|DIRECT DIGITAL CONTROL ENERGY MANAGEMENT SYSTEM|
Direct digital control (DDC) refers to the application of microprocessor technology to building environmental controls. With DDC it is possible to control heating and cooling functions with software that takes into account a wide range of variables, thereby achieving greater efficiency.
Overview of Procedure
At the University of Michigan (U-M), DDC is most often used to manage fan systems, controlling the supply and return fan speeds and fan discharge temperature (which may involve four or more DDC sequences for the various dampers and heating/cooling coils). Some systems require humidity and/or exhaust fan control, as well as energy recovery (using the available heating/cooling from the exhaust air to heat/cool the outside air that is being drawn into the building by the supply fans).
DDC also controls most chillers, some outside and inside lights, most hot water and chilled water pumps, and some cooling tower fans.
Currently there are more than 260 remote computer panels connected to seven networks serving 88 buildings with more than 7,400 sensors/control output "points" (and more than 5,000 additional software points for control adjustments), all linked to two host file servers in the Utilities Department. The number of remote computer panels has more than tripled in the last seven years.
& Health Precautions/Personal Protective Equipment
DDC saves time by eliminating the need to change various time clocks for holidays and schedule changes.
In addition, DDC has replaced pneumatic controllers that tend to drift out of calibration and suffer from "offset" (i.e., the pneumatic controllers don't have the ability to maintain the temperature at setpoint under changing load conditions).
Other design changes that save energy, in addition to DDC, include: more energy efficient motors, chillers, pumps, and basic changes to fan system design. Furthermore, there have been efforts to educate building occupants about the need to turn off lights, keep fume hoods closed when not in use, etc. Breaking each item down into individual associated cost savings is nearly impossible. However, since fiscal year 1988, the combined projects have resulted in estimated savings of $12.9 million.