Air conditioners, Air leakage, Air-handling equipment, Building envelope, Compressed air, Energy information systems, Exterior lighting, Fans, High-bay lighting, HVAC distribution systems, Industrial and manufacturing, LEDs, Light sensing and switching, Lighting controls, Manufacturing, Motor efficiency, Retrocommissioning, Rooftop units (RTUs), Surge protection, Tank-type water heaters, Variable-frequency drives (VFDs), Ventilation and air handling
In 2018 the industrial sector accounted for approximately 32% of all energy consumption in the US, according to the US Energy Information Administration. It consumed approximately 27,000 trillion Btu that year—much of it to fuel manufacturing processes. On average, manufacturing facilities use 95.1 kilowatt-hours (kWh) of electricity and 536,500 Btu of natural gas per square foot each year, though actual consumption varies widely across subsectors. Figure 1 shows a breakdown of energy use for the five manufacturing subsectors that consume the most energy. The petroleum and coal subsector uses the most energy, accounting for 25% of the entire manufacturing sector’s energy use. The chemicals subsector consumes about 20%, followed by paper, primary metals, and food.
Average energy-use data
As a whole, manufacturing uses the most energy for process heating, drivepower, cogeneration, and industrial boiler use. Collectively, these end uses account for over 85% of the energy used in the top five subsectors. Facility HVAC and lighting are the next largest energy consumers at less than 4% of total energy consumption. Although they rank lower in consumption, these categories can undergo proven energy-efficiency improvements that won’t interrupt plant processes. Most efficiency measures in manufacturing facilities tend to address these common end uses, but they only begin to scratch the surface of the total energy-savings potential.
To better manage your facility’s energy costs, it helps to understand how you’re charged for energy. Most utilities charge for natural gas based on the amount of energy delivered, in therms. They charge for electricity based on two measures: consumption and demand. The consumption component of the bill is the amount of electricity (in kWh) that the building uses during a month. The demand component is the highest (or peak) usage in kilowatts (kW) occurring within the month, or, for some utilities, during the previous 12 months. Demand charges can range from a few dollars to nearly $20 per kilowatt-month. Because energy costs make up a considerable portion of your bill, reduce peak demand whenever possible. As you read the following recommendations for managing energy costs, keep in mind how each one will affect both consumption and demand.
Turn things off
Turning off a power switch seems simple, but for every 1,000 kWh that you save by turning off a power switch, you save $70 on your utility bill (assuming an average electricity cost of $0.07 per kWh).
Walk-through auditsOne method to identify energy-efficiency opportunities is to walk through the facility with an industrial energy auditor or strategic energy manager. For more details on conducting audits and creating an audit plan for your facility, refer to Lawrence Berkeley National Laboratory’s Industrial Energy Audit Guidebook (PDF).
Idle equipmentSome industrial equipment must run 24-7, or it can’t power down between uses. Other equipment can turn off automatically when left idle for a time. But many other pieces of equipment needlessly run idle for extended periods. For example, compressors in compressed air systems waste energy when not in use; be sure they’re turned off when not needed. To ensure that equipment isn’t left idling unnecessarily, document and post the power-down procedure or schedule. Doing so can reduce maintenance requirements and extend the useful life of the equipment, besides saving energy.
Plug loadsItems such as computers, speakers, radios, water coolers, and coffee pots burn energy even when no one uses them. Use the energy-saving settings on computers and printers and turn the equipment off after hours. Install smart power strips, which sense when devices are in “off” mode and cut all power to the devices plugged into them, eliminating phantom loads. And look for smart strips that control loads based on occupancy. Give power strips to employees so they can easily switch off all their often-forgotten energy users at the end of the day.
Space heatersPlug space heaters into power strips controlled by occupancy sensors. Other loads, such as task lights and monitors, can also be plugged into these power strips. Note that when employees feel the need for their own space heating, it’s usually a sign of poor HVAC system control.
LightsTurn lights off when they’re not in use. Where lights cover large areas of the floor, you can save substantial energy by turning lights on only as they’re needed. Occupancy sensors and timers can capture these savings, but they need to be combined with lighting systems that you can control effectively. For a no-cost option, train staff to turn off lights as part of closing procedures (you can also help by identifying the location of light switches on a posted notice).
