How do building operators interpret energy use data to optimize building performance?

High-resolution datasets and simple data visualization techniques help us identify common scheduling irregularities and pinpoint sources of energy waste

A building automation system is a network that connects and controls a commercial building, such as its lighting systems and heating, ventilating, and air conditioning (HVAC) systems. A building operator or energy manager determines when certain automations take place by creating a schedule.

Intentionally or unintentionally, a building’s scheduling may deviate from its optimum settings. If left unchecked, improper scheduling can wreak havoc on a building’s operational profile—impacting energy budgets, comfort conditions, equipment longevity, and your ability to meet performance standards or service-level agreements (SLAs).

Two simple data visualization techniques make optimizing building scheduling easier. Tree maps speed up the identification of buildings with potentially errant scheduling, and heat maps visualize the extent of their scheduling irregularities.

When used together, these tools help building operators deliver quality comfort conditions and cut energy and lifecycle costs by reducing how often lighting, heating, or cooling systems operate.

Identify your top-consuming buildings

If you manage many buildings, then a campus- or portfolio-wide comparison can provide a useful view of the top-consuming buildings where you stand to reap the greatest savings.

A tree map shows how individual buildings contribute to the overall performance of your portfolio—and how they “drift” over time. A rectangle’s size represents energy use, and its color indicates relative change from the previous period.

In this tree map showing this month compared to the previous month, Austin Warehouse and Mountain View Lab (both red) have significantly increased consumption. Because of both the size and color of Mountain View Lab, its savings potential is greater than Austin Warehouse.

A visualization like this can help guide and prioritize your investigation into buildings’ scheduling. Once you’ve found the top-consuming buildings, or the buildings exhibiting the most drift, then you’re ready to begin examining their demand and consumption trends.

Visualize a building’s scheduling irregularities

A heat map shows how a building performs throughout the day and year. The x-axis represents hour of day, the y-axis represents day of year, and a rectangle’s color indicates average electricity demand during each one-hour period. In the following examples, red indicates very high consumption, while dark green indicates very low consumption.

With a heat map visualization in hand, you can now ask the following questions:

Is time-of-day scheduling in place?

Time-of-day scheduling ensures that a building curtails usage during partially occupied periods and shuts down during unoccupied periods, such as at night.

Reduced temperature or lighting levels during these periods are called “setbacks.” If properly scheduled, nightly setbacks should also recede during the morning hours to meet building demands during the day.

Is day-of-week scheduling in place?

Day-of-week scheduling ensures that a building curtails usage on partially occupied days and shuts down on unoccupied days, such as weekends and holidays.

The minimum amount of electricity being consumed is called “base load.” Depending on building type, higher or lower base loads may be observed—regardless of occupancy. For instance, a grocery store will always have 24/7 refrigeration requirements.

Prominent dark green regions at the far left and right indicate that time-of-day scheduling is in place, while dark-green horizontal bands on the weekends indicate that day-of-week scheduling is in place.

Are seasonally-adjusted temperature setpoints in place?

Building automation systems should be programmed to respond to seasonal variations in temperature. These systems rely on a measure of how much (in degrees), and for how many days, the outside air temperature was below the point at which the building needs heating and above the point at which it needs cooling.

These measurements are called heating degree days (HDD) and cooling degree days (CDD). The target temperature is called “balance point.”

Here’s an example: If the average temperature yesterday was 70 °F and the heating balance point in your building is set to 65 °F, you would have cooled your building down by 5 degrees for the duration of a day. Therefore, the cooling demand was 5 CDD. If the weather persisted for 5 straight days, the overall cooling demand would have been 5 days * 5 CDD per day = 25 CDD.

For a building with electric cooling and gas heating, during warmer months there should be a correlation between higher electricity consumption and cooling degree days, while during cooler months there should be a correlation between lower electricity consumption and heating degree days.

Red and yellow bands at the top left indicate higher electricity consumption, which correlate with the blue bars in the horizontal bar graph at right, which show the number of cooling degree days.

Have temporary overrides been reverted to typical settings?

Temporary overrides are commonly implemented to accommodate special situations, such as an event or after-hours maintenance. Overrides should usually be set according to expected building occupancy levels during those times. Most importantly, they should be reverted as soon as possible to the prior scheduling settings.

In a worst-case scenario, an override may go unnoticed for months or even years, increasing costs and reducing the lifespan of the equipment.

After being implemented, the temporary override had not been reverted. Consequently, electricity use soared for several days during the evening hours before the schedule was eventually reverted.

Are new systems and equipment properly commissioned?

New equipment often requires an extensive quality assurance process called “commissioning.” Commissioning ensures that equipment operates efficiently and safely and meets a building owner’s operational needs.

Commissioning is particularly important if new equipment is introduced into an existing building system with many complex parts. An evaluation of building scheduling should be included before (and soon after) any maintenance or replacement of equipment.

After installation, the HVAC system does not seem to follow any apparent schedule. Either it is not properly interfacing with the schedule, or there is more fine-tuning required by the installer of the equipment.

Does system or equipment performance merit maintenance or replacement?

Malfunctioning equipment can lead to more than just comfort complaints—it can drastically reduce the equipment’s useful life. When equipment is turning on and off too frequently, this is called “short cycling.”

For instance, if an HVAC unit appears to be short cycling in rapid succession, this behavior may point to other undetected problems, such as broken sensors, dirty filters, or leaky valves. If left unchecked, costly equipment failure may occur.

The HVAC system is turning on in the middle of the night on Sundays. This suggests that it needs to run harder and longer to raise the temperature from the weekend set point of 55 °F to the workweek set point of 68 °F on Monday morning. Equipment may need cleaned, tuned, or even replaced.

High-quality, high-resolution datasets are essential for pinpointing sources of energy waste. Simple, powerful data visualization techniques, like tree maps and heat maps, can help building operators do their jobs better and faster by making energy use trends more easily interpretable.