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Title:
REDUNDANT HEATING, VENTILATION, AND AIR CONDITIONING CONTROL SYSTEM
Document Type and Number:
WIPO Patent Application WO/2016/126270
Kind Code:
A1
Abstract:
Redundant heating, ventilation, and air conditioning (HVAC) control systems are described herein. One redundant HVAC control system includes an operator workstation and a first BACnet communication connection connected thereto, a first HVAC system controller running a first instance of a control application and a second HVAC system controller each HVAC system controller connected to a second BACnet connection. The first HVAC system controller and a second HVAC system controller can communicate with the operator workstation via the first BACnet communication connection and the second HVAC system controller is configured to execute a set of instructions to monitor the health of the first controller via the second BACnet connection to identify if the second HVAC system controller has to take over for the first HVAC system controller by initiating control of the HVAC system via a second instance of a control application run by the second HVAC system controller.

Inventors:
KOMANDURU VAMSI KRISHNA (US)
MAKAM ANKITH (US)
Application Number:
PCT/US2015/014894
Publication Date:
August 11, 2016
Filing Date:
February 06, 2015
Export Citation:
Click for automatic bibliography generation   Help
Assignee:
HONEYWELL INT INC (US)
International Classes:
F24F11/00; F24F11/02
Foreign References:
JP2011247516A2011-12-08
KR100940489B12010-02-04
KR100892314B12009-04-08
KR100773803B12007-11-06
US20130242798A12013-09-19
Attorney, Agent or Firm:
BERGER, Mark (Patent Services M/S AB/2BP.O. Box 2245,101 Columbia Roa, Morristown New Jersey Jersey -22, US)
Download PDF:
Claims:
Claims

What is claimed:

1 . A redundant heating, ventilation, and air conditioning (HVAC) control system, comprising:

an operator workstation and a first BACnet communication connection connected thereto;

a first HVAC system controller running a first instance of a control application and a second HVAC system controller each HVAC system controller connected to a second BACnet connection;

wherein the first HVAC system controller and a second HVAC system controller can communicate with the operator workstation via the first BACnet communication connection; and

wherein the second HVAC system controller is configured to execute a set of instructions to monitor the health of the first controller via the second BACnet connection to identify if the second HVAC system controller has to take over for the first HVAC system controller by initiating control of the HVAC system via a second instance of a control application run by the second HVAC system controller.

2. The redundant HVAC control system of claim 1 , wherein the first HVAC system controller is configured to execute a set of instructions to monitor the health of the second controller to identify if the first HVAC system controller has to take over for the second HVAC system controller by initiating control of the HVAC system via the first instance of the control application.

3. The redundant HVAC control system of claim 1 , wherein the first HVAC system controller is configured to execute a set of instructions to synchronize data received by the second controller in case the first HVAC system controller has to take over for the second HVAC system controller by initiating control of the HVAC system by processing the data with the first instance of the control application.

4. The redundant HVAC control system of claim 1 , wherein the second HVAC system controller is configured to execute a set of instructions to synchronize data received by the first controller in case the second HVAC system controller has to take over for the first HVAC system controller by initiating control of the HVAC system by processing the data with the second instance of the control application.

5. The redundant HVAC control system of claim 1 , wherein the first instance of the control application running on the first system controller and the second instance of the control application on the second system controller are running in parallel.

6. The redundant HVAC control system of claim 1 , wherein the first BACnet communication connection is a BACnet Internet protocol (IP) communication network.

7. The redundant HVAC control system of claim 6, wherein the second BACnet connection is a BACnet master slave token passing (MSTP) connection.

8. The redundant HVAC control system of claim 1 , wherein the second BACnet connection is a BACnet master slave token passing (MSTP) connection.

9. A redundant heating, ventilation, and air conditioning (HVAC) control system, comprising:

an operator workstation and a first BACnet communication connection connected thereto; a first HVAC system controller running a first instance of a control application and a second HVAC system controller each HVAC system controller connected to a second BACnet connection;

wherein the first HVAC system controller and a second HVAC system controller can communicate with the operator workstation via the first BACnet communication connection;

wherein the second HVAC system controller is configured to execute a set of instructions to monitor the health of the first controller via the second BACnet connection to identify if the second HVAC system controller has to take over for the first HVAC system controller by initiating control of the HVAC system via a second instance of a control application run by the second HVAC system controller; and

at least one input or output module that is in communication with the first and second HVAC system controllers.

