The BACtwin as the Basis for Planning and Tendering Future-Proof Building Automation Systems in Practice.

The sixth and final part of the BACtwin series highlights the benefits of the digital twin of building automation as the basis for planning and tendering future-proof building automation systems in practice. Daniel Rörich from ICONAG-Leittechnik GmbH, outlines the differences between planning building automation (GA) without and with BACtwin.

Process of GA Planning: The process for GA planning typically proceeds as follows: The specialist planners design the systems for their trades. When the specialist planners submit their work, concepts, performance specifications, cost estimates, topologies, system diagrams, and much more are on the table. In most cases, this is intended to complete the building automation planning in the shortest possible time.

Planning without BACtwin: How planning without BACtwin proceeds is illustrated in the following example of a fan or pump: The HVAC (Heating, Ventilation, and Air Conditioning) planner submits their system diagrams to the building automation planner, assigns functions to the equipment based on their expertise, and transfers them to the GA function list according to VDI 3814 "Building Automation (GA) - Fundamentals" (2019). The problem here is that a client may have multiple properties or projects and different building automation planners involved. Identical equipment may then be considered with divergent functions during planning.

Figure 1: One Client, Multiple Properties/Projects, and Various GA Installers: Without BACtwin, the quality of the project depends on the expertise of the installer. (All figures © ICONAG-Leittechnik)

In construction without BACtwin, the question arises of how the GA function lists can be transferred to the programming of automation stations. The building automation planner hands over the GA function lists to the building automation installer. If available, the installer applies the specifications from the GA specification to the functions to be implemented, then transfers them to BACnet design based on their expertise, and finally transfers the programming to the automation station. The quality of the BACnet design thus depends on the planner's specifications and the installer's expertise. In the BACnet network, specific differences of the following kinds can arise:

Different labels and clear text designations for identical equipment and functions: Labeling systems often lack clarity regarding the choice of equipment or function identifiers, offering multiple variants. As a result, depending on the programmer's interpretation, different labels and clear text designations may be used for identical equipment and functions as Object Name or Description.

Different object types for identical functions: Depending on the automation system and the programmer's habits, identical functions may be provided via different BACnet object types.

Examples:

Operating status indication: Binary_Object <> Multistate_Object Operating mode switch: Binary_Object <> Multistate Object <> Integer_Object <> Analog_Object

Different or incomplete object properties: Without clear specifications, the installer may forget or execute the design of properties differently.

Examples:

Units: No indication of units for Analog_Objects State_ as well as Active_ and Inactive_Texts: Replacement texts for Multistate_ and Binary_Objects are specified differently or not at all for identical functions.

Different or non-configured management functions: Objects with alarm conditions are assigned different or no Notification_Classes. Proprietary time switch functions are used instead of Schedule_Objects for time control functions.

Issues with GA planning without BACtwin The common planning and execution procedure described above in the GA trade leads to:

Inhomogeneous BACnet designs and thus to heterogeneous control, display, and management functions on the management and operating device Possibly required revisions of the BACnet design and thus to additional costs and increased time Avoidable effort and frustration for clients, planners, and contractors Complicated operation of identical systems for the building technician

Planning with BACtwin

In planning with BACtwin, the process differs significantly, as illustrated by the example of a fan or a pump:

The HVAC planner hands over their system diagrams to the building automation planner. The building automation planner identifies the appropriate sample system in BACtwin, populates the planner properties (attributes and information) - in the case depicted in Figure 2, in sample system "HKR-2" - with the objects and properties required by the client, and transfers the information to the GA function list with left and right extension.

In a project involving one client, multiple properties/projects, and various GA planners, this leads to identical systems and equipment.

Installation with BACtwin

Installation with BACtwin follows a similar process: The building automation planner hands over the GA function lists with left and right extension to the installer. The installer expands the right part of the GA function list with the installer properties, transfers the GA functions to the BACnet design, and finally transfers the programming to the automation station. This results in identical BACnet designs for identical systems and aggregates across the entire BACnet network of the property portfolio.

Advantages of Planning and Execution with BACtwin

Planning and executions based on BACtwin result in:

Homogeneous BACnet designs and thus homogeneous and simple control, display, and management functions on the management and operating device Smooth project implementations Significantly less effort and more satisfaction for clients, planners, and contractors

Figure 2: Same starting point as in Figure 1, but now with BACtwin, there are identical designs for identical systems and aggregates.

Conclusion

Planning and execution based on BACtwin lead to homogeneous BACnet designs, resulting in consistent operation, display, and management functions on the management and control devices, smoother project implementations, and ultimately, satisfied clients, planners, and contractors. However, it should be noted that while BACtwin provides guidelines for BACnet objects and their properties, it does not fully replace a BACnet specification. Additional specifications are still required for BACnet-based building automation systems, including:

• Structuring of Device IDs
• Basic determinations of supported BACnet services
• Permissible BACnet device types
• BACnet Network Management, such as the use of BACnet Broadcast Management Devices or BACnet Time Master