Akanksha Inamdar
6 min readJun 22, 2022



HVAC SYSTEMS (Heating, Ventilating and Air-Conditioning)

HVAC systems are active and more power consumed subsystems in BAS. Due to the great impact of HVAC Systems on power and energy consumption, knowing the structure and operation of HVAC systems is becoming important. Energy efficiency and indoor climate conditions are most important goals of designing HVAC systems. Almost 50% of the total used energy in buildings is consumed by HVAC systems. So, the selection of control method and protocols is very important in case of HVAC.

Common HVAC communication protocols

Common use cases for HVAC protocols include lighting, metering, air filtering, shutter control, process control, home automation, device monitoring, heating, ventilation, remote control, transportation, outdoor lighting, air conditioning, remote access, audio visual control and energy management.


The Building Automation and Control Network (BACnet) protocol is the most commonly used communication protocol for BASs. It is the de-facto standard for building automation in more than 30 countries. Maintained by the American Society of Heating, Refrigerating and Air Conditioning Engineers (ASHRAE) Standing Standard Project Committee 135, BACnet is easy to set up, supported by more than 800 manufacturers and requires no license to use.

ASHRAE is the definitive organization dedicated to the development and implementation of HVAC technologies.


The terms Lon, LonTalk and LonWorks are sometimes used ambiguously. “Lon” stands for local operating network and LonWorks is a distributed control network system that uses the proprietary LonTalk communication protocol (ANSI/CEA 709.1 and IEEE 1473-L).

The main disadvantage of LonWorks is that it requires the use of a proprietary dedicated controller, the neuron chip. Originally designed by Echelon as a general communication platform for smart devices, it was a popular BAS tool and still has a wide following but the cost is prohibitive for smaller projects. LonMark International administers the standard and provides device certification. LonWorks requires a license to use, paid for by manufacturers.

BACnet Devices can all Share a Common LAN Selected from the Four Approved BACnet Choices


BACnet (Building Automation Control network) and LON (Local Operating Network) are most popular protocols used for BAS. BACnet was developed by a committee formed by the American Society of Heating, Refrigerating and Air-Conditioning Engineers (ASHRAE). LonWorks was designed by Echelon Corporation for use with virtually all types of control systems. BACnet was designed specifically for HVAC control and BAS. This is an important distinction from LonWorks, which was not designed for complex system-level devices, nor was it designed specifically to meet the needs of the HVAC/ BAS industry.

BACnet developed specifically for Building Services, defines how all the elements of the Building Management System work together. Uniquely, BACnet is applicable to every kind of building system: HVAC, Security, Access Control, Fire, Maintenance, Lighting etc. It offers compatibility with devices made by different vendors as well as with future generations of systems. Another important benefit of BACnet is that it supports a wider range of communication transports than LonWorks.

BACnet can communicate with different LAN technology for transporting BACnet application messages via BACnet routers, providing significant flexibility in choosing the best fit for each situation. Its high-speed capabilities provide room for future growth, while its flexibility in networking options allows it to be used in even small zone controller subnets. Ethernet capability allows connection directly to wide area networks that link remote building sites as well as multiple local area networks.

Major Difference between BACnet and LONWorks


Modbus is a serial communications protocol (IEC 61158) originally developed by Modicon and now supported by Schneider Electric. It is the most widely used communication protocol for industrial electronics devices with millions of nodes globally. Modbus is considered a de-facto standard for industrial automation and can be used in BASs, particularly to connect electronic equipment. There are no license fees to use Modbus.


The DALI (stands for digital addressable lighting interface) communication protocol is used exclusively for lighting applications, for example to integrate building systems with emergency lighting applications. DALI supports bi-directional communication. It is an International Electrotechnical Commission (IEC) 62386 standard administered by the DALI Alliance (DiiA). Members may use the protocol for free; non-members must pay a license fee.


M-Bus is a European standard (EN 13757–2, EN 13757–3 and EN 13757–4) designed principally for the remote reading of consumption meters like air conditioning, water, gas and electricity meters in HVAC systems. Based on M-Bus, the Open Metering System (OMS) integrates all media across Europe under one standard. M-Bus does not require a license to use.


The Konnex (KNX) protocol is popular for use in European BASs but KNX complies with numerous global standards including ISO/IEC 14543–3 and ANSI/ASHRAE 135. In Europe, sometimes it is called the European Installation Bus (EIB). KNX has a tree topology, suitable for use in large networks. BMSs typically use KNX, while BASs tend to use BACnet. The KNX Association supports the standard and administers product certification processes. It requires a license to use, paid for by manufacturers.


OPC Unified Architecture (OPC UA) is a widely adopted de-facto standard for data communication between devices from different vendors. OPC stands for Open Platform Communications. It provides connectivity in building automation between different protocols, for example those used by standalone security, lighting and heating applications, and complex HVAC systems. The OPC Foundation provides developers with tools to build and test applications, and administers compliance certificates. OPC UA requires a license to use, paid for by manufacturers.


EnOcean is a wireless communication protocol (ISO/IEC 14543–3–10) administered by the EnOcean Alliance. It specifies energy-harvesting techniques for the development of easy-to-use, economical and environmentally friendly devices for building automation applications like lighting control. EnOcean sensors are entirely self-powered. EnOcean is a non-profit but a license is required, paid for by manufacturers.


The W3C Web Services Architecture Working Group maintains standards, for example BACnet/WS, for web services architecture that allows devices to communicate over the internet.


ZigBee is a wireless standard (IEEE 802.15.4) developed by the ZigBee Alliance and currently administered by the Connectivity Standards Alliance (CSA). ZigBee is distinguished by its mesh network, which makes it very reliable. It is used extensively in sensor networks for home automation and commercial projects and has a range of up to 300 ft. A fee is required for commercial use.

Clipsal C-Bus

Clipsal C-Bus is an open protocol developed for use mainly in home automation to control lighting, audio visual and other electrical devices. It is administered by the C-Bus Enabled Program, which provides certification for commercial products and accreditation for developers and vendors. The C-Bus model source code is open source (since 2009) but vendors may charge license fees for their products.


Developed by Panasonic, high-definition power line communication (HD-PLC) is a wired communication technology that uses a high-frequency band over existing cables like power lines, phone lines and coaxial cables. Developed to address challenges in IIoT systems, HD-PLC is used in numerous industries, including smart HVAC systems.

Numerous organizations, including LonMark International, have adopted HD-PLC Multi-Hop as their wireline channel standard. The HD-PLC Alliance, a private organization founded in 2007, maintains the standard (IEEE 1901 and ANSI/CTA 709.8). HD-PLC is open technology but manufacturers have to be a member of the Alliance to use the HD-PLC logo on their products.


A review of different HVAC Communication protocols for energy efficiency and comfort in buildings is presented. BACnet and LonTalk protocols are discussed with their merits and demerits. The comparison of two main protocols says that the BACnet is more superior than LonTalk protocol. BACnet is a unique object-oriented model for data representation makes it the most advanced protocol of its kind, and provides maximum flexibility than LonTalk.