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 an 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.

An 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, an 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., with the existing controllers of the HVAC system). 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 redundant HVAC control system in accordance with one or more embodiments of the present disclosure.

Figure 2 illustrates a method of operating a first HVAC system controller and a method of operating a second HVAC system controller in accordance with one or more embodiments of the present disclosure.

Figure 3 illustrates a method of installing HVAC system controllers in accordance with one or more embodiments of the present disclosure. Detailed Description

Redundant heating, ventilation, and air conditioning (HVAC) control systems are described herein. For example, one or more embodiments include a first HVAC system controller and a second HVAC system controller, wherein the first HVAC system controller is configured to execute a set of instructions of a control application for controlling an HVAC system and synchronize (e.g., sync) an output of only a subset of the executed instructions to the second HVAC system controller.

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 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.

Redundant HVAC control systems in accordance with the present disclosure may not be able to recover and continue the operation of an 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 an 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 redundant heating, ventilation, and air conditioning (HVAC) control system 100 in accordance with 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 network 126. Further, active controller 1 10 and standby controller 120 can be coupled (e.g., communicate) via a network 1 16, as illustrated in Figure 1 . Networks 1 16 and 126 can be wired or wireless networks of HVAC control system 100. For instance, in the embodiment illustrated in Figure 1 , network 1 16 can be a master slave token passing (MSTP) network, and network 126 can be an internet protocol (IP) network.

However, embodiments of the present disclosure are not limited to a particular type of network.

As used herein, a "network" (e.g., networks 1 16 and 126) 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 1 16 and 126 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 or print on a network printer.

Applications may also communicate with network management software, which can interact with network hardware to transmit information between devices on the network.

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. Memories 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, memories 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 memories 1 14 and 124, respectively, to perform various examples of the present disclosure.

Memories 1 14 and 124 can be volatile or nonvolatile memory.

Memories 1 14 and 124 can also be removable (e.g., portable) memory, or non-removable (e.g., internal) memory. For example, memories 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 readonly 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 memories 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, memories 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 network 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 network 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.

As an example, the set of instructions can be arranged in a sequence of columns and rows, and the execution of the instructions by active controller 1 10 can be column based, such that active controller 1 10 executes the set of instructions one column of the sequence at a time. That is, active controller 1 10 can execute the instructions of one column before moving on to the next column (e.g., active controller 1 10 may execute the first column of instructions, then execute the second column of instructions, then the third column, etc.). Further, the output (e.g., data) of one column of instructions executed by active controller 1 10 may be used as the input for the next column to be executed. That is, the output of the first column of instructions executed by active controller 1 10 can be input into the second column of instructions, the output of the second column can be input into the third column, etc.

In some embodiments, the first column of instructions in the sequence (e.g., the first column of instructions executed by active controller 1 10) can include instructions that can be executed independent of (e.g. instructions that do not depend on) the output of the other instructions in the sequence (e.g., the output of the remaining columns of instructions to be executed by active controller 1 10). Rather, these independent instructions may be executed using information (e.g., data and/or variables) received from sensors of the HVAC system by active controller 1 10, and may be the source of data for the other (e.g., remaining) instructions in the sequence. In some embodiments, the set of instructions can include private state information associated with the control application (e.g., information needed to continue to execute the instructions in subsequent cycles of the control application). Whether the set of instructions includes such private state information can depend on the quantity of complex instructions in the control application. For example, not all instructions of the control application will include private state information; rather, only complex instructions, such as, for instance, proportional-integral- derivative (PID) instructions, may include private state information.

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 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.

Active controller 1 10 can send the output of the subset of the executed instructions to standby controller 120 at a particular frequency. Active controller 1 10 can determine (e.g., dynamically calculate) the frequency based on, for example, the available bandwidth (e.g., of network 1 16) for sending the output of the subset to standby controller 120, and/or the size of (e.g., the quantity of packets in) the output of the subset to be sent. For example, the lower the available bandwidth and/or the greater the size of the output of the subset, the lower the frequency with which the output is sent. As such, the synchronization of the output of the subset may work effectively even in poor bandwidth conditions.

The output of the subset of the executed instructions sent to standby controller 120 can be, for example, the output of the executed instructions of a single (e.g., only) one of the columns of the column sequence executed by active controller 1 10. For instance, the output of the subset of the executed instructions sent to standby controller 120 can be the output of the first column of instructions (e.g., the independent instructions) executed by active controller 1 10. That is, the single one of the columns can be the first column of the column sequence.

In embodiments in which the set of instructions include private state information associated with the control application, active controller 1 10 can send (e.g., via network 1 16) the private state information to standby controller 120 along with the output of the subset of the executed instructions. That is, the private state information can be synchronized between active controller 1 10 and standby controller 120 along with the synchronization of the output of the subset of the executed instructions.

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 1 16 and/or 126).

Further, in embodiments in which the set of instructions of the control application include private state information associated with the control application (e.g., embodiments in which standby controller 120 receives the private state information from active controller 1 10), standby controller 120 can execute the set of instructions upon the failure of active controller 1 10 using the private state information along with the output of the subset of the executed instructions.

