% 220,0 54,85 263 4723 86,12 100,1% 230,0 54,80 256 4718 86,10 100,0% 100,1% 240,0 54,86 248 4724 86,11 250,0 54,72 242 4723 86,32 207,0 44,73 5,88 38,82 502 3481 89,66 77,82 13,1% 80,4% 230,0 55,64 8,95 46,38 627 4109 88,59 73,84 16,1% 100,0% 101,5% 99,9% 232,3 56,50 9,19 47,12 640 4156 88,20 73,56 16,3% 253,0 66,08 13,66 52,56 775 4459 84,84 67,48 20,7% 207,0 48,16 245 4145 118,8% 86,07 100,2% 230,0 48,06 226 4153 86,44 100,0% 253,0 47,84 213 4120 86,12 99,6% Table 2: Measurements on 5 different ballasts at different line voltages with the same lamp. of energy saving, it does not suffice. In order to avoid the permanent filament heating required for dimmability during the day, mechanisms will have to be added to make sure the lamp is fully shut off at night and during weekends, otherwise it will only be “dimmed down to 0” when the light is off. Adding to this, each sensor and each actuator of such a monitoring system may need its own power supply from the mains. The net DC requirement may be as low as a few milliwatts each, but each one of them employs a mains adaptor that includes a small transformer. However, the smallest commercially feasible transformer is a unit rated around 1 VA which has about 1 W of no-load loss. Load loss is negligible with such a low loading factor – but most such power supply units form the major constituent of the standby consumption in the entire lighting arrangement. September2008 - Vector - Page 29 Advanced control systems that are easy and not too costly to install if the cabling has been prewired correctly during the construction phase of a building, employ one central AC adaptor for all connected units. This technique has the potential to cut the gross standby consumption down to a fraction. Therefore it remains to be considered in each individual case whether the use of high-efficiency magnetic ballasts plus some less sophisticated control technique, such as simply shutting off parts or all of the lamps completely while not needed, could be both the cheaper and the more effective approach. Considerations on magnetic and electronic ballasts The EU classified fluorescent lamp ballasts by the total power intake of the ballast and lamp circuit. The aim was gradually to phase out the less efficient models. The classes and limits for linear Fig. 2: Test samples for the measurements documented in Table 2 and Fig. 3. lamps are displayed in Table 1 (class A1 being reserved for dimmable electronic ballasts). In principle, Table 1 is a correct approach, yet the good idea to fix the entire gross power consumption as a criterion turns out as a disadvantage for magnetic ballasts, since electronic ballasts feed less than the 50 Hz rated power into the lamp. It is argued that on account of the high operating frequency of the electronic ballast, the lamp efficiency is better and therefore the luminous density will be nearly the same, only 4% less. First of all, the criteria neglect these 4%, since the Directive values and classes specify electric power only, not light output. Second, the EU realized later that the price premium for an electronic ballast was high, while converting from a poor to a good type of magnetic ballast proved more cost efficient. A magnetic ballast with the same lamp as an electronic ballast, will be about 4% brighter as will be seen in the next section. The 5 W difference between a class B1 magnetic ballast and a class A3 electronic ballast for a 58 W lamp thereby dwindles away to leave hardly more than 2 W. Three different philosophies can be used for calculating the payback time: l Use the ratings, neglect the true measured values and receive wrong results. l Use the values measured at rated voltage, since the line voltage is as it is, and ignore the fact that magnetic ballasts offer you 4% more light. For practical reasons this approach has some relevance and advantages. l Use the purist scientific approach and compare the data at the respective voltages where the light outputs are equal. The results may differ substantially, but the payback time for a better magnetic ballast against a poor magnetic ballast is always short and that of an electronic ballast is always longer. Therefore, any drive aimed at phasing out classes C and D is not futile. This is clearly not a displacement plan for magnetic ballasts, as is commonly found in practice. How to make magnetic ballasts more efficient than electronic ones Rated power is mostly quoted, but what happens at reduced power, e.g. when a lamp with a magnetic ballast is fed with the power as rated for the operation with an electronic ballast, or even substantially less power? To find out, five different ballasts for a 58 W lamp were tested (see Fig. 2): l An old magnetic ballast of class D according to Table 1. l One new “superslim” magnetic ballast, inevitably falling into class C, since in electrical engineering restrictions of space nearly always come at the price of restricted efficiencies. l One new magnetic ballast efficiency class B2. l One new magnetic ballast efficiency class B1. l One mint condition electronic ballast rated efficiency class A3. The same lamp was used for each of these five ballasts. Active and reactive energy consumption of the complete system was measured as was the active power consumption (a loss) of the ballast, and of course the light output of the lamp. All of the results are listed in Table 2. The graphic presentation thereof September 2008 - Vector - Page 30 (Fig. 3) provides easier interpretation. Unfortunately, on account of the high output frequency at the terminals of the electronic ballast, it was not possible to measure its output power. This is not a tragedy, though, since the most important data, system input power and light output, could be measured. The following conclusions on the electronic ballast can be drawn: l The electronic ballast under test fully compensates for a varying supply voltage within the tested range. Neither the system input power nor the light output (lumens) varies with input voltage. This is usually seen as an advantage, and one commonly expected from electronic ballasts. A deliberate variation of power input and thereby of light output with an electronic ballast via the feeding voltage is therefore not feasible. l The energy efficiency comparison turns out best for the electronic ballast at 230 V, but at 200 V the A3 electronic one is only about the same as the class B1 and even the class B2 magnetic ballasts, and at 190 V the electronic one performs poorer! The implication is that at a supply voltage of 190 V, the B1 and even the B2 magnetic ballast should be classified as A3, since the efficiency