Building automation (DDC) controllers for HVAC and other building systems · BACnet objects, device and network numbering, MS/TP, Ethernet and BACnet/IP links, BBMDs and change-of-value reporting, plus the deadband, setback, scheduling and optimum-start control capabilities that energy codes check
A building automation controller, also called a DDC controller, reads sensor inputs, runs control sequences and drives outputs such as fan speed, valves and pumps in a building. It exchanges data with other controllers and with a central automation server. Ask three things first: which equipment and sequences it must control, which communication protocol and network it must join (for example native BACnet on MS/TP or IP), and which energy-code control capabilities the design must show.
Programmable controllers for building HVAC and related systems, their input/output points and their network communication. Thermostats are covered where energy-code requirements apply to them. Industrial PLCs, process control systems and network routers have their own pages except where compared.
CNFX editorial research · Sources checked October 12, 2026 · 4 sources
In an LLNL article for large campuses, Masica and Tom describe BACnet as a protocol designed for interoperability among building automation vendors. They write that specifying native BACnet in the design phase widens the range of vendors and equipment that can be used, and lets equipment be added or replaced while staying compatible with the existing system. DDC systems in buildings may communicate with a central server whose software provides configuration, user interface, reporting, alarming and supervisory control. [1]
BACnet packages a controller's data into documented objects. In their example, an outdoor air temperature sensor wired to a controller becomes an Analog Input object with properties such as Present Value, Units and Reliability, which other vendors' devices can discover and read. The controller itself is a Device object with a Device Name and Device ID. Object names and IDs must be unique within each device, and device names and IDs unique within the system. [1]
The article lists the link types BACnet supports: MS/TP (RS-485 multi-drop) and PTP (RS-232) serial links, ARCNET and LonTalk, Ethernet, and BACnet/IP across a backbone between buildings. Every subnet gets a network number from 1 to 65,534. On MS/TP or ARCNET the hardware address is one byte (0–254), set by DIP or rotary switches. BACnet routers connect networks. Because campus IP routers block broadcasts, what the article calls BACnet Broadcast Messaging Devices (BBMDs) pass the broadcasts on. Change-of-value (COV) reporting is an optional feature in which a device is notified when a value changes by more than a configured amount. [1]
The authors warn that circular routes between BACnet routers can flood a network with duplicate broadcasts, and that inconsistent network numbers cause communication problems when separately installed systems are later joined. They recommend a campus-wide numbering plan applied to every project, even before systems are interconnected. [1]
Give the supplier the equipment and sequences to be controlled, the input and output point list, the protocol and link type (for example BACnet MS/TP or BACnet/IP), the device and network numbering plan, the front-end or server it must report to, any optional services needed (such as COV), the supply voltage, enclosure and operating environment, and the codes that apply.
02
Check the control capabilities energy codes ask for
A 2011 DOE Building Energy Codes Program guide for plan examiners and inspectors explains HVAC control requirements in the 2009 and 2012 IECC and ASHRAE Standard 90.1-2007 and 2010. Zone temperature controls must provide a deadband of 5 °F in which no heating or cooling occurs, for example 70 °F heating and 75 °F cooling setpoints. Setback controls must be able to set back unoccupied temperatures to 55 °F for heating and 85 °F or 90 °F for cooling. [2]
Under the same guide, programmable thermostats must handle different programs for different daily occupancy schedules, retain information through a 10-hour power outage and offer a temporary manual override. Optimum start controls vary the start time so that each space reaches setpoint just before scheduled occupancy; systems below 10,000 CFM may be exempt. Where a DDC system is specified, inspectors look for a supply fan pressure reset strategy, with the DDC controller modulating fan speed to hold the duct static pressure setpoint. Its compliance checks include confirming that the building automation system specified in the approved design is installed and operational. [2]
These requirements come from code editions published in 2007–2012. Confirm the edition adopted where the building is located.
03
Match controller class, point count and network link
Automated Logic's ZN253 shows a zone-level controller: a programmable native BACnet Advanced Application Controller (AAC) for a single zone, with 10 points — 2 binary outputs, 5 universal inputs and 3 analogue outputs for modulating valves or dampers — communicating on an EIA-485 LAN over BACnet MS/TP or BACnet over ARCNET, for unit ventilators, packaged HVAC, fan coils, lighting and exhaust fans. [3]
Its OptiFlex OF683-E2 advanced application controller instead connects over BACnet/IP through dual Ethernet ports that allow daisy-chaining with Spanning Tree Protocol, ships with pre-engineered control algorithms that Automated Logic states comply with ASHRAE Guideline 36, stores programs and trend history in non-volatile memory without batteries, keeps its real-time clock for at least three days on a capacitor after power loss, and has a USB port for local updates. [4]
Editorial calculation: a fan coil needing 2 valve or damper signals, 4 sensor inputs and 2 on/off outputs uses 8 of the ZN253's 10 points (3 AO, 5 UI, 2 BO), leaving 1 analogue output and 1 universal input spare; count points per output type, not just in total. [3]
04
Trace what each part of the controller does
This is a functional reference built from the sources cited; it is not one maker's design.
Fill the specification fields with values for your project
A controller quotation needs values for your building. The table explains each field, gives published information where a reviewed source states it, and says what to ask the supplier for.
Field
What it means and published information
Ask the supplier for
Protocol
Native BACnet aids multi-vendor interoperability. [1]
Send the point list, network and code data together
Paste it into your enquiry below or into an email to a maker, then replace every bracket.
Equipment: [systems and sequences]
Points: [inputs; outputs; types]
Protocol: [BACnet MS/TP / IP / other]
Numbering: [device and network plan]
Front end: [server or software]
Power and environment: [voltage; enclosure; temperature]
Codes: [energy code edition]
Explore company information and manufacturing capabilities, then discuss the scope of your project with a relevant supplier.
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Compiled and source-reviewed by the CNFX editorial team.
Published product pages show what a company offers, not tested performance. Confirm the legal seller, factory and scope for your order. How we source and review
· Page last updated 13 October 2026
Buyer questions
What does a building automation controller do?
It runs direct digital control sequences, for example modulating supply fan speed to hold a duct static pressure setpoint, and shares data with other controllers and a central server. [2][1]
Why does BACnet numbering matter?
Duplicate or inconsistent device and network numbers cause communication problems when systems are joined, so LLNL authors recommend a campus-wide numbering plan. [1]
What deadband do energy codes require?
The DOE guide states a 5 °F deadband between heating and cooling setpoints under the 2009/2012 IECC and ASHRAE 90.1-2007/2010. [2]
How many I/O points does a zone controller have?
Automated Logic's ZN253 zone controller has 10: 2 binary outputs, 5 universal inputs and 3 analogue outputs, on BACnet MS/TP or ARCNET. [3]
Sources and what still needs a direct check
Sources checked 2026-10-12. The LLNL article explains BACnet for large campuses; the DOE guide summarises energy-code HVAC control requirements for the code editions it names.
