by N Benton · 2014 · Cited by 4 — 1.eere.energy/manufacturing/tech_assistance/pdfs/motor_tip_sheet11.pdf. Marshall, R. (2013). “Finding and Fixing Leaks.” Compressed Air Challenge –
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NREL is a national laboratory of the U.S. Department of Energy Office of Energy Efficiency & Renewable Energy Operated by the Alliance for Sustainable Energy, LLC This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications. Contract No. DE -AC36 -08GO28308 Chapter 22: Compressed Air Evaluation Protocol The Uniform Methods Project: Methods for Determining Energy Efficiency Savings for Specific Measures Created as part of subcontract with period of performance September 2011 ΠDecember 2014 Nat hanael Benton Nexant, Inc. San Francisco, California NREL Technical Monitor: Charles Kurnik Subcontract Report NREL/SR -7A40- 63210 November 2014
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NREL is a national laboratory of the U.S. Department of Energy Office of Energy Efficiency & Renewable Energy Operated by the Alliance for Sustainable Energy, LLC This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications. Contract No. DE -AC36 -08GO28308 National Renewable Energy Laboratory 15013 Denver West Parkway Golden, CO 80401 303-275- Chapter 22: Compressed Air Evaluation Protocol The Uniform Methods Project: Methods for Determining Energy Efficiency Savings for Specific Measures Created as part of subcontract with period of performance September 2011 ΠDecember 2014 Nathanael Benton Nexant, Inc. San Francisco, California NREL Technical Monitor: Charles Kurnik Prepared under Subcontract No. LGJ -1- 11965 -01 Subcontract Report NREL/SR -7A40- 63210 November 2014
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NOTICE This report was prepared as an account of work sponsored by an agency of the United States government. Neither the United States government nor any agency thereof, nor any of their employees, makes any warranty, express or implied, or assumes any legal liability or responsibility for the accuracy, completeness, or use fulness of any information, apparatus, product, or process disclosed, or represents that its use would not infringe privately owned rights. Reference herein to any specific commercial product, process, or service by trade name, trademark, manufacturer, or otherwise does not necessarily constitute or imply its endorsement, recommendation, or favoring by the United States government or any agency thereof. The views and opinions of authors expressed herein do not necessarily state or reflect those of the Uni ted States government or any agency thereof. This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications. Available electronically at http://www.osti.gov/ scitech Available for a processing fee to U.S. Department of Energy and its contractors, in paper, from: U.S. Department of Energy Office of Scientific and Technical Information P.O. Box 62 Oak Ridge, TN 37831 -0062 phone: 865.576.8401 fax: 865.576.5728 email: mailto:reports@adonis.osti.gov Available for sale to the public, in paper, from: U.S. Department of Commerce National Technical Information Service 5285 Port Royal Road Springfield, VA 22161 phone: 800. 553.6847 fax: 703.605.6900 email: orders@ntis.fedworld.gov online ordering: http://www.ntis.gov/help/ordermethods.aspx Cover Photos: (left to right ) photo by Pat Corkery, NREL 16416, photo from SunEdison, NREL 17423, photo by Pat Corkery, NREL 16560, photo by Dennis Schroeder, NREL 17613, photo by Dean Armstrong, NREL 17436, photo by Pat Corkery, NREL 17721. NREL prints on paper that contains recycled content .
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iii This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications. Acknowledgments The chapter author wishes to thank and acknowledge Jeff Bartels and Patrick Burns of Nexant for their thoughtful contributions.
