Multiple Dial LAN Support
In a system’s architecture, the local sites have the ability to call an alternate communication interface, if the primary is not available (Figure 17).
In a system’s architecture, the local sites have the ability to call an alternate communication interface, if the primary is not available (Figure 17).
One-Way Dial System Architecture
One-way dial systems, Figure 18, are typically used to enable system owners to access their systems from a remote location, such as their home. It is used where auto-dial monitoring is not required. It can also be used by the installation and service company or by the commissioning authority to troubleshoot and program from remote locations. One-way dial can also be used to dial into remote site LANs or sub-networks.
One-way dial systems, Figure 18, are typically used to enable system owners to access their systems from a remote location, such as their home. It is used where auto-dial monitoring is not required. It can also be used by the installation and service company or by the commissioning authority to troubleshoot and program from remote locations. One-way dial can also be used to dial into remote site LANs or sub-networks.
Two modems are required, one located at the remote computer and one at the system site. Typically, the DDC operating software must be installed on the remote computer.
Communication
Communication between two different devices controlling equipment, requires a common protocol, a common communication speed and known data formatting. Vendors build their devices around these criteria, so communication between devices by the same manufacturer is routine.
Third Party Interfaces
In many installations, it is desirable for a proprietary building DDC system to communicate with other proprietary DDC systems controlling pieces of equipment. Examples would include a building DDC system and a chiller DDC system (Figure 19) or a fume hood DDC system. Communication between the two systems will require an interface or gateway, due to different proprietary protocols, communication speeds and data formatting.
Communication
Communication between two different devices controlling equipment, requires a common protocol, a common communication speed and known data formatting. Vendors build their devices around these criteria, so communication between devices by the same manufacturer is routine.
Third Party Interfaces
In many installations, it is desirable for a proprietary building DDC system to communicate with other proprietary DDC systems controlling pieces of equipment. Examples would include a building DDC system and a chiller DDC system (Figure 19) or a fume hood DDC system. Communication between the two systems will require an interface or gateway, due to different proprietary protocols, communication speeds and data formatting.
The gateway or interface translates protocol between the two proprietary systems. The proper operation of the gateway is dependent on the continued use of the specific revised levels of software on both systems. It typically requires the support of the manufacturer at the corporate level to implement and cooperation between the manufacturers. In addition, the costs can vary widely.
Protocols
In the DDC world, there are the three classifications of protocols: closed protocol, open protocol and standard protocol.
A closed protocol is a proprietary protocol used by a specific equipment manufacturer. An open protocol system uses a protocol available to anyone, but not published by a standards organization. A standard protocol system uses a protocol available to anyone. It is created by a standards organization.
Open Systems
An open system is defined as a system that allows components from different manufacturers to co-exist on the same network. These components would not need a gateway to communicate with one another and would not require a manufacturer specific workstation to visualize data. This would allow more than one vendor’s product to meet a specific application requirement.
The sole use of an open or standard protocol does not guarantee that a DDC system will be an open system. A manufacturer has the ability to use open or standard protocols, yet create a closed system, thus continuing a building owner’s dependence on a single manufacturer. This can be accomplished by using unique communication speeds, unique data formatting and by not adopting the full range of an open protocol.
Note: A building owner/engineer should thoroughly research a manufacturer’s claim of an open system.
BACNET
BACNET is a standard protocol published by a standards organization (American Society of Heating, Refrigerating and Air-conditioning Engineers or ASHRAE). It is a specification for a protocol. DDC vendors create a communication protocol that complies with this specification.
BACNET is a relatively complex standard. The standard defines protocol implementation conformance statements (PICS) that define different levels of compliance. A given vendor may or may not support the level required for a given application. In other words, a vendor could meet a very low level of compliance and be BACNET-compatible. The key question is, “At what level?”
In Figure 20 the chiller control unit’s DDC will communicate with the building DDC system if each has a BACNET gateway and their PICS match.
Protocols
In the DDC world, there are the three classifications of protocols: closed protocol, open protocol and standard protocol.
A closed protocol is a proprietary protocol used by a specific equipment manufacturer. An open protocol system uses a protocol available to anyone, but not published by a standards organization. A standard protocol system uses a protocol available to anyone. It is created by a standards organization.
Open Systems
An open system is defined as a system that allows components from different manufacturers to co-exist on the same network. These components would not need a gateway to communicate with one another and would not require a manufacturer specific workstation to visualize data. This would allow more than one vendor’s product to meet a specific application requirement.
The sole use of an open or standard protocol does not guarantee that a DDC system will be an open system. A manufacturer has the ability to use open or standard protocols, yet create a closed system, thus continuing a building owner’s dependence on a single manufacturer. This can be accomplished by using unique communication speeds, unique data formatting and by not adopting the full range of an open protocol.
Note: A building owner/engineer should thoroughly research a manufacturer’s claim of an open system.
BACNET
BACNET is a standard protocol published by a standards organization (American Society of Heating, Refrigerating and Air-conditioning Engineers or ASHRAE). It is a specification for a protocol. DDC vendors create a communication protocol that complies with this specification.
BACNET is a relatively complex standard. The standard defines protocol implementation conformance statements (PICS) that define different levels of compliance. A given vendor may or may not support the level required for a given application. In other words, a vendor could meet a very low level of compliance and be BACNET-compatible. The key question is, “At what level?”
In Figure 20 the chiller control unit’s DDC will communicate with the building DDC system if each has a BACNET gateway and their PICS match.
If a vendor states their product is native BACNET, they are using the BACNET protocol in lieu of a proprietary protocol on their LAN. In Figure 20, a native BACNET building system would be able to communicate to the chiller control DDC with one less gateway.
Overlay Systems
An overlay system is a high-end workstation that communicates with multiple manufacturers’ proprietary EMS systems. An overlay system supplier creates drivers to “talk” to the different systems. The vendors must have a cooperative relationship and revision control is important for continued successful use. The workstation typically displays data, allows manual control and setpoint changes, and handles alarms and messaging. Any detailed editing of the control sequence will still require knowledge of the underlying proprietary software.
LON
The Echelon Corporation has created an open protocol that uses a standard processor and a set of standard transceivers, which allows components from different manufacturers to co-exist on the same LAN. The protocol is available to anyone and is called LONTALK. A unique chip is required for any device that uses LON. Standard network variable formats have been established to allow the transfer of data from one device to another regardless of origin.
Presently, various vendors are competing to become the defacto standard for the network database structure. The network database is a map of the components and the relationship of the data moving between them. The operator workstation needs this structure to visualize the data.
Software suppliers providing the software for the operator workstation may be independent of those providing the software for the database structure and the EMS vendors.
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