10. The redundant HVAC control system of claim 9, wherein the first BACnet communication connection is a wireless connection between the first and second HVAC system controllers and the operator workstation.

1 1 . The redundant HVAC control system of claim 9, wherein the system further includes executable instructions to provide a status of at least one controller at the operator workstation such that the operator can identify the status.

12. The redundant HVAC control system of claim 1 1 , wherein the system further includes executable instructions to allow the operator to initiate an action in response to the one or more identified status.

13. The redundant HVAC control system of claim 9, wherein the system further includes executable instructions to provide a failure notification such that the operator can identify that a failure has occurred.

14. The redundant HVAC control system of claim 13, wherein the system further includes executable instructions to allow the operator to initiate an action response to the failure notification.

15. The redundant HVAC control system of claim 1 1 , wherein a BACnet protocol is used to communicate a status of at least one of the first and second controller.

16. A redundant heating, ventilation, and air conditioning (HVAC) control system, comprising:

an operator workstation and a BACnet Internet protocol communication connection connected thereto;

a first HVAC system controller running a first instance of a control application and a second HVAC system controller each HVAC system controller connected to a BACnet master slave token passing (MSTP) connection;

wherein the first HVAC system controller and a second HVAC system controller can communicate with the operator workstation via the BACnet IP communication network;

wherein the second HVAC system controller is configured to execute a set of instructions to monitor the health of the first controller via the BACnet MSTP connection to identify if the second HVAC system controller has to take over for the first HVAC system controller by initiating control of the HVAC system via a second instance of a control application run by the second HVAC system controller.

17. The redundant HVAC control system of claim 16, wherein first and second HVAC system controllers are located remotely from each other.

18. The redundant HVAC control system of claim 16, wherein at least one of the first HVAC system controller, the second HVAC system controller, and the operator workstation has a separate power supply from the rest of the control system.

19. The redundant HVAC control system of claim 18, wherein the computer readable instructions are executable by the processor to execute, by the second HVAC system controller upon the failure of the first HVAC system controller, the set of instructions of the control application using state information obtained from the first or second HVAC system controllers.

20. The computer readable medium of claim 16, wherein the computer readable instructions are executable by the processor to send a status of the first and second HVAC system controllers to an operator workstation of the HVAC system.

Description:
REDUNDANT HEATING, VENTILATION, AND AIR CONDITIONING

CONTROL SYSTEM

Technical Field

The present disclosure relates to redundant heating, ventilation, and air conditioning control systems.

Background

A heating, ventilation, and air conditioning (HVAC) system can be used to control the climate within a facility (e.g., building). For example, a control system (e.g., controller) of a HVAC system can be used to control the operation of the HVAC system (e.g., the operation of the components of the HVAC system) in order to control the air temperature, humidity, and/or air quality of the facility.

A HVAC system may include redundancies to maintain control over the operation of the HVAC system in the event of a failure of the HVAC system. For example, a HVAC system may include a specially designed redundant (e.g., backup) control system to ensure that the HVAC system continues to operate in the event of a controller failure in the HVAC system.

Previous redundant control systems may be designed to recover and continue the operation of the HVAC system within a very short time (e.g., a few milliseconds) from when the failure occurs. Such high speed redundant control systems, however, can be expensive, and may not be compatible with an existing HVAC system (e.g., as some HVAC systems are older, their legacy hardware and/or software may be incompatible with newer redundancy solutions). For example, such high speed redundant control systems may be designed from scratch, may include complex high speed processors, may need to be separately installed in the existing HVAC system, and/or may use a large amount of network bandwidth in the HVAC system. Brief Description of the Drawings

Figure 1 illustrates a channel redundancy architecture for HVAC control systems according to one or more embodiments of the present disclosure.

Figure 2 illustrates a BACnet MSTP failure scenario utilizing a channel redundancy HVAC control system according to one or more embodiments of the present disclosure.

Figure 3 illustrates a BACnet IP failure scenario in channel redundancy HVAC control system according to one or more

embodiments of the present disclosure.

Figure 4 illustrates both a BACnet IP and BACnet MSTP failure scenario in a channel redundancy HVAC control system according to one or more embodiments of the present disclosure.

