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

Computer Networks and Securityand fewer options.BACnet provides an alternative since there are a set of rules thatallow the major components of a system, even if they are manufacturedby different vendors, to function together. They can interoperate. Thisinteroperability promises to provide competitive pricing, more choicesfor products and service, and the ability to even operate two differentsystems with a single computer station.BACnet is well documented and robust in design. It has the featuresneeded and has headroom for the future. Manufacturers that seeBACnet as an opportunity will adopt it.The complete BACnet standard covers about seven different datalink layer models. But, a BACnet compliant product on an ARCNET leveland a BACnet compliant product on a sensor level does not establishinteroperability. If BACnet is not used internally in some new products,then a gateway will be required and that gateway can act as a firewall.A firewall might be used by an equipment manufacturer of chillersand boilers, to protect the equipment’s internal safety logic and criticalcontrol algorithms. If this logic is compromised, it can create a warrantyor liability issue.At minimal compliance, it does not make much difference whatkind of system or what communications protocols are used in collectingdata or in issuing field commands. What is important, is what data aregathered from any given piece of equipment, and how that data arestructured. Using this strategy and basic network tools, informationgathered from multiple field systems can be presented as a single system,to multiple users.One problem with a BACnet minimum level of compliance, is thatit is not easy to make programming changes. In most cases, programmingmust be done at the controller connected to the field equipment.Full compliance allows programming as well as monitoring andcontrol functions at the user level. Most manufacturers have offeredBACnet compatibility at the minimum compliance level.Conformance ClassificationsThe BACnet standard defines conformance classes which aregroups of functions and capabilities needed to allow specific levels inBACnet communications. The protocol’s hierarchy of conformance©2001 by The Fairmont Press, Inc. All rights reserved.