Despite their intentions to run facilities more efficiently, the fact is that many manufacturers are wasting hundreds of thousands of dollars each year in unnecessary energy costs. With the start of 2012, it is an ideal time to make some New Year's resolutions to eliminate energy waste and boost the bottom line in the process. In particular, manufacturers should look at the five areas that can have the greatest impact on a facility's overall energy efficiency.
Take Advantage of Free Cooling
Many facilities operate chillers to provide water at 40F to 50F, which is used to cool manufacturing operations and data centers. This requires refrigeration compressors-the main energy consumers-along with evaporators, condensers, cooling towers, pumps, and other equipment.
However, in colder months manufacturers can provide the required chilled water by idling the compressor and instead taking advantage of low outside temperatures and humidity to allow direct rejection of the heat into the environment. When facilities fail to take advantage of this free cooling, they are losing the opportunity to reduce their cooling energy by up to 75%.
Free cooling requires an upfront capital investment-typically, a heat exchanger to chill water, valves-and control modifications. However, there is a clear payoff.
For example, one manufacturer projects that a recent free cooling project in Nebraska will deliver annual savings of $75,000, with an estimated capital cost of $235,000. Significantly, this manufacturer is not only looking at current savings, but also using free cooling as a hedge against future costs. Assuming that energy prices double in the next two decades, which is a fairly safe assumption, the company's savings could jump up to $150,000 per year.
Recover Wasted Heat
Air compressors must be cooled to remove the heat of compression, and about 70% of the input energy is lost in this way. Other sources of excess heat are cooling towers, hot exhaust, and boiler flue gas. Manufacturers may find it economical to recover this heat and use it for winter space heat and/or process heat. In fact, the value of this energy is often underestimated. For instance, one automobile plant throws out $1.3 million per year in unused hot energy.
It is often practical to recover heat using a simple air duct and summer/winter damper to direct the energy in or out of the building. However, despite this simple adjustment, some sites do not attempt to recover heat. This is because their manufacturing processes throw off so much hot energy that there is no need to recover heat from other systems. In Europe and Japan, there are now efforts to collocate manufacturing sites that generate hot energy with offices, storage sites, or other facilities that could benefit from the recovered heat.
Minimize Peak Energy Use
Most commercial and industrial electric rates include energy charges [¢/kWh] and peak power (demand) charges [$/kW]. Still many manufacturers do not know when the peak usage occurred or what electric loads contributed to the peak.
The solution here is simple. First, use a data logger to record electric loads at 1-minute intervals. Then calculate and average the power over a 15-minute interval. Using this monitoring approach, one small facility determined that it had a peak load of 359 kW at 8:00 am every morning caused by the simultaneous defrosting of all freezers. By simply offsetting the timers to avoid the peak load, the business realized annual savings of almost $10,000. In this case, the energy savings may be challenged because defrosting still occurs later in the day. However the financial savings are very real.
Take Control of Air Compressors
Compressed air supports many factory functions, but it's a very inefficient way to deliver energy throughout the facility. Less than 10% of the input energy ever does useful work. There are two actions manufacturers can take to optimize the energy efficiency of air compression machines.
The first is to ensure that compressors are fully loaded, since partially loaded ones are less efficient. The correct way to control the machines is to base-load all except one machine, which is designated as the "swing machine." The swing machine controls the maintain system pressure by changing the output of the compressor as needed. All other machines are either operated with constant output at their maximum efficiency point, or left idle if not needed to meet the load.
The second is to avoid increasing compressed air operating pressure, since this dramatically raises costs. It takes more energy for the compressor to supply the higher pressure, and flow to unregulated loads/leaks is increased. An increase of just 10 psi will increase the operating cost by 5%-8%.
Most industrial compressed air systems should be operated below 100 psig. However, many operators try raising pressure to resolve equipment issues that seem to be related to air pressure. Rarely do they go back and reduce the pressure, even when the ultimate cause of the problem is found to be unrelated. Before increasing pressure above 100 psig, operators should record and study air pressure profiles; most likely, they will discover that the problem can be resolved by changes to distribution piping or the addition of receiver volume.
Turn Off Unused Equipment
It seems obvious and simple to save money by turning lights and equipment off when not in use. However, a surprising amount of energy and money continues to be wasted. The solution here is to equipment for a week to determine when it is and is not being used-typically in15-minute intervals for electrical equipment and 30-minute intervals for gas-powered equipment. Then use timers or manually turn off the equipment during those periods when it is not in use.
Monitoring gas-powered engines can be more challenging than electrical equipment because gas flow meters are prohibitively expensive for most energy management work. A good workaround is to use data loggers to monitor runtime on related electric equipment such as combustion fans. Data loggers with CTV sensors can indicate when the equipment is operating, and a motor on/off logger can also record run status.
Savings Start With Energy Monitoring
The five actions outlined here enable manufacturers to realize moderate to significant energy cost savings. However, the benefits to individual companies can vary greatly. Therefore, the first step should be monitoring existing conditions to determine the potential for reducing energy costs by reducing consumption, harnessing unused energy, or optimizing the timing of operations.
Often it is not necessary to invest in permanent metering. Instead data loggers, such as those from Onset Computer Corp., serve as small, robust measurement and recording devices, which are available for about $200. They offer a cost-effective option for obtaining critical information about energy consumption. Then expensive metering can be added later if analysis justifies the value of a permanent monitoring system.
It can be difficult to stick to New Year's resolutions. However, by gaining insight into their manufacturing sites' energy consumption, managers can determine which resolutions are worth investing in to improve the company's efficiency and its bottom line.
Paul H. Stiller is director of energy management for Summit Energy Services, a subsidiary of Schneider Electric.
