n System reports
n System scheduling
n Archive and analysis of historical data
n Backup of controller databases
n Alarm reporting and analysis
n Trend analysisThe HVAC system is usually managed by a server and operator workstation
using standard operating systems, specific HVAC software applications, GUI
interfaces, and web access. The HVAC control system may be interfaced or
integrated with fire alarm, video surveillance, access control, and lighting con-
trol systems. The HVAC system is also a significant part of a facility manage-
ment and maintenance management system, primarily for tracking, managing,
and optimizing energy use.
System-Level or Building-Level Controllers
The system-level or building-level controllers are networked back to the manage-
ment level. In a campus environment, the building-level controllers are net-
worked via a campus network to the management level of the HVAC control
system. These controllers can manage HVAC equipment directly (typically,
major components such as air-handling units) or indirectly through networked
downstream, lower-level controllers. System level controllers handle the opera-
tions of all downstream field level controllers, collect and maintain data, and
can operate as standalone units if communication is lost to the management
level. System controllers have a peer-to-peer relationship with other controllers.
Field-Level Controllers
Field-level controllers serve building floors, and specific areas, applications,
and devices. Field level controllers are limited controllers in terms of both
functionality and connectivity. Included in this group are DDC controllers,
mechanical controllers, and application-specific controllers.
DDC controllers may support multiple applications, specific device net-
works, or a particular equipment component, such as an air handling unit.
The DDC controller usually has onboard memory, an operating system, and
a database. Both DDC and mechanical controllers perform control through
control algorithms. For example, the controller may measure temperature or
Heating, Ventilating, and Air Conditioning Systems 45