Consulting-Specifying Engineer - April 2008 - (Page 40) DDC BY JAY SANTOS, PE, Principal, Facility Dynamics Engineering Inc., Columbia, Md. master planning Several items must be considered when designing an HVAC direct digital control system. Make sure you ask the right questions. stand-alone commercial building with packaged rooftop equipment. There is no planned expansion for this project in the foreseeable future. Or, the building could be a similar building, but it is on a university campus where there already exists a preferred vendor or multiple acceptable DDC systems. And instead of packaged equipment, the building systems now are connected to a campus steam and/or chilled water system. So ask yourself: How sophisticated is the monitoring of this system going to be? Does an existing information technology (IT) infrastructure exist that the project can use locally? Can this project use that communication network? If so, what are the requirements or does that change the design? Does this system need to be seen from other sites on the existing system? In the simple standalone project, this may require remote monitoring through the Internet. The campus project may require specific IT connection specifics based on the campus IT standards. Many questions, and from a big-picture perspective the answers, depend on the specific project being considered. It would be ideal if all of the DDC systems available to us today were similar in their architectural robustness, but things are never that simple. The design engineer should ensure that the system designed is robust for the applications being controlled and for the operator’s intended use of the system. Some of the criteria that impact DDC communication robustness include technical details like speed and communication protocols, ‘M aster planning” for direct digital control (DDC) conveys a number of meanings. In this article, we’ll use two perspectives. The first is a need for a DDC system master plan that should exist for an institution, site, or logical group of buildings. This could be for a college campus, a local K-12 school system, a portfolio of commercial properties, a corporate site, a military base, or a national chain of retail stores. Any logical grouping of facilities maintained and operated by the same group of individuals would benefit from a similar design approach for the control of the HVAC systems in these buildings. The second type is planning that should occur for almost every project. An engineer should not design the DDC system for a specific project without consideration for future expansion, existing DDC systems, preferences, and standardization—and numerous other considerations relative to that project. System architecture Start the project by asking some basic questions: How big is this project? How will future projects tie in to this network? How will this project tie in to the existing network? The project could be a relatively simple Five centrifugal chillers supply cooling to the 52-story vehicle assembly building at NASA’s Kennedy Space Center in Florida. This shows the control panel, starter, and a portion of the compressor for a new parallel driveline. Photo: Johnson Controls Inc. 40 Consulting-Specifying Engineer • APRIL 2008
For optimal viewing of this digital publication, please enable JavaScript and then refresh the page. If you would like to try to load the digital publication without using Flash Player detection, please click here.