Outside-air intake controlsMany air-conditioning systems use a dampered vent called an economizer to draw in cool outside air to reduce the need for mechanically cooled air. You can set these economizers to run only when spaces are occupied, which is commonly called demand-controlled ventilation.
Turn things down
HVAC temperature setbacksIf your building doesn’t use an energy management system to control temperature, use a programmable thermostat to increase energy savings and enhance comfort. These thermostats automatically adjust to preset levels. Set heating temperatures lower on weekends and holidays and set higher temperatures for cooling.
Lighting controlsIn larger buildings, lighting controls such as photosensors and dimmable ballasts will reduce maintenance costs and save energy by reducing lighting levels. Photosensors adjust the light output according to the amount of light in the area. Dimmable ballasts allow each fixture to adjust light levels as needed. But it’s important to combine these technologies with the appropriate type of lamp. For example, high-intensity discharge (HID) light sources have long start-up and restrike times, so they can’t be shut off based on occupancy. But you can dim them to about 50% of initial power. Fluorescent lamps are a better choice for dimming due to their faster start-up time, but frequent on-off switching reduces their life span. LEDs also work well for dimming and can be networked to incorporate controls that adjust according to light levels, occupancy, or work schedules. LEDs can save substantial amounts of energy in systems such as high-bay lighting.
Vending machine controlsUse occupancy sensors or timers to power down vending machines when the area is unoccupied or closed for the day. Sensors or timers can save nearly 50% of the $170 to $250 in annual electricity costs incurred to operate a single vending machine.
Perform regular maintenance and cleaning
Process heatingYou can improve the energy efficiency of process heating in many ways. To maximize burner efficiency, optimize the ratio of air to fuel with flow metering or flue-gas analysis. In indirect heating systems, inspect and clean heat-transfer surfaces regularly to avoid soot, scale, sludge, or slag buildup that can significantly reduce system efficiency. Reduce air infiltration into the heating process by repairing system leaks and keeping furnace doors closed whenever possible. For more guidance and tools you can use to inspect, maintain, and optimize the performance of your process-heat systems, refer to the US Department of Energy’s (DOE’s) Process Heating Systems page.
MotorsMechanical problems are the main cause of premature failures in electric motors. Check for adequate ventilation around motors and clean and lubricate the motors appropriately. To help motors achieve their full-life potential while minimizing energy consumption, ensure that they aren’t suffering from a voltage imbalance: Make sure voltage is the same on all phases of input power (for three-phase motors).
Fan bearings and beltsInspect the blades, bearings, and belts on fans at least once a year to prevent failure and maintain efficiency. Clean the fan blades and check bearings for adequate lubrication. Reset belt tension or change belts as needed. For more energy savings, upgrade to a more-efficient style of belt drive, which will vary by specific motor application. It will cost more up front but will quickly pay back in savings. One example involves replacing a classic V-belt with a notched or synchronous belt drive.
BoilersDevelop a program for treating makeup water to prevent damage to equipment and losses in efficiency. Buildup inside the tank will decrease heat transfer to the water and necessitate more-frequent blowdown, which wastes both water and energy. Similar to process heating, the air-fuel ratio has the largest impact on combustion efficiency, so check it periodically to ensure that the combustion process is operating efficiently.
Air compressorsIn compressed air systems, check hoses and valves for leaks regularly, and make repairs if needed. You may not always see or hear the leak, so consider using an ultrasonic leak detector. A poorly maintained system can waste between 25% and 35% of its air due to leaks alone and can effectively double the cost of compressed air. Leaks cause lower pressure at the endpoint, which operators try to compensate for by setting pressure levels higher than otherwise necessary. This further increases energy consumption. A leak detector provides long-lasting benefits and can pay for itself in less than six months.
Clean intake vents, air filters, and heat exchangers regularly to increase both equipment life and productivity. The Compressed Air Challenge, a collaboration of compressed-air users, offers a wealth of knowledge about these systems.
Building envelope and sealsOne major source of energy loss is air leakage, such as through gaps around doors on receiving and loading docks. Regularly check and repair gaps in door seals, and make sure employees keep the doors closed on conditioned buildings.