Detailed Description

Redundant heating, ventilation, and air conditioning (HVAC) control systems are described herein. One redundant HVAC control system includes an operator workstation and a first BACnet

communication connection connected thereto, a first HVAC system controller running a first instance of a control application and a second HVAC system controller each HVAC system controller connected to a second BACnet connection. The first HVAC system controller and a second HVAC system controller can communicate with the operator workstation via the first BACnet communication connection and the second HVAC system controller is configured to execute a set of instructions to monitor the health of the first controller via the second BACnet connection to identify if the second HVAC system controller has to take over for the first HVAC system controller by initiating control of the HVAC system via a second instance of a control application run by the second HVAC system controller. Typical HVAC building management systems containing components such as an operator workstation, supervisory plant controller devices, unitary controller devices, and/or input and/or output (I/O) modules, communicate with an operator workstation and/or with other devices using BACnet (a data communication protocol for building automation and control networks) over an Internet protocol (IP) network. The operator monitors and controls all devices and equipment using the workstation. The reliability of monitoring and/or controlling the devices and equipment depends on the availability of one or more supervisory plant controller devices over the BACnet IP network.

Various controllers also communicate with each other using the BACnet over IP network. These controllers share the data which are required to run various control algorithms.

In case of any failures in the IP network, the operator may be able to identify the failure but the system will be down until the issue is resolved. Also, the IP network failure detection happens only when the operator identifies the failure status at the operator workstation.

If the IP network, wired or wireless (e.g., Wi-Fi, VLAN, etc.), fails, the system and/or user may face the following problems:

1 ) The operator cannot make any changes to the plant controllers or down the line connected equipment thereby running the system with old values which are not intended;

2) Monitoring the system is not possible due to missing alarms from the devices;

3) Control algorithms may drive unintended outputs due to nonavailability of data shared from various devices across the network;

4) The system may not be able to run effective schedules such pre- cooling or heating or exceptions that may need to run from the devices in regular schedules as writing to these devices may not be possible;

and/or 5) The user may choose to put the equipment to manual mode due to monitoring and controlling doesn't happen thereby potentially making the system inefficient.

The above issues can lead to system down time, as down time depends on the failure detection and rectification of the issue causing the failure. This downtime may cause a non-comfort environment for the building occupants and/or in critical applications where an environmental condition such as temperature, humidity, and/or air pressure needs to be maintained without any deviation and where a failure will potentially cause a production loss to the user.

Possible scenarios for network failures, include:

1 ) Controller is switched off or no power provided to the controller

2) Network failure

3) Controller enters into a non-recoverable state, such as continuous restart or device hang.

To avoid this down time, various systems provide redundant solutions where another controller will be running as a "hot backup" and takes the role of primary controller when the original device is down. Some redundant systems work on devices checking the health of each other using a heartbeat or other mechanism and also keep synchronizing the data between each other. To perform this synchronization and heartbeat check, redundant systems use a dedicated channel between them; however, if this channel breaks or there are any disturbances in this dedicated channel, making the system potentially unreliable for some applications.

Redundant HVAC control systems in accordance with the present disclosure may be less expensive than previous (e.g., high speed) redundant HVAC control systems, and may be compatible with an existing HVAC system (e.g., with the existing/legacy controllers of the HVAC system). For example, redundant HVAC control systems in accordance with the present disclosure may not need to be separately installed in an existing HVAC system, may be compatible with the existing hardware and software of the existing HVAC system, and/or may use a lower amount of network bandwidth than previous redundant HVAC control systems.

In some situations, redundant HVAC control systems in accordance with the present disclosure may not be able to recover and continue the operation of a HVAC system as quickly as previous (e.g., high speed) redundant HVAC control systems. For example, redundant HVAC control systems in accordance with the present disclosure may recover and continue the operation of a HVAC system within a few seconds (e.g., less than five seconds) from when a failure (e.g., a controller failure) occurs in the HVAC system. Such a response time, however, may be appropriate for (e.g., within the acceptable limits of) non-critical (e.g., normal and/or standard) HVAC systems, such as HVAC systems of office buildings, hospitals, and shopping malls, among other facilities.

In the following detailed description, reference is made to the accompanying drawings that form a part hereof. The drawings show by way of illustration how one or more embodiments of the disclosure may be practiced.

These embodiments are described in sufficient detail to enable those of ordinary skill in the art to practice one or more embodiments of this disclosure. It is to be understood that other embodiments may be utilized and that mechanical, electrical, and/or process changes may be made without departing from the scope of the present disclosure.

As will be appreciated, elements shown in the various

embodiments herein can be added, exchanged, combined, and/or eliminated so as to provide a number of additional embodiments of the present disclosure. The proportion and the relative scale of the elements provided in the figures are intended to illustrate the embodiments of the present disclosure, and should not be taken in a limiting sense.

