HVAC Control System Overview
A typical HVAC control system consists of functionally and/or geographically distributed controllers capable of controlling various processes throughout a building or group of buildings either from a central host computer or over the Internet from a unit that combines the functions of host computer and web server. Today’s controllers have extensive computational capabilities and can generally control processes, such as off-normal alarms, event-initiated programs, time-based programs, and energy management programs. Through a communication protocol, the controllers share data with each other and with the host computer. Many of today’s controllers also have the intelligence to operate as standalone control systems in the absence of a host computer. Increasingly, HVAC equipment comes equipped with embedded controllers and the IO can be integral with the controller or located remotely.
Depending on the system, configuration can be performed at a workstation, off-line personal computer, HMI terminal, or, increasingly, with web-enabled devices, including laptops and mobile devices. The control network typically handles communications, with transmission over shielded twisted pair copper cable, direct dial telephone lines, and/or fiber optic cable, although wireless connections are becoming common.
ARC’s relatively narrow definition of HVAC systems focuses on the core hardware and software technologies, plus the project and maintenance-related services provided by the HVAC supplier. Hardware begins at the IO level and extends to controllers, host computers, communications networks, networking equipment, and end products with embedded con-trol. We exclude non-intelligent end products, such as fans, pumps, chillers, and boilers. Software includes basic embedded controller software and a range of bundled software, including HMI, programming, energy mainte-nance/management, advanced control, and simulation software. The ser-vices segment includes project and maintenance services provided by direct employees of HVAC suppliers. It excludes indirect contributions as well as revenues attributable to multi-year maintenance/performance contracts.
HVAC control systems are one of the four key segments that comprise the overall building automation system (BAS) industry. The remaining three segments are security-access, fire & life safety, and lighting control systems. ARC covers these segments in detail in separate reports. In some buildings, two or more of these systems may be integrated. Therefore, they may share some of the same controllers, network equipment, workstations/HMI, and cable infrastructure.
HVAC Control System Hardware
Due to the increasingly amorphous nature of evolving HVAC architecture, as well as the expanding business models of HVAC suppliers, ARC has made an effort to narrow its definition of HVAC. Hardware specifically includes controllers, host computers and web servers, work stations, IO, communications networks, and end products with embedded control. ARC does not include the chillers, evaporators, valves, actuators, cabling, or remote sensors that are often connected to controllers.
HVAC Control System Software
A variety of software types are typically included in full-scale HVAC control systems. HVAC software includes embedded controller software, web server-based applications, and a wide range of software that is typically sold bundled with a system. These components may include standalone human machine interface (HMI) software, as well as programming and configuration software used to set up the system. Control software is used to execute physical commands, such as turning a chiller on/off. Analytics and simulation software may be used to analyze a facility’s energy usage, identify ways to further optimize energy consumption, simulate the energy profile under different facility configurations, or monitor the health and efficiency of HVAC equipment by comparing the current per-formance of an asset to its historical averages.
Aside from performing human interface functions, HMI software can also perform other functions, such as IO communications. HMI software typical-ly resides on the host computer or workstation, and increasingly in the HMI unit itself. Control software typically resides in the controllers and performs basic control functions.
Third party system integrators may also be used to install and configure the software provided by the HVAC control systems supplier.
HVAC Control System Services
Services are an important component for both intelligent HVAC system providers and their third party distribution and integration partners. The services category of HVAC generally includes both project services and maintenance services. Typical project services include project definition, process engineering, application software development, checkout and startup services, and project management. Maintenance services include all aftermarket services provided by the supplier's field organization. These can include not only maintenance, but also engineering, programming, training, and network management services. Multi-year, contract-based services, such as facilities management and energy management agree-ments, are excluded from this report.
This study only includes services provided by direct employees of HVAC suppliers. For example, project services performed for HVAC suppliers by distributors and authorized system integrators (SI) are excluded. Project services incurred during system implementation by building owners, con-sultants, AEC, and independent SIs are also excluded. Only services ren-dered during the 2011 base year are included.
Key HVAC Control System Network Types
As integration with other building automation systems becomes more important, HVAC control systems are migrating from the traditional use of serial networks to more robust interfaces. Serial interfaces, such as RS232 and RS485, remain popular options for interfacing readers to higher-level controllers, but Ethernet, fiber, and even wireless or wireless mesh options are also gaining popularity.
Network protocols employed with intelligent HVAC control systems can range from serial building automation-oriented interfaces, such as BACnet or LonWorks, to more generic computing protocols like TCP/IP over Ethernet. Migration in this category is a primary indicator of the move toward more IP-based building automation and HVAC control systems.
Web-Based vs. Non Web-based
Availability of an Internet interface and onboard web server in a HVAC control device is a key enabler behind remote monitoring and increasingly sophisticated analytical techniques. These systems use web-enabled hardware and associated software to communicate with users via a web browser. Administrators and system operators can use the web interface for centralized command and control, as well as for manual local commands and extensive database reporting and analysis. HVAC information is downloaded to controllers, subcontrollers, readers, and other IP-enabled devices to enable localized access.
Standalone vs. Integrated
This segmentation looks at whether the intelligent HVAC control systems are integrated with other building control systems – such as lighting, physical security and access control, enterprise asset management, and others - or not. This does not imply common responsibility, i.e. that the same personnel are responsible for the control system, but rather whether the different types of systems communicate bidirectionally with one another, can share common software code, databases, or computing platforms, as noted in the next segmentation.