In fulfilling the role of an Energy Manager, it is important to understand how energy is consumed. This is true not only for the facility or plant as a whole, but also by an individual piece of equipment. At some point in time, you’ve either been asked or will be asked to assess or evaluate an energy-saving opportunity. This request provides you with an opportunity to go back to the basic principles and remember the relationship between energy consumption and the device consuming the energy. These basic principles consist of 3 factors that govern how energy is consumed by equipment.
When asked to assess an energy-saving opportunity, it usually requires one to determine whether or not one piece of equipment consumes more or less energy than an alternative piece of equipment. Here’s the funny thing about that task, since it is not possible to measure energy savings (you cannot measure the absence of energy consumption) this evaluation really comes down to measuring and assessing how much energy is consumed by each piece of equipment and then evaluating how energy is consumed relative to other parameters.
Okay, so here is where we need to take a quick run through the basics of energy calculations so we ensure we are evaluating the systems appropriately. The first question we must answer is how energy consumption is determined. Putting it in basic terms the equation for energy consumption looks like this:
Now, since efficiency is equal to the load divided by power (or, output/input), the equation can be transformed to:
So this means that energy is equal to the load divided by efficiency integrated over some period of time. In reality, this equation can be quite a bit more difficult. I say this because for many systems, the load will varies over time. In some causes, it can vary drastically over a short duration. In similar fashion, the efficiency is a function of load but can also vary as a function over other variables. Some such variables would include temperature, which will likely also vary over time. Isn’t real life fun! These are the variables that we love to model.
Well, if the time interval is short enough, then we can assume the load and efficiency are constant over the time interval and our equation can be simplified to:
If we look at energy consumption from the perspective of the last equation, it draws attention to an important insight. Because energy consumption is a function of three basic variables, it reveals that energy consumption can only be saved by three means.
- You can reduce load.
- You can increase efficiency.
- You can reduce operating time.
There you have it. These are the only three ways to reduce energy consumption. Now, it goes without saying that you could also reduce energy consumption by combinations of these three means. It is critically important to remember these three means when evaluating energy consuming equipment to either estimate energy consumption or, when comparing multiple alternatives, to estimate energy savings.
When it comes to assessing energy consumption, or more likely asked “potential for energy savings”, the question you will need to address is which of these three factors will be the source of energy savings?
- Will it come from reducing load? If so, how?
- Will it come from improving efficiency? If so, how?
- Will it come from reducing run time? If so, how?
Then the last question to ask in summary, if it is changing more than one of these factors, is the combination enhancing or negating the net outcome? That’s all for now. Let me know what you think by submitting your comments. Until next time, keep driving towards increased energy efficiency.