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When it comes to energy efficiency in an industrial setting, it’s easy to get lulled into a false sense of accomplishment with an unexpectedly lower-than-usual utility bill. A temporary reduction in costs might have you thinking, “I must have done something right last month.” In reality, you could be mistaken. In fact, you could be headed in the opposite direction.
Getting at a facility’s true energy performance—or its energy intensity—doesn’t have to be a mystery. The first step involves being able to identify your facility’s energy drivers.
What Are Energy Drivers?
Energy drivers are factors that can cause energy use to vary. They generally fall into two camps: Those you can and should manipulate and others you usually can’t or wouldn’t want to. For instance, you can’t control the weather and you likely wouldn’t slow production simply to save energy. But you can (and definitely would want to) determine the efficiency of the equipment you purchase, or recognize the positive influence of operations and maintenance (O&M) actions on the energy efficiency of the systems at your facility.
The point of identifying energy drivers is to remove the ones you typically can’t or wouldn’t want to control from your facility’s overall energy-use equation. In the grand scheme of things, this group of energy drivers blurs the true picture of energy consumption at your facility. All of the other drivers that you can and should control constitute the purview of energy efficiency.
Factoring out this first group of energy drivers from your facility’s energy data is done through sophisticated statistical regression analysis. Don’t worry; we’re not about to get stat crazy. Our objective for the remainder of the post is to help you understand which of the drivers you can’t control, are in play at your facility. As you identify them, you’ll be more prepared to pinpoint your facility’s true energy performance with the help of statistical modeling (and the data geeks that do the analysis). Gaining insight into your facility’s energy drivers won’t make you an expert in screening every potential variable, but an increased familiarity could help you save time and money in building a viable statistical model that accounts for them.
Common Industrial Energy Drivers
Rather than examine an extensive list of all possible hard-to-control energy drivers, we’ll focus on four we find most frequently in an industrial context: weather, production, schedule, and the quality of raw goods.
Does your energy use vary seasonally (over the course of the year)?
You might guess that thermal systems work harder to heat in the winter, while refrigeration systems use more energy to keep product cool during the summer. If your facility’s industrial process requires maintaining the temperature of a space, product, process, or tool, then weather will play a hand in how much energy the facility consumes. In fact, the same driver is in play for human-occupied spaces when an HVAC system keeps office temperatures comfortable, in spite of the scorching summer sun.
Temperature plus humidity play a role in energy used for drying processes. Before a lumber mill finalizes its production of dimensional lumber, roughly cut wet timber is kiln-dried then run through a planer to achieve its final dimension. Colder, wet weather affects how much energy is required to dry the lumber.
And, wouldn’t you know it—inclement weather (read: rain and snow) in some climates even determines how much energy is used to process wastewater. Precipitation, snow accumulation, storm events, and saturated ground conditions can increase influent flow substantially during non-summer months or a monsoon season. The extra water in the system means more energy is required throughout the collection and treatment processes.
Ask Yourself: Is Weather an Energy Driver?
- Check your utility bill history for a pattern of seasonal peaks and valleys—a strong indication that weather is an energy driver at your facility.
Does energy use vary based on long-term production volume? Does your facility have high re-work or scrap-work rates?
For all industrials, energy is simply a means to an end. You’ve got a product to make, and you need energy to do it. Your business is about converting raw materials into something that meets customer needs. Though every facility would love to slow the rate at which their meter spins, you certainly wouldn’t turn down orders for finished goods to do it.
But production as an energy driver isn’t just about volume or the rate at which product is moving down the a conveyor belt. Energy use per product will jump if the product doesn’t meet customer specifications after the initial run and must be reprocessed. In extreme cases, you can double the amount of energy that goes into a product by processing it again. More likely, you might have to repeat a portion of the process again. For example, food processors of seasonal frozen products are often at the mercy of the harvest. As a result, a facility could be up to its eyeballs in raw goods all at once. The pressure to process more quickly creates the potential for inadequately frozen products that need to be reprocessed. From an energy-per-finished-product standpoint, maintaining a proven production process is a more efficient approach.
Ask Yourself: Is Production an Energy Driver?
