What is the difference between the BACnet interface and dry contact linkage of the air conditioning box?

The BACnet interface can exchange multiple status and control data within the agreed implementation scope. Dry contacts are usually used for independent switch status or commands. The capabilities, connection methods and fault behaviors of the two are different. They can be used together according to project needs. Just because they both have 'start and stop' functions cannot be considered to be completely equivalent.

Select interfaces based on amount of information and action responsibilities

If only a simple enable or fault signal is required, independent contacts may be suitable; if multiple measured values, settings or operating states are required, the objects and attributes supported by the communication need to be confirmed. BACnet still needs to clarify the network form, device identification, and reading and writing rules. Dry contacts need to confirm whether they are normally open and normally closed, whether they are passive, and their electrical rating conditions.

The communication interface needs to write the object list, network parameters, permissions and exception handling; the contact interface needs to write the purpose, normal state, capacity, passive and wiring responsibilities; for combined use, different command priorities and local protection retention methods need to be written. The three types of information correspond to different docking depths, and the solution cannot be determined based on just one interface name. Please refer to the table of points that need to be provided before the air-conditioning box is connected to the building automation system.What point tables need to be provided before the air-conditioning box is connected to the building automation system?。

What data can the BACnet interface exchange?

The BACnet interface can exchange various data such as analog quantities, switching quantities, alarm status and set values ​​within the agreed implementation scope. It is suitable for projects that require centralized monitoring of multiple parameters, remote adjustment of settings or recording of operating trends. However, the specific objects and attributes supported depend on the implementation of the device controller, and all BACnet devices cannot be fully functional by default.

BACnet also needs to clarify the network form, device instance number, object type and read and write permissions. The object naming and attribute definitions of different manufacturers may be different. The object list should be exchanged and checked point by point before docking. For control point table and signal definition, please refer toWhat point tables need to be provided before the air-conditioning box is connected to the building automation system?。

What scenarios are dry contacts suitable for?

Dry contacts are usually used for simple switch status or command transmission, such as fan operation feedback, fault alarm, remote start and stop permission or filter differential pressure alarm. It does not rely on communication protocols and has simple wiring. It is suitable for independent protection or hard linkage with equipment of different brands. However, the amount of information transmitted by dry contacts is limited and usually can only represent one state.

Dry contacts need to be confirmed as normally open and normally closed, whether they are passive, contact capacity and electrical rating conditions. When wiring, attention should be paid to power isolation and signal matching to avoid direct connection of active signals to passive contacts. The linkage logic and priority also need to be clear to avoid conflicts between local control and remote commands.

Failure behavior and reliability are different

When the communication interface is interrupted, all remote data and commands may be lost; when the dry contact is disconnected, the signal may be lost or the status may be uncertain. Both methods require defining failure states and recovery strategies. Important protection (such as emergency stop, fire linkage, antifreeze protection) usually requires a hard loop independent of communication and cannot rely solely on BACnet writing.

For important linkage, the complete link must be verified according to the design. Please refer toWhat point tables need to be provided before the air-conditioning box is connected to the building automation system? . Just because the communication interface is writable cannot replace the independent protection circuit required by design. The alarm definition of the control point table should also include the handling method of communication interruption and contact disconnection.

Please write down the priority when using in combination.

In actual projects, BACnet and dry contacts are often used in combination: BACnet is responsible for data collection and routine adjustment, and dry contacts are responsible for emergency stop, fire linkage or independent protection. When used in combination, the priorities, local priority rules, and status after fault recovery of different commands should be clarified. When there is a conflict of orders, which party has priority needs to be agreed in advance.

For the relationship between control logic and local protection, please refer toHow to change the debugging sequence of air conditioning box from stand-alone unit to system linkage? . During debugging, normal commands, abnormal commands, communication interruption and other scenarios should be verified to confirm that the protection loop is always effective.

Interface selection must comply with the project control plan

The interface form is not the more complex, the better, nor is the simpler the better. The selection should be based on the amount of data exchanged by the project, linkage objects, reliability requirements and maintenance capabilities. Small projects may be satisfied by dry contacts, while large projects or projects that require trend recording and remote settings may require BACnet. Both can also be used together in the same project.

For the relationship between control interface and device configuration, please refer toWhat driving conditions need to be matched when using a DC fan in an air-conditioning box? . Interface selection should be considered as a whole in the control scheme rather than comparing interface names alone.

Aili industrial supporting equipment

When confirming the building control interface with Aili Industrial, please provide the data that needs to be exchanged and the actions that must be completed, and then jointly check the communication, contacts and local control boundaries. Aili's industrial manufacturing end covers independent R&D and production of motors and fans, control systems, sheet metal, air filters and complete machine assembly. BACnet interfaces, dry contact configurations and local control logic can be matched in the same package; non-standard interfaces can be adjusted according to the project control plan.

Product form can be viewedAir handling unit andFan box page; clean air supply package can be combinedFFU fan filter unit andEFU equipment end fan filter unit verification; multiple equipment linkage can understandMatching method of FFU computer group control system ; terminal particle filtering can be combinedHEPA/ULPA filter confirmation; when it comes to gaseous pollution control, you can communicate separatelyChemical filter solutions. The specific interface form, control boundary and delivery scope still need to be verified based on the corresponding configuration data and on-site working conditions. The actual effect is subject to on-site joint debugging and performance test results.

Submit project parameters:https://ailigy.com/contactus.html

Related questions and answers

Can the BACnet interface completely replace dry contacts?
Not recommended. Important protection usually requires a hard loop independent of communication. BACnet is suitable for data exchange and routine regulation and cannot replace the independent protection required by design.

Only start and stop requirements are required, should I use dry contacts or BACnet?
If only simple start-stop or status feedback is required, dry contacts may be more direct; if operating parameters, alarm recording or remote settings are also required, BACnet needs to be evaluated.

Can Aili Industrial help choose the interface type?
The interface plan can be checked based on the data to be exchanged, linkage objects and reliability requirements. The specific configuration needs to be confirmed according to the project control plan.

Related articles

1. What point tables need to be provided before the air-conditioning box is connected to the building automation system?

2. What driving conditions need to be matched when using a DC fan in an air-conditioning box?

3. How to change the debugging sequence of air conditioning box from stand-alone unit to system linkage?

4. What conditions need to be checked before the air conditioner is turned on for the first time?

Key points for selection and acceptance inspection