graph is the image of the business’ average energy performance, and conveys a lot of information: The y-intercept gives the minimal consumption in the absence of the variable (no production, zero degree-day...). This is the base load of the system, the minimal consumption when it is not operating. The slope represents the relationship between the consumption and the previously identified variable. This represents the efficiency of the process. The scatter is the degree of variability of the consumption with operational factors. The slope is not used quite as often for M&T purposes. However, a high y-intercept can mean that there is a fault in the process, causing it to use too much energy with no performance, unless there are specific distinctive features which lead to high base loads. Very scattered points, on the other hand, may reflect other significant factors playing in the variation of the energy consumption, other than the one plotted in the first place, but it can also be the illustration of a lack of control over the process. Monitor variations The next step is to monitor the difference between the expected consumption and the actual measured consumption. One of the tools most commonly used for this is the CUSUM, which is the CUmulative SUM of differences. This consists in first calculating the difference between the expected and actual performances (the best fit line previously identified and the points themselves). The CUSUM can then be plotted against time on a new graph, which then yields more information for the energy efficiency specialist. Variances scattered around zero usually mean that the process is operating normally. Marked variations, increasing or decreasing steadily usually reflect a modification in the conditions of the process. In the case of the CUSUM graph, the slope becomes very important, as it is the main indicator of the savings achieved. A slope going steadily down indicates steady savings. Any variation in the slope indicates a change in the process. For example, in the graph on the right, the first section indicated no savings. However, in September (beginning of the yellow line), an energy efficiency measure must have been implemented, as savings start to occur. The green line indicates an increase in the savings (as the slope is becoming steeper), whereas the red line must reflect a modification in the process having occurred in November, as savings have decreased slightly. Identify causes Energy efficiency specialists, in