Frequently Asked Questions
Shared by: rrboy
Frequently Asked Questions 2002 What is "BAS"? Building Automation Services (BAS) is a group within the Maintenance Services Department. The Building Automation System (sometimes also referred to as the “BAS”), which serves most of the University's General Fund Buildings, is included in this group. BAS implements schedule and operational changes for various types of equipment, and monitors the many building systems for alarm conditions and energy efficient operation. During “After-Hours”, Plant Order Services’ maintenance request line is also handled by BAS. What is DDC? Direct Digital Control, known as "DDC", logs electronic temperature measurements and compares them to the desired settings (set-points), then calculates an appropriate response if the two aren't equal, and finally sends out new signals to correct for any difference. Start/stop control and alarm reporting are also incorporated into DDC. What types of equipment are being controlled at the U. of M.? At the University of Michigan, DDC is typically used to control fan systems, namely the supply and return fan speeds, fresh-air mixing dampers, heating and cooling coils and humidification systems, all to maintain the desired fan discharge temperature and humidity and ultimately the occupied spaces of buildings. Additionally, BAS may control and/or monitor fume hood exhaust fan and energy recovery controls (using the available heating/cooling from the exhaust air to heat/cool the outside air that's being drawn into the building by the supply fans). CO2 monitoring also provides for controls that adjust fresh air to auditoriums as the occupancy level changes. BAS also controls complex chilled water systems, including primary/secondary/tertiary chilled water loops, cooling towers start/stop and where available variable-speed controls, free-cooling systems, as well as outside and inside lights, hot water pumps and in recent years a rapidly growing trend toward individual DDC room controls. What did we use before DDC? To turn fans on/off, we used time clocks. The main drawback was the amount of time it took to go around to all of the various time clocks to prepare for holidays and whenever occupancy schedule changes occurred, and so many times clocks were placed in the “always on” mode. Therefore time clocks are seldom used at the University of Michigan today. For temperature control, we used pneumatic controllers. Their principal drawback is that they tend to drift out of calibration, and the vast majority suffers from "offset", which is the inability to keep the desired conditions at set- point under changing load conditions. They are still in use today in some smaller systems, but most have been replaced with DDC, and more are being replaced when there is a reasonable payback for doing so. For individual room controls, most are still pneumatic, but in time these will also be converted to DDC where it makes good economic sense. Can you control the temperature in my room? In some cases the answer is yes. In recent years advancements in room control technology have resulted in more cost-effective means of applying the advantages of DDC to the individual room level. So far this innovation has only reach a hand-full of buildings, but it is expected that over time the majority of rooms on campus will be controlled this way. Advantages include; the ability to use computerized schedules to turn off individual rooms when it's not possible to turn off the entire fan system, and the improved comfort and reduced maintenance that comes with controls that don't drift out of calibration the way the older pneumatic systems do. Regardless of whether you have DDC or not in your rooms, the local thermostat should be able to adjust individual room/zone temperatures. If all of the areas served by a particular fan system are too hot or cold, the fan system's DDC may need attention. However, if there is a problem in one specific area while other areas served by that same fan system are fine, it usually means the local controls are at fault. Who determines the fan schedules? The building occupants determine the schedules. Generally each building has a representative for building scheduling who collects schedule information from various departments before passing it along to BAS. Schedule changes can be sent (or faxed…7-0967) to: Building Automation Services, 326 E. Hoover, Campus zip 1002. How are changes to our schedules or building controls made? We have several computer consoles that are connected directly to our campus-wide networks, from which BAS (and the Control System Specialists from Facilities Maintenance) can make program changes that alter schedules and modify control operation. These changes are then sent out to remote computer panels, which control the building systems. These panels perform control without the aid of the host (server) computer, which simply acts as a file server and alarm reporting/archiving device. When global information is required for control (such as outside air temperature/humidity) the information is sent directly, independent of the file server. How large is the DDC system? We currently have 387 remote computer panels connected to 95 networks serving nearly 100 buildings with over 36,000 "points" (hardware and software system inputs and outputs), all linked to 17 operator consoles and 1 main file server. The system has been growing at a rate of over 15%/year, however in the past year has grown by nearly 28%. How do I obtain more information or assistance? BAS can be reached 24 hours/day at (734) 763-4013, or after-hours (all hours other than M-F 7:00 AM – 4:45 PM) via the 647-2059 Plant Services maintenance line.