Comparison of two different ballasts from energy saving viewpoint has a basic importance. The introduction of Energy Saving Factor and a formula for Compensation Time make the numerical calculations and financial predictions easy. If you do not have time for equations and diagrams, please go to Conclusion   A. Average Yearly Energy Consumption 1. Definitions and Notations PLN Nominal lamp power tl Average lamp life time( appr. 5 yrs) td Average daily operation time(10 - 24hrs) ty Average operation time for a year b Power control coefficient (see Fig.1/A, [1], and [2]) a Dimming coefficient (see Fig.1/B) D Dimming duty cycle (see Fig.1/B) h Efficiency of ballast(Pout/Pin) 2. Formula The energy consumption for a year can be calculated as follows: where Wy is energy consumed by the lighting unit (ballast + lamp) during a year. The quantity (PLNty) can be interpreted as the ideal energy consumption for a year and it is shown in Fig. 2 as the function of daily lighting time, parameterized by nominal lamp powers (100W, 250W and 400W).     B. Energy Saving Factor 1. Definition Let consider two different ballasts B1 and B2. Therefore where Wi is the yearly energy consumption for ballast Bi (from now "y" subscript will be omitted) Assuming W1 > W2 the difference gives the yearly saved energy if ballast B1 is substituted with ballast B2. The energy saving factor can be defined as follows Therefore the energy saving factor gives the yearly saved energy as the percentage of the yearly ideal energy consumption if the ballast B1 is substituted with ballast B2 where W1 > W2. 2. D1 = D2 = 1 If no dimming applied the expression for the energy saving factor simplified to Fig, 3 shows a diagram for the energy saving factor, parameterized by b1, if none of the ballasts B1 and B2 are dimmed and h2=0.95. 3. D1 = 1 and 0 < D2 < 1 In this case no dimming applied for ballast B1, therefore Fig. 4 shows a diagram for the energy saving factor, parameterized by the efficiency of ballast B1, where a2=0.5 and h2=0.95.   C. Compensation Time The price of a high efficient electronic ballast can be essentially higher than a conventional core & coil one. Therefore it is important to know in advance the price compensation time provided by the energy saving of the more expensive electronic ballast. 1. Notations C1 Price of the ballast B1(conventional core & coil) C2 Price of the ballast B2(electronic) q Cost of energy[$/kWh] PLN Nominal lamp power Fe Energy saving factor W12 Average yearly saved energy   2. Formula The formula for compensation time can be written as where C21=C2 - C1 and Ny is the compensation time in number of years requiered for the compensation of price difference. For more accurate result the interest rate and other economical factors should be taken into consideration. As an example, a diagram for 100W ballasts is shown in Fig. 5 where q=0.07[$/kWh] was taken for calculation.   . PLN[W] td[hrs] PLNty [kWh] h b Fe(D1=1,a2=0.5) D2=1 D2=0.75 D2=0.5 B1 100 12 440 0.82 1.05 0.23 0.38 0.5 B2 100 12 0.95 1.0     D. Conclusion Energy and cost savings are summarized in the following table if the conventional core & coil ballasts (CWA, efficiency: 80%(100W), 83%(250W) and 87%(400W) are substituted with high efficient, for instance Ballastronic's (95%) electronic ballasts. Compensation time can be expected from one to two years. This time can be essentially less if dimming is applied.   Lamp power [W] Yearly energy consumption Yearly saved energy [kWh] Yearly saved energy cost (0.1$/kWh) Core & Coil [kWh] Electronic [kWh] 100 575 460 115 $11.5 250 1385 1152 233 $23.3 400 2115 1843 272 $27.2   A high efficient electronic ballast for HID lamps can provide significant energy saving versus conventional HID ballasts (CWA, reactor, etc.) affecting the customer's energy cost and the planned utilization of power resources considerably.   References [1] Unglert,M.C., The need for high-pressure sodium ballast classification, Lighting Design and Application, March 1982. [2] Melis,J., Ballast Curves for HPS Lamps Operating on High Frequency, IAS 1992 Technical Conference, Houston, Texas. Home | Ballast Overview | Design Considerations | Energy Saving Factor | Design Aid | About | Contact
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