- Do you have equipment that operates intermittently, with significant idle time? For example, do you ever have to fire up additional equipment at a certain capacity, or use a different process for a given product line? If the answer is “yes,” it will be easy to identify how your production process influences your energy data.
- If your operation runs 24-7 with infrequent variance in production levels, it might be hard to detect a production influence. You may need to look at energy data over a much longer time horizon and compare a 12-month rolling average of production with energy use in order to determine any long-term trends.
- Bonus Energy Tip: Re-work or scrap work is the bane of efficiency (based on the amount of energy used to produce one unit of finished goods). If your “do over” rates seem high or erratic, consider having staff or third-party experts take a second look at your facility’s process. You could save not only energy, but also time and money.
Does your energy use vary throughout the week?
Schedule has to do with the normal daily and weekly patterns of production activity at a facility. Because operators run equipment, the amount of energy consumed is typically tied to the number of employees on the floor. Whether you realize it or not, employees make energy efficiency decisions every day by powering up and keeping equipment running, or turning it off when it’s not needed.
If you have an office located within a facility that is closed while the facility operates over the weekend, you might notice that the energy per unit produced (energy intensity) decreases. Since no one occupies the office on Saturdays and Sundays, overall energy use at the facility drops. This doesn’t mean that firing your accounting staff will make you more energy efficient. (Try explaining the overdue power bills to your utility!) It does mean, however, that an energy model created for your facility may need to account for the missing personnel on the weekend.
Ask Yourself: Is Schedule an Energy Driver?
- If you have access to energy data, compare your energy use during week days with weekends or compare shifts with more personnel on the clock to lighter shifts. If major differences exist, schedule could be an energy driver at your facility.
- Bonus Energy Tip: It’s important to examine energy use when a facility is idle. This is the “base metabolism” of the facility. If your facility shuts down on weekends and holidays, comparing energy data from the two could be beneficial. Suppose your facility uses 25 percent less energy on average over the weekends than on weekdays. Now, what if holiday use is 50 percent less than your average weekday use? Since you don’t manufacture on either weekends or holidays, comparing your shut-down procedures on weekends to your procedure before holidays could help you save more energy.
4. The Nature or Quality of Raw Goods:
What factors constrain your processing time and/or the amount of saleable output? Is the same amount of energy used for operating systems regardless of the rate of manufacture?
Raw goods entering a facility aren’t always of uniform quality, which may cause your production process to slow down. Since most facilities have multiple fixed loads that are on when producing, a slowdown in the process increases the amount of energy cost per unit of finished goods. At a lumber mill, for example, when the head rig handles logs that are comparatively small in diameter, the process slows and energy intensity climbs. In the food industry, cold storage facilities often blast freeze their product. If the temperature of incoming food products is higher than normal, the process may take longer and require more energy to get product down to final temperature.
In some cases, the same amount of energy is expended with diminishing returns. For example, in solution mining an underground cave is flooded with water to dissolve water-soluble mineral deposits, so they can be pumped out for more processing. Over time, the concentration of soluble minerals decreases and the mine realizes less saleable product for the same amount of energy.
Ask Yourself: Is the Nature or Quality of Raw Goods an Energy Driver?
- Pay attention when product yields fluctuate despite the same per unit input of raw goods or despite employing the same process. If you don’t have an indication that this is a driver already, chances are personnel close to production know which characteristics of raw goods influence output levels. Ask them.
Disentangle Your Drivers
Looking at your utility bill history to get a read on your facility’s energy efficiency is kind of like sorting through a crowded power strip to locate the cord belonging to a particular device. It’s messy, the cords are interwoven and indistinguishable, and you might unplug something important before finding the right cord. Energy drivers are like the jumbled tangle of cords. By taking the time to tease them out, you can get a much better sense for your facility’s overall energy picture. Better still, by accounting for your energy drivers in order to track your facility’s true energy performance, you can then turn your attention to lowering energy intensity knowing that you now have an accurate measure of progress. And when you see the resulting cost savings on your utility bill (or the avoided cost from your energy model), then you’ll really have cause for celebration.
Check out and save our energy driver infographic (above) to use as a quick reference. Share it with colleagues whom you think would find it useful, too.