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45 Chapter 10 â Operations and Maintenance Considerations Current Guide The current AASHTO guide 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 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, light loss factor (LLF) is determined in several different ways. Assuming that LLF = Lamp Lumen Depreciation (LLD) x Luminaire Dirt Depreciation (LDD) x Luminaire Ambient Temperature Factor (LATF), 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 when the LED is considered 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 32 demonstrates some of the factors when considering LLD. The LED source has a rated life of about 60,000 hours 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 lumen depreciation has reached 70%. The driver within the fixture will likely fail before this point, probably 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/replaced until the LED has reached the end of 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 true end of life is used and 217,000 hours is expected, that amounts to close to 50 years of operation. Because it is unlikely that structural components and gasketing for any luminaire would last that long, however, it is generally accepted practice to assume a service life for an LED luminaire (e.g., 20 to 25 years) and determine the LLD based on the product used and the results of the LM-80 testing. LLF for LEDs are specific to each individual luminaire. The lumen depreciation can vary greatly between different models and manufacturers and longevity due to fixture design and thermal management.
46 Figure 22. TM-21 Worksheet Typically, an enclosed and gasketed roadway luminaire would have an LDD of 0.9 for a clean environment (less than 150 Âµg/mÂ³ airborne particulate matter). This assumes a cleaning every 8-10 years. An LLD of 0.9 is commonly used unless the environment is less than not 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 night time ambient temperature under 25 degrees C could be greater than 1, and, for warmer climates with an average night time temperature over 25 degrees C, the factor could be much less. Typically, these factors range from 1.04 to 0.96. This factor is climate and product specific and should be obtained from the manufacturer of the proposed luminaire. Asset Management Asset management features often included as part of an adaptive lighting system allow tracking and mapping of outages and/or other diagnostics. 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, day burners, and provide analysis (such as hours of usage) that may be specifically relevant to design, operations, and maintenance.
47 Mapping allows for visual management of operational performance of each luminaire on an individualâs computer monitor (Figure 33). The luminaire status is typically color coded for easy identification of system outages. Dynamic map interfaces can also provide zooming, panning, etc. 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. Figure 23. Map Example 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 34). Trimming of the on and off offsets for dawn and dusk can be provided to reduce power consumption.
48 Figure 24. Energy Usage Example 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 of the devices for about4,300 hours of use per year. Some systems are available for accurate measurement of power consumption for unmetered roadway lights. If accepted by power utilities as an accurate means to measure power consumption, owners will be billed for power used, taking 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 accuracy of the street light meter (defined by utility commission), who owns the meter, audit process, who maintains the data, and questions related to how data is presented and used for billing (i.e. in aggregate or by individual fixtures?). Use of roadway lighting metering as part of a system will need to be discussed and agreed upon by the local power utility. A typical metering system usually requires recalibration. By using upgradeable firmware, however, the system can be recalibrated over its lifetime. Even if not acceptable to the local utility, smart metering can be used for usage comparisons to utility flat rate billing and to track power costs. Comparing Lighting System Costs Costs can be broken down into capital, operating, and life cycle costs. Capital cost (also known as construction cost) varies widely for each area depending on the state of the economy and material used. Because labor and material costs 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.
49 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 calculating power cost, confirm the method of payment used by the local electrical utility. Some utilities establish a monthly flat rate for various luminaire wattages. Others use a set kilowatt- hour (kW h) rate for streetlighting. If a kWh rate is defined as the method of calculating power costs by the utility, calculate the actual kilowatts consumed by using data obtained from the ballast supplierâs web site. The actual costs per fixture may be calculated using the following formula: kW x R = per hour cost where R is the cost per kilowatt hour (kW h) charged by the utility and kW is the kilowatt rating of the fixture. Example â 0.2 kW (typical 150-watt luminaire) x $0.06* = $0.12 per hour). *Consult utility for actual cost of power. To confirm the yearly cost, assume the luminaire will be operating for 430 hours per year and multiply by the hourly costs. 4300 hours is based on the luminaire operating slightly less than 12 hours per day, 365 days a year. This may vary depending on the local utility tariff. Preventive maintenance activities, which for SSL could include driver replacement, can be budgeted. Generally, mean time between failure data will show and 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 of SSL because relamping is not performed, and frequency and cost would be based on the luminaire dirt depreciation assumptions used. Life Cycle Cost Comparison Life cycle costs are mainly used by designers to evaluate and compare various lighting system such as conventional and high-mast lighting. Often a lighting system may have a less expensive capital cost, but when life cycle costs are considered, a lighting system with a higher capital cost may result in significant cost savings over the life of the system. Life cycle costing will include the capital cost, as defined above, as well as 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 using life cycle costs to compare lighting systems, current operating costs (defined at the time of 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 35 and Figure 36. In the case shown, the davit lighting ($951,420.00) would have a higher estimated life cycle cost than the high-mast lighting ($824,120.00). Note this example is not an endorsement of high-mast over davit-style
50 lighting. It is provided to give a general example of the considerations which need to be taken into account when undertaking a life cycle cost analysis. In the case of this example, inflation has not been factored into the totals. Costs and information noted above should not be used in life cycle analysis, as they will vary depending on costs for the given area. Figure 35. Example Life Cycle Cost Calculation, High-mast Lighting, TAC
51 Figure 36. Example Life Cycle Cost Calculation, Davit Style Lighting, TAC
52 ASSESSING AND EVALUATING BENEFITS OF LIGHTING CONVERSION Roadway lighting operations consume a significant portion of system-wide electricity. Reducing the amount of energy consumed by roadway lighting can offer significant savings to owners and reduce the burden on taxpayers/utility ratepayers. To reduce power, improve overall efficiency, and reduce environmental impacts, consider new lighting and controls technologies. Capital cost, return on investment, and environmental benefits are factors to consider when 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 cost-benefit analysis tool designed to help cities, utilities, and other organizations estimate the cost 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: www.ssl.energy.gov/financial-tool.html. Using the 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 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. Power costs can be determined by obtaining the 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 37 shows how to calculate annual energy costs.
