I spend a lot of time with building engineers deciphering what’s happening in their VAV systems. Unfortunately, it’s often not what the design engineer intended, or what the controls company envisioned when they set up the system. When identifying problems with building control systems, it’s much easier to do when you can see the data, rather than read it from a table or a screen.
Traditional Energy Analysis Tools Sometimes Fall Short
Anyone who’s dealt with controls in a building knows the devil is in the details. There are a lot of parts that must function correctly for a system to work. So, it can be tricky to isolate problems using traditional analysis tools.
“MS Excel or Google Sheets are great for plotting time series data. But those tools are limited in the number of variables that you can show coherently without jumping through lots of hoops (i.e. workarounds) to do it.”
Sure Excel or Google Sheets are great for plotting time series data. But those tools are limited in the number of variables that you can show coherently without jumping through lots of hoops (i.e. work-arounds) to do it.
Tableau Brings Energy Data to Life
Enter Tableau. Tableau makes it much easier to customize and save data visualizations, connect to various data sources and even integrate with online tools. The added dimensions and filtering capabilities are particularly well suited for diagnostic data like we have available from Building Automation Systems (BAS) and electricity interval data.
Let’s take an example from a recent retro-commissioning (RCx) project. In this visualization you can quickly review temperatures, flows and control systems outputs in this dual max VAV system.
Visualization of Proper VAV Box Performance – Dual Max Sequence
In the lower graphs, you see the same data plotted on two scatter plots so that you can see the performance of the system over the range of control zone output signals, and as a function of zone temperature.
On the lower left graph, you can see that the zone is correctly reducing the flow in response to negative call for heat (here negative loop signal is heating call) and increasing to a different maximum flow under increasing calls for cooling.
The plot to the right shows that the zone is (correctly) calling for increased or maximum call for heating when the zone temperature is low, and calling for cooling when the zone temperature is high.
The first time you see it, it takes a few minutes to understand but once you’ve got it for one VAV, you can then quickly assess the next one.
A Picture Paints the Story of a Building’s Energy Performance
Contrast the prior zone with the plots of this one. What jumps out?
So much red.
In this case, the red indicates a constant call for heat, no matter what the zone temperature. What’s going on here?
This zone is not making it to setpoint because the reheat valve is not being enabled. In addition, we need to look at the minimum flow for the zone to make sure it’s not too high. If there’s a lower minimum flow rate, the zone may warm up by itself from its internal load. My guess is that we might resolve some occupant complaints when we fix this one.
Saving Time and Money with Energy Data Visualization
A picture really is worth a thousand words, and a lot of consulting hours. Using data visualization is just one of the ways that we’re using analytics and visualization to get better and faster at commissioning controls and identifying opportunities for making your buildings more comfortable, healthier and energy efficient.
If you’re interested in other ways to visualize energy data, check out this article.
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