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42 Current Guide The current AASHTO Roadway Lighting Design Guide (AASHTO 2018) includes a discussion about luminaire maintenance factors, support structure maintenance, and electrical systems. Additional Considerations for LED Sources Several maintenance considerations are different for LED lighting systems, many of which are part of the planning and design phases of the project and others that occur during the maintenance period. Also, all aspects of installation and operations and maintenance must be considered during planning. Determination of Light Loss Factor Because an LED luminaire degrades differently than an HID luminaire and the LED will likely continue operating but at a steadily decreasing lumen output, the light loss factor (LLF) is determined in several different ways. Assuming that LLF = LLD Ã LDD Ã LATF where LLD = lamp lumen depreciation, LDD = luminaire dirt depreciation, and LATF = luminaire ambient temperature factor. consider the following items. For use until rated end of life, the lumen output of an LED fixture has an LLD of 0.7 (70% of rated output). This is the point at which the LED is considered to be at its end of life. Other components within the fixture may fail before the LED module reaches this point, but these elements are not considered in the L70 rated life value. The TM-21 worksheet in Figure 31 demonstrates some of the factors to be considered in LLD. The LED source has a rated life of about 60,000 hours, as based on the allowable reporting of the LM-80 testing of no more than 6 times the test duration. The projected life for the LED source, however, is 217,000 hours before the LLD has reached 70%. The driver within the fixture will likely fail before this point, probably C H A P T E R 1 0 Operations and Maintenance Considerations Light loss factors for LEDs are specific to each individual luminaire. Lumen depreciation and rated life can vary greatly between different models and manufacturers due to fixture design and thermal management.
Figure 31. TM-21 worksheet.
44 Solid-State Roadway Lighting Design at about 100,000 to 120,000 hours. If 100,000 hours is assumed, the LLD of the LED at that point is 83%. If, during the design, it is assumed that the expected life of the luminaire is until some component failure renders it inoperable, then for this LED, the LLD would be 0.83. If internal components of the luminaire were expected to be repaired or replaced until the LED had reached the end of its rated life, then the LLD would be 0.7. Generally, 100,000 hours of operation for a typical roadway lighting fixture is about 23 years. If the true end of life is used, and a life of 217,000 hours is expected, then the expected period of operation is close to 50 years. However, because it is unlikely that the structural components and gasketing of any luminaire would last that long, it is generally accepted practice to assume a service life for an LED luminaire (e.g., 20 to 25 years) and determine the LLD on the basis of the product used and the results of the LM-80 testing. Typically, an enclosed and gasketed roadway luminaire would have an LDD of 0.9 for a clean environment (less than 150 mg/m3 airborne particulate matter). This assumes cleaning every 8 to 10 years. An LLD of 0.9 is commonly used unless the environment is highly polluted (high amount of particulates in the atmosphere). The luminaire ambient temperature factor is based on the temperature testing of the luminaire and how that effects luminaire output. For a cold environment, LATF factors with an average nighttime ambient temperature below 25Â°C could be greater than 1, and for warmer climates with an average nighttime temperature above 25Â°C, the factor could be much less. Typically, these factors range from 0.96 to 1.04. This factor is climate and product specific and should be obtained from the manufacturer of the proposed luminaire. Asset Management Adaptive lighting systems often contain asset management features that allow tracking and mapping of outages and may include other diagnostics as well. The systems are generally capable of generating reports for asset management. Asset management allows for detailed records of outages, and repairs of individual roadway lights can be kept for an accurate picture of the performance of luminaires, lamps, and other components. This information was not previously available and will allow a jurisdiction to objectively compare the performance of products; manage warranties; track knockdowns, outages, and day burners; and provide analysis (such as hours of usage) that may be specifically relevant to design, operations, and maintenance. Mapping allows for visual management of the operational performance of each luminaire on an individualâs computer monitor (Figure 32). The luminaire status is typically color coded for easy identification of system outages. Dynamic map interfaces can also provide zooming and panning. Some mapping systems even define maintenance routes to reduce fuel consumption and improve efficiency. Mapping services can be provided and updated by the supplier or can be set up and operated by the jurisdiction operating the street lights. Mapping systems offer improved maintenance efficiency through a systemwide inventory that provides accurate locations for outages. This system can eliminate night patrols and reliance on the public reporting of outages. Systems manage energy by defining schedules for individual, group, or total system control. Energy usage can also be monitored and tracked by day, month, and year (Figure 33). Trimming of the on and off offsets for dawn and dusk can be provided to reduce power consumption. Most municipally owned roadway lights in North America are supplied power on an unmetered (flat rate) basis, with power charges based on the hourly energy consumption
Operations and Maintenance Considerations 45 Figure 33. Example of energy usage. Figure 32. Map example.