53 Figure 37. Energy Usage Calculation Once existing costs are calculated, compare them to costs for the proposed system. Maintenance costs, which can be obtained from operations staff, mainly include re-lamping costs (spot and group re-lamping). However, these costs should also include luminaire repair and replacement costs. Costs for damage repairs from pole knock-downs or 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 re-lamping cycle, which can be 3 to 5 years. Define costs on an annual basis. Addition of power and maintenance costs on an annual basis is required to define overall operational costs. Return on investment (ROI). The profit generated by the money an owner puts into an 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 the cityâs ROI when investing in more energy efficient lighting and controls. Simple ROI = Gain from investment - cost of investment/cost of investment x 100 For example, in an LED retrofit of 1,000 street lights, use the following assumptions to define the ROI. Gain from Investment Calculation - Define Luminaire Life - For LEDs, this is based on the usable life that is tied into lamp lumen depreciation. For the example, 15 years is used, however, it is possible to review shorter and longer periods to define the optimal ROI. Define Annual Energy Savings - This is the difference in power usage for the existing lighting system minus estimated power usage of the new lighting system. For the example, $55K annual savings is used. It is based on:
54 Existing Lighting - 4400 hours luminaire operation per year x $0.10 per kw/h (utility rate) x 0.2 kW (200W /1000) luminaire consumption x 1000 luminaires = $88,000. Proposed Lighting - 4400 hours luminaire operation per year x $0.10 per kw/h (utility rate) x 0.075 kW (75W /1000) luminaire consumption x 1000 luminaires = $33,000. Power Savings Example = $88,000.00 (existing) - $33,000.00 (proposed) = $55,000.00 x 15 years = $825,000.00 savings. Define Maintenance Cost Savings - This is the difference in the cost of the maintenance of the existing lighting system minus the estimated maintenance cost of the new lighting system. For the example, $190,725 15 a year in savings is used. It is based on: Existing lighting: Group Re-Lamping - Two (2) re-lamps (at year 5 and year 10) at $95.00 each =$190.00 x 1000 luminaires = $190,000.00. Product Failures - Ten (10) % product failures: 1000 luminaire x 10% failure rate = 100 luminaires x $300.00 replacement/repair costs = $30,000.00. Total - $30,000.00 (repair or replace) + $190,000.00 (re-lamping) = $220,000.00 Proposed Lighting: Cleaning - Ten (10) year cleaning by power wash: $20.00 per luminaire x 1000 luminaires = $20,000.00. Under Warranty Period - Five (5) % product failures: Assume only labor in first 10 years (10 year warranty) so labor only: 0.05 (5%) x1000 luminaire x $75.00 each (labor) x 0.66 (10 of 15 years) = $2475.00. Non-Warranty Period - Five (5) % product failures (refer to product failure prediction in 18.104.22.168 Reliability): Assume only labor and product for 5 years: 0.05 (5%) x 1000 luminaire x $400.00* each (labor and materials) x 0.33 (5 of 15 years) = $6600.00. Assumes cost of LED will be reduced over time. Total - $20,000.00 (cleaning) + $2475.00 (labor and repairs during warranty period) + $6600.00 (labor, repairs and replacements outside of warranty period) = $29,275.00. Maintenance Savings Example - $220,000.00 (existing) - $29,275.00 (proposed) = $190,725.00 savings. Calculation Example for 15 years - $825,000 power and $190,725.00 maintenance = $1,015,725.00 savings. Cost of Investment Calculation â¢ Luminaire supply cost - Obtain cost and include taxes, and mark-ups. â¢ Estimated installation cost - Obtain install costs, taxes, and mark-ups. â¢ Calculation Example - $560.00 (supply and install) x 1000 luminaires = $560,000.00 ROI Calculation - Simple ROI = $1,016,715 - $560,000 / $560,000 x 100 = 81.38% The simple ROI for the example LED retrofit would be approximately 81%. This is an example and results will thus vary, necessitating a separate calculation for each application. The simple payback period refers to the period of time to pay for the sum of the original investment. For example, a $100,000 investment which returned $10,000 per year would have a ten 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
55 take product life cycle into account. For example, if a product has 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 calculation for LED lighting is: Cost of investments (supply and install) / Gain from Investment (yearly power and maintenance costs) Using the ROI costs listed above the payback example would be as follows: $560,000 (supply and install) / $67,781K (annual power and maintenance savings) = 8.3 years Key Issues â¢ Calculate light loss factors on a luminaireâs expected service life determined by the DOT or agency installing the lighting system. â¢ Consider an adaptive lighting system as part of an overall control and operation and maintenance cost reduction tool as well as an asset management tool. â¢ Use benefit/cost analysis to help determine the best design approach for a proposed lighting system.