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

Computer Networks and Securitymost basic BACnet device. This data exchange capability should besupported by suppliers of BACnet systems, as well as suppliers ofBACnet gateways. A PC workstation performs data exchange by checkingthe information that is contained in BACnet controllers and changingsetpoints and other values on these controllers. This is done with aseries of BACnet functions or services called Read Property and WriteProperty.This interoperable capability allows a workstation to display temperature,pressures, and other values. It also allows the operator tochange setpoints, and store data for historical trending.BACnet supports different network methods including Ethernet.Read data are used for viewing on graphics and write are used forchanging setpoints. In BACnet the workstation needs to use the Read(Initiate) and Write (Execute) Services in Clauses 15.5 and 15.8 of theASHRAE Standard 135-95. It uses these services to communicate withBACnet objects in the internetwork.These objects are also known as points and to perform a function,a point or object list is used to show how an object is related to a servicein the BACnet internetwork.Legacy systems need a gateway to connect the BACnet and thelegacy system. The gateway will transfer alarm, trend, schedule, andpoint data between BACnet and the legacy system.BACnet Interoperable FunctionsData exchange between devices such as PC workstations andbuilding controllers is the most basic interoperable function. It involvesthe viewing or reading of data as well as making changes or writing tothis data.In BACnet, data are modeled as objects that have properties. Analarm and event function allows the exchange of alarm information.This function can be used to trigger a control action, or an operatoroverride. A set of functions allows the editing and creation of scheduleson a BACnet PC workstation.A network management function provides the ability to managethe devices on the network. This includes monitoring for a loss of communicationand coordinating the time settings of the clocks in each controller.©2001 by The Fairmont Press, Inc. All rights reserved.