46 Solid-State Roadway Lighting Design of the devices for about 4,300 hours of use per year. Some systems are available for accurate measurement of power consumption for unmetered roadway lights. If smart metering systems are accepted by power utilities as an accurate means of measuring the power consumption of roadway lights, the owners will be billed for the power used and will be able to take full advantage of the energy saved. Use of this technology will put an end to the shortcomings and abuses of the flat rate system and make the full financial benefits of dimming available to owners. Issues will include the accuracy of the street light meter (as defined by utility commission), who owns the meter, the audit process, who maintains the data, and questions related to how the data are presented and used for billing (i.e., in the aggregate or by individual fixtures?). A typical metering system usually requires recalibration. By using upgradeable firmware, however, the system can be recalibrated over its lifetime. The use of metering as part of a roadway lighting system will need to be discussed and agreed upon by the local power utility. Even if not acceptable to the local utility, smart metering can be used for usage comparisons with flat rate utility billing and to track power costs. Comparing Lighting System Costs Costs can be broken down into capital, operating, and life-cycle costs. Capital costs (also known as construction costs) varies widely for each area, depending on the state of the economy and the material used. Because costs for labor and material typically vary across the country, it is difficult to establish a standard cost for a lighting installation. For budgeting purposes, however, it is appropriate to establish a per-mile cost or a unit pole cost, including wiring, boxes, and conduit between each set of typical poles. Operating costs should include power and preventative maintenance costs and are typically calculated annually. These costs are used by a jurisdiction to establish operating budgets. An owner may wish to establish a per luminaire cost for power and maintenance and update this regularly to reflect current labor and material costs as well as power costs. When power cost is being calculated, the method of payment used by the local electrical utility should be confirmed. Some utilities establish a monthly flat rate for various luminaire wattages. Others use a set kilowatt-hour (kW-h) rate for street lighting. If the utility defines a kilowatt-hour rate as the method of calculating power, the actual kilowatts consumed can be calculated by using data obtained from the ballast supplierâs web site. The actual costs per fixture may be calculated with the following formula: kW Ã R = cost per hour where kW is the kilowatt rating of the fixture and R is the cost per kilowatt-hour charged by the utility and. For example, 0.2 kW (typical 150-W luminaire) Ã $0.6 = $0.12 per hour Note: Consult the utility for the actual cost of power. To confirm the yearly cost, assume the luminaire will be operating for 4,300 hours per year and multiply by the hourly costs. The total of 4,300 hours is based on the luminaire operating slightly less than 12 hours per day, 365 days a year. The yearly cost may vary, depending on the local utility tariff.
Operations and Maintenance Considerations 47 Preventive maintenance activities, which for SSL could include driver replacement, can be budgeted. Generally, the mean time between failure data will show an expected failure rate (e.g., 1% per year), and this cost can be included as one of the operating costs. Cleaning is also a consideration for SSL because relamping is not performed; the frequency and cost would be based on the assumptions made for luminaire dirt depreciation. Life-Cycle Cost Comparison Life-cycle costs are mainly used by designers to evaluate and compare various lighting systems, such as conventional and high-mast lighting. When life-cycle costs are taken into account, a lighting system with a lower capital cost may ultimately cost more than one with a higher capital cost; that is, the lighting system that initially costs more may yield significant cost savings over the life of the system. Life-cycle costing includes the capital cost, as defined above, as well as the operating costs over the estimated life of the system. Operating costs should include power and preventative maintenance costs, which are also calculated over the life of the system (typically 30 years, although this will vary depending on the grade of the equipment used). It is doubtful that, after 30 years of operation, existing equipment would be reused; therefore, no residual value should be considered. When life-cycle costs are used to compare lighting systems, current operating costs (defined at the time of the estimate) can be used as the basis over the operating period. As costs are most likely to increase over time, inflation may be factored in to provide a more accurate estimate of the total costs. To calculate the life-cycle cost, determine the capital cost of each lighting system combined with the operating cost over a 30-year period. Life-Cycle Cost Calculation Example Examples of life-cycle cost calculations for the comparison of high-mast and conventional davit