The figures herein follow a numbering convention in which the first digit or digits correspond to the drawing figure number and the remaining digits identify an element or component in the drawing. Similar elements or components between different figures may be identified by the use of similar digits.

As used herein, "a" or "a number of" something can refer to one or more such things. For example, "a number of controllers" can refer to one or more controllers.

Figure 1 illustrates a channel redundancy architecture for a HVAC control system according to one or more embodiments of the present disclosure. As shown in Figure 1 , redundant HVAC control system 100 can include a first (e.g., active) HVAC system controller 1 10, a second (e.g., standby) HVAC system controller 120, and an operator workstation 130.

Active controller 1 10 and standby controller 120 can be, for example, direct digital control (DDC) controllers. Operator workstation 130 can be, for example, a computing device, such as a laptop computer, desktop computer, or mobile device (e.g., smart phone, tablet, PDA, etc.). However, embodiments of the present disclosure are not limited to a particular type of controller or workstation.

As shown in Figure 1 , operator workstation 130 can be coupled to (e.g., communicate with) active controller 1 10 and standby controller 120 via a connection to a network 126, among potentially other networks.

Further, active controller 1 10 and standby controller 120 can be coupled (e.g., communicate) via a direct connection or network connection 128, as illustrated in Figure 1 . The first HVAC system controller can be configured to execute a set of instructions to monitor the health of the second controller to identify if the first HVAC system controller has to take over for the second HVAC system controller by initiating control of the HVAC system via the first control application, for example, via network 128 or other suitable direct or indirect connection between the first and second controller.

Networks 126 and 128 can be wired or wireless networks of HVAC control system 100. For instance, in the embodiment illustrated in Figure 1 , network 128 can be a master slave token passing (MSTP) network, and network 126 can be Internet protocol (IP) networks. However, embodiments of the present disclosure are not limited to a particular type of network for either network 126 or 128.

As used herein, a "network" (e.g., networks 126 and 128) can provide a communication system that directly or indirectly links two or more computers and/or peripheral devices and allows users to access resources on other computing devices and exchange messages with other users.

A network can allow users to share resources on their own systems with other network users and to access information on centrally located systems or on systems that are located at remote locations. For example, networks 126 and 128 can tie a number of computing devices together to form a distributed control network.

A network may provide connections to the Internet and/or to the networks of other entities (e.g., organizations, institutions, etc.). Users may interact with network-enabled software applications to make a network request, such as to get a file, print on a network printer, or actuate a device. Applications may also communicate with network management software, which can interact with network hardware to transmit information between devices on the network.

Figure 1 illustrates a channel redundancy architecture for a HVAC control system according to one or more embodiments of the present disclosure. In embodiments of the present disclosure, failure protection can be provided through use of a number of redundant components.

For example, in the embodiment of Figure 1 , a first HVAC controller 1 10 and a second HVAC controller 120 are connected to a workstation 130 and other devices (e.g., BACnet IP devices) over a network or wired or wireless direct connection 126 (e.g., using BACnet over IP) via ports connected to the connection 126 at 1 18 and 1 19. The HVAC controllers 1 10, 120 are connected to one or more I/O Modules 132 (e.g., using RS-485 via wired or wireless connection 134).

The first HVAC controller 1 10 and second HVAC controller 120 are redundant to each other. They can also communicate with each other, for example, using Ethernet IP communication, via connection 126 and also a dedicated link BACnet MSTP 128 which can, for example, be an RS-485 communication.

In some embodiments, the first HVAC controller 1 10 and second HVAC Controller 120 can be running with the same application and can be powered up, simultaneously. In some such embodiments, whichever controller comes online first after completing the startup sequence can become the active controller and the other controller becomes the standby. This determination can be made via software or firmware that handles the monitoring between the controllers (e.g., it could be resident on one or both controllers).

If the first HVAC controller is in active mode and the second HVAC controller is in standby mode, the active controller communicates with the workstation (e.g., using, for example, BACnet IP and also other I/O modules, for example, using RS-485 communication). The standby controller doesn't communicate with workstation.

The standby controller reads all inputs to the active controller and runs the control application in parallel, however, it doesn't drive any outputs. The standby controller also checks the health of the active controller and the active controller synchronizes the data which is externally written to it to the standby controller using, for example, a dedicated BACnet MSTP network to allow the standby controller to see the traffic in order to monitor the health of the active controller.

