30 November 1998
(b) Define your inter-operability needs at each level of the system: supervisory computer,
operator interfaces, field panels, sensors/actuators.
(c) Choose which devices will be capable of sending and receiving messages.
(d) Define the functionality of the communicating devices (based on specifics/ definitions in
the standard -- conformance class and functional groups).
(e) Define networking options. Be aware of the need for inter-networking devices (LANs,
routers, repeaters, segments, gateways, and bridges).
Rule 1: It isn't as simple as saying, "All devices shall conform to BACnetTM standard."
(6) The standard recommends use of a Protocol Implementation Conformance Statement
(PICS) - although recent developments indicate that the PICS may be replaced by a related, but not yet
official, requirement referred to as a BACnetTM Interoperability Building Block (BIBB). The PICS is a
vendor developed document/submittal that defines the BACnetTM specifications supported by the product.
The PICS includes:
(a) Basic Product Information
(b) Conformance Class. A product/device that meets one conformance class meets the
requirements of all other classes with a lower number.
(c) Devices (or Functional Groups) supported (a collection of Object types and the Services
(d) Object types that are supported (18 possible).
(e) Services provided (standard and proprietary) (35 standard ones).
(f) Data Link Layer
Rule 2: Products claimed to be "BACnetTM compatible" require further clarification.
(7) The information provided above is intended as a primer to BACnet. Further information on
BACnet and how to specify BACnet compliant systems is available from ASHRAE as well as the major
control system vendors.
9. PROJECT IMPLEMENTATION.
a. Impact of other design disciplines on control system design. Design of HVAC control systems is
largely driven by decisions on the overall building HVAC mechanical and electrical design. Therefore,
design of the HVAC control system must be incorporated into the overall design process to insure
adequate consideration of the space requirements for the HVAC control system's mechanical and
electrical support services. Early involvement of the HVAC control system designer in the project can
help prevent unfortunate HVAC system design choices that could result in marginally controllable HVAC
systems. The control system designer's involvement should start with the development of the design