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. The process of installing the control application in active controller 1 10 and standby controller 120, whether the controllers are existing controllers of an HVAC control system or before the controllers are installed in the HVAC control system, will be further described herein (e.g., in connection with Figure 3).

Figure 2 illustrates a method 240 of operating a first HVAC system controller and a method 260 of operating a second HVAC system controller in accordance with one or more embodiments of the present disclosure. For example, methods 240 and 260 can be performed concurrently by the first and second HVAC system controllers, respectively. The first and second HVAC system controllers can be, for example, active controller 1 10 and standby controller 120, respectively, previously described in connection with Figure 1 .

At blocks 242 and 262 of methods 240 and 260, respectively, the first and second controllers can synchronize (e.g., sync) their respective states and commands. For example, the first and second controllers can send their respective states and commands to each other (e.g., via network 1 16 previously described in connection with Figure 1 ) to confirm that they are synchronized and in communication.

At blocks 244 and 264 of methods 240 and 260, respectively, the first and second controllers can receive (e.g., scan) inputs from their respective sensors of the HVAC system. For example, the first controller can receive information (e.g., data and/or variables) from the sensors of the HVAC system controlled by the first controller, and the second controller can receive information from the sensors of the HVAC system controlled by the second controller.

At block 246 of method 240, the first controller can execute the set of instructions of its control application, as previously described in connection with Figure 1 . For example, the first controller can execute the complete cycle of the control application, as previously described in connection with Figure 1 .

At blocks 248 and 268 of methods 240 and 260, respectively, the first and second controllers can sync (e.g., via network 1 16) an output of only a subset of the executed instructions of the application, as previously described in connection with Figure 1 . That is, the first controller can send the output of only the subset of the executed instructions to the second controller, and the second controller can receive the output of only that subset from the first controller, as previously described in connection with Figure 1 .

At block 250 of method 240, the first controller can write the outputs of the executed control application cycle to the components of the HVAC system. For example, the first controller can write the outputs of the executed control application cycle to the devices of the HVAC system controlled by the first controller.

At blocks 252 and 272 of methods 240 and 260, respectively, the first and second controllers can communicate that the control application cycle is complete. For example, the first and second controllers can send (e.g., via network 126 previously described in connection with Figure 1 ) a communication indicating that the control application cycle is complete to operator workstation 130 described in connection with Figure 1 . The communication that the control application cycle is complete can be an indication to move on to the next cycle of the application. Method 240 can then return to block 242, as illustrated in Figure 2.

At block 274 of method 260, the second controller can monitor the condition of the first controller (e.g., whether the first controller is active). Upon detecting a failure of the first controller, the second controller can execute the set of instructions of the control application using the output of the subset of the executed instructions, as previously described in connection with Figure 1 . Method 240 can then return to block 262, as illustrated in Figure 2.

Figure 3 illustrates a method 380 of installing (e.g.,

commissioning) HVAC system controllers in accordance with one or more embodiments of the present disclosure. The HVAC system controllers can be, for example, active controller 1 10 and standby controller 120 previously described in connection with Figure 1 .

Method 380 can be performed on existing controllers of an HVAC control system, or "out of the box" controllers that have not yet been configured with applications. In embodiments in which the controllers are "out of the box" controllers, the installation of the controllers may begin at block 382 of method 380. In embodiments in which the controllers are existing controllers of an HVAC control system, the installation of the controllers may include deleting the existing applications from the controllers and removing the input/output (I/O) bus from one of the controllers (e.g., the standby controller) prior to block 382. After the existing applications are deleted and the I/O bus is removed, the installation of the existing controllers may then proceed to block 382.

At block 382, method 380 (e.g., the installation of the controllers) includes assigning unique IP addresses to the controllers. At block 384, method 380 includes downloading the firmware for the control application to the controllers.

At block 386, method 380 includes confirming the network connections of the controllers are operational. Confirming the network connections of the controllers are operational can include, for example, conforming both controllers are connected to the IP network of the HVAC control system (e.g., network 126 previously described in connection with Figure 1 ), and confirming a dedicated MSTP network (e.g., network 1 16 previously described in connection with Figure 1 ) is connected between the controllers. Confirming the network connections of the controllers are operational can also include confirming the I/O bus is connected to only one of the controllers (e.g., the active controller).

At block 388, method 380 includes downloading the control application to the active controller. The control application can be downloaded to the active controller from an operator workstation via the IP network of the HVAC control system, as previously described in connection with Figure 1 .

At block 390, method 380 includes confirming communication between the controllers (e.g., confirming that the controllers are communicating with each other). Confirming communication between the controllers can include, for example, confirming that the I/O LEDs of the controllers are blinking.

At block 392, method 380 includes confirming the status of the controllers. Confirming the status of the controllers can include, for example, confirming that the LED of the active controller indicates it is in active mode, confirming that the LED of the standby controller indicates it is in maintenance mode, and restarting the standby controller and confirming it resumes operation in standby mode. Further, the I/O bus may be looped to the terminals of the standby controller's I/O channel, and it can then be confirmed that the I/O communication is still intact without any abnormal LED status.

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.