Unit Heater Control with BACnet® Communication

June 12, 2018
Tech Tuesday

Recently our BACnet® compatible Analog Input RIB® was updated to include a set point function, which I summarized in my previous blog post. Any model with “BCAI” in the name will include this feature. The function allows the user to define a set point and differential in the device. These parameters are compared with the reading from the Analog Input (AI1), and the relay output (BO1) is turned ON or OFF depending on the mode. In this post I will highlight an application where this new feature can be utilized, specifically control of a Cabinet Unit Heater (CUH).

Since CUHs reside outside the main HVAC system of a building, they require independent control and, if necessary, monitoring. Typically, this would require two devices, one for control and one for monitoring. With the added feature to our BCAI model, it can serve both purposes. With a thermistor connected to the Analog Input of the BCAI, it will monitor the temperature in the space and control a connected load based on the user settings. This relay output can be used to control a fan in a CUH or Fan Coil Unit (FCU), a hydronic valve and/or a resistive heating element.

A benefit of using the BCAI in this type of application is that the unit will continue to control the CUH even if network communication is lost or removed. The control logic resides in the device itself, and the network connection is only necessary for configuration, overriding or monitoring. When the relay output of the BCAI is commanded by the set point function, it is written at priority 16. That means any higher priority can be written to the device to take precedence. That allows BAS control of the CUH at any time, and when that control is relinquished, the BCAI takes over again, as a sort of setback control.

If you would like more details about this product or its features, refer to the Misc. Download section of the product page HERE or the product datasheet HERE. If you would like more information on this product or this feature, please contact our Technical Support team.


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About the Author

Henry Smith is a 34-year-old engineer at Functional Devices, Inc. He has a BS EET obtained from Purdue University in 2014 and a lifelong interest in electronics. As an engineer at Functional Devices, he gets to provide Technical Support to our customers, from distributors to specifying engineers and installers.

Henry enjoys providing tech support, as it allows our company to assist at every level of our product’s lifecycle and exposes us to interesting and unique applications. While not every technical question is unique, even answering a simple question or providing someone with the information in a timely manner can go a long way to helping him or her meet a deadline.