LightingCleaning dirty lightbulbs and fixtures can increase lighting output by 10%, according to the DOE. Over time, diffusers and lenses often turn yellow or brown, significantly reducing light output. Replace these discolored diffusers or lenses for a 20% boost in output. Calibrate occupancy sensors and photocells to restore correct operation and reduce energy use by up to 50%. If you don’t already have a lighting maintenance plan, develop one to ensure that light output is maintained and energy isn’t wasted.
EconomizersThe linkage on an economizer’s damper, if not checked regularly, can seize up or break. An economizer stuck in the fully open position can add as much as 50% to a building’s annual energy bill by allowing hot air in during the air-conditioning season and cold air in during the heating season. Have a licensed technician calibrate the controls; check, clean, and lubricate the linkage at least once a year; and make repairs if necessary.
Air filtersChange air filters every one to three months. Change filters more often if they handle a heavy particulate load or large particulates. Also change filters more often if the building is near a highway or construction site, or if the system uses an economizer.
HVAC leaksA leak in an HVAC rooftop unit can cost $100 per unit per year in wasted energy. Every three months, check for leaks in cabinet panels and ducts on rooftop HVAC equipment. Also be sure that the units are secure, with all screws in place. Every year, inspect all access panels and gaskets, paying close attention to those on the supply-air side where pressure is higher.
Condenser coilsCleaning the condenser coil is one of the most cost-effective maintenance steps for HVAC rooftop units. A dirty coil that raises condensing temperatures by as little as 10° Fahrenheit (F) or about 5° Celsius (C) can increase power consumption by 10%. This costs about $120 in electricity for a 10-ton unit operating 1,000 hours per year. Check condenser coils for debris each quarter and clean them at least once a year.
Process heating uses the most energy in the manufacturing sector, averaging almost one-third of a facility’s total energy consumption. Monitor the heating process from start to finish and maintain the equipment to control energy costs.
Waste-heat recoveryIn most fuel-fired heating equipment, the largest heat loss occurs when spent combustion gases are exhausted because these gases still contain a significant amount of thermal energy. You can recover this waste heat and use it in processes such as preheating combustion air before it enters the system, preheating load material before it enters the heating process, steam generation for secondary processes, and water or space heating. If you haven’t implemented a heat-recovery project before, consult with a process-heating engineer to help you assess the options.
Furnace pressure controllersWhen heating systems exhaust hot combustion gases into ambient air that’s significantly cooler, negative pressure builds within the furnace. This allows cooler ambient air to infiltrate the furnace through the flue or leaks and other openings within the system. This additional air will then be heated and exhausted, wasting energy and lowering system efficiency. Consider installing furnace pressure controllers to adjust the pressure within the furnace. This helps to maintain a positive pressure within the furnace, reducing cool-air infiltration into the heating system.
LFL monitoring equipmentProcess heating that involves the removal of flammable solvents can benefit from lower flammable limit (LFL) monitoring equipment. When flammable solvents are used in production processes, high oven temperatures evaporate them, emitting flammable vapors. The National Fire Protection Association (NFPA) Standard for Ovens and Furnaces sets LFL guidelines for concentrations of low-vapor solvents and requires proper ventilation ratios to reduce solvent vapor concentration to appropriate levels. Although solvent vaporization rates aren’t uniform, the NFPA calculates ventilation guidelines based on the theoretical peak ventilation needs for safety. LFL monitoring equipment tracks the solvent extraction rate in real time and adjusts the ventilation rate according to system needs, maintaining a safe ventilation ratio while saving the energy to run the equipment at higher levels.
Industrial electrotechnologiesIf your company has a carbon-reduction goal, you may find it difficult to meet this goal if you rely on a lot of process heat for manufacturing. One decarbonization strategy involves using electricity for process heating combined with sourcing low-carbon electricity (for example, participating in your utility’s green-power program). Different electrotechnologies are appropriate for different industrial applications, and some may offer other benefits beyond reducing your carbon footprint. For example, you can use isothermal immersion heaters in primary aluminum casting and recycling to increase both efficiency and the consistent quality of the melted metal. Transportable electric ladles are also suitable for primary metals manufacturing. They eliminate the need for gas-fired holding furnaces and the overheating of molten metal, which is inherently wasteful.
Motors consume almost 70% of the electricity used in the manufacturing sector. To eliminate energy losses, properly size and maintain the motors.