of the A3 model has not altered, while those of both the B1 and the B2 models have exceeded it! l It is confirmed that the light output with an electronic ballast is about 4% less than that of an efficient magnetic ballast at the same rated value of input voltage (not necessarily rated input power, see next bullet point). l The rated lamp power is not always reached precisely at rated voltage. Other than the old ballast, the later magnetic ballast models of all classes reach their rated power only considerably above the rated system voltage. At 230 V the electric lamp input power still falls considerably below the 58 W rating. l Still, this does not yet mean that the electric values are now totally comparable to those of an electronic ballast! With classes C, B2 and B1, the light output is around 5000 lm, while the electronic ballast tested here provided only 4720 lm. l The improved magnetic ballast models under test only feed about 53,5 W into the lamp instead of the rated 58 W, and yet the lamp shines 4% brighter than with the electronic ballast! Hence, for reasons of objectivity, in order not to compare apples with pears, the light output of the electronic ballasts at 230 V Fig. 3: Comparison of different ballasts, including an incandescent lamp. Magnetic ballast Class D Magnetic ballast Class C Magnetic ballast Class B2 Magnetic ballast Class B1 Electronic ballast Class A3 Reduction in ballast losses 65,9 % 70,2 % 70,0.% 69,5 % 0% Reduction in lamp power 31,2 % 38,3 % 37,0 % 38,3 % 0% Reduction in lumens output 27,1 % 36,5 % 35,1 % 36,2 % 0% Overall efficiency gained 18,6 % 15,2 % 12,2 % 10,6 % 0% Table 3: Energy savings (and lumen losses) as result of reduced operating voltage (190 V). should rather be compared to those values metered on the improved magnetic models at about 220 V actual voltage. l At this point of operation the actual lamp inputs were only around 50 W – matching the rating given for an electronic ballast. This makes the deviation in lamp ratings for operation with magnetic versus electronic ballast operation appear equivalent, and raises doubts about the improvement of efficiency at high frequencies. The limitation to this statement is the lack of measured electric output power at the electronic ballast. However, the system power consumption with electronic A3 and magnetic B1 ballasts at the points of equal light outputs deviated from each other only by 2,5 W, interpolating between the two measured points at 220 V (4662 lm) and 230 V (4952 lm) to the 4720 lm the lamp achieved with an electronic ballast. l By switching from a poor class C magnetic ballast to a class B1 model the efficiency at rated lamp power is improved by 10% from 70,3 lm/W to 77,4 lm/W, since the share of ballast losses in the total input power drops from 22,9% to 15,0%. The price premium for the more efficient magnetic ballast therefore pays off in nearly all applications, short payback periods guaranteed. l Contrary to this, the persistent use of very old poor efficiency ballasts, especially if still designed for 220 V line voltage rating, leads to a significant lamp overload with highly over-proportional increase of losses and reduced lamp life but only little increase of light output. l By reducing the operating voltage from 230 V to 190 V, the efficiency of a lamp with a class C ballast is improved from 73,0 lm/W to 84,1 lm/W which is more than 15%. When a class B1 ballast is used, the light efficiency rises from 80,6 lm/W to 89,1 lm/W (by about 10,6%). The reduction of the feeding voltage also pays off, especially in cases where poor magnetic ballasts are not replaced with better ones. However, this shall not be an excuse for further operation of old magnetic ballasts any longer. Even with high-efficiency magnetic ballasts the fairly simple and usually rather inexpensive voltage reduction technique provides pretty short payback periods. The upgrade from anything to a B1 ballast really is the best option, and some greater or smaller voltage reduction may come on top of it as a bonus. For a concise insight into the economic potentials, a review of all the saving September 2008 - Vector - Page 32 attained is listed in Table 3. Reducing the voltage from 230 V to 190 V (by 17,4%) enabled these savings. It must be borne in mind, though, that at 230 V and with a class B1 magnetic ballast the lamp already supplied 4,7% more light than was the case with the electronic ballast (at any voltage between 190 V and 230 V). Therefore the true light loss is not 36,2% but only 31,5%. Therefore, South African energy conservation programmes should rather adapt the latest EU Directive on this issue which simply reads: “This Directive aims at reducing energy consumption …… by moving gradually from the less efficient ballasts, and to the more efficient ballasts which may also offer extensive energy saving function.” The practical aspect of how to harvest these energy savings by controlling the voltage of the lighting circuit is well established. Various solid-state voltage controllers exist, of which certain versions will regulate the output voltage regardless of the input voltage variation. Further sophistication (and savings) is possible by means of controlling the level of electrically generated light in a building as a function of the availability of natural light. Another opportunity of the voltage reduction technique is to regulate the voltage gradually back up again from, say, 190 V to 230 V as lamps lose luminous output due to ageing and hence keep the level of lighting constant. Conclusion A change from incandescent lamps to fluorescent lamps will already raises the efficacy from 10 lm/W to 80 lm/W, as can be seen in Fig. 3. Fluorescent lamps are a very efficient light source under all circumstances, whichever way they are operated. It is also necessary carefully to evaluate the cost of ownership of fluorescent lamps equipped with electronic ballasts in terms of expected higher failure rates and that lamp life could be another source of concern. In other words, it does not make sense to replace losses (energy) with losses (financial). Care must also be taken in the costly retrofitting of current lighting installations by means of replacing magnetic ballasts with electronic ballasts. This paper has shown that the reduction of the supply voltage to existing lighting circuits equipped with magnetic ballasts by means of the installation of a single solid-state voltage controller could yield even more savings, a shorter payback period and a lower cost of ownership scenario. Contact Dr. Johan Rens, North-West University, Potchefstroom, Tel 018 299-1978, [email protected] D