lighting at a typical interchange are shown in Figure 34 and Figure 35. In the case shown, the davit lighting ($891,420.00) would have a higher estimated life-cycle cost than the high-mast lighting ($798,200.00). Note: This example is not an endorsement of high-mast over davit lighting. It is provided to give a general example of the considerations that need to be taken into account in the undertaking of a life-cycle cost analysis. In the case of this example, inflation has not been factored into the totals. The costs and information noted above should not be used in life-cycle analysis, as they will vary according to the costs for the given area. Assessing and Evaluating the Benefits of Lighting Conversion Roadway lighting operations consume a significant portion of systemwide electricity. Reducing the amount of energy consumed by roadway lighting can offer significant savings to owners and reduce the burden on taxpayers and utility ratepayers. To reduce power, improve overall efficiency, and reduce environmental impacts, consider- ation of new lighting and controls technologies is advised. Capital costs, return on investment, and environmental benefits are factors to consider in the process of designing for these new technologies. The following section includes methods and examples of how to assess and evaluate the economic and environmental benefits of LED conversion. Capital Costs. Application of energy-efficient lighting technologies has a capital cost that, over time, may be recouped in energy and maintenance savings. The level of detail required to evaluate the costs and savings can vary and depends on the level of certainty required. DOEâs Municipal Solid-State Street Lighting Consortium has released an economic costâ benefit analysis tool designed to help cities, utilities, and other organizations estimate the cost
48 Solid-State Roadway Lighting Design and impact of switching to LED-based street lighting. The Retrofit Financial Analysis Tool, which is an Excel-based tool developed in collaboration with the Clinton Climate Initiative, is available for download at https://www.energy.gov/eere/ssl/retrofit-financial-analysis-tool. With this DOE spreadsheet, users can input data for their particular applicationâsuch as the incumbent technology, quantities, phase-in period, prevailing electricity and labor rates, sales tax, installation cost, loan interest rate, and rebatesâand receive a detailed analysis that includes annualized energy cost savings, maintenance savings, greenhouse gas reductions, and a simple payback period. This information is useful for planning, budgeting, and applying for financing. However, because the DOE spreadsheet is very complex and detailed, it is best suited Source: Adapted from TAC (2006). Figure 34. Example of calculation of life-cycle costs for high-mast lighting.
Operations and Maintenance Considerations 49 Source: Adapted from TAC (2006). Figure 35. Example of calculation of life-cycle costs for davit lighting.
50 Solid-State Roadway Lighting Design for very knowledgeable users. More simplified financial assessment methods, such as payback and return on investment, are described in the following section. Operational Costs. For the retrofit of existing roadway lighting systems and new lighting systems, operational costs include power and maintenance costs. â¢ Power costs can be determined by obtaining roadway lighting power bills from the utility(s) and defining overall power costs on an annual basis. If that information is not available or must be verified, Figure 36 shows how to calculate annual energy costs. Once existing costs are calculated, compare them with the costs for the proposed system. â¢ Maintenance costs, which can be obtained from operations staff, are primarily for spot and group relamping; however, maintenance costs should also include the cost of luminaire repair and replacement. Costs for damage repairs from pole knockdowns, lightning, or damage to wiring by rodents should not be included, because they are required regardless of the lighting technology used. The lamp replacement costs may have to be calculated over a relamping cycle, which can be 3 to 5 years. Costs should be defined on an annual basis. The calculation of total power and maintenance costs on an annual basis is required to define overall operational costs. Return on Investment. The profit generated by the money an owner puts into an investment, or the return on investment (ROI), is typically expressed as a percentage of return. The benefits of using more energy-efficient lighting, such as LEDs and adaptive lighting, can be assessed through an ROI analysis. Although the costs and assumptions are very basic, this analysis gives an overview of a cityâs ROI when it invests in more energy-efficient lighting and controls: simple ROI = (gain from investment â cost of investment)/(cost of investment Ã 100) For example, in an LED retrofit of 1,000 street lights, use the assumptions in the text box âExample of Calculation of Gain from Investmentâ to define the ROI. The simple ROI for the example LED retrofit would be approximately 81%. Note that this is an example, and results will thus vary. A separate calculation is necessary for each application. Figure 36. Calculation of energy usage.