Properly size motorsThough motors often operate under varying loads, they’re generally selected based on the highest anticipated load. This causes facilities to use more-costly motors than necessary and presents the risk of underloading them. Consider selecting a motor based on the load duration curve (LDC) of its specific application rather than its highest anticipated load. The LDC shows the relationship between motor capacity and utilization, indicating the average load demand for the motor. Motors selected according to an LDC will be smaller, less expensive, and more efficient over their lifetimes. They will, however, have a rating slightly below the highest anticipated load. This method does risk overloading and overheating the motor, but most motor manufacturers design them with a service factor above the stated rate that allows motors to temporarily overload without harm.
Improve power qualityWhen you improve power quality and minimize voltage imbalances, motor efficiency increases. Industrial facilities can receive additional utility charges for poor power factor, so add capacitors to improve power factor and lower your energy bills. Voltage imbalances also disrupt motor performance. In a three-phase system, the voltage of all phases should be equal. Balance these single-phase loads equally among all phases to reduce performance losses from voltage imbalances. Isolate any disruptive loads and feed them from a separate line to improve power quality.
Use high-efficiency motorsImprove motor efficiency by upgrading to new, higher-efficiency models instead of rebuilding old motors. Rebuilding old motors may improve efficiency by 1 or 2 percentage points at most. Motor shops will install new bearings, rewind the core, and “dip and bake” the motor (to keep the core electrically insulated). A new, high-efficiency motor may cost more than rebuilding an existing one, but new motors can more than make up for the expense in energy savings, higher service factor, longer bearing and insulation life, lower vibration levels, and diagnostic maintenance systems. Some new motors draw a larger start-up current, so verify that your system has the appropriate capacity before you make a purchase. And remember that the cost of electricity to operate a motor for its lifetime far exceeds its purchase price.
Install VFDsWhen loads change, variable-frequency drives (VFDs) alter the speed of a motor accordingly, often significantly reducing electrical consumption. You can install VFDs in most existing systems because they’re designed to operate standard induction motors. VFDs might cause problems with power quality due to induced harmonic distortion. To mitigate these problems, explore harmonics filtering or other measures.
Boilers account for the largest nonprocess consumption of natural gas within the manufacturing sector. Optimized operational setpoints and regular maintenance will ensure boilers perform at their peak efficiency.
Add boiler controlsTake advantage of a boiler control system’s onboard efficiency strategies, such as outside-air reset and outside-air, high-temperature shutoff. If no controls exist, consider retrofitting boiler controls onto the system to optimize performance and eliminate unnecessary cycling. A particularly effective control system measures real-time heat load using a flow meter and temperature sensors in conjunction with an advanced software algorithm to enable the boiler to deliver only enough heat to match the load. By reducing short-cycling losses, this control strategy can reduce boiler energy consumption by as much as 45%. The first company to commercialize this type of control system was Thermodynamic Process Control. More recently, United Technologies demonstrated a similar advanced boiler control system in partnership with the US Department of Defense.
Install a waste-heat recovery systemOn average, stack loss from boilers is around 15%. Blowdown also produces waste heat that’s lost through drainage. Consider installing waste-heat recovery systems for both of these processes. You can use the waste heat from the boiler and stack to preheat the intake air or makeup water for the boiler.
Inspect steam trapsSteam traps are automatic valves that release condensed steam from the boiler while preventing the loss of live steam. According to the Boiler Efficiency Institute, in a steam line of 150 pounds per square inch gauge, a 0.125-inch steam trap with a valve that’s stuck open will lose 75.8 pounds of steam per hour. Unnoticed, a leak of this nature could result in thousands of dollars in wasted energy. As with compressed air systems, an ultrasonic leak detector will reveal faulty steam traps. It isolates sound frequencies, compares the frequencies to those of a properly functioning steam trap, and shows the results to users via a digital display.
Operate boilers at peak efficiencyIn facilities with more than one boiler, optimize load management across boilers and save energy by operating them at peak efficiency. As demand increases, use the most-efficient units first, and as demand decreases, cut the least-efficient boilers. Scheduling loads across boilers to minimize short cycling can also improve system performance.
