Winter is around the corner, and for many areas of the country, snow and ice buildup are major factors to contend with on commercial buildings. tekmar recently launched its BACnet Snow/Ice Sensor Interface 681 to address these specific issues. The device automatically detects snow or ice through tekmar sensor technology and is designed to interface with building automation systems via the BACnet MS/TP.

Plumbing Engineer recently spoke with Cleber Alves, product manager, and Eric Balt, technical sales manager, who explained how the new product works and interfaces with building automation systems (BAS). 

Plumbing Engineer: How does the BACnet Snow/Ice Sensor Interface 681 ease the integration of snowmelting systems in a building automation system?

Cleber Alves & Eric Balt: The value proposition of the 681 is to automate the start and stop operation of a snowmelting system by integrating tekmar snow/ice sensors with a BAS controller through BACnet MS/TP. Here is where the integration happens: With the 681, the BAS has snow/ice sensors that can communicate digitally with its BAS controllers. They also have access to proven snowmelting functionality in a simple-to-integrate device. 

In addition, due to the BACnet MS/TP, the 681 can interface with any MS/TP controller, which makes it easier for the BAS to provide a start/stop operation for any snowmelting application. Contractors will have a standard solution that can be applied to any snowmelt job without custom coding and complex installation.

PE: How does the BACnet snow/ice sensor technology interface with a building automation system? 

 CA & EB: The communication between the 681 and the BAS happens through a BACnet MSTP master/slave network topology and an RS-485 interface (see Figure 1). The RS-485 is the physical layer for point-to-point communication of electrical devices. 

 The 681 is a master slave device as is the BAS device. These devices intercommunicate. The RS-485 allows long cabling distances in a noisy environment and supports multiples devices on the same bus, which is appropriate for BAS architecture. 

The 681 uses two signal lines, –A and +B, which are balanced with two lines that share a twisted pair cable with the same impedance on each line. In this physical layer, the BAS can have up to 128 devices installed on a single network. The 681 can reach a baud rate of up to 115,200 bps to transmit data in this communication
channel.

PE: Can you describe the physical installation of the project on a commercial building? 

CA & EB: The location of the Snow/Ice Sensor 090 and the Socket 091 determines how well the snowmelt detector responds to conditions on the snowmelting slab. The location is crucial and should represent the average slab surface temperature and moisture conditions. The Socket 091 and conduits are installed on the slab surface before the concrete pour. Once the concrete is ready, the Sensor 090 and its cable to connect to the 681 are installed.

The 681 is designed to be installed in a mechanical room using an electrical enclosure. A 24 V (AC) power supply within the electrical enclosure runs the 681 and the 090 or 095 sensor.

The 681 and the BAS controller are physically connected using the RS-485 and an MS/TP master and slave topology (see Figure 2). Once the physical communication is complete, contractors only need to input the device ID and MAC address in the 681, then code the sequence of operation in the BAS controller to automate the start/stop operation.

PE: When it comes to connectivity, what information is being passed back and forth?

CA & EB: Multiple data points are communicated between the BACnet Sensor Snow/Ice Sensor Interface 681 and a BAS controller. Through these data points, the BAS can automatically operate the start/stop operation of a snowmelting system. Also, using the data points, the slab temperature is controlled to increase efficiency. 

These data are signals using BACnet objects; contractors only need to incorporate the objects in the sequence of operation to complete the connectivity.

List of data shared with the BAS controller:

• Snow or ice has been detected;

• Snow or ice has not been detected;

• Outdoor air temperature;

• Slab temperature;

• Slab target temperature;

• Snow/ice sensor sensitivity;

• Warm weather shutdown (WWSD);

• Cold weather cutoff (CWCO);

• Error codes.

PE: What elements do you need for the operation of the unit? 

CA & EB: The 681 requires the following elements for proper operation:

• tekmar Snow/Ice Sensor 090 or Snow Sensor 095;

• tekmar Outdoor Sensor 070 or an outdoor sensor installed directly to the BAS controller;

• tekmar Slab Sensor when the Snow Sensor 095 is installed;

• Communication with a BAS controller through BACnet MS/TP;

• Device ID and MAC address. 

PE: In terms of signaling, how does the device start and stop? What conditions do you need to start the system? What are the temperature ranges?

