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

HVAC Control in the New MillenniumProducer/consumer ModelsNetworks can be grouped into one of two categories; source/destinationor producer/consumer. In a source/destination network, messagesare passed from the source to each destination at a time. Withproducer/consumer, the producer broadcasts the message to every consumerat once. In the network environment, devices use identifierswhich are embedded into each message to determine which messagesthey should consume. The source/destination model does not impactthe baud rate at which data are transmitted—it affects the bandwidth.Since the producer/consumer network transmits a piece of informationonly once, it uses less bandwidth.Redundancy and SecurityController redundancy allows users to specify a backup for anynumber of nodes or connections. Until the backups are needed, thenodes are in listening mode and can take over for a failed device withoutpowering down the system. ControlNet provides physical level redundancy.Guaranteed bandwidth means that critical data should not be lost.In ControlNet a user can configure a temperature sensor to update everyfew milliseconds to control proportional-integral-derivative loops.Most source/destination networks can only send I/O updates asfast as polling the network allows and all nodes are updated at the samerate. The data may come too late for some uses and too often for others.Future DirectionsFuture advancements for ControlNet include conformance testing,reductions in the size and cost of ControlNet chips and real-time I/O(implicit messaging) to ControlNet services over Ethernet.Open systems like ControlNet need products that are tested toensure they are compliant with the network’s specifications. Any networklike Profibus, ControlNet, or Foundation Fieldbus, can haveinteroperability problems and there could be difficulty integrating productsfrom multiple vendors.©2001 by The Fairmont Press, Inc. All rights reserved.