In various embodiments, the first HVAC controller and the second HVAC controller both can use different unique MAC address, IP addresses over an IP network, and also unique MAC addresses over, for example, an MSTP network. However, they can be using the same BACnet instance ID over both the networks.

As shown in Figure 1 , active controller 1 10 can include a processor 1 12 and a memory 1 14, and standby controller 120 can include a processor 122 and a memory 124. Memory locations 1 14 and 124 can be any type of storage medium that can be accessed by processors 1 12 and 122, respectively, to perform various examples of the present disclosure.

For example, memory locations 1 14 and 124 can be a non- transitory computer readable medium having computer readable instructions (e.g., computer program instructions) stored thereon that are executable by processors 1 12 and 122, respectively, to perform various examples of the present disclosure. That is, processors 1 12 and 122 can execute the executable instructions stored in memory locations 1 14 and 124, respectively, to perform various examples of the present disclosure.

Memory locations 1 14 and 124 can be volatile or nonvolatile memory. Memory locations 1 14 and 124 can also be removable (e.g., portable) memory, or non-removable (e.g., internal) memory. For example, memory locations 1 14 and 124 can be random access memory (RAM) (e.g., dynamic random access memory (DRAM) and/or phase change random access memory (PCRAM)), read-only memory (ROM) (e.g., electrically erasable programmable read-only memory (EEPROM) and/or compact-disk read-only memory (CD-ROM)), flash memory, a laser disk, a digital versatile disk (DVD) or other optical disk storage, and/or a magnetic medium such as magnetic cassettes, tapes, or disks, among other types of memory.

Further, although memory locations 1 14 and 124 are illustrated as being located in active controller 1 10 and standby controller 120, respectively, embodiments of the present disclosure are not so limited. For example, memory locations 1 14 and 124 can also be located internal to another computing resource (e.g., enabling computer readable instructions to be downloaded over the Internet or another wired or wireless connection).

An operator (e.g., a field engineer or technician) of operator workstation 130 can use (e.g., via connection 126) active controller 1 10 and/or standby controller 120 to control the HVAC system of a facility. That is, active controller 1 10 and/or standby controller 120 can be used by the operator of workstation 130 (e.g., via connection 126) to control the climate within the facility (e.g., building). The facility may be, for example, an office space, a hospital, or a shopping mall, among other types of facilities.

The HVAC system of the facility may include a number of components whose operating parameters can be controlled by active controller 1 10 and standby controller 120. For example, the HVAC system may include objects, control components, equipment, devices, networks, sensors, and/or actuators such as, for instance, valves such as a heating and/or cooling valves, chillers (e.g., chiller plant), boilers (e.g., boiler plant), pumps such as hot water and/or chilled water pumps, fans, compressors, air dampers such as a variable air volume (VAV) damper, air handling units (AHUs) (e.g., AHU plant), coils such as a heating and/or cooling coil, air filters, and/or cooling towers, among other components.

The HVAC system may also include connections (e.g., physical connections) between the components, such as a chain of equipment (e.g., duct work, pipes, ventilation, and/or electrical and/or gas

distribution equipment) that connects the components, among other connections. Further, the HVAC system may include (e.g., be divided into) a number of zones, which can correspond to different zones (e.g., rooms, areas, spaces, and/or floors) of the building.

For example, active controller 1 10 can execute a set of

instructions of a control application for controlling the HVAC system (e.g., for controlling the operating parameters of the components of the HVAC system). The control application (e.g., the set of instructions executed by active controller 1 10) can be executed in a particular sequence for an indefinite number of cycles over an indefinite amount of time in order to continuously maintain the desired control of the HVAC system. A cycle can be considered a complete execution of the entire set of instructions of the control application.

In some embodiments, active controller 1 10 may execute the set of instructions based on the status of active controller 1 10 and standby controller 120 (e.g., based on whether the status of the controllers is active, standby, error, or maintenance). For example, active controller 1 10 may use the status of active controller 1 10 and/or standby controller 120 to determine when and/or how to execute the set of instructions (e.g., when to log, what control actions to take, etc.).

Further, active controller 1 10 and standby controller 120 can send (e.g., via network 126) their respective status (e.g., active, standby, error, or maintenance) to operator workstation 130. That is, the status of active controller 1 10 and standby controller 120 can be monitored from operator workstation 130 (e.g., by the operator of operator workstation 130).

