Large Commercial Symbio R-454B Refrigerant Leak Sensor Information

Refrigerant Leak Sensor System

• UL requirement for units using A2L refrigerant
• Detect the leakage of the refrigerant
• Sensor is provided by Danfoss
• The sensors self-calibrate
• The sensor auto resets
• Sensors are calibrated to trip at 15% Lower Flammable Limit (LFL)
• The factory-provided sensor is only set up to detect R-454B

Mitigation Action in the Event of a Leak

When the system detects a leak, the following mitigation actions will be initiated until the refrigerant is no longer detected for at least 5 minutes.

Leak Detection - Heat Mode - All types of heat (including External heat) will continue to be enabled. This is not a change from normal control for heating. Heating is allowed because surface
temperatures will not exceed the ignition point with air flow. If heat were to be shut off, in cold climates, this could become problematic in other building areas, i.e.,
pipes freezing, etc.

Leak Detection - Cool Mode - Compressor Operation being disabled is a change from normal control for cooling. There is a stipulation in UL requirement that the unit could continue to cool; however, location of a potential leak is unknown therefore compressors will be disabled.

Leak Detection - Off Mode - Symbio 800 controls do not have a time delay between the VAV box relay energizing and the Supply Fan turning on. Although VAV boxes are typically closed while in “Off” or “Unoccupied” mode, the supply fan will ramp up and the unit will stay in duct pressure control, as it does in normal control, to minimum speed. If the boxes do not open fast enough and pressure builds based on supply fan running, the unit will trip on high static duct pressure.

Note: If the leak detection sensor has a fault, at the end of its life, or is disconnected, the unit will initiate mitigation actions. Disconnecting the sensor may verify mitigation actions.

Location

Connection Description and Troubleshooting

The leak detection sensor is a 6-pin plug: a 2-pin Modbus and a 2-pin contact. 

V3 wiring

IPAK wiring 

 IPAK 1 and 3 will only have 1 sensor.  Note: It is possible to have up to four but that would only be offered with certain design specials.

A2L Sensor & Failure Handling

The A2L sensor is required for refrigerant detection. Symbio units detects sensor failures and implements mitigation actions for the duration of the failure. The system reverts to normal operation once all failure states are cleared.

• End-of-life indication or fault
• The sensor is unpowered
• Sensor wiring fault or misapplication
• Sensor disconnected
• Communication loss

Replacement

• Replacement A2L sensors are supplied pre-programmed at Modbus address 50 (V3).
• Replacement IntelliPak A2L must be addressed after installation.  Symbio 800 - Modbus Device Addressing

Alarms

BACnet Points Available

WARNING:

Information in this article is intended for use by individuals possessing adequate backgrounds of electrical and mechanical experience and who comply with all federal, state, and local laws, rules, orders, or regulations related to the installation, service, or repair of a heating or central air conditioning product. Any attempt to install, service, or repair a heating or central air conditioning product may result in personal injury and/or property damage. The manufacturer or seller cannot be responsible for the interpretation of the information contained herein, nor can it assume any liability in connection with its use.