Certification Requirements
Technicians handling low-pressure appliances (such as chillers) must be Type III certified or hold Universal certification.
Low-pressure systems operate under a vacuum, increasing the risk of air and moisture infiltration.
Leak Detection for Low-Pressure Systems
Purge Units: Essential for removing non-condensables that leak into the system, often indicated by high head pressure or frequent purge operation.
Hydrostatic Tube Testing: Used to test for leaks; a maximum test pressure of 10 psig is applied.
Moisture Prevention: Moisture commonly enters low-pressure systems through gaskets or fittings; leak detection should be frequent.
Air Accumulation Prevention: Maintain slightly positive pressure during system downtime to avoid air entry.
Leak Repair Requirements
Leak Thresholds:
Comfort Cooling: 10% per year.
Commercial Refrigeration: 20% per year.
Industrial Process Refrigeration (IPR): 30% per year.
Repair or Retirement: If leak thresholds exceed these values, repairs, retrofitting, or retirement of the appliance are mandatory.
Repair Deadlines
30 Days: For appliances exceeding the threshold leak rate, repairs must reduce leaks below the threshold within 30 days.
18 Months: If the leak rate exceeds 50 pounds, 18 months is allowed to retrofit or retire the appliance if using a refrigerant exempt from venting prohibition.
System Mothballing
Does not require removal of the appliance. If refrigerant is recovered, storing the appliance at atmospheric pressure can extend deadlines.
Recovery Techniques for Low-Pressure Systems
High-Pressure Cut-Out: The cut-out level for low-pressure recovery units is set at 10 psig.
Recovery Process:
Begin with liquid refrigerant removal followed by vapor recovery.
Large systems like 350-ton R-123 chillers may retain about 100 pounds of refrigerant in the vapor state at 0 psig.
Dehydration with Nitrogen: For moisture-heavy systems, use nitrogen to prevent water from freezing during evacuation.
Recovery Equipment and Requirements
Water-Cooled Recovery: Recommended for faster recovery and to prevent freezing.
Oil Heating: Before replacing refrigerant oil, heat to 130°F to release refrigerant trapped in oil.
Evacuation Levels: Recover refrigerants to an absolute pressure of 25 mm Hg. Disposal of low-pressure appliances requires records for three years.
Recharging Techniques
Oil Sampling: Before recharging, take an oil sample if the unit has had a compressor burn-out.
Prevent Freezing: For systems charged in a vacuum, avoid freezing by referencing the pressure-temperature (P-T) chart.
Pressure Adjustments: Charge refrigerant vapor into the system to avoid freezing; liquid refrigerant is added through the evaporator charging valve.
Safety Protocols
TLV-TWA Standard: When exposure limits are exceeded, ASHRAE Standard 15-2013 mandates alarms and mechanical ventilation.
Room Sensors: Required to detect refrigerant leaks for all safety groups due to the asphyxiation risk of refrigerants.
Pressure Relief Valve: Relief valves must be vented outdoors and installed in parallel, not in series.
Protective Equipment: Technicians should wear gloves and safety goggles when handling liquid refrigerants.
General Handling and Precautions
Rupture Discs: Located on evaporators, rupture at 15 psig to release pressure.
Refrigerant Charging: Avoid over-pressurizing the system when charging through the evaporator.
Sight Glass Maintenance: Use isopropyl alcohol to remove ice from sight glasses and other components.
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