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iv This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications. Acronyms ACFM Actual cubic feet per minute CAGI Compressed Air and Gas Institute CFM Cubic feet per minute ECM Electronically commutated motor psi Pounds per square inch psia Pounds per square inch absolute psig Pounds per square inch gauge RMS Root mean square SCFM Standard cubic feet per minute VSD Variable -speed drive
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v This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications. Table of Contents 1 Measure Description .. .. .. . 1 1.1 High -Efficiency/Variable -Speed Drive Compressor Replacing Modulating Compressor .. 1 1.1.1 Inlet Valve Modulation/Inlet Throttling . 1 1.1.2 Load/No -Load (Dual) Control 2 1.1.3 Variable -Displacement Control . 2 1.1.4 Variable -Speed Control .. 2 1.2 Compressed -Air Leak Survey and Repairs .. 2 2 Application Conditions of Protocol .. .. .. . 3 2.1 High -Efficiency/Variable -Speed Drive Compressor Replacement Measures 3 2.2 Compressed -Air Leak Surveys and Repairs 3 3 Savings Calculations .. .. .. 4 3.1 Savings Calculations for Installing a High -Efficiency Air Compressor 4 3.1.1 Compressor Power at Full Load . 4 3.1.2 Compressor Power at Part Load . 5 3.1.3 Addressing Uncertainty .. 8 3.2 Savings Calculations for Compressed -Air Leak Surveys and Repairs .. 9 3.2.1 Quantifying the Compressed -Air Leakage 9 3.2.2 Compressed -Air Leak Survey and Repairs 10 4 Measurement and Verification Plan .. .. .. .. 13 4.1 International Performance Measurement and Verification Protocol Option 13 4.1.1 Option A: Retrofit Isolation (Key Parameter Measurement) ŠPreferred Approach 13 4.1.2 Option B: Retrofit Isolation (All Parameter Measurement) .. 14 4.1.3 Option C: Whole Facility 14 4.1.4 Option D: Calibrated Simulation 14 4.2 Verification Process .. 14 4.3 Data Requirements . 15 5 Data Collection Methods .. .. .. .. 18 5.1 Metering .. 18 5.2 Ultrasonic Leak Detectors for Compressed Air Leak Surveys 18 6 Methodology .. .. .. .. . 19 6.1 General Discussion 19 6.2 Step -by-Step Procedures for Evaluating High -Efficiency/Variable -Speed Drive Air Compressor Installation Projects 20 7 Sample Design .. .. .. .. . 27 7.1 Program Evaluation Elements .. 27 7.2 Net-to-Gross Estimation . 27 References .. .. .. .. .. 28 Resources .. .. .. .. 29 Compressed Air Challenge Internet Resources .. .. .. 30
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1 This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications. 1 Measure Description Compressed -air systems are used widely throughout industry for many operations, including pneumatic tools, packaging and automation equipment, conveyors, and other industrial process operations. Compressed -air systems are defined as a group of subsystems c omposed of air compressors, air treatment equipment, controls, piping, pneumatic tools, pneumatically powered machinery, and process applications using compressed air. A compressed -air system has three primary functional subsystems: supply, distribution, a nd demand. Air compressors are the primary energy consumers in a compressed -air system and are the primary focus of this protocol. 1 The two compressed -air energy efficiency measures specifically addressed in this protocol are: High -efficiency/variable sp eed drive (VSD) compressor replacing modulating compressor Compressed -air leak survey and repairs. This protocol provides direction on how to reliably verify savings from these two measures using a consistent approach for each. 1.1 High -Efficiency/Variable -Speed Drive Compressor Replacing Modulating Compressor This measure pertains to the installation of a rotary screw compressor with a VSD. Most incentive programs and technical reference manuals use a baseline system definition of a standard modulating compres sor with blowdown valve. The energy -efficient compressor is typically defined as an oil -flooded, rotary -screw compressor with variable -speed control. This measure is frequently offered for the replacement of an existing unit at the end of its useful life or for the installation of a new system in a new building (i.e., time of sale). Several control methods are available for air compressors, and control methods greatly affect the overall operating efficiency of a compressor. In order to accurately estimate energy savings, it is important to know the baseline method of control. A brief description of each common control method is provided below. 1.1.1 Inlet Valve Modulation/Inlet Throttling Inlet valve modulation throttles off the air inlet to a compressor as disc harge pressure rises above the set point pressure. The part -load performance of modulating compressors is relatively poor. Some modulation -controlled machines may be adjusted to fully unload if capacity reduces to a certain level, such as 40%. This reduces energy consumption compared to modulation -only 1 As discussed in fi Considering Resource Constraintsfl in the introduction of this report, small utilities (as defined under the Small Business Administration regulations ) may face additional constraints in undertaking this protocol. Therefore, al ternative methodologies should be considered for such utilities. http://www.sba.gov/category/navigation -structure/contracting/c ontracting -officials/small -business -size -standards
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2 This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications. compressors but requires the use of air storage receivers to meet demand when in the fully unloaded state. 1.1.2 Load/No -Load (Dual) Control Load/no -load or dual controls, also known as constant -speed controls, re quire storage receiver volume and operate a compressor at full capacity until the unload pressure (cutout) set point is reached. The compressor then unloads and blows down the oil separator and operates at minimum power while producing no air. 1.1.3 Variable -Displacement Control Variable -displacement controls change compressor capacity by opening ports in the compressor that limit the amount of the cylinder or air -end that is used for compression. This can be implemented in either discrete steps (e.g. 50%, 75%, and 100%) or by continuously varying capacity. Compressor -specific power is typically good within the variable displacement range, but these compressors typically have a limited turndown range. At minimum turndown, the compressor commonly uses inlet modula tion to further reduce flow, resulting in poor specific power (kW/CFM). 1.1.4 Variable -Speed Control VSD or variable -frequency drive compressor controls use an integrated variable frequency alternating current or switched -reluctance direct current drive to control the electrical signal to the motor and, in turn, vary the speed of the motor and compressor. Compressors equipped with VSD controls continuously adjust the drive motor speed to match variable demand requirements. VSD compressors typically have an e xcellent turndown range and efficiently produce air over the entire range of operating speeds. Below the minimum turndown speed, the compressor typically cycles between off and minimum -load states. This method of control is typically the high -efficiency ca se and not the base case. 1.2 Compressed -Air Leak Survey and Repairs Leaks are a significant cause of wasted energy in a compressed -air system and can develop in many parts of a compressed air system. The most common problem areas are couplings; hoses; tubes; fittings pipe joints quick disconnects; filters, regulators, and lubricators; condensate traps; valves; flanges; packings; thread sealants; and other point -of-use devices. Leakage rates are a function of the supply pressure, typically quantified in SCFM, and proportional to the square of the orifice diameter (hole or crack size). There are three common methods of compressed -air leak detection: auditory and sensatory observation, soapy water test, and ultrasonic leak detection. The industry standard and be st practice is ultrasonic leak detection. This relies on the ability of specialized directional microphones and amplifiers to detect high -frequency noise generated by the turbulent flow of compressed air escaping a compressed -air system through an orifice or crack. The high -frequency sound produced by a compressed -air leak is both directional and localized to the source.
