Buildings are dynamic. Small control programming changes, sequence resets, manual overrides and equipment failures combine to push buildings away from optimal performance. Experts refer to this steady accumulation of problems as building drift (pdf), and have identified drift as a major source of excess energy use as well as a massive savings opportunity if monitored and corrected by facilities professionals.
Gridium’s Billcast provides a simple way for customers to monitor building drift from month to month, and we’re excited to announce that RCx now has an even more sophisticated set of drift tracking features, appropriate for commissioning firms or for facilities engineering teams.
The example below shows a drift report for one week of energy use. The black line represents current demand, the shaded orange region shows increases in energy use vs. a year ago, and the shaded blue region shows decreases in energy use vs. a year ago. The comparison is weather-adjusted, meaning that changes in energy use due to environmental conditions such as outside temperature are removed from the demand curve. The result is a comparison that shows true operational change — or drift — independent of external factors. In the example here, we see savings (in blue) from a later start time and better daytime energy management. Below the chart, summary statistics tally up the total increases and decreases to show the net change in energy use over the course of the week.
Example 1: A year-on-year look at project savings (click for larger image)
This drift report is interesting, but the baseline is somewhat arbitrary. You may want to compare today’s energy use to a year ago to monitor general building drift, or you may instead want to pick a specific baseline period so that you can gauge the effect of, for example, a capital project, occupancy change, or efficiency measure.
RCx allows you to change the baseline to any day you want. In the next example, we’ll adjust the baseline to see what effect a project completed in November had on building operations. The result is striking. Although the building is performing better than it did a year ago, it is performing substantially worse than it did after November’s project. The start time has shifted back, and baseload is higher across the entire week. In short, all the good work done last fall is slowly eroding. It might be time to schedule a controls review.
Example 2: Reframing the baseline shows performance degradation since a controls project (click for larger image)
Let’s take a more fun example: Below, we see amazing year-on-year savings from a large solar PV installation.
Example 3: A solar installation shows dramatic savings (click for larger image)
However, big projects like this can mask small sources of drift that drive up your energy costs. It’s well known that efficiency projects don’t always perform as well as engineering calculations suggest they should. Part of the reason is that operational drift eats away at the initial gains over time.
Here’s where the drift report really shines. By resetting the baseline to after the solar array was installed, we reveal a clear increase in baseload. The facility is still saving massively overall, but even a small erosion in performance can threaten the project’s payback. The drift report reveals small problems that can be corrected before they become expensive.
Example 4: Adjusting the baseline reveals a baseload jump after the solar array was installed (click for larger image)
These are a just two ways Gridium RCx customers can use drift reports. We’re excited to hear feedback and see the unique ways our customers use the tool to monitor building performance.