Install circulating fluidized-bed boilers (CFBBs)Long used to control emissions for coal-fired boilers, CFBBs are a fuel-flexible industrial boiler technology with a high potential for energy efficiency. Particularly where a steady stream of organic waste is readily available, such as pulp and paper mills, CFBBs help reduce both natural gas consumption and overall carbon emissions. CFBBs use a cyclone particulate trap to recirculate fuel and flue gas back to the combustion chamber, as well as a “fluidizing agent” like sand that helps to improve heat transfer. This enables a very efficient, low-emissions combustion process that can run an industrial boiler to supply process heat, steam, or hot water.
Upgrade to more-efficient lightingHID light sources, such as metal halide and high-pressure sodium lamps, have long dominated the market for high-bay lighting, but today other technologies have proven more efficient under many common situations. LEDs can offer significant efficiency, controllability, and performance benefits over HIDs. But high temperatures can reduce LED efficiency and lamp life. The best application of LEDs is in cold-storage areas, warehouses, and conditioned spaces with high ceilings. LED product quality can be uneven, so choose LEDs with care and refer to the DesignLights Consortium’s Qualified Products List.
Retrofit wireless controlsWireless controls give you a high degree of lighting control and will offer plenty of savings. These systems use sensors that measure factors like occupancy and ambient light levels. You can control the settings of either individual lights or groups of fixtures through a desktop or mobile app. Controls save energy by only allowing light fixtures to turn on when they’re needed. They also adjust light levels based on actual user needs and ambient lighting conditions. You can configure these systems to react to your utility’s demand-response events (either automatically or manually) by dimming lights as much as possible based on previously established settings and on real-time occupancy and ambient light levels. By using wireless mesh networks for these controls, you’ll have a faster installation than with wired systems, thereby reducing downtime and up-front costs.
Use smart lighting design in parking lotsParking lots are often overlit. An average of 1 foot-candle of light or less is usually sufficient. The most common lamps used for outdoor lighting are HID sources—metal halide and high-pressure sodium—but LEDs are the preferred technology for parking lot lighting because they reduce light pollution while offering efficiency and long life. Use dimming and occupancy-sensing controls to save even more energy.
Overlit parking areas not only waste energy but can actually be dangerous if drivers have trouble adjusting their eyes between highly lit and dark areas. It’s important to find a balance to prevent safety concerns involved with underlighting.
Install LED signageUsing LEDs for exit signs and other applications can cut energy costs and also reduce maintenance costs compared to incandescent, CFL, neon, and other lighting types. To see what you could save by replacing aging exit signs with contemporary models, use the exit signs savings calculator from the US Environmental Protection Agency’s ENERGY STAR program.
Air infiltrationAirflow through open loading docks and doors wastes energy in manufacturing facilities. To reduce energy losses, make sure that the doors are closed and sealed whenever possible. That can be easier said than done. People working on loading docks find it tedious to open and close doors several times a shift, so they save time by propping the doors open. One solution is to install specially designed doors that open and close quickly (but safely) and encourage employees to use them as much as is practical. Another option is to use doors that automatically close if left open. In doorways with so much traffic that even rapidly opening doors would be too slow, strip curtains are an inexpensive solution.
Radiant heatersOne challenge with efficiently heating a manufacturing facility is the wide range of functions and spaces in the facility. If a large facility has a small section used as an office, people working there will expect a reasonable indoor room temperature year-round. The same applies to individuals working on a loading dock on a cold winter day. Maintaining a comfortable temperature throughout the entire space can be costly and inefficient. In these situations, mount gas or electric radiant heaters (also known as beam or panel radiant heaters) above or near the areas that require heat, keeping workers comfortable even with the building air as low as 40° to 50°F (4° to 10°C). These devices provide heating comfort to people directly in front of them, but they aren’t designed to raise overall air temperature.
Large ceiling fansIf a space is cooled, high-volume, low-speed ceiling fans save energy by improving air circulation. These fans, such as those described on Washington State University’s High-Volume, Low-Speed Fans web page, allow you to raise the temperature by as much as 4.5°F (2.5°C) while still maintaining occupant comfort. If the facility is heated, warmer air will naturally stagnate near the ceiling where it won’t do much good. Change the direction of ceiling fans to circulate the heated air vertically. Several case studies have shown that a few large ceiling fans provide better air circulation and greater energy efficiency than multiple smaller, high-velocity fans.