Operations and Maintenance Considerations 51 ExamplE of CalCulation of Gain from invEstmEnt Define Luminaire Life The life of LED luminaires is based on the usable life that is tied into lamp lumen depreciation. For this example, 15 years is used; however, it is possible to review shorter and longer periods to define the optimal ROI. Define Annual Energy Savings The annual energy savings are the difference in power usage for the existing lighting system minus the estimated power usage of the new lighting system. This example uses an annual savings of $55,000. This amount is based on the following calculations: existing lighting = 4,400 hours luminaire operation per year Ã $0.10 per kW-h utility rate Ã 0.2 kW luminaire consumption Ã 1,000 luminaires = $88,000 where luminaire consumption = 200W/1,000. proposed lighting = 4,400 hours luminaire operation per year Ã $0.10 per kW-h utility rate Ã 0.075 kW luminaire consumption Ã 1,000 luminaires = $33,000 where luminaire consumption = 75W/1,000. Power savings power savings over 15 years = $88,000 existing lighting costs â $33,000 proposed lighting costs = $55,000 Ã 15 years = $825,000 (continued on next page)
52 Solid-State Roadway Lighting Design ExamplE of CalCulation of Gain from invEstmEnt (continued) Define Maintenance Cost Savings The maintenance cost savings are the cost of the maintenance of the existing lighting system minus the estimated maintenance cost of the new lighting system. This example defines a 15-year savings of $190,525. This amount is based on the following considerations: Existing Lighting group relamping = 2 relamps [at Year 5 and Year 10] at $95.00 each = $190 Ã 1,000 luminaires = $190,000 10% product failures = 1,000 luminaires Ã 10% failure rate = 100 luminaires Ã $300 repair/replacement costs = $30,000 total costs for existing lighting = $190,000 relamping + $30,000 repair/replacement = $220,000 Proposed Lighting 10-year cleaning by power wash = $20 per luminaire Ã 1,000 luminaires = $20,000 Under Warranty Period. Assume 5% product failures and labor only during the first 10 years (10-year warranty). cost under warranty period = 0.05 Ã 1,000 luminaires Ã $75 each labor Ã 0.66 (10 of 15 years) = $2,475 Non-Warranty Period. Assume 5% product failures, labor and materials for 5 years, and that the cost of LEDs will decrease over time. cost under non-warranty period = 0.05 Ã 1,000 luminaires Ã $400.00 each labor and materials Ã 0.33 (5 of 15 years) = $6,600.
Operations and Maintenance Considerations 53 ExamplE of CalCulation of Gain from invEstmEnt (continued) total costs for proposed lighting = $20,000 cleaning + $2,475 labor and repairs under warranty period + $6,600 labor, repairs, and replacements outside of warranty period = $29,075 Maintenance Savings maintenance savings = $220,000 existing lighting â $29,075.00 proposed lighting = $190,925 Calculate Total Savings total savings over 15-year period = $825,000 power savings + $190,925 maintenance savings = $1,015,925 Cost of Investment Calculation â¢ Luminaire supply cost: Obtain cost and include taxes and mark-ups. â¢ Estimated installation cost: Obtain installation costs, taxes, and mark-ups. â¢ Investment calculation: $560 supply and installation Ã 1,000 luminaires = $560,000. ROI Calculation simple ROI = ($1,015,925 â $560,000)/($560,000 Ã 100) = 81.42% The simple payback period refers to the period of time to pay for the sum of the original invest- ment. For example, a $100,000 investment that returned $10,000 per year would have a 10-year payback period. The time value of money is not taken into account. Therefore, a shorter payback period is preferable to a longer payback period. The payback period is widely used to assess the viability of an opportunity because of its ease of application. However, it is lacking as a method of evaluation because it does not take product life cycle into account. For example, if a product has a 2-year payback and has a life cycle of 5 years, it would be less effective than a product with a 5-year payback and 20-year life cycle. Simple payback for LED lighting is calculated as follows: simple payback = cost of investment (supply and installation)/gain from investment (annual power and maintenance costs)
54 Solid-State Roadway Lighting Design For the ROI calculated in the text box, the simple payback period would be as follows: simple payback period = $560,000 supply and install/$69,666.67 (annual power and maintenance savings) = approximately 8 years Key Issues for Operations and Maintenance â¢ Calculate light loss factors on a luminaireâs expected service life as determined by the DOT or agency installing the lighting system. â¢ Consider an adaptive lighting system as a means of reducing costs for overall control and for operation and maintenance as well as an asset management tool. â¢ Use benefitâcost analysis to help determine the best design approach for a proposed lighting system.