Refrigerant Leak Sensor System

Sensor

1. Sensor Purpose

   • UL requirement for units using A2L refrigerant
   • Detect the leakage of the refrigerant
    

2. Who manufactures the R-454B Leak Detection Sensor used

   • 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.

• Alarm Activation & Mitigation: When refrigerant concentration exceeds the threshold, the supply fan starts, and mitigation actions are invoked via the Modbus interface (Address 50). Units only have one sensor.
• Continued Mitigation: Even after the refrigerant concentration falls below the threshold and the alarm resets, mitigation actions continue for an additional 5 minutes.
• Return to Normal Operation: After the 5-minute mitigation period, the system reverts to normal operation.

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

A.0 and B.0 Cabinets

D.0 Cabinets

Access D.0:

• Lock unit disconnect.
• Detach the pipe, P-trap connected to the condensate drain opening in the post.
• Remove the indoor refrigeration coil panel, indoor fan panel, and heat section panel(s), followed by the vertical post to which these were attached.
• The leak sensor is located just above and to the right of the drain pan outlet.

Connection Description

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

Factory-installed wiring

• Equipment with R-454B refrigerant may require a refrigerant detection system based on the refrigerant charge. The refrigerant detection system consists of a refrigerant detection sensor that communicates information to the Symbio™ 700 controller. When the refrigerant detection sensor is in a normal operating state, the equipment provides normal heating, cooling, and ventilation. The refrigerant sensor creates an alarm signal when the sensed refrigerant concentration has exceeded a predetermined threshold.
• When the refrigerant detection system is in an alarm state, the Symbio 700 mitigates the refrigerant leak alarm condition for a minimum of 5 minutes after the refrigerant detection system has reset to a normal state. Mitigation actions:
  • All compressor operation is disabled.
  • The supply fan operates continuously at or above a defined minimum speed.
  • After the supply fan operation is proven; electric heat, gas heat, economizer cooling and ventilation operate normally.
  • Alarm output energizes on the Customer Options Module (if installed).

A2L Sensor & Failure Handling

The A2L sensor is required for refrigerant detection. Symbio 700 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.

BACnet® or Modbus™

The following Symbio 700 points are available on BACnet® or Modbus™; however, the points are not available on LonTalk®.

• A Multi-Zone VAV application, the Symbio controller energizes the VAV Box Relay Output and the Refrigerant Mitigation Active point will be active to signal building systems to drive VAV boxes open. If the supply fan is off, the supply fan operation initiates within 15 seconds. When utilizing LON communications, wiring the VAV Box Relay Output to VAV boxes must be used to coordinate with building multi-zone VAV system.
• In the event the control system detects the refrigerant sensor has failed, become disconnected or unpowered; the controls will respond with a Diagnostic: Refrigerant Leak Sensor Failure, Refrigerant Mitigation Active, and the Alarm Output are active. The Symbio controller provides all mitigation actions (outlined above) for the duration of the sensor failure mode.
• Building fire and smoke systems utilizing Ventilation Override or Emergency Override will override the refrigerant detection system. Service Test mode and the Emergency Stop input will also override the refrigerant detection system.
• After mitigation actions are completed and the condition triggering mitigation actions are no longer active, the unit will return back to normal operation.

Alarms

• Refrigerant Leak Sensor Communication Status Sensor A
• Diagnostic: Refrigerant Leak Sensor Failure Sensor A
• Diagnostic: Refrigerant Concentration Sensor A

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.