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3 This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications. 2 Application Conditions of Protocol 2.1 High -Efficiency/Variable -Speed Drive Compressor Replacement Measures Demand -side management programs typically offer a prescriptive compressor replacement measure. Many programs and technical reference manuals assume the baseline compressor system to be a modulating or constant -speed compressor. New energy -efficient compressors are assumed to be VSD cont rolled. Incentives for air compressor replacements are typically paid on a dollar -per -compressor -horsepower basis or a fixed percentage of project cost. Common eligibility requirements for compressor replacement measures include: The air compressor must b e a primary system component and not a backup system component. Replaced equipment must be removed or the customer must attest that the baseline system, if remained connected, will be used only for emergency backup purposes and will rarely (if ever) operat e. Only one VSD compressor per system is eligible for incentive. This measure is commonly offered for retrofit (or early replacement) projects and new construction or replace on burnout/time -of-sale projects. For a new construction project or if the base line unit has failed or is near the end of its useful life, the baseline efficiency standard it must meet is generally developed by the local jurisdiction or utility. 2.2 Compressed -Air Leak Surveys and Repairs Compressed -air leak surveys are typically perform ed by a program -approved third party or a trade ally. Programs typically establish specific guidelines for conducting the survey and reporting the findings. Energy savings from compressed -air system repairs are determined by multiplying the estimated reduc tion in compressed air loss in SCFM by the power input per CFM (also known as efficacy) of the air compressor serving the system for the range of loading experienced by the system. Incentives are typically paid as the least of: A fixed dollar amount per ra ted compressor horsepower Full reimbursement for the cost of the leak survey A program -defined maximum, not -to-exceed dollar amount.
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4 This report is available at no cost from the National Renewable Energy Laboratory (NREL) at www.nrel.gov/publications. 3 Savings Calculations 3.1 Savings Calculations for Installing a High -Efficiency Air Compressor 3.1.1 Compressor Power at Full Load Energy use reduction for all compressor projects can be calculated by the difference between the energy consumed in the baseline operation minus the energy consumed in the post -retrofit operation. Generally, information is required for compressor capacity in both the baseline and post -retrofit scenarios. Appropriate adjustments are made to ensure the flow profile is equivalent between pre – and post -retrofit conditions unless demand improvements have been made that result in a change in the flow profile. Com pressor power at full load can be calculated as follows: Full Load kW rated = (Compressor hp) × LF rated × (0.746 kW/hp) (1) motor ) Full Load kW rated = (Compressor hp) × LF rated × (0.746 kW/hp) (2) motor VSD) where: Compressor hp = compressor horsepower, nominal rating of the prime mover (motor) 0.746 = horsepower to kW conversion factor motor = motor efficiency (%) VSD = variable -speed drive efficiency (%) LFrated = load factor of compressor at full load (typically 1.0 to 1.2) VSDs have losses, just like other electronic devices that transform voltage. VSD efficiency decreases with decreasing motor load. The decline in efficiency is more pronounced with drives of smaller horsepower ratings. VSD efficiencies typically range from 94% to 97% depending on the load and compressor horsepower (DOE 2012). Alternatively, full load power may be available from manufacturers or Compressed Air and Gas Institute (CAGI) performance sheet data. Measuring full – and part -load power is e ven more accurate for a specific site. Air compressor full load performance values provided on CAGI data sheets are reported at standard atmospheric conditions (14.7 psia at sea level). Typically, air compressor operating conditions will differ from these standard values, so these values must be corrected to actual operating conditions. The full -load kW is influenced by site elevation and the compressor operating pressure. The following expressions are used to correct the compressor full -load performance based on site -specific conditions.
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