Reflective roof coatingsIf the roof of your building needs recoating or painting, consider white or some other highly reflective color to minimize the amount of heat the building absorbs. This change can often reduce peak cooling demand by 15% to 20%. For a list of suitable reflective roof coating products, visit the ENERGY STAR Roof Products page.
If your facility doesn’t already have a cogeneration system—also called combined heat and power (CHP)—consider installing one. These systems simultaneously supply heat and electricity from a single fuel source. By design, they’re very efficient and produce power at double the efficiency of power delivered from a central plant. Cogeneration systems are commonly found in plants with large heating needs, such as oil refineries and paper mills. For more information about how to successfully deploy a CHP system, refer to the DOE Better Buildings Combined Heat and Power page.
Building systems and operations and maintenance (O&M) programs
Track energy useUse the ENERGY STAR Portfolio Manager to track your facility’s energy consumption. Once you’ve entered basic information such as building floor area and utility bill data, this tool calculates an index of energy consumption per square foot that will enable you to compare individual buildings, either across your portfolio, against their past performance, or to other similar facilities. Armed with such comparisons, you can identify and prioritize the plants with the biggest energy-consumption problems or track your progress for those plants in which you’ve implemented energy-efficiency measures.
Install an enterprise energy management (EEM) systemIt’s impossible to optimize what you don’t measure, so consider using an EEM system to track your facility’s use of electricity, water, compressed air, gas, and steam. An EEM system is a combination of data-acquisition hardware and software that allows for a broad-based understanding of how your facility uses energy. The information an EEM system collects will allow you to track costs, identify anomalies, and automate demand-response reactions. You can then compare one facility against another or monitor how performance varies over time. An EEM system also helps with determining the actual payback periods of any efficiency measures you’ve implemented.
Integrate process controls with energy managementTraditionally, energy monitoring and management systems for facilities are isolated from manufacturing process controls. This is partly for the sake of simplicity but also because, in relative terms, energy management is considered less important in manufacturing. If your company instead integrates process controls with energy management, which is a step toward “smart manufacturing,” you’ll open up the possibility of optimizing and automating more of your business operations. Integrating process controls with the EEM system ultimately enables better decision-making across the company.
Upgrade your O&M program
To improve your facilities’ energy efficiency with little or no capital investment, ensure that the building shell and the expensive systems within it are properly operated and maintained. Both senior management and O&M staff must commit to the O&M program. Be sure to document O&M activities thoroughly and provide staff with training and resources to execute the plan. In the Federal Energy Management Program’s Operations & Maintenance Best Practices Guide, Chapter 9: O&M Ideas for Major Equipment Types (PDF) explains options for major equipment common to industrial facilities.
Retrocommission your facilityRetrocommissioning (RCx) is a process performed on facilities already in operation that identifies facility performance objectives, tests and verifies that those objectives are met, and provides documentation of the process. Though most RCx programs focus on HVAC and lighting improvements, RCx objectives for an industrial facility will also focus on other systems within the building. RCx will evaluate systems that typically offer energy improvement opportunities, such as compressed air, steam, chilled water, process ventilation, pumps, and fans. Facility upgrades performed through RCx provide an initial boost in efficiency, but an effective O&M program is essential for maintaining those improvements. And recommissioning every few years will keep your facility operating efficiently.
Purchase electric forkliftsDiesel- or propane-fueled forklifts require extra ventilation in a manufacturing facility, which adds to the HVAC load in conditioned spaces and increases overall energy use. Electric forklifts have higher initial costs (capital plus installation) but lower energy and total operating costs. So the total life-cycle costs are comparable. One often-unexpected cost when deploying electric forklifts is increased demand charges, but these can be avoided by using a timer to only charge the forklift batteries during off-peak hours. In addition, some electric forklifts use regenerative braking technologies to extend the period between battery recharges. To charge electric forklifts more efficiently, use high-frequency chargers. Another type of efficient forklift is the fuel cell–powered lift truck, which uses hydrogen to create electricity.
Upgrade materials-handling control systemsSome facilities use sophisticated systems for conveying and sorting manufactured items and work in process. If conveyors constantly move at top speed regardless of how much they’re carrying, they’re operating inefficiently. Upgrade to custom distribution systems that will meet the functional requirements but slow down or switch off when possible to save energy.
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