Upon executing the set of instructions of the control application, active controller 1 10 can send (e.g., via network 1 16) the output of only a subset of the executed instructions to standby controller 120, such that only the output of that subset of the executed instructions is synchronized between active controller 1 10 and standby controller 120. That is, the output of the other executed instructions may not be sent to standby controller 120 by active controller 1 10 (e.g., the output of the other executed instructions are not synchronized between active controller 1 10 and standby controller 120). Synchronizing the output of only a subset of the executed instructions in such a manner can significantly reduce the amount of data to be synchronized, and can make the amount of data synchronized independent of the quantity of instructions in the control application, in some implementations.

After receiving the output of the subset of the executed

instructions from active controller 1 10, and upon a failure of active controller 1 10, standby controller 120 can execute the set of instructions of the control application using the received output. For example, upon a failure of active controller 1 10, standby controller 120 can use the received output to initialize its control application runtime and continue the execution of the set of instructions from the point of failure. The failure of active controller 1 10 can be detected by standby controller 120 (e.g., via networks 126 and/or 128).

In some embodiments, active controller 1 10 and standby controller 120 may be existing controllers of HVAC control system 100 (e.g., controllers that did not include the control application when they were installed in HVAC control system 100). In such embodiments, the control application can be installed in existing active controller 1 10 and existing standby controller 120 by downloading the control application to existing controllers 1 10 and 120 using the existing (e.g., previously engineered and commissioned) hardware and software of HVAC control system 100 and existing controllers 1 10 and 120. That is, the control application can be downloaded to existing active controller 1 10 and existing standby controller 120 from operator workstation 130 via network 126, and can be compatible with existing controllers 1 10 and 120 (e.g., compatible with the existing application format and algorithms of controllers 1 10 and 120).

In some embodiments, the control application can be installed in active controller 1 10 and standby controller 120 before they are installed in an existing HVAC control system such as HVAC control system 100 (e.g., the control application can be installed in controllers 1 10 and 120 "out of the box"). That is, the control application can be installed in active controller 1 10 and standby controller 120, and controllers 1 10 and 120 can then be installed in an existing HVAC control system (e.g., HVAC control system 100) subsequent to the installation of the control application.

In various embodiments, the system (e.g., system 100) can include one or more I/O modules 132. These modules can be used, for example, to communication instructions and/or actions to a device to accomplish a task and/or receive information from other devices, such as sensor and/or status information. The interaction with the I/O module can be accomplished via a wired or wireless direct or network connection 134.

Further, in some embodiments, the system components can have separate power supplies to enable them to keep power if there is a power failure to the facility or area therein containing the components. For example, the embodiment of Figure 1 includes a power supply 1 16 for the first system controller 1 10, a power supply 121 for the second system controller 120, and a power supply 135 for I/O module 132.

In one example embodiment, a redundant heating, ventilation, and air conditioning (HVAC) control system, includes an operator workstation and a first BACnet communication connection connected thereto and a first HVAC system controller running a first instance of a control application and a second HVAC system controller each HVAC system controller connected to a second BACnet connection. The first HVAC system controller and a second HVAC system controller can

communicate with the operator workstation via the first BACnet communication connection. The second HVAC system controller is configured to execute a set of instructions to monitor the health of the first controller via the second BACnet connection to identify if the second HVAC system controller has to take over for the first HVAC system controller by initiating control of the HVAC system via a second instance of a control application run by the second HVAC system controller.

In some embodiments, the first HVAC system controller can be configured to execute a set of instructions to monitor the health of the second controller to identify if the first HVAC system controller has to take over for the second HVAC system controller by initiating control of the HVAC system via the first instance of the control application. The health of the controller is, for example, whether the controller is sending and/or receiving data or instructions. In various embodiments, the first HVAC system controller is configured to execute a set of instructions to synchronize data received by the second HVAC system controller in case the first HVAC system controller has to take over for the second HVAC system controller by initiating control of the HVAC system by processing the data with the first instance of the control application. In this manner, the standby controller will have the data available to be able to assume control of the system if a failure occurs.

In some embodiments, the second HVAC system controller is configured to execute a set of instructions to synchronize data received by the first controller in case the second HVAC system controller has to take over for the first HVAC system controller by initiating control of the HVAC system by processing the data with the second instance of the control application. As discussed above, in this manner, the standby controller will have the data available to be able to assume control of the system if a failure occurs.

