HVAC Control in the New Millennium.pdf - HVAC.Amickracing

HVAC Control in the New MillenniumSoftware TrendsBuilding system software is available from multiple sources today.Much of how this software should work is based upon the operation ofsuch software as Microsoft Windows. This creates a demand for softwarethat has a Windows look and feel for programming and monitoring.This software must be mouse driven with a point and click graphicalinterface. Beyond ease of use, systems are in demand that will doalarm dial outs to pagers and telephones with voice synthesis. ExpandedPC-based operator interfaces may even include features likepreventive maintenance and on-line diagnostics.Nonvolatile memory storage to avoid program loss has evolvedfrom the early minicomputer years. The technology continues to improve.The early minicomputer approach used Uninterruptible PowerSupplies (UPS) to eliminate the effects of power failures. This approachwas costly, but most computer hardware was costly then.The first microprocessor-based systems used battery backup withRandom Access Memory (RAM). This was as effective as the battery.Then, Electrically Erasable Programmable Read Only Memory(EEPROM) chips were used. These were nonvolatile chips that did notrequire either a battery on power to hold memory. This was more effectiveand cost effective, but the limited read/write capacity of the chipbecome a problem as programs and data increased. The more recentcontrollers use flash memory. This is a type of nonvolatile memory andhas no limitation on read/write capability.Control TrendsGeneral-purpose controllers tend to use the same hardware, andoperate at the same level of architecture, but they implement differentcontrol sequences. These sequences include such expanded applicationsas start/stop of non-HVAC loads and the on/off control of lighting andother electrical equipment.In these applications there are greater requirements for controlintegration due to the distributed nature of the control system. At thislevel, as well as the building-wide level, peer-to-peer controllers aremost common.General-purpose controllers provide full local control requirementsand can integrate with both the building-wide controller and the appro-©2001 by The Fairmont Press, Inc. All rights reserved.