June 2009

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BAS Graphics

Take a virtual tour of your building’s mechanical systems

Steven R. Calabrese
Steven R. Calabrese
Control Engineering Corp.

Contributing Editor

Graphical user interfaces (GUIs) have been around for some time now, decades I suppose, if you want to include some of the early front-ends that accompanied the pioneering technologies of the building automation industry. When I first started in this business, DDC systems were still in the early stages of development, and the graphics for these systems were pretty rudimentary. Building floor plan graphics were more or less rough renderings of the actual plans, and equipment graphics were two-dimensional cartoons compared to what we’re used to seeing in this day and age. 

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This month’s column will endeavor to explore a typical present-day graphical workstation, what to expect, how to get around, etc. Many system graphics packages these days are web-based, meaning that you can access web pages of the system graphics from just about anywhere there’s a computer and an internet connection. In this respect, navigating a DDC system via its graphics package is not unlike navigating a typical website, utilizing a web browser to get around and “surf the system”, so to speak. 

By way of example, we consider a hypothetical commercial office building standing six stories tall, with a central plant in the basement (boilers and chillers), a VAV air handling unit up in the penthouse, and VAV and fan-powered boxes serving all of the office spaces on all floors. 

To get started, you need to launch the application, perhaps from an icon on your desktop. If the system is web-based, you would open your web browser, just as you would if you were to “surf the internet”, and enter the system site’s IP address. Whether you’re accessing the system via proprietary front-end software or via a web browser, you will be prompted to provide your credentials, i.e., your user name and password. In the initial setup of your graphical interface, a profile would have been needed to be created for your access, to the level merited for your use. You may have full rights to all views and all editable parameters, as would the chief engineer or system programmer. Or you may have limited access, perhaps only being able to view some of the screens, and being “locked out” from changing any setpoints or other editable parameters. It’s likely that your profile, as an active user of your system’s front-end, will fall somewhere in between full access and “monitor-only” access, with the ability to view most screens and edit important setpoints. 

Upon successful login, a “front page” graphic will typically be displayed, which can be an image of your facility, along with a couple of other items and pieces of information. Among these will be: current outside air temperature (as read from the system’s outside air temperature sensor), date and time, and maybe a realtime feed from the web of the current weather conditions. Also included in the front page will be a jump button that will take you to the building floor plan graphics. 

When you reach the building-wide floor plans, you should be able to navigate to anywhere in the building that has equipment attached to the Building Automation System (BAS). Included in these “hyperlinks” displayed on the building floor plans are links to plant and equipment level systems, as well as links to the individual zones. We’ll start by navigating to the central plant and VAV air handler system, and then we’ll drill down to the “zone level”. 

Okay, so we established earlier that we have a boiler/chiller plant in the basement, so if we navigate to the basement floor plan, we should be able to find the mechanical room. And if we’re lucky, there will be a button or hotspot that we can mouse over and click, and be magically transported to a three-dimensional graphical representation of the central plant! Seriously though, in this high-tech era of instant messaging and wireless internet access, it’s more or less a given that you’re graphical renderings of your facility’s mechanical systems will be in 3D and extremely detailed, not to mention eye-catching and attractive! More importantly, the graphics will display all pertinent operating parameters in real-time values. For instance, the hot water supply temperature will be displayed, at a spot on the 3D graphic where the actual sensor is located. Same goes with the rest of the “wired-in” sensors and monitoring devices. The graphic may even go so far as to take, for instance, the wired-in current sensing switch that indicates pump status, and show an “on” condition graphically, as the pump impeller actually rotating! Okay, so maybe that doesn’t thrill us as much anymore as it used to, but it still makes for some pretty neat stuff. 

Next we visit the penthouse, where we find the VAV air handler. Like with the central plant, we find a 3D rendering of the unit, with all of the mechanical components represented, along with the control components as well (valves, dampers, sensors, transmitters, etc.). Here, as far as animation goes, you can expect to see dampers opening and closing, valves modulating (perhaps showing chilled water flow as varying shades of blue), and supply and return fans spinning. All pretty standard these days for an air handling unit graphic. 

Reliable Controls You will also see pertinent values as measured and read from the sensors and transmitters, and will have access to editable parameters such as discharge air temperature setpoint and duct static pressure setpoint. You may also be able to jump to a “summary screen”, which may be more text-based, but will have much more information than the graphic. The graphic will have info that’s important and good for a quick glance, whereas the summary will have more detailed info that may be required for troubleshooting a problem or trying to attain more efficient operation. You should also find, as with any graphics or text-based page, the trusty old “back” button, that will take you to the screen previously viewed. Of course with a web-based front-end, you can simply use the browser’s back button, just as you would with any website that you may visit. 

Now that we’ve explored the plant and equipment level systems, time to get down to the zone level equipment, i.e., the VAV boxes. How we do that varies among manufacturers, however it’s all pretty similar when you come right down to it. Start at the building floor plan graphic. Now each zone will be characterized as having a zone temperature associated with it. This temperature is what is being read from the zone’s temperature sensor, which is wired to the zone’s VAV box controller, and read via the network communications. Each zone’s temperature will be displayed on the floor plan, within the zone and in close relative proximity to the location of the actual zone sensor. There will be a link or hot button within each zone as well, which will take you to the particular zone’s equipment graphic. As in the case of a terminal unit such as a VAV box, the graphic will look very much like the actual piece of equipment, showing the ductwork connections, primary air damper, flow measuring devices, etc. 

At the zone level equipment graphic for this building, we see the VAV box, along with pertinent monitored values such as zone temperature and primary airflow. We also see the editable parameters such as zone temperature setpoint and minimum allowable airflow. At a moment’s glance we can ascertain what’s going on in the zone, and make appropriate adjustments as required, in order to fulfill and maintain each zone’s environmental comfort requirements. Given a web-based system, this can be done from virtually anywhere in the world! And that, my friends, is one of the true beauties of networked DDC. 

There’s much more to all of this, but you get the picture. Other functions of the BAS front-end, though not necessarily graphical in nature, include scheduling, alarming, trend logging, maintenance alerts, and so on. And then there’s also all of the built-in DCC strategies and control programs that make automated building control all worthwhile. Programs such as Demand Limiting, Night Setback, Optimal Start, and Reset, to name just a few, will be covered in an upcoming column entitled Common Routines in DDC, or something to that effect. So stay tuned! 

Tip of the Month: Don’t forget your login information! As with many web-based applications, you are required to know your user name and password in order to gain access to your GUI. No password, no entry! Commit your passwords to memory (I know, easier said than done), or at least keep them in a password-protected file. Some will say that that is not such a good idea, to have your passwords in a file on your computer. I guess it depends on how many people have daily access to your computer. If you have a laptop and you take it with you wherever you go, then your risk of password theft is pretty much equal to your risk of laptop theft. So why not, right?
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