In various embodiments, the first instance of the control application running on the first system controller and the second instance of the control application on the second system controller are running in parallel. As used herein, the term in parallel means that the first and second instances are executing the same instructions of the control program at substantially the same time. In this manner, if a failure of one controller occurs, the other controller will be ready to quickly become the active controller.

In some embodiments, such as the example above, the first BACnet communication connection is a BACnet Internet protocol (IP) communication network. Such embodiments allow, for example, for the workstation and/or one or more of the first and second controllers to be located remotely (e.g., in different buildings or areas of a building) such that if one of the controllers is, for example, burned in a fire or is offline for another reason having to do with its location, the other controller may be able to take over. In various embodiments, the second BACnet connection is a BACnet master slave token passing (MSTP) connection. Such connections can be dedicated to one or multiple communications functions. For example, such a connection can be used to monitor the health of one or both of the controllers and/or synchronize data between the two controllers.

Another example redundant heating, ventilation, and air conditioning (HVAC) control system embodiment includes an operator workstation and a first BACnet communication connection connected thereto and a first HVAC system controller running a first instance of a control application and a second HVAC system controller each HVAC system controller connected to a second BACnet connection.

The first HVAC system controller and a second HVAC system controller can communicate with the operator workstation via the first BACnet communication connection. The second HVAC system controller is configured to execute a set of instructions to monitor the health of the first controller via the second BACnet connection to identify if the second HVAC system controller has to take over for the first HVAC system controller by initiating control of the HVAC system via a second instance of a control application run by the second HVAC system controller. The system also includes at least one input or output module that is in communication with the first and second HVAC system controllers.

As discussed herein, the first BACnet communication connection can be a wired or wireless connection between the first and second HVAC system controllers and the operator workstation. A wired connection can be beneficial for many reasons as can a wireless connection and such a decision may be based on the application to which the system is to be implemented.

In some embodiments, the system can further include executable instructions to provide a status of at least one controller at the operator workstation such that the operator can identify the status. The status can include an indicator (e.g., symbol or text indicating the state of a controller) or can include more information, such as the type of failure or information about how the failure occurred among other information that could be provided.

In some embodiments, the system further includes executable instructions to allow the operator to initiate an action (change a HVAC value, such as a temperature, or switch a HVAC device on or off, among many other functions) in response to the one or more identified status.

The system can further include executable instructions to provide a failure notification such that the operator can identify that a failure has occurred. The notification can be any mechanism that would attract the attention of the operator, such as a visible, audible, or tactile mechanism. In some embodiments, the system further includes executable

instructions to allow the operator to initiate an action (e.g., initiate a change in status, sound an alarm, contact a maintenance person) in response to the failure notification.

Another example redundant heating, ventilation, and air conditioning (HVAC) control system embodiment includes an operator workstation and a BACnet Internet protocol communication connection connected thereto and a first HVAC system controller running a first instance of a control application and a second HVAC system controller each HVAC system controller connected to a BACnet master slave token passing (MSTP) connection.

The first HVAC system controller and a second HVAC system controller can communicate with the operator workstation via the BACnet IP communication network. The second HVAC system controller is configured to execute a set of instructions to monitor the health of the first controller via the BACnet MSTP connection to identify if the second HVAC system controller has to take over for the first HVAC system controller by initiating control of the HVAC system via a second instance of a control application run by the second HVAC system controller.

In some embodiments, such as that shown in Figure 1 , at least one of the first HVAC system controller, the second HVAC system controller, and the operator workstation has a separate power supply from the rest of the control system. Such power arrangement can be beneficial in a number of ways. For example, the controllers and/or the workstation can be located in other locations, if the power is lost to one controller, it may not also be lost with the second controller.

In various embodiments, the computer readable instructions are executable by the processor to execute, by the second HVAC system controller upon the failure of the first HVAC system controller, the set of instructions of the control application using state information obtained from the first or second HVAC system controllers. Further, in some embodiments, the computer readable instructions are executable by the processor to send a status of the first and second HVAC system controllers to an operator workstation of the HVAC system.

Figure 2 illustrates a BACnet MSTP failure scenario utilizing a channel redundancy HVAC control system according to one or more embodiments of the present disclosure. The first HVAC controller being the active controller, in this example, communicates with the workstation over IP, to the I/O module, for example, using RS-485, and to the standby controller, using BACnet MSTP (e.g., via connections 1 18 and 126), at block 240. The standby controller continuously checks the health of the active controller using dedicated MSTP communication (e.g., 128), at block 242, and detects any failures in the active controller.