CA & EB: The 681 communicates with the BAS controller to signal if snow or ice has been detected. With the 090 or 095 sensor, the 681 automatically detects snow or ice on the slab surface. Upon detection, the 681 uses BACnet objects to signal the BAS controller to turn on the snowmelting system. 

Once the sensors detect the slab surface is dry and the slab temperature is up to target, the 681 uses the BACnet objects to signal the BAS controller to turn off the snowmelting system. 

In addition, the WWDS and the CWCO support the BAS controller to save energy by turning off the melting operation when the outdoor air temperature and slab temperature are below or above the setpoint temperatures range. The 681 uses the following setpoint temperatures: WWSD (32 F to 95 F) and CWCO (-30 F to 50 F).

PE: How does the snowmelting system work? 

CA & EB: A snowmelting system offers a safe, convenient and cost-effective way of removing snow and ice from the slab surface. Safety is increased by activating the snowmelting system as soon as the snow falls rather than waiting for mechanical removal after snow has accumulated. This reduces slip hazards and the risk of injury, also reducing potential liability costs. 

When the snow/ice sensor is activated, the snowmelting system automatically turns on to transfer heat energy from the heat source (hydronic or electrical) to the melting area. This operation increases the temperature surface above the freezing temperature to melt the snow off. 

Once the sensor detects the slab surface is dry, the snow melting system is automatically turned off. With the 681, the BAS can use the tekmar sensors to detect snow or ice and operate the snowmelting system automatically. 

PE: What happens if it’s too cold to melt the snow? 

CA & EB: The 681 includes a feature called CWCO (cold weather cutoff) to support the BAS and save energy. When the outdoor air temperature is too cold, the BAS heat source is not able to increase the slab temperature above freezing to melt the snow off. 

The 681 signals the BAS the CWCO condition to turn off the snowmelting system to save energy. Once the outdoor air temperature increases above the CWCO temperature setpoint, the 681 signals the BAS to turn on the snowmelting system and resume the operation. 

PE: What types of alerting systems are used to alert the building manager? 

CA & EB: The BACnet Sensor Snow/Ice Sensor Interface 681 uses error codes to signal the BAS controller if there are operational problems with the sensors. 

This allows the BAS to receive feedback on the system and determine if any action needs to be taken. Error codes include:

• Outdoor Sensor 070 code;

• Slab Sensor 072 code;

• Snow/Ice Sensor 090 code;

• Snow Sensor 095 code.

PE: Does the 681 allow contractors to control the sequence of operation of the mechanical equipment? 

CA & EB: The 681 does not interact with the sequence of operation but provides BACnet objects input to the BAS controller to automate the start/stop.

Contractors can include these inputs into their coding and have full control of the sequence of operation to meet the requirements of the snowmelting system.

PE: With the BACnet sensor interface, do contractors receive feedback on the mechanical equipment? 

CA & EB: The 681 does not impact how contractors monitor the mechanical equipment. When using the 681 to detect snow or ice, the BAS still operates all mechanical equipment. Contractors only need to log in to their systems to identify how boilers, pumps and mixing valves are running. 

PE: Can a contractor use the 681 with any snowmelting application controlled by BAS controllers? 

CA & EB: The 681 is compatible with any snowmelting system application since the BAS controller includes BACnet MS/TP communication. The snowmelting applications can range from a dedicated boiler to a multiboiler plan with multiple zones and mixing valves. The 681 communicates to the BAS controller to signal the BACnet objects and automate the start and stop operation, regardless of the type of application. 

PE: Why is it important to control the slab temperature? 

CA & EB: Controlling the slab temperature is crucial for an efficient snowmelting system. If the slab temperature is too low, the snow will not melt off. On the other hand, if the temperature is too high, the slab will be damaged by thermal shock and also will become a very expensive system to operate due to energy waste. 

PE: How can contractors automate the slab temperature to melt the snow off?

CA & EB: The 681 supports customers with an efficient snowmelting system by controlling the slab temperature. Through tekmar sensor technology, the interface continually measures the outdoor air temperature. Based on that, it calculates the ideal slab temperature to melt the snow off. 

The 681 signals the slab target temperature to the BAS controller via BACnet objects. Contractors need only to incorporate these objects in their sequence of operation to allow the BAS controller to operate the slab temperature automatically. l