If the MSTP channel, which is used for checking health of active device and can also be used for data synchronization, is down due to some reason, at block 244. The switchover will not happen and the redundant channel (e.g., connection 134) which is, for example, an Ethernet communication, can be used for checking the health of the device and can also be used to synchronize the data, at block 246. In such an example, the standby controller can change the state to "error", so that the active controller can report the failure to the workstation, at block 244.

In this scenario, the active controller can remain active. The active controller can continue to communicate with the workstation as well as I/O modules, whereas the standby controller continues checking the health of the active controller and can keep the data synchronized using a redundant channel (e.g., Ethernet connection), at block 246. Once the failure in MSTP channel of the first HVAC controller is recovered, at block 248, it can comes back into the system as active and again start communicating over MSTP, at block 250. The second controller can then be returned to a standby state, at block 252.

Figure 3 illustrates a BACnet IP failure scenario in a channel redundancy HVAC control system according to one or more

embodiments of the present disclosure. The active controller is communicating with workstation over IP, to the I/O module, for example, using RS-485, and to the standby controller, for example, using BACnet MSTP, at block 360. The standby controller continuously checks the health of the active controller, for example, using dedicated MSTP communication, at block 362, and detects any failures in the active controller, the second HVAC controller will then become the active controller, if a failure occurs.

If the BACnet IP channel (e.g., via connections 1 18 and 126) of the first HVAC controller which is used to communicate with workstation and other BACnet devices is down, at block 364, the second HVAC controller which is checking the failures of the first HVAC controller can become the active controller and the first HVAC controller will go into error state 366.

Hereon, the first HVAC controller which is in standby state will continue monitoring the health of the second HVAC controller which is active and the health monitoring and/or data synchronization can occur, for example, over BACnet MSTP channel (e.g., connection 128), at block 368. When the failure in the channel (e.g., via connections 1 18 and 126) of the first HVAC controller is recovered, at block 370, it can continue as the standby controller, at block 372.

Figure 4 illustrates both a BACnet IP and BACnet MSTP failure scenario in a channel redundancy HVAC control system according to one or more embodiments of the present disclosure. In such a scenario, the active controller is communicating with workstation over IP (e.g., via connections 1 18 and 126), to the I/O module using RS-485 (via connection 134, and to the standby controller using BACnet MSTP (e.g., via connection 128), at block 480. The standby controller continuously checks the health of the active controller using a dedicated MSTP communication (e.g., via connection 128), at block 482, and detects any failures in the active controller.

In such a scenario, both the BACnet IP and the MSTP channels of first HVAC controller, which can be used to communicate with the workstation and other BACnet devices, is down, at block 484, the second HVAC controller, which is checking the failures of first HVAC controller, can become active and the first HVAC controller will be in an error state, at block 486.

Once a failure in either MSTP or IP channel of first HVAC controller is recovered, at block 488, and returns to service the first controller can continue as the standby controller, at block 490, and can again start communicating on the recovered channel.

In some embodiments, the states of each controller are

maintained in both the controllers in BACnet multi-state value points so that it can be read by any BACnet compatible clients.

Also, the system can include a BACnet alarm notification to the operator for these multi-state value points, whenever the state changes so that the operator can take one or more required actions, based on the information provided in the notification, information accompanying the alarm, or when the system is accessed by the operator when notified.

Although specific embodiments have been illustrated and described herein, those of ordinary skill in the art will appreciate that any arrangement calculated to achieve the same techniques can be substituted for the specific embodiments shown. This disclosure is intended to cover any and all adaptations or variations of various embodiments of the disclosure. It is to be understood that the above description has been made in an illustrative fashion, and not a restrictive one. Combination of the above embodiments, and other embodiments not specifically described herein will be apparent to those of skill in the art upon reviewing the above description.

The scope of the various embodiments of the disclosure includes any other applications in which the above structures and methods are used. Therefore, the scope of various embodiments of the disclosure should be determined with reference to the appended claims, along with the full range of equivalents to which such claims are entitled.

In the foregoing Detailed Description, various features are grouped together in example embodiments illustrated in the figures for the purpose of streamlining the disclosure. This method of disclosure is not to be interpreted as reflecting an intention that the embodiments of the disclosure require more features than are expressly recited in each claim.

Rather, as the following claims reflect, inventive subject matter lies in less than all features of a single disclosed embodiment. Thus, the following claims are hereby incorporated into the Detailed Description, with each claim standing on its own as a separate embodiment.